Efficient activation of peroxymonosulfate by manganese oxide for the degradation of azo dye at ambient condition

Synthesis of self-supported NiCoFe(OH)x via fenton-like effect corrosion for highly efficient water oxidation

Efficientandinexpensiveoxygenevolutionreaction(OER)catalysts are essential for the electrochemical splitting of water into hydrogen fuel. Herein, we have successfully synthesized NiCoFe(OH)x nanosheets on Ni-Fe foam (NFF) by exploiting the Fenton-like effect of Co2+ and S2O82- to corrode the NFF foam. The as-prepared NiCoFe(OH)x/NFF exhibits the porous structure with the interconnected nanosheets that are firmly bonded to the conductive substrate of NFF, thereby enhancing ions and charge transfer kinetics. The unique structure and composition of NiCoFe(OH)x/NFF result in the low overpotentials of 200 and 262 mV at current densities of 10 and 100 mA cm-2, respectively, as well as a low Tafel slope of 53.25 mV dec-1. In addition, NiCoFe(OH)x/NFF displays low overpotentials of 267 and 294 mV at a high current density of 100 mA cm-2 in simulated and real seawater, respectively. Furthermore, the assembled NiCoFe(OH)x//Pt/C water electrolysis cell has achieved a current density of 10 mA cm-2 at a low voltage of 1.49 V, and displayed the good stability with slight attenuation for 110 h. The high OER performance of NiCoFe(OH)x is attributed to the co-catalytic effect of the three metal ions and the interconnected porous nanosheet structure.

CuO nanosheets incorporated scrap steel slag coupled with persulfate catalysts for high-efficient degradation of sulfonamide from water

A highly efficient and magnetically recoverable persulfate (PS) catalyst was prepared for the removal of sulfonamide (SMD) from wastewater, which is difficult to be degraded by the conventional biological treatment. In this study, the scrap steel slag (SSS) was used as supporting carrier and the CuO nanosheet was incorporated on the surface of SSS. The optimal conditions were determined as follows: the dosage of CuO/SSS was 1 g L^-1, the PS concentration was 4 mM and the optimal initial pH was 6.85. Under the optimal conditions, the maximum SMD removal efficiency of 80.29% was achieved within 30 min by using CuO/SSS + PS. In addition, the CuO/SSS + PS system had a wide pH range (5-9) and more than 60% removal efficiency of SMD could be obtained with the pH between 3 and 11. The mechanism based on the phase transformation of Cu(I/II), Cu(II/III) and Fe(II/III) was elucidated by using different analytical techniques, such as SEM, XRD, XPS, BET, FTIR, VSM characterization and free radical analysis. This study provided a new pathway for the SSS resource utilization and the effective degradation of SMD from the refractory wastewater by using CuO/SSS catalyst coupled with PS system.

Comparative study of the performance of controlled release materials containing mesoporous MnOx in catalytic persulfate activation for the remediation of tetracycline contaminated groundwater

Controlled release materials (CRMs) are an emerging oxidant delivery technique for in-situ chemical oxidation (ISCO) that solve the problems of contaminant rebound, backflow and wake during groundwater remediation. CRMs were fabricated using ordered mesoporous manganese oxide (O-MnOx) and sodium persulfate (Na₂S₂O₈) as active components, for the removal of antibiotic pollutants from groundwater. In both static and dynamic groundwater environments, persulfate can first be activated by O-MnOx within CRMs to form sulfate radicals and hydroxyl radicals, with these radicals subsequently dissolving out from the CRMs and degrading tetracycline (TC). Due to their excellent persulfate activation performance and good stability, the constructed CRMs could effectively degrade TC in both static and dynamic simulated groundwater systems over a long period (>21 days). The TC removal rate reached >80 %. Changing the added content of O-MnOx and persulfate could effectively regulate the performance of the CRMs during TC degradation in groundwater. The process and products of TC degradation in the dynamic groundwater system were the same as in the static groundwater system. Due to the strong oxidizing properties of sulfate radicals and hydroxyl radicals, TC molecules were completely mineralized within the groundwater systems, resulting in only trace levels of degradation products being detectable, with low- or non-toxicity. Therefore, the CRMs constructed in this study exhibited good potential for practical application in the remediation of organic pollutants from both static and dynamic groundwater environments.

