Electron-transfer-based peroxymonosulfate activation on defect-rich carbon nanotubes: Understanding the substituent effect on the selective oxidation of phenols

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This perspective presents the latest advancements in selective polymerization pathways in advanced oxidation processes (AOPs) for removal of featured organic pollutants in wastewater. In radical-based homogeneous reactions, SO 4• − -based systems exhibit superior oxidative activity toward aromatics with electron-donating substituents via single electron transfer and radical adduct formation (RAF). The produced organic radical cations subsequently undergo coupling and polymerization reactions to produce polymers. For • OH-based oxidation, metal ions facilitate the production of monomer radicals via RAF. Additionally, heterogeneous catalysts can mediate both coupling and polymerization reactions via persulfate activation without generating inorganic radicals. Metal-based catalysts will mediate a direct oxidation pathway toward polymerization. In contrast, carbon-based catalysts will induce coupling reactions to produce low-molecular-weight oligomers (≤4 units) via an electron transfer process. In comparison to mineralization, polymerization pathways remarkably reduce peroxide usage, quickly separate pollutants from the aqueous phase, and generate polymeric byproducts. Thus, AOP-driven polymerization systems hold significant promise in reducing carbon emission and realizing carbon recycling in water treatment processes.

Section: Polymerization Reaction In Carbon-based Catalyst Systemsmentioning

confidence: 99%

Transformative Removal of Aqueous Micropollutants into Polymeric Products by Advanced Oxidation Processes

Chen,

Ren,

et al. 2024

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“…Some investigations studied the reaction of phenolic compounds with EDGs and 1 O 2 , and observed that the compounds lose one electron forming radical cations, and 1 O 2 gains one electron forming O 2 •– . In addition, 1 O 2 can react with compounds containing nitrogen atoms via electron transfer, and this pathway can be assessed by Fukui functions of f – and f 0 . , For example, the highest f – value of sulfamethoxazole (SMX) is located on amino N atom, indicating that this atom is the most vulnerable to lose electron and be attacked by electrophilic 1 O 2 …”

Section: Comparison Of Radical and Nonradical Oxidation Processesmentioning

confidence: 99%

“…102 In addition, 1 O 2 can react with compounds containing nitrogen atoms via electron transfer, and this pathway can be assessed by Fukui functions of f − and f 0 . 103,104 For example, the highest f − value of sulfamethoxazole (SMX) is located on amino N atom, indicating that this atom is the most vulnerable to lose electron and be attacked by electrophilic 1 O 2 . 105 The different reactivities between radicals and 1 O 2 may be partially attributed to the combined effect of their lifetimes and redox potentials (Table 3).…”

Section: 1mentioning

confidence: 99%

Merits and Limitations of Radical vs. Nonradical Pathways in Persulfate-Based Advanced Oxidation Processes

Yan

Wei

Duan

et al. 2023

189

Urbanization and industrialization have exerted significant adverse effects on water quality, resulting in a growing need for reliable and eco-friendly treatment technologies. Persulfate (PS)-based advanced oxidation processes (AOPs) are emerging as viable technologies to treat challenging industrial wastewaters or remediate groundwater impacted by hazardous wastes. While the generated reactive species can degrade a variety of priority organic contaminants through radical and nonradical pathways, there is a lack of systematic and in-depth comparison of these pathways for practical implementation in different treatment scenarios. Our comparative analysis of reaction rate constants for radical vs. nonradical species indicates that radical-based AOPs may achieve high removal efficiency of organic contaminants with relatively short contact time. Nonradical AOPs feature advantages with minimal water matrix interference for complex wastewater treatments. Nonradical species (e.g., singlet oxygen, high-valent metals, and surface activated PS) preferentially react with contaminants bearing electron-donating groups, allowing enhancement of degradation efficiency of known target contaminants. For byproduct formation, analytical limitations and computational chemistry applications are also considered. Finally, we propose a holistically estimated electrical energy per order of reaction (EE/O) parameter and show significantly higher energy requirements for the nonradical pathways. Overall, these critical comparisons help prioritize basic research on PS-based AOPs and inform the merits and limitations of system-specific applications.

“…Specially, the electrondonating abilities of organics are determined by the electronic parameters, such as the Hammett constant (σ), 21,22 ionization potential (IP), 23 one-electron oxidation potential (E ox ), 24−27 and energy of the highest occupied molecular orbital (E HOMO ). 28,29 Based on the results of quantitative structure− activity relationships (QSARs), organics with a stronger electron-releasing group (lower IP/E ox /σ or higher E HOMO ) are removed by the nonradical reactive species at a faster oxidation rate, while the electron-withdrawing organics are refractory under the attack of the nonradical reactive species. 30−32 Thus, the threshold for selective oxidation of reactive species can be calculated semiquantitatively after the survey of kinetic experiments and theoretical calculations.…”

Section: •−mentioning

confidence: 99%

“…Nonradical reactive species, such as singlet oxygen ( 1 O 2 ), catalyst-activated persulfate (Cat-PS*) complexes, and high-valent metal-oxo complexes, are able to selectively attack electron-rich organic pollutants even in complicated water matrices. − Generally, the selective oxidation process mainly depends on the electron nature of organics and nonradical reactive species, which can accurately determine the direction and extent of nonradical oxidation. Specially, the electron-donating abilities of organics are determined by the electronic parameters, such as the Hammett constant (σ), , ionization potential (IP), one-electron oxidation potential ( E ox ), − and energy of the highest occupied molecular orbital ( E HOMO ). , Based on the results of quantitative structure–activity relationships (QSARs), organics with a stronger electron-releasing group (lower IP/ E ox /σ or higher E HOMO ) are removed by the nonradical reactive species at a faster oxidation rate, while the electron-withdrawing organics are refractory under the attack of the nonradical reactive species. − Thus, the threshold for selective oxidation of reactive species can be calculated semiquantitatively after the survey of kinetic experiments and theoretical calculations. Our previous studies found that the reduction potential of Cat-PS* complexes and the oxidation potential of organics are critical in regulating the thermodynamic feasibility of the carbon-based electron-transfer pathway (ETP). , Specifically, the thermodynamic prerequisite for initiating ETP is that the reduction potential of complexes surpasses the oxidation potential of organics.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic and Kinetic Behaviors of Persulfate-Based Electron-Transfer Regime in Carbocatalysis

Peng,

Zhang,

Ren

et al. 2023

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A carbon-based advanced oxidation process is featured for the nonradical electron-transfer pathway (ETP) from electron-donating organic compounds to activated persulfate complexes, enabling it as a green technology for the selective oxidation of organic pollutants in complex water environments. However, the thermodynamic and kinetic behaviors of the nonradical electron-transfer regime had been ambiguous due to a neglect of the influence of pH on the mechanisms. In this study, three kinds of organic pollutants were divided in the carbon-based ETP regime: (i) physio-adsorption, (ii) adsorption-dominated ETP (oxidation rate slightly surpasses adsorption rate), and (iii) oxidation-dominated ETP (oxidation rate outpaces the adsorption rate). The differential kinetic behaviors were attributed to the physicochemical properties of the organic pollutants. For example, the hydrophobicity, molecular radius, and positive electrostatic potential controlled the mass-transfer process of the adsorption stage of the reactants (peroxydisulfate (PDS) and organics). Meanwhile, other descriptors, including the Fukui index, oxidation potential, and electron cloud density regulated the electrontransfer processes and thus the kinetics of oxidation. Most importantly, the oxidation pathways of these organic pollutants could be altered by adjusting the water chemistry. This study reveals the principles for developing efficient nonradical systems to selectively remove and recycle organic pollutants in wastewater.