Durable and Stable MnMoO4-Coated Copper Mesh for Highly Efficient

Jun 11, 2019 - (2−4) As an alternate option, membrane separation has been demonstrated to be an effective means to purify oily wastewater, especiall...
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Research Article Cite This: ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

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Durable and Stable MnMoO4‑Coated Copper Mesh for Highly Efficient Oil-in-Water Emulsion Separation and Photodegradation of Organic Contaminants Xinyu Chen, Dongyun Chen,* Najun Li, Qingfeng Xu, Hua Li, Jinghui He, and Jianmei Lu* College of Chemistry, Chemical Engineering, Materials Science, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, China Downloaded via NOTTINGHAM TRENT UNIV on July 18, 2019 at 07:21:29 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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ABSTRACT: Wastewater pollution has always been a major environmental problem worldwide. Furthermore, in light of the frequent oil spills that have occurred in recent years, the treatment of oily wastewater is particularly important. Herein, a MnMoO4-coated copper mesh was synthesized via a facile two-step hydrothermal route for application in the separation of oil-in-water emulsions. The mesh showed exceptional wettability and separation efficiency (more than 99.9% for toluene-in-water emulsions). In addition, the mesh possessed excellent photocatalytic activity toward the photodegradation of organic dyes in emulsions. The findings also demonstrated the durability and stability of the mesh, as evidenced by the sustained high separation efficiency that they displayed after abrasion or corrosion. Taken together, the findings indicate that the mesh prepared herein has great potential for application in oily wastewater treatment. KEYWORDS: manganese molybdate, superwettability, emulsion separation, photodegradation, hydrothermal route

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INTRODUCTION In the current highly industrialized society that we live in, wastewater treatment is increasingly becoming an essential technology to rely on to solve environmental problems surrounding the pollution of the ecological environment. In the past four decades, a total of 5.73 millions tons of oil has accidentally leaked, which has a continuous negative impact on the global ecological environment.1 Thus, necessary measures are required to address these pollution challenges. Conventional industrial oil−water separation technology presents shortcomings such as low separation efficiency, high cost, and secondary pollution.2−4 As an alternate option, membrane separation has been demonstrated to be an effective means to purify oily wastewater, especially the separation of oil−water emulsions.5 This technology relies on the surface wettability of the membrane, which can be divided into superhydrophilicity and superhydrophobicity. In addition, many studies have focused on underwater superoleophobic membranes and meshes with demulsification ability for effective oil-in-water emulsion separation.6,7 The design and preparation of such materials require consideration of their wettability and demulsification ability to ensure that only water passes through. For example, a tungsten oxide-coated mesh, prepared by Feng and co-workers,8 and a cobalt oxide-coated mesh, prepared by Xu and co-workers,9 have shown exceptional wettability performance and have successfully achieved efficient oil−water emulsion separation. Herein, we thus focus on the engineering of inorganic materials because of © 2019 American Chemical Society

their excellent wettability, ease of preparation, and great emulsion separation capacity, as reported in the literature.10−18 However, many inorganic materials developed to date are limited by their single function, thus restricting their application scope in multicomponent emulsions such as emulsions containing organic contaminants. Conversely, multifunctional materials, specifically membranes, are expected to have a broader application scope in complex emulsions. A common class of contaminants in industrial oily wastewater are organic dyes. These pollutants can be degraded by various methods, and photocatalysis is the most commonly used method.19 Many metal compounds are known to exhibit excellent photocatalytic properties and good stability, which are highly sought after in many fields.20−23 It is thus feasible to introduce photodegradation function into inorganic membranes, as relevant to more practical oily wastewater treatment. Presently, only few metal compounds such as TiO2,24 BiVO4,25 CuWO4,26 and Fe3O427 have been successfully fabricated into membranes for oil−water mixture separation and pollutant photodegradation. Widening the choice of inorganic membranes would help extend the application of such materials to the separation and photodegradation of oil−water emulsions, rather than simply oil−water mixtures. Received: April 23, 2019 Accepted: June 11, 2019 Published: June 11, 2019 23789

DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

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ACS Applied Materials & Interfaces Scheme 1. Fabrication of MMO@CM Mesh and Mechanisms of Emulsion Separation and Photodegradation

the same ratio of 1:100 (v/v), and the oils were toluene, hexane, and xylene, respectively. The emulsifier was SDS and the added amount was 0.5 g L−1. Stirring was continued for 2 h to obtain uniform and stable milky white emulsions. Oil-in-water emulsions with organic dyes were prepared by adding MB and MO in the above emulsions. The concentration of the dyes in the prepared emulsions is 5 ppm. These emulsions were used for photodegradation tests. Oil-in-Water Emulsion Separation and Photodegradation Experiments. The mesh was firmly fixed in a glass vacuum filter by a clamp. Then, the newly prepared emulsion was poured into the glass funnel gradually, and the filtration time was also recorded. The entire filtration process was merely driven by gravity. After the filtration was completed, the filtrate water was collected to detect its oil content. The separation efficiency (R) was measured by the formula

In the present study, a manganese molybdate (MnMoO4)coated copper mesh (MMO@CM) was prepared by a simple two-step hydrothermal method. MMO@CM efficiently separated emulsions under gravity and photodegraded organic contaminants under UV light. The emulsion-separation performance displayed by MMO@CM was attributed to its superamphiphilicity and underwater superoleophobicity. Moreover, the mesh maintained high separation efficiency and flux after abrasion. The photocatalytic properties of this compound have been reported in previous studies; however, its emulsion-separation capacity has not been reported until now. Scheme 1 illustrates the fabrication of MMO@CM. Copper mesh is used as a substrate onto which compounds can grow densely, as it is inexpensive, durable, and commonly used in the field of oil−water separation.28,29

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ij C yz R = jjj1 − f zzz × 100% j Co z{ k

EXPERIMENTAL SECTION

(1)

where Cf and Co are the oil contents in the filtrate and the previous oil-in-water emulsions, respectively. The oil contents can be measured by a UV−vis spectrometer. The flux (F, L m−2 h−1) was calculated from the following equation

Materials. Manganese(II) chloride tetrahydrate (MnCl2·4H2O) and sodium molybdate (Na2MoO4) were purchased from Macklin. Sodium carbonate (Na2CO3), sodium citrate (Na3C6H5O7), ethanol, toluene, xylene, hexane, cyclohexane, chloroform, chlorobenzene, methylene blue (MB), methyl orange (MO), and sodium dodecyl sulfate (SDS) were bought from Sinopharm Chemical Reagent Co., Ltd. Commercial copper mesh (200, 300, and 400 mesh) was bought from Shanghai Yuren Co., Ltd. Fabrication of MMO@CM. The product was fabricated by a facile two-step hydrothermal route based on previous articles.30−33 First, a copper mesh (400 mesh, 8 × 8 cm2) was ultrasonically cleaned for 15 min in acetone, ethanol, and deionized water. The MnCO3-coated mesh was synthesized by a hydrothermal route: 0.0125 mol of MnCl2· 4H2O and 0.0125 mol of sodium citrate were dissolved in 100 mL of deionized water, and the solution was stirred for 30 min. Then, sodium carbonate solution (25 mL, 0.5 M) was added dropwise and the mixture stirred for 30 min. Next, the precursor solution and the precleaned copper mesh were together transferred into a Teflon-lined stainless autoclave, and the autoclave was heated in an oven at 160 °C for 12 h. After the reaction, the copper mesh was washed with ethanol and deionized water and then dried in an oven at 50 °C for 4 h. Finally, MMO@CM was prepared also via a facile hydrothermal method as follows: 0.0125 mol of Na2MnO4 was dissolved in 120 mL of deionized water, and the transparent solution was stirred for 15 min. Subsequently, the solution and the as-prepared MnCO3-coated copper mesh were transferred into the autoclave and heated at 140 °C for 12 h. Lastly, the sample was washed with ethanol and deionized water and dried to obtain the final product. Preparation of Oil-in-Water Emulsions Containing Organic Dye. Three different types of oil-in-water emulsions were prepared in

