Visible light-induced degradation of propranolol with peroxymonosulfate as an oxidant and a radical precursor

A cost-effective method for the degradation of propranolol, which does not require a high amount of energy and expensive materials/chemicals, was developed. The degradation of propranolol by peroxymonosulfate (PMS) was slow under dark conditions. However, visible-light irradiation significantly accelerated the PMS-mediated propranolol degradation (degradation efficiency after 2 h = 71.0% under visible light vs. 9.7% under dark conditions), although neither PMS nor propranolol absorbed the visible light. The degradation products generated from the oxidation of propranolol by PMS absorb visible light, which facilitates the photochemical reduction of PMS and oxygen and the production of various free radicals, such as superoxide (O-2(center dot-)), hydroxyl ((OH)-O-center dot), and sulfate radicals (SO4 center dot-). These behaviors were verified by ultraviolet-visible absorption spectroscopy, electron spin resonance spectroscopy, fluorescence spectroscopy, and radical quenching experiments. The production of radical species (particularly (OH)-O-center dot), which was negligible under dark conditions, is responsible for the enhanced degradation of propranolol in the presence of PMS under visible light. The positive effect of visible light on the propranolol degradation was observed in the PMS concentration range and the pH range of 100-3000 mu M and 3-9, respectively. Compared to the visible light/platinum-loaded tungsten oxide (Pt-WO3) system, the visible light/PMS system showed a superior ability to degrade propranolol (degradation efficiency after 2 h of visible-light irradiation = 71.0% in the visible light/PMS system vs. 58.3% in the visible light/Pt-WO3 system).