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Iron-based sulfite (S(IV)) activation has emerged as a novel strategy to generate sulfate radicals (SO 4 •- ) for contaminants degradation. However, numerous studies focused on dissolved iron-induced homogeneous activation processes while the potential of structural Fe(III) remains unclear. In this study, five iron (hydr)oxide soil minerals (FeO x ) including ferrihydrite, schwertmannite, lepidocrocite, goethite and hematite, were successfully employed as sources of structural Fe(III) for S(IV) activation. Results showed that the catalytical ability of structural Fe(III) primarily depended on the crystallinity of FeO x instead of their specific surface area and particle size, with ferrihydrite and schwertmannite being the most active. Furthermore, in-situ ATR-FTIR spectroscopy and 2D-COS analysis revealed that HSO 3 - was initially adsorbed on FeO 6 octahedrons of FeO x via monodentate inner-sphere complexation, ultimately oxidized into SO 4 2- which was then re-adsorbed via outer-sphere complexation. During this process, strong oxidizing SO 4 •- and •OH were formed for pollutants degradation, confirmed by radical quenching experiments and electron spin resonance. Moreover, FeO x /S(IV) system exhibited superior applicability with respect to recycling test, real waters and twenty-six pollutants degradation. Eventually, plausible degradation pathways of three typical pollutants were proposed. This study highlights the feasibility of structural Fe(III)-containing soil minerals for S(IV) activation in wastewater treatment., Competing Interests: Declaration of Competing Interest There are no conflicts to declare., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Sulfite-based advanced oxidation technology has received considerable attention for its application in organic pollutants elimination. However, the potential of natural sediments as effective catalysts for sulfite activation has been overlooked. This study investigates a novel process utilizing suspended sediment/sulfite (SS/S(IV)) for degradation of metronidazole (MNZ). Our results demonstrate that MNZ degradation efficiency can reach to 93.1 % within 90 min with 12.0 g SS and 2.0 mM sulfite. The influencing environmental factors, including initial pH, SS dosage, S(IV) concentration, temperature, and co-existing substances were systematically investigated. Quenching experiments and electron paramagnetic resonance analyses results indicate that SO 3 •- is the primary active substance responsible for MNZ degradation, with involvement of SO 4 •- , SO 5 •- , and • OH. X-ray photoelectron spectroscopy and Mössbauer spectra reveal that Fe (III)-silicates play a crucial role in activating S(IV). Furthermore, analysis of degradation intermediates and pathways of MNZ is conducted using liquid chromatography with mass spectrometry (LC -MS). The toxicity of MNZ and its intermediates were also systematically evaluated by the T.E.ST. program and wheat seeds germination test. This study offers valuable insight into the activation of sulfite by natural sediments and could contribute to the development of SS-based advanced oxidation processes (AOPs) for the in-situ remediation of antibiotics-contaminated water environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The sulfite (S(IV))-based advanced oxidation process (AOP) has emerged as an appealing alternative to the traditional persulfate-based AOP for the elimination of organic contaminants from diverse water matrices. In this work, a silica reinforced ZIF-67(Co) catalyst (CZS) is fabricated, characterized and tested in the activation of S(IV) for the sulfamethoxazole (SMX) degradation. The prepared CZS demonstrates superior stability and catalytic ability for the degradation of SMX compared to ZIF-67(Co) across a broad pH range. Unlike the conventional radical-dominated oxidation systems, the CZS/S(IV) system for SMX degradation operates through a non-radical mechanism, featuring high-valent Co(IV) and singlet oxygen ( 1 O 2 ) as the predominated reactive species. The hydroxylated Co species exposed on the CZS surface is identified as the pivotal active site, realizing the S(IV) activation through a complexation-electron transfer process, resulting in the production of various reactive intermediates. Co(II) undergoes the conversion to Co(IV) by generated HSO 5 - , and 1 O 2 predominantly originates from the intermediate SO 4 •- . Profiting from the highly selective oxidation capacities of Co(IV) and 1 O 2 , the established oxidative system demonstrates a remarkable interference resistance and exhibits an exceptional decontamination performance under real-world