Influence of pH on the formation of sulfate and hydroxyl radicals in the UV/peroxymonosulfate system

Green mechanochemical activation of solid persulfate to remove PAHs in soil: Performance and mechanism

Due to the high biotoxicity and persistence of polycyclic aromatic hydrocarbons (PAHs), the remediation of PAHs-contaminated soil becomes an intractable problem. Persulfate-based advanced oxidation processes are widely used to degrade PAHs in aquatic environment. However, they are not convenient for used in soil due to the heterogeneity and complexity of soil matrix. In this study, a green and convenient ball milling process is introduced to activate persulfate for the remediation of PAHs-contaminated soil. About 82.5% PAHs were removed with 10% wt. Na2S2O8 (PS) addition and ball-milling for 2 h under 500 r/min. The degradation of PAHs is attributed to the attack of radicals (SO4·- and·OH) generated from the activation of PS by mechanochemistry. Moreover, stable Si-O bonds were disrupted during ball-milling process, and formed free electron on the surface of soil particles. This facilitates the electron transfer from oxidants to contaminants. The particle size, surface element composition, functional group, and thermogravimetric analysis confirmed the slight disturbance of ball-milling-assisted PS process on the physical and chemical properties of soil. Therefore, ball-milling assisted PS approach would be a promising technology for the remediation of PAHs-contaminated soil.

Electron transfer mediated photo-Fenton-like synergistic catalysis of Fe,Cu-doped MIL-101 coupled with Ag3PO4: Quantitative evaluation and DFT calculations

Widespread use of tetracycline (TC) results in its persistent residue and bioaccumulation in aquatic environments, posing a high toxicity to non-target organisms. In this study, a bimetal-doped composite material Ag3PO4/MIL-101(Fe,Cu) has been designed for the treatment of TC in aqueous solutions. As the molar ratio of Fe/Cu in composite is 1:1, the obtained material AP/MFe1Cu1 is placed in an aqueous environment under visible light irradiation in the presence of 3 mM peroxydisulfate (PDS), which forms a photo-Fenton-like catalytic system that can completely degrade TC (10 mg/L) within 60 min. Further, the degradation rate constant (0.0668 min-1) is 5.66 and 7.34 times higher than that of AP/MFe and AP/MCu, respectively, demonstrating a significant advantage over single metal-doped catalysts. DFT calculations confirm the strong adsorption capacity and activation advantage of PDS on the composite surface. Therefore, the continuous photogenerated electrons (e-) accelerate the activation of PDS and the production of SO4•-, resulting in the stripping of abundant photogenerated h + for TC oxidation. Meanwhile, the internal circulation of FeⅢ/FeⅡ and CuⅡ/CuⅢ in composite also greatly enhances the photo-Fenton-like catalytic stability. According to the competitive dynamic experiments, SO4•- have the greatest contribution to TC degradation (58.93%), followed by 1O2 (23.80%). The degradation intermediates (products) identified by high-performance liquid chromatography-mass spectrometry (HPLC/MS) technique indicate the involvement of various processes in TC degradation, such as dehydroxylation, deamination, N-demethylation, and ring opening. Furthermore, as the reaction proceeds, the toxicity of the intermediates produced during TC degradation gradually decreases, which can ensure the safety of the aquatic ecosystem. Overall, this work reveals the synergy mechanism of PDS catalysis and photocatalysis, as well as provides technical support for removal of TC-contaminated wastewater.

Were Persulfate-Based Advanced Oxidation Processes Really Understood? Basic Concepts, Cognitive Biases, and Experimental Details

Persulfate (PS)-based advanced oxidation processes (AOPs) for pollutant removal have attracted extensive interest, but some controversies about the identification of reactive species were usually observed. This critical review aims to comprehensively introduce basic concepts and rectify cognitive biases and appeals to pay more attention to experimental details in PS-AOPs, so as to accurately explore reaction mechanisms. The review scientifically summarizes the character, generation, and identification of different reactive species. It then highlights the complexities about the analysis of electron paramagnetic resonance, the uncertainties about the use of probes and scavengers, and the necessities about the determination of scavenger concentration. The importance of the choice of buffer solution, operating mode, terminator, and filter membrane is also emphasized. Finally, we discuss current challenges and future perspectives to alleviate the misinterpretations toward reactive species and reaction mechanisms in PS-AOPs.

Unveiling the activity difference cause and ring-opening reaction routes of typical radicals induced degradation of toluene

This study employs five UV-AOPs (PMS, PDS, H2O2, NaClO and NaClO2) to produce radicals (•OH, SO4•-, ClO•, O2•- and 1O2) and further comparatively studies their activity sequence and activity difference cause in toluene degradation. The toluene mineralization efficiency as a descending order is 73 % (UV-PMS) > 71 % (UV-PDS) > 70 % (acidified-UV-NaClO) > 55 % (UV-H2O2) > 36 % (UV-NaClO) > 35 % (UV-NaClO2); that of conversion efficiency is 99 % (acidified-UV-NaClO) > 95 % (UV-PMS) > 90 % (UV-PDS) > 74 % (UV-H2O2) > 44 % (UV-NaClO) > 41 % (UV-NaClO2). Acidic pretreatment significantly boosts the reactivity of UV-NaClO. ESR combined with radical quenching tests reveals the radicals' generation and evolution, and their contribution rates to toluene conversion, i.e. ClO• > SO4•- > O2•- > 1O2 > •OH. Theoretical calculations further unveil the ring-opening reaction routes and the nature of the activity difference of different radicals. The minimum energy required for ring-opening reaction is 116.77, 150.63, 168.29 and 191.92 kJ/mol with respect to ClO•, SO4•-, 1O2 and •OH, and finding that the ClO•-HO• pair is the best for toluene mineralization. The difficulty for eliminating typical VOCs by using UV-AOPs method is determined as toluene > chlorobenzene > benzene > ethyl acetate.

Superior performance of oxygen vacancy-enriched Cu-Co3O4/urushiol-rGO/peroxymonosulfate for hypophosphite and phosphite removal by enhancing singlet oxygen

The treatment of wastewater containing hypophosphite [P(I)] and phosphite [P(III)] is challenged by limitations of traditional Fenton oxidation such as low efficiency, secondary pollution and high costs. This study introduced a facile solvent-thermal method to synthesize Cu-Co3O4 nanoparticles uniformly loaded on graphene (Cu-Co3O4/U-rGO) through the reduction and coordination effects of urushiol (U). As prepared Cu-Co3O4/U-rGO exhibited excellent activity in activating peroxymonosulfate (PMS) for the oxidation of P(I)/P(III) to phosphate [P(V)] (0.229 min-1), along with high stability and reusability (91.5 % after 6 cycles), low metal leaching rate (Co: 0.2 mg/L, Cu: 0.05 mg/L), insensitivity to common anions in water and a wide pH range (3-11). The activation mechanism involved the synergistic effects from both urushiol and graphene, which promoted redox of Cu+/Cu2+ and Co2+/Co3+ and induced abundant oxygen vacancies for PMS activation to produce singlet oxygen. Furthermore, the Cu-Co3O4/U-rGO/PMS was also excellent in the oxidative removal of organic phosphorus. This study is expected to advance strategies for the treatment of P(I)/P(III)-rich wastewater and provide new insights for the development of low-cost, highly efficient heterogeneous catalysts with abundant oxygen vacancies.

Activation of peroxymonosulfate with ZIF-67-derived Co/N-doped porous carbon nanocubes for the degradation of Congo red dye

In this study, porous carbon nanocubes encapsulated magnetic metallic Co nanoparticles (denoted as Co@N-PCNC) was prepared via pyrolyzing ZIF-67 nanocubes precursor at 600 °C and characterized by various technologies. It was used to activate peroxymonosulfate (PMS) to degrade Congo red (CR) dye efficiently. Over 98.45% of 50 mg L-1 CR was degraded using 0.033 mM PMS activated by 75 mg L-1 Co@N-PCNC within 12 min. The free radical quenching experiments were performed to reveal the nature of the reactive oxygen species radicals generated throughout the catalytic oxidation of CR. The effects of common inorganic anions and the water matrix on CR removal were studied. Moreover, the results of the kinetic study revealed the suitability of the pseudo-first-order and Langmuir-Hinshelwood kinetic models for illustrating CR degradation using the Co@N-PCNC/PMS system. Ultimately, the Co@N-PCNC displayed good operational stability, and after five cycles, the CR removal rate can still maintain over 90% after 12 min.

Direct Determination of Absolute Radical Quantum Yields in Hydroxyl and Sulfate Radical-Based Treatment Processes

The absolute radical quantum yield (Φ ) is a critical parameter to evaluate the efficiency of radical-based processes in engineered water treatment. However, measuring Φ is fraught with challenges, as current quantification methods lack selectivity, specificity, and anti-interference capabilities, resulting in significant error propagation. Herein, we report a direct and reliable time-resolved technique to determine Φ at pH 7.0 for commonly used radical precursors in advanced oxidation processes. For H2O2 and peroxydisulfate (PDS), the values of Φ •OH and Φ SO 4 • - at 266 nm were measured to be 1.10 ± 0.01 and 1.46 ± 0.05, respectively. For peroxymonosulfate (PMS), we developed a new approach to determine Φ • OH PMS with terephthalic acid as a trap-and-trigger probe in the nonsteady state system. For the first time, the Φ • OH PMS value was measured to be 0.56 by the direct method, which is stoichiometrically equal to Φ SO 4 • - PMS (0.57 ± 0.02). Additionally, radical formation mechanisms were elucidated by density functional theory (DFT) calculations. The theoretical results showed that the highest occupied molecular orbitals of the radical precursors are O-O antibonding orbitals, facilitating the destabilization of the peroxy bond for radical formation. Electronic structures of these precursors were compared, aiming to rationalize the tendency of the Φ values we observed. Overall, this time-resolved technique with specific probes can be used as a reliable tool to determine Φ , serving as a scientific basis for the accurate performance evaluation of diverse radical-based treatment processes.

