Sonocatalytic degradation of Acid Red 1 by sonochemically synthesized zinc sulfide-titanium dioxide nanotubes: Optimization, kinetics and thermodynamics studies

Abstract

The present study reports sonocatalytic activity of zinc sulfide-titanium dioxide nanotubes (ZnS-TNTs) in degradation of Acid Red 1 (AR1). Co-precipitation, hydrothermal and sonochemical methods were used to synthesize ZnS, TNTs and ZnS-TNTs, respectively. The physicochemical characteristics of the synthesized powders were determined by XRD, FE-SEM, TEM, SAED, EDX, UV–Vis, BET and BJH techniques. The effect of the operational parameters on the sonocatalytic process was evaluated and optimized using the response surface methodology. Under optimal conditions (initial AR1 concentration = 15 mg L−1, ZnS-TNTs amount = 1 g L−1, pH = 6, ultrasonic power = 75 W and time = 20 min), more than 75% of the dye molecules were degraded. The Langmuir-Hinshelwood's kinetics model was well obeyed by the involved process (kap = 0.0631 min−1). The thermodynamics of the process was studied based on the transition state theory and it was found that the sonocatalytic process was endothermic and nonspontaneous. Ultimately, the main products of AR1 degradation were identified by the GC-MS technique.