Hierarchical heterojunction comprising of in-situ derived TiO2 and salicylaldimine-supported Co catalysts in metal-organic frameworks for enhancing photocatalytic hydrogen generation

Abstract

We present the design of a novel functional metal-organic framework here, denoted as Co-sal–NH2–MOF@TiO2, featuring the comprise of controllably in-situ grown TiO2 sheets from NH2-MOF(Ti) and [Co] catalytic sites stabilized by salicylaldimine moiety via site isolation for visible-light-driven hydrogen evolution from water. The hierarchical organization of TiO2 and Co catalyst within NH2-MOF (Ti) leads to outstanding photocatalytic performance, as evidenced by a H2 yield of 15,584 μmolg−1h−1 and turnover numbers (TON) reaching 5844 over 24 h. This catalyst also signifies distinctly enhanced activities of approximately 105-fold, 354-fold, 15-fold, and 100-fold, compared to the pristine NH2-MOF(Ti), MOF-derived TiO2, NH2-MOF(Ti)@TiO2 and the combination of [Co catalyst + NH2-MOF(Ti) + TiO2], respectively. EXAFs and XPS etc. analyses revealed a stable coordination environment for salicylaldimine-supported Co(II) catalytic unit, which integrated with in-situ grown TiO2 sheets can not only guarantee catalyst stability, but also generate much more densely packed light-harvesting heterojunction units and thus promote separation and transfer of photogenerated carriers between TiO2 and Co catalyst in NH2-MOF(Ti) under light through optimized band gap structure. This work outlines the in-situ construction of organic and inorganic hybrid heterojunction for H2 production from water.