One-pot synthesis of NiCo-phyllosilicate supported on zeolite for enhanced degradation of antibiotic contaminants

The overuse of antibiotics currently results in the presence of various antibiotics being detected in water bodies, which poses potential risks to human health and the environment. Therefore, it is highly significant to remove antibiotics from water. In this study, we developed novel rod-like NiCo-phyllosilicate hybrid catalysts on calcined natural zeolite (NiCo@C-zeolite) via a facile one-pot process. The presence of the zeolite served as both a silicon source and a support, maintaining a high specific surface area of the NiCo@C-zeolite. Remarkably, NiCo@C-zeolite exhibited outstanding catalytic performance in antibiotic degradation under PMS activation. Within just 5 min, the degradation rate of metronidazole (MNZ) reached 96.14%, ultimately achieving a final degradation rate of 99.28%. Furthermore, we investigated the influence of catalyst dosage, PMS dosage, MNZ concentration, initial pH value, and various inorganic anions on the degradation efficiency of MNZ. The results demonstrated that NiCo@C-zeolite displayed outstanding efficacy in degrading MNZ under diverse conditions and maintained a degradation rate of 94.86% at 60 min after three consecutive cycles of degradation. Free radical quenching experiments revealed that SO•-4played a significant role in the presence of NiCo@C-zeolite-PMS system. These findings indicate that the novel rod-like NiCo-phyllosilicate hybrid catalysts had excellent performance in antibiotic degradation.

Synergistic oxidation induced by underwater bubbling plasma and diatomite-CoFe2O4 activated peroxymonosulfate for the degradation of ciprofloxacin hydrochloride

Underwater bubbling plasma (UBP) coupled with diatomite-CoFe2O4 (Dt-CFO) activated peroxymonosulfate (PMS) was proposed for the degradation of ciprofloxacin hydrochloride (CIP) in this work. The catalyst sample of Dt-CFO with large specific surface area, rich active sites and excellent magnetic property was prepared by the hydrothermal method and systematically characterized to investigate its material properties. The combination of UBP and Dt-CFO activated PMS (UBP/Dt-CFO/PMS) showed excellent synergy with the synergistic factor of 1.98, and reached the CIP degradation percentage of 94.7%, which corresponded to the kinetic constant of 0.097 min-1. Dt-CFO with the diatomite content of 30 wt% achieved the best catalytic activity in the reaction system. Higher catalyst and PMS dose, peak voltage, pulse frequency and lower initial CIP concentration were beneficial for CIP removal. The addition of Cl-, HCO3-, SO42- and humic acid suppressed CIP degradation, while NO3- had no effect on CIP removal. The Dt-CFO composite exhibited excellent reusability and low leaching metal amount, demonstrating its good stability. SO4-·, ·OH, ·O2-, 1O2, eaq, O3 and H2O2 were the active species confirmed to be involved in CIP degradation. The redox circles of ≡ Co(Ⅱ)/≡Co(Ⅲ) and ≡ Fe(Ⅱ)/≡Fe(Ⅲ) on Dt-CFO surface and the plasma-induced physicochemical effects dominated PMS activation. The decomposition process of CIP was explored through fluorescence spectra. Three degradation pathways were inferred, and the toxicity analysis showed the toxicity of CIP solution weakened after discharge treatment.

Single-crystal vs polycrystalline boron-doped diamond anodes: Comparing degradation efficiencies of carbamazepine in electrochemical water treatment

The ongoing challenge of water pollution by contaminants of emerging concern calls for more effective wastewater treatment to prevent harmful side effects to the environment and human health. To this end, this study explored for the first time the implementation of single-crystal boron-doped diamond (BDD) anodes in electrochemical wastewater treatment, which stand out from the conventional polycrystalline BDD morphologies widely reported in the literature. The single-crystal BDD presented a pure diamond (sp3) content, whereas the three other investigated polycrystalline BDD electrodes displayed various properties in terms of boron doping, sp3/sp2 content, microstructure, and roughness. The effects of other process conditions, such as applied current density and anolyte concentration, were simultaneously investigated using carbamazepine (CBZ) as a representative target pollutant. The Taguchi method was applied to elucidate the optimal operating conditions that maximised either (i) the CBZ degradation rate constant (enhanced through hydroxyl radicals (•OH)) or (ii) the proportion of sulfate radicals (SO4•-) with respect to •OH. The results showed that the single-crystal BDD significantly promoted •OH formation but also that the interactions between boron doping, current density and anolyte concentration determined the underlying degradation mechanisms. Therefore, this study demonstrated that characterising the BDD material and understanding its interactions with other process operating conditions prior to degradation experiments is a crucial step to attain the optimisation of any wastewater treatment application.

Ultrasensitive Electrochemiluminescence Biosensor Based on Efficient Signal Amplification of Copper Nanoclusters Induced by CaMnO3 for CD44 Trace Detection

Metal nanoclusters (Me NCs) have become a research hotspot in the field of electrochemiluminescence (ECL) sensing analysis. This is primarily attributed to their excellent luminescent properties and biocompatibility along with their easy synthesis and labeling characteristics. At present, the application of Me NCs in ECL mainly focuses on precious metals, whose high cost, to some extent, limits their widespread application. In this work, Cu NCs with cathode ECL emissions in persulfate (S2O82-) were prepared as signal probes using glutathione as ligands, which exhibited stable luminescence signals and high ECL efficiency. At the same time, CaMnO3 was introduced as a co-reaction promoter to increase the ECL responses of Cu NCs, thereby further expanding their application potential in biochemical analysis. Specifically, the reversible conversion of Mn3+/Mn4+ greatly promoted the generation of sulfate radicals (SO4•-), providing a guarantee for improving the luminescence signals of Cu NCs. Furthermore, a short peptide (NARKFYKGC) was introduced to enable the fixation of antibodies to specific targets, preventing the occupancy of antigen-binding sites (Fab fragments). Therefore, the sensitivity of the biosensor could be significantly enhanced by releasing additional Fab fragments. Considering the approaches discussed above, the constructed biosensor could achieve sensitive detection of CD44 over a broad range (10 fg/mL-100 ng/mL), with an ultralow detection limit of 3.55 fg/mL (S/N = 3), which had valuable implications for the application of nonprecious Me NCs in biosensing analysis.

Development of a Five-Chemical-Probe Method to Determine Multiple Radicals Simultaneously in Hydroxyl and Sulfate Radical-Mediated Advanced Oxidation Processes

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO•)- and sulfate radical (SO4•-)-mediated oxidation, are attractive technologies used in water and wastewater treatments. To evaluate the treatment efficiencies of AOPs, monitoring the primary radicals (HO• and SO4•-) as well as the secondary radicals generated from the reaction of HO•/SO4•- with water matrices is necessary. Therefore, we developed a novel chemical probe method to examine five key radicals simultaneously, including HO•, SO4•-, Cl•, Cl2•-, and CO3•-. Five probes, including nitrobenzene, para-chlorobenzoic acid, benzoic acid, 2,4,6-trimethylbenzoic acid, and 2,4,6-trimethylphenol, were selected in this study. Their bimolecular reaction rate constants with diverse radicals were first calibrated under the same conditions to minimize systematic errors. Three typical AOPs (UV/H2O2, UV/S2O82-, and UV/HSO5-) were tested to obtain the radical steady-state concentrations. The effects of dissolved organic matter, Br-, and the probe concentration were inspected. Our results suggest that the five-probe method can accurately measure radicals in the HO•- and SO4•--mediated AOPs when the concentration of Br- and DOM are less than 4.0 μM and 15 mgC L-1, respectively. Overall, the five-probe method is a practical and easily accessible method to determine multiple radicals simultaneously.

Removal of sulfonamide antibiotics by non-free radical dominated peroxymonosulfate oxidation catalyzed by cobalt-doped sulfur-containing biochar from sludge

The reuse of activated sludge as a solid waste is severely underutilized due to the limitations of traditional treatment and disposal methods. Given that, the sulfur-containing activated sludge catalyst doped with cobalt (SK-Co(1.0)) was successfully prepared by one-step pyrolysis and calcinated at 850 ℃. The generation of CoSx was successfully characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), indicating that the sulfur inside the sludge was the anchoring site for the externally doped cobalt. Cobalt (Ⅱ) (Co2+), as the main adsorption site for peroxymonosulfate(PMS), formed a complex (SK-Co(1.0)-PMS* ) and created the conditions for the generation of surface radicals. The SK-Co(1.0)/PMS system showed high degradation efficiency and apparent rate constants for Sulfamethoxazole (SMX) (91.56% and 0.187 min-1) and Sulfadiazine (SDZ) (90.73% and 0.047 min-1) within 10 min and 30 min, respectively. Three sites of generation of 1O2, which played a dominant role in the degradation of SMX and SDZ in the SK-Co(1.0)/PMS system, were summarized as：sulfur vacancies (SVs), the Co3+/Co2+ cycles promoted by sulfur(S) species, oxygen-containing functional groups (C-O). The degradation mechanisms and pathways had been thoroughly investigated using DFT calculations. In view of this, a new idea for the resource utilization of activated sludge solid waste was provided and a new strategy for wastewater remediation was proposed.

