Regulating the Selectivity of Nitrate Photoreduction for Purification or Ammonia Production by Cooperating Oxidative Half-Reactions

Abstract

The removal and conversion of nitrate (NO₃^–) from wastewater has become an important environmental and health topic. The NO₃^– can be reduced to nontoxic nitrogen (N₂) for environmental remediation or ammonia (NH₃) for recovery, in which the tailoring of the selectivity is greatly challenging. Here, by construction of the CuO_x@TiO₂ photocatalyst, the NO₃^– conversion efficiency is enhanced to ∼100%. Moreover, the precise regulation of selectivity to NH₃ (∼100%) or N₂ (92.67%) is accomplished by the synergy of cooperative redox reactions. It is identified that the selectivity of the NO₃^– photoreduction is determined by the combination of different oxidative reactions. The key roles of intermediates and reactive radicals are revealed by comprehensive in situ characterizations, providing direct evidence for the regulated selectivity of the NO₃^– photoreduction. Different active radicals are produced by the interaction of oxidative reactants and light-generated holes. Specifically, the introduction of CH₃CHO as the oxidative reactant results in the generation of formate radicals, which drives selective NO₃^– reduction into N₂ for its remediation. The alkyl radicals, contributed to by the (CH₂OH)₂ oxidation, facilitate the deep reduction of NO₃^– to NH₃ for its upcycling. This work provides a technological basis for radical-directed NO₃^– reduction for its purification and resource recovery.