Hydrogen Production from Oxalic Acid in the Presence of Tantalum-containing Composites under Ultraviolet and Visible Light Irradiation

The photocatalytic activity of silicon nitride-based iron-containing composites synthesized by the combustion of ferrosilicon aluminum (FSA) with tantalum additives (5, 10, 15 wt % Ta) in H2 production from aqueous solutions of H2C2O4 under UV and visible light irradiation is studied. Using the X-ray diffraction method, it is found that the main phases of the ceramic matrix of the composites are β-Si3N4 and α-Fe; in addition, a TaON semiconductor phase is detected. The morphological features of the samples are studied by electron microscopy. The composite synthesized from FSA with 10% Ta exhibits the highest photocatalytic activity, which is attributed to the optimum composite structure of Si3N4–TaON–Fe. The mechanisms of H2C2O4 adsorption and photocatalytic H2 evolution from H2C2O4 in the presence of Ta-containing composites synthesized from FSA and a mixture of elemental powders (silicon, aluminum) with 10% Ta are studied with and without the addition of H2O2. It is found that the dependence of the photocatalytic H2 evolution on the H2C2O4 concentration can be described in terms of the Langmuir–Hinshelwood model. The highest rate of H2 evolution from H2C2O4 (6.34 μmol min−1) is achieved in the case of adding H2O2 in the presence of the iron-containing composite; this fact is attributed to the occurrence of both heterogeneous and homogeneous photocatalysis processes.