Sulfate Radical Advanced Oxidation Processes Research Articles

A two dimensional Co(OH)2 catalytic gravity-driven membrane for water purification: a green and facile fabrication strategy and excellent water decontamination performance.

Cobalt-based materials are reported to be the most efficient catalysts in sulfate radical advanced oxidation processes (SR-AOPs). A green and facile method was developed in this work to prepare uniform Co(OH)2 hexagonal nanosheets, which was void of any organic solvents via mere ambient temperature stirring. The obtained nanosheets were assembled into a catalytic gravity-driven membrane, through which the removal efficiency of a typical pharmaceutical contaminant, ranitidine (RNTD), could reach ∼100% within 20 min. Meanwhile, the catalytic membrane also demonstrated effective removal performance towards various pollutants. In order to augment the long-term stability of catalytic membranes, Co(OH)2/rGO composites were fabricated using the same strategy, and a Co(OH)2/rGO catalytic membrane was prepared correspondingly. The Co(OH)2/rGO membrane could maintain a ∼100% removal of RNTD over a constant reaction period lasting for up to 165 hours, which was approximately 11 times that of the sole Co(OH)2 membrane (15 h). Analysis of element chemical states, metal ion concentration in filtrates, and quenching experiments suggested that the combination with rGO could promote the electron transfer to accelerate the Co(II) regeneration, restrain the cobalt dissolution to alleviate the active site loss, and contribute to the production of 1O2via synergistic effects of oxygen-containing groups in rGO. Toxicity assessment was performed on RNTD and its degradation intermediates to confirm the reduction in ecotoxicity of the treated feed. Overall, this work not only offered guidance for the application of nanosheets in AOP membranes, but also had implications for the environmentally-friendly preparation protocol to obtain functional metal hydroxides.

Efficient persulfate activation by photo-excited organic dyes: Mechanism and application for actual dyeing wastewater self-purification

Sulfate Radical-Advanced Oxidation Processes are considered an efficient way for purifying dyeing wastewater, which commonly resists conventional treatment processes owing to the complex components, low biodegradability and high toxicity. However, this emerging technique is associated with issues of secondary pollution and great energy consumption during peroxymonosulfate (PMS) or persulfate (PS) activation processes. Herein, a dye pollutant/PS/visible light self-catalytic system was constructed, based on the photosensitive property of organic dyes for PS activation without catalyst and energy input. In this system, the degradation ratio of 100 mL 10 mg L−1 basic fuchsin, rhodamine B and eosin Y significantly increased by 60%, 76% and 50%, compared with the process without light irradiation. Such improvements were attributable to an efficient photo-induced electron transfer from photo-excited dyes to PS, which has the precondition that the lowest unoccupied molecular orbital (LUMO) energy level of the dye is higher than that of PS, thereby generating oxidizing species like ·SO4−, ·OH and 1O2 for pollutants degradation. Due to the high performance of pollutants simultaneous removal, wide pH adaptability and anti-interference, the complex self-catalytic system consisted of nine dyes and bis-phenol A exhibited the possibility for practical application. Expectedly, the actual dyeing wastewater self-purification system featured a decolorization efficiency of 54% accompanied by the removal of co-existing aromatic proteins and tryptophan-like substances; moreover, the acute bio-toxicity of the raw wastewater greatly decreased by 61.6%. Owing to its high efficiency, eco-friendliness and low consumption, the constructed “using waste to treat waste” system provides a promising way for wastewater treatment.

Sequential treatment of landfill leachate by electrocoagulation/aeration, PMS/ZVI/UV and electro-Fenton: Performance, biodegradability and toxicity studies

