Visible-light-induced activation of peroxymonosulfate by TiO2 nano-tubes arrays for enhanced degradation of bisphenol A

Chitosan-derived N-doped carbon supported Cu/Fe co-doped MoS2 nanoparticles as peroxymonosulfate activator for efficient dyes degradation

Peroxymonosulfate (PMS), which is dominated by free radical (SO4•-) pathway, has a good removal effect on organic pollutants in complex water matrices. In this article, a new catalyst (CFM@NC) was synthesized by hydrothermal carbonization method with chitosan (CS) as N and C precursors, and used to activate PMS to degrade dye wastewater. CFM@NC/PMS system can degrade 50 mg·L-1 rhodamine B by 99.59 % within 30 min, and the degradation rate remains as high as 97.32 % after 5 cycles. It has good complex background matrices, acid-base anti-interference ability (pH 2.6-10.1), universality and reusability. It can degrade methyl orange and methylene blue by >98 % within 30 min. The high efficiency of the composite is due to the fact that CS-modified MoS2 as a carrier exposes a large number of active sites, which not only disperses CuFe2O4 nanoparticles and improves the stability of the catalyst, but also provides abundant electron rich groups, which promotes the activation of PMS and the production of reactive oxygen species (ROS). PMS is effectively activated by catalytic sites (Cu+/Cu2+, Fe2+/Fe3+, Mo4+/Mo6+, pyridine N, pyrrole N, edge sulfur and hydroxyl group) to produce a large number of radicals to attack RhB molecules, causing chromophore cleavage, ring opening, and mineralization. Among them, free radical SO4•- is the main ROS for RhB degradation. This work is expected to provide a new idea for the design and synthesis of environmentally friendly and efficient heterogeneous catalysts.

Mechanically treated Mn2O3 triggers peracetic acid activation for superior non-radical oxidation of micropollutants: Identification of reactive complexes

This study used a simple mechanical ball milling strategy to significantly improve the ability of Mn2O3 to activate peracetic acid (PAA) for sustainable and efficient degradation of organic micropollutant (like bisphenol A, BPA). BPA was successfully removed and detoxified via PAA activation by the bm-Mn2O3 within 30 min under neutral environment, with the BPA degradation kinetic rate improved by 3.4 times. Satisfactory BPA removal efficiency can still be achieved over a wide pH range, in actual water and after reuse of bm-Mn2O3 for four cycles. The change in hydrophilicity of Mn2O3 after ball milling evidently elevated the affinity of Mn2O3 for binding to PAA, while the reduction in particle size exposed more active sites contributing partially to catalytic oxidation. Further analysis revealed that BPA oxidation in the ball mill-treated Mn2O3 (bm-Mn2O3)/PAA process mainly depends on the bm-Mn2O3-PAA complex (i.e., Mn(III)-OO(O)CCH3) mediated non-radical pathway rather than R-O• and Mn(IV). Especially, the existence of the Mn(III)-PAA complex was definitely verified by in situ Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Simultaneously, density functional theory calculations determined that PAA adsorbs readily on manganese sites thereby favoring the formation of Mn(III)-OO(O)CCH3 complexes. This study advances an in-depth understanding of the underlying mechanisms involved in the manganese oxide-catalyzed activation of PAA for superior non-radical oxidation of micropollutants.

Chitosan derived N-doped carbon anchored Co3O4-doped MoS2 nanosheets as an efficient peroxymonosulfate activator for degradation of dyes

