Photochemical conversion of nitrate to ammonium ions by a newly developed photo-reductive titanium dioxide catalyst: implications on nitrogen recovery

Abstract

Global nitrate contamination in source water poses a threat to both natural ecosystems and public health. This study developed photo-reductive titanium dioxide (TiO₂) nanoparticles with surface-grafted diethylene glycol (DEG) ligands to photochemically degrade nitrate under medium-pressure UV irradiation and convert it to the desirable end product ammonium. The new catalyst was synthesized via a sustainable and non-harsh synthesis approach. Nitrate was efficiently removed at a rate 6 times faster than a standard commercial photo-oxidative photocatalyst, and the formation of the intermediate by-product nitrite was minimized. The ammonium selectivity highly depended on the synthesis temperature of the catalyst. The synthesis temperature was examined from 190 °C to 230 °C and revealed that the higher temperature of 230 °C enhanced nitrate reduction and ammonia production, likely by means of increasing the crystallinity of the catalyst. Ammonium can be harvested at approximately 70% of the initial nitrate concentration. This study highlights the efficacy of photo-reductive TiO₂ to remove nitrate while simultaneously producing ammonium ions, providing a promising technology for denitrification and nitrogen resource recovery.