CoAl₂O₄-g-C₃N₄ Nanocomposite Photocatalysts for Powerful Visible-Light-Driven Hydrogen Production

There is no doubt that the rate of hydrogen production via the water splitting reaction is profoundly affected to a remarkable degree based on the isolation of photogenerated electrons from holes. The precipitation of any cocatalysts on the substrate surfaces (including semiconductor materials) provides significant hindrance to such reincorporation. In this regard, a graphite-like structure in the form of mesoporous g-C₃N₄ formed in the presence of a template of mesoporous silica has been synthesized via the known combustion method. Hence, the resulting g-C₃N₄ nanosheets were decorated with varying amounts of mesoporous CoAl₂O₄ nanoparticles (1.0-4.0%). The efficiencies of the photocatalytic H₂ production by CoAl₂O₄-doped g-C₃N₄ nanocomposites were studied and compared with those of pure CoAl₂O₄ and g-C₃N₄. Visible light irradiation was carried out in the presence of glycerol as a scavenger. The results showed that the noticeable photocatalytic enhancement rate was due to the presence of CoAl₂O₄ nanoparticles distributed on the g-C₃N₄ surface. The 3.0% CoAl₂O₄-g-C₃N₄ nanocomposite had the optimum concentration. This photocatalyst showed extremely high photocatalytic activities that were up to 22 and 45 times greater than those of CoAl₂O₄ and g-C₃N₄, respectively. This photocatalyst also showed 5 times higher photocatalytic stability than that of CoAl₂O₄ or g-C₃N₄. The presence of CoAl₂O₄ nanoparticles as a cocatalyst increased both the efficiency and productivity of the CoAl₂O₄-g-C₃N₄ photocatalyst. This outcome was attributed to the mesostructures being efficient charge separation carriers with narrow band gaps and high surface areas, which were due to the presence of CoAl₂O₄.