Agar Aerogel Containing Small-Sized Zeolitic Imidazolate Framework

Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article

Agar Aerogel Containing Small-Sized ZIFs Loaded Carbon Nitride: a Solar-Triggered Regenerable Decontaminant for Convenient and Enhanced Water Purification Wentao Zhang, Shuo Shi, Wenxin Zhu, Lunjie Huang, Chengyuan Yang, Sihang Li, Xinnan Liu, Rong Wang, Na Hu, Yourui Suo, Zhonghong Li, and Jianlong Wang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02376 • Publication Date (Web): 21 Aug 2017 Downloaded from http://pubs.acs.org on August 22, 2017

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 free 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 accessible to all readers and 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.

ACS Sustainable Chemistry & Engineering 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 25

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

Agar Aerogel Containing Small-Sized ZIFs Loaded Carbon Nitride: a Solar-Triggered Regenerable Decontaminant for Convenient and Enhanced Water Purification Wentao Zhang,† Shuo Shi,‡ Wenxin Zhu,† Lunjie Huang,† Chengyuan Yang,† Sihang Li,† Xinnan Liu,† Rong Wang,† Na Hu,§ Yourui Suo,§ Zhonghong Li,† Jianlong Wang*† †

College of Food Science and Engineering, Northwest A&F University, Yangling, 712100,

Shaanxi, P. R. China. ‡

School of Medicine, Xi'an Jiaotong University, Xi'an, 710061, Shaanxi, P. R. China.

§

Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining, 810008,

Qinghai, P. R. China. *E-mail: [email protected]

KEYWORDS: aerogel, MOFs, carbon nitride, photocatalysis, regeneration, sustainable

ACS Paragon Plus Environment

1


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 25

ABSTRACT: Although ZIFs-based adsorbents are promising for environmental remediation, their performances are limited by the big crystal size, intrinsic fragility, and poor processability and reusability. To this end, in this work, highly dispersed and small sized (14.95 nm) MOFs via the restriction of overgrowth and agglomeration on carbon nitride (C3N4) nanosheets are integrated into agar aerogel, forming a flexible and efficient aerogel absorbent with photocatalytic activity. This separation-free hybrid aerogel mantaining the crystal structure of ZIF-8 with smaller size exhibits 1.44 times adsorption capacity for dye than that of pristine bulk ZIF-8. Most importantly, the introduction of C3N4 nanosheets not only regulates the growth of ZIF-8 crystals but also enables the hybdrid aerogel with stable reusability throughout 5 consecutive adsorption–degradation cycles, obtained via solar irradiation. This eco-friendly regeneration technology provides a convenient and sustainable approach to reduce the cost and eliminate the use of hazardous substances for environmental remediation. Dramatically, for the practical use under sunlight, contributed to the photocatalysis effect of the uniquely designed adsorbent, the active adsorption sites of aerogel can be continuously provided, resulting in enhanced dye removal ability. Therefore, this work establishes an innovative, low-cost, convenient and solar-triggered sustainable solution for the management of water contamination by MOFs-based aerogel decontaminant.

INTRODUCTION

Annually, over 50000 tons of dyes are discharged, making water contamination by dyes a major environmental concern.1 Most toxic dyes are often non-biodegradable, and even carcinogenic and teratogenetic, affecting aquatic product, as well as human health. To eliminate dyes contamination, adsorption is one of the most attractive options owing to its process simplicity


2

Page 3 of 25

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 eco-friendliness.2 From this prospect, metal-organic frameworks (MOFs) have generated intense interest for their structural and functional tunability, and received a fair share of attention for dyes separation.3-6 When used as adsorbents, MOFs and their derivatives, which can efficiently adsorb organic pollutants, have been extensively investigated for environmental remediation.5-6 However, pristine MOFs with high crystallinity show big crystal size, intrinsic fragility and poor processability, significant hurdles in achieving their effective performance.7 As MOF materials are currently available in powder forms which are not very convenient to retrieve from a sample matrix, suitable format fabrications will facilitate the convenience of separation and simplify purification devices. To address these problems, the fabrication of MOFs into membranes, films, or localized growth on a variety of substrates is required for these important industrial processes.8-11 However, from a practical perspective, MOFs obtained by using aforementioned methods are suffering from poor stability and fragility. Moreover, the fabrication often requires expensive, tedious time and energy-consuming processes. As an alternative facile approach, loading nanoparticles into hydrogels/aerogels has received much attention.12-18 On the other hand, although reusability of the adsorbents is one of preconditions for practical use, because of the leaching of active/guest species during adsorption and/or regeneration of the used MOFs, they have not yet been successfully reused. So far, most of MOFs-based adsorbents are often disposable or regenerated by various unsustainable and harsh methods, such as elution with organic solvent, NaOH or HCl solution, which debase the performance of adsorbents and are adverse to sustainable development.19-22 As such, considerable effort has been dedicated to broadening the species and improving adsorption ability of MOFs, but minimal studies of their reutilization have been reported.10, 23-25 At this point, an attractive strategy for the regeneration of MOFs-based adsorbents is to combine MOFs


