Monomolecular VB2-doped MOFs for photocatalytic oxidation with enhanced stability, recyclability and selectivity

Abstract

Monomolecular VB₂ (vitamin B₂) was doped into UiO-66 [Zr₆O₄(OH)₄(BDC)₁₂, BDC = 1,4-benzenedicarboxylic acid] via chemical bonds and the obtained VB₂@UiO-66 could be used as a heterogeneous photocatalyst. The coordination with UiO-66 was found to be able to positively shift the conduction band of VB₂, which thermodynamically precluded the formation of other reactive oxygen species (like O₂˙⁻) except ¹O₂ under visible light irradiation and led to ¹O₂ as the only reactive oxygen species for VB₂@UiO-66. This result was totally different from that for VB₂, which produced various reactive oxygen species, such as O₂˙⁻ and ¹O₂. Due to the fact that ¹O₂ was the only reactive oxygen species, VB₂@UiO-66 displayed excellent photocatalytic selectivity (∼100%) towards benzyl alcohol oxidation. At the same time, chemical bonding with UiO-66 greatly improved the stability of VB₂ under visible light. After 5 cycles, the conversion was still 91% and the selectivity was close to 100%. This work offers not only a solution to the poor recyclability, stability and selectivity of VB₂ as a photocatalyst but also a new efficient strategy to extend the photocatalytic applications of MOFs by immobilizing common biological antioxidants on their particular sites.