Designing of Recyclable Attapulgite for Wastewater Treatments: A

Subscriber access provided by University of South Dakota

Feature

Designing of recyclable attapulgite for wastewater treatments: A review Yaquan Wang, Yi Feng, Jinlong Jiang, and Jianfeng Yao ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05823 • Publication Date (Web): 18 Dec 2018 Downloaded from http://pubs.acs.org on December 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Designing of recyclable attapulgite for wastewater treatments: A review Yaquan Wanga, Yi Fenga, Jinlong Jiangb, Jianfeng Yaoa,* a

College of Chemical Engineering, Jiangsu Co-Innovation Center of Efficient Processing and Utilization of

Forest Resources, Jiangsu Key Lab for the Chemistry & Utilization of Agricultural and Forest Biomass, Nanjing Forestry University, 159 Longpan Road, Nanjing, Jiangsu 210037, China. Email: [email protected] bJiangsu

Provincial Key Laboratory of Palygorskite Science and Applied Technology, Huaiyin Institute of

Technology, 1 Meicheng Road, Huai'an, Jiangsu 223003, PR China.

ABSTRACT Due to the low cost, extraordinary physical and chemical properties, attapulgite (ATP) has sparked considerable interest as water remediation materials. Since traditional ATP nanomaterials have inherent limitations in separation and recycle, this mini review focuses on designs of recyclable attapulgite composites, which show great potential in practical environmental remediation. Firstly, the advantages of ATP properties are highlighted and discussed in comparison with other one-dimensional materials. Then, three types of strategies are summarized to fabricate recyclable ATP nanocomposites: (1) magnetic attapulgite adsorption materials; (2) millimeter-sized attapulgite-based adsorbents; and (3) filtration membranes/meshes. Additionally, the syntheses, applications, and corresponding mechanisms towards numerous pollutants are included. Finally, challenges and future prospects of fabrications and applications are given as well.

Key

words:

Attapulgite;

Adsorption;

Filtration;

1

ACS Paragon Plus Environment

Recyclable;

Water

treatment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 40

INTRODUCTION Nowdays, common water pollutants (e.g. organic molecules, oil contamination, or heavy metal ions) willfully discharged from industry to ecosystem have become one of the toppest environmental issues.1-3 When unpurified water inevitably entering into soil or surface or groundwater, not only has severely jeopardized animals or plants but also threaten to human beings owing to highly toxic or non-biodegradable ingredients.4,5 Therefore, it is urgent to develop advanced materials or versatile technologies for environmental remediation.6 Recently, due to high specific surface area or controllable surface chemical properties, nanomaterials have become a rising star in environmental pollution remediation over recent years.7 Notably, nanoscale materials may be inconvenient to utilize in water purification when they were directly applied as water remediation materials, most of which may also pose a potential safety risk to ecosystem and human beings.8,9 As a representative example, Chen et al. prepared ATP@carbon (C) nanocomposites as an effective sorbent by a hydrothermal method for Cr (VI) and Pb (II) adsorption in 2011.10 However, after removing heavy metal ions, filtration or centrifugation technologies are usually used to separate powdery nanocomposites for next use from water medium, so it actually becomes extremely difficult and time-consuming to recover and separate nanocomposites in real applications.4,11 Additionally, traditional powder-form materials may also block filters due to fine size, and cause secondary harmful pollutants associated with itself leakage, especially in flowing liquids.12 These aforementioned drawbacks have severely hindered their applications in large scale. Recently, more significant research efforts have been devoted to synthesizing millimeter-sized materials,13-16 filtration membranes/meshes,17,18 and magnetic materials19 for effective contaminants removal. Allowing for recyclable and safe applications, those 2


Page 3 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


materials exhibited a more predominant performance than traditional nanosized materials. To date, a whole view on ATP nanocomposites, particularly in separation and recycle from water medium, is still missing. This mini review focused on designing recyclable ATP nanocomposites combined with Fe3O4 or different substrates materials and traditional ATP nanocomposites were excluded. These recyclable attapulgite composites were classified into three main types: (1) magnetic attapulgite adsorption materials; (2) millimeter-sized attapulgite-based adsorbents; and (3) filtration membranes/meshes (Scheme 1). Such materials are easier to be collected, and more important in many applications, such as heavy metal ions adsorption, organic contaminants removal, and oil/water separation. In each part, we illustrated some typical examples and discussed their relevant mechanisms, regeneration, recyclable methods. Finally, this mini review also highlighted challenges and outlooks of the fabrication and applications in the future trend.

Scheme 1. Schematic illustration of three types of recyclable attapulgite nanocomposites and applications.

THE BRIEF INTRODUCTION OF ATTAPULGITE Attapulgite (ATP, also called as palygorskite, PAL) is a kind of natural magnesium aluminum 3



Page 4 of 40

silicate clay mineral, whose theoretical formula is Si8(Mg,Al,Fe)5O20(OH)2(OH2)4·4H2O.20,21 As shown in Figure 1a, ATP crystal structure is always described that two bands of silica tetrahedra were linked by Al (III) and Mg (II) ions in octahedral coordination, leading to the formation of a large number of free nanoscale channels (dimensions about 0.37 nm × 0.64 nm and 0.56 nm × 1.1 nm).22-24 Figure 1b clearly exhibits that ATP has a rod-like morphology with a length ranging from 100 nm to several micrometers and a width of approximate 30 nm. Therefore, one-dimensional (1D) pristine ATP has large specific surface area ranging from 100.8 m2/g to 216 m2/g with pore volume of 0.38 cm3/g to 0.58 cm3/g.10,22,25,26 Furthermore, abundant hydroxyl groups (Si-OH) on the ATP nanorods surface could be hydrolyzed, resulting in positively/negatively charged surfaces that mainly depend on pH values of solutions. These processes can be described as follows (Eq. 1) and (Eq. 2). Moreover, we classified different kinds of pollutants into inorganic and organic contaminants, and corresponding interaction mechanisms can be mainly divided into four aspects: cation exchange, electrostatic attraction, surface complexation, and external surface area (Figure 1c).27,28 Si-OH + H+ → R-OH2+

(1)

Si-OH + OH- → R-O- + H2O

(2)

The following three aspects can be explained why we choose ATP as raw materials. First of all, the average cost of ATP is around 0.14 $/kg in China, in marked contrast with other 1D carbon nanotube or TiO2 commonly for basic scientific research, cost-effective ATP-based functional materials can be prepared at low cost in the industrial-scale production.29 Secondly, abundant ATP has been widely employed as an effective reinforce filler owing to high mechanical strength.30 Compared to other 1D natural cellulose fiber that should be dissolved in traditional solvents before use, ATP can be easily obtained and used without complicated pretreatment.31,32 After introduction 4


Page 5 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of ATP into matrix materials, particularly for hydrogels, mechanical property can be tremendously improved after swelling.33 Last but not least, typical characteristics, such as Si-OH or excellent physical and chemical stability, which endow ATP hydrophilicity and allow its extraordinary dispersion in water medium including corrosive solution.26,34,35 Furthermore, it can be modified for further functionalization via chemical modifications as well (e.g. organosilicons, aminopropyl triethoxysilane and others).36-38

Figure 1. Crystal structure (a), Reprinted with permission from ref 39. Copyright 2015 Royal Society of Chemistry. Scanning electron microscopy (SEM) images of ATP (b), Reprinted with permission from ref 40. Copyright 2010 Elsevier, and the schematic diagram of interaction mechanisms (c).

MAGNETIC ATTAPULGITE ADSORPTION MATERIALS In recent years, the development of Fe3O4 nanomaterials have grown intensely in many fields due to non-toxic, stable physical and chemical properties, and easy separation.41 Particularly, previous studies have demonstrated that magnetic nanocomposites with good performance can be efficiently separated by magnetic field when contaminants were removed in environmental remediation.42,43 5



Page 6 of 40

Therefore, it was a straightforward way to modify ATP coupled with Fe3O4 for repeated use at laboratory and in the large-scale field. In this section, we mainly introduced and compared chemical co-precipitation and hydrothermal methods for preparation of magnetic nanocomposites. Besides, several chemical modifications for improving adsorption performance and corresponding adsorption mechanisms also were discussed.

Co-precipition method. During chemical co-precipitation process, negatively charged ATP combined with cationic iron via adsorption, and Fe3O4 subsequently grew at ATP nanorods surface after adding alkaline solution (Figure 2a).44,45 Figure 2b and c clearly show that Fe3O4 were less than 50 nm and uniformly deposited on ATP surface. The Fe3O4 preparation process was described as follows (Eq. 3): Fe2+ + 2Fe3++ 8OH- + ATP → ATP-Fe3O4 + 4H2O

(3)

Over the past few years, ATP/Fe3O4 nanocomposites have been directly u

tilized as a series

of sorbents for heavy metal ions or organic pollutants removal.46-48 In adsorption process, ATP usually ensured adorption active sites, and Fe3O4 responded to an external magnetic field, making them separate and operate conveniently without complicated centrifugation or filtration process. As a typical example, Lu et al. synthesized magnetic ATP sorbents to trap Eu (III) ions and maximum adsorption capacity reaching 4.94 × 10-4 mol/g was achieved at pH 5.49 More interestingly, adsorption mechanisms were distinctly different due to different Eu (III) species in different pH values. At low pH values, adsorption mechanisms were attributed to ion exchange or outer-sphere surface complexation when positively charged Eu (III) species (Eu3+, Eu (OH)2+, Eu (OH)2+, or EuCO3+) existed. On the contrary, due to the existence of Eu (CO3)2- and Eu (CO3)33-, the Eu (III) 6


Page 7 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


removal were mainly ascribed to inner-sphere surface complexes or surface co-precipitation. Moreover, high saturation magnetization value (32.7 emu/g) enabled them collect conveniently by a magnetic field.

Figure 2. The preparation of ATP/Fe3O4 nanocomposites via chemical co-precipitation method (a), Transmission electron microscope (TEM) images of ATP (b), and ATP/Fe3O4 nanocomposites (c). Reprinted with permission from ref 45. Copyright 2016 Elsevier.

