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Sulfite (S(IV))-based advanced oxidation process has attracted widespread attention due to the generation of strongly oxidizing sulfate radicals (SO 4 •−) and hydroxyl radicals (HO•) for contaminants remediation. However, the contaminant degradation by singlet oxygen (1O 2) through a nonradical pathway was still unclear in the S(IV) activation system. Herein, a magnetic Fe 3 O 4 /g-C 3 N 4 (MCN) composite was synthesized for the utilization as a visible-light catalyst to activate S(IV) under visible-LED (Vis-LED) for the organic degradation. The incorporation of Fe 3 O 4 in g-C 3 N 4 up-regulated the photocatalytic performance in the S(IV) activation for X-3B degradation, and > 98% of X-3B (20 mg L−1) was degraded with the degradation rate constant (k obs) of 0.110 min−1 within 30 min. The SO 4 •− and 1O 2 produced in the MCN/S(IV)/Vis-LED system were identified as the primary reactive species through the quenching experiments and electron spin resonance. Interestingly, the light-induced generation of superoxide radical (O 2 •−) played a negligible role in the formation of 1O 2 , and most of 1O 2 was corroborated to be originated from SO 4 •− besides SO 5 •−, which was rarely reported in other S(IV) activation processes. The catalysts before and after utilization were characterized to further elucidate the mechanisms for the S(IV) activation. There were two possible pathways for the S(IV) activation: the electron transfer from S(IV) to the photo-generated holes and the ligand-to-metal charge-transfer (LMCT) within the surface Fe(III)−S(IV) complexes. Furthermore, the MCN/S(IV)/Vis-LED system was of high resistance to complex water matrixes (pH, inorganic anions, etc.), demonstrating its application perspective in the purification of wastewater containing organic pollutants. [Display omitted] • A novel sulfite-based AOP for organic degradation, MCN/S(IV)/Vis-LED, is developed. • Organic degradation relies on the SO 4 •− and 1O 2 generated via S(IV) activation. • Besides SO 5 •−, most of 1O 2 is originated from SO 4 •− instead of O 2 •−. • S(IV) activation is through electron transfer and ligand-to-metal charge-transfer. • Procedure to realize the purification of organic-contaminated water is proposed. [ABSTRACT FROM AUTHOR]

As sulfite has been employed currently in the catalytic degradation of various pollutants, the construction of more suitable and cheaper catalytic systems is required. Herein, a heterogeneous system for S(IV) activation by iron(III) titanium oxide (Fe 2 TiO 5) was proposed to proceed the removal of acid orange 7 (AO7) and seven typical pharmaceutical and personal care products (PPCPs). Typically, the AO7 (10 mg L−1) can be degraded up to 67% within 60 min ([Fe 2 TiO 5 ] = 0.8 g L−1, [S(IV)] = 2.0 mM, pH = 6.0). The effects of initial AO7 concentration, pH, Fe 2 TiO 5 dosage, S(IV) concentration, and co-existing anions (HCO 3 − and H 2 PO 4 −) were examined to explore the application conditions and resistance of Fe 2 TiO 5 −S(IV) system. Moreover, the stability of Fe 2 TiO 5 −S(IV) system was tested by sequential runs, while XRD was also performed for the robustness evaluation of catalyst. The scavenging experiment showed that the active species in the system mainly include SO 5 •−, HO•, and SO 4 •−, while SO 4 •− being the dominant one. Through the competitive experiments of EDTA, the density functional theory (DFT) computation and the XPS analysis, a sensible mechanism was proposed that the electron transfer within Fe(III)−SO 3 2− complex and the Fe(III)−Fe(II)−Fe(III) redox process were crucial for the sulfite activation. Meanwhile, a quantitative structural-activity relationship (QSAR) model for pseudo-first-order rate constants (k obs) was established with a high significance (R2 = 0.991, p = 0.006) by using four descriptors. This work provides an innovative strategy of sulfate radical-based advanced oxidation processes (SR−AOPs) for organic contaminants degradation using metal oxide catalysts. • Fe 2 TiO 5 –sulfite system is proposed as a novel sulfate-radical-based AOP. • Near-neutral pH favors sulfite activation by Fe 2 TiO 5 to produce oxysulfur radicals. • SO 4 •−, HO•, and SO 5 •− are main oxidative species for organic contaminants oxidation. • QSAR in degradation of seven PPCPs in Fe 2 TiO 5 –sulfite system is established. [ABSTRACT FROM AUTHOR]