Intramolecular generation of endogenous Cu(III) for selectively self-catalytic degradation of Cu(II)-EDTA from wastewater by UV/peroxymonosulfate

HO•/SO4•--based advanced oxidation processes for the decomplexation of heavy metal-organic complexes usually encounter poor efficiency in real scenarios. Herein, we reported an interesting self-catalyzed degradation of Cu(II)-EDTA with high selectivity in UV/peroxymonosulfate (PMS). Chemical probing experiments and competitive kinetic analysis quantitatively revealed the crucial role of in situ formed Cu(III). The Cu(III) species not only oxidized Cu(II)-EDTA rapidly at ∼3 × 107 M-1 s-1, but also exhibited 2-3 orders of magnitude higher steady-state concentration than HO•/SO4•-, leading to highly efficient and selective degradation of Cu(II)-EDTA even in complex matrices. The ternary Cu(II)-OOSO3- complexes derived from Cu(II)-EDTA decomposition could generate Cu(III) in situ via the Cu(II)-Cu(I)-Cu(III)-Cu(II) cycle involving intramolecular electron transfer. This method was also applicable to various Cu(II) complexes in real electroplating wastewater, demonstrating higher energy efficiency than commonly studied UV-based AOPs. This study provids a proof of concept for efficient decomplexation through activating complexed heavy metals into endogenous reactive species.

Progress on mechanism and efficacy of heterogeneous photocatalysis coupled oxidant activation as an advanced oxidation process for water decontamination

The rising debate on the dilemma of photocatalytic water treatment technologies has driven researchers to revisit its prospects in water decontamination. Nowadays, heterogeneous photocatalysis coupled oxidant activation techniques are intensively studied due to their dual advantages of high mineralization and high oxidation efficiency in pollutant degradation. This paved a new way for the development of solar-driven oxidation technologies. Previous reviews focused on the advances in one specific coupling technique, such as photocatalytic persulfate activation and photocatalytic ozonation, but lack a consolidated understanding of the synergy between photocatalytic oxidation and oxidant activation. The synergy involves the migration of photogenerated carriers, radical reaction, and the increase in oxidation rate and mineralization. This review systematically summarizes the fundamentals of activation mechanism, advanced characterization techniques and synergistic effects of coupling techniques for water decontamination. Besides, specific cases that lead researchers astray in revealing mechanisms and assessing synergy are critically discussed. Finally, the prospects and challenges are put forward to further deepen the research on heterogeneous photocatalytic activation of oxidants. This work provides a consolidated view of the existing heterogeneous photocatalysis coupled oxidant activation techniques and inspires researchers to develop more promising solar-driven technologies for water decontamination.

Targeted regulation of digestate dewaterability by the ozone/persulfate oxidation process

Dewatering is the first step in the subsequent treatment and disposal of food waste digestate (FWD). However, FWD is difficult to dewatering. In this study, persulfate was synergistic oxidized by ozone to improve digestate dewaterability. The optimal conditions was at pH = 3, O3＝40 mg/g TS and PDS＝0.1 g/g TS, under which the reductions in the normalized capillary suction time (NCST) and bound moisture (BM) of the FWD were 89.97% and 65.79%, respectively. Hydrophilic functional groups (oxygen- and nitrogen-containing groups) and hydrophilic protein molecular structures were decomposed by the reactive species of sulfate radical (SO4·-) and hydroxyl radicals (·OH) generated in the ozone-persulfate oxidation process, disrupting the binding between EPS and water molecules. The contributions of SO4·- and ·OH to digestate dewaterability were 42.51% and 28.55%. In addition, the introduction of H+ reduced electrostatic repulsion and contributed to the condensation of digestate flocs. The environmental implication assessment and economic analysis suggested that the O3/PDS oxidation process was cost-effective and has a low environmental implication when applied to the FWD dewaterability improvement process. These results can serve as a reference for the management of FWD and further improvement of FWD treatment and disposal efficiency.

A combined experimental and computational approach to unravel degradation mechanisms in electrochemical wastewater treatment

Electrochemical wastewater treatment is a promising technique to remove recalcitrant pollutants from wastewater. However, the complexity of elucidating the underlying degradation mechanisms hinders its optimisation not only from a techno-economic perspective, as it is desirable to maximise removal efficiencies at low energy and chemical requirements, but also in environmental terms, as the generation of toxic by-products is an ongoing challenge. In this work, we propose a novel combined experimental and computational approach to (i) estimate the contribution of radical and non-radical mechanisms as well as their synergistic effects during electrochemical oxidation and (ii) identify the optimal conditions that promote specific degradation pathways. As a case study, the distribution of the degradation mechanisms involved in the removal of benzoic acid (BA) via boron-doped diamond (BDD) anodes was elucidated and analysed as a function of several operating parameters, i.e., the initial sulfate and nitrate content of the wastewater and the current applied. Subsequently, a multivariate optimisation study was conducted, where the influence of the electrode nature was investigated for two commercial BDD electrodes and a customised silver-decorated BDD electrode. Optimal conditions were identified for each degradation mechanism as well as for the overall BA degradation rate constant. BDD selection was found to be the most influential factor favouring any mechanism (i.e., 52-85% contribution), given that properties such as its boron doping and the presence of electrodeposited silver could dramatically affect the reactions taking place. In particular, decorating the BDD surface with silver microparticles significantly enhanced BA degradation via sulfate radicals, whereas direct oxidation, reactive oxygen species and radical synergistic effects were promoted when using a commercial BDD material with higher boron content and on a silicon substrate. Consequently, by simplifying the identification and quantification of underlying mechanisms, our approach facilitates the elucidation of the most suitable degradation route for a given electrochemical wastewater treatment together with its optimal operating conditions.

Oxidation of emerging contaminants by S(IV) activated ferrate: Identification of reactive species

Studies on the Fe(VI)/S(IV) process have focused on improving the efficiency of emerging contaminants (ECs) degradation under alkaline conditions. However, the performance and mechanisms under varying pH levels remain insufficiently investigated. This tudy delved into the efficiency and mechanism of Fe(VI)/S(IV) process using sulfamethoxazole (SMX) and ibuprofen (IBU) as model contaminants. We found that pH was crucial in governing the generation of reactive species, and both Fe(V/IV) and SO4•- were identified in the reaction system. Specifically, an increase in pH favored the formation of SO4•-, while the formation of Fe(VI) to Fe(V/IV) became more significant at lower pH. At pH 3.2, Fe(III) resulting from the Fe(VI) self-decay reactedwith HSO3-to produce SO4•-and •OH. Under near-neutral conditions, the coexistance of Fe(V/IV) and SO4•- in abundance contributed to the optimal oxidation of both pollutants in the Fe(VI)/S(IV) process, with the removal exceeding 74% in 5 min. Competitive quenching experiments showed that the contributions of Fe(V/IV) to SMX and IBU destruction dimished, while the contributions of radicals increased with an increase in pH. However, this evolution was slower during SMX degradation compared to IBU degradation. A comprehensive understnding of pH as the key factor is essential for the optimization of the sulfite-activated Fe(VI) oxidation process in water treatment.

Insights into the mechanism of multiple Cu-doped CoFe2O4 nanocatalyst activated peroxymonosulfate for efficient degradation of Rhodamine B

The multiple metal catalyst as a promising nanomaterial has shown excellent activity in the peroxymonosulfate (PMS) activation for pollutant degradation. However, the role of special sites and in-depth understanding of the PMS activation mechanism are not fully studied. In this study, a Cu-doped CoFe2O4 nanocatalyst (0.5CCF) was synthesized by a sol-gel and calcination method, and used for PMS activation to remove Rhodamine B (RhB). The results showed that the Cu doping obviously enhanced the catalytic performance of CoFe2O4, with 99.70% of RhB removed by 0.5CCF while 74.91% in the CoFe2O4 within 15 min. Based on the X-ray photoelectron spectroscopy and electrochemical analysis, this could be ascribed to the more low valence of Co and Fe species generated on the 0.5CCF and faster electron transfers occurred in the 0.5CCF due to the Cu doping. In addition, Cu doping could provide more reaction sites for the 0.5CCF to activate PMS for RhB removal. The metal species and the surface hydroxyl were the reaction sites of PMS activation, and the surface hydroxyl played an important role in surface-bound reactive species generation. During the PMS activation, the Cu not only activated PMS to produce reactive oxygen species (ROS), but also regenerated Co2+ and Fe2+ to accelerate the PMS activation. The non-radical of 1O2 was the main ROS with a 99.35% of contribution rate, and the SO5•- self-reaction was its major source. This study provides a new insight to enhance the PMS activation performance of multiple metal catalysts by Cu doping in wastewater treatment.