Heterogeneous Metal-Activated Persulfate and Electrochemically Activated Persulfate: A Review

The problem of organic pollution in wastewater is an important challenge due to its negative impact on the aquatic environment and human health. This review provides an outline of the research status for a sulfate-based advanced oxidation process in the removal of organic pollutants from water. The progress for metal catalyst activation and electrochemical activation is summarized including the use of catalyst-activated peroxymonosulfate (PMS) and peroxydisulfate (PDS) to generate hydroxyl radicals and sulfate radicals to degrade pollutants in water. This review covers mainly single metal (e.g., cobalt, copper, iron and manganese) and mixed metal catalyst activation as well as electrochemical activation in recent years. The leaching of metal ions in transition metal catalysts, the application of mixed metals, and the combination with the electrochemical process are summarized. The research and development process of the electrochemical activation process for the degradation of the main pollutants is also described in detail.

Hydroxylamine-enhanced Fe(II)-peroxymonosulfate activation for efficient degradation of organic pollutants: optimization by response surface methodology

In this work, the response surface methodology (RSM) was used to model and optimize the hydroxylamine (HA) enhanced Fe(II)/peroxymonosulfate (PMS) process. The enhanced effect of HA on the degradation efficiency of Orange II (AO7) in the Fe(II)/PMS system was quantitatively analyzed. Pareto analysis showed that the individual and interactive effects of HA, Fe(II) and PMS were of the following order: HA > Fe(II) > PMS and Fe(II)/PMS > HA/PMS > Fe(II)/HA. The optimal conditions of HA/Fe(II)/PMS system were as follows: Fe(II) concentration was 34.0 μM, HA concentration was 0.4 mM, and PMS concentration was 0.9 mM. When the initial pH was 4.0-6.0, the degradation efficiency of AO7 in the HA/Fe(II)/PMS system was significantly higher than that in the Fe(II)/PMS system (P < 0.05). Hydroxylamine enhances the degradation of AO7 in the Fe(II)/PMS system by reducing Fe(III) to Fe(II). The results of quenching experiment showed that SO₄^•- was the dominating reactive oxygen species (ROS) in the HA/Fe(II)/PMS system. In the HA/Fe(II)/PMS system, CO₃^2- and humic acid inhibited the degradation efficiency of AO7. This work provides a novel mathematical model for the degradation of AO7 in the HA/Fe(II)/PMS system, which can be popularized and applied in similar experiments.

Fe0-loaded superfine powdered activated carbon prepared by ball milling for synergistic adsorption and persulfate activation to remove aqueous carbamazepine

The massive use of personal medicines makes them widely enter the aquatic environments and cause pollution, drawing a great deal of attention over the last few years. In this study, a novel nano Fe⁰-loaded superfine powdered activated carbon (Fe⁰@SPAC) was prepared via a simple ball milling method. Fe⁰@SPAC showed a rapid and effective removal for aqueous carbamazepine (CBZ) via the process of synergistic adsorption and persulfate (PDS) activation. The removal efficiency of CBZ (30 mg L^-1) could be up to 96% by Fe⁰@SPAC (0.05 g L^-1) with the presence of PDS (2 mM), and the maximum pseudo-first-order rate constant was 0.12 min^-1. The performance of Fe⁰@SPAC was superior to other reported iron-bearing activator materials, and its dosage was much lower. Fe⁰@SPAC was also effective to remove other typical drug pollutants and had excellent reusability in five cycles. The loaded Fe⁰ could activate PDS to generate OH and SO₄^-, which played the major role for CBZ removal. It is interesting that carbon base of Fe⁰@SPAC could also activate PDS via surface defects, making the minor contribution to CBZ degradation. Besides, Fe⁰@SPAC showed rapid and high adsorption for CBZ due to the superfine particle diameter, partially contributing to CBZ removal. Finally, the possible break sites of CBZ and its degradation pathway were proposed based on DFT theoretical calculation and product identification. Fe⁰@SPAC would be a promising material for the removal of drug pollutants, and this study may help understand the mechanisms of synergistic adsorption and persulfate activation by carbon composite material.