Peroxymonosulfate (PMS), which is dominated by non-free radical pathway, has a good removal effect on organic pollutants in complex water matrices. In this article, a biodegradable cobalt-based catalyst (Co3O4/MoS2@NCS) was synthesized by a simple hydrothermal method with chitosan (CS) as nitrogen‑carbon precursor and doped with Cobaltic‑cobaltous oxide (Co3O4) and Molybdenum disulfide (MoS2), and was used to activate PMS to degrade dye wastewater. Electrochemical tests showed that Co3O4/MoS2@NCS exhibited higher current density and cycling area than MoS2@NCS and MoS2. In the Co3O4/MoS2@NCS/PMS system, the degradation rate of 30 mg·L-1 rhodamine B (RhB) reached 97.75 % within 5 min, and kept as high as 94.34 % after 5 cycles. Its rate constant was 1.91 and 8.37 times that of MoS2@NCS/PMS and MoS2/PMS, respectively. It had good complex background matrices and acid-base anti-interference ability, and had good universality and reusability. The degradation rate of methyl orange (MO) and methylene blue (MB) were more than 91 % within 5 min at pH 4.8. The experimental results demonstrated that MoS2-modified CS as a carrier exposed a large number of active sites, which not only dispersed Co3O4 nanoparticles and improved the stability of the catalyst, but also provided abundant electron rich groups, and promoted the activation of PMS and the production of reactive oxygen species (ROS). PMS was effectively activated by catalytic sites (Co3+/Co2+, Mo4+/Mo5+/Mo6+, CO, pyridine N, pyrrole N, hydroxyl group and unsaturated sulfur), producing a large number of radicals that attack RhB molecules, causing chromophore cleavage, ring opening, and mineralization. Among them, non-free radical 1O2 was the main ROS for RhB degradation. This work is expected to provide a new idea for the design and synthesis of environmentally friendly and efficient MoS2-modified cobalt-based catalysts.

CS/CoFe2O4 nanocomposite as a high-effective and steady chainmail catalyst for tetracycline degradation with peroxymonosulfate activation: performance and mechanism

Tetracycline becomes a crucial measure for managing and treating communicable diseases in both human and animal sectors due to its beneficial antibacterial properties and cost-effectiveness. However, it is important not to trivialize the associated concerns of environmental contamination following the antibiotic's application. In this study, cobalt ferrate (CoFe2O4) nanoparticles were loaded into chitosan (CS), which can avoid the agglomeration problem caused by high surface energy and thus improve the catalytic performance of cobalt ferrate. And it can avoid the problem of secondary contamination caused by the massive leaching of metal ions. The resulting product was used as a catalyst to activate peroxymonosulfate (PMS) for the degradation of tetracycline (TC). To determine the potential effects on TC degradation, various factors such as PMS dosing, catalyst dosing, TC concentration, initial solution pH, temperature, and inorganic anions (Cl-, H2PO4- and HCO3-) were investigated. The CS/CoFe2O4/PMS system exhibited superior performance compared to the CoFe2O4-catalyzed PMS system alone, achieving a 92.75% TC removal within 120 min. The catalyst displayed high stability during the recycling process, with the efficiency observed after five uses remaining at a stable 73.1%, and only minor leaching of dissolved metal ions from the catalyst. This confirms the high stability of the catalyst. The activation mechanism study showed that there are free radical and non-free radical pathways in the reaction system to degrade TC together, and SO4•- and 1O2 are the primary reactive oxygen radicals involved in the reaction, allowing for effective treatment of contaminated water by TC.

Efficient and sustainable photocatalytic inactivation of E. coli by an innovative immobilized Ag/TiO2 photocatalyst with peroxymonosulfate (PMS) under visible light

A novel catalytic system for effective photocatalytic inactivation of Escherichia coli (E. coli) was constructed by anchoring Ag nanoparticles (AgNPs) on silane coupling agent (SCA) pretreated TiO2 nano-tube arrays (Ag/SCA/TiO2NTAs). Morphology and structural analyses revealed that SCA could disperse AgNPs evenly on TiO2NTAs, thus inducing a superior surface plasmon resonance (SPR) effect. Ag/SCA/TiO2NTAs catalyst exhibited excellent inactivation performance when in the presence of peroxymonosulfate (PMS) and visible light (VL), with 6-log E. coli was completely inactivated within 60 min, which was 5.3, 12.5 and 13.2 times higher than that of Ag/SCA/TiO2NTAs/VL, PMS/VL and Ag/SCA/TiO2NTAs/PMS/dark systems, respectively. Additionally, the photocatalyst exhibited a highly reusable property, with the inactivation performance almost unchanged after ten cycles of uses with minimal Ag leaching. The inactivation mechanism analysis demonstrated that both radical (SO4•-, OH) and non-radical (h+, 1O2) pathways involved in E. coli inactivation, and SCA played a pivotal role in the production of reactive species. Chloride ions (Cl-) greatly enhanced the inactivation efficiency, while bicarbonate (HCO3-) and phosphate (H2PO4-) showed an inhibitory effect. Humic acid (HA) displayed a dual effect on inactivation performance, where the low concentration of HA facilitated the bacteria inactivation, while the higher dose suppressed bacteria inactivation. Moreover, the system exhibited excellent inactivation performance in tap water. This work first used SCA as the binder to fix AgNPs on TiO2NTAs for VL photocatalytic inactivation of bacteria with the assistance of PMS, which was expected to provide some insights into the practical treatment of drinking water.

