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Sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs) have been studied to date by utilizing metal-organic frameworks as efficient catalysts to generate sulfate radicals by peroxymonosulfate (PMS) activation in water purification. It is important to select high-performance and reliable catalysts for efficient water remediation, and separation and recovery of catalysts are essential in the practical application of MOFs. Herein, we adapted thermally curable, shape-controllable, and cost-effective agarose (AG) as a smart matrix and ZIF-67, as a powerful catalyst to prepare nanoarchitectured aerogel (Z67@AG). This nanoporous aerogel composite can efficiently generate sulfate radicals and hydroxyl radicals by activating PMS in the nanopores. Z67@AG aerogel could be easily fabricated in various molds to make desired shapes. This approach enables its utilization for different filtering systems and demonstrates cost-effective and stable performance by mass production and reusability. In the SR-AOP, aerogel exhibited excellent catalytic decomposition performances of 95 % and 88 % efficiencies within 8 and 10 min for dye and levofloxacin, respectively. It is believed that the proposed highly catalytic nanoporous aerogel nanocomposite having cost-effectiveness, excellent catalytic activity, facile fabrication of desired shapes, and an excellent porous structure can be extended to the synthesis of various nanocomposites and emerging applications.

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The inefficiency of catalysts in sulfate radical-based advanced oxidation processes (SR-AOPs) is primarily attributed to the sluggish circulation of redox couples. Herein, a carbon defects-enriched NBC-C3N5@CoMn (NCC) was synthesized through a self-assembly approach. The carbon defects within the NCC induce the electron trap effect, thereby facilitating the efficient cycling of redox couples in photo-Fenton-like processes during contaminant degradation. This effect enables the self-regeneration of the NCC catalyst. The reductive redox couples (Co (II) and Mn (II)) are continuously regenerated following the degradation process. Within the NCC, CoMn layered double hydroxides (LDHs) act as primary active sites, promoting the generation of hydroxyl radicals (•OH), sulfate radicals (SO4•-) and singlet oxygen (1O2) through continuous electron gain and loss. Additionally, the internal electric field established within the NCC further accelerates electron transfer. Density Functional Theory (DFT) calculations confirm that the carbon defects-enriched NCC exhibits lower adsorption energies and higher electron transfer efficiencies than carbon defect-deficient NCC. This study introduces a novel photocatalyst with self-regenerating capabilities, presenting an innovative approach to regulate redox couples in SR-AOPs for sustainable degradation.

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Three-dimensional (3D) magnetic flower-spherical Fe2O3-NiO derived from NiFe-layered double hydroxides (NiFe-LDHs) was fabricated through urea hydrothermal and calcination methods. The as-prepared materials were applied to activate PMS to degrade one of herbicide named Bensulfuron methyl (BSM). Fe2O3-NiO-1 demonstrated the highest catalytic activity and the lowest ions leaching by comparing the performance of LDHs and derivative bimetallic oxide synthesized by co-precipitation method, urea hydrothermal method and direct calcination method. Based on the results of SEM, BET and CV, the high catalytic activity of Fe2O3-NiO-1 originated from 3D morphology, lager specific area and pore size and faster electron transfer capability. The factors influencing the degradation performance were investigated and 0.1 g·L-1 Fe2O3-NiO could effectively activate PMS (1 mmol·L-1) to completely remove 10 mg·L-1 BSM within 30 min at pH 7.0. In Fe2O3-NiO/PMS system, OH, SO4- and 1O2 were produced and contributed to the BSM removal according to the results of EPR and quenching experiments. In order to expand its application range, Fe2O3-NiO/PMS system was used to degrade aniline (AN), sulfamethoxazole (SMZ), phenacetin (PNT), bisphenol A (BPA) and 2,4,6-triclofen (2,4,6-TCP) and the results showed the degradation efficiency could reach 90 % or more. Additionally, the application of catalysts in different actual water samples and the ability of reuse were tested. Based on the strategies of bimetallic synergy and morphology control, Fe-based bimetallic oxides with 3D morphology were developed in this study, which could effectively enhance the catalytic activity and inhibit the dissolution of metal ions, providing the design ideas for the construction of efficient catalysts and the removal of complex organic pollutants.

