Ultrasonic-assisted degradation of a triarylmethane dye using combined peroxydisulfate and MOF-2 catalyst: Synergistic effect and role of oxidative species

Combination of various advanced oxidations processes (AOPs) for effective water treatment is significant from a practical viewpoint. In this study, metal-organic framework-2 (MOF-2) nanomaterial (NM) was synthesized and then coupled with ultrasound (US) process in the presence of peroxydisulfate (S₂O₈ ²⁻) for Acid Blue 7 (AB7) degradation as a triarylmethane model dye. The XRD, FT-IR, SEM, TEM, BET, and DRS analyses were utilized to confirm the appropriate formation of nanoporous flake-like MOF-2 with a high specific surface area of 942.6 m²/g. The combined US/MOF-2/S₂O₈ ²⁻ process demonstrated the highest performance compared to the US and US/S₂O₈ ²⁻ processes in the same operational conditions. The mentioned processes obeyed pseudo-first-order kinetic and their synergistic effect for the AB7 degradation was determined according to the obtained apparent rate constants (k_app) as 63.4%. Radical quenching experiments using various scavengers revealed the oxidative species role for the AB7 treatment, which were generated during the sonolysis and sonolycatalytic process in the presence of the S₂O₈ ²⁻ based on the hot spot explanation. Consequently, the dominant reactive species were hydroxyl ([rad]OH), sulfate (SO₄[rad]^-), superoxide (O₂[rad]^-) and singlet oxygen (¹O₂[rad]) radicals. The GC–MS method was carried out to identify the main degradation intermediates, and five intermediates were detected.