From the perspective of adsorption capacity or efficiency, this type of naked ATP/Fe3O4 nanocomposites had low adsorption capacities, and was not a good choice to employ in real applications. Therefore, there is of great significance to modify original ATP/Fe3O4 nanocomposites to adjust adsorption capacity or improve efficiency to meet requirements of actual applications. In this case, the key point mainly comprises two aspects: (1) surface imprinting technique to selectively remove pollutants, (2) surface modification with functional groups to adsorb contaminants via ion exchange, electrostatic attraction or chelation. In the surface imprinting process, templates (e.g., organic molecules or metal ions) were firstly printed within a polymer network, then removed to form imprinted cavities for the sake of selective adsorption. For example, Pan et al. reported a molecular imprinting technique using 2,4-dichlorophenol (2,4-DCP, organic molecules) as a template for synthesis of magnetic ATP-based 7



Page 8 of 40

polymeric sorbents.50 Results showed that magnetic ATP nanocomposites selectively recognized and removed 2,4-DCP in complex conditions, capable of adsorbing 145.8 mg/g at 298 K. After completing 5 cycles, the adsorption performance for 2,4-DCP was decreased by ca. 7.5% when the mixture solution of methanol and acetic acid was used as an eluant, suggesting good regeneration. Notably, surface imprinting method also can be designed to remove metal ions selectively.51 In other work conducted by Shi et al., nonmagnetic Cu (II)-imprinted chitosan (CTS) /attapulgite sorbents were prepared to remove Cu (II).52 For the competitive adsorption towards Cu (II)/Pb (II) and Cu (II)/Cd (II) binary mixtures, as-prepared sorbents exhibited a good preference for Cu (II) removal. The main reason was that Cu (II)-imprinted cavities were not suitable for Pb (II) and Cd (II) in size, shape and spatial arrangement of action sites. After ten consecutive adsorption/desorption cycles, they still maintained 86% adsorption performance, and showed good regeneration. Additionally, surface modifications with functional groups also have great impacts on adsorption performances. In this regard, some polymers with functional groups (e.g., -COOH(Na), -NH2, -SO3H(Na), -SH, and -OH) were employed to construct high-efficient adsorption materials for impurities adsorption.11,53-56 For example, Mu et al. synthesized ATP/Fe3O4/polyaniline (PANI) nanocomposites for removal of dyes via a chemical oxidative polymerization and co-precipitation method.57 Among the system, Fe (III) was introduced as not only the oxidant for aniline, but also the precursor of Fe3O4. Figure 3a shows that the obtained anthurium andraeanum-like structures were favorable to disperse Fe3O4 and avoided aggregates between PANI and Fe3O4. Since the existence of functional amine and imine groups of PANI, synthetic sorbents could selectively adsorb different charged dyes by varying surface charge under different pH values. Experimental data showed that negative charged ATP had higher affinity towards cation Methylene blue (MB) than anion Congo red 8


Page 9 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(CR) while ATP/Fe3O4/PANI nanocomposites exhibited superior removal efficiency for CR was 96% while MB was 16.5% at pH = 7 (Figure 3b). In a similar design, Yang et al. further put forward ATP/Fe3O4/PANI nanocomposites as sorbents for the extraction of benzoylurea insecticides.58 It revealed that the interaction mechanism was π-π bonding between PANI with benzene ring of benzoylurea insecticides. Significantly, the adsorption of PANI towards different pollutants may ascribe various mechanisms.

Hydrothermal method. It was worth noting that hydrothermal process also can be a versatile method to fabricate ATP/Fe3O4 nanocomposites.59,60 As a significant example, Mu et al. prepared magnetic ATP nanocomposites decorated with modified β-cyclodextrin and chitosan to adsorb precious metals, and systematically investigated adsorption process and mechanisms.61 In this method, mixture solutions including FeCl3·6H2O, sodium acetate (precipitator), ethylene glycol (reducing agent) and polyethylene glycol were added into Teflon autoclave at 190 °C for 8 h to prepare magnetic ATP. Subsequently, modified β-cyclodextrin (-COOH) and chitosan (-NH2) via electrostatic interaction were decorated onto ATP/Fe3O4 to develop COOH/NH2-ATP/Fe3O4 sorbents by a layer-by-layer self-assembly method. The adsorption rates for Ag (I), Pd (II), and Pt (IV) were 90%, 90%, and 60% at pH = 4, which indicated ATP/Fe3O4 nanocomposites had a preference for Ag (I) and Pd (II). As revealed by X-ray photoelectron spectroscopy (XPS) analysis, after metal ions adsorption, electron density was reduced. It is because that the binding energy of -NH2 increased from 400.27 eV to 400.34 eV and three individual component peaks of -C=O (531.4 eV), -C-O (532.2 eV), -COO- (533.3 eV) showed a shift, which were attributed to the combination between metal ions and ATP/Fe3O4 nanocomposite adsorbents. All results clearly proved that chemical 9



Page 10 of 40

interactions between metal ions and -NH2 or -COOH groups were involved during the adsorption process. Nevertheless, the as-prepared sorbents faced the problem of complicated preparation process and high-cost solvents (e.g., sodium acetate, ethylene glycol) and cannot simultaneously treat various kinds of organic/inorganic impurities. With regard to mixed inorganic/organic components in real wastewater, liquid treatments always require many steps, and it is more vital that versatile sorbents should be developed to simultaneously remove organic/inorganic pollutants. Meanwhile, green and facile preparation process, and extraordinary adsorption capacities also should be well guaranteed. For instance, Tang et

al.

developed

magnetic

carboxyl-functionalized

attapulgite/carbon

(COOH-ATP/C)

nanocomposites through a hydrothermal method for metal ions and dyes removal.62 The precursor containing sodium citrate, FeCl3·6H2O, CH3COONa·3H2O and by-product spent bleaching earth (SBE, carbon source) were sealed into a 100 mL Teflon autoclave at 200 oC for 12 h. Notably, the concentration of sodium citrate as reductant was a significant parameter, which played a crucial role in determining Fe3O4 growth in the hydrothermal process. Only when sodium citrate was in the low concentration, partial Fe (III) was reduced into Fe (II) via redox reaction, and then produced Fe (II) reacted with the residual Fe (III) to generate Fe3O4 (Figure 3c). Fourier transform infrared spectra (FTIR) analysis provided evidence that functional groups (e.g., -COOH, -OH) could facilitate interactions between sorbents and MB by forming electrostatic attraction, hydrogen bond, and π-π interaction while electrostatic attraction, surface complexes, and ion exchange are mainly involved in Pb (II) adsorption (Figure 3d). This is particularly important to improve adsorption performance, and as a result, these sorbents with functional groups can adsorb a maximum of pollutants like MB (254.8 mg/g) and Pb (II) (312.7 mg/g). Besides functional groups, layered double hydroxides (LDHs) 10


Page 11 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


can be deposited on ATP/Fe3O4 for adsorption performances enhancement. Tang et al. further proposed synthesis of magnetic NiFe-LDHs/ATP/C for various contaminants adsorption.63 After modification, the specific surface area and pore volume simultaneously have an obvious improvement because ATP can disperse carbon species and NiFe-LDHs sheets greatly due to its unique surface morphology, where sheets uniformly were anchored together to form more mesopores. Therefore, exposure to more active sites (e.g., oxygen-containing groups of carbon species and NiFe-LDHs sheets) and negative charges can improve adsorption performance via π-π stacking interaction, ion exchange, hydrogen bond, π-p stacking interaction and electrostatic attraction. Moreover, this composite featured better recyclability and reusability, and showed that adsorption capacities for MB, Pb (II), and chlortetracycline hydrochloride (CTC) were 271.3, 180.9, and 308.2 mg/g, which was considerably higher than many reported ATP/C/Fe3O4 adsorbents. Except for modification methods mentioned earlier, a large number of studies supplied new insights to functionalize ATP to increase adsorption capacity, even though these materials were difficult to recycle. Generally, there are five main ways to improve adsorption capacity: (1) physical and chemical pre-treatments (such as heat or acid treatment);20,64-66 (2) controlling of Si and Mg or Zn ratio;67,68 (3) disaggregation of crystal bundles via high-pressure homogenization;69,70 (4) surface coating (e.g., chitosan or carbon);71-73 (5) grafting of functional groups especially amino or carboxyl groups.37,74,75 Among five methods, physical and chemical pre-treatments are the easiest methods, but adsorption performance are always unsatisfactory. The modification method of controlling of Si and Mg or Zn ratio is not universal, only for low-grade mineral. Disaggregation of crystal bundles may be accepted as a highly efficient method for improvement of adsorption property. Unfortunately, it is impractically applied in the large-scale production due to complicated equipments (high-pressure 11



Page 12 of 40

homogenizer) and harsh conditions. Currently, both surface coating and grafting of functional groups would be the most promising strategies for mass production. In terms of ATP/Fe3O4 preparation methods, co-precipitation method is relatively easy and cost-effective, but the apparent drawback is corrosive alkaline solution. Hydrothermal method mainly involves environmentally friendly preparation process and simply synthetic method, while it requires a large amount of solvents, and thus increases production costs. In short, all these significant studies provided new insights into possible adsorption mechanisms and preparation methods. Notably, magnetic materials can be conveniently recovered and recycled by a magnet, allowing its repeated use in water and making it a promising candidate for liquid treatment in the future.

Figure 3. Magnetic ATP/PANI sorbents with an Anthurium andraeanum-like or peanut chocolate bar structure, and corresponding SEM and TEM images (a), Digital photo of adsorption and separation process in 100 mg/L of CR solution (b). Reprinted with permission from ref 57. Copyright 2015 Royal Society of Chemistry. The synthetic route of magnetic carboxyl-functionalized ATP/carbon nanocomposites (c), and adsorption mechanisms (d). Reprinted with permission from ref 62. Copyright 2017 Elsevier.

MILLIMETER-SIZED ATTAPULGITE-BASED ADSORBENTS Millimeter-sized ATP-based monoliths sorbents have been increasingly studied for pollutants 12


Page 13 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


removal over the past few years. This is understandable due to the fact that those materials have some features in common, such as millimeter-sized size or shape, which help them recycle easily. In this section, we mainly summarized preparation methods of self-making all-inorganic ATP monolith and ATP immobilizing into porous substrates based on different substrates and their applications.

Self-making all-inorganic ATP monolith. Nowadays, direct applications of conventional ATP nanocomposites for pollutants removal have been seriously limitted due to poor recyclability. Solidification powdery clays under high-temperature calcination may be a better way to prepare monolith with millimeter-sized shape, and separation process can be simplified when they are used in liquid purification. This kind of monolith intrinsically has porous structure, and also can be functionalized them through different surface modification to satisfy different practical needs. For example, Yin et al. proposed that porous ATP granules (1-2 mm) were obtained at 700 oC, and post-treated via a simple iron salt solution impregnation method to improve arsenic adsorption performance.76 As Fe-modified ATP granule was positively charged in a wide range pH value from 5 to 9, which made it favorable to capture arsenic via a mechanism of complexation. At this wider pH, the maximum adsorption capacity of As (III) and As (V) onto ATP granule was 3.3 mg/g and 5.1 mg/g, respectively. Importantly, the resultant sorbents were easily regenerated after using 0.5 mol/L NaOH as the elution agent and above 75% of adsorption efficiency remained after 5 times adsorption-regeneration experiments. Besides, ATP monolith also has been modified as sorbents for organic pollutants removal via surface decoration. According to the same principle, porous ATP supporter with tunable surface wettability (PDMS-ATP monolith) for oils and dyes adsorption were reported by Liang et al. They 13



Page 14 of 40

used polydimethylsiloxane (PDMS) to endow it hydrophobicity by chemical vapor deposition (CVD) at 240 oC.77 More interestingly, hydrophobicity was reversibly transformed into hydrophilicity by thermal treatment (400 °C) (Figure 4a), so it selectively adsorbed oils, non-polar or polar dyes. Figure 4b shows that the saturated ATP monolith was easily recovered by burning in air because of its excellent heat stability, proving its excellent regeneration. Although adsorption efficiency was relatively low, these works creatively offered some new strategies to design multifunctional ATP-based monoliths for contaminants adsorption. Attractively, low-cost all-inorganic sorbents can be recycled and separated from water medium via tweezers, sieve or strainers instead of complicated centrifugation method, showing a promise in practical applications.