Visible-light-driven peroxymonosulfate activation by robust TiO2-base nanoparticles for efficient removal of sulfamethoxazole

In this study, a novel bimetallic Co-Mo-TiO2 nanomaterial was fabricated through a simple two-step method, and applied as photocatalyst to activate peroxymonosulfate (PMS) with high efficiency for sulfamethoxazole (SMX) removal under visible light. Nearly 100% of SMX was degraded within 30 min in Vis/Co-Mo-TiO2/PMS system, and its kinetic reaction rate constant (0.099 min-1) was 24.8 times higher compare with the Vis/TiO2/PMS system (0.014 min-1). Moreover, the quenching experiments and the electronic spin resonance analysis results confirmed that both 1O2 and SO4•- were the dominant active species in the optimal system, and the redox cycles of Co3+/Co2+ and Mo6+/Mo4+ promoted the generation of the radicals during the PMS activation process. Additionally, the Vis/Co-Mo-TiO2/PMS system exhibited a wide working pH range, superior catalytic performance toward different pollutants and excellent stability with 92.8% SMX removal capacity retention after three consecutive cycles. The result of density functional theory (DFT) suggested that Co-Mo-TiO2 exhibited a high affinity for PMS adsorption, as indicated by the length O-O bond from PMS and the Eads of the catalysts. Finally, the possible degradation pathway of SMX in optimal system was proposed through intermediate identification and DFT calculation, and a toxicity assessment of the by-products was also conducted.

Preparation of di-[EMIM]CoCl3 Ionic Liquid Catalyst and Coupling with Oxone for Desulfurization at Room Temperature

The intermediate di-[EMIM]Cl was synthesized from methyl imidazole and 1,4-dichlorobutane and then reacted with cobalt chloride at 105 °C to prepare a bi-[EMIM]CoCl3 ionic liquid catalyst. The di-[EMIM]CoCl3 catalyst coupled with oxone to remove sulfur-containing organics in octane. The di-[EMIM]CoCl3 catalyst was characterized by HNMR, FTIR, TG, and SEM–EDS. The dibenzothiophene (DBT) was dissolved in octane to prepare a model oil with an initial sulfur content of 500 ppm. Six grams of the model oil was added. The results showed that the optimal dosages of di-[EMIM]CoCl3, oxone (20 wt%), and [BMIM]BF4 extractant were 1 g, 2 g, and 2 g, respectively. At the optimum temperature of 45 °C, 100% of sulfur was removed after 40 min. After di-[EMIM]CoCl3 was recycled five times, the sulfur removal percentage remained above 91%. The sulfur removal percentages for different sulfur-containing organics followed the order of dibenzothiophene (DBT) > benzothiophene (BT) > 4,6-dimethyldibenzothiophene (4,6-DMDBT). The oxidation product was determined to be DBTO2 by GC–MS analysis, and the oxidation mechanism was discussed. The active oxygen atoms of oxone oxidized DBT to form DBTO, and then persulfate oxidized DBTO to DBTO2 via an identical oxidation mechanism.

State-of-the-Art on the Sulfate Radical-Advanced Oxidation Coupled with Nanomaterials: Biological and Environmental Applications

