Construction of robust DA@CNTs/CS hydrogel coatings on hydrophobic PVDF membrane by deposition of self-assembly for efficient separation of oil-water emulsion and dye wastewater

Abstract

With the rapid development of industry, the problem of water pollution has become increasingly serious. Though there are many separation materials available to solve this problem, how to separate multiple wastewater at the same time remains a challenge. Hydrogel coating is suitable for use in the field of oil–water separation, and chitosan (CS) is effective in removing anionic dyes. Therefore, the preparation of separation membranes with hydrogel coating containing CS and dopamine (DA) can effectively separate oil–water emulsion and anionic dye wastewater. In this paper, DA@CNTs/CS hydrogel coating was prepared by sequentially coating Cu2+, DA@CNTs, Cu2+ and CS on the surface of polyvinylidene fluoride (PVDF) membrane by deposition of self-assembly, which enhanced the hydrophilicity of the membrane and made it highly underwater oleophobic and antifouling. The alkali treated PVDF membrane contained a large amount of –OH, Cu2+, which formed coordination bonds with –OH, CS, and DA and the hydrogel coating could be stably loaded on the membrane. In addition, the introduction of rigid CNTs effectively improved the performance of the modified membrane under extreme conditions such as high pH and high salt concentration. PVDF-DA@CNTs/CS membrane had an ideal pure water flux (PWF) of 1470 (L·m−2·h−1) and the separation efficiency of 99.7 % for anionic dye and 99.4 % for oil–water emulsion. The contaminant on the membrane surface can be quickly removed by washing with DI water. The overall performance of the membrane is also maintained at a very high level of long-term filtration of wastewater. In summary, this study provides a new approach to complex wastewater treatment technology.