Exfoliated 2D Carbon Nitride Enables Efficient Visible-Light-Driven Nitrogen Reduction to Ammonium under Mild Conditions.

The carbon footprint and energy demand of the photocatalytic ammonia system underscore the need for high catalytic performance and efficient catalyst recovery while operating under mild conditions. This study demonstrates efficient ammonia synthesis using metal-free exfoliated 2D carbon nitride (GCN-T) immobilized over a 3D-printed support (GCN-T/3D) under Vis-LED irradiation (maximum wavelength at 435 nm). This sustainable photocatalyst improves nitrogen (N₂) activation, showcasing its potential for effective recovery and reuse in ammonia production. GCN-T and GCN-T/3D were evaluated under identical photocatalytic conditions to compare the powder catalyst with its immobilized counterpart. In the presence of glycerol as a hole scavenger, GCN-T produced 334 μmol. L^-1 of ammonium (NH₄⁺), while GCN-T/3D produced 357 μmol. L^-1 at the end of one hour of irradiation. Both systems achieved ammonia production rates approximately three times higher than those of other GCN-based catalysts reported in the literature, highlighting the potential of GCN-T-based photocatalysts for sustainable ammonia production. FTIR-ATR, photoluminescence, photoelectrochemical, and UV-Vis DRS analyses were conducted to characterize the prepared GCN materials. BET analysis showed that applying a second thermal treatment to GCN material increased the pore volume, thereby improving N₂ adsorption across the catalyst surface and photogenerated carrier separation. Remarkably, the 3D structure with 2D-immobilized catalyst increased the rate of NH₄⁺ generation and enabled at least 4 recyclable runs without loss of activity, unlike the powdered catalyst. The study also examined the effect of various scavengers on the NH₄⁺ generation rate. Additionally, experiments using different water matrices, including seawater, yielded moderate results within one hour, highlighting the real-world potential for sustainable ammonia production. This research introduces a novel photocatalytic approach that combines a 2D metal-free carbon nitride with a reusable 3D-printed framework for sustainable and decentralized ammonia synthesis.