Electrochemical activation of periodate with graphite electrodes for water decontamination: Excellent applicability and selective oxidation mechanism

Site-Specific Spin State Modulation in Spinel Oxides for Enhanced Nonradical Oxidation

Spinel oxides hold tremendous potential for driving advanced oxidation processes, yet the underlying mechanism for maximizing their activity remains unclear. In this study, we leverage tetrahedral and octahedral site interactions in MnxCo3-xO4 to modulate the spin states, specifically spin alignment and spin moment, thereby enhancing periodate (PI) activation and catalytic performance in contaminant degradation. Through combined experimental and density functional theory (DFT) analyses, we elucidate the role of spin alignment at synergetic tetrahedral and octahedral sites in facilitating quantum spin exchange interactions (QSEI) with an efficient electronic spin channel for charge transfer. Meanwhile, the engineered high spin configuration in CoMn2O4 raises the d-band center, favoring stable PI* surface complex formation and accelerating the rate-determining desorption of IO3 - with a lower-ICOHP value during the catalytic degradation of ciprofloxacin. As a result, the fine-tuned spin state of CoMn2O4 leads to enhanced overall reaction kinetics, with a 2.5-fold increase compared to MnCo2O4 and up to 22-fold increase compared to the octahedrally-active only catalysts. Such a site-specific modulation has been found applicable to other spinel oxides, enlightening fine-tuned electronic structure for maximizing catalytic performance.

Isotope Techniques in Chemical Wastewater Treatment: Opportunities and Uncertainties

A comprehensive and in-depth analysis of reaction mechanisms is essential for advancing chemical water treatment technologies. However, due to the limitations of conventional experimental and analytical methods, the types of reactive species and their generation pathways are commonly debatable in many aqueous systems. As highly sensitive diagnostic tools, isotope techniques offer deeper insights with minimal interference from reaction conditions. Nevertheless, precise interpretations of isotope results remain a significant challenge. Herein, we first scrutinized the fundamentals of isotope chemistry and highlighted key changes induced by the isotope substitution. Next, we discussed the application of isotope techniques in kinetic isotope effects, presenting a roadmap for interpreting KIE in sophisticated systems. Furthermore, we summarized the applications of isotope techniques in elemental tracing to pinpoint reaction sites and identify dominant reactive species. Lastly, we propose future research directions, highlighting critical considerations for the rational design and interpretation of isotope experiments in environmental chemistry and related fields.

Electrical activation of periodate by nano-zero-valent cobalt/nitrogen-doped carbon for sulfisoxazole degradation: Insights into rapid electron transfer mechanisms

Periodate (PI) activation via three-dimensional electrochemical (E) is a promising approach for degrading sulfisoxazole (SIZ), while the scarcity of active sites significantly limits the efficient electron-transfer rate. Herein, we synthesized multiple strongly active zero-valent cobalt (Co0) nanoparticles encapsulated in nitrogen-doped carbon (NC) shells through Co-potassium chloride (KCl) doping pyrolysis of Zeolitic Imidazolate Framework-8 (ZIF-8) to induce the rapid electron transfer pathways (ETP). Specifically, molten KCl doping provides confined structures for Co0 with a diameter of 12.57 nm embedded in the NC shell, thereby expanding the active space of Co0/NC. The generated Co0/NC exhibited an enormous electrochemically active surface area (ECSA, 736.92 cm2/mg), low charge transfer resistance (Rct, 38.50 Ω), and strong adsorption energy (-6.003 eV), which together promote robust electron transfer kinetics. Capitalizing on these properties, the E-Co0/NC-PI system achieved 100% SIZ removal at a degradation rate of 1.587 min-1 under near-neutral (pH 5.00-9.00) conditions, with ultra-low energy consumption (0.011 kWh m-3, $0.125/L). This study highlights a Co0/NC-induced rapid ETP for SIZ removal, offering insights into enhanced electrical activation of PI for wastewater treatment.

