The Effects of Coupling Photocatalysis and Sonolysis on Malonic Acid Solution

Sonophotocatalysis of malonic acid solution was carried out in an argon atmosphere. The coupling effects of the combination of photocatalysis and sonolysis were observed. The decomposition rate of malonic acid was improved; that is, the reaction rate for a combined system was higher than the sum of the rates of photocatalysis and sonolysis. Hydrogen peroxide formed from solvent (water) during sonolysis plays an important role for the synergistic effect. A small amount of succinic acid was detected by sonophotocatalysis. It is a characteristic product of the combined system and was not observed for each individual irradiation system. In this process, the carbon numbers of dicarboxylic acid increased from C = 3 (malonic acid) to C = 4 (succinic acid), namely increasing molecular weight or alkyl carbon chain elongation. Therefore, sonophotocatalysis has the potential to make a valuable contribution to organic reactions in water.