Polyoxometalate (POM) boosting the light-harvesting ability of graphitic carbon nitride for efficient photocatalytic hydrogen production

Abstract

Phosphomolybdic acid (PMA) was used to achieve simultaneously P-doping and heterojunction construction of graphitic carbon nitride (gCN). P-gCN/PMA_x composites were obtained via post-thermal annealing of bulk gCN/PMA_x and characterized in detail using different techniques including XRD, XPS, SEM, and DRS. As an in situ hard templating agent and doping source, the loaded PMA helps to provide porous structured materials and reinforced electronic properties whereby many transitions are enhanced resulting in the improvement of light-harvesting. The electronic properties of gCN are improved strongly with the increased amount of PMA loaded, but the crystallinity becomes worse and the material becomes much more amorphous and disordered. The materials were investigated for the hydrogen evolution reaction (HER) showing the highest H₂ evolution performance of 625 μmol g⁻¹ h⁻¹ for the P-gCN/PMA_1.5 sample, which is almost 4 times higher than that of gCN with 167 μmol g⁻¹ h⁻¹. The P-gCN/PMA_1.5 sample was investigated under long-term irradiation and in recycling tests indicating the good photocatalytic stability of this material. The apparent quantum efficiency (AQE) exhibited by P-gCN/PMA_1.5 (0.7%) is 7 times higher than the AQE measured exhibited by gCN. This is evidence of the boosting effect exhibited by the loading of PMA onto the surface of gCN (0.1%). Thus, this study aims to offer a novel strategy to improve the activity of gCN by applying polyoxometalates as modifiers for better light harvesting.