This study presents a systematic study on sequential treatment of highly resistant landfill leachate by electrocoagulation (EC)/aeration, sulfate radical advanced oxidation process (SR-AOP) and electro-Fenton (EF). In case of SR-AOP, peroxymonosulfate (PMS) catalyzed by zero valent iron (ZVI) and ultraviolet irradiation (UV) system was developed. Treatment process was optimized in respect to COD removal. Analysis of results revealed that sequential application of EC/aeration, PMS/ZVI/UV, and EF processes provide an extraordinary performance and meet the environmental regulations. The source of iron for EF process was provided from previous process reducing the cost of sequential process. Separately, EC/aeration (inlet COD = 4040 mg/L), PMS/ZVI/UV (inlet COD = 1560 mg/L), and EF (inlet COD = 471 mg/L) removed 61, 69 and 82% of COD respectively. Overall, sequential processes of EC/aeration, PMS/ZVI/UV and EF could remove the COD, TOC and ammonia of the landfill leachate around 98%, 93% and 94%, respectively. The comparison of different sequences of following processes indicated that current configuration (EC/aeration-PMS/ZVI/UV-EF) could meet the discharge standards. Furthermore, humification degree was significantly improved after oxidative processes. Biodegradability study was also performed by means of BOD/COD, average oxidation state (AOS), and Zahn-Wellens test, and the best results associated with these indices were obtained 0.56, 2.37, and over 98%, respectively. Phytotoxicity of leachate was remarkably reduced and the final effluent can be considered as a non-phytotoxic wastewater.

Treatment of Winery Wastewater by Combined Almond Skin Coagulant and Sulfate Radicals: Assessment of HSO5- Activators.

The large production of wine and almonds leads to the generation of sub-products, such as winery wastewater (WW) and almond skin. WW is characterized by its high content of recalcitrant organic matter (biodegradability index < 0.30). Therefore, the aim of this work was to (1) apply the coagulation-flocculation-decantation (CFD) process with an organic coagulant based on almond skin extract (ASE), (2) treat the organic recalcitrant matter through sulfate radical advanced oxidation processes (SR-AOPs) and (3) evaluate the efficiency of combined CFD with UV-A, UV-C and ultrasound (US) reactors. The CFD process was applied with variation in the ASE concentration vs. pH, with results showing a chemical oxygen demand (COD) removal of 61.2% (0.5 g/L ASE, pH = 3.0). After CFD, the germination index (GI) of cucumber and corn seeds was ≥80%; thus, the sludge can be recycled as fertilizer. The SR-AOP initial conditions were achieved by the application of a Box-Behnken response surface methodology, which described the relationship between three independent variables (peroxymonosulfate (PMS) concentration, cobalt (Co2+) concentration and UV-A radiation intensity). Afterwards, the SR-AOPs were optimized by varying the pH, temperature, catalyst type and reagent addition manner. With the application of CFD as a pre-treatment followed by SR-AOP under optimal conditions (pH = 6.0, [PMS] = 5.88 mM, [Co2+] = 5 mM, T = 343 K, reaction time 240 min), the COD removal increased to 85.9, 82.6 and 80.2%, respectively, for UV-A, UV-C and US reactors. All treated wastewater met the Portuguese legislation for discharge in a municipal sewage network (COD ≤ 1000 mg O2/L). As a final remark, the combination of CFD with SR-AOPs is a sustainable, safe and clean strategy for WW treatment and subproduct valorization.

Fate of dissolved organics and generated sulfate ions during biofiltration of oil sands process water pretreated with sulfate radical advanced oxidation process

Fate of dissolved organics and sulfate ions was studied in fixed bed biofilters (FBBs) treating pre-treated oil sands process water (OSPW) in the presence of industrially relevant substrates namely petroleum coke (PC) and sand. For pre-treatment, the solar-activated sulfate radical advanced oxidation process (SR-AOP) was performed using 2.5 and 5 mM peroxymonosulfate (PMS) as a precursor with solar irradiation of 119.5 W h m−2. Excellent degradation of naphthenic acids (NAs) was attained by SR-AOP, attaining 88 % and 97 % total NAs after 9 h of treatment at 2.5 and 5 mM of PMS, respectively. However, the treatment increased the toxicity due to byproducts and metabolites following the poor removal of dissolved organics, i.e., 13 % and 21.5 %, respectively. Electron paramagnetic resonance spectrometry (EPR) analysis exhibited that hydroxyl radical (⋅OH) and singlet oxygen (1O2) were the predominant active species produced during SR-AOP. The post-treatment biofiltration improved the mineralization of dissolved organics (45 %) and NAs (99 %) as well as removed the residual toxicity (>80 %). Taxonomy-based transcriptomics analyses (RNA) confirmed the enrichment of microbes involved in the degradation of hydrocarbons and carboxylic acids, methylotrophy, and potentially C(1)-sulfur compounds metabolism. Scanning electron microscopy with energy-dispersive X-ray spectroscopy indicated the potential of PC to support sulfur deposition, but at slower rates. This study indicates that the produced water can be efficiently reclaimed by using advanced oxidation and biofiltration approaches.

