Significantly enhanced visible-light-driven photocatalysis in Ag0.94Nd0.02NbO3 nanoparticles via oxygen vacancy engineering

A series of Ag 0.94 Nd 0.02 NbO 3 photocatalysts with tunable surface oxygen vacancy (OV) concentrations ranging from 9% to 46% were successfully synthesized via hydrothermal synthesis followed by air annealing. The band gap ( E g ) narrows from 2.91 to 2.75 eV with an enhancement in light harvesting as the annealing temperature is reduced. Mechanistic studies on photogenerated charge transfer, separation, and recombination reveal that the photocatalytic activity for rhodamine B (RhB) degradation is governed by charge recombination and separation efficiency rather than band-gap narrowing. Moreover, charge recombination depends non-monotonically on OV concentration: it is significantly suppressed at moderate OV concentrations (9–29%) due to electron trapping by OV-induced defect states, thereby enhancing the charge separation efficiency; at higher levels (46%), these defect states become charge recombination centers, severely impairing photocatalytic performance. The optimal photocatalyst A600 (29% OV concentration, E g  = 2.85 eV) degrades over 98% of both concentrated and diluted RhB solutions within 30 min with reaction rate constants up to 0.475 min −1 , demonstrating excellent visible-light-driven photocatalytic activity that outperforms comparable photocatalysts. These findings indicate that optimizing OV concentration to suppress charge recombination and promote charge separation efficiency is a critical factor in developing high-performance visible-light photocatalysts.