Peroxymonosulfate activation by trace iron(III) porphyrin for facile degradation of organic pollutants via nonradical oxidation

Nonradical species with great resistance to interference have shown great advantages in complex wastewater treatment. Herein, a novel system constructed by biodegradable tetrakis-(4-carboxyphenyl)-porphyrinatoiron(III) (FeIII-TCPP) and peroxymonosulfate (PMS) was proposed for facile decontamination. Nonradical pathway is observed in FeIII-TCPP/PMS, where 1O2 and high-valent iron-oxo species play dominant roles. The genres and valence of high-valent iron-oxo species, including iron(IV)-oxo porphyrin radical-cationic species [OFeIV-TCPP•+] and iron(IV)-hydroxide species [FeIV-TCPP(OH)], are ascertained, along with their generation mechanism. The axial ligand on the iron axial site affects the ground spin state of FeIII-TCPP, further influencing the thermodynamic reaction pathway of active species. With trace catalyst in micromoles, FeIII-TCPP exhibits high efficiency by degrading bisphenol S (BPS) completely within 5 min, while Co2+/PMS can only achieve a maximum of 26.2% under identical condition. Beneficial from nonradical pathways, FeIII-TCPP/PMS demonstrates a wide pH range of 3-10 and exhibits minimal sensitivity to interference of concomitant materials. BPS is primarily eliminated through β-scission and hydroxylation. Specifically, 1O2 electrophilically attacks the C-S bond of BPS, while high-valent iron-oxo species interacts with BPS through an oxygen-bound mechanism. This study provides novel insights into efficient activation of PMS by iron porphyrin, enabling the removal of refractory pollutants through nonradical pathway.

Elucidating the performance of UV-based photochemical processes for the removal of trace organic contaminants: Degradation and toxicity evaluation

In this study, the performance of standalone ultraviolet (UV) photolysis and UV-based advanced oxidation processes (AOPs), namely, UV/hydrogen peroxide, UV/chlorine, UV/persulphate, and UV/permonosulphate, were investigated for the degradation of 31 trace organic contaminants (TrOCs). Under the tested conditions, standalone UV photolysis did not achieve effective removal of TrOCs. To improve the degradation efficiency of UV photolysis, four different oxidants were added individually to the test solution. The effect of these oxidants in the absence of UV irradiation was also explored and only chlorine showed promising degradation of some contaminants. During the chlorination of 31 investigated TrOCs, only six demonstrated greater than 50% degradation. The combined UV-based AOPs demonstrated much improved degradation (ranging from 65 to 100%) depending on TrOC-structure and oxidant concentration. The UV/hydrogen peroxide process showed similar degradation of TrOCs, irrespective of the functional groups (i.e., electron withdrawing groups, EWGs and electron donating groups, EDGs) present in their structures. Conversely, the UV/sulphate and UV/chlorine based processes achieved better degradation of the TrOCs with EDGs in their structures. TrOCs degradation improved up to 40% when oxidants concentrations were increased from 0.1 to 1 mM, and further increasing the concentration to 2 mM did not improve degradation. Toxicity evaluation using bioluminescence test (BLT assay) demonstrated that except for UV/hydrogen peroxide, all UV-based AOPs increased the toxicity of the treated effluent, indicating generation of toxic by-products. This study elucidates the performance of four different UV-based AOPs for the removal of commonly detected diverse TrOCs for the first time.

Assessment of the UV/DCCNa and UV/NaClO oxidation process for the removal of diethyl phthalate (DEP) in the aqueous system

In this work, the removal and transformation process of diethyl phthalate (DEP) in UV/dichloroisocyanurate (UV/DCCNa) and UV/sodium hypochlorite (UV/NaClO) systems were compared to evaluate the application potential of UV/DCCNa technology. Compared with UV/NaClO, UV/DCCNa process has the advantage of DEP removal and caused a higher degradation efficiency (93.8%) within 45 min of oxidation in ultrapure water due to the sustained release of hypochloric acid (HOCl). Fourteen intermediate products were found by high-resolution mass spectrometry, and the transformation patterns including hydroxylation, hydrolysis, chlorination, cross-coupling, and nitrosation were proposed. The oxidation processes were also performed under quasi-realistic environmental conditions, and it was found that DEP could be effectively removed in both systems, with yields of disinfection byproduct meeting the drinking water disinfection standard (<60.0 μg/L). Comparing the single system, the removal of DEP decreased in the mixed system containing five kinds of PAEs, which could be attributed to the regeneration of DEP and the competitive effect of •OH occurred among the Dimethyl phthalate (DMP), DEP, Dipropyl phthalate (DPrP), Diallyl phthalate (DAP) and Diisobutyl phthalate (DiBP). However, a greater removal performance presented in UV/DCCNa system compared with UV/NaClO system (69.4% > 62.1%). Further, assessment of mutagenicity and developmental toxicity by Toxicity Estimation Software Tool (T.E.S.T) software indicated that UV/DCCNa process has fewer adverse effects on the environment and is a more environmentally friendly chlorination method. This study may provide some guidance for selecting the suitable disinfection technology for drinking water treatment.

Carbon and hydrogen isotopic evidence for atrazine degradation by electro-activated persulfate: Radical contributions and comparisons with heat-activated persulfate

The activation ways of persulfate (PS) were dominate for pollutant degradation and energy consumption. For the first time, this research compared electro-activated PS and heat-activated PS from the perspective of isotope fractionation, in order to "fingerprinted" and precisely interpretate reaction contributions and degradation pathways. As results, PS can be electrochemically activated with atrazine (ATZ) removal rates of 84.8% and 88.8% at pH 4 and 7. The two-dimensional isotope plots (ɅC/H) values were 6.20 at pH 4 and 7.46 at pH 7, rather different from that of SO4·- -dominated process with ɅC/H value of -4.80 at pH 4 and -23.0 at pH 7, suggesting the weak contribution of SO4·-. ATZ degradation by electro-activated PS was controlled by direct electron transfer (DET) and ·OH radical, and ·OHPS (derived from PS activation) played the crucial role with contributing rate of 63.2%-69.1%, while DET and ·OHBDD (derived from electrolysis of H2O) contributed to 4.5-7.9% and 23.0%-30.8%, respectively. This was different from heat activation of PS, of which the latter was dominated by SO4·- with contributions of 83.9%-100%. The discrepant dominating reactive oxygen species should be responsible for their different degradation capabilities and pathways. This research provided isotopic interpretations for differences of PS activation mode, and further efforts can be made to realize the selective degradation by enhancing the specific reaction process.

A novel DBD/VUV/PMS process for efficient sulfadiazine degradation in wastewater: Singlet oxygen-dominated nonradical oxidation

In this study, a novel process of dielectric barrier discharge plasma/vacuum ultraviolet/peroxymonosulfate (DBD/VUV/PMS) for the nonradical-dominated degradation of sulfadiazine (SDZ) was investigated. The hybrid system has significant synergistic effects, with 95.5% SDZ and 68.3% TOC removal within 10 min. The activation efficiency of DBD/VUV (69.0%) on PMS via multipath was 2.07 times higher than that of single DBD (33.3%) under alkaline conditions. Electron paramagnetic resonance analyses and trapping experiments showed 1O2 was the primary active substance in the DBD/VUV/PMS process. The predominant role of 1O2 revealed that SDZ removal mainly followed the nonradical reaction pathway, contrary to the previously reported non-thermal plasma (NTP)-based radical-dominated process. Multiple spectroscopy analysis showed the efficient degradation process of SDZ. Unlike the radical attack sites, the SDZ transformation pathway by nonradical 1O2 was probably initiated by an aniline ring site attack based on density functional theory (DFT) calculations and product analyses. The DBD/VUV/PMS process reduced energy consumption by 69% compared to DBD. Finally, the evaluation of ecotoxicity and PMS utilization demonstrated the advantages and application prospects of the DBD/VUV/PMS process. This research developed a new nonradical-dominated pathway for antibiotic degradation by the photo/plasma/persulfate process.

Preparation of chitosan-iron oxide modified sludge-based biochar for effective removal of tetracycline from water: performance and mechanism

The release of antibiotics has attracted wide attention due to their abuse and discharge. How to remove these emerging contaminants is an urgent need to be solved. In the present study, sludge-based biochar combining chitosan and iron oxide was prepared via municipal sewage sludge. The novel biochar modified with chitosan and iron oxide exhibited satisfying performance in eliminating antibiotics from water. The application of modified biochar combined with activated persulfate (PS) showed a remarkable removal efficiency of 96.98% for tetracycline (TC). Analysis of the surface characteristics of the modified biochar showed the presence of structural defects, dispersed iron oxides, abundant functional groups, a porous structure, and a relatively stable crystal structure. These characteristics attributed significant importance to facilitating the degradation of TC. A series of experimental conditions including preparation temperature (600-900 ℃), reaction temperature (15-45 ℃), contaminant concentration (30-180 mg/L), adsorbent usage (0.1-1 g/L), pH (2-10), and persulfate addition concentration (1-5 mmol) were conducted. The results revealed that the highest removal efficiency was achieved at 96.98% under the conditions of TC concentration at 30 mg/L, reaction temperature at 35 ℃, pH of 4, adsorbent addition amount of 0.6 g/L, and PS concentration of 2 mmol, respectively. Three degradation pathways and seven intermediate products of TC were proposed. Therefore, our study provides a promising approach for developing effective removal of antibiotic pollutants.

