Functionalization of Commercial Sand Core Funnels as Hydrophobic

Subscriber access provided by University of Winnipeg Library

Surfaces, Interfaces, and Applications

Functionalization of Commercial Sand Core Funnels as Hydrophobic Materials with Novel Physicochemical Properties Lisha Yu, Yanhui Kang, Hongding Tang, and Jinping Zhou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18396 • Publication Date (Web): 24 Jan 2019 Downloaded from http://pubs.acs.org on January 24, 2019

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 41 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 Applied Materials & Interfaces

Functionalization of Commercial Sand Core Funnels as Hydrophobic Materials with Novel Physicochemical Properties Lisha Yu1, Yanhui Kang1, Hongding Tang1,2, Jinping Zhou1,2 L. Yu, Y. Kang, Prof. H. Tang, Prof. J. Zhou 1Department

of Chemistry and Key Laboratory of Biomedical Polymers, Ministry of

Education, Wuhan University, Wuhan 430072, China 2Engineering

Research Center of Organosilicon Compounds & Materials, Ministry of

Education, Wuhan University, Wuhan 430072, China E-mail: [email protected]



Corresponding author, Tel: +86-27-68752977, Fax: +86-27-68754067

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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

ABSTRACT: A solid surface morphology is of great importance for the fundamental research in the field of hydrophobic materials. Commercial sand core funnels (SCs) are embedded with multilevel pore size and surface roughness, which are excellent models to study the mechanism of surface wettability. This article described a simple, green and facile method to fabricate hydrophobic surface on SCs via reacting with the perfluorooctyltriethoxysilane (PFTS) vapor. Systematic analyses on the reaction, properties and applications of the PFTS-modified SCs were conducted, which involved the reaction time and temperature, water resistance, mechanical durability, selfcleaning test, surface adhesion and underoil superhydrophobicity. The water contact angle (WCA) of the modified SCs increased with a decrease of the pore size and an increase of the surface roughness of the sand core particles. The wettability of the modified SCs is agreed well with the intermediate state between Wenzel and CassieBaxter. The PFTS-modified SCs retained excellent chemical stability in rigid conditions and good mechanical properties. The hydrophobic SCs showed oil/water separation performance for excellent efficiency, reusability and high flux. Especially for the PFTS-modified SCs with small pore sizes, water-in-oil emulsion separation was successfully realized. The easily accessible, relatively cheap raw materials and facile process in this work are very desirable to obtain a specific wetting surface, which will offer promising applications in various fields. KEYWORDS: sand core funnels, perfluorooctyltriethoxysilane, water contact angle, hydrophobicity, oil/water separation


Page 2 of 41

Page 3 of 41 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


 INTRODUCTION The interest in surfaces with special wettability has grown in recent years due to the desire for their fundamental research and potential applications in oil/water separation, self-cleaning, antipollution, anticorrosion, and so on.1-3 Different types of materials including metallic meshes,4 inorganic particles,5 fabrics,6 membranes,7 polymer sponges8 and foams9 have been used to fabricate the hydrophobic surfaces. Based on the conventional theories of Young, Wenzel, and Cassie-Baxter models, the water contact angle (WCA) is a key parameter to study surface wettability ranging from hydrophilic to hydrophobic.10 Commonly, the surface with WCA greater than 90° can be considered as hydrophobicity.11 To achieve the required WCA, the hydrophobicity of surfaces could be controlled mainly by two ways: One is to create a rough surface and the other is to modify the surface with chemicals of low surface free energy, such as silicon compounds.10,12 Numerous works have been reported the fabrication of hydrophobic materials based on the above ways.13-16 For example, Jiang et al. spent great efforts in mimicking biological functions, such as the self-cleaning and aquatic high-loading of lotus leaves, to construct hydrophobic micro/nanostructures.17,18 Superhydrophobic Ag-coated copper meshes with a WCA of 164.1° were fabricated by an immersion method.19 The WCA of the aligned carbon nanotubes modified by fluoroalkysilane was high as 171°.20 Polylactic acid Janus fabric was fabricated via an efficacious electrospinning techniques, and showed a WCA of 152° and oil contact angle (OCA) of 0°.21 A hydrophobic 3D printed polysulfone membrane for oil/water separation was prepared by selective laser sintering.22 Carbon-based aerogels with a large WCA were obtained by pyrolyzing bacterial cellulose at 700–1300 C in an argon atmosphere, which can be used to adsorb organics with excellent recyclability.23 However, the applications of such materials are greatly limited by the complicated steps,



high-cost, poor mechanical durability and chemical stability.24-26 It is necessary to find a suitable material embedded with a great durable performance to meet the urgent requirement in applications. Commercial sand core funnels (SC), a commonly used simple filter device, is made of sintered glass frit that embedded with good mechanical durability. Different from the ordinary flat and dense glass, SC has a natural rough surface and is embedded with numerous pores for liquid to pass through. The perfect surface properties make SC an excellent model to study the surface wettability. However, to the best of our knowledge, no report has been studied the hydrophobic modification of SC. Silica is the main component of SC that is not selective for water and oil. The surface of silica has numerous hydroxyl groups, which can be rendered hydrophobic by lowering the surface energy or attaching groups that do not interact with water.27,28 Chemical modification,29 polymer grafting,30 blending,31 chemical vapor deposition (CVD),32 layer-by-layer assembly,33,34 lithography-based35 and plasma etching36 are common used methods to fabricate the hydrophobic silica surface. Among the conventional techniques, CVD is becoming increasingly prevalent due to its environmental benefits, and is efficient in the preparation of hydrophobic materials.37-39 For example, waterrepellent surface on Si substrates was prepared based on a plasma-enhanced CVD.40 Super-hydrophobic silicon surface pretreated with laser etching was fabricated via CVD.41 However, the CVD process involves the use of a special reaction apparatus with a carrier gas or a high temperature.42,43 A vacuum-assist chemical vapor reaction (CVR) process is highly efficient, low cost, no need for special solvent or equipment and no limitation for the substrate.44 Therefore, the hydrophobic SCs constructed via CVR method are more appropriate in practical applications for their outstanding mechanical durability and oil/water separation ability.


Page 4 of 41

Page 5 of 41 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


In this work, the one-step based CVR method was used to fabricate the hydrophobic SCs for the first time, and the physicochemical properties of the modified SCs

were

studied.

The

SCs

and

a

low

surface

energy

reagent-

perfluorooctyltriethoxysilane (PFTS) were placed in a closed system. Under vacuum and heating, SCs were fully exposed to the PFTS vapor, and the process was fast, adequate, and even. PFTS-modified SCs were used to investigate the relationship between the morphology and wettability. Wetting conditions on the three-phase interfaces were studied qualitatively and quantitatively. Moreover, the modified SCs were endowed with superior chemical stability under harsh conditions such as acidic, alkaline and salt environments and excellent self-cleaning properties. They showed remarkable layered oil/water separation performance and high permeate fluxes. Especially, PFTS-modified SCs with small pore size were successfully applied in the water-in-oil emulsions separation.

