Article pubs.acs.org/IECR
A Facile Electrodeposition Process for the Fabrication of Superhydrophobic and Superoleophilic Copper Mesh for Efficient Oil−Water Separation Yan Liu,†,‡ Kaiteng Zhang,† Wenguang Yao,† Chengchun Zhang,*,† Zhiwu Han,† and Luquan Ren† †
Ministry of Education, Key Laboratory of Bionic Engineering, Jilin University, Changchun 130022, China State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130022, China
‡
ABSTRACT: A superhydrophobic and superoleophilic copper mesh with excellent oil−water separation efficiency was successfully fabricated via electrodeposition and then surface modification with lauric acid. The surface morphologies, chemical composition, and wettability were characterized by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and water contact angle (WCA) measurements. It was found that the as-prepared surface is both superhydrophobic and superoleophilic, with static WCA values as high as 155.5° ± 3° and an oil contact angle (OCA) of 0°. Furthermore, the as-prepared surface exhibited excellent oil− water separation efficiency including petroleum, toluene, hexane, gasoline and diesel, even after being recycled 10 times. In addition, the as-prepared copper mesh shows self-cleaning character with water and chemical stability. This study provides a facile, inexpensive, and environmentally friendly route to fabricate large-scale and excellent oil−water separation surface with high separation efficiency for a great number of potential applications.
1. INTRODUCTION In the past few years, with the increase of oil spill accidents and industrial oily wastewater, oil−water separation has become a worldwide challenge and has aroused much attention.1−4 To resolve these water pollution issues, many approaches have been used for the treatment of oil−water pollution, including filtration, oil skimmers, centrifugal machine, precipitation tanks, magnetic separations, flotation technologies, oil-absorbing materials, and combustion.5−11 However, most of the methods involve harsh conditions, such as expensive equipment, complex devices, complicated processing steps, high processing cost, long processing time, and so on. Taking all factors into account, separation treatment stands out from the rest as a simple, universal, scalable approach for valid removal of oil from water. In addition, surfaces with superhydrophobic and superoleophilic wettability have triggered unprecedented research excitement in the field of filtration.12−15 Many plants and insects exhibit excellent superhydrophobicity, such as lotus leaves, rose petals, marigold petals, water striders, butterfly wings, rice leaves, mosquito eyes, and so on. Taking inspiration from nature, superhydrophobic surfaces are fabricated by simulating typical structures of plant surface and considering chemical composition simultaneously.16−20 Also, materials with special wettability and micro-nanoscale structures have attracted increasing attention for oil−water separation. This filtration process needs excellent wettability materials, which are both superhydrophobic (water contact angle (WCA) of >150°) and superoleophilic (oil contact angle (OCA) of 150°) with water droplets. 3.3.2. Effect of the Electrodeposition Time on Wettability. The fabrication of nanostructures on a copper mesh by electrodeposition is an inexpensive and facile technique; however, this method always needs to accurately control the deposition time and solution concentration, which play important roles in crystal growth. Because the roughness and crystallinity are positively related. Thus, we explored the effect of different electrodeposition times on wettability. The samples were prepared under 100, 150, 200, 250, 300, 350, and 400 s of deposition time. Figure 7a shows the relationship between electrodeposition times and static CAs on the as-prepared surface. The CA value reached 134° after a deposition time of 100 s. With the time was extended to 250 s, the CA value reached 155.5° ± 3° and the sliding angle reached 13° ± 4°. Meanwhile, the advancing and receding angles shown in Figure 7b were measured, still showing very good hydrophobic
Figure 6. (a) Macroscopic images of the pristine and as-prepared samples; (b) mirror-like phenomenon can be observed on the resulting superhydrophobic mesh submerged in water. (c) reflectance of the original mesh (red trace) and as-prepared superhydrophobic copper mesh (black trace). E
DOI: 10.1021/acs.iecr.5b03503 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
Figure 7. (a) Contact angles and (b) sliding angles of the different electrodeposition time on simple surfaces for 100, 150, 200, 250, 300, 350, and 400 s after modification by lauric acid.
Figure 8. Influence of pore sizes of copper mesh on water contact angle (WCA).
cleaning properties were observed on the pristine copper mesh surface. 3.5. Chemical Stability. It is well-known that Cassie-like wetting is temporary under water. We have explored temporal changes to the CA value over extended periods. We put the asprepared sample into the water for different time periods and then removed it and immediately measured the CA. Figure 10 shows the relationship between the soaking time and static CA. After 2 h of soaking, the sample can keep a CA value of 140° ± 3° and has good hydrophobicity. However, after the sample was dried after a certain period of time, its original superhydrophobicity was again restored. Therefore, the as-prepared sample could exist stably in the water and lauric acid does not dissolve into the water phase. In order to further illustrate the stability of samples prepared under corrosive environment, the sample was estimated by measuring the static WCA values for samples that were immersed in aqueous solutions for 10 min at various pH values (ranging from 1 to 14). Figure 11 shows the relationship between the pH values and the static CA; the measured static CA ranged from 143° ± 3° to 152° ± 2°. After immersion in the corrosive solution, the samples still have excellent hydrophobic proprities. The results indicate that the asprepared surface has good chemical stability in aqueous solutions of most acidic, alkali, and some aqueous salts.
