Efficient Oil-water Separation at the g-C3N4/TiO2-PVDF Photoresponsive Membrane Interface: Permeability and Selectivity Differences Induced by Different Exposed Crystal Planes and Performance

Membrane technology is constrained by membrane fouling of oil droplet obstruction in oil-water separa ⁃ tion. A crucial step toward effective oil-water separation is the construction of a functional interface for selective sepa ⁃ ration of the oil-water mixture. In this paper, g-C3N4/TiO2-PVDF(polyvinglidene fluoride) photocatalytic membranes with different exposed crystal planes of TiO2 were prepared, and the effects of different exposed crystal planes on oil-water separation were studied. The experimental results show that the TiO2(001) surface endows the g-C3N4/ TiO2(001)-PVDF membrane with excellent superhydrophilicity and underwater superoleophobicsuperoil transport properties under sunlight irradiation, and compared with the TiO2(101) surface exposed membrane, g-C3N4/ TiO2(001)-PVDF membrane has better oil-water separation performance. Under visible light, the pure water flux of g-C3N4/TiO2(001)-PVDF membrane reaches 2002.9 L & BULL;m-2 & BULL;h-1, which is 60.8% higher than that of g-C3N4/TiO2(101)- PVDF membrane, and 47.1% higher than that under dark conditions. Simultaneously, the rejection efficiency of the five kinds of oil substances is more than 99%, and the high permeation flux of 420.4-665.2 L & BULL;m-2 & BULL;h-1 is maintained. The highest rejection efficiency of g-C3N4/TiO2(101)-PVDF membrane is only 61.8%, and the permeation flux is less than 200 L & BULL;m-2 & BULL;h-1. The mechanism of different crystal planes was explored by transient photocurrent response and electron paramagnetic resonance technology. The results showed that the g-C3N4/TiO2(001)-PVDF membrane had a stronger light response current and more hydroxyl radical production. The permeation flux of g-C3N4/TiO2(001)-PVDF membrane was still 264 L & BULL;m-2 & BULL;h-1 after a 360 min continuous experiment. High rejection efficiency and permeation flux were always maintained in the 8 cycles of regeneration experiments. Obviously, the photocatalytic membrane with exposed TiO2(001) has a greater permeability, selectivity, and stability, which is more appropriate for the effec ⁃ tive separation of oil-water wastewater.