Kinetic and mechanistic investigations of the degradation of propranolol in heat activated persulfate process

Abstract

This study investigated the heat activated persulfate (heat/PS) process in the degradation of propranolol from water. Various factors (e.g., temperature, persulfate dose, initial pH and natural water constituent) on PRO degradation kinetics have been investigated. The results showed that the PRO degradation followed a pseudo-first-order kinetics pattern. As temperature rises, the pseudo-first-order rate constant (k_obs) was improved significantly, and the k_obs determined at 40–70 °C satisfied the Arrhenius equation, yielding an activation energy of 99.0 kJ mol⁻¹. The radical scavenging experiments and the EPR tests revealed that both SO₄˙⁻ and ·OH participated in degrading PRO, with SO₄˙⁻ playing a dominant role. Higher PS concentration and neutral pH favored PRO degradation. The impact of Cl⁻ and HCO₃⁻ were concentration-dependent. A lower concentration of Cl⁻ and HCO₃⁻ could accelerate PRO degradation, while the presence of HA showed inhibitory effects. Seven degradation products were recognized through LC/MS/MS analysis. Cleavage of ether bond, hydroxylation, and ring-opening of naphthol moiety are involved in the PRO's degradation pathway. Finally, the formation of disinfection byproducts (DBPs) before and after pre-treated by heat/PS was also evaluated. Compared with direct chlorination of PRO, the heat/PS pre-oxidation greatly impacted the DBPs formation. The higher PRO removal efficiency in natural water indicated the heat/PS process might be capable of treating PRO-containing water samples, however, its impacts on the downstream effect on DBPs formation should be also considered.