Multi-functional CNT-BiOBr/cellulose acetate composite membrane with strong photocatalytic activity and self-cleaning performance for the purification of oily wastewater under simulated solar light

BiOBr and carbon nanotubes (CNTs) were used to form a heterojunction, which was subsequently immobilized within a cellulose acetate (CA) membrane to facilitate the separation of oil emulsions from water under visible light irradiation. The resulting composite exhibited remarkable super-hydrophilicity and high oil hydrophobicity. The incorporation of nanoparticles into the CA membrane enhanced its porosity, with the CNT-BiOBr/CA composite achieving the highest porosity value of 0.61. UV–Vis DRS analysis demonstrated that the CNT-BiOBr/CA composite exhibited superior light absorption and reduced electron-hole recombination compared to both CNT/CA and BiOBr/CA membranes. This improvement is attributed to the formation of the heterojunction, which resulted in enhanced photocatalytic efficiency. Filtration experiments using 1 % (v/v) oil-in-water emulsions indicated that the permeate flux through the CNT-BiOBr/CA membrane was significantly higher when the lamp was illuminated, reaching a peak flux of 28.63 L/m²·h. The CNT-BiOBr/CA membrane also demonstrated self-cleaning properties, reducing the irreversible fouling ratio to 1.75 % under lamp-on conditions, which contributed to a flux recovery ratio of 98.24 % and a separation efficiency of 97.8 %. Additionally, the stability of the CNT-BiOBr/CA membrane was sustained over four consecutive uses, and it followed first-order kinetics for the degradation of oil droplets during photocatalysis.