A bioinspired floatable system with a 3D sandwich-type triphase interface for highly efficient nitrogen fixation

Abstract

Photocatalytic nitrogen fixation is an ecologically friendly technique for synthesizing ammonia, and a key factor in the improvement of efficiency is the effective mass transfer of nitrogen and water simultaneously. Here, by anchoring BiVO₄ on PDMS-modified Janus melamine sponge (BiVO₄@PDMS@MS), we have prepared a floatable system that forms a 3D sandwich-type triphase reaction interface in the air phase, allowing nitrogen and water to reach the reaction active sites from separate diffusion pathways in different directions, effectively ensuring mass transfer of nitrogen and water simultaneously so that the performance improvement of photocatalytic nitrogen fixation can be guaranteed in kinetics. In Janus BiVO₄@PDMS@MS, BiVO₄ disperses uniformly on each surface of MS micropores, where many microreactors form, leading to a large triphase interface area that exposes a considerable number of active sites. In addition, the triphase interface is constructed above the water surface, and sunlight can irradiate the reaction interface directly and cause multiple scattering in the macropores of MS, enhancing light utilization. BiVO₄@PDMS@MS demonstrated an ammonia synthesis rate of 624.87 μmol g_cat⁻¹ h⁻¹ with high selectivity and stability, which is approximately 1.67 times and 353 times higher than that of the related diphase system (BiVO₄@MS) and the powder system (BiVO₄), respectively. We employed the triphase interface that forms in the gas phase for photocatalytic nitrogen fixation for the first time, effectively ensuring nitrogen and water mass transfer to improve photoactivity and selectivity, offering a promising option in optimizing highly efficient mass transfer for gas-consuming reactions.