Sulfamethoxazole degradation via peroxydisulfate activation over WO3/MIL-100(Fe) under low power LED visible light

Series of WO3/MIL-100(Fe) (WxMy) composites were synthesized via the mild solvent evaporation method, which were used as a heterogeneous sulfate radical-advanced oxidation process (SR-AOP) catalyst for sulfamethoxazole (SMX) degradation. The as-prepared W4M1 (0.25 g/L) demonstrated excellent SR-AOP catalysis activity with 100 % SMX (5 mg/L) degradation efficiency within 15 min under visible light. The influences of initial pH, peroxydisulfate (PDS) concentration, catalyst dosage, and inorganic anions as well as the degradation pathway were investigated. The effective transfer of the photo-generated electrons from WO3 to MIL-100(Fe) via Z-scheme mechanism contributed to the outstanding SR-AOP catalysis activity of W4M1, which were affirmed by both the active species capture experiments and electron spin resonance (ESR) experiments. Moreover, W4M1 displayed excellent stability and reusability throughout five runs’ cycling experiments. This work offered a new SR-AOP catalyst alteration to eliminate emerging pollutant under visible light, which might provide insight clue for catalyst design and fabrication.

Peroxymonosulfate activation for effective atrazine degradation over a 3D cobalt-MOF: Performance and mechanism

In this work, a three-dimensional cobalt-MOF ([Co3(cis-chhc)(H2O)6]n, Co-H6chhc) (cis-H6chhc = 1,2,3,4,5,6-cyclohexane-hexacarboxylic acid) was hydrothermally synthesized to activate peroxymonosulfate (PMS). Co-H6chhc showed excellent sulfate radical-advanced oxidation processes (SR-AOPs) activation performance toward ATZ removal, in which 100% ATZ was degraded within 30 min due to the recycle of Co2+/Co3+. The effects of pH, PMS dosage, catalyst dosage, co-existing anions and natural organic matters (NOMs) for ATZ degradation were explored detailly. The reusability, stability and universality experiments were proceeded under optimal condition. It is worth noting that the long-term continuous ATZ degradation was accomplished via a self-developed device.

A newly-integrated FeCo-layered double hydroxides photocatalytic system for UV-induced degradation of various heterocyclic amines against complex sample matrix

For several decades, toxic thermally processed hazards, represented by heterocyclic amines (HCAs), have gradually become a challenge in the field of purification owing to their increasing exposure, wide variety, and the complexity of the matrix. In this study, the first example of degradation-removal of HCAs was illustrated by using a newly-integrated Fe/Co co-doped layered double hydroxide (FeCo-LDH) as photocatalysts based on sulfate radical advanced oxidation processes (SR-AOPs). Under the excitation of UV light, a FeCo-LDH/sodium persulfate (PS) photocatalytic degradation system combined with ultra-performance liquid chromatography mass spectrometer (UPLC-MS) was established. The synthesized photocatalysts were optimized by varying the Fe/Co ratio, and a series of photochemical activities and reaction conditions were investigated for a better performance. As a result, the FeCo-LDH/PS system was able to degrade 12 kinds of common HCAs efficiently and simultaneously, and was also well applicable in real edible oil samples with completely degraded. Moreover, it exhibited well reusability, preserving 97.75% of initial activity after being used for 5 cycles. It is the first application of photocatalytic combined with SR-AOPs technology for the degradation of HCAs and provides a promising example for the regulation of thermally processed hazards.

