Deciphering the degradation/chlorination mechanisms of maleic acid in the Fe(II)/peroxymonosulfate process: An often overlooked effect of chloride

Liu

2020

Environ. Sci. Technol.

291

Graphite carbon nitride (g-C 3 N 4 ) has a stable structure but poor catalytic capability for activating peroxymonosulfate (PMS). In this study, the codoping of g-C 3 N 4 with bimetallic oxides (iron and cobalt) and oxygen was investigated to enhance its catalytic capability. The results showed that iron, cobalt, and oxygen codoped g-C 3 N 4 (Fe−Co−O−g-C 3 N 4 ) was successfully prepared, which was capable of completely degrading sulfamethoxazole (SMX) (0.04 mM) within 30 min, with a reaction rate of 0.085 min −1 , indicating the superior catalytic activity of Fe−Co−O−g-C 3 N 4 . The mineralization efficiency of SMX was 22.1%. Sulfate radicals and singlet oxygen were detected during the process of PMS activation. However, the role that singlet oxygen played in degrading SMX was not obvious. Surface-bound reactive species and sulfate radicals were responsible for SMX degradation, in which sulfate radicals contributed to 46.6% of SMX degradation. The superior catalytic activity was due to the synergistic effect of metal oxides and O−g-C 3 N 4 , in which O−g-C 3 N 4 could act as a carrier and an activator as well as an electron mediator to promote the conversion of Fe(III) to Fe(II) and Co(III) to Co(II). Four main steps of SMX degradation were proposed, including direct oxidation of SMX, bond fission of N−C, bond fission of N−S, and bond fission of S−C. The effect of the pH, temperature, PMS concentration, chloridion, bicarbonate, and humic acids on SMX degradation was investigated. Cycling experiments demonstrated the good stability of Fe−Co−O−g-C 3 N 4 . This study first reported the preparation of bimetallic oxide and oxygen codoped g-C 3 N 4 , which was an effective PMS activator for degradation of toxic organic pollutants.

Section: ■ Introductionmentioning

confidence: 99%

Peroxymonosulfate Activation by Fe–Co–O-Codoped Graphite Carbon Nitride for Degradation of Sulfamethoxazole

Liu

2020

Environ. Sci. Technol.

291

“…The rate constants in Sun et al require a value of 5.8 × 10 12 M –1 s –1 for k 27r , which is impossible because it considerably exceeds the diffusion-controlled limit. Loop E also appears in several other published mechanisms. ,,,− ,− ,,,,,− ,, This loop also appears in another proposed mechanism if it is supplemented with eq Illegal loop F In loop F, the stoichiometric sum of eqs and is equal to eq , and the loop is illegal because it contains only one irreversible step.…”

Section: Resultsmentioning

confidence: 96%

“…Loop E also appears in s e v e r a l o t h e r p u b l i s h e d m e c h anisms. 12,13,15,[17][18][19][21][22][23][24][25][26][27][28][29]32,33,36,37,[42][43][44]46,47 This loop also appears in another proposed mechanism if it is supplemented with eq 11. 48 Illegal loop F…”

Section: ■ Introductionmentioning

confidence: 99%

Mechanisms of Advanced Oxidation Processes, the Principle of Detailed Balancing, and Specifics of the UV/Chloramine Process

Stanbury

2020

Environ. Sci. Technol.

Advanced oxidation processes tend to have very complex reaction mechanisms, and models containing over 150 steps have been developed to describe the chemistry. Without the aid of automation, it is extremely difficult to avoid the development of kinetic mechanisms that violate the principle of detailed balancing. Here, we apply DETBAL, a computer application, to systematically identify many violations of the principle of detailed balancing in a model proposed for the UV/chloramine process. We then show that these violations can also be found in dozens of other proposed models for advanced oxidation processes. Suggested repairs to these violations are provided. These repairs lead to no significant changes in the model predictions because the illegal loops include steps that are unnecessary under the conditions modeled. The model omits certain steps that do have significant effects on the model predictions.

“…The slightly lower removal efficiency of ATZ in natural waters could be due to the interference of various cations/anions and the scavenging effects of electron-rich organic molecules. The impacts of common water constituents such as Mg 2+ , Cl – , Br – , and NOMs on PMS-based systems are still not well-understood and require additional investigation, especially when multiple constituents co-exist (e.g., real surface water). ,− …”

Section: Resultsmentioning

confidence: 99%

Activation of Peroxymonosulfate by Phosphate and Carbonate for the Abatement of Atrazine: Roles of Radical and Nonradical Species

Wen

Sharma

2022

ACS EST Water

While the activation mechanisms of peroxymonosulfate (PMS) by various homogeneous and heterogeneous catalysts have been reported, the chemistry of PMS in a catalyst-free system and its interactions with background oxyanions are still poorly understood. This paper demonstrated the activation of PMS by two prevalent oxyanions (phosphate and carbonate) and revealed the mechanisms for the enhanced atrazine (ATZ) degradation by PMS at neutral pH. Both oxyanions activated PMS to produce a sulfate radical (SO4 •–), which reacts with ATZ rapidly, but phosphate exhibited a stronger effect than carbonate. The reaction between SO4 •– and ATZ produced other possible radicals in the presence of dissolved oxygen (e.g., ATZ–O–O•), which subsequently generated singlet oxygen (1O2) with superoxide radical (O2 •–) as a precursor. However, their contributions to ATZ degradation were minimal. The formation of radical species in the PMS–ATZ–phosphate system was supported by selective quenching and electron paramagnetic resonance measurements under different conditions [oxic, anoxic, and different solvents (H2O and D2O)]. Direct oxidation of ATZ by PMS was also observed. Overall, SO4 •– and direct oxidation by PMS accounted for 75–78% and 22–25% of ATZ degradation, respectively.