Porous Co3O4/CuO hollow polyhedral nanocages derived from metal-organic frameworks with heterojunctions as efficient photocatalytic water oxidation catalysts

• New materials of Co3O4/CuO hollow polyhedral nanocages are synthesized.
• The materials of Co3O4/CuO are efficient and stable water oxidation catalysts.
• Two mechanisms in this light-driven water oxidation system are proposed.
• The heterojunctions improve the activity of photocatalytic water oxidation.

A novel material of porous Co3O4/CuO hollow polyhedral nanocages (HPNCs) derived-from metal-organic frameworks (MOF) for photocatalytic water oxidation was reported for the first time and the molar ratio of Co/Cu in this kind material was optimized. The Co3O4/CuO HPNCs composites were characterized by multiple experiments (FETEM, HRTEM, SEM, TGA, PXRD, EDX, ICP-AES, BET, XPS) to confirm the structure and the component. A high turnover frequency (TOF) of 4.9 × 10−3 s−1 per metal atom was obtained over Co3O4/CuO-3 HPNCs, which is comparable to those published cobalt based catalysts. At the same time, Co3O4/CuO-3 HPNCs showed a maximum oxygen yield of 50% and quantum yield of 49%. This composite of Co3O4/CuO HPNCs containing heterojunctions may enhance the photocatalytic performance of water oxidation.Various characterization methods prove that Co3O4/CuO HPNCs composites are stable and robust heterogeneous photocatalytic catalysts that can be used repeatedly without any loss in activity. According to the experimental results, we speculate that there are two kinds of reaction mechanisms in this light-driven water oxidation system. One mechanism is widely accepted that high valence metal species play a role in the reaction system. The other one is that the heterojunctions of Co3O4/CuO HPNCs make a great contribution to improve the activity of photocatalytic water oxidation. Meanwhile, we put forward a new idea to design a series of metal oxide catalysts with heterojunctions derived from MOF for light-driven water oxidation.

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