 EXPERIMENTAL SECTION Materials. Sand core funnels (SCs) including G1~G6 were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). PFTS was purchased from Bide Pharmatech Ltd (Shanghai, China). All other reagents were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China) and were used without further purification. Deionized water (Millipore) was used for all experiments. Hydrophobic Surface Modification of SCs. A vacuum-assist chemical vapor reaction (CVR) was developed for the surface modification of SCs. A desiccator was preheated at 60 C for 20 min. A small glass vial containing PFTS (1 mL) and the pristine SCs were placed in the desiccator. Then, the desiccator was vacuumed for 20 min until the initial vacuum pressure of 0.095 ~ 0.1 MPa was reached. The desiccator



was sealed and heated at 140 ℃ for 4.0 h, and the as-prepared samples were coded as G1-4.0h, G2-4.0h, G3-4.0h, G4-4.0h, G5-4.0h, G6-4.0h, G6-4.0h for G1~G6, respectively. Additionally, the desiccator containing G6 and PFTS was heated for 0.5 h at 40, 50, 60, 70, 80, 90, 100, 110, 130, and 140 ℃, and heated at 80 ℃ for 10 min, 15 min, 20 min, 0.5 h, 1.0 h, 2.0 h, 4.0 h, 6.0 h, and 12.0 h, respectively. To remove the excess amount of unreacted PFTS, the modified samples were kept in a desiccator with the cover open for >1.0h. Characterization. Water contact angle (WCA) was measured on a dynamic mode on a Data Physics Instrument (DSA100, Krüss, Germany). One drop of water (2 μL) was put on the surface of the samples with an automatic piston syringe and photographed. For the measurements of advancing contact angle (θA) and receding contact angle (θR), one drop of water (4 μL) was put on the surface of sample, and liquids were steadily injected to the initial drop by a syringe until the contact line advances.45,46 The WCA of the drop observed when it is just set in motion is the θA. On the contrary, the liquids were steadily sucked out from the initial drop by a syringe until the contact line retracts. The WCA of the drop observed when the contact line is just set in motion is the θR. For the test of surface wettability underoil, the PFTS-modified SCs were placed in corn oil. Next, 2 μL of water was injected on the surface of the modified SCs to characterize their underoil hydrophobicity. Scanning electron microscopy (SEM) images were taken on a field-emission scanning electron microscope (FESEM, Zeiss Sigma) with an accelerating voltage of 5 kV. The samples were sputtered with gold, then observed and photographed. Atomic force microscope (AFM, Cypher S, Asylum Research) images were obtained in a dynamic force mode at ambient temperature (20 C). Accordingly, silicon probes (AC240TS, BRUKER), with the average tip radius below 10 nm, spring constant of 1.7


Page 6 of 41

Page 7 of 41 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


N/m and resonance frequency of 70 kHz were employed for scanning to investigate the SCs. X-ray photoelectron spectra (XPS) were recorded using an ESCALAB 250Xi (Thermo Scientific) X-ray photoelectron spectrometer with monochromatic Al K (1486.6 eV) radiation as the excitation source. The binding energy charge was corrected to 284.6 eV for C1s. Water Uptake Testing. The SCs and PFTS-modified SCs were dried at 60 °C for 24 h, and then immersed in distilled water for 1 h. Finally, the samples were blotted with filter paper carefully to remove the excess water on the surface and weighed. The water absorption was calculated as follows Water absorption (%) = (W-W0)/W0×100

(1)

where W0 and W are the weights of the dried and wet samples, respectively. Mechanical Durability Testing. The hardness of the samples were tested by using the pencil hardness technique (QHQ, China). The pencils of 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B and 6B (list in order of decreasing hardness) and 1000 g counterweights were used. To conduct the test, the lead holder was gripped tightly and the tip was placed on the samples, pointing it toward the tester at an angle of approximately 45°. With a steady pressure, the tester pushed down and pulled the lead toward himself to scratch the samples. The shore D hardness was tested on a LX-D hardness tester (Shanghai, China). The abrasion resistance test was conducted on a RCA paper abrasion tester (275 g) according to ASTM F2357 at a speed of 16 rpm for 100, 200, 500, 900 and 1500 cycles. The RCA paper (0.6875 in wide) is the commercial product from Norman Tool of USA. Compress tests of the samples were performed on an universal tensile-compressive tester (SANS, China). The cylindrical samples were placed on the lower plate and compressed by the upper plate at a strain rate of 0.1 mm min-1. The maximum strain



Page 8 of 41

was set as 10% to protect the machine. All the tests were repeated at least three times. Self-Cleaning Testing. Methyl green powders were placed on the surface of the PFTS-modified SCs (G4-4.0h, G5-4.0h, G6-4.0h) with a slight inclination angle of 30°. A small water stream from the washing bottle was used to clean the powders. Water/Oil Separation Testing. Water (30 mL) was poured into the interior of the PFTS-modified SCs. The vacuum degree increased from zero until the water passed through the samples. Then the value of the vacuum degree was recorded. Toluene (30 mL, dyed with oil-red) was poured into the interior of the PFTSmodified SCs. The flux of toluene was measured by permeating it through the modified SCs under a given vacuum degree (0, 3.8, 17.7, 40.0 and 48.5 kPa for G2-4.0h, G34.0h, G4-4.0h, G5-4.0h and G6-4.0h, respectively). The flux (J, L m−2 h−1) was calculated as follows: J = V/(A × t)

(2)

where V is the volume of the permeation oil or organic solvents, A is the effective area (45 cm2) of the PFTS-modified SCs, and t is the time of measurement. The fluxes of chloroform, dichloromethane, n-hexane, ethyl ether and corn oil of G2-4.0h and G34.0h were also measured. Driven vacuum degree for G2-4.0h and G3-4.0h is 0 and 3.8 kPa, respectively. The mixtures of water (15 mL) and oil-red dyed toluene and chloroform (15 mL) were separated by G2-4.0h (gravity) and G3-4.0h (3.8 kPa). The red liquid permeated the bottom surface, entering the collecting vessel, while the water remained in the interior of the box. The separation efficiency (η1) was calculated as follows: η1 = m2/m1 × 100%

(3)

where m1 is the weight of the initial organic component, and m2 is the weight of the organic component after separation. The experiments were repeated 20 times to


Page 9 of 41 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


determine the recyclability of G2-4.0h. Separation of Water-in-Oil Emulsion. To prepare the water-in-oil emulsions, distilled water (1 mL) was added into isooctane/toluene/dichloroethane/petroleum ether/hexadecane (99 mL) with Span-80 (1 mg Span 80 per mL) as the surfactant. Then, the mixtures were emulsified by a high-speed stirrer (1200 rpm) for 4 h, and the emulsions were stable over 48 h under the ambient condition. The freshly prepared emulsions go through the G4-4.0h, G5-4.0h and G6-4.0h under gravity.

 RESULTS AND DISCUSSION Fabrication of Hydrophobic SCs. According to the pore size, commercial SCs are divided into six specifications including G1, G2, G3, G4, G5, and G6 to meet the various demands. Figure 1 shows the SEM images of the top and bottom surfaces of the pristine SCs. They show irregular pebble-shaped particles with multilevel roughness at the micro/nanoscale, which is important for creating determined wettability. It can be clearly observed the top surface of SC had a smaller particle size than that of the bottom surface. As shown in Figure 1, the corresponding statistic illustrated that the particle size distributions of G1 to G6 were approximately 200-500, 100-400, 20-120, 10-70, 5-30, and 1-20 m, respectively. The stack of different size of the sand core particles resulted in the 3D filters with numerous pores.47 As shown in Figure S1, the pore sizes of G1 to G6 calculated from SEM images were 144 ± 26, 87 ± 29, 31 ± 10, 17 ± 5, 8 ± 3 and 2 ± 1 m, respectively. Take the advantage of the surface structure and pore size, a simple, facile and one-step CVR method was used to prepare hydrophobic SCs (Figure 2a). PFTS molecules possess highly reactive siloxy end groups. Upon heating and evacuation, hydrophobic surface gradually formed on the SCs by means of the hydrolysis and condensation reaction of PFTS, and the further



