Effects of an N-hydroxyimide mediator on the visible-light-induced oxidation of toluene over the bismuth vanadate photocatalyst

•NHPI and NHSI are oxidized into radicals by the photogenerated holes in BiVO4.•NHPI oxidation into radicals is easier than that of NHSI.•SINO interaction with BiVO4 accelerates recombination with photogenerated electrons.•The NHPI/PINO mediator is thus superior to NHSI/SINO in photocatalytic oxidation.•A mediator requires appropriate interactions with BiVO4 to exhibit high activity.