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[Display omitted] • A novel oxidative degradation process, FeO x @C/sulfite/UVA, was developed. • Synergy of photo-generated holes and Fe active sites promotes sulfite activation. • Radicals and non-radicals are majorly derived from the crucial SO 5 −. • Both Fe(IV) and 1O 2 are the dominant non-radical species to OFL degradation. • Procedure to realize the remediation of antibiotic-spiked water is proposed. Advanced oxidation processes (AOPs) based on sulfite (S(IV)) activation are gaining recognition as a promising Fenton-like strategy, primarily due to their ability to generate potent radicals (e.g., SO 4 − and HO). However, the existence and role of a non-radical-driven oxidation pathway in the S(IV)-mediated degradation of contaminants remain under debate. Herein, a magnetic iron-carbon composite (FeO x @C) was fabricated using the MOF-templated method and utilized as a stable photocatalyst to activate S(IV) under UVA light, achieving >93.6 % degradation of 20 μM ofloxacin (OFL) with a high degradation rate constant of 0.073 min−1 within 45 min. The catalyst's porous carbon structure facilitated the transport of substrates to active sites and shortened the diffusion distance between reactive species and contaminants. Adsorbed S(IV) donated one electron to photo-generated holes and exposed Fe(III) sites with the formation of SO 5 −, which then followed two distinct pathways to produce radicals (SO 4 −) and non-radicals (Fe(IV) and 1O 2) responsible for OFL degradation. By leveraging the synergy of both radicals and non-radicals, this innovative oxidative system showcased robust anti-interference capacities and exceptional performance in degrading contaminants from complex water matrices. This study provides new insights into the significant role of non-radical species in S(IV)-mediated decontamination processes. [ABSTRACT FROM AUTHOR]

• A novel Fe/Mn@CF composite electrode is fabricated for the activation of sulfite. • Fe/Mn@CF-sulfite system exhibits satisfied degradation activity and stability. • Both free radical and non-free radical pathways boost pollutant degradation. • The presence of redox cycles of Fe and Mn promotes the activation of sulfite. • The synergistic interactions of electric field and metals lead to efficient sulfite activation. Sulfite has been proven to promote advanced oxidation processes (AOPs) to achieve low-cost and efficient degradation of contaminants, serving as an alternative to persulfate. In this study, a novel composite Fe/Mn@carbon felt (CF) electrode was successfully constructed to remove carbamazepine (CBZ). The capacity of the Fe/Mn@CF anode to activate sulfite was evaluated under various electrode preparation conditions and operating parameters. Results clearly indicated that the complete removal of CBZ was achieved in Fe/Mn@CF anode activated sulfite system under the specific conditions including Na 2 SO 4 electrolyte concentration of 50 mM, sulfite dosage of 1 mM, initial pH of 7, and current density of 1 mA/cm2. The capacity of Fe/Mn@CF anode for sulfite activation was further presented by its excellent reusability and stability in terms of CBZ removal and metal ion release. Both radical and non-radical pathways were significantly contributed to the CBZ removal, including OH, SO 4 · - , O 2 · - , 1O 2 , and other reasons. Density functional theory (DFT) calculations demonstrated that Fe-Mn bimetals effectively promoted sulfite activation, with the electric field further boosting the process of Fe-Mn valence cycle and oxidation. Overall, the novel Fe/Mn@CF activated sulfite system exhibited outstanding performance and had great potential for sustainable use in removing organics. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel carbon/sulfite system showed efficient removal of pharmaceuticals. • Quinone groups and conductivity were the key factors in sulfite activation. • The toxicity of pharmaceuticals could be significantly reduced. • Carbon/sulfite system exhibited effectiveness in actual wastewater treatment. • A continuous flow membrane reactor showed excellent reactivity and durability. Sulfite [S(IV)] activation processes have aroused increasing attention in the field of wastewater treatment. In this study, a novel humic acid-derived carbon (HAC-10) material was demonstrated as highly active and environmentally friendly S(IV) activator for the efficient elimination of recalcitrant pharmaceutical contaminants. The results suggested that quinone groups and conductivity served as the active site/structure for S(IV) activation, while the rapid adsorption process of contaminant significantly reduced the migration distance of generated SO 4 –, thus facilitating the degradation processes. The carbon–S(IV)* complexes were confirmed to be the primary step to produce SO 4 –. The mineralization process of tetracycline hydrochloride (TC, a model pharmaceutical) could effectively reduce its biological toxicity. In addition, S(IV)/HAC-10 system exhibited excellent adaptability to different pharmaceuticals, natural water matrix and was capable of effectively eliminating contaminants in actual wastewater. Furthermore, a continuous flow reactor consisting of HAC-10 catalyst membrane showed excellent reactivity and durability. Overall, this study provides novel insights into the activation mechanism of S(IV) by carbon materials, and advances the practical application of S(IV) activation processes in the decontamination and detoxification of pharmaceutical wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Promoted removal of arsenic by ZIF-67/sulfite than ZIF-67 is achieved. • Fast As(III) removal is through an integration of oxidation and adsorption. • SO 4 − is responsible for As(III) oxidation in solution and on catalyst surface. • The sulfite activation by ZIF-67 provides extra sites for As(III,V) adsorption. • Operating parameters of ZIF-67/sulfite system for arsenic removal are optimized. Elimination of As(III) from water has gotten more attention in comparison with As(V) due to its higher mobility and toxicity. In this work, we provide an effective method by integrating a cobalt-based metal–organic framework ZIF-67 and sulfite (S(IV)) to purify As(III)-laden water. The coupled oxidation with adsorption process (i.e., As(III) removal by ZIF-67/S(IV)) surpasses a divided preoxidation-adsorption process (i.e., As(V) removal by ZIF-67) for arsenic removal from the multi-component water containing various coexisting anions. Herein, the mechanism investigation corroborated that the S(IV) plays dual roles as a complexing ligand and a precursor of oxysulfur radicals. The enhanced As(III) removal is attributed to the S(IV) activation on the ZIF-67 surface via various reactions (e.g., surface complexation and intramolecular electron transfer), which not only generates SO 4 − radicals for rapid oxidation of As(III) to As(V), but also provides more adsorption sites for the immobilization of the oxidized product (As(V)). Furthermore, the combined process can rapidly treat arsenic in the realistic contaminated water from 242 to 7 μg L−1 within 15 min, directly meeting the provisional maximum contaminant level (<10 μg L−1). Overall, the proposed work may aid the rational design of S(IV) mediated oxidation-adsorption process to remove arsenic from a variety of contaminated waters. [ABSTRACT FROM AUTHOR]