condensation reaction of hydroxyl groups between PFTS and silica in the presence of trace water.48 The pristine SCs were easily wetted by water, and their water resistances were markedly improved after introducing PFTS. Nearly sphere-like shapes were observed when water was dropped on their surfaces (Figure 2b). Figure 3a shows the WCAs of the top and bottom surfaces of the PFTS-modified SCs. From G1-4.0h to G6-4.0h, an increase trend in WCA was observed as the surface micro/nano-roughness increased. Air was more trapped in the surface cavities, creating a macroscale solid-water-air interface and an improved WCA from G1-4.0h to G6-4.0h. For the top surface, the static WCAs reached 130.5 ± 1.0, 132.7 ± 2.2, 139.3 ± 2.5, 145.7 ± 0.8, 146.8 ± 1.3, and 148.4 ± 1.5°, and for the bottom surface, the static WCAs were 124.0 ± 2.7, 126.0 ± 2.3, 125.5 ± 2.1, 132.3 ± 4.6, 132.8 ± 4.3, and 134.3 ± 1.3°, respectively. As shown in Figure 1, the top surface has the smaller sand core particles compared with the bottom surface, resulted in a relatively smooth bottom surface and a rough top surface. So the WCAs on the top surface are larger than those of the bottom surface. It concluded that increasing the hydrophobicity of the material itself and enhancing the roughness of a surface are the two main factors to fabricate a high hydrophobic surface. Consequently, the wettability inside the modified SCs was investigated. As shown in Figure S2, for the top surface rubbed by sandpaper, the static WCAs of G1-4.0h ~ G6-4.0h reached 123.7 ± 0.6, 126.7 ± 4.0, 128.0 ± 1.0, 139.7 ± 0.6, 140.3 ± 2.9, and 146 ± 3.0°, and for the cross section, the static WCAs were 101.3 ± 10.2, 108.7 ± 6.5, 114.0 ± 7.0, 118 ± 9.6, 131.0 ± 3.6, and 133.3 ± 2.08°, respectively. The results indicated that the inside of the modified SCs also have good hydrophobicity. It also showed that the chemical vapor based reaction for the fabrication of hydrophobic materials is adequate and uniform. SEM images of the PFTS-modified SCs are shown in Figure S3. The modified SCs maintained intact sand core particles and pores,


Page 10 of 41

Page 11 of 41 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


implying that the original structure was not damaged. More importantly, a distinct rough surface was evident in the high-resolution images of G4-4.0h ~ 6-4.0h, and the sand core particles have a size ranging from tens to several hundred nanometers, which is essential for a hydrophobic material. Figure 3b shows the dependence of the water absorption on the type of SCs. The water absorption of the pristine G1 ~ G6 was 19.8, 23.5, 18.4, 24.0, 25.0 and 26.4%, respectively. After the PFTS modified for 4.0 h, the values decreased to 0.38, 0.28, 0.17, 0.14, 0.11 and 0.13%, respectively. The relatively low water uptake indicated that the PFTS-modified SCs had an enhanced hydrophobicity. To further explore the process of the CVR method, the reaction time and temperature were studied, and G6 was chosen as the investigated sample (Figure 3c,d). Fixing the reaction time of 0.5 h, the WCA of G6 increased from 124 to 142° as the temperature increased from 40 to 80 ℃. As the temperature further increased to 140 ℃, the WCA slightly increased to 145°. Next, fixing the reaction temperature of 80 ℃, the WCA of G6 increased from 0 to 134° as the reaction time increased from 0 to 0.5 h. The further increase in the reaction time to 12.0 h resulted in a slight increase of WCA. Correspondingly, the SEM images of the PFTS-modified G6 with different reaction time are shown in Figure S4. Aggregated particles for the deposition of PFTS were observed with increasing reaction time. It also concluded that the experiment conditions of the CVR method were mild, efficient and convenient. Figure S5a shows the XPS wide scan spectra of G6 and G6-4.0h. For the pristine G6, only peaks of C, O, and Si were detected. After the PFTS modification, new peaks at 689 and 836 eV attributed to F1s and F auger appeared. Figure S5b and c shows the high-resolution XPS spectra of C1s and F1s. The C in the functional groups of -CF2 and -CF3 present in PFTS were confirmed at 292 and 294 eV, respectively. The XPS scan



Page 12 of 41

of F1s further confirmed the presence of fluorine (689 eV), which is ascribed to the grafted PFTS molecules.49 The elemental compositions are listed in Table S1. The C/O/Si/F ratio for the pristine G6 was 23.08/53.94/22.98/0%, and changed to 15.49/47.39/22.15/14.96%

after

modification,

which

further

confirmed

the

incorporation of PFTS molecules. Contact Angle on a Rough Surface with Partial Wetting. To better understand how the surface structure and roughness affect the water-repellent behavior, four cases in which a liquid droplet is put on a solid surface provided (Figure S6).50 Case a is an ideal planar surface, the wettability is mainly controlled by the chemistry compositions of the surface. Case b is the Wenzel state, which is completely wetted. Case c is the Cassie model with partially wetting on a rough solid surface. The contact areas of solidliquid and liquid-gas is equivalent to the dimension at the bottom of the droplet. In most practical cases, the contact friction of the solid-liquid and liquid-gas is greater than one (Figure S6d). Referring to the SEM images in Figure 1, the surface of SCs composed of most flat sand core particles is suitable for the case c. Therefore, the contact angle between Wenzel and Cassie wetting regime is given by50 cos θ = f1cos θ0- f2

(4)

where θ is the contact angle of rough surface, θ0 is the Young’s contact angle of smooth surface, f1 is the fraction of the solid/water interface, f2 is that of the air/water interface, and f1 + f2 = 1. From G1 to G6, the size of the sand core particles gradually decreased and small protrusions increased as shown in the SC models (Figure 4a). Before modification, SC endowed the superhydrophilicity with a WCA of 0° for the hydrophilic silica and the surface roughness. For the PFTS-modified SC, a bright and reflective surface


Page 13 of 41 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


underneath water droplets (Figure 2b2) suggests the presence of air pockets between water and the SC surface that ensures impregnating Cassie wetting regime. The WCA increased from G1 to G6 via the same modification because of the enhanced roughness and the change of the solid-liquid-air three-phase contact state. The highest known WCA on a smooth low-energy surface is around 110 to 120°. The WCA on the planar surface composed of a pure array with CF3 as terminal group is given as 120°.51 Therefore, based on the case c model and the impregnating Cassie wetting equation (1), the values of f1 and f2 were calculated and listed in Table 1. The value of f1 for G1-4.0h to G6-4.0h reduced from 0.728 to 0.270. On the contrast, the f2 value of G1-4.0h to G64.0h increased from 0.272 to 0.730. It is a higher fraction of liquid-air contact area that leads to a stronger surface water-repellence. Surface Adhesion of the PFTS-modified SCs. The texture of hydrophobic surface at the microscopic scale determines the liquid-solid contact ways, and plays an important role in controlling the adhesion of water droplets on the surface. The solid– liquid contact ways can effectively modulate the contour, length, and continuity of the three-phase (solid–air–liquid) contact line. The magnitude of the adhesive force of a droplet for a hydrophobic surface descends in the order “area-contact”>“line-contact”> “point-contact”. 52 In such case, the decreased sand core particle size lowered the liquidsolid contact area, and more and more air pockets were trapped under the liquid from G1 to G6. As shown in Figure 4b, advancing (θA) and receding contact angles (θR) were determined to explore the surface adhesion property. Table S2 lists the values of θA and θR. From G1-4.0h to G6-4.0h, the θA increased from 125.7 ± 2.7 to 150.5 ± 2.3° for the enhanced surface roughness. The value of the difference of θA and θR reflects the surface adhesion force. The larger the value, the more difficult the water droplets are to move on the surface and the larger the surface adhesion force. Figure 4c shows the



