ZnO nanorod array-coated mesh film for the separation of water and oil
© Li et al.; licensee Springer. 2013
Received: 13 March 2013
Accepted: 11 April 2013
Published: 20 April 2013
Dense and vertically aligned ZnO nanorod arrays with a large area have been fabricated successfully on the stainless steel mesh by a simple chemical vapor deposition method. The coated mesh exhibited both superoleophilic and superhydrophobic properties, even if it was not modified by low surface energy materials. The separation efficiencies were more than 97% in the filtration of water and oil. Besides, the wettability of the coated mesh was still stable after it was soaked in the corrosive solutions for 1 h. A detailed investigation showed that the coated mesh has the best superhydrophobic property when the stainless steel mesh pore size was about 75 μm.
KeywordsSuperhydrophobicity Superhydrophilicity ZnO nanorod arrays
With the development of economy and society, the oil pollution has become a worldwide challenge due to its serious threat to people’s livelihoods and the ecological environment [1–4]. Therefore, the removal of oil from water is becoming imperative. Many methods were employed to solve the oil pollution, such as chemical dispersant , in situ burning , and oil-absorbing materials [7–9]. However, these methods usually have some drawbacks, including low separation efficiency, poor recyclability, and high operation costs. In order to overcome these problems, the solid surfaces with both superoleophilicity and superhydrophobicity have incited broad attention due to the application in the separation of oil and water .
The wettability of the solid surface is a very important property, and it can be regulated by surface free energy and surface structure [11–15]. The superhydrophobic surfaces were usually achieved by modifying rough surfaces with low-surface energy materials . The filtration of water and oil has been achieved using the stainless steel mesh modified through polytetrafluoroethylene . Wang et al.  have fabricated successfully the copper filter which can be used in the filtration of water and oil by grafting hexadecanethiol. However, the organic matters which were used in chemical modification are usually expensive and harmful. In addition, they were easily removed from the surface due to their solubility in oil.
In this paper, ordered ZnO nanorod arrays have been fabricated successfully on the stainless steel mesh by a simple chemical vapor deposition method. The superhydrophobic and superoleophilic mesh could separate water from oil effectively, and its wettability kept stable even if it was soaked in the corrosive solutions for 1 h. The coated mesh will have a potential application in oil spill cleanups.
The ZnO nanorod arrays which were coated on the surface of the stainless steel mesh were synthesized via a chemical vapor deposition process. A piece of stainless steel mesh whose pore size was 75 μm and whose surface area was about 1 × 5 cm2 was cleaned by being soaked in acetone for 20 min, and then, ultrasonic cleaning was done for 15 min. After being rinsed with deionized water, they were soaked in ethanol for 30 min, rinsed with deionized water again, and dried in the oven at 50°C for 30 min. Then, an Au film whose thickness was about 50 nm was deposited on the substrate. High-purity Zn powders (99.999%) were placed in the quartz boat, and then, the quartz boat was put in the center of the tube furnace. The substrate was placed about 5 cm away from the quartz boat. Previous to the growth, the tube furnace was pumped to 5 Pa. Subsequently, the temperature of tube furnace was raised to 650°C for 30 min under the protection of Ar (120 sccm). Then, O2 (80 sccm) was introduced into the furnace. The growth lasted for 40 min. Then, the whose system was cooled to 25°C. After that, the ZnO nanorod arrays were grown on the surface of the stainless steel mesh. Lastly, the as-prepared sample was stored in the dark room for 2 weeks before it was measured.
The surface morphology of the ZnO nanorod was studied using scanning electron microscope (SEM, Hitachi S4700, Chiyoda-ku, Japan). The phase identification of the ZnO nanorod was carried out with X-ray diffraction (XRD, Cu Kα). The contact angles on the as-grown sample were measured by contact angle meter (DSA100, KRÜSS, Hamburg, Germany).
Results and discussion
All the parameters refer to reference . The coated mesh shows superhydrophobicity due to the lower surface free energy and the higher surface roughness. It can be shown from Figure 8a and Equation 2 that the ΔP > 0 when θ > 90°. So, the water cannot penetrate the coated mesh. From Figure 8b and Equation 2, we can see that ΔP < 0 when θ < 90°, so the coated mesh cannot sustain a little oil, and good penetration can be achieved. In addition, it can also be seen from Equation 2 that the oil which has the larger surface tension will penetrate the coated mesh easier. So the water/diesel oil mixture has the maximum value, which is in accord with our experimental result.
In this paper, high-quality ZnO nanorod arrays were achieved by chemical vapor deposition route on the stainless steel mesh. The coated mesh exhibited superhydrophobic properties due to the special micro/nanoscale hierarchical ZnO nanorod arrays and the highly c-axis-oriented crystal. At the same time, the coated mesh was superoleophilic, and the stability of the wettability was also good. So, the coated mesh can filter water/oil mixtures, and the separation efficiencies were more than 97%. In addition, the effect of different pore sizes of the original stainless steel mesh on the superhydrophobicity and superoleophilicity of the coated mesh was studied. The coated mesh promises a potential application for the water/oil separation.
Oil contact angle
Scanning electron microscope
Water contact angle
This work was supported by the Natural Science Foundation of China (no.11004071) and youth research projects of Huaibei Normal University (no.2013xqz14).
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