Efficient transformation of DDT with peroxymonosulfate activation by different crystallographic MnO2

In this study, three different structures of MnO₂ were synthesized and used to activate peroxymonosulfate (PMS) for the degradation of DDT in aqueous solutions. It was found that DDT was efficiently degraded in the MnO₂/PMS system and the degradation rate was dependent on the properties of MnO₂ including crystal structure (followed the order: α-MnO₂ > γ-MnO₂ > β-MnO₂), surface area and Mn(III) content. Sulfate radicals (SO₄^-) was primarily responsible for the degradation of DDT based on the results of electron paramagnetic resonance (EPR) and quenching experiments. The degradation of DDT was suppressed at alkaline pH because the formation of SO₄^- was inhibited. The results of GC-MS indicated that dichlorobenzophenone, 4-chlorobenzoic acid and benzylalcohol were the dominant intermediates for DDT degradation. The possible pathways of DDT degradation were proposed according to the identified products.

Heterogeneous catalytic oxidation degradation of BPAF by peroxymonosulfate active with manganic manganous oxide: Mineralization, mechanism and degradation pathways

In this study, the catalytic ability and mechanisms involved in activating peroxymonosulfate (PMS) with Mn₃O₄ and the degradation pathways of bisphenol-AF (BPAF) removal was investigated. SO₄^-• and ·OH which were explored by and scavenging tests were the major reactive radicals in the Mn₃O₄/PMS system. A simple simulation algorithm was also used to calculate the relative concentrations of SO₄^-• ([SO₄^-•]) and ·OH ([·OH]) which were 8.39 × 10 ^-15 M and 6.96 × 10 ^-13 M, respectively. The mechanism for the electron transfer between the Mn (II) and Mn (III) species was discussed. Three degradation pathways of BPAF were determined by the GC/MS and LC/MS technology, including chemical mechanism of oxidation, hydroxylation, electron transfer, polymerization, and ring-cleavage. In addition, the results suggested that the Mn₃O₄/PMS system had an efficient total organic carbon (TOC) removal rate and excellent environmental adaptability, the removal rate of TOC being as high as 73.2% in the control condition. Furthermore, the reuse experiments and the comparison on the structural and componential changes of Mn₃O₄ powder before and after reaction demonstrated that the Mn₃O₄ catalyst possessed excellent stability and reusability. Finally, a maximum BPAF degradation of approximately 90.0% was achieved on the optimal conditions for 500 mg/L Mn₃O₄ dosage, 4 mM PMS concentration, 7.0 ± 0.2 initial pH, and 5 mg/L BPAF concentration respectively. And the effect of the coexisting anions and natural environmental water quality were also considered. This study demonstrated the Mn₃O₄/PMS system can be considered as a green approach for the removal of environmental reluctant pollutants.

Peroxymonosulfate-enhanced photocatalysis by carbonyl-modified g-C3N4 for effective degradation of the tetracycline hydrochloride

In this work, carbonyl-modified g-C₃N₄ (CO-C₃N₄) is prepared through one-step calcination of the melamine-oxalic acid aggregates. The visible light-assisted photocatalytic degradation efficiency of the tetracycline hydrochloride (TCH) for CO-C₃N₄ is significantly enhanced by introducing the peroxymonosulfate (PMS), and the apparent rate constant is greatly increased from 0.01966 min^-1 in CO-C₃N₄/vis system to 0.07688 min^-1 in CO-C₃N₄/PMS/vis system. It is found that carbonyl for CO-C₃N₄ might offer possible reactive sites for PMS activation and collection sites of photo-generated electrons, greatly accelerating carrier's separation for PMS activation. The favorable conditions, such as the higher catalyst dosage, higher PMS amount and alkaline pH, contribute to TCH degradation. The deleterious effects of co-existing anions on the TCH degradation efficiency are ranked in a decline: H₂PO₄^- > SO₄^2- > HCO₃^- > NO₃^- > Cl^-, and it may be affected by the type and amounts of anions and active radicals generated. The radical trapping tests and electron spin resonance (ESR) detection display that the O₂^-, h⁺, ¹O₂, OH and SO₄^- all contribute to TCH degradation. Meanwhile, possible degradation mechanism, intermediates and degradation pathway of TCH are revealed in CO-C₃N₄/PMS/vis system. This study will offer a new insight for constructing PMS activation with carbonyl modified g-C₃N₄ photocatalysis system to achieve effective treatment of organic wastewater.