variations of (θA- θR) of the PFTS-modified SCs. The (θA- θR) values of G1-4.0h ~ G34.0h are larger than that of G4-4.0h ~ G6-4.0h, indicating that the former had a higher surface adhesion and the latter had the lower surface adhesion. Furthermore, the adhesion tests of G3-4.0h ~ G6-4.0h are shown in Video S1 and S2. Water droplets were dropped on the surface of the modified SCs which were rotated 360° at a given angular velocity (ω). For G3-4.0h, both at a low ω of 3.2 rpm and high ω of 27.8 rpm, the state of the water droplets showed no any change from start to the end. It indicated that G3-4.0h endowed a high surface adhesion. While for G4-4.0h ~ G6-4.0h, almost no water droplets were reserved after a lap of rotation at the ω of 3.2 rpm, suggesting low surface adhesion properties. G4-4.0h ~ G6-4.0h had the close (θA - θR) values and the similar surface adhesion. AFM topography was used to explore their surface roughness (Figure S7). The results indicated that the surface of G4-4.0h ~ 6-4.0h had the nanoscale roughness and the root-mean-square roughness (RMS) was 58.4, 61.1 and 74.7 nm, respectively. The modified SC surfaces with tunable water adhesion exhibited promising applications in water transportation and self-cleaning effect. For example, the surface with high water adhesion can be used as “mechanical hand” to transport small droplets without any loss. A 5 μL water droplet was placed on G4-4.0h (low adhesion), and then G3-4.0h (high adhesion) was lowered to touch the droplet and then pull it up. The droplet is transferred from G4-4.0h to G3-4.0h without any loss (Figure 4d). Physiochemical Properties of the PFTS-Modified SCs. The mechanical durability of the SCs before and after modification were investigated. The results of pencil hardness are listed in Table S3. G1 had the largest pencil hardness (> 6H), and G4~G6 had the lower hardness (4B-5B). Since the SCs were hard and almost had no elasticity, the shore D hardness was also tested. The results showed that the hardness of


Page 14 of 41

Page 15 of 41 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 SCs was in the range of soft plastic. The pencil hardness and shore D hardness of the PFTS-modified SCs were almost the same as the pristine SCs. Meanwhile, the compression strength was explored. As shown in Figure S8, the SCs before and after modification have good compression resistance. The stress increased rapidly as the strain slightly increased, and the maximum strength of 4.2 MPa was achieved. What’s more, G4-4.0h displayed a good resistance to bending, which could hold a weight of 2 kg without deformation. The abrasion resistance was studied on the RCA paper abrasion tester. After tested for 1500 cycles, the weight loss of G2-4.0h and G6-4.0h was 0.0005 and 0.0078 g, respectively. As summarized in Table S4, the WCA of G64.0h decreased from 140.0° to 124.7° with the abrasion cycles increased from 100r to 1500r, indicating the PFTS-modified SCs have a good mechanical durability. The value of θR has an obvious decrease, and (θA - θR) showed a slightly increase with increasing abrasion cycles (Table S4), suggesting an increased surface adhesion. The PFTS-modified SCs own lots of fascinating properties including chemical stability, self-cleaning effect and underoil superhydrophobicity, which are important for their practical applications.53 As shown in Figure 5, in the condition of acid (pH=1), alkali (pH=13) and 5 wt% NaCl solution, the measured WCAs of the modified SCs showed no significant changes compared with the initial WCA of pH=7. Since the droplets were colored with dye, no marks were observed after wiping the droplets placed onto their surfaces. Specifically, for G6-4.0h, the WCAs are all kept above 140° toward to the different concentrations of acid, alkali and salt aqueous solutions (Figure 5d). The results suggested the PFTS-modified SCs remained good durable performance after the rigorous tests of strong acid/alkali (highly to 8 mol/L), which endowed the



materials with potential for practical applications. The self-cleaning effect, inspired by the lotus leaf, is an intriguing property to protect the surfaces from the pollutants such as dust and dirt.54 In terms of the hydrophobic surface, an air layer gets trapped between the formation of a composite air/liquid/solid interface and increases in the WCA. Since the PFTS-modified G4~6 samples endowed good hydrophobicity with low water adhesion ability, weak water current can easily roll off from their surfaces and take away the surface dirt. Figure 6 and Video S3 show the self-cleaning test for G4-4.0h ~ G6-4.0h. The methyl green powders could be wiped off efficiently and completely as the small water current rolled down from the surface. Therefore, the surfaces of G4-4.0h ~ G6-4.0h demonstrated excellent self-cleaning properties. The increase of oil leakage and oil spill accidents pose a great threat to the environment.55 However, lots of materials lost their hydrophobicity for the increase of the surface tension after being polluted by oil. Figure 7a shows the photographs of the PFTS-modified SCs after immersing in chloroform. Obviously, the modified samples were easily wetted by the organic solvents. Except for lipophilicity, underoil superhydrophobicity is a critical property in application. As shown in Figure 7b, c, the water droplets dyed by CuSO4 maintain a spherical shape on the surfaces of G1-4.0h ~ G6-4.0h after being immersed into corn oil. It is ascribed to the fact that the modified SCs are firstly full wetted by oil and a stable oil/solid composite interface would be formed that the water suspend on the composite triphase interface rather than access the surface. To illustrate the water-repellent behavior of the hydrophobic SCs, the underoil water-adhesion test was investigated via an approach-compress- detach process (Figure 7d). The water droplet suspending on the syringe can be hardly pulled down to the surface even when the droplet was squeezed. When the water droplet was gradually


Page 16 of 41

Page 17 of 41 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


removed, it could overcome the adhesion force to detach from the surface of the modified SCs, and no deformation was observed, suggesting good hydrophobicity with a low water adhesion. Only for G1-4.0h, the water droplet cannot be removed from the surface after being squeezed, while its WCA is still high as 160°. Oil/Water and Water-in-Oil Emulsion Separations. Taking the advantage of their hydrophobicity, porous 3D structure and stability, PFTS-modified SCs were ideal candidates for the oil/ water separation. Figure 8a shows the vacuum degree required for water to pass through the modified SCs. From G1-4.0h to G6-4.0h, the needed vacuum degree increased with a decrease of pore size. The specific pressure values for G1-4.0h ~ G6-4.0h were 0, 1.3, 4.0, 22, 44 and 55 kPa, respectively. The pore size of G1 is as large as 144 m, and water still could pass through G1-4.0h. As shown in Figure 8b, the toluene fluxes of G2-4.0h to G6-4.0h were determined to be 6272 ± 111, 7328 ± 255, 6424 ± 178, 2333 ± 80 and 1932 ± 31 L m-2 h-1 under a given vacuum degree of 0, 3.8, 17.7, 40, 48.5 kPa, respectively. For G2-4.0h and G3-4.0h, the fluxes of various organics were performed as shown in Figure 8c. The fluxes of chloroform, dichloromethane, n-hexane, ethyl ether and corn oil were 8698±350, 9205 ± 436, 764 ± 286, 11022 ± 141, and 12 ± 1 L m-2 h-1 for G2-4.0h under gravity, and were 2473 ± 309, 2331 ± 59, 8852 ± 626, 19292 ± 1495, and 10 ± 2 L m-2 h-1 for G3-4.0h under 3.8 kPa, respectively. Such fast mass transport is attributed to the superoleophilic rough surface as well as the pore structure of SCs. The values are comparable to or even higher than those of other advanced filtration materials as listed in Table 2.56-66 Compared with the pressure-driven filtration materials, G2-4.0h for oil/water separation is advantageous for its energy-efficient and ultrahigh permeate fluxes. To verify the practicability of the modified SCs in a realistic environment (e.g. heavy or light oil on water, where the water is neutral, acidic, alkaline or salt solution),



