Decahedral BiVO₄/tubular g-C₃N₄ S-scheme heterojunction photocatalyst for formaldehyde removal: Charge transfer pathway and deactivation mechanism

Designing a durable and efficient heterojunction photocatalyst for the removal of indoor air pollutants has attracted significant attentions. However, the interfacial charge transfer pathway and deactivation mechanism of photocatalysts are still challenges. In this study, the decahedral BiVO₄/tubular g-C₃N₄ (BiVO₄/TCN) S-scheme heterojunction photocatalyst was synthesized, which exhibited excellent photocatalytic activity and stability for the removal of formaldehyde (HCHO) in a continuous-flow reactor. The formation of the S-scheme heterojunction promoted spatial separation of charges, enhanced the redox capability, and maintained favorable charge carrier potentials. Based on Central Composite Design, a semi-empirical equation was successfully established to predict the removal efficiency of HCHO, and photocatalyst load and initial concentration played important roles in the removal of HCHO. The interfacial charge transfer pathway in the S-scheme heterojunction was clearly confirmed through photo-irradiated Kelvin probe and in situ irradiated X-ray photoelectron spectroscopy analysis. The superficial state changes of BiVO₄/TCN before and after the reaction indicated that the formation of coke could inhibit separation and transfer of electron-hole pairs, resulting in a slight decrease in photocatalytic activity. In summary, this study not only presents an effective technology for constructing S-scheme heterojunction photocatalyst, but also offers a new insight on the deactivation mechanism of photocatalyst during removal of volatile organic compounds.