Developing a facile graphitic carbon nitride (g-CN)-coated stainless steel mesh with different superhydrophilic/underwater superoleophobic and superoleophilic behavior for oil-water separation.

There is an increasing demand for the development of inexpensive and effective approaches for the oil-water separation due to the global concern in oil industries. The present study was conducted to fabricate graphitic carbon nitride/thermoplastic polyurethane (g-CN/TPU)-coated stainless steel meshes via the dip-coating method to investigate the capability of g-CN nanosheets (CN-NS) in oil-water separation. CN-NS was synthesized using the polycondensation process followed by exfoliation with Hummer's method. We studied the effect of TPU and CN-NS concentration on wettability behavior to obtain an optimized coating solution. CN-NS-coated mesh showed superoleophilic/hydrophobic behavior at CN-NS:TPU ratio of 50:50, and it efficiently passed oil from the emulsified water-in-oil mixture (with 50 wt.% oil) with the efficiency of 99%. The wettability behavior of superhydrophilic/underwater superoleophobic was also obtained at CN-NS:TPU ratio of 80:20, and it was able to separate water from the emulsified water-in-oil mixture with the efficiency of 79% under gravity. Both filters were able to separate free water and oil mixtures with flux and efficiency of 6114 L.m.h and ~ 99.99%, respectively. The mechanism of wettability behavior of the coating is mainly related to the functional groups on the edge of g-CN-NS, thus increasing the hydrophilic properties of the surface. In addition, the micro-nano hierarchical structure of the surface coating improves its roughness due to the presence of CN-NS, which is effectively embedded into the hydrophilic TPU. More importantly, commercially available TPU chemical and simple fabrication of g-CN from an inexpensive precursor make the method reported herein as a significant alternative for large-scale application.