Heterogeneous Advanced Oxidation Processes Research Articles

Catalyst for the Generation of OH Radicals in Advanced Electrochemical Oxidation Processes: Present and Future Perspectives

Heterogeneous Advanced Oxidation Processes (H-AOPs) are considered a new process for removing emerging pollutants. In this case, the high reactivity of hydroxyl radicals is used to degrade persistent organic pollutants. This review explores the state-of-the-art catalyst for hydroxyl radical generation in AOPs. As a parasite reaction, chloride ions appear in alkaline conditions and compete with the active sites. The theoretical foundation of catalyst performance is explored, focusing on the fundamental principles that govern the efficiency and mechanism of hydroxyl or chloride radical production. The synthesis and electronic modification sections explore the modifications of catalysts. It discusses key methodologies for catalyst preparation, with a particular emphasis on electronic modification that enhances both activity and stability. Finally, laboratory and pilot applications highlight the effectiveness of novel or modified catalysts in different scenarios. These last findings provide insights into the future directions for research and application, aiming to draw attention to the gap between laboratory studies and real-world implementations.

A tandem dual-pathway non-radical water purification simultaneously induced by single-molecule peroxymonosulfate with a catalyst of coexisting Cu single atoms and Fe3C nanoparticles

The non-radical pathways of persulfate (PMS/PS)-based heterogeneous advanced oxidation processes offer effective means for treating complex water matrices. However, the large-scale application is hindered by the increased input costs and substantial accumulation of SO42–. Therefore, it is crucial to develop novel pathways for efficient PMS/PS activation. Here, we construct a CuSA/Fe3C-NC catalyst with Cu single atoms (SAs) and Fe3C nanoparticles (NPs) co-anchored on a carbon support. The improved d-band centers of Cu and Fe elements optimize the PMS adsorption and activation. Unlike previous studies, the electron acceptor PMS in electron transfer process is not be converted to SO42– but rather to singlet oxygen (1O2) via superoxide radicals (O2•–). A tandem dual-pathway non-radical oxidation system induced by a single-molecule PMS leads to higher PMS utilization. Under extremely low catalyst and PMS dosage conditions (catalyst dosage = 0.04 g/L, PMS dosage = 0.2 mmol/L), CuSA/Fe3C-NC + PMS system can rapidly remove bisphenol A within 30 min and achieve a mineralization rate of 85 %. This work provides strong support for the rational design of catalyst structures to achieve low-input and high-efficiency water purification processes.

Synergistically enhanced heterogeneous activation of dissolved oxygen for aqueous carbamazepine degradation over S(III) coupled with siderite

The wide occurrence of emerging contaminants (ECs) was drawing more attention due to the potential hazard and threat on human and environment. Carbamazepine (CBZ) is a widely prescribed medication that has garnered considerable research interest with the exposures exceeding the environmental carrying capacity. We have established the innovative heterogeneous advanced oxidation process (AOPs) based on the activated dissolved oxygen (DO) coupled with S(III) and natural iron ore (siderite). In S(III)/O2/siderite system, we investigated the degradation efficiency, reactive species generation mechanism, and degradation pathway of CBZ. CBZ degradation and mineralization rate were 90% above and ∼15% with the reaction time of 40 min. The degradation of CBZ conformed to a pseudo-first-order kinetic model, with an activation energy determination of 76.36 kJ/mol. The optimal initial solution pH was the weak acid condition (pH = 4–6) for CBZ degradation. Moreover, the inhibition effects of coexisting substance including Cl−, HCO3−, and natural organic matter (NOM) on CBZ removal were observed, while the coexisted SO42− exhibited no significant influence. In addition, the reactive species generated in S(III)/O2/siderite system were predominantly identified as sulfate radical (SO4∙-) and hydroxyl radical (∙OH). The crucial intermediate complexes, Fe(III)S(IV)O3(+) and Fe(II)HS(IV)O3(+), was proposed to form in the initial stages of the reaction, which upon decomposition, yielded SO4∙- along with other reactive species. The degradation pathway of CBZ primarily involved deamination, oxidative ring-opening, hydroxylation, decarboxylation, and ketone degradation processes. This work provides the effective approach for the CBZ degradation with the mild reaction conditions and the sustainable technology for ECs treatment and control.

