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•CoM/TNTs showed high ACE degradation efficiency after PMS activation.•Efficient PMS activation was due to the synergic effect of Co(OH)2 and TNTs.•TNTs with abundant surface –OH ...facilitated formation of CoOH+.•PES analysis well explained the higher feasibility of Co(OH)+ on PMS activation.•ACE atoms with high Fukui index are active sites for electrophilic attack.
Pharmaceuticals and personal care products (PPCPs) are of great concern due to their increasing health effects, so advanced treatment technologies for PPCPs removal are urgently needed. In this study, titanate nanotubes decorated Co(OH)2 hollow microsphere (CoM/TNTs) composites were synthesized by a two-step solvothermal method, and used to activate peroxymonosulfate (PMS) through heterogenous catalysis for acetaminophen (ACE) degradation in water. The optimum material (CoM/TNTs0.5) activated PMS system exhibited high ACE removal efficiency and quick kinetic, as 93.0% ACE was degraded even within 10 min. The two components in CoM/TNTs showed a synergetic effect on PMS activation for radicals production: Co(OH)+ from CoM was the primary active species to active PMS, while TNTs could offer abundant –OH groups for Co(OH)+ formation. Density functional theory (DFT) calculation further interpreted the mechanism of Co(OH)+ for PMS activation by means of reaction potential energy surface (PES) analysis. Both the scavenger quenching tests and electron paramagnetic resonance analysis revealed that the sulfate radical (SO4-·) played a dominant role in ACE degradation. Moreover, DFT calculation also suggested that the ACE atoms with high Fukui index (f-) represented the active sites for electrophilic attack by SO4-·. The toxicity analysis based on quantitative structure-activity relationship (QSAR) verified the reduced toxicity of transformation products. Furthermore, CoM/TNTs also had good reusability and stability over five cycles. This work provides deep insights into the reaction mechanisms of radical production and organics attack in cobalt-based PMS activation system.
•Dynamic electronic structure analysis is applied to reveal radical attack mechanism.•SO4•− has higher oxidation potential and electrophilic index than •OH.•Only SO4•−can react with CAF through ...single electron transfer reaction (SET) route.•Only •OH can react with CAF through hydrogen atom abstraction (HAA) route.••OH shows larger energy barriers than SO4•− through radical adduct formation (RAF).
Hydroxyl radical (•OH) and sulfate radical (SO4•−) produced in advanced oxidation processes (AOPs) have been widely studied for organic contaminants degradation, however, the different radical characteristics and reaction mechanisms on organics degradation are still needed. In this study, a homogeneous Co(II)/peroxymonosulfate activation system was established for caffeine (CAF) degradation, and pH was controlled to regulate the radicals production. The different attack routes driven by SO4•− and •OH were deeply explored by transformation products (TPs) identification and theoretical calculations. Specifically, a method on dynamic electronic structure analysis of reactants (R), transition state (TS) and intermediates (IMs) during reaction was proposed, which was applied to elucidate the underlying mechanism of CAF oxidation by •OH and SO4•− at the molecular orbital level. In total, SO4•− is kinetically more likely to attack CAF than •OH due to its higher oxidation potential and electrophilicity index. Single electron transfer reaction (SET) is only favorable for SO4•−due to its higher electron affinity than •OH, while only •OH can react with CAF via hydrogen atom abstraction (HAA) route. Radical adduct formation (RAF) is the most favorable route for both •OH and SO4•− attack according to both kinetics and thermodynamics results. These findings can significantly promote the understanding on the degradation mechanism of organic pollutants driven by •OH and SO4•− in AOPs.
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•The most efficient route was designed for 3D mesoporous α-Co(OH)2 on Ni foam (NF).•Extraordinary catalytic activity of Co(OH)2/NF for peroxymonosulfate was observed.•The cobalt ...leaching was alleviated by the macroscopic Co(OH)2/NF.•The readily recyclable monolith catalyst benefits the practical application.