Underwater bubbling plasma assisted with persulfate activation for the synergistic degradation of tetracycline hydrochloride

The performance and mechanism of persulfate consisting of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation by underwater bubbling plasma (UBP) for the synergistic removal of tetracycline hydrochloride (TCH) were comparatively investigated. Both PMS and PDS addition significantly promoted the removal of TCH in UBP system, indicating persulfate exhibited highly synergistic effect with UBP. Furthermore, enhancing the persulfate dosage, peak voltage and pulse frequency, as well as reducing initial TCH concentration were favorable for the elimination of TCH. Compared with neutral condition, acidic and alkaline condition were advantageous to TCH removal. The presence of coexisting substances including Cl-, SO42- and humic acid (HA) had an adverse effect on TCH degradation, while Fe2+ could improve the removal of TCH. The degradation of ciprofloxacin and metronidazole proved the applicability for other antibiotics degradation of the reaction system. SO4-·, ·OH, ·O2-, hydrated electrons, O3 and H2O2 were the active substances responsible for TCH removal. The reduction of aqueous O3 concentration and enhancement of H2O2 concentration were observed after persulfate addition. UV-vis spectra and TOC analysis illustrated the addition of PMS or PDS facilitated the degradation and mineralization of TCH. 3D-EEMF spectra visually displayed the degradation process of TCH. Plausible degradation routes were deduced based on LC-MS and the toxicities of TCH and its intermediates were evaluated by Toxicity Estimation Software Tool.

Efficient degradation and detoxification of antibiotic Fosfomycin by UV irradiation in the presence of persulfate

Fosfomycin (FOS) as a widely used antibiotic has been found in abundance throughout the environment, but little effort has been devoted to its treatment. In this study, we systemically looked into the degradation of FOS by ultraviolet-activated persulfate (UV/PS) in aqueous solutions. Our findings demonstrated that FOS can be degraded efficiently under the UV/PS, e.g., >90 % of FOS was degraded with 19,200 mJ cm-2 of UV irradiance and 20 μM of PS. HO was the dominant radical responsible for FOS degradation. FOS degradation increased as PS dosage increased, and higher degradation efficiency was observed at neutral pH. Natural water constitutes either promoted (e.g., Cu2+, Fe3+, and SO42-) or inhibited (e.g., humic acid, HCO3-, and CO32-) FOS degradation to varying degrees. Hydroxyl substitution, CP bond cleavage, and coupling reactions were the major degradation pathways for FOS degradation. Finally, the toxicity evaluation revealed that FOS was toxic to E. coli and S. aureus, but the toxicity of the intermediate products of FOS to E. coli and S. aureus rapidly decreased over time after UV/PS treatment. Therefore, these findings provided a fundamental understanding of the transformation process of FOS and supplied useful information for the environmental elimination of FOS contamination and its toxicity.

Thermodynamic and Kinetic Behaviors of Persulfate-Based Electron-Transfer Regime in Carbocatalysis

A carbon-based advanced oxidation process is featured for the nonradical electron-transfer pathway (ETP) from electron-donating organic compounds to activated persulfate complexes, enabling it as a green technology for the selective oxidation of organic pollutants in complex water environments. However, the thermodynamic and kinetic behaviors of the nonradical electron-transfer regime had been ambiguous due to a neglect of the influence of pH on the mechanisms. In this study, three kinds of organic pollutants were divided in the carbon-based ETP regime: (i) physio-adsorption, (ii) adsorption-dominated ETP (oxidation rate slightly surpasses adsorption rate), and (iii) oxidation-dominated ETP (oxidation rate outpaces the adsorption rate). The differential kinetic behaviors were attributed to the physicochemical properties of the organic pollutants. For example, the hydrophobicity, molecular radius, and positive electrostatic potential controlled the mass-transfer process of the adsorption stage of the reactants (peroxydisulfate (PDS) and organics). Meanwhile, other descriptors, including the Fukui index, oxidation potential, and electron cloud density regulated the electron-transfer processes and thus the kinetics of oxidation. Most importantly, the oxidation pathways of these organic pollutants could be altered by adjusting the water chemistry. This study reveals the principles for developing efficient nonradical systems to selectively remove and recycle organic pollutants in wastewater.

Photolysis Products of Fluorinated Pharmaceuticals: A Combined Fluorine Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry Approach

The aqueous photolysis of four pharmaceuticals with varying fluorinated functional groups was assessed under neutral, alkaline, advanced oxidation, and advanced reduction conditions with varying light sources. Solar simulator quantum yields were 2.21 × 10-1  mol Ei-1 for enrofloxacin, 9.36 × 10-3  mol Ei-1 for voriconazole, and 1.49 × 10-2  mol Ei-1 for flecainide. Florfenicol direct photolysis was slow, taking 150 h for three degradation half-lives. Bimolecular rate constants between pharmaceuticals and hydroxyl radicals were 109 to 1010  M-1  s-1 . Using a combined quantitative fluorine nuclear magnetic resonance spectroscopy (19 F-NMR) and mass spectrometry approach, fluorine mass balances and photolysis product structures were elucidated. Enrofloxacin formed a variety of short-lived fluorinated intermediates that retained the aryl F motif. Extended photolysis time led to complete aryl F mineralization to fluoride. The aliphatic F moiety on florfenicol was also mineralized to fluoride, but the resulting product was a known antibiotic (thiamphenicol). For voriconazole, the two aryl Fs contributed more to fluoride production compared with the heteroaromatic F, indicating higher stability of the heteroaromatic F motif. The two aliphatic CF3 moieties in the flecainide structure remained intact under all conditions, further supporting the stability of these moieties found in per- and polyfluoroalkyl substances under a variety of conditions. The advanced treatment conditions generating hydroxyl radicals or hydrated electrons accelerated the degradation, but not the defluorination, of flecainide. The combination of 19 F-NMR and mass spectrometry proved powerful in allowing identification of fluorinated products and verifying the functional groups present in the intermediates and products. The results found in the present study will aid in the understanding of which fluorinated functional groups should be incorporated into pharmaceuticals to ensure organofluorine byproducts are not formed in the environment and help determine the water-treatment processes that effectively remove specific pharmaceuticals and more generally fluorinated motifs. Environ Toxicol Chem 2023;00:1-12. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Coupled Surface-Confinement Effect and Pore Engineering in a Single-Fe-Atom Catalyst for Ultrafast Fenton-like Reaction with High-Valent Iron-Oxo Complex Oxidation

The nanoconfinement effect in Fenton-like reactions shows great potential in environmental remediation, but the construction of confinement structure and the corresponding mechanism are rarely elucidated systematically. Herein, we proposed a novel peroxymonosulfate (PMS) activation system employing the single Fe atom supported on mesoporous N-doped carbon (FeSA-MNC, specific surface area = 1520.9 m2/g), which could accelerate the catalytic oxidation process via the surface-confinement effect. The degradation activity of the confined system was remarkably increased by 34.6 times compared to its analogue unconfined system. The generation of almost 100% high-valent iron-oxo species was identified via 18O isotope-labeled experiments, quenching tests, and probe methods. The density functional theory illustrated that the surface-confinement effect narrows the gap between the d-band center and Fermi level of the single Fe atom, which strengthens the charge transfer rate at the reaction interface and reduces the free energy barrier for PMS activation. The surface-confinement system exhibited excellent pollutant degradation efficiency, robust resistance to coexisting matter, and adaptation of a wide pH range (3.0-11.0) and various temperature environments (5-40 °C). Finally, the FeSA-MNC/PMS system could achieve 100% sulfamethoxazole removal without significant performance decline after 10,000-bed volumes. This work provides novel and significant insights into the surface-confinement effect in Fenton-like chemistry and guides the design of superior oxidation systems for environmental remediation.

Generation and identification of 1O2 in catalysts/peroxymonosulfate systems for water purification

Catalysts for peroxymonosulfate (PMS) activation are appealing in the purification of organic wastewater. Singlet oxygen (1O2) is widely recognized as a crucial reactive species for degrading organic contaminants in catalysts/PMS systems due to its adamant resistance to inorganic anions, high selectivity, and broad pH applicability. With the rapid growth of studies on 1O2 in catalysts/PMS systems, it becomes necessary to provide a comprehensive review of its current state. This review highlights recent advancements concerning 1O2 in catalysts/PMS systems, with a primary focus on generation pathways and identification methods. The generation pathways of 1O2 are summarized based on whether (distinguished by the geometric structures of metal species) or not (distinguished by the active sites) the metal element is included in the catalysts. Furthermore, this review thoroughly discusses the influence of metal valence states and metal species with different geometric structures on 1O2 generation. Various potential strategies are explored to regulate the generation of 1O2 from the perspective of catalyst design. Identification methods of 1O2 primarily include electron paramagnetic resonance (EPR), quenching experiments, reaction in D2O solution, and chemical probe tests in catalysts/PMS systems. The principles and applications of these methods are presented comprehensively along with their applicability, possible disagreements, and corresponding solutions. Besides, an identifying procedure on the combination of main identification methods is provided to evaluate the role of 1O2 in catalysts/PMS systems. Lastly, several perspectives for further studies are proposed to facilitate developments of 1O2 in catalysts/PMS systems.