ATP immobilizing into porous substrates. Phase inversion method is commonly applicable for a variety of substrates, and not limited to prepare asymmetric membranes. In this strategy, directly adding sorbent ATP into polymer precursor solutions and then injecting them into water at room temperature through a traditional syringe, was an effective method to prepare macroporous sorbents (Figure 4c). For example, our group fabricated porous millimeter-sized ATP/polyethersulfone (PES) beads, and investigated their applications in metal ions removal.26 Briefly, ATP as adsorption active sites was caged in the polymeric network that was served as supporter. We found that ATP was well dispersed inside inner pore structures and the loss of ATP was reduced during the adsorption process. The resultant beads have been demonstrated for extraordinary adsorption capacity of Cu (II) and Cd (II) (25.3 and 32.7 mg/g), as well as exhibiting excellent chemical and physical stability. Remarkably, such porous beads could float on water surface, and be easily recycled and separated due to their millimeter size and buoyancy (Figure 4d). 14


Page 15 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


As mentioned earlier, ATP with plentiful oxygen-containing groups, could be further functionalized via a simple surface grafting reaction for wider range of applications. For example, Pan et al. decorated ATP with divinylbenzene (DVB) by atom transfer radical polymerization (ATRP), and then prepared polymeric microcapsules via a facile phase inversion method.78 The water contact angles (WCA) was measured ca. 140o, proving that microcapsules were transformed from superhydrophilicity to hydrophobicity. As a result, these as-prepared microcapsules exhibited excellent adsorption efficiency and superior recyclable properties for crude oils (17.1 g/g).

Figure 4. Surface wetting reversibility of ATP monolith via heat treatment (a), optical image of oil adsorption process and burning ATP monolith in air for reuse (b). Reprinted with permission from ref 77. Copyright 2015 Royal Society of Chemistry. The preparation process of polymer beads via a phase inversion (c). Reprinted with permission from ref 79. Copyright 2013 Springer. ATP/PES beads floating on the water surface and separation using a sieve (d). Reprinted with permission from ref 26. Copyright 2017 Elsevier.

As sodium alginate (SA) or chitosan also can be easily shaped into different bulk structures, they have been adopted as supporters for ATP immobilization.14,15 Polysaccharide slurry was continually pumped, and subsequently solidified in coagulation solutions (NaOH, CaCl2). It is rationally reasonable for polysaccharides replacing PES to further improve the adsorption capacity when sorbents are designed to remove metal ions or organic pollutants via ion exchange, electrostatic 15



Page 16 of 40

attraction and complexing reactions.80,81 Very recently, our group developed floatable and porous ATP/SA foams with 1 × 1 ×1 cm3 size for Cu (II) and Cd (II) adsorption (Figure 5a).12 This kind of synthetic method has some significant advantages, such as cubic foams would exert the capacity of both components, and reduce the cost of sorbents when ATP was introduced into SA polymer matrix. Porous foams with sponge-like pore structure (size ca. 100 μm) may facilitate alginate-based ATP foams to directly interact Cu (II) and Cd (II) (Figure 5b), and the adsorption capacity of foams was up to 119 mg/g for Cu (II) and 160 mg/g for Cd (II), respectively. Moreover, the reusability of foams also has been carefully investigated after being treated with 0.2 mol/L HCl as desorbing agent, we found that the adsorption capacity for Cd (II) rose and remained unchanged from the second cycle. It was mainly explained that adsorption active sites originally occupied by Ca (II) were released, and so adsorption capacity was increased. Such foams were conveniently recycled by a simple strainer collection method because of their excellent floatability (low density 0.714 g/cm3) in water solution (Figure 5c). Three-dimensional (3D) commercial sponges, well-known as magic eraser, recently have been widely used as an ideal porous substrate to design numerous multi-functional composites aimed at different applications, due to their characteristic properties, such as low cost, high porosity, good elasticity, and easily large-scale fabrication.82-84 Li et al. put forward an example to develop superhydrophobic ATP/polyurethane (PU) sponges for oil/water separation by a dip-coating method.85 Briefly, ATP pre-modified with octadecyltrichlorosilane (OTCS) was ultrasonically coated on the skeleton of sponges to simultaneously construct superhydrophobic and tough surface (Figure 5d). After that, these as-prepared PU sponges exhibited both excellent superhydrophobic property and environmental stability under a series of harsh conditions (e.g., corrosive solutions, hot water 16


Page 17 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and turbulent conditions). Additionally, the porous network structure with pore size (100 µm ~ 700 µm) played an important role in high adsorption due to the mechanism of physical adsorption. Benefiting from its excellent properties, the modified sponge could float on the water surface to automatically adsorb oil up to 3200 times its own weight, and also showed superior separation performance with efficiency over 99.9% for oil/water emulsion (Figure 5e). Significantly, ATP-coated sponges made a promise as a filter to continuously collect oils from water medium via an oil-collecting device, and displayed extraordinary reusability by squeezing method owing to elasticity of PU sponges.

Figure 5. The digital photo (a) and SEM image of porous SA/ATP-0.5 foams (b), and the digital photo of SA/ATP-0.25 adsorbed Cu (II) floating on the water (c). Reprinted with permission from ref 12 Copyright 2017 Elsevier. The preparation process of hydrophobic ATP-coated sponge (d), and the digital image of modified sponge floating on the water surface and original sponge immersing into the water (e). Reprinted with permission from ref 85. Copyright 2016 Royal Society of Chemistry.

With the feature of 3D network structure, easy separation, and recyclable property, hydrogel sorbents have been widely applied for pollutants removal.86 Unfortunately, they always suffered 17



Page 18 of 40

from poor mechanical properties because of swelling problems for long-time water purification. Recent investigations have demonstrated that ATP acting as reinforced fillers were directly incorporated into porous network structure of hydrogels to enhance their strength.30,87 In a typical example, high-strength ATP/fly ash/poly(acrylic acid) hydrogels composed of inorganic powders (ATP and fly ash) as reinforced components as well as cross-linkers were successfully fabricated via a inverse suspension polymerization (Figure 6a).33 Among the ternary system, poly(acrylic acid) was grafted onto the inorganic skeletons to form 3D network hydrogels for selective Pb (II) removal. The experiment results showed that the affinity between -COO- and metal ions was mainly dependent on ionic radius, electronegativity, and ionization potential, following the order of Pb (II) > Cu (II) > Cd (II) > Zn (II) > Ni (II). At pH around 5, the concentration of H+ decreased and more deprotonated -COO- increased, facilitating the electrostatic interaction between -COO- and Pb (II). Therefore, the resultant hydrogels selectively adsorbed Pb (II), and showed good adsorption capacity up to 38 mg/g for 24h at the initial concentration of 100 mg/L, and still maintained outstanding mechanical stability after exposure to high pressure and shearing force (Figure 6b-d). Similarly, Jiang et al. prepared ATP/fly ash/poly(acrylic acid-co-acrylamide) microgels for selective Pb (II) adsorption.88 Except for -COO-, the introduction of -CONH2 further improved the adsorption capacity prior to ATP/fly ash/poly(acrylic acid) hydrogels when pH was increased to 6 as well. This meant that increasing pH value promoted the linkage formation between the amide groups of polyacrylamide and Pb (II) in the solution. Among the current ATP hydrogels, a detailed and scientific explanations about mechanical changes were not given. In another example, Mao et al. proposed ATP/SA/poly(acrylic acid) hydrogels for Cu (II) and Pb (II) adsorption.89 Researchers clearly proved that the mechanical strength of hydrogels can be significantly improved according to 18


Page 19 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


stress–strain curves, in which showed that stress of hydrogels modified with 10% attapulgite was 4.1 times higher than original hydrogels. More attractively, the adsorption capacity of hydrogels for Cu (II) and Pb (II) was 272.8 and 391.7 mg/g, and also showed a large dependence on the low ATP content (10 %), under which had little influence on content of functional groups. After 2 M HCl elution, adsorption performance was retained above 90% after five cycles, which exhibited an excellent reusability. Besides strengthening agent, hydrophilic ATP has been increasingly applied as stabilizers for oil-in-water Pickering emulsions as well.90 Zhu et al. reported that porous hydrogel spheres were prepared from Pickering high internal phase emulsions (Pickering-HIPEs) for monovalent metal ions removal.91 Hydroxypropyl cellulose (HC) and acrylic acid (AA) were employed as active binding sites for metal ions uptake. ATP employed as the stabilizer of emulsion was favorable to form interconnected pore structure (1.6 - 5.9 μm), which helped add more opportunities to interact with metal ions due to exposure of a large number of functional groups (Figure 6e and f). Therefore, these micron-meter spheres showed fast adsorption rates and adsorption capacity towards both Rb (I) and Cs (I) were above 200 mg/g within 30 minutes (Figure 6g). However, in this work, toxic organic solvents (e.g. p-xylene and liquid paraffin) and surfactant were introduced as the dispersed phase and stabilizer to prepare Pickering emulsion, and increased costs of preparation and possibly caused more damage to environment. Pickering-medium internal phase emulsions method was proposed by Wang et al. for synthesis of carboxymethylcellulose-graft-poly(acryl amide)/PAL polymer monoliths.92 Researcher utilized non-toxic and low-cost edible oil as dispense phase instead of liquid paraffin or p-xylene in Pickering-HIPEs. Additionally, the adsorption capacity of MB and Methylene Violet (MV) dye can reach 1625 and 1585 mg/g, respectively. The reused monoliths were regenerated after 19



Page 20 of 40

they were orderly immersed into 0.5 mol/L HCl and 0.5 mol/L NaOH solution, and maintained high adsorption capabilities after 5 continuous adsorption-desorption cycles.

Figure 6. Digital photos of ATP/fly ash/poly(acrylic acid) hydrogels (a) before and after exposure to high pressure (b), swollen ATP/fly ash/poly(acrylic acid) hydrogels before and after shearing force (c, d). Reprinted with permission from ref 33. Copyright 2014 American Chemical Society. SEM image of porous structure the hydrogel spheres (e), the schematic diagram of emulsion stabilized by magnetic ATP composites (f), and digital image of hydrogel spheres (g). Reprinted with permission from ref 91. Copyright 2017 Elsevier.