Cobalt-based catalysts with high stability and facile recovery for heterogeneous peroxymonosulfate (PMS) activation are still rather sparse and therefore highly desirable. Herein, 3D mesoporous α-Co(OH)2 nanosheets was created on robust nickel foam (NF) via facile electrodeposition approach at 6 mA/cm2 for only 400 s. Almost complete removal of phenol can be achieved within 7 min with a degradation rate of 0.39 min−1, 2 times higher than that with ever-prevalent Co3O4 derived from direct calcination of α-Co(OH)2/NF. This can be attributed to the hydrotalcite-like hexagonal structure of α-Co(OH)2 with large interlayer spacing for enhancing the catalytic performance. The low activation energy of Co(OH)2/NF (53.8 kJ/mol) indicates its lower reaction energy barrier for PMS activation. Moreover, the influences of electrodeposition parameters (i.e. current density, deposition time), PMS dosage, initial pH and coexisting anions (HCO3−, SO42−, Cl−) on the phenol degradation were systematically evaluated. The recycling tests revealed the prominent stability of Co(OH)2/NF. The quenching tests verified that SO4− radicals acted as the predominant reactive species for phenol decomposition. The possible reaction mechanisms were proposed based on the intermediates identification. The findings of this work suggest the great potentials of the 3D macroscopic Co(OH)2/NF in water purification, and open up new avenues for scalable preparing recyclable heterogeneous catalysts.
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•A novel advanced oxidation process, Fe0/sulfite, was developed.•Sulfate radical was the vital reactive species in the Fe0/sulfite system.•Fe0/sulfite system could degrade organic ...pollutants at near-netural conditions.•Fe0/sulfite system was effective in improving biodegradability of textile effluent.
A novel advanced oxidation process, combined zero-valent iron and sulfite (Fe0/sulfite) system containing oxygen, was firstly developed to efficiently degrade organic pollutants at weak acidic and neutral conditions by selecting X-3B as a target compound. The removal of X-3B was attributed to the formed reactive radicals, such as SO4-, SO5- and HO, in the Fe0/sulfite system, and SO4- was evidenced as the principal reactive species. The quite low removal efficiency of X-3B (less than 5%) after reaction for 90min with purging nitrogen gas suggests oxygen to be an essential factor for producing SO4- in the system. Optimal dosages of Fe0 and sulfite were suggested to be 0.5mM and 1.0mM, respectively, in the system as both the two chemicals would scavenge the reactive radicals at overdosing. The presence of 2mM bicarbonate significantly inhibited the removal of X-3B from 74.1% to 37.5% in the system. Halide ions inhibited the removal of X-3B following a trend that Cl−<Br−<I−. HSO3−, being effective in complexion of Fe(II) and transferring Fe(III) to Fe(II), is the main species during pHs 4–6, which results in the good reuse of Fe0 and the highest removal efficiency of X-3B at weak acidic condition. Fe0/sulfite system was also evidenced to be effective in the treatment of actual textile effluents along with improving biodegradability, and the removal of nitrobenzene, methylparaben, bisphenol A, imipramine and amitriptyline. Overall, this study provided a cheap and easy operational advanced oxidation process in treatment of aqueous organic pollutants.
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•kapp of isoproturon and chlorotoluron reacting with SO4•− and HO• were determined.•QSAR model implied the great effect of ring substituents in phenylureas on UV/PS behaviors.•Effects ...of PS dosages, UV intensity, pH and water matrixes (ions and NOM) were examined.•The UV/PS destruction pathways of phenylureas were proposed by MS analysis.•Compared with UV and UV/H2O2, UV/PS was superior in controlling the DBPs formation.
The degradation performance of selected phenylurea herbicides (isoproturon and chlorotoluron) by UV/persulfate (PS) as well as toxicity assessments associated with disinfection by-products (DBPs) in subsequent oxidation were comparatively studied. The elimination of herbicides followed pseudo first-order kinetics well. Then effects of UV intensity, pH, PS dosage and water matrix (background ions and Nature organic matter (NOM)) were investigated detailedly. Increased kobs values were observed at higher PS dosages and greater UV intensity, but the degradation was basically resistant to pH variation. kobs could be inhibited by coexistent ions and NOM. Radical scavenging study revealed the more important role of sulfate radical (SR, SO4•−) than hydroxyl radical (HR, HO•). kapp of HO• and SO4•− towards isoproturon and chlortoluron were determined respectively. The results also indicated that the relative reactivity of alkyl- or halogen- substituted phenylurea herbicides with HO• and SO4•− can be correlated with Hammett constants as the molecular descriptor. Then a quantitative structure-activity relationship was established to predict the structure-dependent reactivity of phenylurea herbicides by UV/PS concerning substituent effects. The energy demand of UV/PS system was evaluated. The degradation intermediates by direct UV, UV/H2O2 as well as UV/PS were comparatively identified and the related destruction pathways were postulated. Compared with UV and UV/H2O2, UV/PS was superior in controlling the DBPs generation in post-disinfection of these herbicides. The data supported that SR-advanced oxidation processes (AOPs) had more advantages in removal efficiency and toxicity control than HR-AOPs. This study provided some theoretical bases for the UV/PS degradation behaviors of structurally similar phenylurea herbicides with regard to different substituents on the aromatic ring.
