Valorization of Nitrate and Carbon Dioxide into Ammonia and Urea under Visible Light

Abstract The energy-intensive manufacture of nitrogen-based fertilizers such as ammonia (NH3) and urea consumes a significant fraction of the global energy supply. At the same time, widespread accumulation of excess nitrate (NO3–) from agricultural runoff poses serious risks to ecological and human health. These escalating environmental and economic costs highlight a pressing need for more sustainable fertilizer production. Photocatalytic conversion of waste NO3– into NH3 underscores a growing interest in circular low-energy alternatives to the traditional Haber–Bosch process. For example, as the most widely applied nitrogen fertilizer, analogous routes to urea remain critically underdeveloped. We demonstrate the valorization of two abundant and harmful pollutants, nitrate and carbon dioxide (CO2) into urea over a mixture of commercially available TiO2 and CuO photocatalysts. The ability to drive this complex transformation under ambient temperature and pressure using solar energy highlights its potential to lower the energy demand of conventional fertilizer production. These results provide a fundamental platform from which to envision a more sustainable, visible light-driven ammonia/urea synthesis.