Strategies for enhancing peroxymonosulfate activation by heterogenous metal-based catalysis: A review

Sulfate radical-advanced oxidation processes (SR-AOPs) are promising technologies for organic pollutants elimination. Heterogeneous metal-based catalysis has been widely studied and applied to activate peroxymonosulfate (PMS) for producing sulfate radicals. Developing highly efficient catalysts is crucial for future extensive use. Importantly, the catalytic activity is mainly determined by mass and electron transfer. This paper aims to overview the recent enhancement strategies for developing heterogeneous metal-based catalysts as effective PMS activators. The main strategies, including surface engineering, structural engineering, electronic modulation, external energy assistance, and membrane filtration enhancement, are summarized. The potential mechanisms for improving catalytic activity are also introduced. Finally, the challenges and future research prospects of heterogenous metal-based catalysis in SR-AOPs are proposed. This work is hoped to guide the rational design of highly efficient heterogenous catalysts in SR-AOPs.

Insights into a newly discovered mechanism for 1O2 formation in a chlorine ion-mediated sulfate radical-advanced oxidation process system for levofloxacin degradation in an aqueous solution

The dual effect of chloride anions (Cl−) on sulfate radical-advanced oxidation process (SR-AOP) systems has recently garnered increasing attention, particularly the inhibitory effects of Cl− on the degradation of organic pollutants. However, few studies have characterized the promoting effect of Cl− on SR-AOPs. Our study investigated the effect of Cl− on the degradation of levofloxacin (LVF) in peroxymonosulfate (PMS) with ZIF-67/VTM (Z-VTM) as an activator. With the addition of Cl−, singlet oxygen (1O2) was the dominant driver of LVF degradation in the Cl−/Z-VTM/PMS system, which differed from the dominant role of HOCl (generated from Cl−) in the degradation of organic pollutants in previous studies. To the best of our knowledge, our study is the first to describe the conversion of HOCl to 1O2 in a Cl−/Z-VTM/PMS system. 1O2 was effectively generated in Cl− containing water at a 3.0–9.0 pH range. This work provides novel insights into the formation of ROS from HOCl during the degradation of organic pollutants in SR-AOPs, which is of great significance for the removal of organic pollutants in wastewater with high salt concentrations.

SARS-CoV-2 pharmaceutical drugs: a critical review on the environmental impacts, chemical characteristics, and behavior of advanced oxidation processes in water.

This review summarizes research data on the pharmaceutical drugs used to treat the novel SARS-CoV-2 virus, their characteristics, environmental impacts, and the advanced oxidation processes (AOP) applied to remove them. A literature survey was conducted using the electronic databases Science Direct, Scopus, Taylor & Francis, Google Scholar, PubMed, and Springer. This complete research includes and discusses relevant studies that involve the introduction, pharmaceutical drugs used in the SARS-CoV-2 pandemic: chemical characteristics and environmental impact, advanced oxidation process (AOP), future trends and discussion, and conclusions. The results show a full approach in the versatility of AOPs as a promising solution to minimize the environmental impact associated with these compounds by the fact that they offer different ways for hydroxyl radical production. Moreover, this article focuses on introducing the fundamentals of each AOP, the main parameters involved, and the concomitance with other sources and modifications over the years. Photocatalysis, sonochemical technologies, electro-oxidation, photolysis, Fenton reaction, ozone, and sulfate radical AOP have been used to mineralize SARS-CoV-2 pharmaceutical compounds, and the efficiencies are greater than 65%. According to the results, photocatalysis is the main technology currently applied to remove these pharmaceuticals. This process has garnered attention because solar energy can be directly utilized; however, low photocatalytic efficiencies and high costs in large-scale practical applications limit its use. Furthermore, pharmaceuticals in the environment are diverse and complex. Finally, the review also provides ideas for further research needs and major concerns.Graphical abstract

Effective elimination of tetracycline antibiotics via photoactivated SR-AOP over vivianite: A new application approach of phosphorus recovery product from WWTP