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•Cl– retards pollutant removal in Co2+/PMS process by shifting radical distribution.•NH4+ reacted with HOCl and induced more severe efficiency loss of Co2+/PMS process.•DOM inhibited ...the formation of chloramine and alleviated the efficiency loss.•The formation of chlorate and DBPs are not concerns in the presence of ammonia.
A significant loss of the treatment efficiency induced by Cl− is a well-recognized drawback of the SO4·−-based AOPs and various mathematical model have been established to achieve quantitative prediction of the treatment efficiency of SO4·−-based AOPs at different levels of Cl−. However, the background water constituents (e.g., ammonia and dissolved organic matter (DOM)) complicate the chemistry of Cl−/SO4·− system and disable these models. This study shows that the degradation of sulfamethoxazole and bisphenol A by Co2+/PMS process decreased with dosing Cl− at fresh water level, due to the shifted distribution of reactive species from SO4·− to Cl2·−, ClO· and HOCl. Besides quenching radicals, HOCl also contributed to pollutant degradation. Though ammonia alone negligibly influence the Co2+/PMS process, ammonia reacts with the in situ formed HOCl in the Cl−/SO4·− process rapidly along with the generation of chloramine which mainly severed as radical scavenger rather than oxidant. Consequently, more severe efficiency loss of the SO4·−-based AOPs occur in the copresence of ammonia and Cl−. Unexpectedly, the efficiency loss was alleviated after dosing DOM, which was attributed to the suppressed formation of chloramine. The occurrence of chlorate and disinfection by-products are not concerns in the Co2+/PMS process when Cl− coexists with ammonia and DOM, because of the decreased formation of HOCl. These results enhance our understanding of the complex chemistry of SO4·−-based AOPs in real water and promote the progress of SO4·−-based AOPs towards the niche applications in water treatment.
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•Fe-N-C was prepared and utilized to activate PMS to degrade organic pollutants.•Fe-N-C showed 37.07 and 6.04-fold higher activity to biochar and N-biochar.•Synergistic effects ...between Fe and N species facilitated the production of ROS.•SO4•−, •OH and 1O2 were identified under the Fe-N-C/PMS treatment.•Fe-N-C showed great separation performance and reusability.
This study shows that the simple pyrolysis of mixed sawdust, FeCl3 and dicyandiamide can produce Fe/N co-doped biochar (Fe-N-C) with great catalytic and separation performances. Fe-N-C had a larger specific surface area (215.25 m2/g), higher defective degree (ID/IG = 0.98) and more active species for PMS activation because of the synergy between Fe and N doping. Furthermore, graphitic N, pyridinic N, Fe-Nx, Fe2O3 and Fe0 were identified as the dominant reactive species contributing to the activation of PMS. As a result, the production of reactive oxidizing species (ROS), including both sulfate radical (SO4•−), hydroxyl radical (•OH) and singlet oxygen (1O2), in the Fe-N-C/PMS system was significantly promoted. As a result, Fe-N-C exhibited 37.07 and 6.04-fold higher reaction rates for activating peroxymonosulfate (PMS) to degrade bisphenol A (BPA) relative to the rates achieved by pristine biochar and nitrogen doped biochar, respectively. Moreover, the mineralization rate of BPA by the Fe-N-C/PMS system was 68.9%, which was much higher than that achieved by the pristine biochar/PMS and N-biochar/PMS systems. Chemical-quenching tests further suggested that SO4•− and •OH played dominant roles in the degradation of BPA under acidic and neutral conditions, while 1O2 played a dominant role under alkaline conditions. Furthermore, the potential of Fe-N-C to be used in practical applications was systematically evaluated in terms of its stability, separability and selectivity to organics; the effect of operating parameters was also studied. Generally, our study highlighted the great potential of Fe/N co-doped biochar and provided valuable insight into the synthesis of highly efficient carbon-based catalysts for environmental applications.
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•The application of SR-AOPs for IWW treatment was systematically reviewed.•The theoretical (reactive species) and practical aspects (IWW composition) were analyzed.•SR-AOPs are vastly ...studied in landfill leachate and petrochemical IWW effluents.•Its advantages include the simultaneous HO/SO4− generation with non-radical pathways.•Limitations include the difficulty to apply heating, microwave and ultrasound activation.
