ZnO-Nanowires-Coated Smart Surface Mesh with Reversible

Jan 26, 2017 - The rapid industrial growth has led to the large production of oily wastewater. Treatment of oily wastewater is an inevitable challenge...
4 downloads 17 Views 3MB Size
Download PDF
Research Article www.acsami.org

ZnO-Nanowires-Coated Smart Surface Mesh with Reversible Wettability for Efficient On-Demand Oil/Water Separation Parul Raturi, Kavita Yadav, and J. P. Singh* Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India S Supporting Information *

ABSTRACT: The rapid industrial growth has led to the large production of oily wastewater. Treatment of oily wastewater is an inevitable challenge to manage the greater demand of clean water for the rapidly growing population and economy. In the present work, we have developed a smart surface mesh with reversible wetting properties via a simple, ecofriendly, and scalable approach for on-demand oil−water separation. ZnO nanowires (NWs) obtained from the chemical vapor deposition method were coated on a stainless steel (SS) mesh. The as-synthesized ZnO-NWs-coated mesh shows superhydrophilic/underwater superoleophobic behavior. This mesh works in “water-removing” mode, where the superhydrophilic as well as underwater superoleophobic nature allows the water to permeate easily through the mesh while preventing oil. The wetting property of ZnO-NWs-coated mesh can be switched easily from superhydrophilic to superhydrophobic state and vice versa by simply annealing it at 300 °C alternatively under hydrogen and oxygen environment. The separation is solely driven by gravity. Thus, the reversible wettability of ZnO NWs provides a smart surface mesh which can be switched between “oil-removing” and “water-removing” modes. It was found that for more than 10 cycles of mesh reutilization in both modes alternatively, the separation efficiency of 99.9% stayed relatively invariant, indicating a prolonged antifouling property and excellent recyclability. This work provides a simple, fast, cost-effective, and on-demand solution for oily wastewater treatment and opens up new perspectives in the field of controllable oil−water separation. KEYWORDS: separation, switchable, underwater superoleophobic, ZnO nanowires, superhydrophobic, recyclable, oil-removing, water-removing

■

INTRODUCTION With the advancement of economy and society, oil contamination has become a challenging issue across the world.1 Everyday, a huge amount of oily wastewater is generated from various industrial processes such as food processing, transportation, metallurgy and petroleum refineries.2 Furthermore, the transportation of oil from production source to areas of consumption involves the dangers of accidental oil spills. The economy and environmental demands emphasize the requirement of a simple and efficient solution for this issue. From the last few decades, organic-polymer-based grafting3−6 strategies have been utilized for surface modification to attain the desired wetting properties for oil−water filtration. The major issues with polymer-based membranes are their chemical instability as the majority of the polymer-based membranes weaken to the extent that their lifetime becomes unacceptably short. Moreover, their tendency to foul more quickly can result in flux decline and rejection deterioration, which are undesirable particularly for oily wastewater treatment. To overcome these drawbacks of polymer-based membranes, researchers have used inorganic materials for oil−water separation.7−11 However, there still remain certain limitations like complex fabrication technique, low filtration efficiency, © 2017 American Chemical Society

inability for large scale production, and so on. For example, Tian et al. have reported photoinduced oil−water separation using ZnO-nanorods-based mesh.8 However, the process involves storing the mesh in the dark for 2 weeks followed by UV irradiation, which makes it time-consuming as well as complex. Furthermore, Li et al. have reported ZnO-nanorodscoated superhydrophobic mesh for oil−water filtration which can work only in “oil-removing” mode, with a very low filtration efficiency of about 97%.9 Thus, inorganic-material-based mesh with high filtration efficiency and time-saving approach for oil− water separation is of great demand. At the current time, most of the reports have described different approaches which can work efficiently either in “oilremoving”12−20 mode or “water-removing”21−26 mode. In “water-removing” mode, the materials having superhydrophilicity as well as underwater superoleophobicity allow the water to permeate easily and block oils, whereas in “oil-removing” mode, the materials having superhydrophobicity and superoleophilicity separate oil from water. The materials with Received: November 11, 2016 Accepted: January 26, 2017 Published: January 26, 2017 6007

DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013

Research Article

ACS Applied Materials & Interfaces

used as precursor. A boat containing precursor was inserted inside the tube furnace in such a way that the precursor was positioned at the center of the furnace. ZnO NWs were grown on the wall of a quartz tube in wool-like structure. The material was collected from the wall of the quartz tube. In the second step, a stainless steel mesh cut into a circular piece of 4 cm diameter was cleaned by ultrasonic cleaning sequentially in acetone, isopropyl alcohol, and water to remove the surface dirt and then dried at 80 °C. The as-grown ZnO NWs were collected and ultrasonically mixed with ethanol for 30 min to obtain a homogeneous mixture. The resulting solution was then drop casted on the SS mesh. The coated mesh was then dried at ambient temperature for 2 h to evaporate ethanol completely. The coating was repeated multiple times. Characterization of Materials. Surface morphology of samples were investigated by scanning electron microscope (SEM, ZEISS EVO 50). The droplet image on sample was captured by CMOS camera equipped with magnifying lens. The contact angle (CA) of water and oil droplets were measured by analyzing the droplet image with ImageJ software (National Institute of Health, U.S.A.). All the CA measurements were performed at three different positions on the sample surface. For the static and rolling measurements of CA, the volume of water and the oil droplet was kept at 5 μL. The crystal structure was determined by glancing angle X-ray diffraction (GAXRD) (Phillips X’pert, PRO−PW 3040 diffractometer) at 1° glancing angle. The chamber for annealing of the samples and setup for oil−water separation were home-built. To check the purity of the filtrate, a Horiba oil content analyzer was used to determine concentration of the oil in water after filtration. Furthermore, these concentration values were used to calculate the separation efficiency.

controllable wettability (i.e., switchable between superhydrophobic and superhydrophilic states) are promising candidates for oil−water separation as they provide the versatility to handle both options. These multifunctional materials have the advantage to be used for handling of different oil−water mixtures with a single separation mesh. In this way, a single mesh can be utilized for an efficient on-demand oil−water separation with a great flexibility. There are few reports that demonstrate the switchable wettability under the influence of external stimuli such as pH value,27−33 temperature,34 electric field,35 chemical modification,36,37 light,38−40 prewetting,41 and so on. Nonetheless, in most of these reports, surfaces with switchable wettability toward oil and water were either fabricated by precious materials such as gold and silver27−30 or via a complicated fabrication process to attain the desirable surface chemistry.33 Moreover, chemical modification was used excessively to attain the desired wettability. For example, Li et al. have fabricated a pH-responsive superhydrophobic fiber membrane by immersing copper mesh in the aqueous solutions of (NH 4 ) 2 S 2 O 8 and NaOH followed by the surface modification with thiol solutions.31 In another report, Zhiguang et al. have shown ammonia triggered reversible oil−water separation by using TiO2 and heptadecafluoronanoic complex coating.37 A variety of acids (e.g., the family of perfluoroalkyl acids) have been used widely as water/oil repellent agents and surfactants in industries for decades. However, the chemical treatment to get controllable wettability is usually harmful. Hence, it is desirable to develop a simple and cost-effective approach in which nontoxic, ecofriendly materials with controllable wettability can be utilized to prepare a mesh for efficient on-demand oil−water separation. In the present work, we report fabrication of ZnO nanowires (NWs)-coated stainless steel (SS) mesh showing reversible wettability making it useful in both “oil-removing” as well in “water-removing” mode with an excellent efficiency of more than 99.9%. The water wettability of the mesh was altered via annealing in hydrogen and oxygen gas environment alternately for 1.5 and 1 h, respectively. We have used chemical vapor deposition technique for growth of ZnO NWs which has been utilized widely in industries. In this technique, the substratebased deposition faces some limitations in production of the material in large amount. Here we are using substrate-less deposition, in which the wool-like structures grown on the wall of quartz tube can be produced in bulk for large scale application. The drop coating method utilized here for coating of ZnO NWs on SS mesh is simple, cost-effective, versatile, and not specific to any particular choice of substrate. This can also be utilized for large-area fabrication. In addition, oil absorbed on the mesh surface during separation can be removed simply by annealing it at high temperature. Therefore, this separation mesh does not require any separate treatment to remove the fouling species after each cycle to maintain efficiency of the mesh. Despite ZnO being used previously for oil−water separation application, this work follows a simple and effective approach for providing all-in-one solution to the different issues in a single separation device.

■

■

RESULTS AND DISCUSSION The choice of the substrate is based upon the inherent porous structure of the SS mesh optimum for separation application along with its good chemical and mechanical stability, low cost, and easy availability. The substrate having a pore size of about 50 μm was used in the present work. As reported in the literature, underwater superoleophobicity cannot be realized with a mesh having a pore size above 200 μm.21 Moreover, researchers found that 50 μm is the optimum pore size to attain a superhydrophobic surface. Below 50 μm, there is an insufficient proportion of air/water interface inhibiting the superhydrophobicity. Whereas above 50 μm, the pore size is too large to confine air into the structure, and the hydrophobic force provided by the micro/nanostructured stainless steel thread is not sufficient to support the water drop, resulting in a decrease in hydrophobicity. It indicates that mesh with an average pore size of about 50 μm is suitable to attain optimum properties for their application in oil−water separation.42,43 The SEM images of pristine mesh reveals that the pristine SS mesh has average pore size of 50 μm, Figure 1a. Mesh wire has diameter of about 30 μm. ZnO was selected for this work because it is an inexpensive, stable, and ecofriendly material. The ZnO NWs used in the present work were grown via chemical vapor deposition method. The ZnO NWs were not directly grown on the SS mesh but were drop casted on the mesh, resulting in the formation of randomly distributed ZnO NWs. ZnO NWs were coated on the mesh without adding any binder. Although some material comes out with sticking to the tape during a scotch tape peel test, for the filtration application, the adhesion of the ZnO coating was found to be sufficient. After coating, the mesh was covered with randomly distributed ZnO NWs, as shown in Figure 1b. The pore size between the dispersed NWs has a wide size distribution. The pore size varies from 0.5 to 1.4 μm. The magnified view of ZnO-NWs-coated mesh is shown in Figure 1c. The average diameter and length of ZnO NWs were