the oil/water separation experiments were carried out. Figure 8d, e shows the visual photographs of two types of oil/water separation. Mixtures of chloroform/water and toluene/water were poured onto G2-4.0h, and gravity was the only force for the separation. The water was retained above the G2-4.0h surface, while the organics both lower density and higher density than water permeated through G2-4.0h quickly. And no visible water was observed in the collected organics, indicating high purity and effective separation of the mixtures. Video S4 shows the separation of the mixtures of toluene/water, chloroform/water, chloroform/ NaOH aq. (pH=13) and chloroform/ H2SO4 aq. (pH=1) respectively. The whole process was completed within a few seconds. The separation efficiency of G2-4.0h was up to 99% for the toluene/water and above 98% for chloroform/water (Figure 8f). G2-4.0h retained a high separation efficiency after 20 separation cycles, indicating a good recyclability and durability. Moreover, when both demands for the oil/water separation and impurities filtration, the types of PFTS-modified SCs can be selected according to the pore size, flux and pressure. Ascribe to the wide pore size distribution, the PFTS-modified G4 ~ G6 were also suitable for the water-in-oil emulsion separation. The water-in-isooctane emulsions (containing 1% water) were poured onto the funnels to allow separation by gravity. The origin emulsion was opaque, and it turned into transparent isooctane after separation (Figure 9a). Digital and optical microscope images of emulsion were taken before and after separation (Figure 9b, c). Dynamic light scattering was adopted to measure the water droplet size distribution. The original emulsion included a broad size distribution of water droplets on the micrometer scale (Inset of Figure 9b). After separation by G44.0h, the emulsion contained exclusively tiny droplets below 100 nm (Inset of Figure 9c), indicating a good separation performance for water-in-oil emulsions. Probably, upon touching the surface of the modified SCs, organics immediately spread and


Page 18 of 41

Page 19 of 41 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


permeated into the SCs because of their preferential affinity with the grafted PFTS, thus a stable organic solvents/solid composite interface would be formed. While the water droplets were blocked well by the dense multilayer hierarchical structure of the modified SCs.67 The micro-scaled water droplets could easily roll on the surface due to the weak adhesion force, thus their sizes would significantly increase due to the coalescence effect. Consequently, the water droplets with a larger size would be remained on the surface of the modified SCs. Moreover, the modified SCs also worked well with other water-in-oil emulsions, such as petroleum ether, toluene, dichloroethane and hexadecane (Figure 9d-g). As shown in Figure 9h, the fluxes of G4-4.0h were determined to be 6.1 ± 0.6, 9.7 ± 2.8, 7.0 ± 0.4, 14.3 ± 1.8, and 1.3 ± 0.04 L m-2 h-1 for the emulsions of isooctane, petroleum ether, toluene, dichloroethane and hexadecane, respectively.

 CONCLUSIONS In summary, we fabricated a series of mechanical durable hydrophobic SCs via the facile CVR method. The CVR approach is applicable in the large-scale production because it gets rid of special apparatus and harsh operation conditions such as determined atmosphere. The WCAs of the PFTS-modified SCs increased from 120 to 149° with increasing the surface roughness of the material itself, as well as increasing the reaction temperature and time. The surface wettability of the modified SCs is adapted for Cassie model with partial wetting, and the fraction of air/water interface increased from G1 to G6 and the solid/water interface decreased correspondingly. The hydrophobic SCs preserved an outstanding chemical stability in extremes of acidic and alkali solutions and remarkable self-cleaning behavior. With good hydrophobicity, high porosity, and proper pore size, G2-4.0h exhibited excellent oil/water separation



efficiency highly to 99%, and a permeation flux of 11000 L m-2 h-1 for ethyl ether under solely gravity. For G3-4.0h, the maximum permeation flux reached to 20000 L m-2 h-1 for ethyl ether under vacuum degree of 3.8 kPa. Moreover, G4-4.0h ~ G6-4.0h with small pore sizes have been successfully applied in water-in-oil emulsion separation. Overall, our work presented a good example for constructing a low-cost durable hydrophobic material with wide applications. Meanwhile, this work provided a deeper understanding of the wettability with the surface structure.

 ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: PP. atom% of G6 and G6-4.0h (Table S1), the results of the advancing contact angle and receding contact angle (Table S2), pencil hardness and shore D hardness of SCs before and after modification (Table S3), list of the WCA, θA, θR and (θA - θR) of G64.0h with different abrasion cycles (Table S4), pore sizes of SCs (Figure S1), WCAs of the top surface rubbed by sandpaper and the cross section of G1~6-4.0h, and photographs of water droplets on the cross section of G2-4.0h and G4-4.0h (Figure S2), SEM images of the modified SCs (Figures S3, 4), XPS spectra of G6 and G6-4.0h (Figure S5), schematic diagram of the wetting state of a liquid on a solid surface (Figure S6), AFM 2D images, the corresponding section roughness profiles and 3D surface structures of G4~6-4.0h (Figure S7), and compressive stress curves of SCs before and after modification (Figure S8). (PDF) Video S1: The water adhesion test process of G3-4.0h at ω=3.2 and 27.8 rpm. (AVI) Video S2: The water adhesion test process of G4~6-4.0h at ω=3.2 (AVI)


Page 20 of 41

Page 21 of 41 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


Video S3: Self-cleaning test for G4~6-4.0h (AVI) Video S4: Separation process of toluene/water, chloroform/water, chloroform/NaOH aq. and chloroform/H2SO4 aq. with G2-4.0h (AVI)

 AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (J.Z.). Notes The authors declare no competing financial interest.

 ACKNOWLEDGEMENTS This work was financially supported by National Natural Science Foundation of China (51473128 and 51273151).

 REFERENCES (1)

Hancock M. J.; Sekeroglu K.; Demirel M. C. Bioinspired Directional Surfaces

for Adhesion, Wetting, and Transport. Adv. Funct. Mater. 2012, 22, 2223-2234. (2)

Gupta R. K.; Dunderdale G. J.; England M. W.; Hozumi A. Oil/water

Separation Techniques: A Review of Recent Progresses and Future Directions. J. Mater. Chem. A 2017, 5, 16025-16058. (3)

Zhang F.; Zhang W. B.; Shi Z.; Wang D.; Jin J.; Jiang L. Nanowire-Haired

Inorganic Membranes with Superhydrophilicity and Underwater Ultralow Adhesive Superoleophobicity for High-Efficiency Oil/Water Separation. Adv. Mater. 2013, 25, 4192-4198. (4) Raturi P.; Yadav K.; Singh J. P. ZnO-Nanowires-Coated Smart Surface Mesh



with Reversible Wettability for Efficient On-Demand Oil/Water Separation. ACS Appl. Mater. Interfaces 2017, 9, 6007–6013. (5) Tian D.; Zhang X.; Tian Y.; Wu Y.; Wang X.; Zhai J.; Jiang L. Photo-induced Water–Oil Separation Based on Switchable Superhydrophobicity–Superhydrophilicity and Underwater Superoleophobicity of the Aligned ZnO Nanorod Array-Coated Mesh Films. J. Mater. Chem. 2012, 22, 19652 -19657. (6)

Gore P. M.; Kandasubramanian B. Heterogeneous Wettable Cotton Based

Superhydrophobic Janus Biofabric Engineered with PLA/Functionalized-Organoclay Microfibers for Efficient Oil–Water Separation. J. Mater. Chem. A 2018, 6, 7457-7479. (7)

