Kinetics of permanganate–sulfuric acid redox reaction with cetyltrimethylammonium bromide

Abstract

The permanganate–H₂SO₄ redox reaction, useful in oxidative treatments under aqueous conditions, was studied spectrophotometrically in the absence and presence of cetyltrimethylammonium bromide (CTAB). The decolorization reactions were influenced by the [MnO₄⁻], [H₂SO₄], and temperature. Permanganate reduction follows first-, and complex–order kinetics with permanganate, and H₂SO₄ concentrations, respectively. The reduction of permanganate (Mn(VII)) proceeds through a complex formation between MnO₄⁻ and H₂SO₄. The characteristic absorption peaks for MnO₄²⁻ (λ_max = 439 and 606 nm), MnO₄³⁻ (λ_max = 667 nm), and MnO₂ (λ_max = 400–418 nm) were not appeared during the redox reaction. The KMnO₄ degradation efficiency remains unaffected with sodium pyrophosphate and sodium fluoride. The results of this study demonstrated the formation of Mn(II) as the stable product in acidic reaction media. The degradation efficiency increases drastically from 15 to 100% with 2.0 × 10⁻⁴ to 16.0 × 10⁻⁴ mol/L CTAB concentration under sub-, and post-micellar reaction conditions, respectively. The thermodynamic parameters (activation energy = 98.8 and 43.2 kJ/mol), activation of enthalpy (96.3, and 39.0 kJ/mol), activation of entropy (16.2 and −149.5 J/K/mol), free energy of activation (93.1 and 83.5 kJ/mol) were calculated without and with CTAB, respectively. Hence, CTAB can be exploited for its multifunctional applications, and specifically for the catalytic role in the permanganate-assisted redox reactions in future.