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The sulfate radical-based advanced oxidation processes (SR-AOPs) is a promising method for the degradation of pollutants, with the development of highly efficient catalysts for persulfate activation has been widely concerned. The novel BiCoFe-LDH (BCF-x) was synthesized successfully by coprecipitation method, which can activate peroxydisulfate (PDS) efficiently to degrade aniline. Comparative analysis with pure CoFe-LDH revealed a remarkable increase in reaction rate constant by approximately 14.66 times; the degradation rate of aniline (10 mg/L) was 100% in 60 min with the condition of 0.5 g/L BCF-1.5 and 0.5 g/L PDS, due to BCF-1.5 which was characterized as a complex of CoFe-LDH and Bi2O2CO3, promoting electron transport to improve the efficiency of activated PDS. In the reaction system, SO4•-, ·OH, and 1O2 were responsible for the aniline degradation and ·OH was the primary one. Furthermore, this work proposes a reaction electron transfer catalytic mechanism, which provided a new insight and good application prospect for efficient activation of PDS for pollutant degradation.

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The development of cobalt-based supported catalysts with high PMS catalytic activity and stability by adjusting the composition of the support is highly desirable yet remains scarce. In the work, a series of catalysts (Co2AlO4/Al2O3-xSiO2) were prepared by impregnation and high-temperature calcination using Al2O3-xSiO2 with a low Si-Al ratio as the support. Measurement techniques such as XRD, XPS, UV-DRS, FTIR, BET, SEM and HRTEM were used to characterize textural and chemical properties (ratio of Co3+/Co2+, specific surface area, pore size, pore volume, etc.). The ratio of Co3+/Co2+ and pore volume of Co2AlO4/Al2O3-xSiO2 can be turned by controlling the ratio of Si to Al, which are closely related to the catalytic performance and reusability of the catalysts. The optimized catalyst (Co2AlO4/Al2O3-0.25SiO2) can completely degrade 10 mg/L p-nitrophenol (PNP) in 40 min in the pH range of 3-9 with excellent reusability. The effects of several reaction parameters (i.e., PMS dosage, Co2AlO4/Al2O3-0.25SiO2 dosage, reaction temperature, initial pH value, and inorganic ions) on PNP removal were comprehensively investigated. Sulfate radical (SO4•-) and singlet oxygen (1O2) are making a major contribution to the degradation of PNP. Moreover, a millimeter-scale catalyst (CoSiAl-0.25/Al2O3 pellet) was prepared by sol adsorption and high-temperature calcination method, which maintained high oxidation activity after treatment of 18 L wastewater (PNP of 10 mg/L) in a continuous flow process. The method is simple and easy to operate on a large scale, providing a new perspective on the design and preparation of cobalt-aluminum spinel catalysts for activated PMS.

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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.

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Due to the increasing of industrial plastic waste and its refractory characteristics, it is extremely urgent to develop new degradation technology and environmentally friendly catalyst for industrial plastic waste. Manganese oxides are one of the most promising candidates for the catalytic degradation of plastic wastes. However, an improved understanding of the structural properties affecting their catalytic activity is required for high-efficient wastewater treatment. We herein report the surface reactivity effects of δ-MnO2 structural defects with regards to Bisphenol A (BPA) degradation/probe in the presence of peroxymonosulfate (PMS). Four δ-MnOx samples with different Mn(III) contents (different Mn(III)-deficient sample) were prepared and their structural properties as well as surface reactivity were characterized by batch test, ESR and XAFS analysis. For the Mn(III)-deficient sample, BPA removal was principally affected by direct electron transfer, with the adsorbed BPA degraded following hydroxylation. In contrast, a small fraction of Mn(III) substitution in δ-MnO2 could significantly encouraged the activation of PMS to produce SO4-☐and ☐OH, and a BPA degradation via beta scission. Moreover, the Mn(III)-rich δ-MnO2 demonstrate a high BPA removal rate even with a low sample load, which performed well following a reuse of five times. Our results provide a new way for the improvement of δ-MnO2 activity for the use of industrial plastic wastes treatment.

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Sulfate radicals (SO4-·) play important biological roles in biomedical and environmental engineering, such as antimicrobial, antitumor, and disinfection. Compared with other common free radicals, it has the advantages of a longer half-life and higher oxidation potential, which could bring unexpected effects. These properties have prompted researchers to make great contributions to biology and environmental engineering by exploiting their properties. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) are the main raw materials for SO4-· formation. Due to the remarkable progress in nanotechnology, a large number of nanomaterials have been explored that can efficiently activate PMS/PDS, which have been used to generate SO4-· for biological applications. Based on the superior properties and application potential of SO4-·, it is of great significance to review its chemical mechanism, biological effect, and application field. Therefore, in this review, we summarize the latest design of nanomaterials that can effectually activate PMS/PDS to create SO4-·, including metal-based nanomaterials, metal-free nanomaterials, and nanocomposites. Furthermore, we discuss the underlying mechanism of the activation of PMS/PDS using these nanomaterials and the application of SO4-· in the fields of environmental remediation and biomedicine, liberating the application potential of SO4-·. Finally, this review provides the existing problems and prospects of nanomaterials being used to generate SO4-· in the future, providing new ideas and possibilities for the development of biomedicine and environmental remediation.