3


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 4 of 25

with photocatalytic compounds for photodegradation of absorbed organic molecules. Photocatalysis-driven degradation of organic dyes might provide a convenient and green approach to reduce the cost and eliminate the use of hazardous substances. As such, the development of adsorbent system that can effectively absorb organic dye and simultaneously harvest visible light for organic dye degradation is an essential task in order to utilize this technology. As an analogue of graphene, graphitic C3N4 has recently been reported to possess the performance of decomposing organic pollutants for water purification under visible light irradiation.26-27 With large surface area, C3N4 nanosheets have been an attractive choice as the matrix for uniformly growing and anchoring well-dispersed nanoparticles, showing a fair share of potential as a platform to integrate with MOFs.28 The performance of MOFs also significantly depends on its morphology, size and dispersity as well.29 This C3N4 combination procedure increases the surface area and the number of surface active sites of guest nanocrystals, thus greatly improving the activity of nanocomposites.30-31 For example, decorated with transparent MOFs,

the

obtained

C3N4/ZIF-8

nanocomposite

showed

enhanced

efficiency

to

photocatalytically convert CO2 into solar fuels.31 Although many C3N4/MOFs nanocomposites have been reported,28, 31-33 growth regulation of MOFs nanocrystals with different morphologies and sizes by C3N4 sheets has not been explored. One can envisage C3N4 as a potential platform and as a structure-directing agent for the growth and stabilization of MOF nanoparticles with enhanced dye adsorption ability. Most importantly, combined with photocatalytic C3N4 nanosheets, MOFs-based decontaminant can be facilely and environmentally friendly regenerated by visible light for the management of organic pollutants.


4

Page 5 of 25

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


Inspired by the advantages of aerogel in retaining nanoparticles and photocatalytic 2D C3N4 nanosheets in restricting the overgrowth and improving the dispersity of guest nanoparticles, herein, we report an advanced hybrid nano-formulation that integrates photocatalytic MOFsbased heterojunction within aerogel to greenly regenerate adsorbent for high efficient water purification. Agar labeled as cheap biomass, commonly used as solid substrate for microbiological culture, was selected as precursor to form gel for nanomaterials loading. Such a nano-heterojunction–hydrogel formulation judiciously integrates three materials into one hybrid system with unique physicochemical properties that either one of the three building blocks cannot achieve independently. Via the restriction of overgrowth and agglomeration by C3N4 nanosheets, highly dispersed ZIF-8 with smaller size is obtained. Compared with free ZIF-8, C3N4 or ZIF-8/C3N4, entrapping them within aerogel can overcome the challenge of processing these powders into a convenient, separation free and tailorable form. Therefore, this hybrid aerogel mantaining the crystal structure of ZIF-8 and C3N4 shows enormous potential for enhanced water purification. As a proof of concept, we demonstrate that the synthesized MOFsbased hybrid aerogel is a solar-regenerable adsorbent with excellent adsorption performance for continues water purification under the irradiation of visible light.

EXPERIMENTAL SECTION

Chemicals and Materials Dicyandiamide (99%), zinc acetate dehydrate (ACS reagent, ≥98%) were purchased from Sigma Aldrich. 2-methylimidazole (MIM) was obtained from Sinopharm Chemical Reagent Co., Ltd. Organic Dye, including methylene blue and Congo red were purchased from Aladdin Chemical Co., Ltd. Agar powder was purchased from Solarbio Science & Technology Co., Ltd.


5


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 6 of 25

All chemicals were used as received without any further purification. Deionized water was used in all experiments. Characterizations Fourier transform infrared (FT-IR) spectroscopy was recorded on a Vetex70 (BRUKER Corp., Germany). The Powder X-ray diffraction (XRD) patterns were gotten by Bruker D8 Advanced Diffractometer System, which equipped with Cu Kα radiation (40 kV, 40 mA). The UV-vis spectra were measured with a UV-2550 spectrophotometer (Shimadzu, Japan) at room temperature. Field emission scanning electron microscope (SEM) image was taken by an S-4800 (Hitachi, Japan). Transmission electron microscopy (TEM) measurements were performed with a JEM-2100 (JEOL, Japan). Synthesis of bulk and nanosheets of C3N4 Bulk and nanosheets of C3N4 were synthesized according to an earlier study.34 Typically, the bulk C3N4 was prepared by polymerization of dicyandiamide under high temperature. In detail, 10 g dicyandiamide was heated at 550 oC for 3 h under argon condition with a ramp rate of 3 oC min−1. This heating rate allows the slow condensation of dicyandiamide so that the polymerization process for C3N4 formation could occur more completely, and the porous structures of resultant C3N4 could be retained (Figure S1).35 To prepare ultrathin C3N4 nanosheets, the obtained yellow powder, bulk C3N4, was liquid exfoliated. In detail, 200 mg of bulk C3N4 powder was dispersed in 100 mL water and then ultrasound for about 20 hours, followed by centrifuged at 3000 rmp for 10 min to remove the residual unexfoliated C3N4 nanoparticles.


6

Page 7 of 25

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


Growth of ZIF-8 on C3N4 nanosheets To grow ZIF-8 on C3N4 nanosheets, 10 mL of C3N4 nanosheets (~0.8 mg mL−1) dispersion was mixed with 40 mL of water under ultrasound, followed by addition of freshly prepared MIM solution (60 mL) and Zn(OAC)2 (50 mL) in sequence with mild stirring. After 2 h reaction at room temperature, the resulting solution was centrifuged at 3000 rpm for 10 min and washed three times with water. Preparation of Hybrid Aerogels 0.4% agar powder was added slowly to a beaker at room temperature with vigorous stirring to create a cloudy suspension. The suspension was then heated until forming a clear solution. Then solution containing ZIF-8/C3N4 hetero-nanosheets at different concentration was added. The resulting suspensions were than sonicated for 2 min. All suspensions were in ultrapure water without pH adjustment. The final suspension of crosslinked clusters was transferred into the well of a 6-wells plate (9.6 cm2) or 24-wells plate (2 cm2) and left undisturbed for 2 h until hydrogel formed, followed by freezing for another 2 h in -80 °C freezer. The final hybrid aerogels were obtained by freeze-drying the ice-gel. Experiments for the removal of water contaminants To determine the adsorption efficacy of the as-synthesized hybrid aerogels for organic pollutants, two dyes (Congo red and methylene blue) were investigated. In a typical experiment, 5 mg of aerogel was soaked into 20 ml of the contaminant solution and shaken at 120 rpm in a shaker for a predetermined time. The solution pH was not controlled. For kinetic studies, a typical adsorption experiment was performed with 200 mg L−1 Congo red. And the organic


