Ultrasound-assisted MnO2 catalyzed homolysis of peracetic acid for phenol degradation: The assessment of process chemistry and kinetics

Abstract

The combination of peracetic acid (PAA) and heterogeneous catalyst (MnO2) was used for the degradation of phenol in an aqueous solution in the presence of ultrasound irradiation (US). As a relevant source of free radicals (e.g. OH), peracetic acid was comprehensively studied by means of electron spin resonance (ESR) spin trapping (ST) techniques with the subsequent identification of free radicals by simulation based fitting (SBF) technique. The radical reaction mechanism, where hydroxyl radical was a primary product of OO bond rupture of PAA, was established taking into account radical reactions, occurring during sonolysis. The potential barriers and the reaction heat were determined by basic density function theory (DFT) calculations to estimate whether the proposed radical pathway is possible. The assessment and optimization of the process parameters for MnO2/PAA/US system to eliminate phenol was accomplished with experimental design. Fractional factorial design (FFD) was executed to relate the removal efficiency of phenol with process parameters such as catalyst and PAA concentrations, the presence of ultrasound and the reaction time. The comparative kinetic study of silent and ultrasound-assisted processes revealed the significant difference between these two processes that was mainly attributed to the complex radical system formed during PAA homolysis.