A triple system of Fe(III)/sulfite/persulfate: Decolorization and mineralization of reactive Brilliant Red X-3B in aqueous solution at near-neutral pH values

Degradation of β-lactam antibiotics by Fe(III)/HSO3- system and their quantitative structure-activity relationship

β-lactam antibiotics, extensively used worldwide, pose significant risks to human health and ecological safety due to their accumulation in the environment. Recent studies have demonstrated the efficacy of transition metal-activated sulfite systems, like Fe(Ⅲ)/HSO3-, in removing PPCPs from water. However, research on their capability to degrade β-lactam antibiotics remains sparse. This paper evaluates the degradation of 14 types of β-lactam antibiotics in Fe(Ⅲ)/HSO3- system and establishes a QSAR model correlating molecular descriptors with degradation rates using the MLR method. Using cefazolin as a case study, this research predicts degradation pathways through NPA charge and Fukui function analysis, corroborated by UPLC-MS product analysis. The investigation further explores the influence of variables such as HSO3- dosage, substrate concentration, Fe(Ⅲ) dosage, initial pH and the presence of common seen water matrices including humic acid and bicarbonate on the degradation efficiency. Optimal conditions for cefazolin degradation in Fe(Ⅲ)/HSO3- system were determined to be 93.3 μM HSO3-, 8.12 μM Fe(Ⅲ) and an initial pH of 3.61, under which the interaction of Fe(Ⅲ) dosage with initial pH was found to significantly affect the degradation efficiency. This study not only provides a novel degradation approach for β-lactam antibiotics but also expands the theoretical application horizon of the Fe(Ⅲ)/HSO3- system.

Development of persulfate-based advanced oxidation processes to remove synthetic azo dyes from aqueous matrices

Azo dyes are largely used in many industries and discharged in large volumes of their effluents into the aquatic environment giving rise to non-esthetic pollution and health-risk problems. Due to the high stability of azo dyes in ambient conditions, they cannot be abated in conventional wastewater treatment plants. Over the last fifteen years, the decontamination of dyeing effluents by persulfate (PS)-based advanced oxidation processes (AOPs) has received a great attention. In these methods, PS is activated to be decomposed into sulfate radical anion (SO4•-), which is further partially hydrolyzed to hydroxyl radical (•OH). Superoxide ion (O2•-) and singlet oxygen (1O2) can also be produced as oxidants. This review summarizes the results reported for the discoloration and mineralization of synthetic and real waters contaminated with azo dyes covering up to November 2023. PS activation with iron, non-iron transition metals, and carbonaceous materials catalysts, heat, UVC light, photocatalysis, photodegradation with iron, electrochemical and related processes, microwaves, ozonation, ultrasounds, and other processes is detailed and analyzed. The principles and characteristics of each method are explained with special attention to the operating variables, the different oxidizing species generated yielding radical and non-radical mechanisms, the addition of inorganic anions and natural organic matter, the aqueous matrix, and the by-products identified. Finally, the overall loss of toxicity or partial detoxification of treated azo dye solutions during the PS-based AOPs is discussed.

Sulfite Poses a Risk of Hexavalent Chromium Rebound in Vadose Zone: A Challenge of the Stability of CrxFe1-x(OH)3

Cr(VI) rebound is the primary risk associated with the reduction remediation of Cr(VI)-contaminated soil. The potential impact of sulfites, which can be produced by microbial activities or originate from sulfur-containing remediation agents, on the Cr(VI) rebound in the vadose zone has been overlooked. When sulfites are present, the stability of CrxFe1-x(OH)3 is compromised and significantly inferior to that of Cr(OH)3, as demonstrated in this paper. First, Fe acts as a catalyst for the conversion of adsorbed sulfite to SO4·-, which subsequently triggers the oxidation of Cr(III) and results in the rebound of Cr(VI). The heterogeneous catalysis by Fe on the surface of CrxFe1-x(OH)3 plays a predominant role, contributing to 78% of the actual oxidation of Cr(III) among all employed catalytic processes. The presence of ambient Cl- can exacerbate the rebound effect of Cr(VI) by promoting the generation of HOCl. Furthermore, a portion of released Cr(VI) was reduced to Cr(III) by dissolved sulfite in the presence of dissolved Fe as a catalyst, thereby increasing the dissolution and migration risk associated with CrxFe1-x(OH)3. Hence, the presence of sulfites results in a significant increase in the Cr(VI) rebound and Cr(III) release from CrxFe1-x(OH)3. This challenges the conventional understanding of the stability of CrxFe1-x(OH)3.