Actually, external conditions in wastewater treatment process were extremely complicated. Smart hydrogels responding to different parameters, such as temperature, pH values, and magnetic property, gradually attracted considerable attention for wastewater treatment.93,94 For example, Yuan et al. incorporated magnetic ATP into multiple stimulus-responsive poly(ethylene glycol)-based hydrogels for cationic RhB dye adsorption.95 By changing pH values of solution from 5.7 to 9.2, the adsorption capacity obviously declined, which was mainly associated with protonation of -COOH groups. By contrast, dye adsorption significantly increased to 1.3 mg/g at pH 4.6 due to ionization behavior of -COOH groups. In addition to that, the adsorption performance is also highly dependent on operating temperatures. When temperature fluctuated the lower critical solution temperature (LCST), the molecular chains of hydrogels network stretched or shrank, thus affecting adsorption efficiency. Specifically, temperature below the LCST can boost dyes diffusion into the inner of the 20


Page 21 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydrogels spontaneously, so removal efficiency rose. In contrast, hydrogels network started to shrink, resulting in lower removal efficiency. Currently, magnetic and millimeter-sized ATP-based materials have been regarded as the most promising adsorbents due to recyclability as well as easy industrial operation. Table 1 summarizes some recyclable sorbents for decontamination of dyes, oil and metal ions. To be a promising sorbent, the absorption capacity is also the key parameter to evaluate the absorption performance. One main drawback of these porous sorbents (naked magnetic ATP or PES supporter composites) for metal ions or dyes removal is their low adsorption capacity. Introducing functional groups aimed at pollutants is a more direct and efficient method to develop high-performance sorbents. In addition, we believe that specific surface area of ATP is not the crucial factor for metal ions, oils, and dyes adsorption. For example, Wang et al. reported a raw attapulgite and the one coated with MgO (MgO/ATP), resulting in the decrement of specific surface areas, which was 137 m2/g for ATP and 114 m2/g for MgO/ATP, respectively. After Cd (II) adsorption, the researchers found that the adsorption capacity for ATP was 10.4 mg/g while for MgO/ATP was 121.1 mg/g.29 Another example was that the specific surface areas of ATP treated with 3-aminopropyltriethoxysilane was dramatically declined from 152.7 m2/g to 62.4 m2/g, but the adsorption performance for dyes increased.75 For oil sorbents, the density of sorbents is an important parameter and directly related to oil capacity because of the mechanism of physical adsorption. If these sorbents had higher density, oils or organic molecules could not be stored in the pores owing to their lower porosity. As a proof of concept, hydrophobic ATP/PU sponges show extraordinary performance than all-inorganic ATP monolith oil sorbents. In particular, the specific surface area of all-inorganic ATP monolith was 71.6 m2/g while the ATP/PU sponges were very low. 21


ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 22


Page 22 of 40

Page 23 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46


Table 1 Summary of adsorption capacities and mechanisms on different recyclable sorbents Strategies Magnetic ATP

Sorbents ATP/Fe3O4

Modifying agent FeCl3·6H2O,

Pollutant Eu (III)

pH

Adsorption capacity

Adsorption mechanisms

Ref.

5

4.94×10-4 mol/g

Low pH: ion exchange, outer-sphere

49

adsorption

FeSO4·7H2O,

surface complexation;

materials

NaOH

High pH: inner-sphere surface complexes, surface coprecipitation

2,4-DCP/ATP/Fe3O4

2,4-DCP

2,4-DCP

6

145.8 mg/g

-

50

Cu/ATP/CTS

CuSO4·5H2O

Cu (II)

5-6

32 mg/g

-

52

ATP/Fe3O4/PANI

PANI

MB; CR

7

MB: 16.5%

Electrostatic interaction, hydrogen bond,

57

CR: 96%

π-π interaction

Ag (I): 90%,

bonding with carboxyl and amine groups

61

MB：electrostatic interraction, hydrogen

62

COOH/NH2-ATP/

β-cyclodextrin,

Ag (I), Pd (II), Pt

Fe3O4

chitosan,

(IV)

4

Pd (II): 90%,

L-cysteine COOH-ATP/C/

CH3COONa·3H2O

Pt (IV): 60% MB, Pb (II)

MB: 6.2,

Fe3O4 NiFe-LDHs/ATP/Fe3O4

Pb (II): 5.5 Fe(NO3)3·9H2O,

MB, Pb (II), CTC

Ni(NO3)2·6H2O

MB: 254.8 mg/g,

bond, π-π interaction；Pb (II): electrostatic

Pb (II): 312.7 mg/g

attraction, surface complexes, ion exchange

MB: 6.2,

MB: 271.3mg/g

MB: electrostatic attraction, π-π

Pb (II):5.5,

Pb (II): 180.9 mg/g,

interaction, hydrogen bond; Pb (II):

CTC: 4.2

CTC: 308.2 mg/g

electrostatic attraction, ion-exchange,

63

chemical complexation; CTC: electrostatic interaction,hydrogen bonds, π-π stacking interaction, π-p stacking interaction Millimeter-

Fe-modified ATP

sized ATP-based

granule

FeCl3·6H2O

As (III), As (V)

5-9

As (III)：3.3 mg/g

Complexation

76

Physical adsorption

77

As (V)：5.1 mg/g

monoliths sorbents PDMS-ATP monolith ATP/PES beads

PDMS, CaCO3, HCl

organics

-

ca.1.2-2.8 v/v

PES

Cu (II), Cd (II)

Cu (II):

Cu (II): 25.3 mg/g

4.7, Cd

Cd (II): 32.7 mg/g

(II): 5.2 23


Ionic exchange, electrostatic attraction

26

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Hydrogel sorbents

Page 24 of 40

DVB-ATP/PES spheres

DVB, PES

Crude oils

-

17.1 g/g

Physical adsorption

78

ATP/SA foams

SA, CaCl2

Cu (II), Cd (II)

Cu (II):4.7,

Cu (II): 119 mg/g

Ion exchange; electrostatic attraction,

12

Cd (II):6.4

Cd (II): 160 mg/g

OTCS-ATP/PU sponges

OTCS,

Oil/water mixture,

21-43 g/g

Physical adsorption

85

anhydrous ethanol

Oil/water emulsion

99.9%

AA

Pb (II)

38 mg/g

Chelating interaction, electrostatic

33

poly(acrylic acid)

(initial concentration :

attraction

hydrogels

100 mg/L)

ATP/fly ash/

ATP/fly ash/

AA, acrylamide

5

Pb (II)

6

40 mg/g

Chelating action,

poly(acrylic

(initial concentration :

ion exchange

acid-co-acrylamide)

100 mg/L)

88

microgels ATP/SA/

AA, SA

Cu (II), Pb (II)

-

poly(acrylic acid) HC/AA/ATP

Cu (II): 272.8 mg/g

Chelating action

89

ion exchange, complexation

91

MB: 1625 mg/g,

electrostatic

92

MV:1585 mg/g

attraction, complexation

Pb (II): 391.7 mg/g HC, AA

Rb (I), Cs (I)

4-11

Rb (I): 322.5 mg/g Cs (I):239.9 mg/g

Carboxymethylcellulose

Carboxymethyl-

-graft-poly

cellulose, acryl amide

MB, MV

4-10

(acryl amide)/PAL Poly(ethylene

association ethylene glycol/ATP

RhB

4.6

glycol)-based hydrogels

1.3 mg/g

electrostaticinteraction, diffusion

24


95

Page 25 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


FILTRATION MATERIALS Although existing ATP-based sorbents for oils removal have been considered as one of the most promising candidates in oil pollutants treatment, one inevitable drawback is time-consuming for self-recovery. Conversely, filtration membranes/meshes materials only allow oil phase or water phase to pass through freely, while blocking another phase from permeating, resulting in continuously selective separation. In this part, a variety of special wettable filtration materials are well discussed on the basis of their substrates used, like metallic meshes and organic/inorganic membranes.

Filtration meshes. Filtration meshes, owing to robust mechanical strength, industrial large-scale production, and high filtration flux, are widely used as substrates for selective oil/water mixture separation.96,97 To construct superhydrophobic and superoleophilic surfaces, an easier method is to decorate filtration meshes with low-surface-energy materials between oil and water phase, and surface roughness also plays an indispensable role in achieving superhydrophobicity (WCA > 150°).98 Following this concept, superhydrophobic ATP/meshes with excellent oil/water separation efficiency were fabricated through a spray-coating method.99 Here, ATP was pre-modified with OTCS, and then coated on the meshes, thus producing hierarchically micro/nanostructures and low-surface-energy surface (Figure 7a). As shown in the Figure 7b, when oil/water mixture was in contact with a mesh, water molecules were retained. More significantly, modified meshes possessed gravity-driven oil/water separation ability, which met requirements for wastewater purification in large-scale real applications. But in this work, the superhydrophobic stability was excluded, particularly in mechanical scratch conditions. To improve the durability and stability of oil/water 25



Page 26 of 40

materials, Yang et al. demonstrated that adding durable polymer in precursor solutions could construct robust superhydrophobic Epoxy/ATP meshes for oil/water separation.100 The researchers directly sprayed precursors containing epoxy resin, curing agent (polyamide), and ATP suspension to stainless steel meshes via a airbrush. After that, the original meshes with smooth surface became rough with some micro/nanostructures, and were endowed superhydrophobic property with WCA of 160 ± 1o and water sliding angle (WSA) of 2 ± 1o (Figure 7c-e). As shown in the Figure 7f, when the oil/water mixture was poured on the mesh, oil passed meshes easily and were collected by a beaker at the same time, indicating its excellent hydrophobicity and oleophilicity. More importantly, exposed to mechanical scratch and humid atmosphere, ATP/meshes still had high separation efficiency in extremely realistic conditions, making them a promising material for selective oil/water separation. Additionally, Li et al. reported superhydrophilic ATP/meshes for oil/water separation.39 Owing to intrinsic hydrophilicity of ATP, these modified meshes allowed water phase to flow through quickly by the driving force of gravity while oil phase was retained. As ATP is non-toxic and eco-friendly, it may also have a promise as coating materials to decorate polymeric sponges.

Figure 7. The preparation of ATP-coated mesh (a) and the separation process of obtained mesh for oil/water 26


Page 27 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mixture (b) Reprinted with permission from ref 99. Copyright 2015 Royal Society of Chemistry. SEM images of original mesh (c), the epoxy/attapulgite-coated mesh (d, e), and the separation process of obtained mesh for hexadecane/water mixture (f). Reprinted with permission from ref 100. Copyright 2015 Elsevier.

Except for DVB,78 PDMS,77 or OTCS,85,99 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES),101-105 and other nonfluorinated polysiloxane (n-hexadecyltrimethoxysilane (HDTMS)), (methyltrimethoxysilane (MTMS))106,107 are applied to create superamphiphobic or other coatings. We have summarized them in the Table 2, but do not discussed them in detail in this mini review.

Filtration membranes. The emulsified liquid droplets (less than 20 µm in size), are much smaller than metallic meshes. It is not suitable for effective filtration of oil/water emulsions separation.97 Furthermore, this kind of hydrophobic and oleophilic filtration materials have high affinity towards oils, so membranes are easily fouled and plugged during selective separation of oil/water emulsion, which seriously affect water flux, reusability, and selectivity. Besides, water barrier layer is always formed between filtration mesh materials and oil layer, and makes it difficult for oil droplets permeation due to water density much higher than water.108 Currently, during the filtration process, water

droplets

transport

freely

while

oil

droplets

are

completely

repelled,

so

superhydrophilic/underwater superoleophobic materials may be a better choice for high-efficiency oil/water emulsions separation. In previous studies, Zhu et al. tuned pore size of ATP-based ultrafiltration membranes for effective oil/water emulsion separation.109 Other researchers also proposed that incorporating hydrophilic ATP in ultrafiltration membranes was one of the most popular methods to improve water flux and anti-oil-fouling property.110,111 27



Page 28 of 40

Based on these principles and strategies, Li et al. reported superhydrophilic and underwater superoleophobic ATP-coated polyvinylidene fluoride (PVDF) membranes for emulsion separation under strong acidic, basic, and concentrated salty conditions.112 From the SEM images (Figure 8a), it was clear that the as-prepared PVDF membrane had an average pore size of less than 100 nm with rough

surface

after

being

completely

covered

with

ATP.