Deeper Defluorination and Mineralization of a Novel PFECA (C7 HFPO-TA) in Vacuum UV/Sulfite: Unique Mechanism of H/OCF3 Exchange

C7 HFPO-TA is a newly identified alternative to PFOA, which possesses a unique structure fragment (CF3O-CF(CF3)-). In this study, we evaluated the chemical reactivity of C7 HFPO-TA in advanced oxidation and reduction processes for the first time, which revealed a series of unexpected transformation mechanisms. The results showed that reductive degradation based on hydrated electrons (eaq-) was more feasible for the degradation of C7 HFPO-TA. For oxidative degradation, the branched -CF3 at the α-position carbon posed as the spatial hindrance, shielding the attack of SO4•- to -COO-. The synergistic effects of HO•/eaq- and direct photolysis led to deeper defluorination and mineralization of C7 HFPO-TA in the vacuum UV/sulfite (VUV/SF) process. We identified a unique H/OCF3 exchange that converted the CF3O-CF(CF3)- into H-CF(CF3)- directly, and the SO3•- involved mechanism of C7 HFPO-TA for the first time. We revealed the branched -CF3 connected to the same carbon next to the CF3O- group affected the C-O bond cleavage site, preferring the H/OCF3 exchange pathway. The defluorination of C7 HFPO-TA was compared with PFOA and three PFECAs in the VUV/SF process, which was highly dependent on structures. Degradation kinetics, theoretical calculations, and products' analysis provided an in-depth perspective on the degradation mechanisms and pathways of C7 HFPO-TA.

The altered treatment efficiency of the bisulfite/permanganate process by chloride

Bisulfite-activated permanganate (S(IV)/Mn(VII)) process has proven to be a promising method for rapidly degrading micropollutants. Previous studies have shown that the treatment efficiency of the S(IV)/Mn(VII) process suffer from significant water matrix effects while the mechanism still remains unclear. This study systematically investigates the influence of chloride, which is a common water constituent, on the S(IV)/Mn(VII) process. Addition of chloride decreased the removal of methyl phenyl sulfoxide, phenol, benzoic acid and carbamazepine by the S(IV)/Mn(VII) process but increased dimethoxybenzene removal. The distribution of reactive species in the S(IV)/Mn(VII) process in the absence and presence of chloride was determined with relative rate method. The S(IV)/Mn(VII) process primarily relies on SO4•- and reactive manganese species (RMnS) for pollutant abatement while dosing chloride decreased the concentration of these reactive species. Reactive chlorine species (RCS), such as Cl2•- and ClO•, are formed through the reaction of SO4•- with chloride, and become more important at high concentrations of chloride. RMnS includes Mn(VI), Mn(V) and Mn(III), but none of these species are capable of oxidizing chloride. However, chloride retarded the consumption of bisulfite which reduced RMnS and RCS in turn. DOM inhibited pollutant removal by the S(IV)/Mn(VII) process while the impact mechanism was significantly altered by chloride. Additionally, the study observed a synergistic inhibition of DOM and chloride on the degradation of pollutants that are highly reactive towards Cl2•- and ClO•.

A review of factors affecting the formation and roles of primary and secondary reactive species in UV254-based advanced treatment processes

The presence of organic micropollutants (OMPs) in water has been threatening human health and aquatic ecosystems worldwide. Ultraviolet-based advanced treatment processes (UV-ATPs) are one of the most effective and promising technologies to transform OMPs in water; therefore, an increasing number of emerging UV-ATPs are proposed. However, appropriate selection of UV-ATPs for practical applications is challenging because each UV-ATP generates different types and concentrations of reactive species (RSs) that may not be sufficient to degrade specific types of OMPs. Furthermore, the concentrations and types of RSs are highly influenced by anions and dissolved organic matter (DOM) coexisting in real waters, making systematic understandings of their interfering mechanisms difficult. To identify and address the knowledge gaps, this review provides a comparison of the generations and variations of various types of RSs in different UV-ATPs. These analyses not only prove the importance of water matrices on formation and consumption of primary and secondary RSs under different conditions, but also highlight the non-negligible roles of optical properties and reactivities of DOM and anions. For example, different UV-ATPs may be applicable to different target OMPs under different conditions; and the concentrations and roles of secondary RSs may outperform those of primary RSs in OMP degradation for real applications. With continuous progress and outstanding achievements in the UV-ATPs, it is hoped that the findings and conclusions of this review could facilitate further research and application of UV-ATPs.

Fast degradation of atrazine by nZVI-Cu0/PMS: Re-evaluation and quantification of reactive species, generation pathways, and application feasibility

Additive metal to zero-valent iron (ZVI) could enhance the reduction ability and the additive Cu0 was incorporated to ZVI to accelerate PMS activation with atrazine (ATZ) as target compound. The efficiencies of ATZ degradation and PMS decomposition climbed up firstly and then declined as Cu0 loading increased from 0.01 to 1.00 wt% with the maximums at 0.10 wt%. SO4•-, HO•, Fe(IV), O2•- and 1O2 were generated by nZVI-Cu0/PMS based on the results of electron paramagnetic resonance (EPR) and simultaneous degradation of nitrobenzene, ATZ, and methyl phenyl sulfoxide (PMSO). The rate constant of Fe(IV) and ATZ was estimated as 7 × 104 M-1∙s-1 via the variation of methyl phenyl sulfone (PMSO2)formation at different ATZ concentrations. However, Fe(IV) contributed negligibly to ATZ degradation due to the strong scavenging of Fe(IV) by PMS. SO4•- and HO• were the reactive species responsible for ATZ degradation and the yield ratio of SO4•- and HO• was about 8.70 at initial stage. Preliminary thermodynamic calculation on the possible activation ways revealed that the dominant production of SO4•- might originate from the atomic H reduction of PMS in the surface layer of nZVI-Cu0. Ten products of ATZ degradation were identified by HPLC/ESI/QTOF and the possible degradation pathways were analyzed combined with theoretical calculation on ATZ structure. The decrease of temperature or increase of solution pH led to the decline of ATZ degradation, as well as the individual addition of common ions (HCO3-, Cl-, SO42-, NH4+, NO3- and F-) and natural organic matters (NOM). In real water, ATZ was still efficiently degraded with the decontamination efficiency decreasing in the sequence of tap water > surface water > simulated wastewater > groundwater. For the treatment of ATZ-polluted continuous flow, nZVI-Cu0 in double-layer layout had a higher capacity than the single-layer mode. Meanwhile, the leaching TFe and TCu were limited. The results indicate nZVI-Cu0/PMS is applicable and the multiple-layer layout of nZVI-Cu0 is suggested for ATZ-polluted ground water and soil remediation.

The role of reactive phosphate species in the abatement of micropollutants by activated peroxymonosulfate in the treatment of phosphate-rich wastewater

This study investigated the mechanisms of forming reactive species to degrade micropollutants through the activation of peroxymonosulfate (PMS) by phosphate, a prevalent ion in wastewater. Considering the density functional theory results, the formation of hydrogen bonds between phosphate and PMS molecules might be the crucial step in the overall reactions, which prefers producing ⋅OH and reactive phosphate species (RPS, namely H2PO4⋅, HPO4⋅-, and PO4⋅2-) to yielding SO4⋅-. Besides, in the phosphate (5 mM)/PMS system at pH = 8, HPO4⋅- was modeled to be the dominant radical with a steady-state concentration of 3.6 × 10-12 M, which was 666 and 773 times higher than those of ⋅OH and SO4⋅-. The contributions of 1O2, ⋅OH, SO4⋅-, and RPS to the micropollutant decomposition in phosphate/PMS were studied, and RPS were found to be selective for micropollutants with electron-donating moieties (such as phenolic and aniline groups). Additionally, the degradation pathways of bisphenol A, diclofenac, ibuprofen, and atrazine in phosphate/PMS were proposed according to the detected transformation products. Cytotoxicity analysis was carried out to evaluate the potential environmental impacts resulting from the degradation of micropollutants by phosphate/PMS. This study confirmed the significance of RPS for micropollutant degradation during PMS-based treatment in phosphate-rich scenarios.

Iron-loaded carbon black prepared via chemical vapor deposition as an efficient peroxydisulfate activator for the removal of rhodamine B from water

The excessive use of organic pollutants like organic dyes, which enter the water environment, has led to a significant environmental problem. Finding an efficient method to degrade these pollutants is urgent due to their detrimental effects on aquatic organisms and human health. Carbon-based catalysts are emerging as highly promising and efficient alternatives to metal catalysts in Fenton-like systems. They serve as persulfate activators, effectively eliminating recalcitrant organic pollutants from wastewater. In this study, iron-loaded carbon black (Fe-CB) was synthesized from tire waste using chemical vapor deposition (CVD). Fe-CB exhibited high efficiency as an activator of peroxydisulfate (PDS), facilitating the effective degradation and mineralization of rhodamine B (RhB) in water. A batch experiment and series characterization were conducted to study the morphology, composition, stability, and catalytic activity of Fe-CB in a Fenton-like system. The results showed that, at circumneutral pH, the degradation and mineralization efficiency of 20 mg L-1 RhB reached 92% and 48% respectively within 60 minutes. Fe-CB exhibited excellent reusability and low metal leaching over five cycles while maintaining almost the same efficiency. The degradation kinetics of RhB was found to follow a pseudo-first-order model. Scavenging tests revealed that the dominant role was played by sulfate (SO4-˙) and superoxide (O2-˙) radicals, whereas hydroxyl radicals (OH˙) and singlet oxygen (1O2) played a minor role in the degradation process. This study elucidates the detailed mechanism of PDS activation by Fe-CB, resulting in the generation of reactive oxygen species. It highlights the effectiveness of Fe-CB/PDS in a Fenton-like system for the treatment of water polluted with organic dye contaminants. The research provides valuable insights into the potential application of carbon black derived from tire waste for environmental remediation.