(Y3+/Sm3+)-doped and co-doped CoFe2O4 for heterogeneous advanced oxidation process: structural, magneto-optical, and photocatalytic investigations.

The photocatalytic properties of CoFe2O4 nanoparticles were activated by the doping and co-doping of a low level of Y3+ and Sm3+ cations. After optimizing the annealing temperature, 900°C was found to be the optimal temperature for the successful incorporation of Y3+ and Sm3+ into the spinel structure. The purity of our samples annealed at 900°C was confirmed using several characterization methods, including PXRD, SEM, XPS, VSM, FTIR, and Raman spectroscopy. Thus, we were able to increase the photocatalytic degradation of orange G dye from 9.9 to 64.63% for the Sm3+-doped sample, 76.42% for the Y3+-doped sample, and even 85.81% for the co-doped sample under 60min of UV-visible light irradiation. The beneficial effect of samarium and yttrium doping and co-doping is attributed to several factors: the first factor is doped and co-doped rare earth impurities induce distortion in the lattice, the larger the ionic radii of dopant element, the highest is the photocatalytic activity; second factor, upon doping and co-doping of rare earth impurities in the structure of CoFe2O4 leads to the creation of donor state level within the band gap, causing the Fermi energy to shift near the conduction band. Third factor, co-doping produced strong interactions, which accelerated photocarrier mobility and transport; lastly, longer electron-holes lifetime. We have provided a detailed study of the structural, vibrational, and optical properties to support our conclusions.

A novel redox synergistic mechanism of peroxymonosulfate activation using Pd-Fe3O4 for ultra-fast chlorinated hydrocarbon degradation

Peroxymonosulfate (PMS)-based heterogeneous advanced oxidation processes for chlorinated hydrocarbons (CHCs) removal in groundwater face the challenge of limited degradation ability. In this work, recyclable catalysts composed of Pd and Fe3O4 nanoparticles were synthesized to activate PMS and generate oxidative HO• and SO4•− and reductive H•, simultaneously. The synergistic attack of different active species led to the ultra-fast degradation and mineralization of multiple CHCs. For trichloroethylene (TCE) degradation, the catalysts mass normalized reaction rate constant of Pd-Fe3O4/PMS system (30.85 L g−1 min−1) was one order of magnitude higher than reported PMS activation systems. The d-band center of Pd in Pd-Fe3O4 was close to the Fermi level, indicating that Pd(0) sites of Pd-Fe3O4 was more conducive to the activation of PMS. In addition, PMS attached Fe3O4 sites caused internal electron transfer to Pd(0) for H• generation. Higher than 97 % of CHCs removal efficiency in continuous flow experiment demonstrated the application potential of Pd-Fe3O4/PMS system.

Enhanced peroxymonosulfate activation by δ-MnO2 nanocatalyst enriched with oxygen vacancies for phenolic pollutants polymerization

Heterogeneous advanced oxidation processes technology holds great potential for the removal of toxic phenolic molecules in water, but is currently challenged by overuse of oxidation agents and undesirable carbon emissions during the mineralization process. The present work demonstrates that with an oxygen-vacancy-rich Fe doped δ-phase MnO2 (δ-MnO2) as the nanocatalyst, the phenol (PhOH) could be removed with high selectivity as well as effective conversion into non-toxic phenolic polymers via a non-radical electron transfer route, instead of complete mineralization by common radical attacking route. Oxygen vacancies in δ-MnO2 were enriched by Fe doping, which greatly improved the activation of peroxymonosulfate (PMS) by extending the length of the O-O bond in PMS. A 6.68-fold enhancement of the removal rate of PhOH was achieved by Fe doping δ-MnO2, compared to the pristine δ-MnO2. Moreover, the consumption of PMS could be reduced by up to 95.08 %, and the carbon emissions were also reduced by up 99.13 % during the polymerization process. The present study manifests that rationally designing a non-radical route offers significant potential for the cost-effective use of oxidation agents as well as reducing carbon emissions, presenting a superior approach for the target of achieving carbon neutrality in environmental remediation.

