Oxygen vacancy-rich BiVO4 modified with mesoporous MIL-88A(Fe) Z-scheme heterojunction for enhanced photocatalytic formaldehyde degradation

The rapid recombination of photogenerated charges, inferior photo-absorption properties, and limited active sites of photocatalysts have hindered the development of photocatalytic removal of formaldehyde. Herein, a richoxygen vacancies BiVO4 modified with mesoporous MIL-88A(Fe) Z-scheme heterojunction (MIL-88A(Fe)-CA/ BiVO4-OVs) was synthesized to enhanced photocatalytic formaldehyde degradation. The MIL-88A(Fe) with citric acid modification (MIL-88A(Fe)-CA) possessed a large specific surface area and mesoporous structure. The construction of Z-scheme heterojunction facilitated the rapid transfer and separated the photogenerated charges. More importantly, the addition of oxygen vacancies in BiVO4 (BiVO4-OVs) strengthened the photo-absorption properties while suppressing the recombination of photosynthesized charges. As a result, MIL-88A(Fe)-CA/ BiVO4-OVs possessed optimum photocatalytic activity (91.0 %) compared with MIL-88A(Fe)-CA (51.8 %) and BiVO4-OVs (65.4 %). Moreover, MIL-88A(Fe)-CA/BiVO4-OVs had favourable stability with a degradation efficiency of 86.3 % after five cycling experiments. EPR and free radical scavenging experiments demonstrated that h+ and & sdot;O2- were the main active substances in photocatalytic degradation of formaldehyde. Additionally, the transformation process of intermediate products was analyzed using in-situ DRIFTS technology. Finally, the mechanism of photocatalytic degradation of formaldehyde was proposed.