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

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 CH3 CHO 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 (CH2 OH)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.