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

We present the design of a novel functional metal-organic framework here, denoted as Co-sal–NH 2 –MOF@TiO 2 , featuring the comprise of controllably in-situ grown TiO 2 sheets from NH 2 -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 TiO 2 and Co catalyst within NH 2 -MOF (Ti) leads to outstanding photocatalytic performance, as evidenced by a H 2 yield of 15,584 μmolg −1 h −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 NH 2 -MOF(Ti), MOF-derived TiO 2 , NH 2 -MOF(Ti)@TiO 2 and the combination of [Co catalyst + NH 2 -MOF(Ti) + TiO 2 ], respectively. EXAFs and XPS etc. analyses revealed a stable coordination environment for salicylaldimine-supported Co(II) catalytic unit, which integrated with in-situ grown TiO 2 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 TiO 2 and Co catalyst in NH 2 -MOF(Ti) under light through optimized band gap structure. This work outlines the in-situ construction of organic and inorganic hybrid heterojunction for H 2 production from water.