Both

surface

hierarchical

micro/nanostructures and hydrophilic chemical compositions granted hydrophilicity in air (WCA：0o) and underwater superoleophobicity (oil contact angle (OCA)：ca. 154o, oil sliding angle (OSA): ca. 5o) (Figure 8b). Moreover, the obtained membrane was still flexible and robust because of the existence of sodium alginate. Benefiting from the synergistic effect between underwater superoleophobicity and the size-sieving effect, the maximum flux of ATP-coated membranes for hexane/water emulsion was around 700 L/(m2/h). From Figure 8c, it was obvious that there were no oil droplets in the filtrate, proving the high efficiency for separating kerosene-in-HCl emulsion (large than 99.2%). Currently, filtration membranes may exhibit low water flux, and it is urgent to develop high-performance membrane materials with high water permeation flux to meet requirements of industrial applications. For example, PAL/graphene oxide (GO) dispersions were vacuum-filtrated on cellulose acetate membrane (pore size: 220 nm) to fabricate superhydrophilic and underwater superoleophobic membranes by a self-assembly method.113 Thereinto, PAL and GO were strongly bonded via hydrogen bond, π-π stacking, and alkoxide or dative bonds (Figure 8d). Intercalating rod-like PAL into GO nanosheets was to tailor the hierarchical nanostructures and enhance water transport performance (Figure 8e). Therefore, the water flux for PAL/GO membranes (1867 L/(m2/h)) was much higher than GO membranes (267 L/(m2h)). It was explained that this kind of 28


Page 29 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


high flux was associated with synergistic effect of the interlayer distance of GO, and nanochannel structures in hybrid membranes. Moreover, the obtained membrane had no crack after bend, suggesting the flexibility did not change after introduction of PAL (Figure 8f). These recyclable membranes can be assembled into membrane devices for practical operation, and were regenerated for many times by a simple alcohol washing method after oil/water emulsions.

Figure 8. SEM images of PVDF membrane before and after covering ATP (a), optical images of water and oil CA of membrane in air, and underwater oil (kerosene) (b), and digital photos of kerosene-in-HCl emulsion before and after filtration (c). Reprinted with permission from ref 112. Copyright 2017 Wiley. Schematic diagram of design of PAL/GO membrane (d), SEM image and digital photo of PAL/GO membrane (e, f). Reprinted with permission from ref 113. Copyright 2016 American Chemical Society.

Table 2 lists recent filtration materials for oil/water separation, and other significant methods for surface modification applied to design superamphiphobic or other coatings. According to detailed discussion, it concluded that each filtration substrates (e.g., meshes, and polymer membranes) possessed unique advantages during selective oil/water separation process. Following aspects should be considered to design oil/water separation materials in face of different industrial requirements. Firstly, the pore size should be well tuned in order to fit different types of oil/water mixture. Secondly, for hydrophobic and oleophilic or superhydrophilic and underwater superoleophobic 29



Page 30 of 40

materials, surface micro/nanostructure and stable chemical composition should be ensured for high separation efficiency. Lastly, durability, stability and flux should be guaranteed when they are applied in the industrial applications. Table 2 Summary different of substrates, surface modification and applications. Substrates

Surface

Method

Applications

modification Stainless steel mesh Stainless steel mesh Copper mesh PVDF membrane Cellulose acetate

Contact

Slide angles

Ref 100

angles Spraying

oil/water

160 ± 1o

2 ± 1o

coating

mixtue

(WCA)

(WSA)

OTCS/ATP/

Spraying

oil/water

158 ± 1o

8o

waterborne polyurethane

coating

mixtue

(WCA)

(WSA)

Epoxy/ATP/polyamide

ATP/

Spraying

oil/water


coating

mixtue

SA/ATP PAL/GO

membrane

vacuum

Oil/water

filtration

emulsion

Vacuum

Oil/water

filtration

emulsion

150o

(OCA)

8o (OSA) 5o (OSA)

112

165o (OCA)

-

113 101

(OCA)

tetraethoxysilane

Spray

Colorful

157.3 ± 0.6o

12.6 ± 0.5o

plastic

(TEOS)/PFDTES/PLA/

coating

superamphiphobic

(OCA)

(OSA)

coating

(n-Decane);

(n-Decane);

166.3 ± 2.4o

2.2 ± 0.4o

(WCA)

(WSA)

Polyurethane plate/

TEOS/PFDTES/PLA

Spray

Self-healing

156.0 ±0.3

9.0 ±1.0

polyester textile/

(sepiolite, halloysite,

coating

superamphiphobic

(OCA)

(OSA)

aluminium plate/

Na+-montmorillonite)/

coating

(n-Decane);

(n-Decane);

wood plate/

ammonia

165.6 ±1.2

1.0

(WCA)

(WSA)

PTFE plate Glass slide

Glass slide

TEOS/PFDTES/ATP/C/

Spray

Superamphiphobic

ammonia

coating

coating

Glass slide

11.3 ± 1.5o

(OCA)

(OSA)

(n-Decane);

(n-Decane);

167.6 ± 1.5o

1.3 ± 0.5o

(WCA)

(WSA) 18.7o

TEOS/PFDTES/PLA/

Spray

Superoleophobic

ammonia/FeCl3/ethylene

coating

Coating/magnetic

(OCA)

(OSA)

liquid marble

(toluene);

(toluene);

161.4o

7.7o

(WCA)

(WSA) 9.5o

HDTMS/PLA/TESO/

Spray

Allochroic

164.5o

ammonia/ Crystal Violet

coating

superhydrophobic

(WCA)

(WSA)

157.9o

7.2o

Lactone Glass slide

154.2 ±

1o

155.3o

glycol

MTMS/PLA/

39

(chloroform) 154o

Glass slide/wood/

ammonia

99

103

102

104

106

coating Spray

Nonfluorinated 30


107

Page 31 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



coating

superhydrophobic

(WAC)

(WSA)

Coatings

CONCLUSION AND OUTLOOK In this review, we have highlighted recent emerged recyclable and porous ATP-based composites as effective water remediation materials, which can selectively adsorb and separate contaminants from water. Although these extraordinary materials have shown promise for wastewater treatment, there are still some challenges and problems to be overcome. From the fundamental adsorption and separation point of view, the most crucial problem is how to obtain porous materials. From preparation process point of view, green preparation process and disposal of waste should be advocated. From industrial applications point of view, the cost of adsorption and filtration materials should be considered in the first place. Furthermore, weak mechanical and unstable chemical properties of materials have been limited under the harsh conditions such as high salinity, strong acid and base, hot temperature, UV radiation and others. In terms of aforementioned challenges, future research trends are suggested to be considered as follows. (1) Development and functionalization of advanced porous and recyclable materials should be put on the agenda. (2) Facile and green methods that are practically suitable for large-scale production should be developed. (3) The improvement of durability and stability of ATP composites is one of the essential requirements. In consideration of strong interest in development of recyclable ATP composites in research community, novel designs and techniques for such materials synthesis will continue to emerge in the near future.

ACKNOWLEDGEMENT The authors are grateful for the financial support of Natural Science Key Project of the Jiangsu 31



Page 32 of 40

Higher Education Institutions (15KJA220001), Jiangsu Province Six Talent Peaks Project (2016-XCL-043) and Key Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province (HPK201702). YF thanks the financial support of the Natural Science Foundation of Jiangsu Province Youth Fund (BK20170919).

REFERENCE 1. Feng, Y.; Liu, S.; Liu, G.; Yao, J. Facile and fast removal of oil through porous carbon spheres derived from the fruit of Liquidambar formosana. Chemosphere 2017, 170, 68-74, DOI 10.1016/j.chemosphere.2016.11.166. 2. Abukhadra, M. R.; Dardir, F. M.; Shaban, M.; Ahmed, E. A.; Soliman, M. F. Superior removal of Co2+, Cu2+ and Zn2+ contaminants from water utilizing spongy Ni/Fe carbonate-fluorapatite; preparation, application and mechanism. Ecotox. Environ. Safe. 2018, 157, 358-368, DOI 10.1016/j.ecoenv.2018.03.085. 3. Qiu, J.; Feng, Y.; Zhang, X.; Jia, M.; Yao, J. Acid-promoted synthesis of UiO-66 for highly selective adsorption of anionic dyes: Adsorption performance and mechanisms. J. Colloid. Interf. Sci. 2017, 499, 151-158, DOI 10.1016/j.jcis.2017.03.101. 4. Saber-Samandari, S.; Saber-Samandari, S.; Joneidi-Yekta, H.; Mohseni, M. Adsorption of anionic and cationic dyes from aqueous solution using gelatin-based magnetic nanocomposite beads comprising carboxylic acid functionalized carbon nanotube. Chem. Eng. J. 2017, 308, 1133-1144, DOI 10.1016/j.cej.2016.10.017. 5. Wang, Y.; Feng, Y.; Yao, J. Construction of hydrophobic alginate-based foams induced by zirconium ions for oil and organic solvent cleanup. J. Colloid. Interf. Sci. 2018, 533, 182-189, DOI 10.1016/j.jcis.2018.08.073. 6. Yin, H.; Yang, C.; Jia, Y.; Chen, H.; Cu, X. Dual removal of phosphate and ammonium from high concentrations of aquaculture wastewaters using an efficient two-stage infiltration system. Sci. Total. Environ. 2018, 635, 936-946, DOI 10.1016/j.scitotenv.2018.04.218. 7. Burakov, A. E.; Galunin, E. V.; Burakova, I. V.; Kucherova, A. E.; Agarwal, S.; Tkachev, A. G.; Gupta, V. K. Adsorption of heavy metals on conventional and nanostructured materials for wastewater treatment purposes: A review. Ecotox. Environ. Safe. 2018, 148, 702-712, DOI 10.1016/j.ecoenv.2017.11.034. 8. Zhu, W.; Li, Y.; Dai, L.; Li, J.; Li, X.; Li, W.; Duan, T.; Lei, J.; Chen, T. Bioassembly of fungal hyphae/carbon nanotubes composite as a versatile adsorbent for water pollution control. Chem. Eng. J. 2018, 339, 214-222, DOI 10.1016/j.cej.2018.01.134. 9. Liu, P.; Jiang, L.; Zhu, L.; Wang, A. Attapulgite/Poly(acrylic acid) nanocomposite (ATP/PAA) hydrogels with multifunctionalized attapulgite (org-ATP) nanorods as unique cross-linker: preparation optimization and selective adsorption of Pb (II) ion. ACS Sustain. Chem. Eng. 2014, 2 (4), 643-651, DOI 10.1021/sc400321v. 10. Chen, L.-F.; Lang, H.-W.; Lu, Y.; Cui, C.-H.; Yu, S.-H. Synthesis of an Attapulgite 32


