Homogeneous activation of peroxymonosulfate using a low-dosage cross-bridged cyclam manganese(II) complex for organic pollutant degradation via a nonradical pathway

Abstract

The high dosage of catalyst requirement and weak anti-interference ability limit current heterogeneous manganese (Mn) catalyst/peroxymonosulfate (PMS) systems to remediate the organic polluted wastewater in complicated environment. Inspired by the concept of atom economy, herein, a homogenous manganese complex bearing a cross-bridged cyclam ligand Mn(cbc)Cl₂ (MnL, L = cbc = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane)) is capable of activating PMS for reactive brilliant red K-2BP (RBR K-2BP) degradation. The dosage of MnL for PMS activation was low, in a range of 0.38∼3.8 mg/L. The quenching experiments demonstrated that the degradation was a nonradical-controlled process. Using methyl phenyl sulfoxide (PMSO) as a probe, the dominated degradation process of substrate was via an oxygen transfer pathway. Moreover, a high-valent Mn-oxo [(O)Mn^VLCl₂]⁺ was directly detected using electrospray ionization mass spectrometry (ESI/MS). This system showed excellent anti-interference ability to both anions and humic acid, a typical natural organic matter. The atom economy, represented by an index ((mg pollutant)/h/(g catalyst)), showed that MnL 22737 in PMS activation was much higher than those of Mn-based heterogeneous catalytic systems 67∼960 and was only behind that of iron-tetraamidomacrocyclic ligand Fe-TAML 59139. This work provides insights into designing an atom-economic Mn-based PMS activator for efficient treatments for organic pollutants in a complicated environment.

Keywords: Atom economy; Homogeneous catalyst; Manganese-cyclam complex; Nonradical pathway; Peroxymonosulfate activation.