Applications of Carbon-Based Materials in Activated Peroxymonosulfate for the Degradation of Organic Pollutants: A Review

In recent years, water pollution has posed a serious threat to aquatic organisms and humans. Advanced oxidation processes (AOPs) based on activated peroxymonosulfate (PMS) show high oxidation, good selectivity, wide pH range and no secondary pollution in the removal of organic pollutants in water. Carbon-based materials are emerging green catalysts that can effectively activate persulfates to generate radical and non-radical active species to degrade organic pollutants. Compared with transition metal catalysts, carbon-based materials are widely used in SR-AOPs because of their low cost, non-toxicity, acid and alkali resistance, large specific surface area, and scalable surface charge, which can be used for selective control of specific water pollutants. This paper mainly presents several carbon-based materials used to activate PMS, including raw carbon materials and modified carbon materials (heteroatom-doped and metal-doped), analyzes and summarizes the mechanism of activating PMS by carbon-based catalysts, and discusses the influencing factors (temperature, pH, PMS concentration, catalyst concentration, inorganic anions, inorganic cations and dissolved oxygen) in the activation process. Finally, the future challenges and prospects of carbon-based materials in water pollution control are also presented.

Merits and Limitations of Radical vs. Nonradical Pathways in Persulfate-Based Advanced Oxidation Processes

Urbanization and industrialization have exerted significant adverse effects on water quality, resulting in a growing need for reliable and eco-friendly treatment technologies. Persulfate (PS)-based advanced oxidation processes (AOPs) are emerging as viable technologies to treat challenging industrial wastewaters or remediate groundwater impacted by hazardous wastes. While the generated reactive species can degrade a variety of priority organic contaminants through radical and nonradical pathways, there is a lack of systematic and in-depth comparison of these pathways for practical implementation in different treatment scenarios. Our comparative analysis of reaction rate constants for radical vs. nonradical species indicates that radical-based AOPs may achieve high removal efficiency of organic contaminants with relatively short contact time. Nonradical AOPs feature advantages with minimal water matrix interference for complex wastewater treatments. Nonradical species (e.g., singlet oxygen, high-valent metals, and surface activated PS) preferentially react with contaminants bearing electron-donating groups, allowing enhancement of degradation efficiency of known target contaminants. For byproduct formation, analytical limitations and computational chemistry applications are also considered. Finally, we propose a holistically estimated electrical energy per order of reaction (EE/O) parameter and show significantly higher energy requirements for the nonradical pathways. Overall, these critical comparisons help prioritize basic research on PS-based AOPs and inform the merits and limitations of system-specific applications.

Pyridine-bridged cobalt tetra-aminophthalocyanine to active peroxymonosulphate for efficient degrading carbamazepine

In this study, each cobalt tetra-aminophthalocyanine (CoTAPc) molecule was immobilised with four isonicotinic acid (INA) molecules by amide bonding, a novel and highly efficient catalyst pyridine-bridged cobalt tetra-aminophthalocyanine (CoTAPc-TINA) was synthesised. The introduction of INA molecules promoted CoTAPc to expose more active sites, and increased the electron cloud density of cobalt ions promoting O-O bond homolysis of PMS to generate more active species, which significantly enhanced catalytic activity. With the pharmaceutical of carbamazepine (CBZ) as model pollutant, 0.1 g/L CoTAPc-TINA in dark in the presence of 0.4 mM PMS, 98.8% CBZ was removed within 10 min. However, under the same conditions the removed of CBZ was only 58.9% by CoTAPc/PMS system. Radical capture experiments combined electron paramagnetic resonance technology demonstrate that hydroxyl radicals, sulphate radicals, superoxide radicals and singlet oxygen are the main active species in the CoTAPc-TINA/PMS system. As the reaction proceeded, all aromatic intermediates were transformed to small molecular acids by these active species. This investigation provided a new insight for application of metal phthalocyanine in wastewater treatment.

Activation of Peroxymonosulfate with ZIF-67-derived Co/N-doped Porous Carbon Nanocubes for the Degradation of Congo Red Dye.. [DOI: 10.21203/rs.3.rs-3174583/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In this study, porous carbon nanaocubes encapsulated magnetic metallic Co nanoparticles (denoted as Co@N-PCNC) was prepared via pyrolyzing ZIF-67 nanocubes precursor at 600°C, and characterized by various technologies. It was used to activate peroxymonosulfate (PMS) to degrade Congo red (CR) dye efficiently. Over 98.45% of 50 mg/L CR with initial pH of 5.5 was degraded by 100 mg/L PMS activated by 10 mg/L Co@N-C within 12 min. The free radical quenching experiments were performed to reveal the nature of the reactive oxygen species radicals generated throughout the catalytic oxidation of CR. The effects of common inorganic anions and water matrix on CR removal were studied. The Co@N-PCNC displayed good operational stability, and after three cycles, the CR removal rate can still maintain over 90% after 12 min reaction.

Ultraviolet-based synergistic processes for wastewater disinfection: A review

Ultraviolet (UV) irradiation is widely used for wastewater disinfection but suffers from low inactivation rates and can cause photoreactivation of microorganisms. Synergistic disinfection with UV and oxidants is promising for enhancing the inactivation performance. This review summarizes the inactivation effects on representative microorganisms by UV/hydrogen peroxide (H₂O₂), UV/ozone (O₃), UV/persulfate (PS), UV/chlorine, and UV/chlorine dioxide (ClO₂). UV synergistic processes perform better than UV or an oxidant alone. UV mainly attacks the DNA or RNA in microorganisms; the oxidants H₂O₂ and O₃ mainly attack the cell walls, cell membranes, and other external structures; and HOCl and ClO₂ enter cells and oxidize proteins and enzymes. Free radicals can have strong oxidation effects on cell walls, cell membranes, proteins, enzymes, and even DNA. At similar UV doses, the inactivation rates of Escherichia coli with UV alone, UV/H₂O₂, UV/O₃, UV/PS (peroxydisulfate or peroxymonosulfate), and UV/chlorinated oxidant (chlorine, ClO₂, and NH₂Cl) range from 2.03 to 3.84 log, 2.62-4.30 log, 4.02-6.08 log, 2.93-5.07 log, and 3.78-6.55 log, respectively. The E. coli inactivation rates are in the order of UV/O₃ ≈ UV/Cl₂ > UV/PS > UV/H₂O₂. This order is closely related to the redox potentials of the oxidants and quantum yields of the radicals. UV synergistic disinfection processes inhibit photoreactivation of E. coli in the order of UV/O₃ > UV/PS > UV/H₂O₂. The activation mechanisms and formation pathways of free radicals with different UV-based synergistic processes are presented. In addition to generating HO·, O₃ can reduce the turbidity and chroma of wastewater to increase UV penetration, which improves the disinfection performance of UV/O₃. This knowledge will be useful for further development of the UV-based synergistic disinfection processes.

S modified manganese oxide for high efficiency of peroxydisulfate activation: Critical role of S and mechanism

Mn₂O₃ as a typical Mn based semiconductor has attracted growing attention due to its peculiar 3d electron structure and stability, and the multi-valence Mn on the surface is the key to peroxydisulfate activation. Herein, an octahedral structure of Mn₂O₃ with (111) exposed facet was synthesized by a hydrothermal method, which was further sulfureted to obtained a variable-valent Mn oxide for the high activation efficiency of peroxydisulfate under the light emitting diode irradiation. The degradation experiments showed that under the irradiation of 420 nm light, S modified manganese oxide showed an excellent removal for tetracycline within 90 min, which is about 40.4% higher than that of pure Mn₂O₃. In addition, the degradation rate constant k of S modified sample increased 2.17 times. Surface sulfidation not only increased the active sites and oxygen vacancies on the pristine Mn₂O₃ surface, but also changed the electronic structure of Mn due to the introduce of surface S^2-. This modification accelerated the electronic transmission during the degradation process. Meanwhile, the utilization efficiency of photogenerated electrons was greatly improved under light. Besides, the S modified manganese oxide had an excellent reuse performance after four cycles. The scavenging experiments and EPR analyses showed that •OH and ¹O₂ were the main reactive oxygen species. This study therefore provides a new avenue for further developing manganese-based catalysts towards high activation efficiency for peroxydisulfate.

