Enhanced CO2 reduction by N-doped C-coated anatase/rutile/NH2-MIL-125(Ti) heterojunctions at low light intensity without sacrificial agents

This study presents the design of a composite photocatalyst that harnesses the combined effects of internal and external heterojunctions for enhanced performance. The internal heterojunction is achieved by annealing NH 2 -MIL-125(Ti) (NM) under an argon atmosphere, forming an N-doped C-coated anatase/rutile heterostructure (A-NM). By controlling the annealing temperature, the A-NM prepared at 650 °C (A 650 -NM) demonstrates superior photocatalytic CO 2 reduction capability, with an outstanding CO production rate of 0.25 μmol h −1  g −1 under a light intensity of 0.1 W cm −2 . An external heterojunction is then created by combining NM and A 650 -NM in an optimized ratio. At an optimal composite ratio of 9:1 (NM: A 650 -NM), the CO production rate reached 6.3 μmol h −1  g −1 , which is 3.5 times higher than NM and 25 times higher than A 650 -NM. Characterization and DFT analyses reveal that the improved performance stems from the internal heterojunction within A 650 -NM's TiO 2 crystal phases and the external heterojunction between NM and A 650 -NM, which enhanced charge separation and carrier mobility. The N-doped carbon layer further boosts charge carrier transfer efficiency. This work introduces a novel Metal–Organic Framework (MOF)-based photocatalyst for CO 2 reduction, offering valuable theoretical insights and practical strategies for optimizing its performance.