Fe3(PO4)2·8H2O (Vivianite) is one of the potential phosphorus recovery products from wastewater treatment plant (WWTP). In this study, we first discovered that vivianite can effectively photoactivate peroxodisulfate (PDS) to produce some reactive oxygen species (ROS) for tetracycline antibiotics (TCs) degradation. The results demonstrated that vivianite could efficiently activate PDS to achieve 100% removal of TCs under LED UV light (UVL), visible light (VL) or real solar light (SL) irradiation within 10 min, respectively. More importantly, ca. 80%, 78% and 40%∼58% of TOC removal efficiencies were achieved under UVL, VL and SL irradiation within 30 min, respectively. As well, toxicological simulation and antibacterial studies showed that the aquatic toxicity of the TCs intermediates was lower than those of the original TCs. This work provided new insights into the application of photoactivated sulfate radical-advanced oxidation process (SR-AOP) for organic pollutants degradation over vivianite, which may encourage the recovery and utilization of vivianite in the wastewater treatment process.

Activation of Peroxydisulfate by Bimetallic Nano Zero-Valent Iron for Waste-Activated Sludge Disintegration

Waste-activated sludge (WAS) disintegration using peroxydisulfate (PDS) has attracted scientific attention over the past few years. Despite several advantages offered by a sulfate radical-advanced oxidation process, there are still too many downsides of this treatment that limit its facile large-scale application. This study investigated whether modifying nano zero-valent iron (nZVI) with a second metal such as Ag and Cu enhanced the disruption of WAS. The disintegration efficiency was assessed using standard techniques, i.e., soluble chemical oxygen demand, Fourier-transform infrared spectroscopy and a scanning electron microscope. The bimetallics were shown to have an improved disintegration efficiency of &gt; 2.5-fold compared with the untreated sample. Furthermore, nZVI/Ag was found to be more efficient than nZVI/Cu for PDS activation, which was validated by the higher ratio (3 and 2.5 for nZVI/Ag and nZVI/Cu, respectively) between the soluble extracellular polymeric substances and the bound extracellular polymeric substances (S-EPS/B-EPS). Similar conclusions were derived from a SEM analysis. The improved disintegration efficiency could be related to the enhanced electron transfer from nZVI to PDS or the intrinsic properties of silver, which was found to be one of the best activators for PDS under homogeneous conditions. We believe that this study deepens the understanding of PDS heterogeneous activation processes.

Marriage of membrane filtration and sulfate radical-advanced oxidation processes (SR-AOPs) for water purification: Current developments, challenges and prospects

• The combination technology of SR-AOPs and membrane filtration (MF) was summarized. • The current scenario of various integrated catalytic filtration membranes methods was centralized. • SR-AOPs/MF was used to remove pollutants and reduce membrane fouling. • The future opportunities and challenges of this technology are discussed. Integration of membrane filtration (MF) and sulfate radical-advanced oxidation processes (SR-AOPs) has progressively attracted extensive attention for environmental remediation because of simultaneous degradation and filtration of pollutants in wastewater. Current development of the integration of MF and SR-AOPs can be divided into three main categories: (1) peroxymonosulfate (PMS)/peroxydisulfate (PDS) are activated by membrane materials to achieve the purpose of synergistic oxidation-filtration process; (2) removal of contaminants was achieved by filtering through the membrane, and then adding PMS/PDS to regenerate the membrane; (3) the membrane can be directly used as an oxidant-catalyst/water contactor to promote SR-AOPs. On this basis, this review comprehensively summarizes the classification, preparation methods and properties of different types of membrane-based materials and filtration devices. In addition, the antifouling effect and self-purification regeneration ability of different SR-AOPs systems on the membrane are highlighted. Moreover, the main mechanisms including the analysis of active sites, the generation of free radicals, and the theoretical calculations in integration of MF and SR-AOPs are defragmented and discussed. Finally, the technical challenges of coupling technology in wastewater treatment are discussed, and the development and application prospects of the collaborative mixing process are prospected.