Ultraviolet-mediated peroxymonosulfate diminution of earthy and musty compound trichloroanisole in water

Taste and odor (T&O) problem in water is one of the main obstacles to improve the quality of drinking water, and efficient water treatment processes are urgently needed to control T&O compounds. Ultraviolet-mediated peroxymonosulfate (UV/PMS) diminution of trichloroanisole (TCA) in water was investigated in this paper. The treatment of 2,3,6-trichloroanisole (2,3,6-TCA) by three advanced oxidation processes (UV, UV/H₂O₂ and UV/PMS) was compared, and UV/PMS stood out. SO₄^•- and HO• were produced in the UV/PMS, and their specific contributions to 2,3,6-TCA oxidation were investigated. The competitive kinetic model was applied to determine the second-order reaction rate between 2,3,6-TCA and SO₄^•- or HO•. The products of 2,3,6-TCA generated in UV/PMS were analyzed with gas chromatography/high resolution-mass spectrometry (GC/HR-MS), and the degradation mechanism was proposed. The effects of water matrices (chloride, bicarbonate and humic acid) on UV/PMS performance were studied, and the decontamination of 2,3,6-TCA in real water was carried out. The disinfection byproducts (DBPs) alteration from 2,3,6-TCA by UV/PMS - chlorination treatment was explored. Overall, UV/PMS can effectively deal with the T&O pollution of TCA in water.

Insight into the improvement of dewatering performance of waste activated sludge and the corresponding mechanism by biochar-activated persulfate oxidation

A novel activator, corn biochar, was produced to activate persulfate to dewater waste activated sludge (WAS). Results demonstrated that the biochar-activated persulfate oxidation can effectively improve the dewatering performance of WAS. After treating WAS by biochar-activated persulfate oxidation (biochar dosage: 2.1 g/L, persulfate concentration: 7.5 mM) at the original WAS pH, standardized-capillary suction time (SCST) increased to 4.21 times and moisture content (MC) decreased to 43.4%, indicating an excellent performance of WAS dewatering. The decrease of residual persulfate with the increasing biochar dosage during WAS dewatering process illustrated that the role of persulfate in improving WAS dewatering was because of the biochar activation. The behaviors of extracellular polymers (EPS) proved that the protein in tightly bound EPS (TB-EPS) linked to WAS dewatering, and its content significantly reduced to 10.5 mg/g-volatile solids (VS) after WAS treatment. Three-dimensional fluorescence spectroscopy for EPS once again proved that the disintegration of tryptophan protein and humic acid (hydrophobic organic substances in EPS) was responsible for the improvement of WAS dewatering. To sum up, the biochar-activated persulfate oxidation was a feasible application in improving WAS dewatering.

Homogeneous activation of peroxymonosulfate using a low-dosage cross-bridged cyclam manganese(II) complex for organic pollutant degradation via a nonradical pathway

The high dosage of catalyst requirement and weak anti-interference ability limit current heterogeneous manganese (Mn) catalyst/peroxymonosulfate (PMS) systems to remediate the organic polluted wastewater in complicated environment. Inspired by the concept of atom economy, herein, a homogenous manganese complex bearing a cross-bridged cyclam ligand Mn(cbc)Cl₂ (MnL, L = cbc = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane)) is capable of activating PMS for reactive brilliant red K-2BP (RBR K-2BP) degradation. The dosage of MnL for PMS activation was low, in a range of 0.38∼3.8 mg/L. The quenching experiments demonstrated that the degradation was a nonradical-controlled process. Using methyl phenyl sulfoxide (PMSO) as a probe, the dominated degradation process of substrate was via an oxygen transfer pathway. Moreover, a high-valent Mn-oxo [(O)Mn^VLCl₂]⁺ was directly detected using electrospray ionization mass spectrometry (ESI/MS). This system showed excellent anti-interference ability to both anions and humic acid, a typical natural organic matter. The atom economy, represented by an index ((mg pollutant)/h/(g catalyst)), showed that MnL 22737 in PMS activation was much higher than those of Mn-based heterogeneous catalytic systems 67∼960 and was only behind that of iron-tetraamidomacrocyclic ligand Fe-TAML 59139. This work provides insights into designing an atom-economic Mn-based PMS activator for efficient treatments for organic pollutants in a complicated environment.

