Fine-tuning metal nodes accessibility of metal-organic frameworks for boosting net photocatalytic H2O2 production

Abstract

Coordination unsaturated metal nodes in metal-organic frameworks (MOFs) work as photocatalytic active sites in H2O2 production, but over-exposed metal nodes also act as decomposing sites towards the photogenerated H2O2, resulting in low net yield. Herein, fine-tuning of metal nodes accessibility in MOFs was applied for boosting net photocatalytic H2O2 production. The accessibility of the nodes was fine-tuning through varying the feeding amount of benzoic acid (BA) during synthesis, treated MOFs with HCl, re-installed with variable BA, etc. The correlation between nodes accessibility and H2O2 production was systematically investigated, which demonstrates that the NH2-UiO-66-XBA with higher compensated BA possessing large steric effect at nodes would hinder the decomposition of photogenerated H2O2, thus promoting the net H2O2 yield. As a contrary, NH2-UiO-66-HCl without BA showed a distinctive decomposition rate of H2O2, resulting in a low net H2O2 production yield. The re-installed NH2-UiO-66-ReBA10 with compensated BA showed a recovered H2O2 production yield. A combination of O2 sorption isothermals, PL spectra, ESR spin-trap plots, and Koutecky-Levich plots disclosed that O2 was enriched by the framework and then reduced at the metal nodes mainly through two-electron pathway, especially for highly compensated MOFs. This strategy had been applied to other MOFs for boosting the H2O2 production like NU-1401 and PCN-222. This work reveals the fine-tuning of metal nodes accessibility in MOFs is an effective way for boosting H2O2 production.