Page 33 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Clay@Carbon Nanocomposite Adsorbent by a Hydrothermal Carbonization Process and Their Application in the Removal of Toxic Metal Ions from Water. Langmuir 2011, 27 (14), 8998-9004, DOI 10.1021/la2017165. 11. Middea, A.; Spinelli, L. S.; Souza, F. G., Jr.; Neumann, R.; Fernandes, T. L. A. P.; Gomes, O. d. F. M. Preparation and characterization of an organo-palygorskite-Fe3O4 nanomaterial for removal of anionic dyes from wastewater. Appl. Clay. Sci. 2017, 139, 45-53, DOI 10.1016/j.clay.2017.01.017. 12. Wang, Y.; Feng, Y.; Zhang, X.-F.; Zhang, X.; Jiang, J.; Yao, J. Alginate-based attapulgite foams as efficient and recyclable adsorbents for the removal of heavy metals. J. Colloid. Interf. Sci. 2018, 514, 190-198, DOI 10.1016/j.jcis.2017.12.035. 13. Dong, K.; Qiu, F.; Guo, X.; Xu, J.; Yang, D.; He, K. Polyurethane-attapulgite porous material: Preparation, characterization, and application for dye adsorption. J. Appl. Polym. Sci. 2013, 129 (4), 1697-1706, DOI 10.1002/app.38874. 14. Liao, Y.; Wang, M.; Chen, D. Production of three-dimensional porous polydopamine-functionalized attapulgite/chitosan aerogel for uranium (VI) adsorption. J. Radioanal. Nucl. Chem. 2018, 316 (2), 635-647, DOI 10.1007/s10967-018-5816-2. 15. Liu, Y.; Feng, Y.; Yao, J. Recent advances in the direct fabrication of millimeter-sized hierarchical porous materials. RSC Adv. 2016, 6 (84), 80840-80846, DOI 10.1039/c6ra17018h. 16. Liu, P.; Jiang, L.; Zhu, L.; Wang, A. Novel approach for attapulgite/poly(acrylic acid) (ATP/PAA) nanocomposite microgels as selective adsorbent for Pb (II) Ion. React. Funct. Polym. 2014, 74, 72-80, DOI 10.1016/j.reactfunctpolym.2013.11.002. 17. Zhang, G.; Qin, Y.; Lv, C.; Liu, X.; Zhao, Y.; Chen, L. Adsorptive removal of Ni (II) ions from aqueous solution by PVDF/Gemini-ATP hybrid membrane. Membr. Water. Treat. 2016, 7 (3), 209-221, DOI 10.12989/mwt.2016.7.3.209. 18. Liang, W.; Wang, Y.; Sun, H.; Chen, P.; Zhu, Z.; Li, A. Superhydrophobic attapulgite-based films for the selective separation of oils and organic solvents from water. RSC Adv. 2015, 5 (127), 105319-105323, DOI 10.1039/c5ra21791a. 19. Zhang, X.; Wang, J. Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium. Solid. State. Sci. 2018, 75, 14-20, DOI 10.1016/j.solidstatesciences.2017.11.003. 20. Chen, H.; Zhao, J.; Zhong, A.; Jin, Y. Removal capacity and adsorption mechanism of heat-treated palygorskite clay for methylene blue. Chem. Eng. J. 2011, 174 (1), 143-150, DOI 10.1016/j.cej.2011.08.062. 21. Chen, H.; Zhong, A.; Wu, J.; Zhao, J.; Yan, H. Adsorption behaviors and mechanisms of methyl orange on heat-treated palygorskite clays. Ind. Eng. Chem. Res. 2012, 51 (43), 14026-14036, DOI 10.1021/ie300702j. 22. Li, X.-Y.; Zhang, D.-Y.; Liu, X.-Q.; Shi, L.-Y.; Sun, L.-B. A tandem demetalization-desilication strategy to enhance the porosity of attapulgite for adsorption and catalysis. Chem. Eng. Sci. 2016, 141, 184-194, DOI 10.1016/j.ces.2015.11.011. 23. Yeh, J.-T.; Wang, C.-K.; Hu, P.; Lai, Y.-C.; Huang, L.-K.; Tsai, F.-C. Ultradrawing properties of ultrahigh-molecular-weight polyethylene/attapulgite fibers. Poly. Int. 2012, 61 (6), 982-989, DOI 10.1002/pi.4169. 24. Wu, M.; Ma, T.; Su, Y.; Wu, H.; You, X.; Jiang, Z.; Kasher, R. Fabrication of composite nanofiltration membrane by incorporating attapulgite nanorods during interfacial polymerization for high water flux and antifouling property. J. Membrane. Sci. 2017, 544, 79-87, DOI 10.1016/j.memsci.2017.09.016. 33



Page 34 of 40

25. Cao, J.-L.; Shao, G.-S.; Wang, Y.; Liu, Y.; Yuan, Z.-Y. CuO catalysts supported on attapulgite clay for low-temperature CO oxidation. Catal. Commun. 2008, 9 (15), 2555-2559, DOI 10.1016/j.catcom.2008.07.016. 26. Feng, Y.; Wang, Y.; Wang, Y.; Liu, S.; Jiang, J.; Cao, C.; Yao, J. Simple fabrication of easy handling millimeter-sized porous attapulgite/polymer beads for heavy metal removal. J. Colloid. Interf. Sci. 2017, 502, 52-58, DOI 10.1016/j.jcis.2017.04.086. 27. Tang, J.; Mu, B.; Zheng, M.; Wang, A. One-Step calcination of the spent bleaching earth for the efficient removal of heavy metal ions. ACS Sustain. Chem. Eng. 2015, 3 (6), 1125-1135, DOI 10.1021/acssuschemeng.5b00040. 28. Thabo Falayi, F. N. Removal of heavy metals and neutralisation of acid mine drainage with un-activated attapulgite. J. Ind. Eng. Chem. 2014, 20 (4), 1285-1292, DOI 10.1016/j.jiec.2013.07.007. 29. Wang, H.; Wang, X.; Ma, J.; Xia, P.; Zhao, J. Removal of cadmium (II) from aqueous solution: A comparative study of raw attapulgite clay and a reusable waste-struvite/attapulgite obtained from nutrient-rich wastewater. J. Hazard. Mater. 2017, 329, 66-76, DOI 10.1016/j.jhazmat.2017.01.025. 30. Huang, D.; Wang, W.; Xu, J.; Wang, A. Mechanical and water resistance properties of chitosan/poly(vinyl alcohol) films reinforced with attapulgite dispersed by high-pressure homogenization. Chem. Eng. J. 2012, 210, 166-172, DOI 10.1016/j.cej.2012.08.096. 31. Zhang, X.-F.; Hou, T.; Chen, J.; Feng, Y.; Li, B.; Gu, X.; He, M.; Yao, J. Facilitated transport of CO2 through the transparent and flexible cellulose membrane promoted by fixed-site carrier. ACS Appl. Mater. Inter. 2018, 10 (29), 24930-24936, DOI 10.1021/acsami.8b07309. 32. Zhang, X.-F.; Feng, Y.; Huang, C.; Pan, Y.; Yao, J. Temperature-induced formation of cellulose nanofiber film with remarkably high gas separation performance. Cellulose 2017, 24 (12), 5649-5656, DOI 10.1007/s10570-017-1529-x. 33. Jiang, L.; Liu, P. Design of magnetic attapulgite/Fly Ash/Poly(acrylic acid) ternary nanocomposite hydrogels and performance evaluation as selective adsorbent for Pb2+ ion. ACS Sustain. Chem. Eng. 2014, 2 (7), 1785-1794, DOI 10.1021/sc500031z. 34. Cui, H.; Qian, Y.; Li, Q.; Zhang, Q.; Zhai, J. Adsorption of aqueous Hg (II) by a polyaniline/attapulgite composite. Chem. Eng. J. 2012, 211, 216-223, DOI 10.1016/j.cej.2012.09.057. 35. Wang, C.; Guo, Z.; Hong, R.; Gao, J.; Guo, Y.; Gu, C. A novel method for synthesis of polyaniline and its application for catalytic degradation of atrazine in a Fenton-like system. Chemosphere 2018, 197, 576-584, DOI 10.1016/j.chemosphere.2018.01.050. 36. Zhou, L.; Xu, S.; Zhang, G.; Cai, D.; Wu, Z. A facile approach to fabricate self-cleaning paint. Appl. Clay. Sci. 2016, 132, 290-295, DOI 10.1016/j.clay.2016.06.015. 37. Wang, J.; Liu, S.; Tang, W. Enhanced adsorption of humic acid on APTES modified palygorskite: behavior and mechanism. Desalin. Water. Treat. 2017, 79, 313-321, DOI 10.5004/dwt.2017.20818. 38. Liu, P. Polymer modified clay minerals: A review. Appl. Clay. Sci. 2007, 38 (1-2), 64-76, DOI 10.1016/j.clay.2007.01.004. 39. Li, J.; Yan, L.; Li, H.; Li, W.; Zha, F.; Lei, Z. Underwater superoleophobic palygorskite coated meshes for efficient oil/water separation. J. Mater. Chem. A 2015, 3 (28), 14696-14702, DOI 10.1039/c5ta02870a. 40. Wang, W.; Wang, A. Nanocomposite of carboxymethyl cellulose and attapulgite as a novel 34


