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

Abstract

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.