Influence of sample positioning and solution volume on distinguishing sonolysis from piezocatalysis in ultrasonic dye degradation.

Piezocatalysis has emerged as an optimistic mechanically assisted catalytic process for the degradation of organic pollutants, in which ultrasonic waves stimulate the piezoelectric material and activate its catalytic activity. Laboratory-scale piezocatalytic investigations commonly utilize an ultrasonicator, which produces a spatially varying acoustic field, while sonolysis, contributes to variations in degradation efficiency. The radicals produced through sonolysis also contribute to pollutant degradation, thereby introducing uncertainty in the assessment of the piezocatalyst's apparent piezocatalytic activity. The present study investigates the contribution of sonolysis in the piezocatalysis process by examining degradation at various locations within the ultrasonicator. The outcomes of the study demonstrate that there is inconsistency in degradation with spatial positioning. Furthermore, a critical minimum pollutant volume was identified above which consistent results were obtained for sonolytic dye degradation. The findings from the investigations strongly recommend mandatory steps of optimizing sample positioning and pollutant volume prior to any piezocatalytic investigation that need to be followed to ensure repeatability and isolate sonolysis contributions.