7


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 8 of 25

pollutants concentration at different time intervals was determined by UV/vis spectrometer and calculated by the standard spectrophotometric method at the maximum absorbance. Adsorption isotherm experiments were conducted by adding 5 mg adsorbent into 20−1000 mg L−1 Congo red. For the synergistic removal of organic pollutants, 10 mg hybrid aerogel was added into prepared 20 mL 100 mg L−1 organic pollutant solution. The suspensions were then mildly magnetically stirred with visible light irradiation. The visible-light source was a solar simulator 300 W Xe lamp. During photocatalytic processes, the sample was periodically withdrawn. The concentration of organic pollutants during the synergistic removal process was monitored using a Shimadzu UV-2500 spectrometer. The amounts of CR adsorbed at specific time were determined by Equation (1):

Q =

(C

0

− Ct ) ⋅ V m

(1)

Herein, Q (mg g−1) and Ct (mg L−1) are the amounts of adsorbed CR and the concentration of CR at time specific time, respectively, and m is the dosage of adsorbent.

RESULTS AND DISCUSSION

The fabrication of the hybrid aerogel is illustrated in Figure 1a. First, C3N4 nanosheets were prepared by dicyandiamide condensation followed by ultrasonic exfoliation in water.34 Then they were dispersed in the 2-methylimidazole precursor solution, where the ZIF-8 was in-situ formed on C3N4 nanosheets by adding zinc acetate. All of synthesis procedures were conducted in water without the use of organic solvent. The formation of ZIF-8/C3N4 heterostructure is firstly confirmed by X-ray diffraction (XRD). The XRD patterns of ZIF-8/C3N4 are shown in Figure S2.


8

Page 9 of 25

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


The ZIF-8/C3N4 samples present a two-phase composition: ZIF-8 and C3N4. A pronounced peak is found at 27.4°, corresponding to the interplanar staking peak of aromatic systems of C3N4.26 The peak located at 12.7°, in our result, might be the overlay of the characteristic interlayer structural packing peak of C3N4 and (112) planes of ZIF-8 and cannot be distinguished in the XRD patterns.26, 36 Peaks at 10.4°, 16.5° and 18.1° are consistent well with the simulated XRD pattern of ZIF-8, while other three peaks at 29.3°, 31.7° and 34.4° are changing in different degrees, indicating a change in crystal structure of the ZIF-8 due to the immobilization.36 The existence of ZIF-8 on C3N4 is also evidenced by FT-IR spectra on the basis of characteristic absorbance peaks of C3N4 and ZIF-8 (Figure S3). The morphology of heterojunctions is then investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Compared to the smooth surface of the as-prepared C3N4 nanosheets (Figure S4), the surface of ZIF-8/C3N4 heterostructure becomes rough (Figure 1b), indicating a substantial loading of small ZIF-8 with a size of about 14.95 nm and high dispersivity rather than largesized bulks (Figure S5 and S6).37 In the inset of Figure 1c, about 0.287 nm size of the lattice fringe is clearly observed, which can be indexed as the (334) plane of ZIF-8.36 When compared with pristine ZIF-8 synthesized by conventional methods, ZIF-8 involved in heterojunctions shows much better dispersity and smaller sizes (14.95 nm), corroborating that C3N4 nanosheets can effectively restrict the overgrowth and agglomeration of ZIF-8.10, 15, 38 With the certitude of successful interaction between ZIF-8 and C3N4, finally, the hybrid aerogels were prepared by mixing dispersed ZIF-8/C3N4 heterostructure with boiled agar solution, cooling, and freeze drying.


9


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 10 of 25

Figure 1. a) Schematic illustration of the fabrication of ZIF-8/C3N4 heterostructure containing hybrid aerogels by sol–gel process. The diagram is not drawn to scale. b) SEM image of the ZIF8/C3N4 heterostructure. c) HRTEM image of ZIF-8/C3N4 heterostructure. d) Photographs of aerogel loading with 0% (top, Hgel-0) and 50% (bottom, Hgel-50) ZIF-8/C3N4. e) XRD patterns of Hgel-0 and Hgel-50. f, g) SEM images of hybrid aerogel with 50.0% ZIF-8/C3N4 (Hgel-50) at different magnifications. h) SEM-EDX elemental mappings of C, N and Zn for hybrid aerogels.

The characterizations of hybrid aerogel were then conducted. XRD of the aerogels, in Figure 1e, showed that the crystallinity of ZIF-8/C3N4 was retained during the processing, indicating that the hybrid aerogel maintains the function ZIF-8/C3N4 heterostructure. The presence of ZIF-8/C3N4 in hybrid aerogel was also verified by FT-IR. Figure S7 shows the FT-IR spectra of agar, ZIF-8/C3N4 heterostructure and hybrid aerogel. The pure aerogel shows rough surface (Figure 1d). SEM was then carried out to investigate the morphology and hierarchical


