Process Intensification Sonocatalytic Degradation of Malachite Green Wastewater over Hydrothermally Engineered M-ZLT@Co₃O₄ Nanocatalyst: Structure–Activity Relationships, Radical-Mediated Mechanism and Degradation Pathways

This study reports the sonocatalytic degradation of malachite green (MG) in media using synthesized Co₃O₄ nanoparticles and a CTAB-modified zeolite supported Co₃O₄ hybrid nanocatalyst (M-ZLT@Co₃O₄). The catalysts were characterized by XRD, FT-IR, SEM-EDX, TEM, XRF, N₂ adsorption–desorption, BET, and BJH analyses, verifying crystalline Co₃O₄ formation, successful immobilization on the modified zeolite support, porous architecture, morphology and elemental distribution. Under optimized conditions of 1 g L⁻¹ catalyst dosage, 20 mg L⁻¹ MG concentration, natural pH, and 300 W L⁻¹ ultrasonic power, M-ZLT@Co₃O₄ achieved 99.31% ± 0.45% degradation within 120 min. Decreasing the MG concentration to 5 mg L⁻¹ increased the efficiency to 99.96% ± 0.64%, confirming high activity at low pollutant loading. The degradation followed pseudo-first-order kinetics, with k_app values of 0.0042–0.0595 min⁻¹ depending on catalyst dosage, 0.0046–0.0667 min⁻¹ for initial MG concentration, and 0.0117–0.0620 min⁻¹ under pH conditions. Water matrix inhibition followed distilled water (99.31%) > tap water (96.08%) > river water (88.84%) > lake water (86.90%), whereas higher ultrasonic power increased degradation from 91.98% at 200 W L⁻¹ to 99.90% at 500 W L⁻¹. Dye degradation followed MG (99.31%) > CR (95.78%) > BY2 (92.15%) > MV (90.24%) > AO7 (85.62%) > RB19 (82.49%). Comparative tests demonstrated performance for US/M-ZLT@Co₃O₄ (99.31%) compared with US/Co₃O₄ nanoparticles (78.48%), US/ZLT (72.86%), and US/MG alone (35.71%). The best activity was obtained at 0.8–2 g L⁻¹ catalyst dosage and 5–20 mg L⁻¹ MG concentration, while reusability tests showed a decrease from 99.31% to 78.82% after six cycles, indicating promising stability.