Selective removal of nitrate via the synergistic effect of oxygen vacancies and plasmon-induced hot carriers

Photoreduction has been proven effective to remove NO3- from water, as NO3- has severely damaged water quality over decades. However, the typical photoreduction of NO3- usually requires sufficient hole scavengers (mostly formic acid) to produce strong reducing carboxyl radical (CO2 center dot-) species for the elementary conversion of NO3-. The excessive employment of hole scavengers increases the cost of water treatment, and further results in secondary chemical pollution. Here, a novel hole-scavenger-free efficient NO3- photoreduction route is developed by using a novel oxygen-deficient photocatalyst (R-P25@Ag/Cu nanoparticles). Graded oxygen vacancies are introduced into P25 nanocrystals via lithiothermic reduction approach, significantly promoting the photocatalytic capability. Subsequently, bimetal (Ag and Cu) nanoparticles are stepwise anchored onto the reduced P25 particles to improve the separation of the photogenerated carriers from the reduced P25 particles; more importantly, the plasmonic nanoparticles trigger the initial elementary step of NO3- reduction to center dot NO32-[E-0(NO3-/center dot NO32-) = -0.89 V versus SHE] with plasmon-induced hot carriers. Consequently, the optimized R-P25@Ag/Cu catalyst shows an outstanding NO3- removal performance with a high removal efficiency of 93% and a N-2 selectivity of 68% (mercury lamp, 180 min) by a synergistic effect without hole scavengers.