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There are numerous studies concerning the impacts of widespread microplastic pollution on the ecological environment, and it shows synergistic effect of microplastics and co-exposed pollutants in risk enhancement. However, the control methods for removing harmful pollutants from microplastic surface to reduce their ecological toxicity has rarely been explored. In this paper, magnetic graphitized biochar as a catalyst is shown to achieve 97% removal of tetrabromobisphenol A (TBBPA) from microplastics by biochar mediated electron transfer. The changes in the surface and structure of microplastics caused by various aging processes affected the pollutant attachment and subsequent removal efficiency. After chlorination, the highest disinfection by-product (DBP) generation potential was observed by the group of microplastics attached with TBBPA. The oxidation system of biochar activating peroxodisulfate (PDS) can not only reduce the kinds of DBPs, but also greatly reduce the total amount of detected DBPs by 76%, as well as reducing the overall toxicity. This paper highlights an overlooked contribution of pollutant attachment to the potential risks of DBP generated from natural microplastics during chlorination process, and provides the underlying insights to guide the design of a biochar-based catalyst from wastes to achieve the removal of TBBPA from microplastics and reduce the risks and hazards of co-contamination.

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Biochar from spent malt rootlets was employed as the template to synthesize hybrid biochar-ceria materials through a wet impregnation method. The materials were tested for the activation of persulfate (SPS) and subsequent degradation of sulfamethoxazole (SMX), a representative antibiotic, in various matrices. Different calcination temperatures in the range 300-500 °C were employed and the resulting materials were characterized by means of N2 adsorption and potentiometric mass titration as well as TGA, XRD, SEM, FTIR, DRS, and Raman spectroscopy. Calcination temperature affects the biochar content and the physicochemical properties of the hybrid materials, which were tested for the degradation of 500 µg L-1 SMX with SPS (in the range 200-500 mg L-1) in various matrices including ultrapure water (UPW), bottled water, wastewater, and UPW spiked with bicarbonate, chloride, or humic acid. Materials calcined at 300-350 °C, with a surface area of ca. 120 m2 g-1, were the most active, yielding ca. 65% SMX degradation after 120 min of reaction in UPW; materials calcined at higher temperatures as well as bare biochar were less active. Degradation decreased with increasing matrix complexity due to the interactions amongst the surface, the contaminant, and the oxidant. Experiments in the presence of scavengers (i.e., methanol, t-butanol, and sodium azide) revealed that sulfate and hydroxyl radicals as well as singlet oxygen were the main oxidative species.

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As a clean and efficient technology for the degradation of organic contaminants, sulfate radical based advanced oxidation processes (SR-AOPs) have attracted more and more attention in the past decades. Cobalt is regarded as the most reactive and efficient non-noble metal catalyst for the activation of persulfate including peroxymonosulfate (PMS) and peroxydisulfate (PDS) to produce sulfate radicals. Due to the limitations of homogeneous catalytic systems, the heterogeneous cobalt-containing catalysts have been emerged and rapidly developed. Various strategies have been schemed to further enhance the activation ability of persulfate by heterogeneous cobalt-containing catalysts. This paper provides an overview on the recent progress in enhancement strategies for the highly efficient activation of persulfate by heterogeneous cobalt-containing catalysts. With a brief introduction on the chemistry and feature of sulfate radical reactions catalyzed by homogeneous Co2+/Co3+ species, the main strategies for enhancing persulfate activation by heterogeneous cobalt-containing catalysts are summarized, such as surface and morphology design, multiple reactive centers design, organic-inorganic hybrids and heterostructure composites. Future perspectives of heterogeneous SR-AOPs systems catalyzed by cobalt-containing catalysts are outlined.

