New insights into the efficient charge transfer of the modified-TiO2/Ag3PO4 composite for enhanced photocatalytic destruction of algal cells under visible light

A novel p-n heterojunction between Ag3PO4 and nitrogen-doped black TiO2 (b-N-TiO2) was successfully synthesized via the calcination and precipitation method. The incorporated nitrogen and produced oxygen vacancies in b-N-TiO2 narrowed the bandgap and shifted the band position of TiO2, which promoted p-n heterojunction formation and subsequently facilitated the separation of photogenerated electrons and holes in the composite b-N-TiO2/Ag3PO4. The b-N-TiO2/Ag3PO4 exhibited enhanced photocatalytic activity for chlorophyll-a degradation in Microcystis aeruginosa cells, which was 2.73, 7.72, and 6.04 times higher than that of the pure Ag3PO4, b-N-TiO2, and P25/Ag3PO4, respectively. Furthermore, the mechanism exploration indicated the transfer pathways of photo-produced electrons and holes to generate the dominant superoxide anion radicals (•O2-) in photocatalytic processes. The charge transfer increased the photocatalytic stability of the composite b-N-TiO2/Ag3PO4 compared with pure Ag3PO4 and P25/Ag3PO4. This research provides a new perspective into the roles of defects to form heterojunctions in photocatalytic composites.