F=

V A×t

(2)

where V (L) is the filtrate volume, A (m ) is the permeation area, and t (h) is the total filtration time. In the purification experiment, the water containing organic contaminants was used for the photodegradation catalyzed by the mesh under UV irradiation from a mercury lamp (250 W). The MnMoO4-coated meshes (4 × 4 cm2) were immersed in 100 mL of 5 ppm MB and MO aqueous solutions. These solutions were stirred in the dark for half an hour to reach an adsorption equilibrium and then placed under illumination. Another MB solution without MnMoO4coated mesh was used as a blank control. The degradation efficiency (1 − C/C0) is calculated based on the contaminant concentration. C is the concentration after degradation at different times and C0 is the original concentration, both of which were measured by a UV−vis spectrometer. Characterization. To study how the coating influences the material wettability, the surface morphology of MMO@CM was obtained from scanning electron microscopy (SEM, Hitachi S-4700, Japan). The elemental analysis was acquired from X-ray energydispersive spectroscopy (EDS). Chemical state and surface composition of the material were examined by X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi), and the crystal phase information was examined by X-ray diffraction (XRD, D8 QUEST, Germany). Water-and-oil contact angles were measured by an optical 2

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DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

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ACS Applied Materials & Interfaces contact angle goniometer (OCA 15EC, Germany). The size and diameter distributions of the oil droplet in oil-in-water emulsions were provided by an optical microscope (BM4700) and dynamic light scattering measurements (DLS, ZEN3690, Germany).

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RESULTS AND DISCUSSION Surface Morphology and Chemical Composition of MMO@CM. Figure 1a shows SEM image of pristine copper

Figure 4. (a) SEM image of MMO@CM and (b−f) element mapping images of MMO@CM in the same zone.

Figure 5. (a) Water contact angle in air. (b) Toluene contact angle in air. (c) Water contact angles under light oils (hexane, cyclohexane, toluene, and xylene) and heavy oil (chloroform and chlorobenzene) contact angles under water.

Figure 1. SEM images of the (a) copper mesh and (b−d) MMO@ CM at different magnifications.

Figure 2. XRD patterns of MMO@CM (black) and MnMoO4·4H2O (red).

Figure 6. (a) Photographs of the toluene-in-water emulsion filtration device. (b) and (c) Magnified images of emulsion and filtrate. (d) Optical microscopy images of the emulsion before and after filtration, and the corresponding photographs of the feed solution and filtrate. (e) Droplet size distribution profile of a toluene-in-water emulsion before and after filtration. (f) UV−vis spectra of a toluene-in-water emulsion before and after separation.

Figure 3. (a) XPS survey spectrum of MMO@CM, and (b) O 1s, (c) Mn 2p, and (d) Mo 3d core-level spectra.

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DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

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Figure 7. (a) Flux and separation efficiency profiles of different oil-in-water emulsions. (b) Flux and separation efficiency of a toluene-in-water emulsion as a function of cycle number.

Scheme 2. Mechanisms of Demulsification Process and Oil-in-Water Emulsion Separation