Applications of periodate activation for emerging contaminants treatment in water: Activation methods, reaction parameters and mechanism

Emerging contaminants pose a serious hazard to the water environment and human health due to their difficult degradation. In recent years, periodate-based oxidation processes have aroused tremendous attention in environment remediation due to their high oxidative potential for the degradation of contaminants and fair stability in the water. Periodate activation methods (i.e., thermal activation, photoactivation, microwave and ultrasonic activation, metal catalyst activation, carbon activation, H2O2 activation and electrochemical activation) were revealed. The generation mechanisms of the main reactive species in the periodate-based advanced oxidation processes were discussed. The degradation mechanisms of periodate-based systems are classified into two categories: radical-based mechanisms (the generation and mutual transformation of reactive radicals (IO3•, •OH, IO4• and O2•-)) and non-radical mechanisms (mainly including electron transfer and 1O2). The IO3• is a common reaction product along with the applications of periodate oxidation. The factors affecting periodate activation have been summarized and the characteristics of various activation methods have been compared. The combination of periodate oxidation with effective methods of activation has been expected to significantly enhance the treatment of organic contaminants in wastewater. This review systematically summarized the various methods for periodate activation and the research progress of its application in water treatment in recent years.

Activation of persulfates on carbon nanotubes for water decontamination: Is the non-radical process consistently considered across different pH levels?

Carbon nanotubes-driven persulfates oxidation processes (CNTs/PS) have been extensively studied for environmental remediation. Solution pH is one of the main factors affecting wastewater treatment, but it is often overlooked. Herein, we report the effect laws of pH on the mechanism of peroxymonosulfate (PMS) or peroxydisulfate (PDS) activation by CNTs. The oxidation of organics (e.g., phenol) in the CNTs/PDS system involves an electron transfer process mediated by metastable intermediates (CNTs-PDS*), whose potential is influenced by pH, reaching the highest oxidation potential under neutral condition. In the CNTs/PMS system, the active species (i.e., SO4•-, CNTs-PMS*) shifted with pH variations. In acidic environment, phenol oxidation is governed by CNTs-PMS* . As pH increases, PMS undergoes accelerated decomposition, generating SO4•-, which plays a crucial role in pollutant oxidation. Moreover, in the CNTs/PMS system, the oxidation products of phenol were not easily accumulated on CNT surfaces, contributing to a lower total organic carbon removal in solution. Additionally, the oxidation rates of phenolic compounds in the CNTs/PMS system, which involve more complex mechanisms, exhibited a weaker correlation with their descriptors (e.g., the octanol-water partition coefficient) compared to CNTs/PDS system. This comprehensive investigation deepens our understanding of CNTs/PS systems and provides guidance for selecting superior oxidants for wastewater treatment.

Unexpected chloride-triggered organics removal in the zirconium oxide activated peroxymonosulfate system

Chloride ion (Cl-) is ubiquitous in diverse water bodies, yet poses a longstanding challenge in water pollution control by hindering the efficiency of pollutant degradation. Herein, we proposed a novel concept involving the direct utilization of endogenous Cl- ions in water for rapid water purification within a non-redox zirconium oxide (ZrO2)-activated peroxymonosulfate (PMS) system. In this process, PMS was complexed on the ZrO2 surface through inner-sphere coordination, and effectively activated by the partial electron cloud deviation from Zr(IV) sites to PMS, thereby forming a metastable surface complex with an elevated redox potential. Afterwards, the coexistence of Cl- could trigger the transformation of the reactive complex into free chlorine species, thus leading to a 255.0-fold enhancement in the elimination rate of micropollutants compared with the ZrO2/PMS system. Quantitative structure-activity relationship analysis revealed that the ZrO2/PMS/Cl- system displayed strong target-dependence towards electron-rich compounds, showcasing a faster oxidation rate for pollutants with higher EHOMO energy levels. Significantly, the novel system performed robust resistance to complex water matrices, achieved low oxidant consumption for pollutant removal, and demonstrated adaptation across a broad range of Cl- concentrations (1.0-100.0 mM). Overall, our findings provide new mechanistic insights into the influence of Cl- ions on PMS activation, which refresh the understanding of the role of Cl- ions on pollutant degradation, and help to guide the treatment design for chloride-containing wastewater.

Increased Toxicity toward Mammalian Cells in the Periodate Oxidation Process of Wastewater: The Overlooked Formation of Noniodinated but Nitrogenous Byproducts