Enhancement of photo-Fenton catalytic activity with the assistance of oxalic acid on the kaolin-FeOOH system for the degradation of organic dyes

The Fenton reaction, as an important member of the advanced oxidation processes (AOPs), has gained extensive attention in recent years. However, the practical applications of the traditional Fenton process have been restricted by the poor degradation efficiency and the rigid pH range. In this study, we report a new strategy regarding the photo-Fenton oxidation of Rhodamine B (RhB) by kaolin-FeOOH (K-Fe) catalysts with the assistance of oxalic acid. It was found that the iron-oxalate complex was formed as oxalic acid was introduced into the K-Fe catalyst system by the chelation ability of oxalate. Benefiting from the high photosensitivity of the iron-oxalate complexes, the K-Fe/oxalic acid/H2O2/visible light system exhibited excellent catalytic activity towards the degradation of RhB under the optimized reaction conditions [(K-Fe) dosage = 1.0 g L-1, initial pH = 7.2, (oxalic acid) = 1.0 mM, (H2O2) = 0.5 mM], and its reaction rate constant for the degradation of RhB was 27.7 times greater than that of the K-Fe/H2O2/visible light system. More importantly, the K-Fe/oxalic acid/H2O2/visible system showed remarkable degradation efficiency over a wide pH range (3.3-10.8), which was superior to that of the traditional Fenton system. In addition, the degradation efficiency of RhB was found to remain at 94.7% after five cycles. This work is expected to provide an important approach for the application of the Fenton system.

Comparing biochar- and bentonite-supported Fe-based catalysts for selective degradation of antibiotics: Mechanisms and pathway

The selective degradation of recalcitrant antibiotics into byproducts with low toxicity and high biodegradability has been increasingly popular using peroxymonosulfate (PMS) based advanced oxidation processes (AOPs). In this paper, two Fe-based heterogeneous catalysts, bentonite supported Fe-Ni composite (BNF) and biochar-supported Fe composite (Fe/C), were tailored and comprehensively characterized for distinctive physicochemical properties, crystalline structures, and interfacial behaviors. Two widely used antibiotics, sulfapyridine (SPY) and oxytetracycline (OTCs) at their common concentrations in pharmaceutical wastewaters (250 and 10 mg L^-1) were tested for degradation in three PMS-based oxidation processes, i.e., PMS, PMS-BNF, and PMS-Fe/C, respectively. Results demonstrated that a large amount of PMS (10 and 1 mM) could effectively remove SPY (0.385 min^-1, 100% removal) and OTC (2.737 min^-1, 100% removal) via¹O₂ derived from PMS self-decomposition and non-radical pathway, respectively. Additional Fe-based catalysts (0.5 g L^-1 Fe/C and BNF) significantly reduced the PMS consumption (1 and 0.25 mM) and accelerated the reaction rate (1.08 and 5.05 min^-1) of SPY and OTC removal. Moreover, the supplementary catalysts shifted the degradation route. The biochar matrix in Fe/C composite contributed to predominant interaction with PMS forming ¹O₂, which preferably attacked SPY via hydroxylation. In contrast, the redox-active Fe-Ni pairs induced SO₄^- formation, which could selectively degrade OTC through decarboxylation. Thus, these results are conducive to tailoring advanced yet low-cost heterogeneous catalysts for eco-friendly treatment of antibiotics-rich industrial wastewaters.

Biochar-supported nanoscale zero-valent iron as an efficient catalyst for organic degradation in groundwater

High-efficiency and cost-effective catalysts are critical to completely mineralization of organic contaminants for in-situ groundwater remediation via advanced oxidation processes (AOPs). The engineered biochar is a promising method for waste biomass utilization and sustainable remediation. This study engineers maize stalk (S)- and maize cob (C)-derived biochars (i.e., SB300, SB600, CB300, and CB600, respectively) with oxygen-containing functional groups as a carbon-based support for nanoscale zero-valent iron (nZVI). Morphological and physiochemical characterization showed that nZVI could be impregnated within the framework of the synthesized Fe-CB600 composite, which exhibited the largest surface area, pore volume, iron loading capacity, and Fe⁰ proportion. Superior degradation efficiency (100% removal in 20 min) of trichloroethylene (TCE, 0.1 mM) and fast pseudo-first-order kinetics (k_obs =22.0 h^-1) were achieved via peroxymonosulfate (PMS, 5 mM) activation by the Fe-CB600 (1 g L^-1) under groundwater condition (bicarbonate buffer solution at pH = 8.2). Superoxide radical and singlet oxygen mediated by Fe⁰ and oxygen-containing group (i.e., CO) were demonstrated as the major reactive oxygen species (ROSs) responsible for TCE dechlorination. The effectiveness and mechanism of the Fe/C composites for rectifying organic-contaminated groundwater were depicted in this study.