Construction of cubic CaTiO3 perovskite modified by highly-dispersed cobalt for efficient catalytic degradation of psychoactive pharmaceuticals

Sulfate radical mediated advanced oxidation processes (SR-AOPs) have emerged as a promising alternative for emerging contaminants degradation. However, high activity and great stability are commonly difficult to juggle, and the structure-activity correlations are still ambiguous. This study constructed the cubic CaTiO3 perovskite modified by highly-dispersed cobalt for peroxymonosulfate (PMS) activation to improve the specific lattice plane exposure and reduce the metal leaching simultaneously. 98% of amitriptyline (AMT) degradation was achieved within 60 min under the condition of 200 mg/L Co0.1-CTO and 100 mg/L PMS. The results indicated that surface Co2+/Co3+ redox couple and lattice oxygen were responsible for PMS activation, and the evolution of ·OH, SO4·- and 1O2 were revealed. According to density functional theory (DFT) calculations, the highly-dispersed Co on cubic surface effectively captured PMS and promoted electron transfer for the generation of ·OH and SO4·-, while more oxygen atoms exposed on Co0.1-CTO(200) surface facilitated the generation of 1O2. Briefly, this study provides a novel strategy of catalyst synthesis in PMS activation for water treatment.

Comparative studies of organic contaminant removal in different calcium sulfite-enhanced oxidant/Fe(II) systems: Kinetics, mechanisms, and differentiated degradation pathways

The application of S(IV) for the regeneration of Fe(II) has been widely investigated. As the common S(IV) sources, sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) are soluble in the solution, resulting in excessive SO32- concentration and redundant radical scavenging problems. In this research, calcium sulfite (CaSO3) was applied as the substitution for the enhancement of different oxidant/Fe(II) systems. The advantages of CaSO3 could be summarized as follows: (1) it could sustainedly supplement SO32- for Fe(II) regeneration, preventing radical scavenging and unnecessary reagent waste; (2) the cost and toxicity of CaSO3 were extremely lower than that of other S(IV) sources; (3) the concentration of reactive species increased in the presence of CaSO3; and (4) after the reaction, SO42- would form CaSO4 precipitate, which would not increase the burden of SO42- in the solution. In the participation of CaSO3, the removal of trichloroethylene (TCE) and other organic contaminants were significantly promoted and different enhanced systems had high tolerance on complex solution conditions. The major reactive species in different systems were determined through qualitative and quantitative analyses. Eventually, the dechlorination and mineralization of TCE were measured and the differentiated degradation pathways in different CaSO3-enhanced oxidants/Fe(II) systems were elucidated.

Hydrogen sulfite promoted the activation of persulfate by μM Fe2+ for bisphenol A degradation

This study evaluated the improvement of bisphenol A (BPA) elimination through hydrogen sulfite (HS) coupling with persulfate (PS) activated by low amounts of Fe²⁺. Under the optimum condition (10 μM Fe²⁺, 0.6 mM HS, 0.8 mM PS, pH = 4.0), 100% BPA (5 μM) was removed within 15 min. Sulfate radical (SO₄^•-) and singlet oxygen (¹O₂) were confirmed as the primary active species for BPA degradation in the Fe²⁺/HS/PS system, and the steady-state concentration of SO₄^•- and ¹O₂ was 2.43 × 10^-9 M and 1.67 × 10^-9 M, respectively. Besides, FeHSO₃⁺ and FeOHSO₃H⁺ were the main iron species in the Fe²⁺/HS/PS system. The removal potency of BPA depended on the operation parameters, such as chemical reagent dosages, reaction temperature, and the solution initial pH. The impact of NO₃^-, SO₄^2-, and humic acid (HA) on BPA removal was negligible, whereas Cl^-, HCO₃^-, and HPO₄^2- restrained BPA decomposition. Two injections of HS could improve the limitation of BPA degradation efficiency due to the rapid consumption of HS in the reaction process. The lower removal efficiency of BPA was observed in real water matrices than that in ultrapure water. Whatever, up to 58.1%, 66.3%, 68.1%, and 88.1% of BPA were removed from domestic wastewater, lake water, river water, and tap water within 10 min, respectively. In addition, the BPA degradation process was characterized by the 3D fluorescence spectra technique, which indicated the BPA oxidation intermediates also have fluorescence characteristics. Moreover, 6 intermediate products were identified, and the possible degradation pathways of BPA were proposed. Additionally, the Fe²⁺/HS/PS system also exerted an excellent performance for the removal of other representative organic contaminants including enrofloxacin, acid orange 7, acetaminophen, and phenol. All results indicated that the Fe²⁺/HS/PS system could be a promising method for organic pollutant removal.

