Nonradical Activation of Peroxydisulfate with In Situ Generated Amorphous MnO₂ in an Electro-Permanganate Process: Involvement of Singlet Oxygen, Electron Transfer, and Mn(III)_aq

Abstract

A novel water treatment process based on a combination of electrolysis (E) with permanganate (PM) and peroxydisulfate (PDS) was systematically investigated. The combination exhibited significant synergy in degrading refractory organics such as diclofenac (DCF), carbamazepine, and nitrobenzene. In comparison to E-PDS (20.45%, 12.448 kWh m–3) and E-PM (36.36%, 5.200 kWh m–3) processes, the E-PM-PDS process could mineralize 70.45% DCF within 180 min with the lowest specific energy consumption (1.007 kWh m–3). The mechanism study revealed that electricity could significantly promote the activation of PDS with the in situ generated amorphous MnO2 via nonradical pathways (1O2 oxidation and electron transfer), and the activated PDS, in turn, facilitated Mn­(II)aq to generate reactive Mn­(III)aq. In the E-PM-PDS process, DCF degradation was enhanced upon increasing PM dosage, PDS dosage, and current density, and also by decreasing the pH. Cations facilitated the DCF degradation with the order of positive effects as Fe3+ > Zn2+ > Ca2+ > Mg2+. The presence of humic acid (HA) significantly enhanced the DCF degradation, while the addition of HCO3 – or HPO4 2– caused adverse effects. This work may provide a high-efficiency and low-cost technology for water treatment.

In Situ Regulation of MnO2 Structural Characteristics by Oxyanions to Boost Permanganate Autocatalysis for Phenol Removal

“…MnO 2 colloids formed from Mn­(VII) decomposition generally exhibit excellent reactivity in removing contaminates through oxidation and/or catalytic processes. , Figure S13 unravels that phenol degradation by ectopically prepared MnO 2 colloids cannot be accelerated by HCO 3 – , suggesting that the enhanced removal of phenol is not associated with an increase in the oxidation ability of MnO 2 . Moreover, a previous study demonstrated the limited role of MnO 2 in phenol removal at pH 3.0–8.0 .…”

“…The renascent MnO 2 colloids with abundant surface hydroxyl groups and large surface areas can drive the removal of micropollutants by Mn(VII) via oxidation, catalysis, and coagulation processes. 11,12 This suggests that colloidal MnO 2 is a paramount intermediate for regulating the overall decontamination performance of Mn(VII). Many studies have reported that solution chemistry, including reductive agent dosage and concomitant ions, strongly impacts the Mn(VII) conversion product MnO 2 .…”

“…Bicarbonate (HCO 3 − ) was selected as a typical oxyanion to study its effect on the degradation of phenolic compounds by Mn(VII) because it has been shown to provide two contrasting outcomes in Mn(VII) activation systems. 10,12,21 . The findings of this study will significantly enhance the mechanistic insights into various oxyanion/ Mn(VII) oxidation systems.…”

“…Among extensively explored oxidants, permanganate (Mn­(VII)) is a promising alternative for in situ chemical oxidation because of its inherent benefits such as low cost, high effectiveness, and strong resistance to a wide array of NOCs. , More importantly, unlike conventional oxidation systems, the oxidation kinetics of Mn­(VII) obtained in natural water and wastewater samples are superior to those measured in the lab because some special NOCs can alter the redox behavior of various Mn species to enhance the Mn­(VII) decontamination activity. − During Mn­(VII) oxidation, Mn­(VII) is reduced by contaminants and other coexisting components to form MnO 2 as an in situ conversion byproduct. The renascent MnO 2 colloids with abundant surface hydroxyl groups and large surface areas can drive the removal of micropollutants by Mn­(VII) via oxidation, catalysis, and coagulation processes. , This suggests that colloidal MnO 2 is a paramount intermediate for regulating the overall decontamination performance of Mn­(VII). Many studies have reported that solution chemistry, including reductive agent dosage and concomitant ions, strongly impacts the Mn­(VII) conversion product MnO 2 . − Therefore, during the actual treatment of Mn­(VII), NOCs have the potential to change the characteristics of MnO 2 , thereby regulating the performance of the Mn­(VII) system; however, the pathway has been scarcely considered in the literature.…”

“…To prove the above hypothesis, the removal of micropollutants by the oxyanion/Mn­(VII) system was restudied. Bicarbonate (HCO 3 – ) was selected as a typical oxyanion to study its effect on the degradation of phenolic compounds by Mn­(VII) because it has been shown to provide two contrasting outcomes in Mn­(VII) activation systems. ,, By systematically studying the structure–activity relation of MnO 2 produced by Mn­(VII) decomposition in the presence or absence of HCO 3 – , we discovered that HCO 3 – can alter the structure of MnO 2 , thereby influencing its catalytic activity. Further, based on experimental and theoretical aspects, we explored the commonality and species dependence of common oxyanions in affecting Mn­(VII) activity, including sulfate (SO 4 2– ), nitrate (NO 3 – ), borate (H 3 BO 3 ), acetate (CH 3 COO – ), metasilicate (H 2 SiO 3 ), molybdate (MoO 4 2– ), and HPO 4 2– .…”