Alginate@ZnCO2O4 for efficient peroxymonosulfate activation towards effective rhodamine B degradation: optimization using response surface methodology

A facile chemical procedure was utilized to produce an effective peroxy-monosulfate (PMS) activator, namely ZnCo₂O₄/alginate. To enhance the degradation efficiency of Rhodamine B (RhB), a novel response surface methodology (RSM) based on the Box-Behnken Design (BBD) method was employed. Physical and chemical properties of each catalyst (ZnCo₂O₄ and ZnCo₂O₄/alginate) were characterized using several techniques, such as FTIR, TGA, XRD, SEM, and TEM. By employing BBD-RSM with a quadratic statistical model and ANOVA analysis, the optimal conditions for RhB decomposition were mathematically determined, based on four parameters including catalyst dose, PMS dose, RhB concentration, and reaction time. The optimal conditions were achieved at a PMS dose of 1 g l^-1, a catalyst dose of 1 g l^-1, a dye concentration of 25 mg l^-1, and a time of 40 min, with a RhB decomposition efficacy of 98%. The ZnCo₂O₄/alginate catalyst displayed remarkable stability and reusability, as demonstrated by recycling tests. Additionally, quenching tests confirmed that SO₄˙^-/OH˙ radicals played a crucial role in the RhB decomposition process.

Cu(II) assisted peroxymonosulfate for antibiotic resistant bacteria inactivation: A potential disinfection technology in swimming pool

Alternative disinfection technology to chlorination is required to control the risk of antibiotic resistance in swimming pools. In this study, copper ions (Cu(II)), which often exist in swimming pools as algicides, were used to activate peroxymonosulfate (PMS) for the inactivation of ampicillin-resistant E. coli. Cu(II) and PMS showed synergistic effects on E. coli inactivation in weak alkaline conditions, obtaining 3.4 log inactivation in 20 min with 10 μM Cu(II) and 100 μM PMS at pH 8.0. Quenching experiments indicated that radicals (i.e., OH and SO₄^-) were not the main disinfectors for E. coli inactivation. Based on the structure of Cu(II) and density functional theory calculations, the Cu(II)-PMS complex (Cu(H₂O)₅SO₅) was recommended as the active species for E. coli inactivation. Under the experimental conditions, the PMS concentration had a greater influence on E. coli inactivation than the Cu(II) concentration, possibly because increasing PMS concentration accelerates ligand exchange reaction and facilitates active species generation. By forming hypohalous acids, halogen ions could improve the disinfection efficiency of Cu(II)/PMS. The addition of HCO₃^- concentration (from 0 to 1.0 mM) and humic acid (0.5 and 1.5 mg/l) did not significantly inhibit the E. coli inactivation. The feasibility of adding PMS to waters containing Cu(II) for the inactivation of antibiotic-resistant bacteria was validated in actual swimming pool waters, where 4.7 log inactivation of E. coli was achieved in 60 min.

Preparation, performance and mechanism of metal oxide modified catalytic ceramic membranes for wastewater treatment

Catalytic ceramic membranes (CMs) integrated with different metal oxides were designed and fabricated by an impregnation-sintering method. The characterization results indicated that the metal oxides (Co₃O₄, MnO₂, Fe₂O₃ and CuO) were uniformly anchored around the Al₂O₃ particles of the membrane basal materials, which could provide a large number of active sites throughout the membrane for the activation of peroxymonosulfate (PMS). The performance of the CMs/PMS system was evaluated by filtrating a phenol solution under different operating conditions. All the four catalytic CMs showed desirable phenol removal efficiency and the performance was in order of CoCM, MnCM, FeCM and CuCM. Moreover, the low metal ion leaching and high catalytic activity even after the 6th run revealed the good stability and reusability of the catalytic CMs. Quenching experiments and electron paramagnetic resonance (EPR) measurements were conducted to discuss the mechanism of PMS activation in the CMs/PMS system. The reactive oxygen species (ROS) were supposed to be SO₄˙^- and ¹O₂ in the CoCM/PMS system, ¹O₂ and O₂˙^- in the MnCM/PMS system, SO₄˙^- and ·OH in the FeCM/PMS system, and SO₄˙^- in the CuCM/PMS system, respectively. The comparative study on the performance and mechanism of the four CMs provides a better understanding of the integrated PMS-CMs behaviors.

Making waves: Opportunities and challenges of applying far-UVC radiation in controlling micropollutants in water

Concerns over human health risks associated with chemical contaminants (micropollutants) in drinking waters are rising due to the increased use of reclaimed water or water supplies impacted by upstream wastewater discharges. Ultraviolet (UV)-driven advanced oxidation processes (UV-AOPs) using radiation sources that emit at 254 nm have been developed as advanced treatments to degrade contaminants, while those UV-AOPs can be improved towards higher radical yields and lower byproduct formation. Several previous studies have suggested that Far-UVC radiation (200-230 nm) is a promising radiance source to drive UV-AOPs because the direct photolysis of micropollutants and production of reactive species from oxidant precursors can both be improved. In this study, we summarize from the literature the photodecay rate constants of five micropollutants by direct UV photolysis, which are higher at 222 than 254 nm. We experimentally determine the molar absorption coefficients at 222 and 254 nm of eight oxidants commonly used in water treatment and present the quantum yields of the oxidant photodecay. Our experimental results also show that the concentrations of HO^·, Cl^·, and ClO^· generated in the UV/chlorine AOP can be increased by 5.15-, 15.76-, and 2.86-fold, respectively, by switching the UV wavelength from 254 to 222 nm. We also point out the challenges of applying Far-UVC for micropollutant abatement in water treatment, including the strong light screening effect of matrix components (e.g., carbonate, nitrate, bromide, and dissolved organic matter), the formation of byproducts via new reaction pathways, and the needs to improve the energy efficiency of the Far-UVC radiation sources.

Stability enhancing of perovskite LaCoO3 by compositing with oxygen doped MoS2 in Fenton-like reactions

Perovskite materials are reported to be effective in peroxymonosulfate (PMS) based Fenton-like reactions, the leaching rates of chalcogenide materials in perovskite materials are however serious, thus leading to bad performance in long-term stability. In this study, an O-doped MoS₂ is synthesized to composite with LaCoO₃, and the high catalytic activity of LaCoO₃ is well preserved with greatly decreased Co leaching. During the BPA degradation with PMS as oxidant, ∼100% degradation can be achieved in 20 min and this degradation efficiency can be maintained for ∼45 h in a simulated fixed bed reactor, which is almost 3 times longer than the pure LaCoO₃. With the compositing of O-doped MoS₂, the leached Co was greatly decreased and the dominated reactive oxidation species (ROS) transformed from SO₄^•- into O₂^•- with longer lifespan, thus resulting in the better stability. This study could promote the application of perovskite materials in the real industrial wastewater treatment.

NiCo2O4-loaded sunflower husk-derived biochar as efficient peroxymonosulfate activator for tetracycline removal in water

In this study, biochar produced from sunflower seeds husk was activated through ZnCl₂ to support the NiCo₂O₄ nanoparticles (NiCo₂O₄@ZSF) in catalytic activation of peroxymonosulfate (PMS) toward tetracycline (TC) removal from aqueous solution. The good dispersion of NiCo₂O₄ NPs on the ZSF surface provided sufficient active sites and abundant functional groups for the adsorption and catalytic reaction. The NiCo₂O₄@ZSF activating PMS showed high removal efficiency up to 99% after 30 min under optimal condition ([NiCo₂O₄@ZSF] = 25 mg L^-1, [PMS] = 0.04 mM, [TC] = 0.02 mM and pH = 7). The catalyst also exhibited good adsorption performance with a maximum adsorption capacity of 322.58 mg g^-1. Sulfate radicals (SO₄^•-), superoxide radical (O₂•-), and singlet oxygen (¹O₂) played a decisive role in the NiCo₂O₄@ZSF/PMS system. In conclusion, our research elucidated the production of highly efficient carbon-based catalysts for environmental remediation, and also emphasized the potential application of NiCo₂O₄ doped biochar.

Ni-Co bimetallic decorated dodecahedral ZIF as an efficient catalyst for photoelectrochemical degradation of sulfamethoxazole coupled with hydrogen production

In this work, a NiCo bimetallic ZIF (BMZIF) dodecahedron material has been synthesized by the precipitation approach and then used for simultaneously photoelectrocatalytic degradation of sulfamethoxazole (SMX) and hydrogen production. The combination of Ni/Co loading in ZIF structure increased the specific surface area 1484 (m² g^-1) and photocurrent density (0.4 mA cm^-2), which can facilitate the good charge transfer efficiency. In presence of peroxymonosulfate (PMS, 0.1 mM), the complete degradation of SMX (10 mg L^-1) was achieved at initial pH of 7 within 24 min, with the pseudo-first-order rate constants of 0.18 min^-1 and TOC removal efficiency of 85 %. Radical scavenger experiments affirm that ^•OH radicals were the primary oxygen reactive species to drive the SMX degradation. Along with SMX degradation at the anode, the H₂ production was observed at the cathode (140 μmol cm^-2 h^-1), which was 1.5 and 3 times higher than that of Co-ZIF and Ni-ZIF, respectively. The superior catalytic performance of BMZIF was assigned to the distinctive internal structure and synergistic effect between ZIF and Ni/Co bimetals, which improves light absorption and charge conduction efficiency. This study may provide insight into the new way to treat polluted water and simultaneously produce green energy using bimetallic ZIF in a PEC system.