Abstract
In order to examine the synergistic effects of combining sonolysis and photocatalysis, sonophotocatalysis of oxalic acid was performed. Oxalic acid can be decomposed by not only sonolysis but also by photocatalysis using TiO_2 powdered photocatalyst in an Ar atmosphere. As the products of sonophotocatalysis, carbon dioxide, carbon monoxide, and hydrogen were obtained in the gas phase. In the case of photocatalysis, CO was hardly detected. In the case of sonophotocatalysis, the yield of CO_2 increased about 14 times larger than that in the case of photocatalysis. The yield was twice larger than the sum of yields of photocatalysis and sonolysis. Thus, synergistic effect was observed in an Ar atmosphere. In this synergistic effect, hydrogen peroxide produced from solvent (H_2O) by sonolysis was thought to be played an important role. It is known that a photocatalytic reaction accelerates by addition of H_2O_2. Active oxygen species were produced in the process of decomposition of H_2O_2 by photocatalysis and they attacked to reactants. In the case of sonophotocatalysis, H_2O_2 also participated in the process of decomposition of oxalic acid. (Sonolysis of solvent) 2H_2O→H_2+H_2O_2 (Photocatalysis) 2H_2O_2→2H_2O+O_2 In order to confirm of role of H_2O_2, pre-irradiation of sonic waves was performed. The accumulation of H_2O_2 in the solution was observed during sonolysis and then the improvement of the rate of CO_2 production under sonophotocatalysis was confirmed.