Page 35 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pH-sensitive superabsorbent: Synthesis, characterization and properties. Carbohyd. Polym. 2010, 82 (1), 83-91, DOI 10.1016/j.carbpol.2010.04.026. 41. Middea, A.; Spinelli, L. S.; Souza Junior, F. G.; Neumann, R.; Gomes, O. d. F. M.; Fernandes, T. L. A. P.; de Lima, L. C.; Barthem, V. M. T. S.; de Carvalho, F. V. Synthesis and characterization of magnetic palygorskite nanoparticles and their application on methylene blue remotion from water. Appl. Surf. Sci. 2015, 346, 232-239, DOI 10.1016/j.apsusc.2015.03.080. 42. Rusmin, R.; Sarkar, B.; Tsuzuki, T.; Kawashima, N.; Naidu, R. Removal of lead from aqueous solution using superparamagnetic palygorskite nanocomposite: Material characterization and regeneratilon studies. Chemosphere 2017, 186, 1006-1015, DOI 10.1016/j.chemosphere.2017.08.036. 43. Zeng, Y.; Yao, J.; Horri, B. A.; Wang, K.; Wu, Y.; Li, D.; Wang, H. Solar evaporation enhancement using floating light-absorbing magnetic particles. Energ. Environ. Sci. 2011, 4 (10), 4074-4078, DOI 10.1039/c1ee01532j. 44. Liu, Y.; Liu, P.; Su, Z.; Li, F.; Wen, F. Attapulgite-Fe3O4 magnetic nanoparticles via co-precipitation technique. Appl. Surf. Sci. 2008, 255 (5), 2020-2025, DOI 10.1016/j.apsusc.2008.06.193. 45. Kim, Y. H.; Sim, B.; Choi, H. J. Fabrication of magnetite-coated attapulgite magnetic composite nanoparticles and their magnetorheology. Colloid. Surface. A. 2016, 507, 103-109, DOI 10.1016/j.colsurfa.2016.07.095. 46. Fan, Q.-h.; Li, P.; Chen, Y.-f.; Wu, W.-s. Preparation and application of attapulgite/iron oxide magnetic composites for the removal of U (VI) from aqueous solution. J. Hazard. Mater. 2011, 192 (3), 1851-1859, DOI 10.1016/j.jhazmat.2011.07.022. 47. Chen, L.; Xu, J.; Hu, J. Removal of U (VI) from aqueous solutions by using attapulgite/iron oxide magnetic nanocomposites. J. Radioanal. Nucl. Chem. 2013, 297 (1), 97-105, DOI 10.1007/s10967-012-2360-3. 48. Lei, C.; Tian, X.; Ma, B. Effect of pH, ionic strength, foreign ions and temperatures on the sorption of Eu (III) on attapulgite-iron oxide magnetic composites. J. Radioanal. Nucl. Chem. 2013, 298 (2), 1127-1135, DOI 10.1007/s10967-013-2480-4. 49. Lu, Z.; Hao, Z.; Wang, J.; Chen, L. Efficient removal of europium from aqueous solutions using attapulgite-iron oxide magnetic composites. J. Ind. Eng. Chem. 2016, 34, 374-381, DOI 10.1016/j.jiec.2015.12.013. 50. Pan, J.; Xu, L.; Dai, J.; Li, X.; Hang, H.; Huo, P.; Li, C.; Yan, Y. Magnetic molecularly imprinted polymers based on attapulgite/Fe3O4 particles for the selective recognition of 2,4-dichlorophenol. Chem. Eng. J. 2011, 174 (1), 68-75, DOI 10.1016/j.cej.2011.08.046. 51. Li, Z.; Kou, W.; Wu, S.; Wu, L. Solid-phase extraction of chromium (III) with an ion-imprinted functionalized attapulgite sorbent prepared by a surface imprinting technique. Anal. Methods 2017, 9 (21), 3221-3229, DOI 10.1039/c7ay00346c. 52. Shi, Y.; Zhang, Q.; Feng, L.; Xiong, Q.; Chen, J. Preparation and adsorption characters of Cu (II)-imprinted chitosan/attapulgite polymer. Korean J. Chem. Eng. 2014, 31 (5), 821-827, DOI 10.1007/s11814-014-0004-8. 53. Liang, X.; Han, J.; Xu, Y.; Wang, L.; Sun, Y.; Tan, X. Sorption of Cd2+ on mercapto and amino functionalized palygorskite. Appl. Surf. Sci. 2014, 322, 194-201, DOI 10.1016/j.apsusc.2014.10.092. 54. Cao, J.-S.; Wang, C.; Fang, F.; Lin, J.-X. Removal of heavy metal Cu (II) in simulated aquaculture wastewater by modified palygorskite. Environ. Pollut. 2016, 219, 924-931, DOI 35



Page 36 of 40

10.1016/j.envpol.2016.09.014. 55. Saleh, T. A.; Tuzen, M.; Sari, A. Polyamide magnetic palygorskite for the simultaneous removal of Hg (II) and methyl mercury with factorial design analysis. J. Environ. Manage. 2018, 211, 323-333, DOI 10.1016/j.jenvman.2018.01.050. 56. Middea, A.; Spinelli, L.; de Souza Junior, F. G.; Neumann, R.; Fernandes, T.; Leite Faulstich, F. R.; Gomes, O. Magnetic polystyrene-palygorskite nanocomposite obtained by heterogeneous phase polymerization to apply in the treatment of oily waters. J. Appl. Polym. Sci. 2018, 135 (15), 46162-46170, DOI 10.1002/app.46162. 57. Mu, B.; Wang, A. One-pot fabrication of multifunctional superparamagnetic attapulgite/Fe3O4/polyaniline nanocomposites served as an adsorbent and catalyst support. J. Mater. Chem. A 2015, 3 (1), 281-289, DOI 10.1039/c4ta05367b. 58. Yang, X.; Qiao, K.; Ye, Y.; Yang, M.; Li, J.; Gao, H.; Zhang, S.; Zhou, W.; Lu, R. Facile synthesis of multifunctional attapulgite/Fe3O4/polyaniline nanocomposites for magnetic dispersive solid phase extraction of benzoylurea insecticides in environmental water samples. Anal. Chim. Acta, 2016, 934, 114-121, DOI 10.1016/j.aca.2016.06.027. 59. Mu, B.; Wang, Q.; Wang, A. Preparation of magnetic attapulgite nanocomposite for the adsorption of Ag+ and application for catalytic reduction of 4-nitrophenol. J. Mater. Chem. A 2013, 1 (24), 7083-7090, DOI 10.1039/c3ta10658f. 60. Wang, W.; Wang, F.; Kang, Y.; Wang, A. Facile self-assembly of Au nanoparticles on a magnetic attapulgite/Fe3O4 composite for fast catalytic decoloration of dye. RSC Adv. 2013, 3 (29), 11515-11520, DOI 10.1039/c3ra41836g. 61. Mu, B.; Kang, Y.; Wang, A. Preparation of a polyelectrolyte-coated magnetic attapulgite composite for the adsorption of precious metals. J. Mater. Chem. A 2013, 1 (15), 4804-4811, DOI 10.1039/c3ta01620j. 62. Tang, J.; Mu, B.; Zong, L.; Zheng, M.; Wang, A. Facile and green fabrication of magnetically recyclable carboxyl-functionalized attapulgite/carbon nanocomposites derived from spent bleaching earth for wastewater treatment. Chem. Eng. J. 2017, 322, 102-114, DOI 10.1016/j.cej.2017.03.116. 63. Tang, J.; Mu, B.; Zong, L.; Wang, A. One-step synthesis of magnetic attapulgite/carbon supported NiFe-LDHs by hydrothermal process of spent bleaching earth for pollutants removal. J. Clean. Prod. 2018, 172, 673-685, DOI 10.1016/j.jclepro.2017.10.181. 64. Fan, Q.; Shao, D.; Lu, Y.; Wu, W.; Wang, X. Effect of pH, ionic strength, temperature and humic substances on the sorption of Ni (II) to Na-attapulgite. Chem. Eng. J. 2009, 150 (1), 188-195, DOI 10.1016/j.cej.2008.12.024. 65. Zhang, Y.; Wang, W.; Zhang, J.; Liu, P.; Wang, A. A comparative study about adsorption of natural palygorskite for methylene blue. Chem. Eng. J. 2015, 262, 390-398, DOI 10.1016/j.cej.2014.10.009. 66. Chen, H.; Zhao, Y.; Wang, A. Removal of Cu (II) from aqueous solution by adsorption onto acid-activated palygorskite. J. Hazard. Mater. 2007, 149 (2), 346-354, DOI 10.1016/j.jhazmat.2007.03.085. 67. Wang, W.; Tian, G.; Zhang, Z.; Wang, A. A simple hydrothermal approach to modify palygorskite for high-efficient adsorption of Methylene blue and Cu (II) ions. Chem. Eng. J. 2015, 265, 228-238, DOI 10.1016/j.cej.2014.11.135. 68. Wang, W.; Tian, G.; Zong, L.; Wang, Q.; Zhou, Y.; Wang, A. Mesoporous hybrid Zn-silicate derived from red palygorskite clay as a high-efficient adsorbent for antibiotics. Micropor. Mesopor. 36


Page 37 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mat. 2016, 234, 317-325, DOI 10.1016/j.micromeso.2016.07.029. 69. Zhang, Z.; Wang, W.; Wang, A. High-pressure homogenization associated hydrothermal process of palygorskite for enhanced adsorption of Methylene blue. Appl. Surf. Sci. 2015, 329, 306-314, DOI 10.1016/j.apsusc.2014.12.187. 70. Xu, J.; Wang, W.; Gao, J.; Wang, A. Fabrication of stable glycine/palygorskite nanohybrid via high-pressure homogenization as high-efficient adsorbent for Cs (I) and methyl violet. J. Taiwan. Inst. Chem. Eng. 2017, 80, 997-1005, DOI 10.1016/j.jtice.2017.09.003. 71. Cheng, W.; Ding, C.; Sun, Y.; Wang, X. Fabrication of fungus/attapulgite composites and their removal of U (VI) from aqueous solution. Chem. Eng. J. 2015, 269, 1-8, DOI 10.1016/j.cej.2015.01.096. 72. Deng, Y.; Wang, L.; Hu, X.; Liu, B.; Wei, Z.; Yang, S.; Sun, C. Highly efficient removal of tannic acid from aqueous solution by chitosan-coated attapulgite. Chem. Eng. J. 2012, 181, 300-306, DOI 10.1016/j.cej.2011.11.082. 73. Tian, G.; Wang, W.; Mu, B.; Kang, Y.; Wang, A. Facile fabrication of carbon/attapulgite composite for bleaching of palm oil. J. Taiwan. Inst. Chem. Eng. 2015, 50, 252-258, DOI 10.1016/j.jtice.2014.12.021. 74. Huang, J.; Liu, Y.; Jin, Q.; Wang, X.; Yang, J. Adsorption studies of a water soluble dye, Reactive Red MF-3B, using sonication-surfactant-modified attapulgite clay. J. Hazard. Mater. 2007, 143 (1-2), 541-548, DOI 10.1016/j.jhazmat.2006.09.088. 75. Xue, A.; Zhou, S.; Zhao, Y.; Lu, X.; Han, P. Effective NH2-grafting on attapulgite surfaces for adsorption of reactive dyes. J. Hazard. Mater. 2011, 194, 7-14, DOI 10.1016/j.jhazmat.2011.06.018. 76. Yin, H.; Kong, M.; Gu, X.; Chen, H. Removal of arsenic from water by porous charred granulated attapulgite-supported hydrated iron oxide in bath and column modes. J. Clean. Prod. 2017, 166, 88-97, DOI 10.1016/j.jclepro.2017.08.026. 77. Liang, W.; Liu, Y.; Sun, H.; Zhu, Z.; Zhao, X.; Li, A.; Deng, W. Robust and all-inorganic absorbent based on natural clay nanocrystals with tunable surface wettability for separation and selective absorption. RSC Adv. 2014, 4 (24), 12590-12595, DOI 10.1039/c3ra47371f. 78. Pan, Y.; Wang, J.; Sun, C.; Liu, X.; Zhang, H. Fabrication of highly hydrophobic organic-inorganic hybrid magnetic polysulfone microcapsules: A lab-scale feasibility study for removal of oil and organic dyes from environmental aqueous samples. J. Hazard. Mater. 2016, 309, 65-76, DOI 10.1016/j.jhazmat.2016.02.004. 79. Li, L.; Yao, J.; Xiao, P.; Shang, J.; Feng, Y.; Webley, P. A.; Wang, H. One-step fabrication of ZIF-8/polymer composite spheres by a phase inversion method for gas adsorption. Colloid. Polym. Sci. 2013, 291 (11), 2711-2717, DOI 10.1007/s00396-013-3024-8. 80. Abas, S. N. A.; Ismail, M. H. S.; Siajam, S. I.; Kamal, M. L. Development of novel adsorbent-mangrove-alginate composite bead (MACB) for removal of Pb (II) from aqueous solution. J. Taiwan. Inst. Chem. Eng. 2015, 50, 182-189, DOI 10.1016/j.jtice.2014.11.013. 81. Rusmin, R.; Sarkar, B.; Liu, Y.; McClure, S.; Naidu, R. Structural evolution of chitosan-palygorskite composites and removal of aqueous lead by composite beads. Appl. Surf. Sci. 2015, 353, 363-375, DOI 10.1016/j.apsusc.2015.06.124. 82. Feng, Y.; Wang, Y.; Wang, Y.; Yao, J. Furfuryl alcohol modified melamine sponge for highly efficient oil spill clean-up and recovery. J. Mater. Chem. A 2017, 5 (41), 21893-21897, DOI 10.1039/c7ta06966a. 83. Feng, Y.; Wang, Y.; Wang, Y.; Zhang, X.-F.; Yao, J. In-situ gelation of sodium alginate 37



