S-scheme polyphenylguanidine / 2D-Bi2WO6 heterojunction photocatalytic composite membrane: H2 production and Congo red degradation.

Photocatalysis is widely applied in fields such as pollutant degradation and clean energy production. However, single photocatalysts have limited light absorption ranges and high carrier recombination rates. Constructing heterojunctions can address these issues. But, existing heterojunctions often suffer from drawbacks such as high fabrication costs, poor synergistic functionality, and susceptibility to catalyst detachment. Therefore, a novel S-scheme heterojunction photocatalytic tri-layer composite membranes (TLCM2) were fabricated, with a polyethersulfone (PES) membrane as the substrate, a conductive polyphenylguanidine benzene sulfonate (SPAG) transition layer, and a functional layer of nanosheets Bi2WO6 particles (2D-BWO). SPAG possessed excellent flexibility due to its acyclic guanidine groups and showed smaller water contact angle, broader absorption range of wave length and slower recombination rate of e--h+ pairs. After combined with 2D-BWO, the band gap of their heterojunction decreased from 2.59 of SPAG to 2.48 eV. After 4 h irradiation by a 300W Xe lamp, the H2 production rate of TLCM2 was 579.12 μmol g-1·h-1, approximately 4 times that of pure SPAG and pure 2D-BWO. Under 50W LED illumination, TLCM2 achieved a 96.9 % degradation rate of Congo Red (CR) within 2.3 h (rate constant: 0.01014 min-1), significantly higher than SPAG (49 %) and BWO (61.5 %). The preparation of TLCM provides an effective process for fabrication of catalytic membrane material with many kinds of raw materials under low cost, which is also facile for possible scale production. The process of TLCM achieves the catalyst loading without obstruction of its functional sites as much as possible, which provides a new solution for effective, repeatable and long-term use of catalytic materials.