Superior activity of metal oxide biochar composite in hydrogen evolution under artificial solar irradiation: a promising alternative to conventional metal-based photocatalysts

A series of new hybrid photocatalysts based on Fe₃O₄ and standard biochar (biochar obtained by pyrolysis of Sewage Sludge (SS), Soft Wood Pellets (SWP), and Rice Husk (RH) at 700 °C) were successfully prepared using impregnation method. The biochar and resulting photocatalysts were characterized by wide range physicochemical techniques and investigated in hydrogen evolution under artificial solar irradiation. It can be noticed that when Fe₃O₄ is supported on SWP700 and RH700, presented a superior photocatalytic activity. Our best hybrid photocatalyst (Fe₃O₄-2.5%/RH700) achieved hydrogen production of 4162 μmol/g. Comprehensive electrochemical measurements reveal that the superior performance of Fe₃O₄- 2.5%/RH700 may be attributed to the lower band gap energy (2.27 eV), higher photocurrent density, and lower charge transport resistance. In addition, SS700 showed extraordinarily high activity (3845 μmol/g) in the conversion of deionized water to hydrogen, which is comparable to those of iron oxide photocatalysts supported on SWP700 and RH700. Based on the ultimate and proximate analyses, unique structure, high electric conductivity, dense aromatic structure, and exclusive mineral composition account for the enhanced activity exhibited by the SS700. These encouraging results showed that biochar derived from SS could be a low-cost, renewable, environmentally friendly and metal-free photocatalyst in hydrogen generation.