Visible light activated photocatalytic behaviour of Eu (III) modified g-C3N4 for CO2 reduction and H2 evolution

The high-efficiency photocatalytic CO2 reduction and H2 evaluation performance are quite attractive and desired for clean energy utilization and environmental pollution alleviation. Herein, the novel visible-light activated Eu (III) doped g-C3N4 composites with different contents (2%, 4%, 6%, 8% and 10%) were successfully synthesized for the first time. The Eu (III) species acted as the Lewis acids could trap photoexcited electrons with superior ability. The photocatalytic activity of Eu/g-C3N4 catalysts exhibited superior performance and stability in both CO2 photoreduction and H2 production with the presence of water under the visible light irradiation. A maximum CH4 and H2 yields of 22.8 μmol/(h·g-cat) and 78.1 μmol/(h·g-cat), respectively, had been obtained on 8% Eu/g-C3N4 catalyst, which was about 2.2 and 7.3 times as high as the pure g-C3N4. In situ FTIR analysis discloses that HCOOH is a major intermediate during the CO2 conversion progress. The Mott–Schottky method also indicated massive photogenetated carriers existed in Eu/g-C3N4 catalysts that in favor of the CO2 conversion to CH4. The origin of such remarkable photocatalytic activities could be explained as follows: (i) Eu3+ species captured photogenerated electrons and inhibited the recombination of photogenerated electron-hole pairs; (ii) the doped Eu3+ narrowed the band gap and enhanced the visible-light absorption capacity; (iii) the introduction Eu3+ increased the activated specific surface area. This work may provide meaningful guidelines for rare earth mental application on improving the performance of photocatalyst.