10

Page 11 of 25

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


structure of hybrid aerogel. As shown in Figure 1f, at low magnification, the hybrid aerogel exhibit the randomly oriented, interconnected microporous three-dimensional structures. The microporous are templated from the ice crystals that grow when the hybrid hydrogel is frozen. In contrast, loading with ZIF-8/C3N4, the hybrid aerogels show well shape. From the SEM images shown in Figure 1g, S8 and S9, the surfaces of aerogels are observed to be rough with the increase of loading ZIF-8/C3N4 amount. Additionally, Figure 1g shows that ZIF-8/C3N4 heterostructure were physically embedded or encapsulated within the aerogels. This structure can minimize the loss and leaching of ZIF-8/C3N4 during use. Moreover, ZIF-8/C3N4 heterostructure are well dispersed within the aerogel and no agglomerates are observed. The energy dispersive X-ray (EDX) spectrum (Figure 1h) shows the presence of carbon (C), nitrogen (N) and zinc (Zn) elements in the sample, thereby confirming the presence of ZIF-8/C3N4 heterostructure and the formation of hybrid aerogel. The hybrid aerogels have ultralow densities, increasing with ZIF8/C3N4 loading from 7.52 ± 0.7 mg cm−3 for 11.1 wt% to 11.02 ± 0.3 and 14.13±0.6 mg cm−3 for 33.3% and 50 wt% hybrid aerogel (abbreviated as Hgel-11.1, Hgel-33.3, and Hgel-50), respectively, lighter than that of a previously reported hybrid aerogel.15 Hybrid aerogels with higher loading amount of ZIF-8/C3N4 are unstable in aqueous solution and visibly broken under mild shake, inapplicable for experimental or practical water remediation. Therefore, we can facilely control over the ZIF-8/C3N4 loading and density of hybrid aerogel. With high loading amount, and without crystallinity change of ZIF-8/C3N4 heterostructure, the obtained hybrid aerogel, which retains the favorable properties of ZIF-8 and C3N4 and integrates the feature of aerogel, is ready as an excellent and reusable adsorbent for water purification. Specifically, we looked at using the hybrid aerogels to remove the Congo red (CR), which is widely used in the textile industry and has resistance to oxidation and decoloration


11


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 12 of 25

under natural conditions. The maximum contamination level of CR is defined to be 30 ppm by the European Union. In view of actual application, we selected CR concentrations higher than 30 ppm for further adsorption and degradation experiments. The uptake of CR by hybrid aerogel from solution was studied by the batch method at room temperature. Figure 2a shows the color change of aerogels and CR solution. The light-yellow hybrid aerogel turned to red, while conversely the CR contaminated water became colorless. In contrast, the ZIF-8/C3N4-free aerogel cannot entirely scavenge the color of CR solution, indicating the better adsorption ability of hybrid aerogel than pure aerogel. Detailly, the adsorption capacities of ZIF-8/C3N4 and hybrid aerogels loaded with C3N4 or different amount of ZIF-8/C3N4 for CR were demonstrated (Figure 2b). All of C3N4, Hgel-0, and C3N4 containing aerogel (Hgel-CN) show limited adsorption capacity for CR. The adsorption capacity of hybrid aerogels is positively related to the content of ZIF-8/C3N4 in aerogels. In all cases, comparable adsorption capacities to calculated values were observed for all aerogels (Table S1), indicating that the package by agar molecular has not suppressed the function of ZIF-8/C3N4. Moreover, compared with the calculated value derived from big-sized bulk ZIF-8, ZIF-8/C3N4 with small-sized dispersed ZIF-8 shows obviously higher adsorption ability. It is reasonable that the restriction of C3N4 can partly improve the activity of ZIF-8. These results indicate Hgel-50 possesses well adsorption ability for CR and also highlight ZIF-8 unit is the primary contributor of hybrid aerogel as a highly effective filter for decontamination of CR.


12

Page 13 of 25

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


Figure 2. a) Photographs of the contaminated CR (50 ppm) aqueous solution (left) and Hgel-50 before (middle) and after (right) adsorption. b) Adsorption capacities of CR from an aqueous solution (200 ppm) over different adsorbents including ZIF-8, C3N4, ZIF-8/C3N4, Hgel-CN, Hgel-0, Hgel-11.1, Hgel-33.3 and Hgel-50.

To determine the adsorption process and the Hgel-50 uptake capacity for CR, adsorption experiments were performed with initial CR concentrations ranging from 20 to 1000 mg L−1. Figure 3a shows the adsorption isotherms of CR on 50%-aerogel at 25°C. At initial section, it shows that the growth of Ce gives rise to Qe, while the amount of CR adsorbed is not significant increase with the further increase of Ce, indicating the saturated adsorption. It is also further verified that the adsorption process includes two phases, namely, surface diffusion and intraparticle diffusion. The experimental data were then analyzed by single-site adsorption, dual-site adsorption and Freundlich isotherm models, displayed as Equations (2),39 (3),39 and (4),40 respectively.

Qe =

K L Q max C e 1 + K LCe

(2)


13


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

Qe

 1   - Qmax = Qmax1 + 2KdCe  

Page 14 of 25

2

 1  1 +  −1 2KdCe  

(3)

Q e = K f C1e / n

(4)

Here, the Qe and Ce are the adsorption capacity of CR and the concentration of CR at equilibrium, respectively. The parameter Qmax is the maximum adsorption capacity of adsorption isotherm. KL, Kd and Kf are adsorption coefficients of the single-site adsorption, dual-site adsorption and Freundlich isotherm models. All of the parameters of single-site adsorption (Figure S10), dual-site adsorption (Figure 3a) and Freundlich (Figure S11) models are summarized in Table S2. The adsorption data of CR on 50%-aerogel is well fitted with dual-site adsorption model with higher R2 values than those of single-site adsorption and Freundlich model, proving that the combination of CR molecules with aerogels is dual-site adsorption.39 According to the calculated data from two-side adsorption model, the maximum adsorption capacity of Hgel-50 is 287.35 mg g−1. Meanwhile, aerogel containing 21.8% ZIF-8 (Hgel-Z, Figure S12), which was equal to the content of ZIF-8 in Hgel-50, was prepared. For CR removal, even after 10 h, this Hgel-Z shows a weaker maximum adsorption capacity than Hgel-50, calculated to be 208.75 mg g−1 based on the well fitted dual-side adsorption model (Figure S13, Table S2). As reported, the diameter of Congo red molecule is estimated to be approximately 21 Å,41 which is much greater than the aperture of ZIF-8 (3.4 Å).42 As ZIF-8 is the primary contributor of hybrid aerogel, the Congo red molecule is mainly adsorbed on the surface of ZIF-8. Therefore, this maximum adsorption capacity difference between ZIF-8 aerogel and ZIF-8/C3N4 aerogel contributed to the C3N4 nanosheets performance by efficiently regulating the growth of nanocrystals on its surface, resulting in small and high dispersed ZIF-8, which in turn shows


14

Page 15 of 25

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


higher performance for water purification. Furthermore, this ZIF-8/C3N4 hybrid aerogel shows well capacity for the removal of methylene blue, and the maximum adsorption capacity is calculated to be 154.87 mg g−1 (Figure S14).