uniformly decorated with manganese molybdate, as evidenced by the reduced pore size and increased surface roughness of the mesh when compared with those of the copper mesh. In addition, the higher-resolution SEM images of MMO@CM (Figure 1c,d) showed that manganese molybdate grew into a hierarchical flowerlike structure of ∼1 μm diameter. The surface morphology features displayed by MMO@CM are expected to influence the wettability and demulsification performance of the mesh; rough surfaces can improve the hydrophilicity of materials and smaller pores can assist in preventing oil droplets in emulsions from penetrating the mesh. In contrast, smoother surfaces and larger pores are less favorable features for emulsion separation. The crystallography features of MMO@CM were analyzed by XRD (Figure 2). The characteristic peaks matched those of MnMoO4·4H2O (JCPDS no. 78-0220). The elemental composition and chemical state of the as-prepared MMO@ CM sample were analyzed by XPS. Figure 3a shows the presence of Mn, Mo, C, and O in the survey spectrum of MMO@CM. Figure 3b displays the O 1s core-level spectrum, containing three peaks at binding energies of 529.3, 530.5, and 532.1 eV, which correspond to absorbed H2O, Mo−O binding, and carbonate ions, respectively. The presence of carbonate (in small amounts) is attributed to the incomplete reaction of manganese carbonate during the hydrothermal treatment. However, its presence is unlikely to affect the related properties of the material. The Mn 2p core-level spectrum (Figure 3c) shows four peaks, 640.2 and 642.1, and 651.5 and 653.8 eV, which were assigned to Mn 2p3/2 and Mn 2p1/2 levels,

Figure 8. Photocatalytic activity of MMO@CM toward the degradation of organic contaminants (MB and MO) under UV light irradiation.

Figure 9. (a) Illustration of the abrasion process. (b) Photographs of the mesh before (left) and after (right) abrasion.

mesh. Figure 1b shows representative SEM image of MMO@ CM, which confirmed that the copper mesh was entirely and 23792

DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

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Figure 10. (a) Separation efficiency and (b) flux profiles of the mesh before and after abrasion obtained for the separation of toluene- and hexanein-water emulsions. (c) Separation efficiency and (d) flux profiles of the mesh after abrasion when subjected to repeated toluene-in-water emulsion separation tests.

filtration using MMO@CM. Because of the excellent wettability and demulsification ability of MMO@CM, the emulsion was successfully separated, driven by gravity, and water was collected in the flask. Figure 6d shows images of the emulsion, captured on an optical microscopy, before and after separation; in addition, the photographs of the emulsion before (feed solution) and after (filtrate) separation are shown. As observed from these images, the toluene-in-water emulsion comprised numerous small emulsified toluene droplets, which were not observed after separation, thereby confirming that separation was successfully achieved. At the same time, it can be seen from the control experiment that the pristine copper mesh had almost no demulsification effect, so the separation effect can be attributed to the MnMoO4 coating (Figure S3). The oil droplet size analyses and UV−vis spectra of a toluenein-water emulsion before and after separation further confirmed that the oil droplets in the emulsion were successfully removed (Figure 6e,f). Besides, two toluene-inwater emulsions with higher concentrations (5, 10%) were tested to prove the separation performance of MMO@CM (Figure S4). The results show that the separation efficiency can reach 99.1% at least, indicating that the mesh has the ability to treat high-concentration emulsions. Figure S5 shows the droplet size distribution of these emulsions before and after filtration. To further explore the separation performance of MMO@ CM, separation tests of several oil-in-water emulsions (that is, toluene-, hexane-, and xylene-in-water emulsions) and cycle separation tests were conducted. The separation efficiencies and fluxes of the three emulsions were comparable. Specifically, the separation efficiency varied between 99.5 and 99.9%, and the flux ranged from 175.8 to 182.7 L m−2 h−1 (Figure 7a). For the cycle test, toluene-in-water emulsion was used as a representative oil-in-water emulsion. Figure 7b shows the flux and separation efficiency over 10 successive separation tests. As observed, the exceptional separation efficiency (>99%) and high flux (≥170 L m−2 h−1) of MMO@CM were maintained throughout the cycle test, confirming the stability of the mesh.

