Novel g-C3N4/h′ZnTiO3-a′TiO2 direct Z-scheme heterojunction with significantly enhanced visible-light photocatalytic activity

Novel g-C3N4/h′ZnTiO3-a′TiO2 (CN/h′ZT-a′T) ternary composites were successfully prepared by combining in-situ precursor-synthesized h′ZnTiO3-a′TiO2 (h′ZT-a′T) nanoparticle with nanoporous g-C3N4 (CN) powders. X-ray diffraction (XRD), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) results revealed that the grains of hexagonal-phase ZnTiO3 (h′ZT) were in-situ generated together with anatase-phase TiO2 (a′T), forming a symbiotic structure of tightly bonded interface. Compared with CN and h′ZT-a′T, the absorption edge of CN/h′ZT-a′T exhibited a red-shift and the absorption intensity was obviously enhanced. With increasing CN content, the degradation efficiency of CN/h′ZT-a′T for methylene blue (MB) initially increased and then decreased, reaching the highest value of 99.8% with the CN content of 50 wt% (50CN/h′ZT-a′T). The 50CN/h′ZT-a′T composites exhibited the highest apparent reaction rate constant of 2.92 h−1, which was 37.4 and 3.0 times higher than that of h′ZT-a′T and CN, respectively. Photocurrent response of 50CN/h′ZT-a′T was indicative of the highest photocurrent value and the elongated lifetime of photogenerated charges. The greatly enhanced photocatalytic activity was attributed to the high mobility of photogenerated electrons. H′ZnTiO3 with high electron mobility in the direct Z-scheme heterojunction played a role of electronic transfer station and reduced the recombination probability of photogenerated carriers.