Single-atom molybdenum immobilized on photoactive carbon nitride as efficient photocatalysts for ambient nitrogen fixation in pure water

A series of Mo single-atom catalysts were prepared by calcining a low-cost primary material of urea with various amounts of Na 2 MoO 4 ·2H 2 O. Isolated Mo centers are immobilized on in situ formed polymeric carbon nitride via coordinating with two N donors to form two-coordinated MoN 2 species. The low-coordinated Mo centers can serve as active sites for N 2 chemisorption and activation, achieving high photocatalytic activity for NH 3 evolution with a rate of 50.9 μmol g cat −1 h −1 in pure water. In the presence of ethanol as the electron scavenger, the NH 3 evolution rate can reach 830 μmol g cat −1 h −1 , and the catalyst shows a quantum efficiency of 0.70% at 400 nm. This is the first single-atom catalyst that can drive photocatalytic N 2 fixation in pure water with comparable performance to recent reports for photocatalytic N 2 reduction. Experimental investigations and density functional theory calculations demonstrate that the coordinatively unsaturated metal center in the single-atom catalysts can strongly adsorb N 2 via an end-on configuration to elongate the N&z.tbd;N bond from 1.11 Å to 1.15 Å, and thus photoexcited electrons can transfer to the weakened N&z.tbd;N bond for efficient nitrogen fixation under ambient conditions. These findings provide new insight for solar-driven N 2 fixation by atomically dispersing low-coordination metal centers on photoactive supports. A series of single-atom Mo-PCN photocatalysts were facilely and large-scale prepared. The two-coordinated Mo center can serve as active site for N 2 chemisorption and activation, first achieving solar-driven N 2 reduction in pure water under ambient conditions.