Periodate (PI) shows promising potential as an oxidant for wastewater treatment; however, its impact on the toxicity of wastewater remains unknown. Here, we found that with 100 μM PI addition, the cytotoxicity of wastewater increased from 4.8 to 7.6 mg-Phenol/L to 9.5 to 12.8 mg-Phenol/L, and genotoxicity increased from 0.3 to 0.9 μg-4-NQO/L. Interestingly, hypoiodous acid (HOI) was not detected during the reaction, and there was no observed increase in the concentration of total organic iodine (TOI). CHON components in dissolved organic matter changed most obviously in PI oxidation, which might serve as primary precursors for toxic byproducts. Cytotoxicity of typical nitrogen-containing precursors of tryptophan, lysine, phenylalanine, and tyrosine after PI oxidation increased from not detected to 14.7, 2.4, 4.1, and 3.2 mg-Phenol/L, respectively. Here, four nonhalogenated aromatic nitrogenous byproducts (N-DBPs) of 3-hydroxyquinoline, 4-hydroxyquinoline, benzopyridine, and benzopyrrole were confirmed using standards, and four byproducts such as 2-formylbenzonitrile were tentatively proposed. The cytotoxicity of the four confirmed byproducts was comparable to those known N-DBPs such as nitrosamines, suggesting attention should be given to these nonhalogenated but nitrogenous byproducts. The four confirmed byproducts were detected in two PI-treated wastewater samples with concentrations of 0.8, 0.98, 0.52, and 0.0038, and 18.28, 1.50, 0.57, and 0.0074 μg/L, respectively, with contributions less than 1.5% to the overall cytotoxicity. Further investigations are warranted to elucidate the primary drivers of toxicity in PI-treated wastewater.

Percarbonate-periodate system: A novel and efficient "oxidant-oxidant" strategy for selective oxidation of micropollutants in water

The development of effective and selective oxidation technology in complex water matrices is crucial for water ecological security. This study reports for the first time the synergistic use of "oxidant-oxidant" about sodium percarbonate (SPC) and periodate (PI) to selectively degrade organic micropollutants. The SPC/PI system showed degradation rates of 0.0946-0.2978 min-1 for various pollutants, which was 3.7-1787 times higher than those in the PI alone and SPC alone systems and can achieve the effect of H2O2/PI systems. Additionally, SPC/PI was a safe water treatment technology without generating reactive iodine species (e.g., HOI). The slightly reduced removal rate of bisphenol F under different ionic species and strengths is indicative of the good anti-interference of the SPC/PI system. Scavenging, probe, and electron spin resonance experiments showed that ▪OH and CO3▪- played a major role in this process, rather than O2▪- and 1O2. Finally, the oxidized products and the possible transformation pathways of three different micropollutants in the SPC/PI and H2O2/PI systems were characterized and clarified, and the toxicity of the degradation products was predicted. Generally, the study proposed a new selective oxidation strategy of SPC/PI that can effectively eliminate micropollutants in water treatment and clarified the interaction mechanisms between PI and SPC.

Mechanism insights into metal-organic framework-derived carbon materials activating periodate for p-chlorophenol removal: The role of S and Fe co-doping

Periodate (PI, IO4-)-based advanced oxidation processes (AOPs) provide an economical and sustainable approach to alleviate water pollution challenges. Developing efficient and stable activators for PI is the focus of current research. Herein, S/Fe-co-doped magnetic porous carbon material (S/Fe-ZIF-950) was prepared by introducing exogenous S atoms using Fe-doped zeolitic imidazolate framework-8 (Fe-ZIF-8) as a precursor, which showed the most superior performance (100 % within 10 min) in activating PI to remove p-chlorophenol (4-CP). Quenching tests, electron spin resonance and electrochemical characterizations revealed that IO3·, 1O2, ·O2- dominated the 4-CP degradation process with Fe3C and ZnS as the main active sites. The synergistic effect of S and Fe was the main reason for the enhanced degradation performance of 4-CP in S/Fe-ZIF-950/PI system, among which the reducing S2- could effectively promote the regeneration of Fe(Ⅱ), thus facilitating the continuous generation of active species. Combined with LC-MS results and density functional theory (DFT) calculations, possible degradation routes of 4-CP in the S/Fe-ZIF-950/PI system were presented. Moreover, toxicity assessment showed that the S/Fe-ZIF-950/PI system exhibited low biotoxicity and no toxic iodine by-products were formed. In addition, S/Fe-ZIF-950/PI system demonstrated excellent activity, good stability, outstanding reusability and durability in a variety of complex water environments. This study investigated the activation mechanism of S/Fe-co-doped porous carbon materials on PI, which shed a new light on the catalytic activation of PI by heteroatom-doped Fe-loaded carbon-based materials.