Yuan S.; Strobbe D.; Kruth J. P.; Puyveldea P. V.; Bruggen B. V. d. Super-

Hydrophobic 3D Printed Polysulfone Membranes with A Switchable Wettability by SelfAssembled Candle Soot for Efficient Gravity-Driven Oil/Water Separation. J. Mater. Chem. 2017, 5, 2540 -25409. (8)

Jiang J.; Zhang Q.; Zhan X.; Chen F. A Renewable Biomass-Derived

Honeycomb-Like Aerogel as Robust Oil Absorbent with Double Way Reusability. ACS Sustainable Chem. Eng. 2017, 5, 10307-10316. (9)

Ge J.; Zong D.; Jin Q.; Yu J.; Ding B. Biomimetic and Superwettable

Nanofibrous Skins for Highly Efficient Separation of Oil-in-Water Emulsions. Adv. Funct. Mater. 2018, 28, 1705051. (10) Feng X. J.; Jiang L. Design and Creation of Superwetting/Antiwetting Surfaces. Adv. Mater. 2006, 18, 3063-3078. (11) Teisala H.; Tuominen M.; Kuusiopalo J. Superhydrophobic Coatings on Cellulose-Based Materials: Fabrication, Properties, and Applications. Adv. Mater. Interface 2014, 1, 1300026. (12) Sun T. L.; Feng L.; Gao X. F.; Jiang L. Bioinspired Surfaces with Special


Page 22 of 41

Page 23 of 41 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


Wettability. Acc. Chem. Res. 2005, 38, 644-652. (13) Gui X. C.; Wei J. Q.; Wang K. L.; Cao A. Y.; Zhu H. W.; Jia Y.; Shu Q. K.; Wu D. H. Carbon Nanotube Sponges. Adv. Mater. 2010, 22, 617-621. (14) Ruan C.; Ai K.; Li X.; Lu L. A Superhydrophobic Sponge with Excellent Absorbency and Flame Retardancy. Angew. Chem. Int. Ed. 2014, 53, 5662-5666. (15) Fan J.; Song Y.; Wang S.; Meng J.; Yang G.; Guo X.; Feng L.; Jiang L. Directly Coating Hydrogel on Filter Paper for Effective Oil–Water Separation in Highly Acidic, Alkaline, and Salty Environment. Adv. Funct. Mater. 2015, 25, 5368-5375. (16) Cao C.; Ge M.; Huang J.; Li S.; Deng S.; Zhang S.; Chen Z.; Zhang K.; Aldeyab S.S.; Lai Y. Robust Fluorine-Free Superhydrophobic PDMS–Ormosil@Fabrics for Highly Effective Self-Cleaning and Efficient Oil–Water Separation. J. Mater. Chem. A 2016, 4, 12179-12187. (17) Jiang L.; Zhao Y.; Zhai J. A Lotus-Leaf-like Superhydrophobic Surface: A Porous Microsphere/Nanofiber Composite Film Prepared by Electrohydrodynamics. Angew. Chem. Int. Ed. 2004, 43, 4338-4341. (18) Lai Y.; Cao X.; Zhuang H.; Huang J.; Lin C.; Jiang L.; Designing Superhydrophobic Porous Nanostructures with Tunable Water Adhesion. Adv. Mater. 2009, 21, 3799-3803. (19) Wang F.; Lei S.; Xu Y.; Ou J. Green Approach to the Fabrication of Superhydrophobic Mesh Surface for Oil/Water Separation. ChemPhysChem 2015, 16, 2237-2243. (20) Feng L.; Li S.; Li H.; Zhai J.; Song Y.; Jiang L.; Zhu D. Super-Hydrophobic Surface of Aligned Polyacrylonitrile Nanofibers. Angew. Chem. Int. Ed. 2002, 41, 1221-1223. (21) Gore P.M.; Kandasubramanian B. Heterogeneous Wettable Cotton Based



Superhydrophobic Janus Biofabric Engineered with PLA/Functionalized-Organoclay Microfibers for Efficient Oil–Water Separation. J. Mater. Chem. A. 2018, 6, 7457-7479 (22) Yuan S.; Strobbe D.; Kruth J. P.; Puyveldea P. V.; Bruggen B. V. D. SuperHydrophobic 3D Printed Polysulfone Membranes with A Switchable Wettability by SelfAssembled Candle Soot for Efficient Gravity-Driven Oil/Water Separation. J. Mater. Chem. A 2017, 5, 25401-25409. (23) Wu, Z., Li, C., Liang, H., Chen, J., Yu, S. Ultralight, Flexible, and Fire ‐ Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose. Angew. Chem. Int. Ed. 2013, 52, 2997-3001. (24) Zeng X.; Qian L.; Yuan X.; Zhou C.; Li Z.; Cheng J.; Xu S.; Wang S.; Pi P.; Wen X. Inspired by Stenocara Beetles: From Water Collection to High-Efficiency Water-in-Oil Emulsion Separation. ACS Nano. 2017, 11, 760−769. (25) Jiao Y.; Wan C.; Qiang T.; Li J. Synthesis of Superhydrophobic Ultralight Aerogels from Nanofibrillated Cellulose Isolated from Natural Reed for HighPerformance Adsorbents. Appl. Phys. A 2016, 122, 686. (26) Lv W.; Mei Q.; Xiao J.; M Du.; Zheng Q. 3D Multiscale Superhydrophilic Sponges with Delicately Designed Pore Size for Ultrafast Oil/Water Separation. Adv. Funct. Mater. 2017, 27, 1704293. (27) Wei Q.; Wang Y.; Nie Z.; Yu C.; Li Q.; Zou J.; Li C. Facile Synthesis of Hydrophobic Microporous Silica Membranes and Their Resistance to Humid Atmosphere. Microporous Mesoporous Mater. 2008, 111, 97-103. (28) Pujari S. P.; Scheres L.; Marcelis A. T.; Zuihof H. Covalent Surface Modification of Oxide Surfaces. Angew. Chem. Int. Ed. 2014, 53, 6322-6356. (29) Su B.; Wang S. T.; Song Y. L.; Jiang L. A Heatable and Evaporation-Free Miniature Reactor Upon Superhydrophobic Pedestals. Soft Matter 2012, 8, 631 -635.


Page 24 of 41

Page 25 of 41 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


(30) Berger S.; Ionov L.; Synytska A. Engineering of Ultra-Hydrophobic Functional Coatings Using Controlled Aggregation of Bicomponent Core/Shell Janus Particles. Adv. Funct. Mater. 2011, 21, 2338-2344. (31) Chakrabarty B.; Ghoshal A. K.; Purkait M. K. Ultrafiltration of Stable Oil-inWater Emulsion by Polysulfone Membrane. J. Membr. Sci. 2008, 325, 427-437. (32) Serp P.; Kalck P.; Feurer R.; Chemical Vapor Deposition Methods for the Controlled Preparation of Supported Catalytic Materials. Chem. Rev. 2002, 102, 30853128. (33) Genzer J.; Efimenko K.; Creating Long-Lived Superhydrophobic Polymer Surfaces Through Mechanically Assembled Monolayers. Science 2000, 290, 21302133. (34) Liu Y.; Wang X.; Fei B.; Hu H.; Lai C.; Xin J. H. Bioinspired, StimuliResponsive, Multifunctional Superhydrophobic Surface with Directional Wetting, Adhesion, and Transport of Water. Adv. Funct. Mater. 2015, 25, 5047-5056. (35) Yao T.; Wang C.; Lin Q.; Li X.; Chen X.; Wu J.; Zhang J.; Yu K.; Yang B. Fabrication of Flexible Superhydrophobic Films by Lift-Up Soft-Lithography and Decoration with Ag Nanoparticles. Nanotechnology 2009, 20, 065304. (36) Tserepi

A.;

Vlachopoulou

M.;

Gogolides

E.