Sulfate radical-based advanced oxidation process could efficiently remove many emerging contaminants from wastewater. Considering the unique properties of MnNb 2 O 6 , an efficient MnNb 2 O 6 /sulfite system was developed to remove doxycycline residue from the aqueous environment. In this research, MnNb 2 O 6 nanomaterial was successfully synthesized through a one-step hydrothermal route at 260 °C for 24 h. The paramagnetic behavior of MnNb 2 O 6 was observed at 300 K. Scanning electron microscopy and transmission electron microscopy images showed that the size of petal-like MnNb 2 O 6 crystals was 250–700 nm. The specific surface area of MnNb 2 O 6 was 24.84 m2/g. Optimization of MnNb 2 O 6 /sulfite process was achieved by Box-Behnken Design based on response surface methodology. Under the predicted optimal conditions (pH of 8.7, MnNb 2 O 6 dosage of 0.29 g/L, doxycycline concentration of 10.8 mg/L, and sodium sulfite concentration of 4.3 mM), the degradation efficiency of doxycycline could reach 85.1%. Mn species was found to be the dominant factor in MnNb 2 O 6 /sulfite system. Both SO 4 •− and •OH were identified as primary active radicals in MnNb 2 O 6 /sulfite system. Furthermore, six transformation products of doxycycline were elucidated. This work offers a simple water treatment process for efficiently removing doxycycline residue in the environment. [Display omitted] • MnNb 2 O 6 /sulfite system was developed for the removal of doxycycline. • The degradation process of doxycycline was optimized by RSM. • Mn species was the dominant factor. • SO 4 •− and •OH were identified as primary active radicals. • Six transformation products of doxycycline were provided. [ABSTRACT FROM AUTHOR]

Sulfite(S(IV))-induced advanced oxidation processes (AOPs) have great prospect in the field of removing organic pollutants, yet developing highly efficient sulfite activation systems and optimizing active sites for favorable catalytic processes are important but still challenging. Herein, we have achieved a composite catalyst with modulated Co electron structure for efficient AOPs by decorating Co(OH) 2 on ultrathin graphitic carbon nitride (g-C 3 N 4) nanosheet through an adjustable strategy, which exhibits high catalytic performance in S(IV) activation system. At optimal pH 9, 92% of paracetamol (APAP) (0.005 mM) is removed with the degradation rate constant of k 1 = 0.193 min−1 within 30 min in presence of the composite material. The in-situ synthesis mode introduces strong heterogeneous interface interaction, resulting in directional electron transfer from cobalt hydroxide layer to g-C 3 N 4 sheet revealed by X-ray photoelectron spectroscopy and density functional theory (DFT) calculations. The underlying activity enhanced mechanisms for APAP in S(IV) activation system using Co(OH) 2 /g-C 3 N 4 are proposed: (i) The ultrathin g-C 3 N 4 nanosheets provide more anchoring centers for generating small Co(OH) 2 nanoparticles with abundant active sites which benefit to form metastable intermediates of Co(II)-SO 3 ; (ii) The strong interface interaction induces charge redistribution between Co(OH) 2 and g-C 3 N 4 conformed by DFT calculation, which modulates the d-band center of Co site and strengthens the bind of Co(II)-SO 3 , thereby giving rise to radicals (•OH, SO 4 • and O 2 • ) and nonradicals (1O 2 and electron transfer) oxidation for highly-efficient removal APAP. Our work will pave the way to build an environmentally friendly strategy for emerging organic pollutant degradation in water through building efficient catalysts in sulfite activation system. [Display omitted] • In-situ construction of Co(OH) 2 decorated ultra-thin g-C 3 N 4 was obtained, possessing strong heterogeneous interface interaction. • DFT calculations elaborated that the charge redistribution modulated d‐band center of Co and strengthened the bind of Co(II)-SO 3. • Synergistic effect of radical and nonradical oxidation for boosting the degradation of paracetamol via sulfite activation system. [ABSTRACT FROM AUTHOR]