Utilizing the oxygen-atom trapping effect of Co3O4 with oxygen vacancies to promote chlorite activation for water decontamination

Heterogeneous high-valent cobalt-oxo [≡Co(IV)=O] is a widely focused reactive species in oxidant activation; however, the relationship between the catalyst interfacial defects and ≡Co(IV)=O formation remains poorly understood. Herein, photoexcited oxygen vacancies (OVs) were introduced into Co3O4 (OV-Co3O4) by a UV-induced modification method to facilitate chlorite (ClO2-) activation. Density functional theory calculations indicate that OVs result in low-coordinated Co atom, which can directionally anchor chlorite under the oxygen-atom trapping effect. Chlorite first undergoes homolytic O-Cl cleavage and transfers the dissociated O atom to the low-coordinated Co atom to form reactive ≡Co(IV)=O with a higher spin state. The reactive ≡Co(IV)=O rapidly extracts one electron from ClO2- to form chlorine dioxide (ClO2), accompanied by the Co atom returning a lower spin state. As a result of the oxygen-atom trapping effect, the OV-Co3O4/chlorite system achieved a 3.5 times higher efficiency of sulfamethoxazole degradation (~0.1331 min-1) than the pristine Co3O4/chlorite system. Besides, the refiled OVs can be easily restored by re-exposure to UV light, indicating the sustainability of the oxygen atom trap. The OV-Co3O4 was further fabricated on a polyacrylonitrile membrane for back-end water purification, achieving continuous flow degradation of pollutants with low cobalt leakage. This work presents an enhancement strategy for constructing OV as an oxygen-atom trapping site in heterogeneous advanced oxidation processes and provides insight into modulating the formation of ≡Co(IV)=O via defect engineering.

Tempospatially Confined Catalytic Membranes for Advanced Water Remediation.

The application of homogeneous catalysts in water remediation is limited by their excessive chemical and energy input, weak regenerability, and potential leaching. Heterogeneous catalytic membranes (CMs) offer a new approach to facilitate efficient, selective, and continuous pollutant degradation. Thus, integrating membranes and continuous filtration with heterogeneous advanced oxidation processes (AOPs) can promote thermodynamic and kinetic mass transfers in spatially confined intrapores and facilitate diffusion-reaction processes. Despite the remarkable advantages of heterogeneous CMs, their engineering application is practically restricted due to the fuzzy design criteria for specific applications. Herein, the recent advances in CMs for advanced water remediation are critically reviewed and the design flow for tempospatially confined CMs is proposed. Further, state-of-the-art CM materials and their catalytic mechanisms are reviewed, after which the tempospatial confinement mechanisms comprising the nanoconfinement effect, interface effect, and kinetic mass transfer are emphasized, thus clarifying their roles in the construction and performance optimization of CMs. Additionally, the fabrication methods for CMs based on their catalysts and pore sizes are summarized and an overview of their application and performance evaluations is presented. Finally, future directions for CMs in materials research and water treatment, are presented.

2D-Like Catalyst with a Micro-nanolinked Functional Surface for Water Purification.

In water purification, the performance of heterogeneous advanced oxidation processes significantly relies upon the utilization of the catalyst's specific surface area (SSA). However, the presence of the structural "dead volume" and pore-size-induced diffusion-reaction trade-off limitation restricts the functioning of the SSA. Here, we reported an effective approach to make the best SSA by changing the traditional 3D spherule catalyst into a 2D-like form and creating an in situ micro-nanolinked structure. Thus, a 2D-like catalyst was obtained which was characterized by a mini "paddy field" surface, and it exhibited a sharply decreased dead volume, a highly available SSA and oriented flexibility. Given its paddy-field-like mass-transfer routine, the organic capture capability was 7.5-fold higher than that of the catalyst with mesopores only. Moreover, such a catalyst exhibited a record-high O3-to-·OH transition rate of 2.86 × 10-8 compared with reported millimetric catalysts (metal base), which contributed to a 6.12-fold higher total organic removal per catalyst mass than traditional 3D catalysts. The facile scale preparation, performance stability, and significant material savings with the 2D-like catalyst were also beneficial for practical applications. Our findings provide a unique and general approach for designing potential catalysts with excellent performance in water purification.