respectively. The two binding energy peaks of the Mo 3d corelevel spectrum were observed at 231.8 and 234.9 eV, corresponding to Mo 3d5/2 and Mo 3d3/2, respectively. EDS was used to determine the elemental distribution of MMO@CM. As observed in Figure 4, Mn, Mo, and O were evenly distributed throughout the mesh, supporting the uniform crystal growth. In addition, the EDS results (Figure S1) confirmed the elemental composition of MMO@CM. Wettability of MMO@CM. The surface wettability of solid materials primarily relies on their surface structure and chemical composition. The wetting behavior of the as-prepared MMO@CM can be ascribed to its hierarchical nanostructure and high surface energy, which can synergistically influence its hydrophilicity. Compared with the original copper mesh, MMO@CM exhibited better wettability. Figure 5 shows the wetting performance of MMO@CM under different conditions including water in air (Figure 5a), toluene in air (Figure 5b), water under light oils, and heavy oils under water (Figure 5c). When water or toluene contacted the mesh, the droplets penetrated the membrane very quickly and spread within 0.5 s, indicating that the mesh is superamphiphilic in air. Furthermore, the mesh is superoleophobic under water and superhydrophobic under oil. It was observed that the water droplet adopted a quasi-spherical shape under different light oils, with the corresponding contact angles of 151.4° (hexane), 153.6° (cyclohexane), 156.6° (toluene), and 154.7° (xylene). Likewise, chloroform and chlorobenzene droplets adopted a quasi-spherical shape with larger contact angles of 157.6 and 155.3° under water, respectively. The enhanced wettability also influenced the water-retention capacity of the mesh. The water-retention capacity improved from 26.35% (pristine copper mesh) to 43.84% (MMO@CM) (Figure S2). This increase is attributed to the high hydrophilicity of the mesh, which can promote the adsorption of water onto the mesh. Emulsion Separation and Associated Mechanism. To investigate the emulsion-separation performance of MMO@ CM, a series of separation experiments were conducted. Figure 6a shows the progress of the toluene-in-water emulsion 23793

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46 55% (MO, 5 ppm) NA 99.72 Tween60 (0.2 wt %) O/W 1:30 (v/v)

rGO, reduced graphene oxide; PDA/PEI, polydopamine/polyethylenimine; SDS, sodium dodecyl sulfate; SDBS, sodium dodecylbenzenesulfonate; GTP, gelatin/TiO2/polyethylenimine; O/W, oil-inwater emulsion.

O/W 1:100 (v/v) O/W 1:100 (v/v) O/W 250 mg L−1 O/W 1:100 (v/v) O/W 3:7 (v/v) O/W 1:100 (v/v) just oil/water mixture 3:5 (v/v) just oil/water mixture 3:7 (v/v) just oil/water mixture 3:7 (v/v)

MMO@CM kaolin-based ceramic membrane carbon membrane rGO/g-C3N4 membrane hydrogel-coated membrane PDA/PEI-modified membrane BiVO4 coated mesh CuWO4/Cu2O coated mesh TiO2 nanotubes based porous membrane GTP aerogel

Taken together, these results demonstrate the potential of MMO@CM for practical usage in oily wastewater treatment. The mesh number can also influence the separation efficiency of a material. Thus, the separation performance of different MMO@CMs prepared using copper meshes of varying mesh numbers was examined. As observed from the results in Figure S6, the higher the mesh number, the higher the separation efficiency of MMO@CM, as the higher mesh facilitates the formation of smaller pores in the final product. Effective emulsion separation is dependent on demulsification and filtration. The general steps involved in oil-in-water emulsion separation are (1) the emulsified oil droplets first contact with the membrane, (2) emulsion breakage occurs, and (3) the oil droplets aggregate. When they contact the mesh surface, the emulsion droplets break instantly under the effect of demulsification caused by the superhydrophilicity, and the water will immediately fill the pores of the mesh under the capillary effect.34,35 Concurrently, provided the membrane is superoleophobic under water, penetration of the oil through the membrane is inhibited, while water passes through the membrane, thereby achieving separation of the oil-in-water emulsion. Scheme 2 illustrates the mechanism of oil-in-water emulsion separation on MMO@CM. Water first permeates the mesh completely to form a continuous water film owing to the very small pores of the mesh. In accordance with Young−Dupré equation,36−38 the oil contact angle under water can be calculated as follows cos θOW =