EXPERIMENTAL SECTION

Preparation of Filtration Mesh. The filtration mesh was prepared via two-step process. First, the ZnO NWs were grown by thermal chemical vapor deposition method. Prior to the growth, a tube furnace was purged with argon gas for 20 min. After that, the furnace was heated up to 1000 °C. ZnO powder mixed with carbon (1:1) was 6008

DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013

Research Article

ACS Applied Materials & Interfaces

needle was used to release the oil droplet under the mesh. An underwater CA image of diesel is shown in Figure 2c, which shows an average CA value of 155°. As can be seen in Figure 3, the contact angle of different oils on the surface of as-synthesized ZnO-nanowire coated mesh in

Figure 1. SEM images of (a) pristine mesh, (b) large-area view of mesh coated with as-synthesized ZnO NWs, (c) magnified view of ZnO-NWs-coated mesh, and (d) XRD pattern obtained from ZnONWs-coated mesh. The XRD spectra shows contribution from ZnO NWs only as the pattern was collected with 1° glancing angle.

Figure 3. Underwater CA of different oils on as-synthesized ZnONWs-coated mesh. Insets show the shapes of oil droplets on the mesh surface. CA images for oils lighter than water are inverted.

100 nm and 4.6 μm, respectively. The GAXRD pattern of ZnO NWs coated on SS mesh is shown in Figure 1d. The peaks were assigned using JCPDS data (JCPDS: 89-1397), which indicated the presence of wurtzite phase of ZnO. The CA measurements were performed to evaluate the wettability of coated mesh toward water and different oils. The mesh coated with assynthesized ZnO NWs shows superhydrophilicity and underwater superoleophobic properties which are optimum for efficient separation of oils lighter than water. When the water droplet comes in contact with the surface coated with as-grown ZnO NWs, it spreads within a few seconds with a CA value of about 0° on the mesh, as shown in Figure 2a. When additional droplets of water were added to the surface, the water was observed to easily permeate the mesh due to its hydrophilic nature. In addition to the water wettability of ZnO-coated SS mesh, wetting behavior of oils was also investigated. The ZnO-NWscoated SS mesh was found to be superoleophilic with CA value of 0° for diesel, as shown in Figure 2b. We have used a variety of oils like diesel, gasoline, mustard oil, chloroform, and dichloroethane, among others, for CA measurements, and the ZnO-coated mesh showed superoleophilic nature for all the oils. Underwater wettability of the mesh toward different oils was determined by immersing the mesh in water. The mesh was first fixed in a glass container full of water. In the case of oils lighter than water (i.e., diesel, gasoline etc.), an inverted

the presence of water displayed superoleophobic behavior. The underwater CA was more than 150° for all types of oil showing that the separation mesh is highly resistant toward the permeation of oils through mesh in the presence of water. Moreover, it was observed that the adhesion between the oil droplet and the coated mesh surface was extremely low. We have also performed the rolling measurements and found that a tilt angle of about 5° is sufficient for rolling of oil droplet from mesh surface in the presence of water. The reason responsible for the low adhesion of oil droplet in water medium was the repulsion of nonpolar oils from the polar water which is already trapped in the mesh pores. Thus, in the presence of water, oil droplets could be detached easily from the surface of coated mesh by a slight disturbance (Supporting Information, movie S1). Before moving further, it is important to understand the mechanism responsible for the underwater superoleophobicity. The ZnO NWs coated on the mesh form a porous structure, and because of the superhydrophilic nature of ZnO NWs, water can be trapped easily in the micro/nano structures of the ZnONWs-coated SS mesh. As a consequence of the trapped water, the effective contact area between the solid surface and oil decreases, which results in a triple-phase discontinuous contact line. This increases the repellent force between water-trapped polar mesh and nonpolar oil phase, which is further increased by surface roughness, causing underwater superoleophobicity.44

Figure 2. CA images of (a) water droplet on as-synthesized ZnO-NWs-coated mesh, (b) diesel droplet on as-synthesized ZnO-NWs-coated mesh, and (c) underwater diesel droplet on as-synthesized ZnO-NWs-coated mesh. 6009

DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013

Research Article

ACS Applied Materials & Interfaces The as-synthesized mesh showing superhydrophilic/underwater superoleophobic nature is suitable for separation of light oils because it allows water to permeate easily through the mesh and block oils, thus working in “water-removing” mode. Recent report on metal oxide nanostructures have shown that oxygen related defects are highly responsible for tuning the water wetting properties.45 The hydrogen- and oxygenannealing treatments are suitable for tuning the oxygen vacancy defects in a controlled manner.46 Here, the hydrogen annealing treatment was utilized to make the ZnO-coated mesh superhydrophobic. The mesh was annealed under 50 sccm flow of hydrogen gas at 300 °C. After annealing for 1.5 h, the separation mesh was cooled to room temperature, and CA measurements were performed to confirm its wettability toward oil and water. The water CA of ZnO-NWs-coated SS mesh after hydrogen annealing was found to be about 154° as shown in Figure 4. Rolling of water droplet was also observed on hydrogen annealed mesh, as shown in Supporting Information, Movie S2.