Dark and sunlight-driven dye degradation over a TiO2–dibenzoylmethane hybrid xerogel

The pursuit of sustainable and inexpensive systems for the degradation of organic aquatic pollutants working under sunlight or even without irradiation is still open. Herein, an amorphous titanium oxide modified with dibenzoylmethane, an aromatic diketone, is proposed as a solar photocatalyst showing oxidative activity also in the dark. Ti(IV)-dibenzoylmethanate (dbm) complexes form during the sol-gel synthesis and are dispersed throughout the oxide gel structure. This ligand-to-metal charge transfer complex plays a dual role: it enables visible light absorption, narrowing the apparent band gap, and provides localized surface charge, promoting the spontaneous formation and stabilization of superoxide radical ions by reduction of O2. The activity of the TiO2-dbm hybrid was assessed in the removal of methylene blue from aqueous solution. The results demonstrated a rather stable photocatalytic activity under natural sunlight, exceeding 80% dye removal after 1 h in four subsequent tests, a value that was mostly recovered after a mild regeneration. Considerable efficiencies were also achieved in the dark, owing to the immobilized superoxide radicals acting as initiators of degradation pathways. Finally, the influence of the operating conditions (pH, illumination, mixing method, water contact) on the efficiency and durability of the performances was evaluated to survey the long-term utilization in water decontamination. The behaviour of this hybrid material resembles a “photocatalytic memory” effect and may widen the perspectives for the development of heterogeneous advanced oxidation processes.

Synthesis of a trivalent copper complex for efficient degradation of antibiotic ofloxacin

Copper-based catalysts have been widely used in heterogeneous advanced oxidation processes (AOPs) to degrade emerging contaminants, with trivalent copper species (Cu(III)) often identified as crucial intermediates. However, the current understanding of the reactivity and potential oxidation mechanism associated with such reactive species remains quite limited. In the present study, a stable Cu(III) complex was synthesized, and its reactivity towards a typical fluoroquinolone antibiotic, ofloxacin (OFX), was comprehensively investigated. The results revealed that Cu(III) itself functioned as the primary oxidizing agent instead of secondary hydroxyl radicals generated during OFX decomposition, which exhibited high reactivity over a wide pH range (3.0–9.0) with molar ratio of Cu(III) to OFX between 1:2 and 3:1. Interestingly, prevalent constituents of natural water, including (bi)carbonate (0–10 mM), chloride (0–10 mM), nitrate (0–10 mM) and humic acid (0–30 mg/L), displayed minimal influence on the oxidation efficiency of Cu(III). Piperazine moiety was identified as the primary reaction site, and three different pathways including tertiary amine oxidation, hydroxylation, and N-demethylation process were proposed. The detailed oxidation mechanisms were further illustrated by density functional theory (DFT) calculations. This study contributes to the theoretical foundation for investigating the mechanism of Cu(III)-mediated oxidation of antibiotics.

Efficient removal of VOCs emission from soil thermal desorption via MnCoOx/Kaolin activating peroxymonosulfate in wet scrubber

The heterogeneous advanced oxidation processes coupling with wet scrubber is a promising method for the treatment of VOCs produced by soil thermal desorption. Mn-Co bimetallic oxides/Kaolin (MnCoOx/Kaolin) were successfully synthesized via cation-exchange based impregnation-calcination. The abundant SiO-OH and AlO-OH groups on the Kaolin carrier can inhibit metal aggregation, and the synergistic effect between Kaolin and metal oxide can improve the catalytic performance. The removal rate of benzene via wet scrubber with MnCoOx/Kaolin as catalyst remained above 98 %, which was better than that of single metal oxide. Moreover, the system exhibited significant application effects on the single component (toluene, ethylbenzene, xylene) and BTEX mixture, with the removal rates maintaining at higher than 90 %. The dosing method of PMS was optimized, and the method of continuous dosing of oxidant was proposed instead of one-time dosing. The main active oxygen in the MnCoOx/Kaolin system was sulfate radical, as shown by the results of characterization analysis and quenching experiments. Based on the intermediates identified by GC–MS, a possible degradation pathway of benzene in MnCoOx/Kaolin + PMS system was proposed.