[Display omitted] • FeO was first used as a ferrous source for sulfite (S(IV)) activation. • DFT and electrochemical analyses confirm the little role of interface catalysis. • The Fe(II/III)–S(IV) complex geometry was determined from thermodynamics. • The RSE decreased with the increase of S(IV) concentration. • The FeO/S(IV) process has an advantage over FeO/persulfate and FeO/peroxymonosulfate. In this study, we constructed an advanced oxidation process using FeO for sulfite (S(IV)) activation. By selecting antidepressant fluoxetine (FLX) as the target, the FeO/S(IV) system's performance was investigated. Up to 84.4% of FLX could be rapidly eliminated in 17.5 min under optimal reaction conditions. The results confirmed that the S(IV) activation was dominantly attributed to the released Fe2+ from FeO, rather than an interface reaction, supported by theoretical calculations and electrochemical characterization. Besides, the Fe–S(IV) complex geometry was determined using density functional theory (DFT), indicating a Fe–O–S ligand form. Energy files demonstrate the decomposition of FeSO 3 + complex might be endothermic. These findings provide new insight into the Fe(II)/S(IV) mechanism. The generated SO 4 •− primarily caused FLX removal, where 23 product types were detected. The degradation pathway was proposed, mostly containing hydroxylation and ring-opening, which decreased the toxicity of FLX. Furthermore, the FeO/S(IV) system had good reusability and applicability, maintaining high efficiency in real water. Compared to peroxydisulfate and peroxymonosulfate, S(IV) had obvious advantages in FeO-induced activation. This research discloses a promising technology for the FeO/S(IV) water treatment system. [ABSTRACT FROM AUTHOR]