γOA cos θO − γWA cos θ W γOW

(3)

where θOW is the oil contact angle under water; θO and θW are the contact angles of oil and water in air, respectively; γOA and γWA are the oil and water interfacial tensions in air; and γOW is the oil interfacial tension under water. For a superamphiphilic surface, the contact angles of water and oil are both 0°, thus eq 3 can be simplified to eq 4, as follows γ − γWA cos θOW = OA γOW (4) ΔPOW = −

2γOW cos θO d

(5)

If γOA is smaller than γWA, the surface exhibits oleophobic property under water. Moreover, according to Laplace equation39 (eq 5), the oil will be subjected to an upward pressure ΔPOW on a superoleophobic surface under water because cos θO is smaller than 0. As a result, the underwater superoleophobic surface can prevent oil from penetrating the mesh. Photodegradation of Organic Dyes. The UV light absorption capacity of MMO@CM was examined by UV− visible diffuse reflectance spectroscopy. As noted in Figure S7, MMO@CM displayed a strong absorption in the UV light region. Accordingly, MMO@CM can generate photoelectrons (e−) and holes (h+) under UV light irradiation, which can convert oxygen and water into ·O2− and ·OH, respectively. The latter two species are highly reactive and can decompose organic contaminants. Two organic dyes, methylene blue (MB) and methyl orange (MO), were used to investigate the photocatalytic ability of MMO@CM. As observed in Figure 8, both MB and MO present in two emulsions degraded over

a

our work 40 41 42 43 44 25 26 45 95% (MB, 5 ppm) 80% (MO, 5 ppm) NA NA NA NA NA 85% (MB, 0.01 mM) 76% (MO, 0.01 mM) 23.9% (MB, 0.1 mM) 90.2% (MB, 0.1 mM, added with Na2S2O8) 25−84.5% (MB, 20 mM) 179.2 79.7 64.3 20−30 56 147.7 NA NA 1357 >99.5 98.5 97.8 99.5 >99 98.0 >97 >95 >97.2 SDS (0.5 g L ) Tween20 (0.05 wt %) SDS SDS (0.2 mg L−1) SDBS (0.1% w/v) Tween80 (0.02 wt %) NA NA NA

photocatalytic efficiency

−1

emulsifier emulsion membrane

Table 1. Comparison of Materials Used in Emulsion Separationa

separation efficiency (%)

flux (L m−2 h−1)

references

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and other corrosive components in emulsions. In addition, MMO@CM can achieve high separation efficiency even after mechanical abrasion. These features are attractive for real practical application of MMO@CM. Table 1 presents a comparison of a few materials that have been examined in the literature for emulsion separation. As observed, relative to these literature materials, MMO@CM shows outstanding separation performance.