Mn-based catalysts for sulfate radical-based advanced oxidation processes: A review

Sulfate radical-based advanced oxidation processes (AOPs) have drawn increasing attention during the past two decades, and Mn-based materials have been proven to be effective catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS) to degrade many contaminants. This article presents a comprehensive review of various Mn-based materials to activate PMS and PDS. The activation mechanisms of different Mn-based catalysts (i.e., Mn oxides MnO_x, MnO_x hybrids, and MnO_x‑carbonaceous material composites) were first summarized and discussed in detail. Besides the commonly reported free radicals (SO₄^-• and ^•OH), non-radical mechanisms such as singlet oxygen and direct electron transfer have also been discovered for selected materials. The effects of pH, inorganic ions, natural organic matter (NOM), dissolved oxygen content, temperature, and the crystallinity of the materials on the catalytic reactivity were also discussed. Then, important instrumentations and technologies employed to characterize Mn-based materials and to understand the reaction mechanisms were concisely summarized. Three common overlooks in the experimental designs for examining the PMS/PDS-MnO_x systems were also discussed. Finally, future research directions were suggested to further improve the technology and to provide a guidance to develop cost-effective Mn-based materials to activate PMS/PDS.

Environmental application of MgMn-layered double oxide for simultaneous efficient removal of tetracycline and Cd pollution: Performance and mechanism

The MgMn-layered double oxide (MgMn-LDO), which was fabricated by calcining MgMn-layered double hydroxide (MgMn-LDH), was used to remove tetracycline (TC) and cadmium (Cd) pollution. In MgMn-LDO activated peroxymonosulfate (PMS) system, 97.1% of TC was degraded within 20 min. The high oxidizing sites exposed on MgMn-LDO surface played a main role on activating PMS to generate OH, SO₄^-, O₂^- and ¹O₂ (the key species) for TC degradation. MgMn-LDO could keep excellent degradation performance in a wide range of pH (from 4 to 10). The degradation degree of TC in distilled water is basically the same as that in Pearl River water, and even above 80% of TC could be degraded in human urine. The good reusability and high structure stability of MgMn-LDO were further verified. Meanwhile, Cd immobilization on MgMn-LDO reached equilibrium within 10 min, and its maximum fixed quantity was 8.234 mmol g^-1 (922.208 mg g^-1). The outstanding Cd fixed ability resulted from the formation of CdCO₃ and Cd (OH)₂. In combined system, the existence of TC promoted the immobilization of Cd on MgMn-LDO. Low concentration of Cd (0.0125 mM) had synergism effect on TC degradation, while high concentration of Cd (0.025 and 0.05 mM) had inhibiting action. Finally, a column filled with MgMn-LDO was designed for repairing TC and Cd pollution hierarchically. This study provided an effective strategy to clean up the organic-heavy metal combined pollution.

Highly efficient degradation of trichloroethylene in groundwater based on peroxymonosulfate activation by bentonite supported Fe/Ni bimetallic nanoparticle

Advanced oxidation processes (AOPs) are promising environmental remediation technologies for in-situ groundwater treatment. In this study, a bentonite supported Fe/Ni bimetallic nanoparticle (BNF) was fabricated for peroxymonosulfate (PMS) activation. The resultant BNF exhibited high catalytic activity for trichloroethylene (TCE) degradation in weak alkaline conditions. The conditions optimal for this activity were assessed in terms of peroxygen type and BNF/PMS dosage ratios. Complete degradation of 0.1 mM TCE was achieved in 25 min at pH = 8.2 when BNF was present at 1 g/L and PMS at 5 mM concentrations. Analysis of the underlying mechanisms indicated that SO₄^- has a dominant role whereas OH was rather trivial. The enhancement of catalytic activity was attributed to the strong oxidization of SO₄^-, dispersion of Fe/Ni nanoparticles and synergistic effects between Fe and Ni. The effects of inorganic anions, pH and temperature on the BNF/PMS activity were also investigated. Cl^- and NO₃^- has little effect on TCE degradation, while PO₄^3- and HPO₄^2- were inhibitory. Higher temperatures favored PMS activation and BNF/PMS exhibited good catalytic activity across a wide range of solution pH. The results indicate that a novel BNF/PMS system holds promise as a superior AOP to remediate emerging organic pollutants in groundwater.