Over the last years, Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) have received considerable attention due to their high versatility and efficacy in disinfection and decontamination. Their advantages over classical AOPs, the generation of sulfate radicals (SO4∙-) from peroxydisulfate (PDS, S2O82-), or joint sulfate and hydroxyl radicals (HO∙) production from peroxymonosulfate (PMS, HSO5-) and their abundant activation methods have facilitated their introduction into various remediation and effluent decontamination processes. In this review, we present the advances in the field of industrial wastewater (IWW) treatment by SR-AOPs, by activation of either PMS or PDS via any suitable method, in homogeneous or heterogeneous (photo)catalytic processes. This review aims to present the state of the art in SR-AOPs application for IWW treatment, and act as a guideline of the field advances, summarize the previous application experiences, hence avoid research pitfalls and empower better IWW treatment practices. After an integrated presentation of the dominant pathways towards IWW decontamination, we discuss the SR-AOPs application in the treatment of effluents such as landfill leachate, petrochemical and pharmaceutical WW, pulp or paper industry effluents, textile and winery WW, as well as less studied processes such as coking, olive mill or soil washing effluents. Finally, the advantages and shortcomings of SR-AOPs for IWW treatment, as well as their perspectives are discussed.
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•Mesoporous MnxCo3−xO4 nanocages were prepared by a self-assembly method.•MnxCo3−xO4 nanocages showed excellent catalytic activity toward PMS.•Co-rich MnxCo3−xO4 nanocages presented ...higher catalytic activity due to the higher Co2+/Co3+ content.•Rational PMS activation mechanism and CBZ oxidation pathway were put forward.•MnxCo3−xO4 nanocages activated PMS system can effectively control the potential risk of the highly toxic intermediates.
Mesoporous MnxCo3−xO4 nanocages with high cobalt content, large surface area and high pore volume were synthesized through a self-assembly method. The as-prepared MnxCo3−xO4 nanocages displayed satisfactory catalytic activity toward peroxymonosulfate (PMS) and the metal ions leaching concentration could be negligible. Sulfate radical was identified as the predominant active species through radical quenching experiments and electron spin resonance spin-trapping technique. The kinetics of the oxidation process was of pseudo-first order. The increasing cobalt content in MnxCo3−xO4 NCs was in favor of enhancing the decomposition of PMS. MnxCo3−xO4 nanocages dosage, PMS concentration and reaction temperature put the promoting effect on the degradation, while initial CBZ concentration had the retarding impact. MnxCo3−xO4 nanocages could efficiently operate over a wide pH range of 5.0–8.0. Coexisting chloride ions exerted a dual role in the decomposition of PMS and this role was concentration-dependent. XPS analysis confirmed the reversible valence equilibrium between metal ions and the recovery of surface adsorbed oxygen, which ensured their sustainable catalytic activity even after five consecutive runs. Based on the main intermediates identified by liquid chromatography-tandem mass spectrometry, a possible pathway of CBZ oxidation was proposed. The potential risk resulting from the highly toxic intermediates can also be effectively controlled by MnxCo3−xO4 NCs activated PMS system.
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•High synergism between AOPs and hydrodynamic cavitation.•Significant lowering of treatment costs.•Hybrid technologies for water and wastewater treatment.•Effective activation of ...oxidants for radicals formation.•Sustainable solutions for environmental protection.
High-performance water treatment systems based on cavitational processes have received an increasing interest of scientific community in the past few decades. Numerous studies indicated the advantageous application of hydrodynamic cavitation as an alternative, reagent-free treatment method of various pollutants in water. Both approaches were proved as an effective method to achieve mineralization of many organic contaminants as well as a disinfection method, which is able to eliminate pathogenic microorganisms. This makes cavitation-based methods a promising candidate implemented in a post-treatment stage of water treatment facilities. Nowadays, hybrid methods based on combination of cavitation with advanced oxidation processes (AOPs), possessing enhanced oxidation capacity were proposed. Compared to the individual utilization of cavitation and AOPs (e.g., O3, H2O2, Fenton’s process), hybrid processes are capable to degrade even highly persistent contaminants and shorten the operation time reducing the overall consumption of energy and oxidants. The improved performance of hybrid methods is attributed to the synergistic effect occurring between integrated technologies, which is expressed by the synergistic index. In this paper, recent reports focusing on coupling of cavitation and AOPs were reviewed to reveal major principles and mechanisms governing the synergistic effect. The review discusses the effect of process parameters (oxidant type, pH, hydraulic and ultrasonic properties, Kow) on the oxidation effectiveness. Comparative analysis was provided in order to highlight the advantages and limits laying behind the discussed methods. The analysis of the economic feasibility was performed to assess the potential applicability of hybrid techniques in large-scale wastewater treatment.
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