Page 38 of 40

supported on melamine sponge for efficient removal of copper ions. J. Colloid. Interf. Sci. 2018, 512, 7-13, DOI 10.1016/j.jcis.2017.10.036. 84. Feng, Y.; Yao, J. Design of melamine sponge-based three-dimensional porous materials toward applications. Ind. Eng. Chem. Res. 2018, 57 (22), 7322-7330, DOI 10.1021/acs.iecr.8b01232. 85. Li, J.; Xu, C.; Zhang, Y.; Wang, R.; Zha, F.; She, H. Robust superhydrophobic attapulgite coated polyurethane sponge for efficient immiscible oil/water mixture and emulsion separation. J. Mater. Chem. A 2016, 4 (40), 15546-15553, DOI 10.1039/c6ta07535e. 86. Wang, X.; Zheng, Y.; Wang, A. Fast removal of copper ions from aqueous solution by chitosan-g-poly(acrylic acid)/attapulgite composites. J. Hazard. Mater. 2009, 168 (2-3), 970-977, DOI 10.1016/j.jhazmat.2009.02.120. 87. Wang, Q.; Chen, D. Synthesis and characterization of a chitosan based nanocomposite injectable hydrogel. Carbohyd. Polym. 2016, 136, 1228-1237, DOI 10.1016/j.carbpol.2015.10.040. 88. Jiang, L.; Liu, P.; Zhao, S. Magnetic ATP/FA/Poly(AA-co-AM) ternary nanocomposite microgel as selective adsorbent for removal of heavy metals from wastewater. Colloid. Surface. A. 2015, 470, 31-38, DOI 10.1016/j.colsurfa.2015.01.078. 89. Mao, X.; Wang, L.; Gu, S.; Duan, Y.; Zhu, Y.; Wang, C.; Lichtfouse, E. Synthesis of a three-dimensional network sodium alginate-poly(acrylic acid)/attapulgite hydrogel with good mechanic property and reusability for efficient adsorption of Cu2+ and Pb2+. Environ. Chem. Lett. 2018, 16 (2), 653-658, DOI 10.1007/s10311-018-0708-9. 90. Pan, J.; Li, L.; Hang, H.; Wu, R.; Dai, X.; Shi, W.; Yan, Y. Fabrication and evaluation of magnetic/hollow double-shelled imprinted sorbents formed by Pickering emulsion polymerization. Langmuir 2013, 29 (25), 8170-8178, DOI 10.1021/la4015288. 91. Zhu, Y.; Zhang, H.; Wang, W.; Ye, X.; Wu, Z.; Wang, A. Fabrication of a magnetic porous hydrogel sphere for efficient enrichment of Rb+ and Cs+ from aqueous solution. Chem. Eng. Res. Des. 2017, 125, 214-225, DOI 10.1016/j.cherd.2017.07.021. 92. Wang, F.; Zhu, Y.; Wang, W.; Zong, L.; Lu, T.; Wang, A. Fabrication of CMC-g-PAM superporous polymer monoliths via eco-friendly Pickering-MIPEs for superior adsorption of methyl violet and methylene blue. Front. Chem. 2017, 5, DOI 10.3389/fchem.2017.00033. 93. Wang, Y.; Dong, A.; Yuan, Z.; Chen, D. Fabrication and characterization of temperature-, pHand magnetic-field-sensitive organic/inorganic hybrid poly (ethylene glycol)-based hydrogels. Colloid. Surface. A. 2012, 415, 68-76, DOI 10.1016/j.colsurfa.2012.10.009. 94. Yuan, Z.; Wang, Y.; Chen, D. Preparation and characterization of thermo-, pH-, and magnetic-field-responsive organic/inorganic hybrid microgels based on poly(ethylene glycol). J. Mater. Sci. 2014, 49 (8), 3287-3296, DOI 10.1007/s10853-014-8037-2. 95. Yuan, Z.; Wang, Y.; Han, X.; Chen, D. The adsorption behaviors of the multiple stimulus-responsive poly(ethylene glycol)-based hydrogels for removal of RhB dye. J. Appl. Polym. Sci. 2015, 132 (28), 42244-42252, DOI 10.1002/app.42244. 96. Lin, X.; Lu, F.; Chen, Y.; Liu, N.; Cao, Y.; Xu, L.; Wei, Y.; Feng, L. One-step breaking and separating emulsion by tungsten oxide coated mesh. ACS Appl. Mater. Inter. 2015, 7 (15), 8108-8113, DOI 10.1021/acsami.5b00718. 97. Ma, Q.; Cheng, H.; Fane, A. G.; Wang, R.; Zhang, H. Recent development of advanced materials with special wettability for selective oil/water separation. Small 2016, 12 (16), 2186-2202, DOI 10.1002/smll.201503685. 98. Ge, J.; Zhao, H. Y.; Zhu, H. W.; Huang, J.; Shi, L. A.; Yu, S. H. Advanced Sorbents for 38


Page 39 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Oil-Spill Cleanup: Recent Advances and Future Perspectives. Adv. Mater. 2016, 28 (47), 10459-10490, DOI 10.1002/adma.201601812. 99. Li, J.; Yan, L.; Li, H.; Li, J.; Zha, F.; Lei, Z. A facile one-step spray-coating process for the fabrication of a superhydrophobic attapulgite coated mesh for use in oil/water separation. RSC Adv. 2015, 5 (66), 53802-53808, DOI 10.1039/c5ra08478d. 100. Yang, J.; Tang, Y.; Xu, J.; Chen, B.; Tang, H.; Li, C. Durable superhydrophobic/superoleophilic epoxy/attapulgite nanocomposite coatings for oil/water separation. Surf. Coat. Tech. 2015, 272, 285-290, DOI 10.1016/j.surfcoat.2015.03.050. 101. Dong, J.; Wang, Q.; Zhang, Y.; Zhu, Z.; Xu, X.; Zhang, J.; Wang, A. Colorful Superamphiphobic Coatings with Low Sliding Angles and High Durability Based on Natural Nanorods. ACS Appl. Mater. Inter. 2017, 9 (2), 1941-1952, DOI 10.1021/acsami.6b13539. 102. Dong, S.; Li, B.; Zhang, J.; Wang, A. Superamphiphobic coatings with low sliding angles from attapulgite/carbon composites. Adv. Mater. Interfaces 2018, 5 (9), 1701520-1701529, DOI 10.1002/admi.201701520. 103. Li, B.; Zhang, J. Durable and self-healing superamphiphobic coatings repellent even to hot liquids. Chem. Commun. 2016, 52 (13), 2744-2747, DOI 10.1039/c5cc09951j. 104. Li, L.; Li, B.; Fan, L.; Mu, B.; Wang, A.; Zhang, J. Palygorskite@Fe3O4@polyperfluoroalkylsilane nanocomposites for superoleophobic coatings and magnetic liquid marbles. J. Mater. Chem. A 2016, 4 (16), 5859-5868, DOI 10.1039/c6ta00758a. 105. Zhang, P.; Tian, N. Zhang, J.; Wang, A. Effects of modification of palygorskite on superamphiphobicity and microstructure of palygorskite@fluorinated polysiloxane superamphiphobic coatings. Appl. Clay. Sci. 2018, 160, 144-152, DOI 10.1016/j.clay.2018.01.015. 106. Zhang, Y.; Dong, J.; Sun, H.; Yu, B.; Zhu, Z.; Zhang, J.; Wang, A. Solvatochromic Coatings with Self-Cleaning Property from Palygorskite@Polysiloxane/Crystal Violet Lactone. ACS Appl. Mater. Inter. 2016, 8 (40), 27346-27352, DOI 10.1021/acsami.6b09252. 107. Zhang, J.; Gao, Z.; Li, L.; Li, B.; Sun, H. Waterborne nonfluorinated superhydrophobic coatings with exceptional mechanical durability based on natural nanorods. Adv. Mater. Interfaces 2017, 4 (19), 1700723-1700732, DOI 10.1002/admi.201700723. 108. Xue, Z.; Cao, Y.; Liu, N.; Feng, L.; Jiang, L. Special wettable materials for oil/water separation. J. Mater. Chem. A 2014, 2 (8), 2445-2460, DOI 10.1039/c3ta13397d. 109. Zhu, Y.; Chen, D. Novel clay-based nanofibrous membranes for effective oil/water emulsion separation. Ceram. Int. 2017, 43 (12), 9465-9471, DOI 10.1016/j.ceramint.2017.04.124. 110. Zhang, Y.; Zhao, J.; Chu, H.; Zhou, X.; Wei, Y. Effect of modified attapulgite addition on the performance of a PVDF ultrafiltration membrane. Desalination 2014, 344, 71-78, DOI 10.1016/j.desal.2014.03.007. 111. Zhu, Y.; Chen, D. Preparation and characterization of attapulgite-based nanofibrous membranes. Mater. Design. 2017, 113, 60-67, DOI 10.1016/j.matdes.2016.10.016. 112. Li, J.; Zhao, Z.; Shen, Y.; Feng, H.; Yang, Y.; Zha, F. Fabrication of attapulgite coated membranes for effective separation of oil-in-water emulsion in highly acidic, alkaline, and concentrated salty environments. Adv. Mater. Interfaces 2017, 4 (16), 1700364-1700372, DOI 10.1002/admi.201700364. 113. Zhao, X.; Su, Y.; Liu, Y.; Lip, Y.; Jiang, Z. Free-standing graphene oxide-palygorskite nanohybrid membrane for oil/water separation. ACS Appl. Mater. Inter. 2016, 8 (12), 8247-8256, DOI 10.1021/acsami.5b12876. 39



Page 40 of 40

TOC

Synopsis: Recyclable attapulgite-based composites, such as magnetic materials, millimeter-sized materials, and filtration materials, are developed for highly effective water remediation.

40


Designing of Recyclable Attapulgite for Wastewater Treatments: A

Recommend Documents