time when the dye-containing emulsions were irradiated under UV light. After 120 min of irradiation, ∼5% of MB and ∼20% of MO remained. These results demonstrate that MMO@CM can also be applied in the photodegradation of organic contaminants in wastewater. The kinetics of the photodegradation of the organic dyes photocatalysis were additionally examined to further understand the photodegradation process. Figure S8 shows that the photodegradation of MB corresponds to the first-order reaction kinetics, whereas that of MO corresponds to the second-order reaction kinetics. The entire reaction follows the process of adsorption−degradation. Durability and Stability of MMO@CM. In real applications, durability and stability are key factors that determine the practical application prospect of a material. To determine the durability and stability of MMO@CM, its abrasion resistance was examined. The mesh was placed on a sandpaper and loaded with a weight of 200 g. The mesh was then pulled forward to a distance of 10 cm (Figure 9). Following abrasion, the water contact angles under oil and oil contact angles under water were measured. Figure S9 compares the contact angles of the mesh before and after abrasion. The contact angles only changed slightly after abrasion, and the mesh retained its superoleophobicity underwater. Following abrasion, the performance of the resulting mesh in separating toluene-in-water and hexane-in-water emulsions was examined. Figure S10a,b shows the images of the mesh before and after abrasion, respectively. As observed in Figure 10a,b, the mesh after abrasion maintained high separation efficiencies of >99.5% and fluxes of 170 L m−2 h−1 when compared with the those achieved by the mesh before abrasion, and the optical micrographs of the emulsion and the filtration are displayed in Figure S10c, showing the high separation efficiency of the mesh. The cyclic performance of the mesh after abrasion was also examined; a toluene-in-water emulsion was used for the cyclic separation test. The results showed that after 10 cycles, despite the separation efficiency decreasing slightly, it remained above 98%. Likewise, only a small decrease was observed in the flux. Industrial oily wastewater often contains corrosive substances such as acids and alkalis. Therefore, the corrosion resistance and chemical stability of the materials are particularly critical in the treatment of such wastewater. Good stability allows the material to work efficiently and increases the service life of the material. To investigate the corrosion resistance of MMO@CM, acetic acid was used as a representative corrosive agent. Following the immersion of MMO@CM in 1 mol L−1 acetic acid solution for 12 h, the contact angle and the emulsion separation efficiency were measured (Figure S11). After the acid treatment, the water contact angle under oil decreased (131.2°), but the separation efficiency of MMO@CM remained relatively high (>98%). In addition, three simulated corrosive emulsions (namely, toluene-in-water emulsions containing acetic acid, NaOH, or NaCl) were used to determine the separation ability of MMO@CM under these corrosive conditions. Figure S12 shows that these corrosive emulsions had little effect on the mesh, which achieved a high separation efficiency comparable to that achieved under noncorrosive emulsion conditions, as discussed above. The above experiments confirm that MMO@CM has very good chemical stability and durability in common acids, bases,

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CONCLUSIONS In summary, we have successfully fabricated a MnMoO4coated copper mesh that is superamphiphilic in air, superhydrophobic under oil, and superoleophobic under water. MMO@CM can efficiently achieve gravity-driven emulsion separation and photodegradation of organic contaminants in emulsions under UV light irradiation. In addition, MMO@CM exhibits excellent durability and stability, which allows the material to perform exceptionally in the treatment of emulsions containing complex components. The findings of the present study demonstrate the potential of MMO@CM in the practical application of oily wastewater treatment.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b07091. EDS image, water-retention capacity, separation efficiency with different mesh numbers, UV spectrum of MMO@CM, droplet size distribution of two emulsions, kinetic model simulation, separation performance of abrasion test, separation efficiency of corrosive emulsions (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (D.C.). *E-mail: [email protected] (J.L.). ORCID

Dongyun Chen: 0000-0003-0083-1843 Hua Li: 0000-0002-0982-5573 Jianmei Lu: 0000-0003-2451-7154 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (51573122 and 21776190) and Natural Science Foundation of the Jiangsu Higher Education Institutions of China (17KJA430014, 17KJA150009) and the project supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

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REFERENCES

(1) Ramseur, J. L. Oil Spills: Background and Governance; Congressional Research Service: Washington, DC, 2017. (2) Zhu, Y.; Wang, D.; Jiang, L.; Jin, J. Recent Progress in Developing Advanced Membranes for Emulsified Oil/Water Separation. NPG Asia Mater. 2014, 6, No. e101. (3) Peng, Y.; Guo, Z. Recent Advances in Biomimetic Thin Membranes Applied in Emulsified Oil/Water Separation. J. Mater. Chem. A 2016, 4, 15749−15770. 23795

DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

Research Article

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DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797

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DOI: 10.1021/acsami.9b07091 ACS Appl. Mater. Interfaces 2019, 11, 23789−23797