Figure 9. Demonstration of the self-cleaning effect of the resultant superhydrophobic mesh through the removal of graphite particles from the surface using water droplets.
4. SEPARATION OF OIL AND WATER Because of a combination of superhydrophobicity and superoleophilicity, the as-prepared mesh has great potential to be applied to oil−water separations. The oil−water separation experiment was performed as shown in Figure 12 The asprepared copper mesh was fixed between two quartz tubes. In order to ensure the sealing performance, there are two sealing rings in the junction of the two quartz tubes. Compared to water, oil has a lower density. Therefore, the measured oil floats on the water, with no contact with the copper mesh. The short glass tube was replaced by a longer bent one, and the device was placed at a tilt angle of ∼30°. In this experiment, F
DOI: 10.1021/acs.iecr.5b03503 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 10. Relationship between the soaking time and the static contact angle (CA) on the as-prepared copper mesh surface.
Figure 12. Oil−water separation device and process: (a) before mixing (petroleum ether and water), (b) after mixing, (c) after separation. Water was colored by Methylene Blue, and oil was colored by Oil Red O.
Figure 11. Relationship between the pH values and the static CA on the as-prepared copper mesh surface.
25 mL of petroleum ether (dyed with oil red) was poured into 25 mL of water (dyed with Methylene Blue) contained in a beaker, and the petroleum ether floated on top of the aqueous phase, because of its lower density. When the mixture of petroleum ether and water with a total volume of 50 mL was poured into the quartz tube, the petroleum ether penetrated the mesh and flowed down the beaker underneath, while the water was retained in the upper glass tube. During the oil−water separation process, no artificial external force was employed, indicating its easy operation and low energy costs. Note that the ubiquitous water loss induced by the water adhesion on the surface of glass vessels during the oil−water separation process was not considered in the efficiency calculations. Oil−water separation efficiency was used to quantitatively describe the oil−water separation ability of the as-prepared copper mesh. Because the superhydrophobic layer is robust, the as-prepared mesh can be reused. Therefore, we investigated the suitability of a copper mesh for the separation of other oils from water. The recycling ability was also investigated by taking the petroleum ether/water mixture as an example. We measured the separation efficiency of the as-prepared copper mesh with different types of oil, such as petroleum, toluene, hexane, gasoline, and diesel. The oil separation efficiency (R, expressed as a percentage) was then calculated based on the following equation:
respectively. The oil concentration were measured using an automatic infrared oil analyzer. As shown in Figure 13, different
Figure 13. Oil collection efficiency of superhydrophobic mesh capped container for five oils after 10 cycles.
types of oils such as gasoline, diesel oil, petroleum, toluene, and hexane, can be separated using the above apparatus at an efficiency of more than 93%. The stability of the as-prepared mesh differs only slightly, even after 10 cycles, indicating its general suitability for various oil−water separations. After 10 separate experiments, the sample was rinsed with sufficient alcohol and distilled water to remove the surface of the oil, and then it was dried under atmospheric conditions for 10 min. Measuring the CA again shows that the CA approached 148° ±
⎛ C ⎞ R (%) = ⎜1 − P ⎟ × 100 CO ⎠ ⎝
Herein, CO and CP are the oil concentrations in the pristine oil−water mixture and after the separation of water, G
DOI: 10.1021/acs.iecr.5b03503 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
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3°, which indicates that the organic solvent will not damage the structure and chemical composition of the hydrophobic surface. There is a good combination of the laurel acid and the rough surface; therefore, the lauric acid does not dissolve into the oil phase.
5. CONCLUSIONS A facile method to fabricate a copper mesh with selective wettability has been demonstrated. Superhydrophobic and superoleophilic meshes were fabricated by an electrodeposition method and then modified on lauric acid coatings. The asprepared copper mesh surface not only exhibits superhydrophobicity, with a water contact angle (WCA) of 155.5° ± 3°, but also superoleophilicity with an oil contact angle (OCA) of 0°. In addition, a series of oil/water mixtures, such as petroleum ether/water, hexane/water, toluene/water, gasoline/ water, and diesel/water, were observed to be separated by the mesh, with a separation efficiency of >93%; it remained high even after 10 cycles. Furthermore, the as-prepared superhydrophobic copper mesh shows self-cleaning character and chemical stability. The fabrication process is facile, inexpensive, and environmentally friendly, and suited to large-scale applications. Because of the excellent oil−water performance, the as-prepared copper meshes have potential applications in treating industrial oil−water mixtures and environmental oil spills.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 431 85095760. Fax: +86 431 85095575. E-mail: address:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank the National Natural Science Foundation of China (Nos. 51275555, 51475200, and 51325501), Science and Technology Development Project of Jilin Province (No. 20150519007JH).
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DOI: 10.1021/acs.iecr.5b03503 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.iecr.5b03503 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
