Dual Z-scheme heterostructured polyoxometalate/activated carbon/TiO2 ternary composite for efficient photocatalytic N2 fixation

Developing effective and robust catalysts with high gas adsorption capacities and electron-hole separation rates for direct photochemical N 2 reduction reaction is extremely crucial but remains quite challenging. Here, a novel dual Z-scheme heterostructured polyoxometalate/activated carbon/TiO 2 (Co 4 PW 9 -C-TiO 2 ) ternary composite was constructed through a well-designed two-step hydrothermal method and first applied for efficient and stable N 2 fixation under mild conditions without any precious-metal cocatalysts and organic scavengers. The rational heterostructure brings a remarkable NH 3 production rate of 399.9 µmol·h −1 ·g cat -1 ·L -1 , which significantly exceeds the corresponding binary composites, and about 9-fold and 6-fold improvement over that of discrete TiO 2 and Co 4 PW 9 , respectively. Further comprehensive characterization and analysis revealed a reasonable dual Z-scheme charge transfer mechanism and demonstrated that such superior photocatalytic performance can be ascribed to the unique structure of the ternary composite, including the improved solar energy utilization efficiency, enhanced N 2 absorption ability, facilitated photoexcited charge carrier transport/separation rate and elevated redox ability. This work provides a reasonable construction strategy to further develop excellent catalysts for photocatalytic ammonia synthesis.