Nanotexturing

of

Poly(dimethylsiloxane) in Plasmas for Creating Robust Super-Hydrophobic Surfaces. Nanotechnology 2006, 17, 3977. (37) Choy K. L. Chemical Vapour Deposition of Coatings. Prog. Mater. Sci. 2003, 48, 57-170. (38) Wang X.; Gong Y.; Shi G.; Chow W. L.; Keyshar K.; Vajtai G. Ye, R.; Lou J.; Liu Z.; Ringe E.; Tay B. K.; Ajayan P. M. Chemical Vapor Deposition Growth of Crystalline Monolayer MoSe2. ACS Nano 2014, 8, 5125-5131.



(39) Li S.; Xie H.; Zhang S.; Wang X. Facile Transformation of Hydrophilic Cellulose into Superhydrophobic Cellulose. Chem. Commun. 2007, 4857-4859. (40) Hozumi A.; Ushiyama K.; Sugimura H.; Takai O. Fluoroalkylsilane Monolayers Formed by Chemical Vapor Surface Modification on Hydroxylated Oxide Surfaces. Langmuir 1999, 15,7600-7604. (41) Song X.; Zhai J.; Wang Y.; Jiang L. Fabrication of Superhydrophobic Surfaces by Self-Assembly and Their Water-Adhesion Properties. J. Phys. Chem. B 2005, 109, 4048-4052. (42) Kettunen M.; Silvennoinen R. J.; Houbenov N.; Nykänen A.; J. Ruokolainen, Sainio J.; Pore V.; Kemell M.; Ankerfors M.; Lindström T.; Ritala M.; Ras R. H. A.; Ikkala O. Photoswitchable Superabsorbency Based on Nanocellulose Aerogels. Adv. Funct. Mater. 2011, 21, 510-517. (43) Cunha A. G.; Freire C.; Silvestre A.; Neto C. P.; Gandini A.; Belgacem M. N.; Chaussy D.; Beneventi D. Preparation of Highly Hydrophobic and Lipophobic Cellulose Fibers by A Straightforward Gas–Solid Reaction. J. Colloid Interface Sci. 2010, 344, 588-595. (44) Wang K. J.; Wang K. X.; Zhang H.; Li G. D.; Chen J. S. Self-Oriented Single Crystalline Silicon Nanorod Arrays through A Chemical Vapor Reaction Route. J. Phys. Chem. C 2010, 114, 2471-2475. (45) Wen L.; Tian Y.; Jiang L. Bioinspired Super-Wettability from Fundamental Research to Practical Applications. Angew. Chem. Int. Ed. 2015, 54, 3387-3399. (46) Li S.; Huang J.; Chen Z.; Chen G.; Lai Y. A Review on Special Wettability Textiles: Theoretical Models, Fabrication Technologies and Multifunctional Applications. J. Mater. Chem. A 2017, 5, 31-55. (47) Gao H.; Yang Y.; Akampumuza O.; Hou J.; Zhang H.; Qin X. A Low Filtration


Page 26 of 41

Page 27 of 41 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


Resistance Three-Dimensional Composite Membrane Fabricated via Free Surface Electrospinning For Effective PM2.5 Capture. Environ. Sci.: Nano. 2017, 4, 864-875. (48) Su X.; Li H.; Lai X.; Zhang L.; Wang J.; Liao X.; Zeng X. Vapor–Liquid Sol– Gel Approach to Fabricating Highly Durable and Robust Superhydrophobic Polydimethylsiloxane@Silica Surface on Polyester Textile for Oil–Water Separation. ACS Appl. Mater. Interfaces 2017, 9, 28089-28099. (49) Ganesh V. A.; Dinachali S. S.; Jayaraman S.; Sridhar R.; Raut H. K.; Góra A.; Baji A.; Nair A. S.; Ramakrishna S. One-Step Fabrication of Robust and Optically Transparent Slippery Coatings. RSC Adv. 2014, 4, 55263-55270. (50) Kang H. C.; Jacobi A. M.; Equilibrium Contact Angles of Liquid Droplets on Ideal Rough Solids. Langmuir 2011, 27, 14910-14918. (51) And E. L. D.; Garoff S. Contact Line Structure and Dynamics on Surfaces with Contact Angle Hysteresis. Langmuir 1997, 13, 6321-6332. (52) Lai Y.; Gao X.; Zhuang H.; Huang J.; Lin C.; Jiang L. Tailoring the Morphology of LiCoO2: A First Principles Study. Adv. Mater. 2009, 21, 3799-3809. (53) Li X. P.; Sun Y. Li.; Xu Y. Y.; Chao Z. S. UV-Resistant and Thermally Stable Superhydrophobic CeO2 Nanotubes with High Water Adhesion. Small 2018, 14, 1801040. (54) He J.; He J.; Yuan M.; Xue M.; Ma X.; Hou L.; Zhang T.; Liu X.; Qu M. Facile Fabrication of Eco-Friendly Durable Superhydrophobic Material from Eggshell with Oil/Water Separation Property. Adv. Eng. Mater. 2018, 20, 1701180. (55) Ge J.; Zhao H.Y.; Zhu H. W.; Huang J.; Shi L. A.; Yu S. H. Advanced Sorbents for Oil-Spill Cleanup: Recent Advances and Future Perspectives. Adv. Mater. 2016, 28, 10459-10490. (56) Zhang W.; Liu N.; Cao Y, Chen Y.; L. Xu, Lin X.; Feng L. A Solvothermal



Route Decorated on Different Substrates: Controllable Separation of an Oil/Water Mixture to A Stabilized Nanoscale Emulsion. Adv. Mater. 2015, 27, 7349-7355. (57) Zhang Q.; Cao Y.; Liu N.; Zhang W.; Chen Y.; Lin X.; Wei Y.; Feng L.; Jiang L. Recycling of PE Glove Waste as Highly Valuable Products for Efficient Separation of Oil-Based Contaminants from Water. J. Mater. Chem. A 2016, 4, 18128-18133. (58) Song J.; Huang S.; Lu Y.; Bu X.; Mates J. E.; Ghosh A.; Ganguly R.; Carmalt C. J.; Parkin I. P.; Xu W.; Megaridis C. M. Self-Driven One-Step Oil Removal from Oil Spill on Water via Selective-Wettability Steel Mesh. ACS Appl. Mater. Interfaces 2014, 6, 19858-19865. (59) Tai M. H.; Gao P.; Tan B. Y.; Sun D. D.; Leckie J. O. Highly Efficient and Flexible Electrospun Carbon–Silica Nanofibrous Membrane for Ultrafast GravityDriven Oil–Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 9393-9401. (60) Xu Z.; Zhao Y.; Wang H.; Zhou H.; Qin C.; Wang X.; Lin T. Fluorine-Free Superhydrophobic Coatings with pH-Induced Wettability Transition for Controllable Oil–Water Separation. ACS Appl. Mater. Interfaces 2016, 8, 5661-5677. (61) Xiong S.; Kong L.; Huang J.; Chen X.; Wang Y. Atomic-Layer-Ddepositionenabled Nonwoven Membranes with Hierarchical ZnO Nanostructures for Switchable Water/Oil Separations. J. Membr. Sci. 2015, 493, 478-485. (62) Obaid M.; Tolba G. M. K.; Motlak M.; Fadali O. A.; Khalil K. A.; Almajid A. A.; Kim B.; Barakat N. A. M. Effective Polysulfone-Amorphous SiO2 NPs Electrospun Nanofiber Membrane for High Flux Oil/Water Separation. Chem. Eng. J. 2015, 279, 631-638. (63) Li J. J.; Zhou Y. N.; Jiang Z. D.; Luo Z. H. Electrospun Fibrous Mat with pHSwitchable Superwettability That Can Separate Layered Oil/Water Mixtures. Langmuir 2016, 32, 13358-13366.


