Peroxymonosulfate activation by ruthenium in homogeneous systems for degradation of triclosan: Comparison between Ru(II) and Ru(III)

Triclosan (TCS) as an emerging pollutant in aquatic environments poses great threats to human health and ecological safety, hence ruthenium (Ru) as a potential transition-metal catalyst was utilized to activate peroxymonosulfate (PMS) and mitigate TCS pollutant in this study. The performances of Ru(II) species (i.e., Ru(bpy)32+) and Ru(III) species (i.e., RuCl3) were compared to systematically investigate the TCS removal capacity of Ru/PMS system in homogeneous systems. The experimental results show that the homogeneous Ru/PMS systems exhibited greater oxidization capacity than other analogous systems such as the Ru/H2O2 system and Fe/PMS system, while the Ru(III) activator had stronger activation capacity for PMS than the Ru(II) activator. Less dosage of Ru(III) (∼1/3 of the Ru(II) dosage) and less reaction time (∼1/4 of that in the Ru(III)/PMS system) were needed in the Ru(III)/PMS system to remove the same amount of TCS. Additionally, there were optimal values for the dosage of Ru species and PMS, while overdose might inhibit the TCS removal. Coexisting components in aquatic environments had similar effects on Ru(II)/PMS and Ru(III)/PMS systems. Cl- at low concentrations inhibited the removal of TCS, while Cl- at high concentrations improved the removal of TCS. HCO3–, Ca2+, Mg2+ and humic acid mainly inhibited the removal of TCS, and dissolved oxygen had a negligible influence. Based on quenching experiments and electron paramagnetic resonance (EPR) technique, the 1O2 played a major role in the homogeneous Ru/PMS systems, while •OH and SO4•- contributed less. Importantly, TCS can be degraded into less toxic intermediates in the Ru(III)/PMS system. This work can facilitate the development of efficient Ru(III)-based activators for organic pollutant remediation in aquatic environments.