Double network cross-linked hydrogel coating membrane with photocatalytic self-cleaning performance for efficient oil-water separation

Oil-water separation is one of the most attractive areas in the field of energy and the environment. However, the synthesis of oil-water separation membranes with high separation efficiency and anti-fouling via simple methods is still a challenge. In this work, a double network with tannic acid and g-C3N4 cross-linked gelatin hydrogel coating membrane was prepared via ultrasound and coating. The prepared hydrogel had excellent mechanical properties and swelling resistance and also endowed the membrane with underwater superoleophobicity. For stratified oil-water mixtures, the separation flux achieved 40,355 ± 1957 L·m−2·h−1 and separation efficiency higher than 99 %. Moreover, after 40 cycles, there was no decrease significantly in separation performance. For oil-in-water emulsions, the separation efficiency is >99.90 % under gravity. The adsorption of MB by the GE-CNTA-PP membrane conformed to a pseudo-first-order kinetic process (R2 = 0.99906), which was consistent with the Langmuir isothermal adsorption model (R2 = 0.99932). The contaminated membrane could self-clean via photocatalytic reaction, which mechanism was explained through theoretical investigation of the band structure of g-C3N4 by DFT. Due to these obvious advantages, the practical application of the gelatin-based hydrogel membrane in the purification of oily wastewater is promising.