Sulfate radicals (SO₄^-·) play important biological roles in biomedical and environmental engineering, such as antimicrobial, antitumor, and disinfection. Compared with other common free radicals, it has the advantages of a longer half-life and higher oxidation potential, which could bring unexpected effects. These properties have prompted researchers to make great contributions to biology and environmental engineering by exploiting their properties. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) are the main raw materials for SO₄^-· formation. Due to the remarkable progress in nanotechnology, a large number of nanomaterials have been explored that can efficiently activate PMS/PDS, which have been used to generate SO₄^-· for biological applications. Based on the superior properties and application potential of SO₄^-·, it is of great significance to review its chemical mechanism, biological effect, and application field. Therefore, in this review, we summarize the latest design of nanomaterials that can effectually activate PMS/PDS to create SO₄^-·, including metal-based nanomaterials, metal-free nanomaterials, and nanocomposites. Furthermore, we discuss the underlying mechanism of the activation of PMS/PDS using these nanomaterials and the application of SO₄^-· in the fields of environmental remediation and biomedicine, liberating the application potential of SO₄^-·. Finally, this review provides the existing problems and prospects of nanomaterials being used to generate SO₄^-· in the future, providing new ideas and possibilities for the development of biomedicine and environmental remediation.

Influences and mechanisms of phosphate ions onto persulfate activation and organic degradation in water treatment: A review

Currently, various strategies have been applied to activate persulfate (PS) for contaminant removal from water. However, the background phosphate ions in water affect PS activation and organic degradation, and the mechanism of their influence on the processes is still controversial. In this review, the possible effects of different phosphate forms (HPO₄^2-, H₂PO₄^-, and PO₄^3-) on PS activation and contaminant degradation were systematically evaluated and summarized. Specifically, HPO₄^2- promotes contaminant degradation in direct peroxymonosulfate (PMS) oxidation and thermal/PMS systems, while it exhibits inhibition to thermal/peroxodisulfate (PDS) and ultraviolet (UV)/PDS systems. Meanwhile, H₂PO₄^- inhibits most oxidation processes based on PMS and PDS, except for non-metal dominated and metal assisted PMS systems. Coexisting HPO₄^2- and H₂PO₄^- could present beneficial effects in thermal, Co²⁺ and non-metal activated and metal assisted PMS systems. Nevertheless, their inhibitory effects were found in direct PMS oxidation, UV/PMS (or PDS) and metal dominated PMS systems. Generally, phosphate ions inhibit PMS/PDS activation through competing adsorption with PMS or PDS on the solid surface, forming a complex with metal ions, as well as occupying active sites on solid catalysts. In addition, phosphate ions can quench radicals for reduced degradation of contaminants. However, phosphate ions could weaken the bond dissociation energy via combining with PMS and contaminants or form a complex with Co²⁺, thus displaying a facilitative effect. This review further discusses major challenges and opportunities of PS activation with co-existing phosphates and will provide guidance for better PS utilization in real water treatment practice.

Comparative study on bisphenols oxidation via TiO2 photocatalytic activation of peroxymonosulfate: Effectiveness, mechanism and pathways

In this work, degradation of bisphenol F (BPF), bisphenol AF (BPAF) and bisphenol S (BPS) by peroxymonosulfate (PMS) with TiO₂ nano-tubes arrays (TiO₂NTAs) under simulated sunlight irradiation was investigated and compared for the first time. All three bisphenols exhibited appreciable degradation following the order of BPS < BPAF < BPF, and acidic conditions were more conducive to their degradation. The SO₄^•-, ·OH, h⁺ and ^•O₂^- were all identified in three bisphenols degradation processes. Among these, SO₄^•- and ^•O₂^- were proven to play a dominant role in BPF oxidation process, but SO₄^•- and h⁺ were confirmed as the main reactive species for BPAF and BPS removal. Owing to the different reactive species worked in different bisphenols degradation processes, the influences of inorganic anions on three bisphenols degradation were also different. By analyzing the oxidation intermediates of the three bisphenols, it was found that there were some common degradation pathways including bond-cleavage and hydroxylation of the benzene ring shared by three bisphenols. Besides, some specific degradation pathways were also identified, for example, the self-coupling was found in BPF and BPS degradation process, while the benzene ring splitting was occurred only in BPAF transformation process.