Figure 3. a) The dual-site adsorption model for the adsorption isotherms of CR by Hgel-50. b) The adsorption kinetics of CR on Hgel-50: full line represents the pseudo-second-order until 2 h and dashed line represents simulated data at higher times.

Based on the data shown in Figure 2b, the adsorption equilibrium time and the kinetic interaction between CR and Hgel-50 were then calculated. As shown in Figure 3b, the adsorption capacities (Qt) increase rapidly in the first 1 h, and achieve the adsorption process equilibrium after 1.5 h with constant adsorption capacities (Qe). The rapid adsorption rate of CR at the early state could be attributed to the abundant adsorption sites on the adsorbents surface. Based on those data, three kinetics models, including pseudo-first-order model (Equation 5), pseudosecond-order kinetics model (Equation 6) and intra-particle diffusion model (Equation 7),40 are


15


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 16 of 25

used to simulate adsorption kinetics of CR by hybrid aerogel, according to the following equations:

Qt = Qe × (1 − e

Qt =

− k1t

Qe2 K 2t 1 + Qe K 2t

Q t = k pt1 / 2 + C

)

(5)

(6)

(7)

Where K1 and K2 are the equilibrium coefficients of the pseudo-first-order and pseudo-secondorder equation, respectively. Qe and Qt represent the adsorption capacity of CR at equilibrium and time t, respectively. kp and C represent the diffusion rate constant of intra-particle and the thickness of boundary layer, respectively. Importantly, the fundamentals behind pseudo-secondorder equation ensure its validity just under intermediate reaction time and in the case that desorption process is insignificant.39 Therefore, pseudo-second-order kinetics analysis at lower time was properly conducted (Figure S15, 3b).39 For comparison, pseudo-second-order kinetics of full time was also performed (Figure S16). The parameters of adsorption kinetics are summarized in Table S3. From Figure 3b, S16, S17 and Table S3, the adsorption process is better fitted to the pseudo-second-order model of lower time than that of full time and pseudofirst-order model, suggesting that the chemisorption in the CR adsorption process may be the rate limiting step. In the region of simulated date at higher time of Figure 3b, the curve deviates from the experimental data, indicating the invalidity of pseudo-second-order kinetics model at higher time. Besides, the experimental data are smaller than the calculated ones, which might be due to the slight desorption of CR during adsorption process. For intra-particle diffusion model of


16

Page 17 of 25

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


hybrid aerogel, a plot of Qt versus t1/2 in Figure S18 shows that there are two stages during the adsorption process of CR onto hybrid aerogel. The first stage is attributed to external diffusion with high slope and intercept. In this stage, the adsorption rate of CR is higher due to the instantaneous availability of large active adsorption sites on the surface of aerogel. The second stage is gradual adsorption stage, where intra-particle diffusion is rate-controlled. From Table S3, the Kp1 (256.24 mg g−1 h1/2) is obviously higher than Kp2 (20.84 mg g−1 h1/2), suggesting the external diffusion play main role in the adsorption kinetics. Besides, similar KP1 value (247.03 mg g−1 h1/2) was calculated for half of ZIF-8/C3N4 conducted at same condition for hybrid aerogel, further indicating the coated agar molecule has not suppressed the function of ZIF8/C3N4. One of the main questions that newly developed sorbents face is the suitability for regeneration as this represents a significant factor in determining the final cost of the technology. Herein, with the integration of photocatalytic C3N4, our MOFs-based hybrid aerogel shows apparent potential to be regenerated by photocatalytically degrading the adsorbed organic pollutant molecules under the irradiation of visible light, a green and low-cost way for sorbents regeneration. As shown in Figure 4a, being short of photocatalytic activity, ZIF-8 containing aerogel cannot be discolored by the irradiation of visible light for 2 h after adsorption experiment, while the color of 50%-aerogel engulfed CR molecules turns from red to yellow, the color of Hgel-50. Following the irradiation of visible light, the hybrid aerogel was compressed to squeeze out the water for reuse. The effect of five consecutive adsorption–regeneration cycles was studied, and the results are shown in Figure 4c. It shows that the adsorption capacity of CR on hybrid aerogel decreases slowly with increasing cycle number. Even at least the fifth run, the adsorption ability of hybrid aerogel was excellent (Figure 4b) and the color of aerogel can be


17


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 18 of 25

recovered by light irradiation (Figure 4a(vi)). As shown in Figure 4b(ii), owing to well water absorption and retention ability from agar macromolecule, at the fifth round the Hgel-50 sank down to the bottom of the bottle, which however had no effect on the adsorption efficiency of Hgel-50. These results show that, with the ability of photocatalytic regeneration, our hybrid aerogel can be recycled for effective CR removal.

