Influence of low level of non-metal doping on g-C3N4 performance for H2 production from water under solar light irradiation

In this paper, a facile one step synthesis method for the preparation of C-, B-, P- and S-doped g-C3N4 by incorporation of small concentration of doping element precursor into urea during thermal polycondensation is reported leading to much lower doping levels than the ones usually reported. The as-obtained doped g-C3N4 photocatalytic materials are deeply characterized in terms of structural, morphological, surface and optical properties. Doping yields beneficial surface morphology modulation along with improved optical, electronic and photocatalytic properties. In particular, C-doped and S-doped g-C3N4 show, after deposition of gold nanoparticles (<1 wt%), enhanced photocatalytic performance (at least twice as high as the undoped photocatalyst, to achieve ca. 610 μmol/h/g) for the production of H2 by water splitting under solar light in the presence of low content (1 vol%) of triethanolamine (TEOA) as sacrificial agent. The most remarkable activity results from the incorporation of traces of S dopant, mainly inserted into interplanar hollow cavities. The enhanced activity is attributed to a combination of high surface area, location of the S dopant and small size of the co-catalyst NPs, which induces enhanced visible light harvesting, enhanced charge carrier separation and enhanced proton recombination. This work highlights the benefits of the optimized low-level doping strategy to overcome the main limitations of g–C3N4–based photocatalysts.