[Display omitted] • VIS/sulfite/Fe/g-C 3 N 4 (N 2) system shows promise in contaminant removal and sterilization. • The introduction of sulfite enhances the formation of SO 4 •− and •O 2 –. • The presence of NVs accelerates Fe3+/Fe2+ redox cycle. • Fe/g-C 3 N 4-x with rich NVs exhibits stronger interaction towards HSO 3 −. • A mechanism of synergy between Fe, NVs, and g-C 3 N 4 in sulfite activation is proposed. A novel Fe-modified g-C 3 N 4 with rich N vacancies (NVs) under N 2 calcination was developed to active sulfite for the efficient removal of contaminants and bacterial inactivation under visible light (VIS). The degradation rates of VIS/sulfite/Fe/g-C 3 N 4 (N 2) for acetaminophen (ACT) were 10.94, 4.88, and 2.85 times higher than those of VIS/Fe/g-C 3 N 4 (N 2), VIS/sulfite/g-C 3 N 4 (N 2), and VIS/sulfite/Fe/g-C 3 N 4 (CO 2), respectively. Escherichia coli (E. coli) with an initial concentration of 2.5 × 108 CFU/mL decreased by 6.1 and 8.4 log CFU/mL within 60 min and 80 min of inactivation, respectively. The activation of sulfite led to the generation of oxysulfur radicals, and the consumption of hole (h+) by sulfite inhibited its recombination with electron (e−), promoting the formation of superoxide radical (•O 2 –). The synergistic effect of Fe, NVs, and g-C 3 N 4 in VIS/sulfite/Fe/g-C 3 N 4 (N 2) system promoted the generation of oxysulfur radicals. Density functional theory (DFT) calculations indicated that NVs facilitated charge transfer from Fe to g-C 3 N 4 substrate, accelerating the Fe3+/Fe2+ and oxysulfur radical cycles. Fe/g-C 3 N 4 with rich NVs exhibited lower adsorption binding energy, faster charge transfer, and longer S-O bond length than pristine Fe/g-C 3 N 4 during sulfite adsorption. This work unraveled the synergistic mechanism of Fe, NVs, and g-C 3 N 4 , which provides new insights into heterogeneous photocatalysts on sulfite activation for water treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag@CNG composites are successful fabricated by one-step hydrothermal reaction. • The composites show excellent visible light response and stability. • Enhanced degradation of dimethoate as sulfite activation and fast charge transfer. • Degradation mechanism and toxicity evolution of dimethoate were investigated. As pesticides are widely found in water, it is still a challenge to find an economical and effective technology to remove organophosphorus pesticides. Therefore, A composite with silver nanoparticles modified graphene oxide-supported graphitic carbon nitride microflowers ternary heterojunction (Ag@CNG) was synthesized by facile hydrothermal process. A novel composite system composed of photocatalysis and sulfite activation under visible light (Vis/Ag@CNG/sulfite) was constructed to realize the efficient removal of pesticides dimethoate (DT). Characterization results showed that the surface plasmon resonance (SPR) effect and ternary heterojunction could promote the photo-electrons transfer, and enhance the absorption of visible light. Moreover, the by-product sulfite added could be activated by holes to introduce novel SO 4 −, and obviously improve the decomposition of DT. Additionally, effects of operating parameters and supporting electrolyte on the degradation of DT were also detailed. Especially, the degradation pathways and mechanism of DT were revealed in depth through trapping experiments and GC–MS analysis combined with theoretical calculation. The toxicity evolution of products was also comprehensively evaluated. It was proved by degradation of different pollutants that the new composite system presented a great application potential for refractory and deleterious pollutants removal in water. [ABSTRACT FROM AUTHOR]

[Display omitted] • The photoelectrochemical performance of BiVO 4 photoanode was significantly improved by controlling morphology. • The PEC activation of sulfite simultaneously promoted PPCPs degradation, H 2 evolution, and E. coli disinfection. • SO 4 − contributed the most to BZP degradation. A new photoelectrochemical (PEC) system by means of adding sodium sulfite (Na 2 SO 3) was developed to treat sewage. The PEC system simultaneously promoted pharmaceuticals and personal care products (PPCPs) degradation, H 2 evolution and E. coli disinfection using an optimized, visible–light driven BiVO 4 photoanode. The PEC reactions were first carried out in 1.5 mM Na 2 SO 3 electrolyte. 92.3% of 2 ppm benzophenone-3 (BZP) was degraded, and 115.36 μmol of H 2 was produced in 90 min at 1.0 V vs. Ag/AgCl, which was a significant improvement over cases where the electrolyte was either Na 2 SO 4 or NaCl. The sulfite ions were first activated by holes and then converted into sulfate radicals, which played a dominant role in the degradation of BZP. As the holes were caught by the sulfite, charge separation was also enhanced, increasing H 2 evolution. The PEC reactions were also used to treat real sewage, in which case an 82% improvement in the rate constant of BZP degradation, 60% increase of H 2 evolution, and 0.78 log enhancement of E. coli disinfection were achieved by adding 1.5 mM Na 2 SO 3. The system was also feasible to degrade various PPCPs, and showed excellent reusability and stability, proving its great potential in sewage treatment. [ABSTRACT FROM AUTHOR]

