Degradation of Organic Contaminants in the Fe(II)/Peroxymonosulfate Process under Acidic Conditions: The Overlooked Rapid Oxidation Stage

Abstract

The iron(II)-activated peroxymonosulfate [Fe(II)/ PMS] process is effective in degrading organic contaminants with a rapid oxidation stage followed by a slow one. Nevertheless, prior studies have greatly underestimated the degradation rates of organic contaminants in the rapid oxidation stage and ignored the differences in the kinetics and mechanism of organic contaminants degradation in these two oxidation stages. In this work, we investigated the kinetics and mechanisms of organic contaminants in this process under acidic conditions by combining the stoppedflow spectrophotometric method and batch experiments. The organic contaminants were rapidly oxidized with rate constants of 0.18−2.9 s −1 in the rapid oxidation stage. Meanwhile, both Fe(IV) and SO 4•− were active oxidants and contributed differently to the degradation of different organic contaminants in this stage. Additionally, the presence of Cl − promoted the degradation of both phenol and estradiol but the effects of Br − and humic acid on phenol degradation differed from those on estradiol degradation in the rapid oxidation stage. In contrast, the degradation of phenol and estradiol was slow and the amounts of Fe(IV) and SO 4•− generated were small in the slow oxidation stage. This work updates the fundamental understanding of the degradation of organic contaminants in this process.

Origin of the Excellent Activity and Selectivity of a Single-Atom Copper Catalyst with Unsaturated Cu-N2 Sites via Peroxydisulfate Activation: Cu(III) as a Dominant Oxidizing Species

“…High-valent metal species becomes the dominant active species for pollutant degradation in certain transition metal/persulfate systems. ,,, The generation of Cu­(III) can be determined by the Raman spectra in homogeneous and heterogeneous systems. , As shown in Figure f, Cu SA -NC does not exhibit obvious peaks and the peaks only occur in the range of 400–500 cm –1 in PDS solution. Obviously, the new peak around 616 cm –1 is observed in the Cu SA -NC + PDS system, confirming the formation of Cu­(III), because it is the typical Cu–O stretching vibration peak of a metastable Cu­(III). , BA and NB ( • OH probe compound) with electron-poor groups can hardly be degraded in the Cu SA -NC system (Figure d), which is attributed to the selective oxidation of Cu­(III) reported in previous studies. , From the EPR spectra (Figure S19), Cu SA -NC alone exhibits a signal at g = 2.003, and its intensity decreases significantly with the addition of PDS solution, and this result is consistent with the phenomenon during the transformation of Cu­(II) to Cu­(III) .…”

“…Nevertheless, PDS ($0.74 per kg) is much cheaper than PMS (sold as Oxone (KHSO 5 ·1/2KHSO 4 ·1/2K 2 SO 4 ), $2.2 per kg), so it exhibits a better application potential. , Meanwhile, the unsaturated coordination (such as Cu-N 2 ) tends to exhibit different catalytic properties owing to distinct electronic and geometric structures . Therefore, it is highly desirable to gain insight into the generation of Cu­(III) in a single-atom Cu catalyst with unsaturated coordination for PDS activation, although PDS with a symmetrical structure is more difficult to be activated than PMS …”

“…17 Therefore, it is highly desirable to gain insight into the generation of Cu(III) in a single-atom Cu catalyst with unsaturated coordination for PDS activation, although PDS with a symmetrical structure is more difficult to be activated than PMS. 24 In this work, a single-atom copper catalyst (Cu SA -NC) with unsaturated Cu-N 2 sites was designed for PDS activation, which exhibited excellent catalytic activity under complex matrix conditions and selective degradation of electron-rich pollutants. Based on the results of experimental characterizations and density functional theory (DFT) calculations, the high-valent copper species Cu(III), which was generated on the unsaturated Cu-N 2 sites by activating PDS, was identified as the main oxidizing species, and the mechanism involved was proposed.…”

Efficient activation of peroxymonosulfate by C3N5 doped with cobalt for organic contaminant degradation

“…This inhibitory effect was ascribed to the fact that Cl − quenched SO 4 ˙ − to produce chorine radicals, which have lower reactivity than SO 4 ˙ − for PCB28 degradation. 65,66…”

“…This inhibitory effect was ascribed to the fact that Cl − quenched SO 4 ˙− to produce chorine radicals, which have lower reactivity than SO 4 ˙− for PCB28 degradation. 65,66 In contrast, NO 3 − had limited inhibitory effects on PCB28 degradation, and PCB28 degradation changed slightly with different concentrations of NO 3 − (1.0 and 10 mM, Fig. 7b).…”