Insights into the role of singlet oxygen in the photocatalytic hydrogen peroxide production over polyoxometalates-derived metal oxides incorporated into graphitic carbon nitride framework

To develop a new strategy of enhancing the photoinduced holes (h(+)) consumption to promote the photoinduced electrons (e(-)) utilization for O-2 reduction to H2O2 and maintaining the chemical stability of g-C3N4-based catalysts, the hybrid catalyst of g-C3N4-CoW0 has been prepared through the calcination of the graphitic carbon nitride (g-C3N4) precursor of 3-amino 1, 2, 4-triazole (3-AT) and the polyoxometalates (POMs) precursor of (NH4)(8)Co2W12O42 (NH4-CO2W12). The hybrid catalyst of g-C3N4-CoW0 with well-defined and stable structure exhibits efficient catalytic performance (9.7 timolh4) for photocatalytic H2O2 production in the absence of organic electron donor under visible light. The value of electrons transfer during the oxygen reduction reaction (ORR) process obtained from the Koutecky-Levich plot for g-C3N4-CoWO (n = 1.95) is higher than that for gC(3)N(4) (n = 1.18), suggesting that the CoWO incorporated into g-C3N4 framework can generate more e- for 02 reduction. The superoxide radicals CO2-) quantitative and scavenger experiments combined with the electron spin resonance (ESR) results reveal that the negative shifts of the conduction band (CB) level from g-C3N4 to gC(3)N(4)-CoW0 can enhance the single-electron reduction of O-2 to 'O-2(-). The h+ and 102 scavenger experiments results combined with the ESR results demonstrate that the CoWO incorporated into g-C3N4 framework can promote the oxidation of 'O-2- to 'O-2 by h+. The 102 quantitative experiments results indicate that the 'O-2 can proceed two-electron reduction to H2O2. The enhanced h(+) consumption and the 102 transferred from 'O-2(-) can promote the photocatalytic H2O2 production over g-C3N4-CoWO. In addition, the recycle experiment results reveal that the heterogeneous g-C3N4-CoWO is catalytic stable.