water conditions. In short, this work provides a sustainable S(IV)-based oxidation strategy for environmental remediation via non-radical mechanism., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The ubiquity of refractory organic matter in aquatic environments necessitates innovative removal strategies. Sulfate radical-based advanced oxidation has emerged as an attractive solution, offering high selectivity, enduring efficacy, and anti-interference ability. Among many technologies, sulfite activation, leveraging its cost-effectiveness and lower toxicity compared to conventional persulfates, stands out. Yet, the activation process often relies on transition metals, suffering from low atom utilization. Here we introduce a series of single-atom catalysts (SACs) employing transition metals on g-C 3 N 4 substrates, effectively activating sulfite for acetaminophen degradation. We highlight the superior performance of Fe/CN, which demonstrates a degradation rate constant significantly surpassing those of Ni/CN and Cu/CN. Our investigation into the electronic and spin polarization characteristics of these catalysts reveals their critical role in catalytic efficiency, with oxysulfur radical-mediated reactions predominating. Notably, under visible light, the catalytic activity is enhanced, attributed to an increased generation of oxysulfur radicals and a strengthened electron donation-back donation dynamic. The proximity of Fe/CN's d-band center to the Fermi level, alongside its high spin polarization, is shown to improve sulfite adsorption and reduce the HOMO-LUMO gap, thereby accelerating photo-assisted sulfite activation. This work advances the understanding of SACs in environmental applications and lays the groundwork for future water treatment technologies., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Copper-manganese composite metal oxides (CuMnO y ) were prepared by hydrolysis-driven oxidation-reduction method and used to activate sulfite to degrade chlortetracycline hydrochloride (CTC) for the first time. The Jahn-Teller ions Mn 3+ and Cu 2+ exist in CuMnO y , which form a solid electric charge transport redox system and ensure the continuous generation of reactive oxygen species (ROS). Through the systematic study of the experimental parameters such as sulfite concentration, catalyst metal molar ratio, catalyst amounts and initial pH, the optimal degradation rate of CTC could reach 91.74% within 10 min and 94.46% after 30 min. The major reactive radicals were determined by radical quenching experiments and electron paramagnetic resonance (EPR) trapping techniques, and it was confirmed that SO 4 •- and •O 2 - played a nonnegligible role in the process of degrading CTC. Density functional theory (DFT) calculations show that higher Fukui indices (f - and f 0 ) of CTC sites are more vulnerable to free radical attack. CuMnO y has low CTC degradation intermediate toxicity, high catalytic performance, good anti-interference ability, reusability and stability, and possesses decent application potential in the actual water treatment field., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Sulfate radical (SO 4 )-based advanced oxidation processes (AOPs) from sulfite activation have recently received attention for abatement of microorganic pollutants in the aquatic environments. Trace-level Co(II) has been demonstrated to be effective for promoting sulfite activation (simplified as the Co(II)/sulfite system) and the corresponding radical formation, yet this process is challenged by the limited valence inter-transformation of Co(II)/Co(III). In order to enhance this valence inter-transformation, a novel Co(II)/HPO •- )-based advanced oxidation processes (AOPs) from sulfite activation have recently received attention for abatement of microorganic pollutants in the aquatic environments. Trace-level Co(II) has been demonstrated to be effective for promoting sulfite activation (simplified as the Co(II)/sulfite system) and the corresponding radical formation, yet this process is challenged by the limited valence inter-transformation of Co(II)/Co(III). In order to enhance this valence inter-transformation, a novel Co(II)/HPO 4 2- can regulate the electronic structure of Co(II), accelerate electron transfer, and promote valence inter-transformation of Co(II)/Co(III) during the sulfite activation process. The Co(II)/HPO 4 2- , as a typical radical scavenging agent, has the advantage of complexing with Co(II) without quenching effect. In this work, complexation of Co(II) with HPO 4 2- can regulate the electronic structure of Co(II), accelerate electron transfer, and promote valence inter-transformation of Co(II)/Co(III) during