Combined solar activated sulfate radical-based advanced oxidation processes (SR-AOPs) and biofiltration for the remediation of dissolved organics in oil sands produced water

• Effective degradation of dissolved organics in produced water by solar activated SR-AOPs. • SO 4 •− , • OH and 1 O 2 reactive species were formed during solar activated SR-AOPs. • Better performance by solar activated peroxymonosulfate compared to persulfate. • Excellent mineralization of dissolved organic by post-treatment biofilm filtration. • Microbial profiling indicated presence of hydrocarbons and carboxylic acid degraders. This study reported for the first time the potential of sequential solar activated sulfate radical advanced oxidation processes (SR-AOPs) and fixed bed biofiltration for the enhanced remediation of dissolved organics in oil sands process water (OSPW). The effect of initial sulfate precursors namely persulfate (PS) and monopersulfate (PMS) was examined on the degradation of naphthenic acid (NA) surrogates and various classes of organics in real OSPW. Effluents from solar activated SR-AOPs treatment of OSPW at specific conditions were subjected to biofiltration for 45 days. Fast and complete degradation of 5-phenylvalveric acid (PVA) and up to 99% degradation of various organics in OSPW were achieved by the solar activated SR-AOPs. Radical scavenger and spin-trap electroparamagnetic spectrometry analysis showed that hydroxyl ( • OH) and sulfate (SO 4 •− ) radicals were the major reactive species generated and participated in the oxidation of organics in SR-AOPs treatment with either PS or PMS along with a small proportion of singlet oxygen. The biofiltration post-treatment showed significant mineralization of dissolved organics in treated OSPW, achieving over 60% and 40% reduction in DOC and COD, respectively, surpassing most of the reported studies for such combined approach. The bacterial metataxonomic analysis indicated significant enrichment of hydrocarbons and carboxylic acid degraders ( Sphingomonas and Sphingopyxis ) in the biofilters treating PMS pre-treated OSPW. However, for biofilters treating raw OSPW and PS, the bacterial community was dominated by hydrocarbon degraders and methanotrophs. The treated OSPW was found completely non-toxic for the OSPW treated with PMS-9 h and biofiltration. This demonstrates the potential of combined treatment for the effective remediation of the oil sand industry effluent.

Eliminating tetracycline antibiotics matrix via photoactivated sulfate radical-based advanced oxidation process over the immobilized MIL-88A: Batch and continuous experiments

• The immobilized MIL-88A(Fe) onto cotton fibers (MC) was prepared. • MC was used to achieve efficient and long-term elimination of tetracyclines matrix. • A fixed bed reactor is constructed from MC in a home-made annular setup. • MC displayed boosted long-term stability in both batch and fixed bed tests. This work demonstrates the successful immobilization of MIL-88A(Fe) MOF on cotton fibers to fabricate MIL-88A(Fe)/cotton fibers (MC) by an eco-friendly method. The prepared MC is used to activate peroxydisulfate for eliminating multiple tetracycline antibiotics, such as oxytetracycline (OTC), tetracycline (TTC), and chlortetracycline (CTC) in simulated wastewater under UV-light irradiation. The photoactivated sulfate radical-advanced oxidation processes (SR-AOPs) towards the removal of tetracycline antibiotics matrix (initial concentration of 10.0 mg/L) using MC were initially investigated using a batch method. The results reveal that 97.5% OTC, 95.2% TTC, and 100.0% CTC can be degraded in the MC/UV/PDS system in the presence of 2 g/L of MC and 1 mM of PDS. The degradation pathways of OTC, TTC, and CTC were clarified via liquid chromatography-mass spectrometry analysis and DFT calculations. The quantitative structure–activity relationship analysis shows that the tetracycline antibiotics are transformed into their corresponding intermediates with lower toxicity within 8.0 min. A self-designed fixed bed reactor, in which the MC was packed into the annular channel, was adopted to test the long-term operation possibility of the MC in the continuous photoactivated SR-AOP system. The findings demonstrate that the whole antibiotics matrix can be removed completely within 22 h. This work is the first to demonstrate the use of MOFs as catalysts for SR-AOP to achieve continuous purification of simulated wastewater. The findings highlight a new possibility for the use of MOFs in large-scale wastewater treatment over.

