Exceptional visible-light activities of g-C3N4 nanosheets dependent on the unexpected synergistic effects of prolonging charge lifetime and catalyzing H-2 evolution with H2O

It is highly desired to develop an efficient g-C3N4-based photocatalyst for energy production under visible-light irradiation. Herein, it is shown that the optimized g-C3N4 nanosheet-based photocatalyst could exhibit exceptional photocatalytic activities for H-2 evolution under visible-light irradiation, by similar to 14-time improvement compared to that of bare g-C3N4 one. It is confirmed by the methods of transient-state surface photovoltage responses, transient-state PL spectra and electrochemical measurements that the exceptional photocatalytic activities are attributed to the unexpected synergistic effects of prolonging the charge lifetime and catalyzing H-2 evolution by coupling nanocrystalline anatase TiO2 as a proper-energy platform to accept visible-light-excited electrons from g-C3N4 and by decorating a nano-sized noble metal as the co-catalyst respectively. Among three decorated noble metals (Ag, Au and Pt), to prolong the photogenerated charge lifetime is much meaningful for the used noble metal cocatalyst with weak catalytic function like Ag in H-2 evolution. Using nanocrystalline SnO2 to replace TiO2 is also applicable for the synergistic effect. Moreover, it is clarified by the designed experiment on photocatalytic CO2 conversion to CD4 in the presence of methanol in D2O that the resource of evolved H-2 is mainly from the adsorbed H2O other than the disassociated H+ from methanol.