Highly-efficient photocatalytic hydrogen peroxide production over polyoxometalates covalently immobilized onto titanium dioxide

The polyoxometalate (POMs) cluster of [PW9O34]9− (PW9) have been covalently immobilized onto anatase TiO2 surface to prepare the catalyst of TiO2-PW9. The photocatalytic hydrogen peroxide (H2O2) production has been carried out over TiO2-PW9 under full wavelength irradiation in the presence of 5 vol.% benzyl alcohol as electron donor. The catalytic results reveal that the amounts of H2O2 can reach 38.2, 6.6, 22.8 and 18.7 μmol within 2 h for TiO2-PW9, Na-PW9, TiO2-PW9-PM (physically mixed) and bare TiO2, respectively. The p-benzoquinone (PBQ) and superoxide dismutase (SOD) quenching experiments, the electron spin resonance (ESR) signal and quantitative experiment of superoxide radicals (O2−) results reveal that the negative shifts of the conduction band (CB) level from TiO2 to TiO2-PW9 (from −0.18 V to −0.36 V vs. NHE) can enhance the single-electron reduction of O2 to O2− and further promote the sequential two-step single-electron O2 reduction reaction to H2O2. In addition, the recycle experiment results reveal that the heterogeneous TiO2-PW9 is catalytic stable.