Figure 4. Visible light triggered the regeneration and continuous enhanced removal activity of Hgel-50 for CR removal. a) Photographs of CR engulfed Hgel-Z (i) and Hgel-50 (ii−vi) with visible light irradiation for 2h (photographs from (ii) to (vi) show five times regeneration of Hgel-50). b) Photograph of the contaminated CR aqueous solution and the fifth run Hgel-50 before (i) and after adsorption (ii). c) Reusability of Hgel-50 for CR removal after multiple cycles. d) The continuous synergistic CR removal by Hgel-CN and Hgel-50 with (on) or without (off) sunlight irradiation.


18

Page 19 of 25

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


For industrial wastewater treatment in real-world environments, adsorbents are exposed to the sunlight, allowing simultaneous dye adsorption and photocatalytic degradation by our hybrid aerogel. Most importantly, fitted well with two-site adsorption model, progress of CR adsorbed by our hybrid aerogel is mainly affected by the active sites of exposed surface area. Predictably, continuously providing active sites can facilitate the removal of adsorbates. To demonstrate the synergistic removal of organic pollutants by adsorption and photocatalytic degradation, ~10 mg hybrid aerogel was added into prepared 20 mL 100 mg L−1 CR solution. The suspensions were then mildly magnetically stirred with visible light irradiation. In contrast, parallel suspensions were magnetically stirred without the presence of visible light. The time dependent dye removal rate was recorded and shown in Figure 4d. Impressively, the introduction of visible light greatly enhances the removal rate of CR, for which hybrid aerogel with light illumination can almost completely remove CR within 50 min. This is reasonable that, under the irradiation of visible light, the hybrid aerogel can degrade the adsorbed CR molecules, continuously maintaining the availability of active adsorption sites on the surface of aerogel. The color of resulted hybrid aerogel was light red, owing to the faster adsorption rate than degradation progress. Subsequently, the light red hybrid aerogel was resoaked into another fresh 20 mL 100 mg L−1 CR solution under visible light and can bleach the red color within 70 min. Even at the fourth run, the used hybrid aerogel showed well removal efficiency. Inversely, hybrid aerogel without light irradiation adsorbs 74.6% CR within 50 min and 91.6% for 1.5 h for the first time and shows unsatisfied performance for the second run. Besides, with poor adsorption ability, Hgel-CN also exhibits weaker dye removal performance. The condition of Hgel-50 after sunlight irradiation was then checked, exhibiting well stability (Figure S19). Moreover, no leaching or breakdown of


19


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 20 of 25

ZIF-8 was detected by using atomic absorption spectrometer (Table S4). These results indicate that our hybrid aerogel, combining adsorption and photocatalytic degradation, shows continuously excellent performance for water purification with presence of sunlight.

CONCLUSION

In summary, MOFs-containing aerogel with photocatalytic activity was fabricated by regulating the growth of ZIF-8 on C3N4 nanosheets and straightforward sol–gel process of agar. Such a nano-heterojunction–aerogel formulation judiciously integrates three materials into one hybrid system with unique physicochemical properties that either one of the three building blocks cannot achieve independently. Compared with free ZIF-8, C3N4 or ZIF-8/C3N4, entrapping them within aerogel can overcome the challenge of processing these powders into a convenient, separation free and tailorable form. In this way, Hgel-50 exhibits fast adsorption for CR with high saturation CR uptake capacity of 287.35 mg g−1. This high performance can be economically and sustainably recovered by the irradiation of visible light. Most importantly, for real-world wastewater treatment exposed under sunlight, continuous active sites can be provided on hybrid aerogel, achieving enduring high performance for pollutant removal. Therefore, our approach of creating aerogel adsorbent integrated with ZIF-8 loaded C3N4 can be practically applied for continuously effective removal of organic pollutant under sunlight. ASSOCIATED CONTENT Supporting Information. XRD patterns and FT-IR spectra of ZIF-8, C3N4 and ZIF-8/C3N4; SEM image of C3N4; size distribution of ZIF-8 nanoparticles on C3N4; SEM image and size distribution of big-sized bulk ZIF-8; FT-IR spectra of agar, ZIF-8, C3N4 and Hgel-50; SEM of


20

Page 21 of 25

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


Hgel-11.1 and Hgel-33.3; adsorption capacities of various absorbents for Congo red; the singlesite adsorption and Freundlich isotherm model of CR adsorption by Hgel-50; thermodynamic parameters of CR adsorption by Hgel-50; photograph, SEM images and XRD pattern of Hgel-Z; thermodynamic isotherm model for the adsorption isotherms of CR by Hgel-Z; thermodynamic isotherm model for the adsorption isotherms of methylene blue by Hgel-50; invalidity of the pseudo-second-order conditions for the full time range; pseudo-second-order, pseudo-first-order and intra-particle diffusion model of CR adsorption by Hgel-50 of full time; adsorption kinetics parameters of CR adsorption by Hgel-50; XRD pattern of the regenerated Hgel-50. ACKNOWLEDGMENT The authors thank the National Natural Science Foundation of China (21675127, 31371813) and the Development Project of Qinghai Key Laboratory (2017-ZJ-Y10) for financial support. REFERENCES 1. Li, D.; Li, Q.; Bai, N.; Dong, H.; Mao, D., One-Step Synthesis of Cationic Hydrogel for Efficient Dye Adsorption and Its Second Use for Emulsified Oil Separation. ACS Sustainable Chem. Eng. 2017, 5 (6), 5598-5607. 2. Chen, C.; Zhang, T.; Dai, B.; Zhang, H.; Chen, X.; Yang, J.; Liu, J.; Sun, D., Rapid Fabrication of Composite Hydrogel Microfibers for Weavable and Sustainable Antibacterial Applications. ACS Sustainable Chem. Eng. 2016, 4 (12), 6534-6542. 3. Li, J.-R.; Kuppler, R. J.; Zhou, H.-C., Selective gas adsorption and separation in metalorganic frameworks. Chem. Soc. Rev. 2009, 38 (5), 1477-1504. 4. Zhang, T.; Lin, W., Metal-organic frameworks for artificial photosynthesis and photocatalysis. Chem. Soc. Rev. 2014, 43 (16), 5982-5993. 5. El-Hankari, S.; Aguilera-Sigalat, J.; Bradshaw, D., Surfactant-assisted ZnO processing as a versatile route to ZIF composites and hollow architectures with enhanced dye adsorption. J. Mater. Chem. A 2016, 4 (35), 13509-13518. 6. Duan, S.; Li, J.; Liu, X.; Wang, Y.; Zeng, S.; Shao, D.; Hayat, T., HF-Free Synthesis of Nanoscale Metal-Organic Framework NMIL-100(Fe) as an Efficient Dye Adsorbent. ACS Sustainable Chem. Eng. 2016, 4 (6), 3368-3378. 7. Zhao, M.; Zhang, X.; Deng, C., Rational synthesis of novel recyclable Fe3O4@MOF nanocomposites for enzymatic digestion. Chem. Commun. 2015, 51 (38), 8116-8119. 8. Falcaro, P.; Buso, D.; Hill, A. J.; Doherty, C. M., Patterning techniques for metal organic frameworks. Adv. Mater. 2012, 24 (24), 3153-3168.