Sulfur vacancies-induced electron delocalization effect of cobalt sulfide for enhanced catalytic activation of peracetic acid and norfloxacin degradation

Antibiotics have attracted widespread attention due to their potential risks to human health and environment. In this study, a heterogeneous advanced oxidation process (AOP) of peracetic acid (PAA) activation by cobalt material was developed to degrade a typical antibiotic, norfloxacin (NOR). Cobalt sulfide materials with sulfur vacancies (CoSx) were synthesized through a two-step hydrothermal process. The optimized material (CoSx-2) could efficiently activate PAA system, achieving 91.8% NOR degradation in 5 min. The Co(II)/Co(III) species in CoSx was key to activating PAA, as Co(II) initiated the reaction and Co(III) activation caused the production of CH3C(=O)OO• species. Moreover, the presence of sulfur vacancies (VS) led to the generation of hydroxyl radicals (•OH) and singlet oxygen (1O2) via chain reactions with CH3C(=O)OO•. Density functional theory (DFT) calculations reveal the contribution of VS to enhanced catalytic PAA activation, as the lower work function (5.76 eV), higher adsorption energy (-3.43 eV), bridge effect of delocalized electrons and shifted d-band center are achieved to reduce the energy barrier for electron transfer during catalytic reaction. In addition, DFT calculation on Fukui index further explains that 18 N and 21 N are reactive sites of NOR for electrophilic attack, leading to primary degradation pathways of C–N cleavage, defluorination, dealkylation and hydroxylation. This study gives a new perspective on the regulation of material structure for efficient activation of PAA and promotes the practical application of heterogenous PAA-based AOPs for emerging contaminants removal in water treatment process.

Activation of peroxymonosulfate by CoFe2O4 layered catalyst derived from steel pickling sludge for the decolorization of tartrazine solution

Steel pickling sludge provides abundant iron resource for the preparation of bimetallic catalyst used in heterogeneous advanced oxidation processes (AOPs). In this study, steel pickling sludge was used to synthesize CoFe2O4 layered catalyst through a convenient one-step solvothermal reaction and applied as a powerful peroxymonosulfate (PMS) activator to decolorize tartrazine solution. The layered microstructure, composition, and structure of the as-prepared CoFe2O4 catalyst were characterized by scanning electron microscope, X-ray photoelectron spectroscopy, and X-ray diffraction. The influences of catalyst dosage, PMS dosage, and initial solution pH on the decolorization efficiency were systematic investigated and optimized, the results showed that CoFe2O4 layered catalyst exhibited excellent catalytic effect with 96% decolorization efficiency in 15 min. SO42−, Cl−, and NO3− had little effect on the decolorization efficiencies compared to HCO3− and CO32−. Both free radicals (∙SO4−, ∙OH, and ∙O2−) and non-radicals (1O2 and mediated electron transfer) pathways coexist in CoFe2O4 layered catalyst/PMS system, and ∙SO4− was the dominate reactive oxygen species. Based on DFT calculation, the plausible decolorization mechanism of tartrazine in CoFe2O4 layered catalyst/PMS system could be well elucidated. This study offers an economic reuse strategy to convert the “steel pickling waste sludge” to low-cost and higher-value bimetallic catalyst for the practical application in AOPs.