Deactivation and regeneration of carbon nanotubes and nitrogen-doped carbon nanotubes in catalytic peroxymonosulfate activation for phenol degradation: variation of surface functionalities

The reuse, deactivation and regeneration of carbon nanotubes (CNT) and N-doped carbon nanotubes (NCNT) were studied in catalytic peroxymonosulfate (PMS) activation for phenol degradation. The results showed that for catalytic PMS activation, marked deactivation was observed on both CNT and NCNT, resulting in marked variation of the surface functionalities of the catalysts. Catalytic PMS activation led to markedly increased oxygen-containing functionalities and decreased points of zero charge (PZCs) of CNT and NCNT. The catalytic activity of CNT was strongly dependent on the initial PMS concentration but was independent of the initial phenol concentration. Furthermore, the dependency of the CNT activity on the initial PMS concentration closely followed the Langmuir-Hinshelwood model, indicating that the catalytic activation of adsorbed PMS was the rate controlling step. For the used CNT and NCNT, chemical reduction by NaBH4 or thermal treatment regeneration under inert atmosphere could effectively remove surface O-containing functionalities and enhance PZCs, restoring their catalytic activities; meanwhile, the N-containing functionalities of NCNT decreased with regeneration treatment, resulting in a negative impact on catalyst regeneration. The present findings indicate that surface functionalities are closely correlated with catalyst deactivation and regeneration, playing crucial roles in the catalytic activation of PMS.

Degradation of dyes by peroxymonosulfate activated by ternary CoFeNi-layered double hydroxide: Catalytic performance, mechanism and kinetic modeling

Ternary CoFeNi-layered double hydroxide (CoFeNi-LDH) was synthesized and initially applied to activate peroxymonosulfate (PMS) for the degradation of Congo red (CR) and Rhodamine B (RhB). The results show that the CoFeNi-LDH/PMS system can efficiently degrade nearly 100% of 20 mg/L CR or 20 mg/L RhB within 6- and 10-min reaction times, respectively. And the catalyst exhibits higher degradation efficiency on CR than on RhB under identical conditions, which is confirmed by electron clouds of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) performed by DFT calculations. Quenching tests reveal that SO₄^- is the dominant active species participating in the degradation process. Mechanism investigation demonstrates that Co(II)-Co(III)-Co(II) cycle is responsible for activating PMS to generate radicals for dyes degradation. A dynamic kinetic model is successfully developed to simulate the concentration profiles of CR and RhB degradation in CoFeNi-LDH/PMS system. The empirical second order rate constants between SO₄^- and CR (k_SO4-/CR), HO and CR (k_OH/CR), SO₄^- and RhB (k_SO4-/RhB), HO and RhB (k_HO/RhB) are determined to be 2.47 × 10⁷, 3.44 × 10⁶, 8.39 × 10⁶ and 2.62 × 10⁷ M^-1s^-1, respectively. In addition, toxic assessment using ECOSAR program suggests that the overall toxicity of CR and RhB decreased after treatment with CoFeNi-LDH/PMS system. Repeating tests and application of CoFeNi-LDH in different water sources give us adequate confidence that the as-synthesized CoFeNi-LDH is favorable for the purification of dye-contaminanted waters in practical.

