Microporous Polyamine (PIM-EA-TB) Modified with Hydrated NiMoO4 Enhances the Photocatalytic Reduction of Nitrogen to Ammonia

Abstract The earth-abundant photocatalyst NiMoO4, readily produced by hydrothermal microwave synthesis, was tested for the light-driven production of ammonia in N2-purched water. In blue LED light (λ = 385 nm; 6 mW cm–2) and under pH-neutral conditions, ammonia is formed as detected via the indophenol blue method and confirmed by 15N isotope experiments. Thermal treatment lowers hydration and affects defect populations in NiMoO4 (detected by photoluminescence) as well as suppressing catalysis. Adding methanol as a sacrificial hole quencher increases the ammonia production rate. In exploratory experiments, a surface coating of the NiMoO4 photocatalyst with a molecularly rigid microporous polyamine (PIM-EA-TB with pKA ∼ 4) is shown to more than double the ammonia production rate. This is tentatively assigned here to a localized pH storage effect, allowing protons from photoanodic processes to be captured by the Tröger base in the polymer backbone and reused in the photocathodic ammonia production.