Enhanced Azo Dye Removal through Sequential Ultrasound-Assisted-Treatment and Photocatalysis Using CdZnS

The treatment of high-concentration azo dyes remains challenging due to the inherent limitations of conventional single-mode approaches. Here, we propose an integrated strategy that sequentially combines ultrasound-assisted adsorption with photocatalysis using CdZnS solid solutions to efficiently and rapidly remove high-concentration azo dyes. CdZnS exhibits high adsorption capacity and exceptional photocatalytic activity, enabling initial dye capture and enrichment, followed by significantly enhanced photocatalytic degradation. The adsorption of Congo Red (CR) on CdZnS solid solutions follows the Freundlich and pseudo-second-order models, demonstrating a multilayer adsorption behavior involving physical and chemical interactions. Ultrasound assistance during the first stage not only significantly reduces equilibrium time, but also results in enhanced negative charges in CdZnS that extend to the subsequent photocatalysis stage. This charge enhancement substantially improves CR photodegradation performance, establishing synergistic interactions between ultrasonic treatment and photodegradation. The system demonstrates excellent performance in treating both concentrated single dyes and complex dye mixtures, maintaining high efficiency over multiple treatment cycles. This integrated approach provides new insights for developing more effective technologies for dye degradation and practical wastewater treatment applications.