Sulfate-Mediated Reactive Oxygen Species for Efficient Photocatalytic Nitrogen Fixation over TiO2

Abstract

Direct photocatalytic nitrogen fixation from air under mild conditions (compared to the harsh conditions of the Haber-Bosch process) remains a fundamental challenge due to the inertness of N≡N bonds and the lack of controllable activation pathways. Here, we report a sulfate-modified TiO2 catalyst (S-TiO2) that enables efficient ammonia synthesis via a temperature-regulated photocatalytic strategy under simulated air. An ammonia production rate of 217.24 μmol h-1 g-1cat. is achieved at 200°C, significantly outperforming pristine TiO2. Mechanistic investigations reveal an oxidation-reduction sequential pathway, in which N2 is first activated and oxidized to NOx intermediates by sulfate-mediated reactive oxygen species, followed by stepwise hydrogenation to NH3 via proton-coupled electron transfer. In situ FTIR spectroscopy and online mass spectrometry consistently support the involvement of NOx intermediates in the reaction process. This work highlights the critical role of sulfatemediated reactive oxygen species in regulating nitrogen activation and establishes an oxidation-first, reduction-later mechanism, offering new insights into the design of solar-driven sustainable nitrogen fixation systems.