Black@ZnO/Gr modified carbon fiber self-cleaning membrane for Resource Disposal of degreasing wastewater

Abstract

Membranes used for the advanced treatment of oily wastewater are susceptible to limitations, including the adhesion of oil-fouling and the residues (ions, emulsifiers, and residual oil droplets) in separated permeate. Here, multifunctional black zinc oxide (Black@ZnO) and graphene (Gr) modified carbon fiber (Black@ZnO/Gr-CF) membrane were prepared by electrodeposition and anodic oxidation, which realized the self-cleaning of oil-fouling and photothermal evaporation of separated permeate. The hierarchical micro-nano rough structure formed by stacked Gr and nanoflower-like Black@ZnO endowed Black@ZnO/Gr-CF with underwater superoleophobicity (154.0°), thereby realizing efficient separation performance in oil-water mixture and (99.8 % and 146882.3 L m⁻² h⁻¹) and emulsion (99.5 % and 27853.7 L m⁻² h⁻¹). Additionally, the reduced band gap (2.45 eV) of Black@ZnO/Gr enabled Black@ZnO/Gr-CF photocatalytic self-cleaning performance for oil-fouling, resulting in a separation efficiency recovery rate (SERR) of 95.6 % and a flux recovery rate (FRR) of 99.0 %. Moreover, the evaporation rate of Black@ZnO/Gr-CF to the separated permeate reached 2.31 kg m⁻² h⁻¹, and the rejections of TOC and ions were all over 99.0 %. In addition, the Black@ZnO/Gr-CF can separate degreasing wastewaters (DGWs) from AW-Volkswagen, achieving separation efficiency of 97.5 and 75.6 %, corresponding fluxes of 6805.2 and 5255.3 L m⁻² h⁻¹, and the SERR and FRR reached 93.9 and 92.8 %. The evaporation rate of the separated permeate reached 2.19 kg m⁻² h⁻¹, and the rejections of TOC and ions were over 98.0 %. Following water impact, wear resistance, and UV aging test, the underwater oil contact angle of the Black@ZnO/Gr-CF stayed above 150.0°. Self-cleaning membranes with special wettability provide new insights into the treatment of actual DGWs.