Treasuring industrial sulfur by-products: A review on add-value to reductive sulfide and sulfite for contaminant removal and hydrogen production

Reductive sulfur-containing by-products (S-BPs) released from industrial process mainly exist in the simple form of sulfide and sulfite. In this study, recent advances to remove and make full use of reductive S-BPs to achieve efficient contaminant removal and hydrogen production are critically reviewed. Sulfide, serves as both reductant and nucleophile, can form intermediates with the catalyst surface functional group through chemical interaction, efficiently promoting the catalytic reduction process to remove contaminants. Sulfite assisted catalytic process could be classified to the advanced reduction processes (ARPs) and advanced oxidation processes (AOPs), mainly depending on the presence of dissolved oxygen (DO) in the solution. During ARPs, sulfite could generate reductive active species including hydrated electron (e_aq^-), hydrogen radical (H·), and sulfite radical (SO₃^•-) under the irradiation of UV light, leading to the efficient reduction removal of a variety of contaminants. During AOPs, sulfite could first produce SO₃^•- under the action of the catalyst or energy, initiating a series of reactions to produce oxysulfur radicals. Various contaminants could be effectively removed under the role of these oxidizing active species. Sulfides and sulfites could also be removed along with promoting hydrogen production via photocatalytic and electrocatalytic processes. Besides, the present limitations and the prospects for future practical applications of the process with these S-BPs are proposed. Overall, this review gives a comprehensive summary and aims to provide new insights and thoughts in promoting contaminant removal and hydrogen production through taking full advantage of reductive S-BPs.

Transient Chemiluminescence Assay for Real-Time Monitoring of the Processes of SO32--Based Advanced Oxidation Reactions

The hydroxyl radical (·OH) is a strong oxidizing agent in situ generated in advanced oxidation processes (AOPs) and crucial for assessing the performances of AOPs toward organic contaminants' degradation. Herein, we developed a specific luminescent probe, APDI (N' N'-di(propylethylenediamine)-perylene-3,4,9,10-tetracarboxylic diimide), to selectively detect ·OH among diverse reactive oxygen species and other radicals. Based on the transient chemiluminescence (TCL) spectra, the in situ concentration profile of ·OH within 0.01 s interval time in classical Fenton reactions and four kinds of SO₃^2--based AOPs was obtained, which provides insights into the high dynamic processes of the whole ·OH generation and consumption processes. Besides, compared with acidic conditions, reduced degradation efficiencies in Fe²⁺-SO₃^2- and Fe²⁺-SO₃^2--H₂O₂ systems were found under neutral conditions. The complete depletion of active free radicals due to SO₂^-̇ radicals generated from Fe²⁺ and SO₃^2- should account most for decreased degradation efficiencies evidenced by a new SO₂* TCL signal discovered in the TCL spectra. In addition, similar phenomena have also been found in other M^(n-1)+-SO₃^2--related AOPs. As SO₃^2- and HSO₃^- often exist naturally in wastewater, more efforts are needed to improve the performance of Fe²⁺-H₂O₂ systems. This discovery has important significance for organic contaminant degradation in a natural environment.

Degradation of an Organic Dye by Bisulfite Catalytically Activated with Iron Manganese Oxides: The Role of Superoxide Radicals

Metal-activated bisulfite systems have been widely used to treat recalcitrant wastewater. However, due to the disadvantages of their narrow effective pH range and difficulty in recovering metal ions, homogeneous systems are severely limited in practical applications. To overcome these problems, Fe/Mn bimetallic catalysts with different molar ratios were prepared using a simple sol-gel method to activate bisulfite. Influential factors, such as catalyst and system types, catalyst dosage, bisulfite concentration, pH value, and bisulfite addition modes, were investigated. The new system exhibited a wide effective pH range and high degradation efficiency, and it was found that the dissolved oxygen content played an important role in the activation system. The radical quenching test showed that a superoxide radical (O2 •-), instead of a hydroxyl radical (HO•) or a sulfate radical (SO4 •-), was the main oxide species for the degradation of rhodamine B (RhB).