Insights into Photo/Electrocatalysts for the Degradation of Per- and Polyfluoroalkyl Substances (PFAS) by Advanced Oxidation Processes

Per- and polyfluoroalkyl substances (PFASs) are an emerging group of persistent organic pollutants in aquatic environments with high levels of toxicity and bioaccumulation. The risks posed by PFASs to the environment and health have attracted increasing attention. To remove them from water, advanced oxidation processes (AOPs), with the merits of high efficiency and low cost, are mainly used. Photo/electrocatalytic heterogeneous AOPs, with the assistance of nanostructured catalysts and external energy in the form of light/electricity, have emerged as one of the most powerful techniques, overcoming the difficulty associated with defluorination and achieving the effective and complete degradation of PFASs in water. The structures of photo/electrocatalysts play a critical role in the production of reactive oxygen species, the electron transfer process, and the degradation pathway and its efficiency. Herein, to elucidate the structure–performance relationship, a review of photo/electrocatalysts for the enhanced degradation of PFASs in heterogeneous AOPs, organized according to their composition and nanostructure design, is provided. This review article is mainly focused on (1) the mechanisms and pathways of PFAS degradation by heterogeneous photo/electrocatalytic AOPs, and (2) the structural designs and modifications of photo/electrocatalysts for the enhanced degradation of PFASs by heterogeneous AOPs. Finally, the challenges and prospects for future research into photo/electrocatalysts of heterogeneous AOPs in the field of PFAS remediation are discussed.

Dual Role of Silicon-based Matrices in Electron Exchange Matrices for Waste Treatment.

Para chloro aniline (PCA) is a common toxic pollutant found in pharmaceutical wastewater. Our study suggests a novel PCA treatment method based on a heterogeneous advanced oxidation process (AOP) that proceeds in an electron exchange matrix (EEM) prepared by the incorporation of redox-active specie in silica matrices using the sol-gel synthesis route. The results, which are supported by DFT calculations, show that the silicon skeleton of the EEM has two important roles, both as a porous matrix that hosts the redox species and as an oxidant species involved in the AOP. The calculations indicate that the formation of a radical on the nitrogen is favored. The suggested mechanism could shed light on the AOP, which proceeds in a heterogenous system, and on its application inside the understudied EEMs that, until now, have been a virtual black box. A better understanding of the mechanism could lead to improved control over the heterogeneous processes that can play a critical role in industries with the need to treat small amounts of toxic compounds at low concentrations, such as in the pharmaceutical industry.

Ultrahigh-flux 2D CoO@MoS2 composite membrane activated peroxymonosulfate through enhanced electron transfer for rapid degradation of refractory benzotriazole

The application of heterogeneous advanced oxidation processes (AOPs) in the removal of refractory pollutants has been hindered by several drawbacks, such as difficult recovery of the powder catalyst, the low yields and inefficient utilization of reactive oxygen species (ROS). We developed a novel catalytic membrane named 2D CoO@MoS2 membrane, its catalytic active layer was a composite material formed by MoS2 nanosheets wrapped and intercalated between 2D CoO porous nanoplates, providing abundant active sites and oxygen vacancies (Ov). 2D CoO@MoS2 membrane was applied to activate peroxymonosulfate (PMS) for benzotriazole (BTA) degradation. DFT calculations and series characterizations demonstrated that electron transfer occurred at the contact interface between 2D CoO and MoS2 phase, while the 2D CoO@MoS2 composite could act as an effective electron donor for PMS. The redox cycles of Mo(IV)/Mo(VI) and Ov/O2− could synergistically enhance the regeneration of Co(II), thereby maintaining the cycle of catalytic active center, which facilitated the spontaneous dissociation of PMS to generate various ROS, including SO4− (30.2 μM), 1O2 (8.6 μM) and OH (5.8 μM). These ROS rapidly degraded 99.7% of BTA (20 mg/L) through the nanoconfined layer of hydrophilic membrane with an ultra-high flux of 2172 L m−2h−1 in a super-fast time (∼195 ms). Surprisingly, the degradation rate constant k exhibited 3 to 5 orders of magnitude higher compared to conventional heterogeneous AOPs. Furthermore, the catalytic stability, degradation pathways and biological toxicity of BTA degradation were also evaluated. This membrane-based AOPs technique provides a new approach to overcome the limitations of conventional heterogeneous catalysis.