Overlooked Complexation and Competition Effects of Phenolic Contaminants in a Mn(II)/Nitrilotriacetic Acid/Peroxymonosulfate System: Inhibited Generation of Primary and Secondary High-Valent Manganese Species

Organic contaminants with lower Hammett constants are typically more prone to being attacked by reactive oxygen species (ROS) in advanced oxidation processes (AOPs). However, the interactions of an organic contaminant with catalytic centers and participating ROS are complex and lack an in-depth understanding. In this work, we observed an abnormal phenomenon in AOPs that the degradation of electron-rich phenolics, such as 4-methoxyphenol, acetaminophen, and 4-presol, was unexpectedly slower than electron-deficient phenolics in a Mn(II)/nitrilotriacetic acid/peroxymonosulfate (Mn(II)/NTA/PMS) system. The established quantitative structure-activity relationship revealed a volcano-type dependence of the degradation rates on the Hammett constants of pollutants. Leveraging substantial analytical techniques and modeling analysis, we concluded that the electron-rich phenolics would inhibit the generation of both primary (Mn(III)NTA) and secondary (Mn(V)NTA) high-valent manganese species through complexation and competition effects. Specifically, the electron-rich phenolics would form a hydrogen bond with Mn(II)/NTA/PMS through outer-sphere interactions, thereby reducing the electrophilic reactivity of PMS to accept the electron transfer from Mn(II)NTA, and slowing down the generation of reactive Mn(III)NTA. Furthermore, the generated Mn(III)NTA is more inclined to react with electron-rich phenolics than PMS due to their higher reaction rate constants (8314 ± 440, 6372 ± 146, and 6919 ± 31 M-1 s-1 for 4-methoxyphenol, acetaminophen, and 4-presol, respectively, as compared with 671 M-1 s-1 for PMS). Consequently, the two-stage inhibition impeded the generation of Mn(V)NTA. In contrast, the complexation and competition effects are insignificant for electron-deficient phenolics, leading to declined reaction rates when the Hammett constants of pollutants increase. For practical applications, such complexation and competition effects would cause the degradation of electron-rich phenolics to be more susceptible to water matrixes, whereas the degradation of electron-deficient phenolics remains largely unaffected. Overall, this study elucidated the intricate interaction mechanisms between contaminants and reactive metal species at both the electronic and kinetic levels, further illuminating their implications for practical treatment.

Selective oxidation decontamination in cobalt molybdate activated Fenton-like oxidation via synergic effect of cobalt and molybdenum

In this study, cobalt molybdate (CoMoO4) activated peracetic acid (PAA) was developed for water purification. CoMoO4/PAA system could remove 95% SMX with pseudo-first-order reaction rate constant of 0.15410 min-1, which was much higher than CoFe2O4/PAA, FeMoO4/PAA, and CoMoO4/persulfate systems. CoMoO4/PAA system follows a non-radical species pathway dominated by the high-valent cobalt (Co(IV)), and CH3C(O)OO• shows a minor contribution to decontamination. Density functional theory (DFT) calculation indicates that the generation of Co(IV) is thermodynamically more favorable than CH3C(O)OO• generation. The abundant Co(IV) generation was attributed to the special structure of CoMoO4 and effect of molybdenum on redox cycle of Co(II)/Co(III). DFT calculation showed that the atoms of SMX with higher ƒ0 and ƒ- values are the main attack sites, which are in accordance with the results of degradation byproducts. CoMoO4/PAA system can effectively reduce biological toxicity after the reaction. Benefiting from the selective of Co(IV) and CH3C(O)OO•, the established CoMoO4/PAA system exhibits excellent anti-interference capacity and satisfactory decontamination performance under actual water conditions. Furthermore, the system was capable of good potential practical application for efficient removal of various organics and favorable reuse. Overall, this study provides a new strategy by CoMoO4 activated PAA for decontamination with high efficiency, high selectivity and favorable anti-interference.

Efficient photochemical conversion of naproxen by butanedione: Role of energy transfer

Photochemical active species generated from photosensitizers, e.g., dissolved organic matter (DOM), play vital roles in the transformation of micropollutants in water. Here, butanedione (BD), a redox-active moiety in DOM and widely found in nature, was employed to photo-transform naproxen (NPX) with peracetic acid (PAA) and H2O2 as contrasts. The results obtained showed that the BD exhibited more applicable on NPX degradation. It works in the lake or river water under UV and solar irradiation, and its NPX degradation efficiency was 10-30 times faster than that of PAA and H2O2. The reason for the efficient transformation of pollutants is that the BD system was proved to be a non-free radical dominated mechanism. The quantum yield of BD (Ф254 nm) was calculated to be 0.064, which indicates that photophysical process is the dominant mode of BD conversion. By adding trapping agents, direct energy transfer from 3BD* to NPX (in anoxic environment) or dissolved oxygen (in aerobic environment) was proved to play a major role (> 91 %). Additionally, the BD process reduces the toxicity of NPX and promotes microbial growth after irradiation. Overall, this study significantly deepened the understanding of the transformation between BD and micropollutants, and provided a potential BD-based process for micropollutants removal under solar irradiation.

