Dual active sites of copper and Ti3+/oxygen vacancies in MOF-derived mesoporous titanium dioxide for promoting photocatalytic nitrate reduction to ammonia by accelerating active hydrogen generation and NOx hydrogenation.

For enhanced photocatalytic nitrate reduction (NO3RR), an efficient catalyst must simultaneously possess strong NO3- activation capability, effective deep reduction of nitrogen oxide intermediates, and sufficient active hydrogen (*H) supply. In this work, a mesoporous TiO2 photocatalyst containing dual active sites of Cu and Ti3+/oxygen vacancies (OVs) was fabricated via MOF-derived TiO2 synthesis followed by a photoreduction strategy. Mechanistic investigations revealed that Cu sites facilitate NO₃- adsorption and activation while promoting the generation of *H. Ti3+/OVs sites favor the adsorption and deep reduction of key intermediates, including (*NO2, *NO, *NOH, etc.), which are subsequently hydrogenated stepwise by *H to produce NH4+. Consequently, the synergistic coupling of Cu and Ti3+/OVs establishes an efficient "hydrogen generation-hydrogen transfer-deep reduction" pathway (*NO3 → *NO2 → *NO→*NOH → *NHOH→*NH2OH → *NH2 → *NH4+). After 2 h of visible-light irradiation, a NO3- removal efficiency of 97.2% was achieved, accompanied by an NH4+ yield rate of 3.62 ± 0.03 mmol g cat-1 h-1 and an NH4+ selectivity of 63.44%.Overall, this work provides valuable insights for the development of efficient and sustainable nitrogen-cycle technologies.