Enhanced visible-light photocatalytic activity of g-C3N4–ZnWO4 by fabricating a heterojunction: investigation based on experimental and theoretical studies

TLDR

The study investigates the microscopic mechanisms of interface interaction, charge transfer, and separation in g‑C3N4–ZnWO4 heterojunctions and their impact on visible‑light photocatalytic activity using theoretical calculations and experimental techniques. DFT and experiments reveal that visible‑light excitation promotes electron transfer from the upper valence band of g‑C3N4 to the W 5d conduction band of ZnWO4, producing well‑separated electron–hole pairs that enhance photocatalytic performance. The heterojunction exhibits superior degradation of methylene blue and phenol under visible light compared to pure g‑C3N4 or ZnWO4, confirming a synergistic effect and validating the proposed interface and charge‑transfer mechanisms.

Abstract

We present a systematic investigation of the microscopic mechanism of interface interaction, charge transfer and separation, as well as their influence on the photocatalytic activity of heterojunctions by a combination of theoretical calculations and experimental techniques for the g-C3N4–ZnWO4 composite. HRTEM results and DFT calculations mutually validate each other to indicate the reasonable existence of g-C3N4 (001)–ZnWO4 (010) and g-C3N4 (001)–ZnWO4 (011) interfaces. The g-C3N4–ZnWO4 heterojunctions show higher photocatalytic activity for degradation of MB than pure g-C3N4 and ZnWO4 under visible-light irradiation. Moreover, the heterojunctions significantly enhance the oxidation of phenol in contrast to pure g-C3N4, the phenol oxidation capacity of which is weak, clearly demonstrating a synergistic effect between g-C3N4 and ZnWO4. Interestingly, based on the theoretical calculations, we find that electrons in the upper valence band can be directly excited from g-C3N4 to the conduction band, that is, the W 5d orbital of ZnWO4, under visible-light irradiation, which should yield well-separated electron–hole pairs, with high photocatalytic performance in g-C3N4–ZnWO4 heterojunctions as shown by our experiment. The microcosmic mechanisms of interface interaction and charge transfer in this system can be helpful for fabricating other effective hetero-structured photocatalysts.