A novel Fe-rectorite composite catalyst synergetic photoinduced peroxymonosulfate activation for efficient degradation of antibiotics

Developing a low-cost and efficient photocatalysts activated peroxymonosulfate (PMS) for organic pollutants degradation are recognized as an importance way for dealing with environmental pollution. In this work, Fe-rectorite catalyst was synthesized by a simple impregnation-calcine method to synergetic photo activate PMS for antibiotics degradation. As expected, the Fe-rectorite/PMS/Light system exhibits superior catalytic performance for tetracycline (TC) removal, which achieving 96.4% removal rate of TC (30 mg/L) under light within 60 min. Fe-retorite has better degradation performance for TC than rectorite under photo-mediation. The enhancement of the degradation performance of TC by Fe-retorite can be attributed to the improvement of the separation efficiency of photogenerated electrons and holes in the rectorite by the loading of Fe₂O₃, and the accelerated active Fe(Ⅱ)/Fe(Ⅲ) cycle on the surface under photo-mediation. The large specific surface area and abundant hydroxyl groups of rectorite can also provide active sites for PMS activation. The quenching experiment and electron paramagnetic resonance (EPR) test were indicated that the h⁺, SO₄•^-, •OH, and O₂^-• all contributed to TC degradation. And the possible degradation pathway was proposed by LC-MS. This work helps induced a novel direction that design green, efficient, and recyclable heterogeneous catalysts to synergetic photoinduced PMS activation for enhanced degradation of TC.

Hydrothermal and Co-Precipitated Synthesis of Chalcopyrite for Fenton-like Degradation toward Rhodamine B

In this study, Chalcopyrite (CuFeS2) was prepared by a hydrothermal and co-precipitation method, being represented as H-CuFeS2 and C-CuFeS2, respectively. The prepared CuFeS2 samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy mapping (EDS-mapping), powder X-ray diffractometer (XRD), X-ray photoelectron spectrometry (XPS), and Raman microscope. Rhodamine B (RhB, 20 ppm) was used as the target pollutant to evaluate the degradation performance by the prepared CuFeS2 samples. The H-CuFeS2 samples (20 mg) in the presence of Na2S2O8 (4 mM) exhibited excellent degradation efficiency (98.8% within 10 min). Through free radical trapping experiment, the major active species were •SO4− radicals and •OH radicals involved the RhB degradation. Furthermore, •SO4− radicals produced from the prepared samples were evaluated by iodometric titration. In addition, one possible degradation mechanism was proposed. Finally, the prepared H-CuFeS2 samples were used to degrade different dyestuff (rhodamine 6G, methylene blue, and methyl orange) and organic pollutant (bisphenol A) in the different environmental water samples (pond water and seawater) with 10.1% mineral efficiency improvement comparing to traditional Fenton reaction.

Bisphenol A degradation by peroxymonosulfate photo-activation coupled with carbon-based cobalt ferrite nanocomposite: Performance, upgrading synergy and mechanistic pathway

Cobalt ferrite (CoFe₂O₄, CF) nanoparticles were anchored on the multiwalled carbon nanotube (MWCNT) for synthesis of CF@MWCNT nanocomposite and enhancing the catalytic activity of CF. After well characterization, it was applied as a catalyst towards photo-activation peroxymonosulfate (PMS) for degradation of bisphenol A (BPA). Based on the identified intermediates, a possible degradation pathway was proposed for BPA. CF@MWCNT coupled with PMS and UV (i.e., CF@MWCNT/PMS/UV) exhibited a better performance than homogeneous UV-assisted PMS processes under Fe and Co ions. A significant synergy on the degradation of BPA was observed in the simultaneous application of catalyst, UV light and PMS. Under optimum conditions, the removal efficiencies of 100 and 72.6% were attained respectively for BPA and TOC by CF@MWCNT/PMS/UV within 60 min reaction. These efficiencies were decreased to 88 and 61% after five times use of catalyst, respectively. The leaching of metal ions dissolved from the catalyst was slight during cyclic utilization of catalyst, confirming high stability of CF@MWCNT. In this process, the participation of radical mechanisms was approximately 60%, which SO₄^•- and HO^• species contributed as predominant oxidizing reactive species. It also showed the excellent catalytic performance towards decomposition of persulfate and hydrogen peroxide. Overall, UV-assisted PMS catalyzed by CF@MWCNT exhibited a good catalytic performance and so it can be potentially introduced as a promising method for efficient treatment of water contaminated by BPA.