Crucial roles of oxygen and superoxide radical in bisulfite-activated persulfate oxidation of bisphenol AF: Mechanisms, kinetics and DFT studies

Though natural reducing agents have been demonstrated as desirable catalysts for environmental remediation, the mechanism of catalytic activation of persulfate (PS) by bisulfite (S(IV)) remains unclear. In this study, an emerging contaminant bisphenol AF (BPAF) was employed as the target compound to examine the activation and degradation mechanism in PS/S(IV) system. Sulfate radical (SO₄•-) was evidenced as the dominant radical accounting for BPAF degradation via quantitative analysis, while hydroxyl radical (•OH) and singlet oxygen (¹O₂) were minor contributors. Superoxide radical (O₂•-) was identified as an intermediate radical in promoting BPAF removal through quenching experiments and electron paramagnetic resonance analysis. Tests in oxygen-rich and oxygen-deficient systems were conducted and the results were contrasted to elucidate the important role of oxygen in BPAF degradation and SO₄•--formation. In addition, the effect of Dissolved Oxygen (DO) was simulated using two separate kinetic models. Decomposition mechanism of BPAF was afterwards clarified via the density-functional theory calculations using Fukui index to predict the vulnerable sites and the intermediate products. This study provides a mechanistic understanding of the activation of PS/S(IV) system on the BPAF removal, especially the critical role of DO and O₂•- in SO₄•- generation.

Rapid and efficient removal of naproxen from water by CuFe2O4 with peroxymonosulfate

Naproxen, a widely used nonsteroidal anti-inflammatory drug, has been detected in many environmental matrixes and is regarded as an emerging pollutant. Sulfate radical (SO₄·^-) -based advanced oxidation processes have attracted wide attention due to their high efficiency and applicability in the removal of emerging contaminants. In this study, CuFe₂O₄ was used as an efficient catalyst to activate peroxymonosulfate to oxidize naproxen. The results suggested that 92.3% of naproxen was degraded and 50.3% total organic carbon was removed in 60 min in the presence of 0.3 g·L^-1 CuFe₂O₄ and 2 mM peroxymonosulfate. This degradation system showed strong adaptability in a wide pH range from 4.0 to 10.0. Free radical scavenger experiments and electron spin resonance analysis indicated that ¹O₂, ·OH, and SO₄·^- are the main active species. Finally, the potential degradation pathways of naproxen were proposed by detecting and analyzing the degradation products with ultra-high-performance liquid chromatography combined with mass spectrometry. The results of this study suggest that the CuFe₂O₄-activated peroxymonosulfate system is a promising technology for the removal of naproxen from natural water.

Comparative Study of the Oxidative Degradation of Different 4-Aminobenzene Sulfonamides in Aqueous Solution by Sulfite Activation in the Presence of Fe(0), Fe(II), Fe(III) Or Fe(VI)

This study is focused on advanced oxidation technologies (AOTs) using the combined effect of Fe(0–VI)/sulfite systems, that produce mainly SO4•− radicals, to remove different 4-aminobenzene sulfonamides (SAs), namely sulfamethazine, sulfadiazine, sulfamethizole, from aqueous solutions. Results obtained showed that neither sulfite nor iron alone is able to degrade SAs; however, the combined effect depends on the oxidation state of iron species whose effectiveness to activate sulfite to promote the degradation of SAs increased following this order: Fe(III) < Fe(II) < Fe(0) < Fe(VI). Using Fe(VI)/sulfite, the complete removal of SAs was obtained in 5 min largely surpassing the effectiveness of the other three systems. The sulfonamides’ removal percentage was markedly influenced by sulfite concentration and dissolved oxygen, which improved the generation of oxidant radicals. Response surface methodology was applied, and a quadratic polynomial model was obtained, which allowed us to determine the percentage of SAs degradation as a function of both the iron species and sulfite concentrations. The study of the influence of the water matrix on these AOTs revealed an inhibition of SAs’ removal percentage when using ground water. This is probably due to the presence of different anions, such as HCO3−, Cl−, and SO42− in relatively high concentrations. According to the byproducts identified, the proposed degradation pathways include hydroxylation, SO2 extrusion, and different bond-cleavage processes. Cytotoxicity of degradation byproducts, using MTS assay with HEK 293 and J774 cell lines for the first time, did not show an inhibition in cell proliferation, sustaining the safety of the process.