Kinetic Mechanisms of the Photocatalytic Generation of Hydrogen from Formic Acid Using Metal–Ceramic Composites under Visible-Light Irradiation

The photocatalytic generation of hydrogen from aqueous solutions of formic acid under irradiation with visible light with the use of tantalum-containing metal–ceramic composites based on silicon nitride was investigated depending on the substrate concentration and the pH of suspension in the absence and with the addition of hydrogen peroxide. These compounds were obtained by self-propagating high temperature synthesis (SHS) using the combustion of ferrosilicon aluminum (FSA) and a mixture of silicon and aluminum powders with tantalum additives in an atmosphere of nitrogen. It was found that the dependence of the rate of photocatalytic hydrogen production on the concentration of formic acid without hydrogen peroxide was described by the Langmuir–Hinshelwood mechanism. In the presence of hydrogen peroxide, the rate of the photocatalytic process sharply increased with the concentration of formic acid. The highest rate of hydrogen evolution from formic acid was observed on an iron-containing composite synthesized from FSA without the addition of hydrogen peroxide, and it amounted to 4.55 µmol/min.