Origins of Selective Oxidation in Carbon-Based Nonradical Oxidation Processes toward Organic Pollutants: Quantitative Structure-Activity Relationships (QSARs)

Metal-free carbon material-mediated nonradical oxidation processes (C-NOPs) have emerged as a research hotspot due to their excellent performance in selectively eliminating organic pollutants in aqueous environments. However, the selective oxidation mechanisms of C-NOPs remain obscure due to the diversity of organic pollutants and nonradical active species. Herein, quantitative structure-activity relationship (QSAR) models were employed to unveil the origins of C-NOP selectivity toward organic pollutants in different oxidant systems. QSAR analysis based on adsorption and oxidation descriptors revealed that C-NOP selectivity depends on the oxidation potentials of organic pollutants rather than on adsorption interactions. However, the dominance of electronic effects in selective oxidation decreases with increasing structural complexity of organic pollutants. Moreover, the oxidation threshold solely depends on the inherent electronic nature of organic pollutants and not on the reactivity of nonradical active species. Notably, the accuracy of substituent descriptors (Hammett constants) and theoretical descriptors (e.g., highest occupied molecular orbital energy, ionization potential, and single-electron oxidation potential) is significantly influenced by the complexity and molecular state of organic pollutants. Overall, the study findings reveal the origins of organic pollutant-oriented selective oxidation and provide insight into the application of descriptors in QSAR analysis.

Improvement of Fe(Ⅲ)/percarbonate system by molybdenum powder and tripolyphosphate: Co-catalytic performance, low oxidant consumption, pH-dependent mechanism

The homogeneous sodium percarbonate (SPC) systems are limited by narrow pH range, ineffective consumption of oxidant, and weak reusability of catalyst. Herein, molybdenum (Mo) powder and sodium tripolyphosphate (STPP) were selected to overcome these challenges. Sulfamethoxazole (SMX), as a model contaminant, was almost completely degraded in 60 min with higher removal rate (0.1367 min-1) than the Mo or STPP-absent system. In addition, Mo/STPP-Fe(Ⅲ)/SPC system was cost-effective in terms of oxidant consumption, requiring only 0.2 mM SPC. About activation mechanism, the main active species for SMX degradation was pH-dependent, with hydroxyl radical (·OH) as the dominant active species at pHi = 7 and ·OH, carbonate radical (CO3·-), and superoxide radical (O2·-) derived from a series of chain reaction at pHi = 10, respectively. Due to the generation of various electrophilic free radical, the system exhibited excellent performance towards electron-rich pollutants under a wide pH range. Furthermore, Mo exhibited excellent stability and reusability. SMX was degraded through hydroxylation, N-S cleavage, amino and sulfanilamide oxidation into intermediates whose toxicities were evaluated by Toxicity Estimation Software Tool (T.E.S.T.) software. This work provided new insights to Fe/SPC system towards high-efficiency and low consumption treatment of practical application.

Selective elimination of sulfonamide antibiotics upon periodate/catechol process: Dominance of quinone intermediates

Natural organic matter, specifically ortho-quinones organics among them, was considered can participate in the transformation of sulfonamide antibiotics (SAs). Herein, based on targeted oxidizing for ortho-dihydroxyl structures (catechol as the model) upon periodate, an efficient approach for SAs elimination was introduced. Results first indicated the generation of ortho-benzoquinone (o-BQ) within periodate/catechol system progresses readily (the energy barriers for 9.6854 kcal/mol). The near-complete eliminations were observed towards sulfamethoxazole (SMX) in periodate/catechol system (with the rate of 0.4229 min-1) as well as other SAs and exhibited unprecedented resistance to operating parameters. Besides, periodate converts little into toxic low-valent iodate species during the reaction process, and both the cytotoxicity and acute toxicity assays revealed a significant decline in antibiotics bioactivity. Mechanistic insight revealed that o-BQ dominated the degradation process, comprehensive analysis further confirmed Michael addition reaction was the first degradation stage, in which electrons flow from o-BQ to SMX and form covalent bonds upon aniline. Furthermore, several catechol derivatives were used to verify the universality of the mechanism, and their wide distribution in both subsurface and wastewater implies the potential applications. Overall, the mechanisms elucidated behind this research proposed an efficient strategy for eliminating trace SAs in aqueous environments and selectively removing SAs from complex wastewater matrices.