Degradation of sulfamethazine by vacuum ultraviolet-activated sulfate radical-advanced oxidation: efficacy, mechanism and influences of water constituents

• VUV/PMS enhanced the SMT removal in greywater than UV/PMS. • HO• was the most effective radical for SMT degradation, followed by SO 4 • − . • VUV/PMS enhanced the oxidative degradation rather than photolysis. • SMT degradation pathways and intermediates toxicology for VUV(UV)/PMS were analysed. In-situ collection, purification and reuse of indoor greywater of public buildings or household is an effective way to save water resources. Refractory organic micropollutants in greywater, such as antibiotic sulfamethazine (SMT), can be potentially removed by sulfate radical-advanced oxidation process (SR-AOP) in the presence of peroxymonosulfate (PMS) or peroxydisulfate. Herein, vacuum ultraviolet (VUV) with irradiation at 185 nm and 254 nm activating PMS was systematically investigated in terms of degradation efficacy and influences of water constituents, and the contribution of photolysis and radical oxidative species was determined. We show that SMT removal efficiency and PMS photolysis efficiency of VUV/PMS were 2.2-fold and 1.45-fold compared to UV/PMS, respectively, and VUV/PMS reached a higher mineralization. The main active radicals of VUV/PMS were HO•, SO 4 •− , and •O 2 − . Compared to UV/PMS, VUV/PMS resulted in a higher proportion of oxidative degradation and a lower proportion of photolysis. Higher SMT concentrations competed for absorption of VUV or UV-generated photons with H 2 O and PMS molecules, resulting in a less efficient reaction. VUV/PMS was more efficient at lower initial SMT concentrations and had an optimal pH of 5. The presence of SO 4 2− slightly accelerated degradation performance while HCO 3 − and NO 3 − inhibited both processes; the inhibitory effect of HCO 3 − and NO 3 − on VUV/PMS are more significant than on UV/PMS. In contrast, the presence of Cl − had no significant effect on each process. In total, 13 intermediates of SMT were identified and four degradation pathways were proposed. VUV/PMS had an advantage over UV/PMS in removing the produced harmful and toxic intermediates. Furthermore, VUV/PMS could remove SMT from real water matrix more effectively than UV/PMS. Generally, the results demonstrate the potential of VUV to displace UV for more effective in-situ treatment of indoor greywater.

Synergetic mechanism of defective g-C3N4 activated persulfate on removal of antibiotics and resistant bacteria: ROSs transformation, electron transfer and noncovalent interaction

The environmental hazards of antibiotics and the resulting antibiotic-resistant bacteria (ARB) have attracted more and more attention. In this study, an efficient synergistic system constructed by vacancy g-C3N4 (CNV0.8) and persulfate (PS) showed excellent oxidation performance to degrade aztreonam (AZT) and Escherichia coli (E. coli) screened from wastewater treatment plant (WWTP), as the typical β-lactam antibiotic and ARB. As the recombination of electron and hole was effectively inhibited and the interaction with PS was enhanced after the introduction of defects, CNV0.8 showed superior PS activation ability compared with bulk-g-C3N4 (BCN). The synergistic mechanism was systematically analyzed at three levels step by step. Firstly, the conversion of reactive oxygen radicals (ROSs) was studied using electron spin resonance (ESR) and quenching experiments. Then based on the DFT simulation, the enhancement of adsorption energy between catalysts and PS from −8.924 eV (BCN) to −11.190 eV (CNV0.8) and the elongation of O–O bond in PS (from 1.496 Å to 1.505 Å) indicated CNV0.8 had better activation performance for PS compared with BCN. The electron transfer results observed by deformation charge density showed that more electrons could be transferred from the CNV0.8 layer to the surrounding of PS for its own activation in the synergistic mechanism. Thirdly, the noncovalent interaction of PS/CNV0.8 belonged to the region of van der Waals force which was defined by the reduced density gradient (RDG) analysis. The intermediate products in the degradation of AZT were first studied in detail using Fukui function calculations and HPLC-QTOF-MS analysis. Subsequently, the environmental practicability of the oxidation system was investigated through wastewater simulation. This research provides a possible strategy for the effective removal of micropollutants and promotes the development of the sulfate radical-advanced oxidation processes (SR-AOPs) in the field of wastewater treatment.