Figure 5. Reversible oil−water separation device containing ZnONWs-coated mesh fixed between two glass tubes. (a) Snapshot of separation of diesel−water mixture. Prewetted as-synthesized superhydrophilic/underwater superoleophobic mesh was used for diesel− water mixture separation. Water passed through the mesh, and diesel was retained above the mesh. (b) Snapshot of separation of chloroform−water mixture through superhydrophobic/superoleophilic mesh. Chloroform passed through the mesh, and water remained above the mesh.

the mesh and water being denser than diesel, water permeates through the mesh and gets collected in the beaker. On the other hand, diesel was blocked by the separation mesh due to its underwater superoleophobic behavior, as shown in Figure 5a (Supporting Information, Movie S3). The permeation of water was solely gravity driven. Water permeates quickly through the mesh, and no oil was visible in the filtrate. The separation mesh was also tested for other light oils having a density less than water (i.e., gasoline, hexane, olive oil, mustard oil, and turpentine oil) with the same process, and the mesh completely separates these oils from water. The water wetting properties of the same mesh have been changed to “oil-removing” mode by annealing it for 1.5 h under hydrogen gas environment at 300 °C, making it superhydrophobic/superoleophilic. Chloroform and 1,2-dichloroethane were used as model oils for demonstration of “oil-removing” behavior of the mesh. The mixture of chloroform and water in volumetric ratio 1:2 was processed in the same way as in the case of hydrophilic mesh. In this case, because the superhydrophobic nature of the mesh and chloroform are denser than water, chloroform quickly permeates through the mesh, as shown in Figure 5b (Supporting Information, Movie S4). The superhydrophilicity was reverted back by annealing the mesh under oxygen ambient for 1 h. To check the recovery of superhydrophilicity, a mixture of diesel and water was poured once again onto the mesh to ensure reversible oil−water separation. The reversibility of the separation mesh between superhydrophobic and superhydrophilic states was investigated by CA measurements as well as by separation of oil−water mixture. The separation mesh was found to be switchable reversibly for more than 10 cycles, as shown by the CA graph in Figure 6a. We have also measured the separation efficiency of our device by using an oil-content analyzer. The separation efficiency of the device was calculated by using the formula given below as21,43

Figure 4. Reversible wettability switching of water droplet on ZnONWs-coated mesh from (a) superhydrophilic state to (b) superhydrophobic state by using alternating hydrogen- and oxygen-gasannealing treatments.

We have also measured the CA of oils on hydrogen-annealed ZnO-NWs-coated mesh and found that regardless of the type of oil, it shows superoleophilic nature and that all the oil spreads quickly on the mesh with a CA value of 0°. It indicates that after hydrogen annealing treatment, the mesh shows superhydrophobic/superoleophilic nature. To filter heavy oils, the superhydrophobic/superoleophilic mesh is suitable, which works in “oil-removing” mode. We have used oxygen-gasannealing treatment to regain its superhydrophilic nature.46 It was found that oxygen-gas annealing for 1 h at 300 °C switched the wetting property of the mesh from superhydrophobic to superhydrophilic state. This process is reversible and alternate annealing in the presence of hydrogen and oxygen gases are sufficient to switch the wettability of ZnO-NWs-coated mesh from superhydrophilic to superhydrophobic state and vice versa. The reversible wettability switching of ZnO NWs was consistent with literature,46 where wetting−dewetting states of ZnO NWs were controlled by using hydrogen- and oxygen-gasannealing treatments. These results show the feasibility of ondemand oil−water separation by alternating hydrogen- and oxygen-annealing treatments. Following the investigation of reversible wettability that is described above, we studied the oil−water separation by incorporating the ZnO-nanowire coated mesh in a model device. For the oil−water separation in “water-removing” mode, superhydrophilic/underwater superoleophobic mesh was first fitted between two Teflon fixtures, each of which were fitted with hollow glass tubes, as shown in Figure 5. The mixture of diesel and water in volumetric ratio 1:2 was poured onto the ZnO-NWs-coated SS mesh. Due to the superhydrophilicity of