Cobalt-based heterogeneous catalysts receive research interests in the sulfite activation to generate reactive radicals for abatement of organic contaminants in the aquatic environments, yet the sulfite activation efficacy is compromised by the limited utilization of available active cobalt sites. To address this problem, the atomically dispersed cobalt loaded on mesoporous silica SBA-15 (simplified as Co/SBA-15) is constructed for sulfite activation process regarding the incorporation of cobalt species into the confined space abundant with silicon hydroxyl groups in SBA-15. Co/SBA-15 exhibits excellent sulfite activation efficacy, in which iohexol can be completely degraded within 30 min. Sulfate radical (SO 4 •−) and hydroxyl radical (HO•) are the dominant reactive radicals responsible for iohexol abatement, in which 7.15 μM of SO 4 •− and 2.23 μM of HO• are produced. The excellent electron transfer efficiency of Co/SBA-15 is demonstrated by electrochemical impedance spectroscopy (EIS). Structural characterization and valence analysis suggest that the formation of atomically dispersed cobalt species facilitates the sulfite activation and Lewis acid sites on Co/SBA-15 can adsorb organic molecular fragments to realize the rapid conversion from >Co(III) to >Co(II) by electron transfer. The iohexol degradation pathways are also proposed based on UPLC-QTOF-MS analysis. In addition, the effects of various influencing factors including the reactant dosage, coexisting anions, humic acid and the different real water backgrounds on iohexol abatement are systematically investigated. This study is expected to provide an efficient heterogeneous catalyst for sulfite activation to achieve the rapid abatement of organic contaminants. [Display omitted] • Atomically dispersed Co/SBA-15 was prepared for efficient sulfite activation. • Co/SBA-15 with Lewis acid exhibited good electron transfer efficiency. • SO 4 •− and HO• were identified as the major radicals in Co/SBA-15/sulfite process. • Iohexol degradation products were identified and possible pathways were proposed. [ABSTRACT FROM AUTHOR]

This paper offers novel insights into the recently reported cobalt(II) sulfide (CoS) activated sulfite (S(IV)) process. After adding 0.5 g/L CoS and 0.4 mM S(IV) at pH 9.0, 83.1% of acetaminophen (ACP) was removed in 10 min. However, this effect was subject to the inhibition of coexisting chloride or humic acid. Dissolved O 2 played an important role in the reaction. The interactive impacts between S(IV) concentration and initial pH were found the most significant. The CoS/S(IV) system involved synchronous homogeneous and heterogeneous catalysis, which demonstrated sizable ACP degradation. The generated sulfate radical (SO 4 •−) and hydroxyl radical (HO•) were primarily responsible for ACP degradation. DFT-based first-principle calculations show the electrons transferred from sulfite to the CoS surface in heterogeneous activation. The pathway of ACP degradation was determined to primarily comprise addition and substitution reactions based on the detected intermediates. Besides, the CoS/S(IV) system demonstrated good reusability and was successful in degrading the other five organics: bisphenol A, metoprolol, estriol, atenolol, and imipramine. The ACP removal performance under real water background was also acceptable. As a result, the CoS/S(IV) system is expected to be a reliable approach for water treatment. [Display omitted] • A synergistic homogeneous-heterogeneous catalysis occurred in CoS/sulfite system. • The rapid conversion of SO 3 •− to HO• was clearly recorded in this process. • The interactive effect between sulfite dosage and initial pH were most significant. • Density functional theory was adopted to help infer the reaction mechanism. [ABSTRACT FROM AUTHOR]