Peracids - New oxidants in advanced oxidation processes: The use of peracetic acid, peroxymonosulfate, and persulfate salts in the removal of organic micropollutants of emerging concern - A review

In recent years, there has been increasing interest in using of advanced oxidation processes in water and wastewater decontamination. As a new oxidants peracids, mainly peracetic acid (PAA) and peracid salts, i.e. peroxymonosulfate (PMS) and persulfate (PS) are used. The degradation process of organic compounds takes place with the participation of radicals, including hydroxyl (^•OH) and sulfate (SO₄^•-) radicals derived from the peracids activation processes. Peracids can be activated in homogeneous systems (UV radiation, d-electron metal ions, e.g. Fe²⁺, Co²⁺, Mn²⁺, base, ozonolysis, thermolysis, radiolysis), or using heterogeneous activation (metals with zero oxidation state, metal oxides, quinones, activated carbon, semiconductors). As a result of oxidation, products of a lower mass than the parent compounds, less toxic, and more susceptible to biodegradation are formed. An important task is to investigate the effect of the peracid activation method and matrix composition on the efficiency of contamination removal. The article presents the latest information about the application of peracids in the removal of organic micropollutants of emerging concern (mainly focuses on endocrine disrupted compounds). The most important information on peracetic acid, peroxymonosulfate and persulfate salts, and methods of their activation are presented. Current uses of these oxidants in organic micropollutants removal are also described. Information was collected on the factors influencing the oxidation process and the effectiveness of pollutant removal. This paper compares PAA, PMS and PS-based processes for the first time in terms of kinetics and efficiency.

Applications of electron spin resonance spectroscopy in photoinduced nanomaterial charge separation and reactive oxygen species generation

Nano-metals, nano-metal oxides, and carbon-based nanomaterials exhibit superior solar-to-chemical/photo-electron transfer properties and are potential candidates for environmental remediations and energy transfer. Recent research effort focuses on enhancing the efficiency of photoinduced electron-hole separation to improve energy transfer in catalytic reactions. Electron spin resonance (ESR) spectroscopy has been used to monitor the generation of electron/hole and reactive oxygen species (ROS) during nanomaterial-mediated photocatalysis. Using ESR coupled with spin trapping and spin labeling techniques, the underlying photocatalytic mechanism involved in the nanomaterial-mediated photocatalysis was investigated. In this review, we briefly introduced ESR principle and summarized recent advancements using ESR spectroscopy to characterize electron-hole separation and ROS production by different types of nanomaterials.

Tetracycline hydrochloride degradation over manganese cobaltate (MnCo2O4) modified ultrathin graphitic carbon nitride (g-C3N4) nanosheet through the highly efficient activation of peroxymonosulfate under visible light irradiation

Peroxymonosulfate (PMS) activation by heterogeneous transition metal oxides is an effective approach for treating emerging pollutants in water. However, the low PMS activation efficiency associated with the valency conversion rate of transition metals has been a major challenge to sulfate radical-based oxidation. In this work, manganese cobaltate (MnCo₂O₄) nanoparticles anchored on graphitic carbon nitride (g-C₃N₄) flakes (MnCo₂O₄/g-C₃N₄) were successfully prepared and showed high PMS activation efficiency under visible (Vis) light. The obtained catalysts degraded 96.1% of the tetracycline hydrochloride (TCH) through the synergistic effect of PMS and photocatalysis. The reaction rate constant (0.2505 min^-1) was 5.3 and 1.8 times higher in the MnCo₂O₄/g-C₃N₄/PMS/Vis system than in the pristine g-C₃N₄ (0.0471 min^-1) and MnCo₂O₄ (0.1435 min^-1) systems, respectively. The characterization results verified that g-C₃N₄, which functions as the electron donor in the photocatalytic heterojunction system, could transmit numerous photogenerated electrons to MnCo₂O₄, thereby increasing the cyclability of divalent-trivalent metal ions. The composites also showed good stability, cycling capability, and cation/anion tolerance. Tentative degradation mechanism and reaction pathways were proposed based on the reactive species and degradation products.

Facile synthesis of layered Co(OH)2 deposited g-C3N4 for activating peroxymonosulfate to degrade organic pollutants

Layered Co(OH)2 deposited g-C3N4 is found to be highly active in the activation of peroxymonosulfate (PMS) for pollutant removal.