DFT Study on the mechanism and kinetics of the gas-phase reaction between methylene blue and OH radicals
Abstract
Methylene blue ( MB ) is a representative aromatic heterocyclic dye extensively employed in industrial applications, particularly in the dyeing of paper, cotton, wool, silk, and related textiles. In this work, the mechanisms and kinetics governing the gas-phase degradation of MB by hydroxyl radicals (HO · ) were elucidated through quantum chemical calculations. The results demonstrated that, at 298.15 K, MB predominantly underwent degradation via a radical adduct formation mechanism involving HO · addition at the C4 position. The overall rate constants for the first and second steps were calculated to be 3.24 × 10 10 and 1.48 × 10 12 M - 1 s - 1 , respectively, leading to three major products. The overall degradation rate exhibited only a slight variation with increasing temperature from 253 to 323 K, suggesting that temperature exerts a limited effect on the oxidative removal efficiency of MB under environmentally relevant conditions.