Enhanced Oxidation of Organic Contaminants by Iron(II)-Activated Periodate: The Significance of High-Valent Iron–Oxo Species

177

Herein, we report that Co(II)-doped g-C 3 N 4 can efficiently trigger peracetic acid (PAA) oxidation of various sulfonamides (SAs) in a wide pH range. Quite different from the traditional radical-generating or typical nonradical-involved (i.e., singlet oxygenation and mediated electron transfer) catalytic systems, the PAA activation follows a novel nonradical pathway with unprecedented high-valent cobalt−oxo species [Co(IV)] as the dominant reactive species. Our experiments and density functional theory calculations indicate that the Co atom fixated into the nitrogen pots of g-C 3 N 4 serves as the main active site, enabling dissociation of the adsorbed PAA and conversion of the coordinated Co(II) to Co(IV) via a unique two-electron transfer mechanism. Considering Co(IV) to be highly electrophilic in nature, different substituents (i.e., five-membered and six-membered heterocyclic moieties) on the SAs could affect their nucleophilicity, thus leading to the differences in degradation efficiency and transformation pathway. Also, benefiting from the selective oxidation of Co(IV), the established oxidative system exhibits excellent anti-interference capacity and achieves satisfactory decontamination performance under actual water conditions. This study provides a new nonradical approach to degrade SAs by efficiently activating PAA via heterogeneous cobalt-complexed catalysts. KEYWORDS: peracetic acid, Co(II)-doped g-C 3 N 4 , high-valent cobalt-oxo, nonradical oxidation, sulfonamide antibiotics, SO 2 extrusion

Section: ■ Results and Discussionsupporting

confidence: 77%

Novel Nonradical Oxidation of Sulfonamide Antibiotics with Co(II)-Doped g-C₃N₄-Activated Peracetic Acid: Role of High-Valent Cobalt–Oxo Species

Liu

Guo

Jia

et al. 2021

177

“…HA was apt to compete with organic contaminants for SO 4 •– since HA could be readily scavenged by SO 4 •– at a rate constant of 6.8 × 10 3 L·mg C –1 s –1 . In contrast, the degradation of organic contaminants by Fe(IV) would be slightly influenced by HA because of the inert reactivity of Fe(IV) toward HA. − The degradation of phenol was mainly ascribed to Fe(IV), whereas Fe(IV) and SO 4 •– contributed almost equally to the degradation of estradiol (Figure d). Therefore, the presence of HA had a negligible effect on the degradation of phenol but inhibited the degradation of estradiol in the rapid oxidation stage of the Fe(II)/PMS process.…”

Section: Resultsmentioning

confidence: 99%

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

Dong

Lian

et al. 2021

154

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.

“…However, specific antibacterial mechanisms of Fe(IV) are unclear. Fe(VI) could inactivate microbial cells via the oxidation of DNA polymerase-I. , In this process, Fe(IV) was regarded as a key reactive intermediate, possibly because of its higher reactivity than that of Fe(VI). , More recently, Zong et al (2021) reported a bactericidal activity of an iron–oxo species [Fe(IV)O]. Therefore, Fe(IV) is believed to have an antimicrobial activity, but further investigation is needed to confirm its role.…”

Section: Discussionmentioning

confidence: 99%

Antibacterial Mechanisms of Reduced Iron-Containing Smectite–Illite Clay Minerals

Guo

Xia

Zeng

et al. 2021

Reduced nontronite has been demonstrated to be antibacterial through the production of hydroxyl radical (•OH) from the oxidation of structural Fe(II). Herein, we investigated the antibacterial activity of more common smectite–illite (S–I) clays toward Escherichia coli cells, including montmorillonite SWy-3, illite IMt-2, 50–50 S–I rectorite RAr-1, 30–70 S–I ISCz-1, and nontronite NAu-2. Under an oxic condition, reduced clays (with a prefix r before mineral names) produced reactive oxygen species (ROS), and the antibacterial activity followed the order of rRAr-1 > rSWy-3 ≥ rNAu-2 ≫ rIMt-2 ≥ rISCz-1. The strongest antibacterial activity of rRAr-1 was contributed by a combination of •OH and Fe(IV) generated from structural Fe(II)/adsorbed Fe2+ and soluble Fe2+, respectively. Higher levels of lipid and protein oxidation, intracellular ROS accumulation, and membrane disruption were consistent with this antibacterial mechanism of rRAr-1. The antibacterial activity of other S–I clays depended on layer expandability, which determined the reactivity of structural Fe(II) and the production of •OH, with the expandable smectite being the most antibacterial and nonexpandable illite the least. Our results provide new insights into the antibacterial mechanisms of clay minerals.