⎛ Cp ⎞ eff = ⎜1 − ⎟ × 100% Co ⎠ ⎝ 6010

(1) DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013

Research Article

ACS Applied Materials & Interfaces

presentation of filtration mechanism, the schematic was prepared with arranged direction of NWs, while the actual distribution of ZnO NWs is random on the mesh. The film of ZnO NWs coated on the mesh remains porous in random arrangement. Thus, the mechanism for formation of air cushion between NWs remains the same, and it prevents water penetration in the superhydrophobic mesh and repulsion of oils because of the polar nature of water-trapped superhydrophilic mesh. The separation mesh coated with ZnO NWs displays superhydrophilicity and θa < 90°, which implies Δp < 0; therefore, water can spontaneously permeate through the mesh. Because water permeates the ZnO-coated SS mesh, the water will be trapped between the ZnO NWs. The trapped water is polar and repels the nonpolar oils. This results in an enhanced oil-repellent force, leading to superoleophobicity with an oil CA value greater than 90°. Given this fact, mesh prewetted with water was used for separation of oils lighter than water. Because the water environment was formed on the surface of prewetted mesh, during filtration function, it repels oils completely and prevents them from penetrating through the mesh. Therefore, the permeation of oil through the mesh gets blocked when θa > 90°and Δp > 0. When the mesh was switched from the superhydrophilic/underwater superoleophobic state to superhydrophobic/superoleophilic state then for water, θa becomes greater than 90°. So, Δp must be greater than zero, and water will be blocked above the separation mesh as mesh will be able to withstand the pressure. In contrast, because the superoleophilic behavior of separation mesh θa for oils will be less than 90°, Δp < 0 and oil will easily pass through the separation mesh as mesh cannot support pressure exerted by the oil. Thus, the mesh shows excellent reversibility between superhydrophilic and superhydrophobic states optimum for on-demand oil−water separation.

Figure 6. (a) Water CA variation with the cyclic use of ZnO-coated mesh for light and heavy oils separation with alternating hydrogen and oxygen annealing treatment and (b) separation efficiency of filtration device after each cycle.

where Co and Cp are concentration of oil in the original oil− water mixture and filtered water, respectively. The separation efficiency for different oils was found to be more than 99.9% for mustard oil, diesel, gasoline, olive oil, and turpentine oil, which is adequate as demanded for a separation device. The separation efficiency was found to stay relatively invariant even after 10 cycles of usage, as shown in Figure 6b, indicating a prolonged antifouling property and excellent recyclability of the separation device. To clearly understand the reversible wettability of the separation mesh, we have used the concept of the intrusion pressure to model the wettability of oil and water. The intrusion pressure Δp can be expressed as47,48 Δp =

lγ(cos θa) 2γ =− R A

(2)

l is perimeter of pore, A is area of pore, R is meniscus’s radius, γ is the surface tension, θa is advancing contact angle. In general, intrusion pressure is the pressure which must be overcome before pore bottom wets by the liquid. It is clear from eq 2 that if advancing angle of any liquid θa is less than 90° then Δp must be less than zero. It means the liquid can spontaneously permeate through the coated mesh because in such cases the coated mesh will not be able to support any pressure. On the other hand, if advancing angle θa is greater than 90°, then Δp must be greater than zero. In this case, to some extent, the ZnO-coated mesh can withstand the pressure. A schematic diagram is shown in Figure 7 to understand the wetting mechanism of the mesh in different modes. To simplify the

■

CONCLUSIONS

In conclusion, an environment friendly ZnO-NWs-based reversible separation mesh has been fabricated simply by drop coating of ZnO NWs grown via chemical vapor deposition. ZnO NWs were coated on the SS mesh without adding any chemical or surface binder. We found that the coating does not wash off with water even after multiple usage. We have done CA as well as cyclic filtration measurement, and the filtration mesh retains its wettability even after 10 cycles, showing that the adhesion is sufficient for our application purpose. The separation mesh can be switched reversibly between “water-removing” and “oil-removing” mode by alternate annealing in oxygen and hydrogen environment. Thus, a single device can be utilized for the efficient separation of all type of oil/water mixtures according to the oil involved. The separation mesh was found to be highly efficient with a high purity of filtrate. This work provides a simple, efficient, and scalable approach for on-demand oil−water separation and opens up new perspectives in the field of oily wastewater treatment. Also, the substrate-less deposition and drop casting approaches used in the present work are advantageous for large-area fabrication of ZnO-coated mesh which can be utilized for a large-scale cleanup process. The annealing treatments are based on the requirement of mesh in “oil-removing” or “waterremoving” modes. The annealing treatments used in the present research work are simple and done in a nonvacuum assembly. The annealing time (90 min) and temperature (300 °C) are conventionally used by the researchers and suit to the

Figure 7. Schematic diagram of oil and water wetting modes. (a) Water can permeate through the as-synthesized mesh as well as oxygen annealed mesh because Δp < 0; (b) water cannot permeate through mesh after hydrogen annealing because Δp > 0; (c) oil cannot pass through the mesh as Δp > 0; and (d) oil will pass the mesh in air even after hydrogen annealing because Δp < 0. 6011

DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013

Research Article

ACS Applied Materials & Interfaces

bicity of the Aligned ZnO Nanorod Array-Coated Mesh Films. J. Mater. Chem. 2012, 22 (37), 19652−19657. (9) Li, H.; Li, Y.; Liu, Q. ZnO Nanorod Array-Coated Mesh Film for the Separation of Water and Oil. Nanoscale Res. Lett. 2013, 8 (1), 183. (10) Badre, C.; Dubot, P.; Lincot, D.; Pauporte, T.; Turmine, M. Effects of Nanorod Structure and Conformation of Fatty Acid SelfAssembled Layers on Superhydrophobicity of Zinc Oxide Surface. J. Colloid Interface Sci. 2007, 316 (2), 233−237. (11) Badre, C.; Pauporté, T.; Turmine, M.; Lincot, D. Tailoring the Wetting Behavior of Zinc Oxide Films by Using Alkylsilane SelfAssembled Monolayers. Superlattices Microstruct. 2007, 42 (1−6), 99− 102. (12) Crick, C. R.; Gibbins, J. A.; Parkin, I. P. Superhydrophobic Polymer-Coated Copper-Mesh; Membranes for Highly Efficient Oil− water Separation. J. Mater. Chem. A 2013, 1 (19), 5943−5948. (13) Wang, F.; Lei, S.; Xu, Y.; Ou, J. Green Approach to the Fabrication of Superhydrophobic Mesh Surface for Oil/Water Separation. ChemPhysChem 2015, 16 (10), 2237−2243. (14) Chen, Q.; de Leon, A.; Advincula, R. C. Inorganic−Organic Thiol−ene Coated Mesh for Oil/Water Separation. ACS Appl. Mater. Interfaces 2015, 7 (33), 18566−18573. (15) Zhang, M.; Wang, C.; Wang, S.; Shi, Y.; Li, J. Fabrication of Coral-like Superhydrophobic Coating on Filter Paper for Water−oil Separation. Appl. Surf. Sci. 2012, 261, 764−769. (16) Li, J.; Yan, L.; Li, H.; Li, J.; Zha, F.; Lei, Z. A Facile One-Step Spray-Coating Process for the Fabrication of a Superhydrophobic Attapulgite Coated Mesh for Use in Oil/water Separation. RSC Adv. 2015, 5 (66), 53802−53808. (17) Ong, W. L.; Yew, K. W.; Tan, C. F.; Adrian, T. K. T.; Hong, M.; Ho, G. W. Highly Flexible Solution Processable Heterostructured Zinc Oxide Nanowires Mesh for Environmental Clean-up Applications. RSC Adv. 2014, 4 (52), 27481−27487. (18) Li, J.; Kang, R.; Tang, X.; She, H.; Yang, Y.; Zha, F. Superhydrophobic Meshes That Can Repel Hot Water and Strong Corrosive Liquids Used for Efficient Gravity-Driven Oil/water Separation. Nanoscale 2016, 8 (14), 7638−7645. (19) Li, H.; Zheng, M.; Ma, L.; Zhu, C.; Lu, S. Two-Dimensional ZnO Nanoflakes Coated Mesh for the Separation of Water and Oil. Mater. Res. Bull. 2013, 48 (1), 25−29. (20) Li, J.; Yan, L.; Tang, X.; Feng, H.; Hu, D.; Zha, F. Robust Superhydrophobic Fabric Bag Filled with Polyurethane Sponges Used for Vacuum-Assisted Continuous and Ultrafast Absorption and Collection of Oils from Water. Adv. Mater. Interfaces 2016, 3 (9), 1500770. (21) Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L. A Novel Superhydrophilic and Underwater Superoleophobic Hydrogel-Coated Mesh for Oil/Water Separation. Adv. Mater. 2011, 23 (37), 4270−4273. (22) Li, J.; Cheng, H. M.; Chan, C. Y.; Ng, P. F.; Chen, L.; Fei, B.; Xin, J. H. Superhydrophilic and Underwater Superoleophobic Mesh Coating for Efficient Oil−water Separation. RSC Adv. 2015, 5 (64), 51537−51541. (23) Liu, J.; Li, P.; Chen, L.; Feng, Y.; He, W.; Yan, X.; Lü, X. Superhydrophilic and Underwater Superoleophobic Modified Chitosan-Coated Mesh for Oil/water Separation. Surf. Coat. Technol. 2016, 307 (Part A), 171−176. (24) Luo, Z.-Y.; Chen, K.-X.; Wang, Y.-Q.; Wang, J.-H.; Mo, D.-C.; Lyu, S.-S. Superhydrophilic Nickel Nanoparticles with Core−Shell Structure To Decorate Copper Mesh for Efficient Oil/Water Separation. J. Phys. Chem. C 2016, 120 (23), 12685−12692. (25) Cao, Y.; Liu, N.; Zhang, W.; Feng, L.; Wei, Y. One-Step Coating toward Multifunctional Applications: Oil/Water Mixtures and Emulsions Separation and Contaminants Adsorption. ACS Appl. Mater. Interfaces 2016, 8 (5), 3333−3339. (26) Li, J.; Yan, L.; Li, H.; Li, W.; Zha, F.; Lei, Z. Underwater Superoleophobic Palygorskite Coated Meshes for Efficient Oil/water Separation. J. Mater. Chem. A 2015, 3 (28), 14696−14702. (27) Wang, B.; Guo, Z. pH-Responsive Bidirectional Oil−water Separation Material. Chem. Commun. 2013, 49 (82), 9416−9418.