Page 28 of 41

Page 29 of 41 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


(64) Gu J.; Xiao P.; Chen P.; Zhang L.; Wang H.; Dai L.; Song L.; Huang Y.; Zhang J.; Chen T. Functionalization of Biodegradable PLA Nonwoven Fabric as Superoleophilic and Superhydrophobic Material for Efficient Oil Absorption and Oil/Water Separation. ACS Appl. Mater. Interfaces 2017, 9, 5968-5973. (65) Li X.; Wang M.; Wang C.; Cheng C.; Wang X. Facile Immobilization of Ag Nanocluster on Nanofibrous Membrane for Oil/Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 15272-15282. (66) Zhou Y. N.; Li J. J.; Luo Z. H. Photo ATRP-Based Fluorinated Thermosensitive Block Copolymer for Controllable Water/Oil Separation. Ind. Eng. Chem. Res. 2015, 54, 10714-10722. (67) Ge J.; Zhang J.; Wang F.; Li Z.; Yu J.; Ding B. Superhydrophilic and Underwater Superoleophobic Nanofibrous Membrane with Hierarchical Structured Skin for Effective Oil-in-Water Emulsion Separation. J. Mater. Chem. A 2017, 5, 497502.


ACS Applied Materials & Interfaces 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

Figure 1. SEM images of the (a1-f1) top and (a2-f2) bottom surfaces of the pristine SCs and their corresponding particle size distributions, from left to right is G1/G2/G3/G4/G5/G6, respectively.


Page 30 of 41

Page 31 of 41 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) Schematic illustration for the hydrophobic modification of SC. (b) Photographs of water droplets on the surface of G4 before (b1) and after (b2) the PFTS modification.



Figure 3. (a) WCAs of the top and bottom surfaces of G1-4.0h~G6-4.0h, (b) Water absorption of the pristine and the PFTS-modified SCs. Dependence of WCA of the PFTS-modified SCs on the reaction time (c) and temperature (d).


Page 32 of 41

Page 33 of 41 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 4. (a) Wetting models of the different types of the pristine and PFTS-modified SCs. (b) The model of θA and θR. (c) Variations of (θA- θR) of G1-4.0h~G6-4.0h. (d) Transportation of a water droplet from the surface of G4-4.0h to G3-4.0h.



Figure 5. (a) Images of the different kinds of droplets at pH=1, pH=13 and 5 wt% NaCl aq. on the surface of G4-4.0h. (b) Images of G1-4.0h~G6-4.0h after wiping the droplets in (a). (c) Variations of WCA of G1-4.0h~G6-4.0h with droplets of pH=1, pH=13 and 5 wt% NaCl aq. (d) Variations of WCA on G6-4.0h with droplets of different concentrations of H2SO4, NaOH, NaCl aq.


Page 34 of 41

Page 35 of 41 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 6. Self-cleaning test for G4-4.0h: The methyl blue powders were placed on the G4-4.0h surface, and were removed by water current.



Figure 7. (a) Photographs of G1-4.0h~G6-4.0h after immersed in chloroform. (b) Top and (c) side view of water droplets on the G1-4.0h~G6-4.0h after immersed in corn oil. WCA measurements under corn oil for (d1) G1-4.0h and (d2) G4-4.0h.


Page 36 of 41

Page 37 of 41 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 8. (a) The vacuum degree required for water to pass through G1-4.0h~G6-4.0h. (b) Toluene fluxes of G2-4.0h~G6-4.0h under the given vacuum degree: G2-4.0h, gravity; G3-4.0h, 3.8 kPa; G4-4.0h, 17.7 kPa; G5-4.0h, 40.0 kPa; G6-4.0h, 48.5 kPa. (c) Fluxes of various organics for G2-4.0h under gravity and G3-4.0h with the vacuum degree of 3.8 kPa. Photographs for the separation of the mixtures of (d) chloroform (red)/water and (e) toluene (red)/water through G2-4.0h. (f) Durability of G2-4.0h for the continuous separation of chloroform/water and toluene/water for 20 cycles.



Figure 9. (a) Photograph of water-in-isooctane emulsion before and after separation with G4-40h, G5-4.0h and G6-4.0h. The microscopy images of water-in-isooctane emulsion (b) before and (c) after separation with G4-4.0h. Inset shows the corresponding water size distribution before and after separation determined by dynamic light scattering. Photographs of emulsions of (d) water-in-toluene, (e) waterin-dichloroethane, (f) water-in-petroleum ether and (g) water-in-hexadecane before and after separation with G4-4.0h. (h) Fluxes for the separation of various water-in-oil emulsions under gravity through G4-4.0h.


Page 38 of 41

Page 39 of 41 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


Table 1. Data of θo, θ, f1 and f2 calculated from the Cassie equation (partial wetting). Sample

G1-4.0h

G2-4.0h

G3-4.0h

G4-4.0h

G5-4.0h

G6-4.0h

θo ()

120

120

120

120

120

120

θ ()

130.5±1.0

132.7±2.2

139.3±2.5

145.7±0.8

146.8±1.3

148.4±1.5

f1

0.728~0.675

0.701~0.588

0.542~0.428

0.332~0.364

0.302~0.352

0.270~0.325

f2

0.272~0.325

0.289~0.412

0.458~0.572

0.636~0.668

0.648~0.698

0.675~0.730


ACS Applied Materials & Interfaces 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

Page 40 of 41

Table 2. Comparison of various materials in permeate fluxes Materials

Permeated substances

Permeate flux (Lm-2h-1)

Ref

PDVB membrane

gasoline, n-hexane, toluene

7000-28000 (gravity)

[56]

PE-coated mesh

n-hexane, toluene, gasoline, diesel

10000-40000 (gravity)

[57]

STA-treated meshes

hexadecane

10000-32000 (0.39-1.57 kPa)

[58]

SiO2-carbon nanofibers

petroleum spirit isooctane, n-hexane

1500−3000 (gravity)

[59]

SiO2 NPs/DA-TiO2 coated fabric

hexadecane

3300 (gravity)

[60]

ZnO-coated PET fabrics

carbon tetrachloride

6900 (gravity)

[61]

PSF-SiO2 NPs nanofibers

n-hexane, kerosene, gasoline

5000-8000 (gravity)

[62]

PDMS-b-P4VP fibrous mat

n-hexane, gasoline, ethyl ether, petroleum ether

8500-9500 (gravity)

[63]

SiO2/PS/PLA nonwoven fabric

n-hexane, toluene, silicone oil, pump oil, vegetable oil

7000-12000 (gravity)

[64]

APAN-Ag-SR nanofibers

chloroform, n-hexane, petroleum ether, vacuum pump oil

450-3500 (gravity)

[65]

PHFBMA-b-PNIPAAm

n-hexane

10000 (gravity)

[66]

G2-4.0h

chloroform, dichloromethane, toluene, n-hexane, ethyl ether

6000~11000 (gravity)

This work

G3-4.0h

chloroform, dichloromethane, toluene, n-hexane, ethyl ether

2000~20000 (3.8 kPa)

This work


Page 41 of 41 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

H2O

Oil

2 G

G 6

Vapor of organosilane

Sand core funnels, a commercial filter device, achieved the transition from hydrophilicity to hydrophobicity via the CVR method. The hydrophobic SCs had good mechanical durability, chemical stability, underoil superhydrophobicity and self-cleaning properties. Multi-level pore size allowed them to be used in both oil/water and emulsion separation.


Functionalization of Commercial Sand Core Funnels as Hydrophobic

Recommend Documents