UV facilitated synergistic effects of polymetals in ore catalyst on peroxymonosulfate activation: Implication for the degradation of bisphenol S

The use of natural ore, especially iron-based ore, in sulfate radical-advanced oxidation processes (SR-AOPs) for organic contaminant control has received increasing attention. However, the rapid exhaustion of Fe(II) in ore has become a bottleneck restricting persulfate activation and radical generation. Herein, a natural Ti- and V-enriched magnetite (Ti-V-M) was exploited both as an activator and catalyst for UV-facilitated peroxymonosulfate (PMS) degradation of bisphenol S (BPS) in a water treatment process. The results revealed superior performance in which 100% of BPS was removed within 20 min in the UV/PMS/Ti-V-M system, and its pseudo-first-order kinetic constant was almost 3.55 times, 42.73 times, and 52.22 times higher than that for the PMS/Ti-V-M, UV/PMS, and UV/Ti-V-M systems, respectively. Under the synergistic action of multi-metals, the photocatalytic activity of the Ti-V-M was greatly improved with relatively low valence band potential (1.88 eV) and charge transfer resistance (12.60 Ω). Meanwhile, distinct from conventional PMS processes activated by monometallic Fe, the Fe(III)/Fe(II) circulation was accelerated significantly, mainly due to the excited h+-e− pairs in photosensitive TiO2 and subsequent electron transfer by V(III)/V(IV)/V(V) redox cycles. The above advantages strongly enhanced radical generation, and SO4–·, ·OH, O2–·, 1O2 and h+ were confirmed to play vital roles in BPS degradation. Furthermore, this system displayed excellent recyclability and stability for water treatment. Our study highlights the mechanism of synergistic action of multi-metals in natural minerals for UV-facilitated PMS activation and sheds new light on using cost-effective ores for highly efficient treatment of highly acidic and alkaline organic wastewater.

In-situ synthesis of highly dispersed Cu-CuxO nanoparticles on porous carbon for the enhanced persulfate activation for phenol degradation

The study reported a straight route to prepare multivalent Cu and carbon composite catalysts with good Cu dispersion serving as copper-base catalysts for sulfate radical-advanced oxidation processes. The proposed copper-base catalysts exhibit excellent degradation efficiency toward refractory organic pollutants. • Multivalent copper coexisted composites were synthesized through a facile method. • Cu-Cu x O were well dispersed on carbon substrates. • The Cu-Cu x O@C composite presented superior catalytic activity in PS activation. • The maximum removal efficiency of phenol reached approximately 100%. Copper-mediated activation of persulfate (PS) has been widely investigated for the degradation of refractory organic pollutants. However, the dispersion of the active copper sites in the catalysts remains a great challenge. Herein, a series of well-dispersed Cu-Cu x O embedded into carbon matrix composites (Cu-Cu x O@C) were fabricated via the pyrolysis of HKUST-1 precursor. The Cu-Cu x O@C catalysts were fully characterized by SEM, HRTEM, XRD, BET, Raman, FT-IR, and XPS. The results show that the Cu-Cu x O@C calcinated at 700 °C (Cu-Cu x O@C-700) contained multivalent Cu components. Their heterogeneous activation of PS for phenol degradation was also investigated. Cu-Cu x O@C-700 removed completely phenol with a k obs value greater than 0.40 min −1 . Such superior catalytic activity is mainly attributed to the synergistic effect of carbon matrix adsorption and multivalent Cu active site electron transfer. The reusability studies reveal that the performance of the used Cu-Cu x O@C-700 could be reactivated through re-calcination. Moreover, quenching tests and EPR analyses revealed that OH and SO 4 − are involved in phenol degradation. The electron transfer process and resistance of Cu-Cu x O@C-700 were described by electrochemical method. Finally, the catalytic mechanism was explored by XPS, FT-IR and Raman analyses. This study provides new insights into the fabrication of heterogeneous catalysts for sulfate radical activiation.