SrCo1-xTixO3-δ perovskites as excellent catalysts for fast degradation of water contaminants in neutral and alkaline solutions

Perovskite-like oxides SrCo_1-xTi_xO_3-δ (SCT_x, x = 0.1, 0.2, 0.4, 0.6) were used as heterogeneous catalysts to activate peroxymonosulfate (PMS) for phenol degradation under a wide pH range, exhibiting more rapid phenol oxidation than Co₃O₄ and TiO₂. The SCT_0.4/PMS system produced a high activity at increased initial pH, achieving optimized performance at pH ≥ 7 in terms of total organic carbon removal, the minimum Co leaching and good catalytic stability. Kinetic studies showed that the phenol oxidation kinetics on SCT_0.4/PMS system followed the pseudo-zero order kinetics and the rate on SCT_0.4/PMS system decreased with increasing initial phenol concentration, decreased PMS amount, catalyst loading and solution temperature. Quenching tests using ethanol and tert-butyl alcohol demonstrated sulfate and hydroxyl radicals for phenol oxidation. This investigation suggested promising heterogeneous catalysts for organic oxidation with PMS, showing a breakthrough in the barriers of metal leaching, acidic pH, and low efficiency of heterogeneous catalysis.

Co2SnO4 nanoparticles as a high performance catalyst for oxidative degradation of rhodamine B dye and pentachlorophenol by activation of peroxymonosulfate

Spinel Co₂SnO₄ NPs, prepared by hydrothermal process, are applied for PMS activation for organic pollutants degradation.

Persulfate-enhanced sonochemical degradation of naphthol blue black in water: Evidence of sulfate radical formation

This work explores the effect of persulfate (PS) on the sonochemical degradation of organic pollutants taking naphthol blue black (NBB), an anionic diazo dye, as a substrate model. The sonolytic experiments were conducted in the absence and presence of PS under various experimental conditions including acoustic power (10-80W), frequency (20 and 585kHz) and saturating gas (argon, air and nitrogen). Experimental results showed that PS decomposition into sulfate radical (SO₄^-) takes place by sonolysis and increasing PS concentration up to 1g/L would result in an increase in the NBB degradation rate. It was found that the PS-enhanced effect was strongly operating parameters dependent. The positive effect of PS decreased with increasing power and the best enhancing effect was obtained for the lowest acoustic power. Correspondingly, the PS-enhanced effect was more remarkable at low frequency (20kHz) than that observed at high frequency ultrasound (585kHz). Nitrogen saturating gas gave the best enhanced effect of PS than argon and air atmospheres. Theoretical (computer simulation of bubble collapse) and experimental measurements of the yields of free radical generation under the different experimental conditions have been made for interpreting the obtained effects of PS on the sonochemical degradation of the dye pollutant. The experimental findings were attributed to the fact that radical-radical recombination reactions occur at faster rate than the radical-organic reaction when the concentration of free radicals is too high (at higher sonochemical conditions).

Activation of peroxymonosulfate by graphitic carbon nitride loaded on activated carbon for organic pollutants degradation

Graphitic carbon nitride supported on activated carbon (g-C3N4/AC) was prepared through an in situ thermal approach and used as a metal free catalyst for pollutants degradation in the presence of peroxymonosulfate (PMS) without light irradiation. It was found that g-C3N4 was highly dispersed on the surface of AC with the increase of surface area and the exposition of more edges and defects. The much easier oxidation of C species in g-C3N4 to CO was also observed from XPS spectra. Acid Orange 7 (AO7) and other organic pollutants could be completely degraded by the g-C3N4/AC catalyst within 20min with PMS, while g-C3N4+PMS and AC+PMS showed no significant activity for the reaction. The performance of the catalyst was significantly influenced by the amount of g-C3N4 loaded on AC; but was nearly not affected by the initial solution pH and reaction temperature. In addition, the catalysts presented good stability. A nonradical mechanism accompanied by radical generation (HO and SO4(-)) in AO7 oxidation was proposed in the system. The CO groups play a key role in the process; while the exposure of more N-(C)3 group can further increase its electron density and basicity. This study can contribute to the development of green materials for sustainable remediation of aqueous organic pollutants.

Evaluating Prussian blue analogues MII3[MIII(CN)6]2 (MII = Co, Cu, Fe, Mn, Ni; MIII = Co, Fe) as activators for peroxymonosulfate in water

[Fe(CN)₆] and [Co(CN)₆]-based Prussian blue analogues (PBAs) were prepared with various metal ions (i.e., Co, Cu, Fe, Mn and Ni) and evaluated as catalysts to activate an important oxidant, peroxymonosulfate (PMS).