Degradation of surfactant SLS in water by singlet oxygen generated by the reaction between hydrogen peroxide and hypochlorite

The synergistic aqueous combination of hydrogen peroxide and hypochlorite which results in the formation of the highly oxidizing intermediate species singlet oxygen (¹O₂) was effective in the degradation of the anionic surfactant sodium lauryl sulphate (SLS) in water. The process was effective in the near neutral pH range of 6–8, and up to initial SLS concentration values of 10 mg/L. For initial [SLS] = 5 or 10 mg/L, pH = 6–8, and excess molar ratio ([H₂O₂] + [NaClO])/[SLS] = 5:1 it was possible to achieve a final concentration of [SLS] < 0.5 mg/L (95% degradation) in t = 60 min at 25 °C in a batch reaction. By comparison, the same reaction with either of the separate oxidants (only H₂O₂ or only NaClO) at the same excess molar ratio oxidant/SLS of 5:1 gave a maximum of about 50% degradation of the SLS over the same 60 min reaction time. An empirical rate equation was derived: −d[SLS]/dt = k[SLS]^0.8([H₂O₂] + [NaClO])^0.3, with k = 4.8 (±1.0) × 10^–1 L/mol s at 25 °C.