the sulfite activation process. The Co(II)/HPO 4 2- in sulfite activation and provides a feasible idea for abatement of the microorganic pollutants.4 •- is identified as the predominant reactive radical contributing to iohexol abatement. The presence of HPO 4 2- broadens the pH adaptability of the Co(II)/sulfite system for iohexol abatement. In addition, the coexisting Cl - exerts an inhibitory effect on iohexol abatement while the other cations and anions show negligible effect. The Co(II)/HPO 4 2- /sulfite system displays good reusability and adaptability towards various organic pollutants. This study highlights the important role of complexation of Co(II) with HPO 4 2- in sulfite activation and provides a feasible idea for abatement of the microorganic pollutants., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The easily synthesized, cost-effective, and stable photocatalysts for sulfite activation are always required for the enhancement of organic contaminants degradation. Herein, the facile coprecipitation synthesis of Bismuth oxybromide (BiOBr)/Montmorillonite (MMT) was reported, which could activate sulfite (SO 3 2- /HSO 3 - ) under sunlight and accelerate the catalytic performance more effectively than pristine BiOBr. After adding sulfite to the photocatalysis system, the photodegradation efficiency of atrazine (ATZ) achieved 73.7% ± 1.5% after 5 min and 94.4% ± 1.6% after 30 min of sunlight irradiation with BiOBr/MMT. The BiOBr/MMT-sulfite system also presented remarkable photocatalytic performance to eliminate various contaminants, including ciprofloxacin, sulfadiazine, tetracycline, and carbamazepine. The various features of the photocatalyst materials were studied, including their surface morphology, structure, optical properties, and composition. The results illustrated that by adding MMT, the bandgap of the pristine BiOBr was reduced and the surface area was increased, which led to an increased ability to adsorb materials. Results of various influence factors showed this enhanced system had satisfactory and stable removal performance of ATZ in the pH range of 3.0-6.5, but HPO 4 2- had a strong negative effect on the system performance. Oxysulfur radicals (SO 5 ·- were discovered as the prevailing active species in the BiOBr/MMT-sulfite system. The proposed degradation mechanism of this photocatalyst-enhanced system revealed that sulfite adsorption on the surface of the photocatalyst played a vital role during the initial phase, and the degradation pathway of ATZ was discussed. This study provides a new synthesis strategy of a photocatalyst for sulfite activation and expands the potential uses of Bi-based photocatalysts in degrading difficult-to-remove organic pollutants.4 ·- ), h + , and 1 O 2 were discovered as the prevailing active species in the BiOBr/MMT-sulfite system. The proposed degradation mechanism of this photocatalyst-enhanced system revealed that sulfite adsorption on the surface of the photocatalyst played a vital role during the initial phase, and the degradation pathway of ATZ was discussed. This study provides a new synthesis strategy of a photocatalyst for sulfite activation and expands the potential uses of Bi-based photocatalysts in degrading difficult-to-remove organic pollutants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Phenols are infamous pollutants in marine environments and present a grave danger to human health, which makes their efficient detection and removal serious issues. Colorimetry is a simple method for detecting phenols in water because phenols can be oxidized by natural laccase and generate a brown product. However, high cost and poor stability impede the wide-spread implementation of natural laccase in phenol detection. To reverse this adverse situation, a nanoscale Cu-S cluster, Cu 4 (MPPM) 4 (Cu 4 S 4 , MPPM = 2-mercapto-5-n-propylpyrimidine), is synthesized. As a stable and inexpensive nanozyme, Cu 4 S 4 shows excellent laccase-mimicking activity and prompts the oxidation of phenols. This characteristic makes Cu 4 S 4 a perfect option for phenol detection with colorimetry. In addition, Cu 4 S 4 also exhibits sulfite activation properties. It can degrade phenols and other pollutants with advanced oxidation processes (AOPs). Theoretical calculations show good laccase-mimicking and sulfite activation properties originating from appropriate interactions between Cu 4 S 4 and substrates. We anticipate that the phenol detection and degradation characteristics of Cu 4 S 4 make it a promising material to be used for practical phenol remediation in water environments., Competing Interests: Declaration of Competing Interest This manuscript is original; it