Near-Infrared-Responsive Photo-Driven Nitrogen Fixation Enabled by Oxygen Vacancies and Sulfur Doping in Black TiO_2–xS_y Nanoplatelets

Solar-driven nitrogen fixation is a promising clean and mild approach for ammonia synthesis beyond the conventional energy-intensive Haber–Bosch process. However, it is still challenging to design highly active, stable, and low-cost photocatalysts for activating inert N2 molecules. Herein, we report the synthesis of anatase-phase black TiO2–xSy nanoplatelets enriched with abundant oxygen vacancies and sulfur anion dopants (VO-S-rich TiO2–xSy) by ion exchange method at gentle conditions. The VO-S-rich TiO2–xSy nanoplatelets display a narrowed bandgap of 1.18 eV and much stronger light absorption that extends to the near-infrared (NIR) region. The co-presence of oxygen vacancies and sulfur dopants facilitates the adsorption of N2 molecules, promoting the reaction rate of N2 photofixation. Theoretical calculations reveal the synergistic effect of oxygen vacancies and sulfur dopants on visible–NIR light adsorption and photoexcited carrier transfer/separation. The VO-S-rich TiO2–xSy exhibits improved ammonia yield rates of 114.1 μmol g–1 h–1 under full-spectrum irradiation and 86.2 μmol g–1 h–1 under visible–NIR irradiation, respectively. Notably, even under only NIR irradiation (800–1100 nm), the VO-S-rich TiO2–xSy can still deliver an ammonia yield rate of 14.1 μmol g–1 h–1. This study presents the great potential to regulate the activity of photocatalysts by rationally engineering the defect sites and dopant species for room-temperature N2 reduction.