21


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 22 of 25

9. Petit, C.; Bandosz, T. J., MOF-graphite oxide composites: combining the uniqueness of graphene layers and metal-organic frameworks. Adv. Mater. 2009, 21 (46), 4753-4757. 10. Chen, Y.; Li, S.; Pei, X.; Zhou, J.; Feng, X.; Zhang, S.; Cheng, Y.; Li, H.; Han, R.; Wang, B., A Solvent-Free Hot-Pressing Method for Preparing Metal-Organic-Framework Coatings. Angew. Chem. Int. Ed. 2016, 55 (10), 3419-3423. 11. Ling, R.; Ge, L.; Diao, H.; Rudolph, V.; Zhu, Z., Ionic Liquids as the MOFs/Polymer Interfacial Binder for Efficient Membrane Separation. ACS Appl. Mater. Interfaces 2016, 8 (46), 32041-32049. 12. Chen, L.; Li, Y.; Du, Q.; Wang, Z.; Xia, Y.; Yedinak, E.; Lou, J.; Ci, L., High performance agar/graphene oxide composite aerogel for methylene blue removal. Carbohyd. Polym. 2017, 155, 345-353. 13. Wan, C.; Li, J., Synthesis of well-dispersed magnetic CoFe2O4 nanoparticles in cellulose aerogels via a facile oxidative co-precipitation method. Carbohyd. polym. 2015, 134, 144-150. 14. Zhang, M.; Jiang, W.; Liu, D.; Wang, J.; Liu, Y.; Zhu, Y.; Zhu, Y., Photodegradation of phenol via C3N4-agar hybrid hydrogel 3D photocatalysts with free separation. Appl. Catal. B: Environ. 2016, 183, 263-268. 15. Zhu, H.; Yang, X.; Cranston, E. D.; Zhu, S., Flexible and Porous Nanocellulose Aerogels with High Loadings of Metal-Organic-Framework Particles for Separations Applications. Adv. Mater. 2016, 28 (35), 7652-7657. 16. 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 Sustainable Chem. Eng. 2014, 2 (7), 1785-1794. 17. Liu, W.; Zhao, Y.; Zeng, C.; Wang, C.; Serra, C. A.; Zhang, L., Microfluidic preparation of yolk/shell ZIF-8/alginate hybrid microcapsules from Pickering emulsion. Chem. Eng. J. 2017, 307, 408-417. 18. Zhu, H.; Zhang, Q.; Zhu, S., Alginate Hydrogel: A Shapeable and Versatile Platform for in Situ Preparation of Metal-Organic Framework-Polymer Composites. ACS Appl. Mater. Interfaces 2016, 8 (27), 17395-17401. 19. Haque, E.; Lo, V.; Minett, A. I.; Harris, A. T.; Church, T. L., Dichotomous adsorption behaviour of dyes on an amino-functionalised metal-organic framework, amino-MIL-101 (Al). J. Mater. Chem. A 2014, 2 (1), 193-203. 20. Li, L.; Liu, X. L.; Geng, H. Y.; Hu, B.; Song, G. W.; Xu, Z. S., A MOF/graphite oxide hybrid (MOF: HKUST-1) material for the adsorption of methylene blue from aqueous solution. J. Mater. Chem. A 2013, 1 (35), 10292-10299. 21. Ahmed, I.; Hasan, Z.; Khan, N. A.; Jhung, S. H., Adsorptive denitrogenation of model fuels with porous metal-organic frameworks (MOFs): Effect of acidity and basicity of MOFs. Appl. Catal. B: Environ. 2013, 129, 123-129. 22. Khan, N. A.; Hasan, Z.; Jhung, S. H., Ionic liquid@ MIL-101 prepared via the ship-inbottle technique: remarkable adsorbents for the removal of benzothiophene from liquid fuel. Chem. Commun. 2016, 52 (12), 2561-2564. 23. Yi, F. Y.; Li, J. P.; Wu, D.; Sun, Z. M., A series of multifunctional metal-organic frameworks showing excellent luminescent sensing, sensitization, and adsorbent abilities. Chem. Eur. J. 2015, 21 (32), 11475-11482. 24. Ahmed, I.; Tong, M.; Jun, J. W.; Zhong, C.; Jhung, S. H., Adsorption of nitrogencontaining compounds from model fuel over sulfonated metal-organic framework: contribution