has not been published previously and is not under consideration for publication elsewhere. It has been approved by all authors of Wei Xu, Yifei Zhang, Xia Zhang, Xinxin Xu* and Qiang Wang* as well as the host authority, no author has financial or other contractual agreements that might cause conflicts of interest. If accepted, it will not be published elsewhere in the same form, in English or in any other language, without the written consent of the Publisher. I am one author signing on behalf of all co-authors of this manuscript, and attesting to the above., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Sulfite (S(IV)) is a promising substitute for sulfate radical-based advanced oxidation processes. Here, a composite of in-situ anchoring NiCo 2 O 4 nanosheets on biochar (BC) was firstly employed as a heterogeneous activator for sulfite (NiCo 2 O 4 @BC-sulfite) to degrade atrazine (ATZ) in the neutral environment. The synergistic coupling of BC and NiCo 2 O 4 endows the resulting composite excellent catalytic activity. 82% of the degradation ratio of ATZ (1 mg/L) could be achieved within 10 min at initial concentrations of 0.6 g/L NiCo 2 O 4 @BC, 3.0 mmol/L sulfite in neutral environment. When further supplementing sulfite into the system at 20 min (considering the depletion of sulfite), outstanding degradation efficiency (∼ 100%) were achieved in the next 10 min without any other energy input by the NiCo 2 O 4 @BC-sulfite system. The features of the prepared catalysts and the effects of some key parameters on ATZ degradation were systematically examined. A strong inner-sphere complexation (Co 2+ /Ni 2+ -SO 3 2- ) was explored between sulfite and the metal sites on the NiCo 2 @BC surface. The redox cycle of the surface metal efficiently mediated sulfite activation and triggered the series radical chain reactions. The generated radicals, in particular the surface-bound radicals were involved in ATZ degradation. High performance liquid chromatography-tandem mass spectrometry (LC-MS) technique was used to detect the degradation intermediates. Density functional theory (DFT) calculations were performed to illustrate the possible degradation pathways of ATZ. Finally, an underlying mechanism for ATZ removal was proposed. The present study offered a low-cost and sustainable catalyst for sulfite activation to remove ATZ in an environmentally friendly manner from wastewater.4 @BC surface. The redox cycle of the surface metal efficiently mediated sulfite activation and triggered the series radical chain reactions. The generated radicals, in particular the surface-bound radicals were involved in ATZ degradation. High performance liquid chromatography-tandem mass spectrometry (LC-MS) technique was used to detect the degradation intermediates. Density functional theory (DFT) calculations were performed to illustrate the possible degradation pathways of ATZ. Finally, an underlying mechanism for ATZ removal was proposed. The present study offered a low-cost and sustainable catalyst for sulfite activation to remove ATZ in an environmentally friendly manner from wastewater., (Copyright © 2022. Published by Elsevier B.V.)

As a prospective member in the family of advanced oxidation processes (AOPs), heterogeneous sulfite activation shows low cost and high safety for poisonous organic pollutants' degradation. To obtain an efficient sulfite activator, sulfite oxidase (SuO x ), a molybdenum-based enzyme that can prompt oxidation and activation of sulfite, inspired us greatly. Based on the structure of SuO x , MoS 2 /BPE (BPE = 1, 2-bis-(4-pyridyl)-ethylene) is synthesized successfully. In MoS 2 /BPE , the BPE molecule is inserted between the MoS 2 layers as a pillar and the N atom links with Mo 4+ directly. MoS 2 /BPE generation and organic pollutants' degradation. At pH 7.0, its tetracycline degradation efficiency achieved is 93.9% in 30 min. Furthermore, its sulfite activation ability also endows x mimic activity. Theoretical calculation implies that BPE insertion optimizes the d-band center position of MoS 2 /BPE , which regulates the interaction between MoS 2 mimic activity and sulfite activation ability is clarified in detail.4 2- . This prompts • SO 4 - generation and organic pollutants' degradation. At pH 7.0, its tetracycline degradation efficiency achieved is 93.9% in 30 min. Furthermore, its sulfite activation ability also endows MoS 2 /BPE with excellent antibiofouling performance because • SO 4 - can kill the microorganisms in water effectively. This work develops a new sulfite activator based on SuO x . The connection between structure and SuO x mimic activity and sulfite activation ability is clarified in detail.

