Study on the Photocatalysis Mechanism of the Z-Scheme Cobalt Oxide Nanocubes/Carbon Nitride Nanosheets Heterojunction Photocatalyst with High Photocatalytic Performances

An efficient Z-scheme Co3O4/g-C3N4 heterojunction photocatalyst was developed via in-situ forming Co3O4 nanocubes on the g-C3N4 nanosheet in the hydrothermal process. The obtained photocatalyst exhibited high photocatalytic activity for the visible-light-driven catalytic reduction of Cr(VI) and catalytic oxidation of tetracycline (TC). Among the as-synthesized catalysts, Co3O4/g-C3N4-0.04 (the mass ratio of g-C3N4 to Co3O4 is 0.04) sample exhibits the most efficient catalytic activities. The photocatalytic reduction and photocatalytic oxidation efficiencies of Co3O4/g-C3N4-0.04 can obtain 81.3 and 92.6 %, respectively. Moreover, the TC is mineralized in the course of photocatalytic degradation, 72.2% of TOC is removed from the reaction system. In addition, the apparent quantum efficiency for the removal of Cr(VI) was also obtained and the the Co3O4/g-C3N4-0.04 could achieve the highest apparent quantum efficiency among the samples. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in Co3O4/g-C3N4-0.04, which is preliminarily confirmed by the photoluminescence spectra, time-resolved photoluminescence spectra and the photoelectrochemical characterizations. Finally, we speculate that the Co3O4/g-C3N4 heterostructures follow a more reasonable Z-scheme charge transfer in this study, which is confirmed by analyzing the results of electron paramagnetic resonance, radical scavenging experiments, and theoretical calculations.