22

Page 23 of 25

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 hydrogen-bonding and acid-base interactions in adsorption. J. Phys. Chem. C 2015, 120 (1), 407-415. 25. Zhu, J.; Qin, L.; Uliana, A.; Hou, J.; Wang, J.; Zhang, Y.; Li, X.; Yuan, S.; Li, J.; Tian, M.; Lin, J.; Van der Bruggen, B., Elevated Performance of Thin Film Nanocomposite Membranes Enabled by Modified Hydrophilic MOFs for Nanofiltration. ACS Appl. Mater. Interfaces 2017, 9 (2), 1975-1986. 26. Hou, Y.; Wen, Z.; Cui, S.; Guo, X.; Chen, J., Constructing 2D Porous Graphitic C3N4 Nanosheets/Nitrogen-Doped Graphene/Layered MoS2 Ternary Nanojunction with Enhanced Photoelectrochemical Activity. Adv. Mater. 2013, 25 (43), 6291-6297. 27. Panneri, S.; Ganguly, P.; Mohan, M.; Nair, B. N.; Mohamed, A. A. P.; Warrier, K. G.; Hareesh, U. S., Photoregenerable, Bifunctional Granules of Carbon-Doped g-C3N4 as Adsorptive Photocatalyst for the Efficient Removal of Tetracycline Antibiotic. ACS Sustainable Chem. Eng. 2017, 5 (2), 1610-1618. 28. Cao, S.-W.; Yuan, Y.-P.; Barber, J.; Loo, S. C. J.; Xue, C., Noble-metal-free gC3N4/Ni(dmgH)2 composite for efficient photocatalytic hydrogen evolution under visible light irradiation. Appl. Surf. Sci. 2014, 319, 344-349. 29. Stock, N.; Biswas, S., Synthesis of metal-organic frameworks (MOFs): routes to various MOF topologies, morphologies, and composites. Chem. Rev. 2011, 112 (2), 933-969. 30. Li, Q.; Li, X.; Wageh, S.; Al-Ghamdi, A.; Yu, J., CdS/Graphene nanocomposite photocatalysts. Adv. Energy Mater. 2015, 5 (14), 1500010. 31. Liu, S.; Chen, F.; Li, S.; Peng, X.; Xiong, Y., Enhanced photocatalytic conversion of greenhouse gas CO2 into solar fuels over g-C3N4 nanotubes with decorated transparent ZIF-8 nanoclusters. Appl. Catal. B: Environ. 2017, 211, 1-10. 32. Chen, R.; Zhang, J.; Wang, Y.; Chen, X.; Zapien, J. A.; Lee, C.-S., Graphitic carbon nitride nanosheet@ metal-organic framework core-shell nanoparticles for photo-chemo combination therapy. Nanoscale 2015, 7 (41), 17299-17305. 33. Gu, W.; Hu, L.; Li, J.; Wang, E., Hybrid of g-C3N4 Assisted Metal-Organic Frameworks and Their Derived High-Efficiency Oxygen Reduction Electrocatalyst in the Whole pH Range. ACS Appl. Mater. Interfaces 2016, 8 (51), 35281-35288. 34. Zhang, X.; Xie, X.; Wang, H.; Zhang, J.; Pan, B.; Xie, Y., Enhanced photoresponsive ultrathin graphitic-phase C3N4 nanosheets for bioimaging. J. Am. Chem. Soc. 2012, 135 (1), 1821. 35. Li, Q.; Zhang, N.; Yang, Y.; Wang, G.; Ng, D. H. L., High Efficiency Photocatalysis for Pollutant Degradation with MoS2/C3N4 Heterostructures. Langmuir 2014, 30 (29), 8965-8972. 36. Venna, S. R.; Carreon, M. A., Highly permeable zeolite imidazolate framework-8 membranes for CO2/CH4 separation. J. Am. Chem. Soc. 2009, 132 (1), 76-78. 37. Torad, N. L.; Hu, M.; Kamachi, Y.; Takai, K.; Imura, M.; Naito, M.; Yamauchi, Y., Facile synthesis of nanoporous carbons with controlled particle sizes by direct carbonization of monodispersed ZIF-8 crystals. Chem. Commun. 2013, 49 (25), 2521-2523. 38. Wu, Y.-n.; Zhou, M.; Zhang, B.; Wu, B.; Li, J.; Qiao, J.; Guan, X.; Li, F., Amino acid assisted templating synthesis of hierarchical zeolitic imidazolate framework-8 for efficient arsenate removal. Nanoscale 2014, 6 (2), 1105-1112. 39. Chavez-Sumarriva, I.; Van Steenberge, P. H. M.; D'Hooge, D. R., New Insights in the Treatment of Waste Water with Graphene: Dual-Site Adsorption by Sodium Dodecylbenzenesulfonate. Ind. Eng. Chem. Res. 2016, 55 (35), 9387-9396.


23


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 24 of 25

40. Wang, J.; Zhang, W.; Yue, X.; Yang, Q.; Liu, F.; Wang, Y.; Zhang, D.; Li, Z.; Wang, J., One-pot synthesis of multifunctional magnetic ferrite-MoS2-carbon dot nanohybrid adsorbent for efficient Pb(II) removal. J. Mater. Chem. A 2016, 4 (10), 3893-3900. 41. Frid, P.; Anisimov, S. V.; Popovic, N., Congo red and protein aggregation in neurodegenerative diseases. Brain Res. Rev. 2007, 53 (1), 135-160. 42. Park, K. S.; Ni, Z.; Côté, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M., Exceptional chemical and thermal stability of zeolitic imidazolate frameworks. P. Natl. Acad. Sci. USA 2006, 103 (27), 10186-10191.


24

Page 25 of 25

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


For Table of Contents Use Only

A flexible agar aerogel containing ZIF-8/C3N4 heterostructure was facilely made and applied as solar-trigged regenerable decontaminant for convenient and enhanced water purification.


25

Agar Aerogel Containing Small-Sized Zeolitic Imidazolate Framework

Recommend Documents