Sulfite (SO 3 2- ) activation is one of the most potential sulfate-radical-based advanced oxidation processes, and the catalysts with high efficiency and low-cost are greatly desired. In this study, the cobalt nanoparticles embedded in nitrogen-doped graphite layers (Co@NC), were used to activate SO 3 2- for removal of Methyl Orange in aqueous solution. The Co@NC catalysts were synthesized via pyrolysis of Co 2+ -based metal-organic framework (Co-MOF), where CoO was firstly formed at 400℃ and then partially reduced to Co nanoparticles embedded in carbon layers at 800℃. The Co@NC catalysts were more active than other cobalt-based catalysts such as Co 2+ , Co 3 O 4 and CoFe 2 O 4 , due to the synergistic effect of metallic Co and Co x O y . A series of chain reaction between Co species and dissolved oxygen was established, with the production and transformation of SO 3 • - , SO 5 2- , and subsequent active radicals SO 4 •- and HO•. In addition, HCO 3 - was found to play a key role in the reaction by complexing with Co species on the surface of the catalysts. The results provide a new promising strategy by using the Co@NC catalyst for SO 3 2- oxidation to promote organic pollutants degradation., (Copyright © 2021. Published by Elsevier B.V.)

Sulfite has been used as a classic reductant for the dehalogenation and reduction of organic compounds for a long time, it is recently deemed as a promising alternative (for persulfate) to generate sulfate radical for wastewater treatment due to its low price and eco-toxicity. In contrast with the enormous work developed in the field of tetracycline (TC) degradation via PMS activization, sulfite activization could play a important role in TC degradation but there is only very few available reports in this area. Herein, the novel and efficient CoNHs nanocatalyst is designed and developed, via immobilization of hydrangea-shaped Co 3 O 4 nanoparticles onto graphitic carbon nanosheet (GCN), for the degradation of tetracycline via sulfite activation. The detailed characterizations have confirmed that CoNHs possesses a nanohydrangea-shaped structure with high microporosity. The comparison with other supports (such as CeO 2 and MoS 2 ), CoNHs provides the highest degradation efficiency in TC degradation, due to the synergistic effect between Co 3 O 4 and GCN. Free radical quenching experiments and EPR analysis confirm that SO 4 • - and O 2 • - are major reactive oxygen species in the CoNHs/sulfite system. This work could provide a simple, economical and durable cobalt-based catalyst for organic wastewater treatment via sulfite activation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this study, a series of glucose-derived carbon catalysts were developed and applied for the activation of sulfite for the oxidation of As(III). The process of sulfite activation with the carbon catalysts is based on the production of oxysulfur free radicals such as SO 3 •- , SO 5 . The factors responsible for the sulfite activation performance of carbon catalysts are conductivity and ketonic functional groups. A complex is formed between the sulfite and carbon catalysts, and the electron transfer that takes place within the complex leads to the generation of semiquinone and oxysulfur radicals, and finally, the oxysulfur radicals are converted into SO •- , and SO 4 •- . The factors responsible for the sulfite activation performance of carbon catalysts are conductivity and ketonic functional groups. A complex is formed between the sulfite and carbon catalysts, and the electron transfer that takes place within the complex leads to the generation of semiquinone and oxysulfur radicals, and finally, the oxysulfur radicals are converted into SO 4 •- by means of O 2 , which results in the As(III) oxidation. The efficiency of the sulfite/carbon system is enhanced under normoxia conditions due to the reversible transformation cycle occurring among C═O/C-O • /C-OH triads. The present study is of great environmental significance as sulfite is a source of SO 4 •- generated, and the activation is achieved by a metal-free carbon material, which makes the process viable and environmentally friendly.