industrial scale. Thus, this approach is fast, simple, costeffective, and scalable, and it can be realized practically.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b14448. Full descriptions of the movie files (PDF) Movie S1: Underwater rolling of chloroform on assynthesized ZnO-coated SS mesh (AVI) Movie S2: Rolling of water droplet on hydrogen annealed ZnO-coated mesh (AVI) Movie S3: Diesel/water mixture separation by using superhydrophilic/underwater superoleophobic mesh (AVI) Movie S4: Chloroform/water mixture separation by using superhydrophobic/superoleophilic mesh (AVI)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The author (PR) is thankful to Department of Science and Technology (DST), India for providing Junior Research fellowship. This research is supported by Department of Science and Technology, India (grant number EMR/2015/ 001477) and Nanoscale Research Facility, IIT Delhi, India. We sincerely acknowledge Prof. KV Lakshmi from Rensselaer Polytechnic Institute, NY, U.S.A. for proof reading of the manuscript

■

REFERENCES

(1) Li, H.; Boufadel, M. C. Long-Term Persistence of Oil from the Exxon Valdez Spill in Two-Layer Beaches. Nat. Geosci. 2010, 3 (2), 96−99. (2) Li, L.; Ding, L.; Tu, Z.; Wan, Y.; Clausse, D.; Lanoisellé, J.-L. Recovery of Linseed Oil Dispersed within an Oil-in-Water Emulsion Using Hydrophilic Membrane by Rotating Disk Filtration System. J. Membr. Sci. 2009, 342 (1), 70−79. (3) Zhu, Y.; Zhang, F.; Wang, D.; Pei, X. F.; Zhang, W.; Jin, J. A Novel Zwitterionic Polyelectrolyte Grafted PVDF Membrane for Thoroughly Separating Oil from Water with Ultrahigh Efficiency. J. Mater. Chem. A 2013, 1 (18), 5758−5765. (4) Liu, C.; Yang, J.; Tang, Y.; Yin, L.; Tang, H.; Li, C. Versatile Fabrication of the Magnetic Polymer-Based Graphene Foam and Applications for Oil−water Separation. Colloids Surf., A 2015, 468, 10−16. (5) Kota, A. K.; Kwon, G.; Choi, W.; Mabry, J. M.; Tuteja, A. HygroResponsive Membranes for Effective Oil−water Separation. Nat. Commun. 2012, 3, 1025. (6) Li, B.; Liu, X.; Zhang, X.; Chai, W.; Ma, Y.; Tao, J. Facile Preparation of Graphene-Coated Polyurethane Sponge with Superhydrophobic/superoleophilic Properties. J. Polym. Res. 2015, 22 (10), 190. (7) Liu, N.; Lin, X.; Zhang, W.; Cao, Y.; Chen, Y.; Feng, L.; Wei, Y. A Pure Inorganic ZnO-Co3O4 Overlapped Membrane for Efficient Oil/ Water Emulsions Separation. Sci. Rep. 2015, 5, 9688. (8) 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 Superoleopho6012

DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013

Research Article

ACS Applied Materials & Interfaces (28) Wang, B.; Guo, Z.; Liu, W. pH-Responsive Smart Fabrics with Controllable Wettability in Different Surroundings. RSC Adv. 2014, 4 (28), 14684−14690. (29) Cheng, Z.; Lai, H.; Du, Y.; Fu, K.; Hou, R.; Li, C.; Zhang, N.; Sun, K. pH-Induced Reversible Wetting Transition between the Underwater Superoleophilicity and Superoleophobicity. ACS Appl. Mater. Interfaces 2014, 6 (1), 636−641. (30) Cheng, Z.; Du, M.; Fu, K.; Zhang, N.; Sun, K. pH-Controllable Water Permeation through a Nanostructured Copper Mesh Film. ACS Appl. Mater. Interfaces 2012, 4 (11), 5826−5832. (31) Li, J.-J.; Zhou, Y.-N.; Luo, Z.-H. Smart Fiber Membrane for pHInduced Oil/Water Separation. ACS Appl. Mater. Interfaces 2015, 7 (35), 19643−19650. (32) Cheng, Z.; Wang, J.; Lai, H.; Du, Y.; Hou, R.; Li, C.; Zhang, N.; Sun, K. pH-Controllable on-Demand Oil/Water Separation on the Switchable Superhydrophobic/Superhydrophilic and Underwater Low-Adhesive Superoleophobic Copper Mesh Film. Langmuir 2015, 31 (4), 1393−1399. (33) Zhang, L.; Zhang, Z.; Wang, P. Smart Surfaces with Switchable Superoleophilicity and Superoleophobicity in Aqueous Media: Toward Controllable Oil/water Separation. NPG Asia Mater. 2012, 4 (2), e8. (34) Wang, Y.; Lai, C.; Hu, H.; Liu, Y.; Fei, B.; Xin, J. H. Temperature-Responsive Nanofibers for Controllable Oil/water Separation. RSC Adv. 2015, 5 (63), 51078−51085. (35) Zheng, X.; Guo, Z.; Tian, D.; Zhang, X.; Jiang, L. Electric Field Induced Switchable Wettability to Water on the Polyaniline Membrane and Oil/Water Separation. Adv. Mater. Interfaces 2016, 3 (18), 1600461. (36) Liu, N.; Cao, Y.; Lin, X.; Chen, Y.; Feng, L.; Wei, Y. A Facile Solvent-Manipulated Mesh for Reversible Oil/Water Separation. ACS Appl. Mater. Interfaces 2014, 6 (15), 12821−12826. (37) Xu, Z.; Zhao, Y.; Wang, H.; Wang, X.; Lin, T. A Superamphiphobic Coating with an Ammonia-Triggered Transition to Superhydrophilic and Superoleophobic for Oil−Water Separation. Angew. Chem. 2015, 127 (15), 4610−4613. (38) Tian, D.; Guo, Z.; Wang, Y.; Li, W.; Zhang, X.; Zhai, J.; Jiang, L. Phototunable Underwater Oil Adhesion of Micro/Nanoscale Hierarchical-Structured ZnO Mesh Films with Switchable Contact Mode. Adv. Funct. Mater. 2014, 24 (4), 536−542. (39) Tian, D.; Zhang, X.; Zhai, J.; Jiang, L. Photocontrollable Water Permeation on the Micro/nanoscale Hierarchical Structured ZnO Mesh Films. Langmuir 2011, 27 (7), 4265−4270. (40) Du, X.; Huang, X.; Li, X.; Meng, X.; Yao, L.; He, J.; Huang, H.; Zhang, X. Wettability Behavior of Special Microscale ZnO Nail-Coated Mesh Films for Oil−water Separation. J. Colloid Interface Sci. 2015, 458, 79−86. (41) Li, J.; Li, D.; Yang, Y.; Li, J.; Zha, F.; Lei, Z. A Prewetting Induced Underwater Superoleophobic or Underoil (Super) Hydrophobic Waste Potato Residue-Coated Mesh for Selective Efficient Oil/ water Separation. Green Chem. 2016, 18 (2), 541−549. (42) Tian, D.; Zhang, X.; Wang, X.; Zhai, J.; Jiang, L. Micro/ nanoscale Hierarchical Structured ZnO Mesh Film for Separation of Water and Oil. Phys. Chem. Chem. Phys. 2011, 13 (32), 14606−14610. (43) Gondal, M. A.; Sadullah, M. S.; Dastageer, M. A.; McKinley, G. H.; Panchanathan, D.; Varanasi, K. K. Study of Factors Governing OilWater Separation Process Using TiO2 Films Prepared by Spray Deposition of Nanoparticle Dispersions. ACS Appl. Mater. Interfaces 2014, 6 (16), 13422−13429. (44) Zhang, L.; Zhong, Y.; Cha, D.; Wang, P. A Self-Cleaning Underwater Superoleophobic Mesh for Oil-Water Separation. Sci. Rep. 2013, 3, 2326. (45) Yadav, K.; Mehta, B. R.; Lakshmi, K. V.; Bhattacharya, S.; Singh, J. P. Tuning the Wettability of Indium Oxide Nanowires from Superhydrophobic to Superhydrophilic: The Effect of Oxygen Related Defects. J. Phys. Chem. C 2015, 119 (28), 16026−16032. (46) Yadav, K.; Mehta, B. R.; Bhattacharya, S.; Singh, J. P. A Fast and Effective Approach for Reversible Wetting-Dewetting Transitions on ZnO Nanowires. Sci. Rep. 2016, 6, 35073.

(47) Youngblood, J. P.; McCarthy, T. J. Ultrahydrophobic Polymer Surfaces Prepared by Simultaneous Ablation of Polypropylene and Sputtering of Poly(tetrafluoroethylene) Using Radio Frequency Plasma. Macromolecules 1999, 32 (20), 6800−6806. (48) Liu, B.; Lange, F. F. Pressure Induced Transition between Superhydrophobic States: Configuration Diagrams and Effect of Surface Feature Size. J. Colloid Interface Sci. 2006, 298 (2), 899−909.

6013

DOI: 10.1021/acsami.6b14448 ACS Appl. Mater. Interfaces 2017, 9, 6007−6013