Surface modification of porous g-C₃N₄ materials using a waste product for enhanced photocatalytic performance under visible light

A facile and low-cost g-C₃N₄ surface modification approach using a biomass-derived liquid product is proposed in this work. Through the incorporation of renewable and sustainable bio-oil that is generated from a solar powered waste biomass pyrolysis, the surface functionality of a pristine g-C₃N₄ material is modified with functional groups that are of electron-withdrawing character, leading to the improvement of the photocatalytic hydrogen evolution rate for the modified C₃N₄ sample. At low reaction temperature (120 °C), the sample is modified through a cleavage of C-N bonds between three heptazine fragments and tertiary nitrogen, followed by the bonding of oxygenated functional groups. As the reaction temperature increases further to a higher temperature (180 °C), a partial de-aromatization of the triazine network in the C₃N₄ sample due to the intercalation of functional groups from this post-synthesis bio-oil modification is further observed. The remarkable hydrogen evolution rate of the modified C₃N₄ sample higher than that of pristine g-C₃N₄ is observed, attributed to the synergistic effects of the extended visible light response, better separation of the photogenerated charge carriers and the enlarged specific surface area.