Superhydrophilic photocatalytic g-C3N4/SiO2 composite membranes for effective separation of oil-in-water emulsion and bacteria removal

Conventional membrane processes, e.g., microfiltration and ultrafiltration, suffer from severe permeation flux decline and fouling during the oily wastewater treatment. The superhydrophilic surface decoration provides an important and effective strategy to address this challenge. Herein, a surperhydrophilic/underwater superoleophobic nanocomposite surface with the photocatalytic properties was constructed via one-step facile vacuum-assisted filtration of a g-C3N4 nanosheet/SiO2 nanoparticle dispersion onto a microfiltration membrane substrate. Specifically, with the intercalation of 20 mg∙L−1 SiO2 nanoparticles into the g-C3N4 nanosheets, the g-C3N4/SiO2 composite membrane showed the superhydrophilic/underwater superoleophobic properties with an underwater oil contact angle of 170.0 ± 0.3°. Such a g-C3N4/SiO2 composite membrane yielded a permeation flux of >1290 LMH·bar−1 with an oil rejection of >99.91% during the vacuum filtration of oil-in-water emulsions. The g-C3N4/SiO2 composite membrane significantly outperformed the pristine microfiltration substrate that had severe fouling caused by oil blockage. Additionally, the g-C3N4/SiO2 composite membrane not only effectively retained the E. coli bacteria through size exclusion effect, but also promoted the inactivation of bacteria via visible-light photocatalysis. Therefore, our membrane has a great promise in practical oily wastewater treatment due to its excellent separation performance and biofouling resistance.