Substituted Ti(IV) in Ce-UiO-66-NH2 Metal–Organic Frameworks Increases H2 and O2 Evolution under Visible Light

Metal–organic frameworks (MOFs) as photocatalysts have received increasing attention. In this work, a dual metal-substituted UiO-66-NH 2 (Ti/Ce-MOF) containing different Ti/Ce mole ratios ( x = 0–2.46) has been prepared via post-synthetic exchange between Ce-UiO-66 and TiCl 4, followed by amination. The solid had a high surface area (828–937 m 2 /g) and a large pore volume (0.451–0.507 m 3 /g). Under visible light, Ti/Ce-MOF showed x -dependent activity for H 2 O reduction and oxidation on a film electrode, respectively. However, such a change for H 2 evolution in a Na 2 S/Na 2 SO 3 aqueous solution was observed only after CdS loading. In combination with the photoluminescence and band parameters, we propose that the photoactivity of Ti/Ce-MOF for redox reaction is determined by its ability for electron transfer. Furthermore, there is an interfacial electron transfer from Ti/Ce-MOF to CdS and a hole transfer from CdS to Ti/Ce-MOF, respectively, significantly improving the efficiency of charge separation for redox reactions. This work offers a new insight that Ti substitution benefits the performance of Ce-based MOF.