• Supramolecular hydrogel assisted fabrication of single-atom Fe deposited bamboo-like porous g-C 3 N 4. • Superior sulfite activation over homogeneous Fe and g-C 3 N 4 due to the synergetic effect of single-atom Fe and g-C 3 N 4. • The contribution of synergetic effect depends on sulfite species. • DFT calculation favors the identification of diclofenac degradation pathways. • Successful dechlorination reduces the toxicity of diclofenac. Herein, through supramolecular gel assisted pre-configuration, a novel bamboo-like porous graphitic carbon nitride (g-C 3 N 4) deposited with single-atom Fe was successfully prepared and used for sulfite (S(IV)) activation. Unexpectedly, owing to the presence of single-atom Fe, hybrid material with only 2.5‰ of Fe exhibited 16 times higher S(IV) activation efficiency for diclofenac removal than pure g-C 3 N 4 under visible light irradiation. Moreover, a synergetic effect of Fe and g-C 3 N 4 was found to play the dominate role, and the synergetic factor was calculated to be 0.84. The synergetic mechanism mainly related to the generation of surface Fe-S(IV) complex, which could be affected by S(IV) species or the presence of H 2 PO 4 −. DCF removal was significantly enhanced at alkaline condition, but the enhancement was mainly attributed to photocatalysis but not synergetic effect. Decarboxylation, hydroxylation, chlorine abstraction and cleavages at bridging N atom were the main degradation pathways of DCF, which agreed well with Fukui index prediction. The toxicity of DCF was alleviated during the degradation process through successful mineralization of chlorine atoms. [ABSTRACT FROM AUTHOR]

• Captured SO 2 reutilization and water remediation were simultaneously achieved. • An EC/CoSi/sulfite system for efficient sulfate radical production was developed. • Insights for synergy mechanism of EC/CoSi/sulfite system were provided. • Influencing factors were investigated and operating conditions were optimized. The desulfurization by-product (e.g. sulfite) treatment and water pollution are two widespread concerns, while the sulfite activation by transition metals can be adopted to solve both of them simultaneously. In this study, a silica-supported cobalt catalyst (CoSi) was used to activate sulfite for the degradation of organic pollutants in an electrochemical system (the EC/CoSi/sulfite system), which demonstrated remarkable water treatment efficiencies due to sulfate radical oxidation. The synergy mechanisms of the EC/CoSi/sulfite system were revealed. (i) The as-prepared CoSi played the dual roles as an electro-adsorbent and a catalyst for sulfite activation. (ii) The electrolytic oxygenation supported the conversion of cobalt species and the chain reactions of oxysulfur radicals. (iii) The anodic oxidation of sulfite also generated oxysulfur radicals. The influencing factors and operating parameters were investigated and optimized systematically. Moreover, the efficient degradation of highly concentrated X-3B and non-selective oxidation of various organic compounds confirmed the promising application of the EC/CoSi/sulfite system in practical water treatment. Overall, the EC/CoSi/sulfite system created new value of the industrial waste (e.g. sulfite) for further application in the environmental remediation. [ABSTRACT FROM AUTHOR]

• Charge transfer efficiency of MoS 2 photoanode was improved by forming heterojunction. • The hybrid photoanode presents enhanced PEC performance and oxidation of ammonia. • Selective and efficient conversion of ammonia to dinitrogen was exclusively achieved. • Oxysulfur radicals are more powerful than OH for ammonia oxidation. • Sulfite serves as both hole scavenger and precursor of oxysulfur radicals. Charge transfer efficiency of semiconductor photoanode in photoelectrochemical (PEC) system is one of crucial factor determining the overall PEC performance. Previously, we have developed a MoS 2 -based PEC system that is able to specifically convert ammonia nitrogen in aqueous solution into gaseous nitrogen (e.g. N 2) utilizing oxysulfur radicals. Herein, in order to solve the slow charge transfer issue of reported MoS 2 -based PEC oxidation system, we further improve the PEC conversion efficiency by tuning composition of MoS 2 /WS 2 nanosheets heterojunction photoanode. The hybrid MoS 2 /WS 2 (1:1) electrode displays the highest PEC performance and ammonia conversion efficiency compared to the individual MoS 2 or WS 2 constituent under visible light irradiation, which can be mainly ascribed to the reduced electrode resistance and improved charge transfer efficiency according to the physiochemical, electrochemical and spectroscopic analysis. The results prove that both interfacial and interior charge carrier transfer processes of photoanode are crucial and tailorable in order to efficiently generate reactive radical species for ammonia conversion. [ABSTRACT FROM AUTHOR]