Biochar/layered double hydroxides composites as catalysts for treatment of organic wastewater by advanced oxidation processes: A review

Heterogeneous advanced oxidation process has been widely studied as an effective method for removing organic pollutants in wastewater, but the development of efficient catalysts is still challenging. This review summaries the present status of researches on biochar/layered double hydroxides composites (BLDHCs) as catalysts for treatment of organic wastewater. The synthesis methods of layered double hydroxides, the characterizations of BLDHCs, the impacts of process factors influencing catalytic performance, and research advances in various advanced oxidation processes are discussed in this work. The integration of layered double hydroxides and biochar provides synthetic effects for improving pollutant removal. The enhanced pollutant degradation in heterogeneous Fenton, sulfate radical-based, sono-assisted, and photo-assisted processes using BLDHCs have been verified. Pollutant degradation in heterogeneous advanced oxidation processes using BLDHCs is influenced by process factors such as catalyst dosage, oxidant addition, solution pH, reaction time, temperature, and co-existing substances. BLDHCs are promising catalysts due to the unique features including easy preparation, distinct structure, adjustable metal ions, and high stability. Currently, catalytic degradation of organic pollutants using BLDHCs is still in its infancy. More researches should be conducted on the controllable synthesis of BLDHCs, the in-depth understanding of catalytic mechanism, the improvement of catalytic performance, and large-scale application of treating real wastewater.

Ultrastable Co-NC membrane for sterilization of Escherichia coli in flowing water

Advanced oxidation technology based on peroxonosulfate (PMS) has attracted extensive attention in water treatment research due to its fast reaction speed and wide pH range adaptability. Cobalt-based catalysts are considered to be one of the most effective reagents for PMS activation in various PMS activation methods. However, Co-ion leaching and difficulty in recovery have greatly hindered its practical applications. Herein, we developed a robust membrane constructed by nitrogen-doped carbon nanotubes embedded with cobalt nanoparticles (Co-NC) to concurrently address the Co-ion leaching and recovery issues. Based on our customization, continuous water flow reactor, the Co-NC membrane exhibited excellent catalytic activity and stability, in which it demonstrated a remarkable sterilization efficiency of 99.9999% against E. coli, and it retained a superior stability of 96.29% after 40 repeated cycles. Fewer attempts to put such efficient heterogeneous advanced oxidation processes (AOPs) into practical application, to mimic real-life applications, the performance of the Co-NC/PMS system was extended to the water taken from Qiuxi River. Remarkably, there is no deterioration in performance over 12 h of continuous real sewage processing. Mechanistic studies revealed that abundant high-valence metals (CoIV=O) were generated in the system, which can attack and penetrate into the cell membrane to destroy its intracellular defense system. This work provides useful insights into designing robust membranes with superior efficiency and stability for PMS-based advanced oxidation technology.

In-situ construction of Co(OH)2 nanoparticles decorated biochar for highly efficient degradation of tetracycline hydrochloride via peracetic acid activation

Peracetic acid (CH3C(O)OOH, PAA)-based heterogeneous advanced oxidation process (AOP) has attacked intensive interests due to production of various reactive species. Herein, Co(OH)2 nanoparticles decorated biochar (Co(OH)2/BC) was fabricated by a simple and controllable method, which was used to degrade tetracycline hydrochloride (TTCH) in water through PAA activation. The results indicated that 100% TTCH (C0 = 10 µmol/L) degradation efficiency was realized within 7 min at pH 7, with a high kinetic rate constant (k1) of 0.64 min−1 by the optimized Co(OH)2/BC. Material characterizations suggested that Co(OH)2 nanoparticle was successfully decorated on biochar, leading to more active sites and electronic structure alteration of biochar, thus greatly promoting the catalytic cleavage of PAA for radicals production. Then, the reactive oxygen species (ROS) quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated the key species were alkoxyl radicals (R–O•, mainly CH3CO2• and CH3CO3•), HO• and 1O2 in this system. Besides, density functional theory (DFT) calculation on Fukui index further revealed that the vulnerable sites of TTCH and three possible degradation pathways were proposed. This study can provide a new strategy for synthesis functional materials in PAA activation AOPs for removal of antibiotics in water.