*Article* **Experimental Investigation of Copper Mesh Substrate with Selective Wettability to Separate Oil**/**Water Mixture**

#### **Jia Yuan 1,2, Chenyi Cui 1, Baojin Qi 1,2,\*, Jinjia Wei 1,3 and Mumtaz A. Qaisrani 3**


Received: 20 October 2019; Accepted: 21 November 2019; Published: 29 November 2019

**Abstract:** To solve the problem of low efficiency and poor adaptability during complex oil/water mixtures separation, two types of membranes with superhydrophilicity/underwatersuperoleophobicity were successfully fabricated by oxidative reaction and in situ displacement reaction methods. A nanoneedle Cu(OH)2 structure was generated on the copper mesh substrate by oxidative reaction and feathery micro/nanoscale composite, while Ag structure was constructed at the surface of copper mesh substrate through in-situ replacement, then, membranes with superhydrophilic/ underwater-superoleophobic properties were separated. The influence of microstructure, wettability of the surface of prepared membranes and the liquid constituents in the separation experiment were studied and the liquid flux and permeation pressure at the membrane were later experimentally investigated. The experimental results show that separation efficiency of both membranes for separating different oil/water mixtures was above 99.8%. However, the separation efficiency of the Ag-CS (Ag on the copper substrate) membrane was obviously higher than that of the Cu(OH)2-CS (Cu(OH)2 on the copper substrate) membrane after 10 instances of separation because of the micro/nanocomposite structures. By comparison, it was found that the Ag-CS membrane showed a relatively higher permeation pressure but lower liquid flux as compared to Cu(OH)2-CS membrane, due to the influence of microscale structure and the wettability of the surface combined. In addition, the outcome for separating the multicomponent oil/water mixture illustrate that the result of TOC (the Total Organic Carbon) test for the Cu(OH)2-CS membrane and Ag-CS membrane were 31.2% and 17.7%, respectively, higher than the average of the two oils probably because some oil droplets created due to mutual dissolution passed through the membranes. However, these two fabricated membranes still retained higher separation efficiencies and good adaptability after 10 instances of separation. It was concluded that based on the good performances of the prepared membranes, especially the modified membrane, they have a vast application prospect and can be widely used.

**Keywords:** oil/water separation; superhydrophilic/underwater-superoleophobic membranes; opposite properties; superhydrophobicity/superoleophilicity; selective wettability; micro/nanoscale composite structure
