Sustainable ZnO-immobilized bentonite for sonophotocatalytic degradation of acridine orange: Synergistic effects of photocatalysis and acoustic cavitation

Advanced oxidation processes have attracted close attention for the removal of persistent organic pollutants from wastewater. Among these processes, sonophotocatalysis combining photocatalysis and ultrasonic irradiation enhances radical generation (HO . , O 2 -. ) and accelerates degradation kinetics of organic dyes. ZnO-based materials are promising photocatalysts; however, their practical application is limited by particle agglomeration and rapid charge recombination. Incorporating ZnO into clay matrices may improve catalyst stability, adsorption capacity, and catalytic performance.This work aimed to synthesize and evaluate a ZnO-Algerian Bentonite (ZnO/Alg-Bent) composite in the sonophotocatalytic elimination of toxic dye Acridine Orange (AO) under simultaneous application of a transducer bath-type sonicator (35 KHZ), US power = 70 W, and a UV-A (350 nm) lamp in the reaction time (0 – 90 min).The catalysts were synthesized by impregnation of ZnO nanoparticles, taking into consideration different mass ratios (W/W) ZnO/Bent (0.5/1; 0.75/1 and 1/1) onto natural Algerian bentonite, aiming to enhance adsorptive capacity and photocatalytic activity. FTIR, XRD, SEM-EDX, BET, TEM, and PL analyses were conducted to characterize the synthesized sonophotocatalysts. The degradation percent of dye was quantified by measuring the absorbance and the chemical oxygen demand (COD). Reaction kinetics were studied, and a possible degradation mechanism was proposed based on the literature and the obtained results.The ZnO/Alg-Bent (0.75/1) proves the best activity in the sonophotocatalysis process. It was found that the ZnO/Alg-Bent nanocomposite had better performance in the sonophotocatalytic degradation of AO dye (98%) as compared to the individual natural Bentonite (Alg-Bent) (12%) and ZnO (18%) because the ZnO/Alg-Bent material had dual functionality and a huge number of active sites. The values obtained by US only were (15%), UV only (18.5%), and US/UV (40%). The synergistic interaction between ultrasonic irradiation and photocatalysis significantly improves the generation of reactive oxygen species and reduces electron-hole recombination. The degradation kinetics followed a pseudo-first-order model, and the synergism between all processes was tested as a synergetic effect.The synthesized ZnO-Bentonite composite demonstrated excellent potential as a sustainable and efficient sonophotocatalyst for wastewater treatment applications. The combination of photocatalysis and ultrasonic cavitation enhanced the degradation performance toward acridine orange dye, suggesting that ZnO-bentonite materials could serve as a promising candidate for the removal of organic contaminants from polluted water.