Dynamic control of the three-phase boundary in hydrogel assisted TiO₂-Graphdiyne photocatalysts for Ammonia production

Abstract

Producing NH3 via photocatalytic N2 reduction requires an ideal three-phase boundary (TPB) among N2 (gas), H2O (liquid), and a catalyst (solid). A promising strategy for developing TPB system involves photocatalyst passivation with temperature-responsive hydrogels that reversibly switch hydrophilic–hydrophobic characteristics. In this study, a self-controlling TPB system that combines a TiO2/graphdiyne photocatalyst with poly(N-isopropylacrylamide) (TiO2/GDY@PNIPAm) is explored. TiO2/GDY offers excellent solar absorption characteristics, efficient charge separation at the heterojunction, and abundant active sites for N2 reduction. Owing to a unique photothermal effect, TiO2/GDY generates a local temperature increase (39.5 °C) under irradiation. The temperature-responsive PNIPAm, utilized as an adaptive porous framework, enables dynamic regulation of interfacial wettability and gas transport within the TPB microenvironment through its hydrophilic–hydrophobic transition, thereby promoting selective N2 transport while inhibiting H2O transport. Under solar-light irradiation, the room temperature NH3 production rate of TiO2/GDY@PNIPAm (59.5 μmol/gh) exceeds that of TiO2 (0.46 μmol/gh). These findings provide valuable insights into photocatalyst design and local environment optimization using stimuli-responsive hydrogels toward green NH3 production.