Owing to the lower toxicity and mobility of inorganic As(V), the oxidative removal of As(III) is deemed as the optimal approach for arsenic elimination from water. Herein, a synthetic TiO 2 -supported CuO material (Cu-TiO 2 ) was coupled with sulfite (S(IV)) to remove As(III) at neutral pH. The combined process coupled oxidation with adsorption (i.e., As(III) removal by Cu-TiO 2 /S(IV)) was superior than a divided preoxidation-adsorption process (i.e., As(V) removal by Cu-TiO 2 ) for arsenic removal. Attractively, low concentration of As(III) (50-300 μg L -1 ) could be completely removed by Cu-TiO 2 (0.25 g L -1 )/S(IV) (0.5 mM) within 60 min. Mechanism investigations revealed that the efficient As(III) removal was attributed to the continuous oxysulfur radicals (SO x •- ) oxidation and Cu-TiO 2 adsorption. The surface-adsorbed and free sulfate radicals (SO 4 •- ) were further identified as the crucial oxidizing species. The Cu-TiO 2 played the dual roles as a catalyst for S(IV) activation and an absorbent for arsenic immobility. The influence of operating parameters (i.e., As(III) concentration and sulfite dosage) and water chemistry (i.e., pH, inorganic anions, dissolved organic matters, and temperature) on As(III) removal were systematically investigated and optimized. Overall, the proposed process has potential application prospects in rehabilitating the As(III)-polluted water environment using industrial waste sulfite., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this study, biochar R550, obtained from rice husk charred at 550 °C, was used to detoxify Cr(VI) and organic pollutant p-nitrophenol (PNP) with the cooperation of sulfite, simultaneously. Cr(VI) was mainly reduced by sulfite, and the reduction was accelerated by biochar. Also, the reactive oxygen species formed in-situ as a result of enhanced oxidation of sulfite with Cr(VI)/R550 system and the activation of O 2 by R550, led to the degradation of PNP. Production of the radicals viz., SO 3 - , SO 4 - and OH was followed by Electron Paramagnetic Resonance (EPR) study, and the predominant role of SO 4 - towards PNP degradation was confirmed by radical quenching tests. The reaction completed biochar sample was undergone the X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) spectral analysis, which suggested that the carboxyl group of the biochar triggered and enhanced the reactivity of Cr(VI) via coordination linkage, which in turn activated the sulfite and converted the SO 3 . Such results could also be verified by the other three biochar (Oxi-R550, H-R550, and R800). The results of the present study shed light on the mechanism of biochar mediated sulfite activation process by Cr(VI) and also assured the viability and green approach of the technique in detoxifying the industrial effluents containing Cr(VI) and organic pollutants.2- into SO 4 - to a higher extent by overcoming the undesirable transformation of SO 3 2- to SO 4 2- . Such results could also be verified by the other three biochar (Oxi-R550, H-R550, and R800). The results of the present study shed light on the mechanism of biochar mediated sulfite activation process by Cr(VI) and also assured the viability and green approach of the technique in detoxifying the industrial effluents containing Cr(VI) and organic pollutants., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled “Enhancement of S(IV)-Cr(VI) reaction in p-nitrophenol degradation using rice husk biochar at neutral conditions”., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The activation of sulfite by heterogeneous catalysts displays a great potential in the development of new sulfate radials based technologies for wastewater treatment. Herein, cobalt nanoparticles embedded in N-doped carbon nanotubes (Co@NC) were prepared by a simple pyrolysis method. Due to the synergistic effects of the cobalt nanoparticles and N-doped carbon nanotubes, the Co@NC catalyst intrinsically shows an outstanding efficiency, excellent reusability and high stability in the catalytic oxidation of methyl orange (MO) in the presence of sulfite and dioxygen. The structure and efficiency of the catalyst was significantly affected by the content of cobalt and pyrolysis temperature. Several quenching experiments and electron paramagnetic resonance were carried out to investigate the catalytic mechanism. It is found that hydroxyl and sulfate radicals worked together to degrade MO in the system. The formation and decomposition of peroxymonosulfate may be an important route of these reactive radicals production. The effect of different anions, bicarbonate concentration, initial solution pH and dye types on the performance of the catalyst was also studied. This study can open a new approach for design and preparation of encapsulated cobalt in carbon materials as effective catalysts for pollutants degradation via sulfite activation., (Copyright © 2018 Elsevier B.V. All rights reserved.)