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The presence of a large number of micropollutants in the environment, including priority and emerging substances, poses a significant risk to surface and groundwater quality. Among them, trichlorobenzenes are widely used in the syntheses of dyes, pesticides, solvents, and other chemicals and have been identified as priority pollutants by the European Water Framework Directive. The main goal of this study was to investigate the behavior of 1,2,3-trichlorobenzene (TCB) during the sulfate radical-based advanced oxidation processes (SR-AOPs) involving UV activation of persulfate or peroxymonosulfate (UV/S2O82- and UV/HSO5- processes). For this purpose, TCB was subjected to SR-AOPs in synthetic water matrices containing humic acids or hydrogencarbonate and natural water samples and a comparative evaluation of the degradation process was made. The toxicity of the oxidation by-products was also assessed. The evaluation of TCB degradation kinetics results using principal component analysis indicates that the efficacy of the SR-AOPs was highly dependent on the pH, initial oxidant concentration, UV fluence, and matrix characteristics. In natural waters, TCB degradation by the UV/S2O82- process proved to be most effective in acidic conditions (pH 5), while the UV/HSO5- process showed the highest efficacy in basic conditions (pH 9.5), achieving a maximum TCB degradations of 97-99%. The obtained results indicate that UV/S2O82- and UV/HSO5- as new generation oxidation processes have significant potential for TCB removal from water and result in only minor toxicity after treatment (14-23% of Vibrio fischeri bioluminescence inhibition).

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In this study, a sulfate radical-advanced oxidation process (SR-AOP) was proposed by utilizing a bimetallic Co/Fe metal-organic frameworks/cellulose nanofiber membrane (Co/Fe bi-MOFs/CNF) as a catalyst for TBBPA degradation. Sulfate radicals (SO4-) and hydroxyl radicals (OH·) were generated through the activation of peroxymonosulfate (PMS) by Co/Fe bi-MOFs/CNF. Co/Fe bi-MOFs/CNF was prepared by a facile solvothermal method and vacuum filtration. CNF acted as a natural substrates material to relieve the agglomeration of loaded MOFs. Additionally the composite membranes was easily separated from the reaction solution. The properties of the composite materials and the main factors that influenced TBBPA degradation were elucidated in detail, along with the TBBPA degradation intermediates, recyclability, and TBBPA degradation pathway. Almost 100 % of TBBPA was degraded within 30 min under optimal conditions, and the rate constant was determined to be 0.764 min-1. Furthermore, the degradation rate of the composite membrane was 60 % after 4 cycles.

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In the present study, biochar from spent coffee grounds was synthesized via pyrolysis at 850 °C for 1 h, characterized and employed as catalyst for the degradation of sulfamethoxazole (SMX) by persulfate activation. A variety of techniques, such as physisorption of N2, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and potentiometric mass titration, were employed for biochar characterization. The biochar has a surface area of 492 m2/g, its point of zero charge is 6.9, while mineral deposits are limited. SMX degradation experiments were performed mainly in ultrapure water (UPW) at persulfate concentrations between 100 and 1000 mg/L, biochar concentrations between 50 and 200 mg/L, SMX concentrations between 500 and 2000 µg/L and initial solution pH between 3 and 10. Real matrices, besides UPW, were also tested, namely bottled water (BW) and treated wastewater (WW), while synthetic solutions were prepared spiking UPW with bicarbonate, chloride, humic acid or alcohols. Almost complete removal of SMX can be achieved using 200 mg/L biochar and 1000 mg/L sodium persulfate (SPS) within 75 min. The presence of biochar is important for the degradation process, while the activity of the biochar increases linearly with SPS concentration. Degradation follows a pseudo-order kinetic model and the rate increases with increasing biochar concentration and decreasing SMX concentration. Although SMX adsorption onto the biochar surface is favored at acidic conditions, degradation proceeds equally fast regardless of the initial solution pH. Reactions in either real matrix are slower, resulting in 55% SMX removal in 60 min for WW. Bicarbonate causes severe inhibition as only 45% of SMX can be removed within 75 min in UPW. The addition of alcohol slightly inhibits degradation suggesting that the reaction pathway is either under electron transfer control or due to the generation of surface oxygen radicals with higher oxidation potential than the homogeneously produced radicals.

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Natural-aged microplastics with changed surface properties accumulate, redistribute and spread in all water fields as carriers of hazardous substances. The combined hazard of co-contamination of microplastics and hazardous substances expands the ecological risks, which urgently needs to design treatment schemes for pollutant removal from microplastics. In this paper, a facile and applicable magnetic biochar with porosity and graphitization (PGMB) was prepared for realizing the goal of metal removal from the microplastics. Heterogeneous catalysis of persulfate (PS) activated by PGMB achieved the decomposition of organics, with the decrease of more than 60% of the attached Pb on the surface of microplastics, and the adsorbed metal amount by PGMB in this system (31.29 mg/g) is much higher than that by the individual PGMB group (7.07 mg/g). Analysis demonstrated that the organic layer covered on the microplastic surface over the long-term weathering provided the key sites for metal sorption, whose decomposition and peeling were the critical steps in whole process. The prepared PGMB was responsible for activating PS to produce reactive species for decomposing the organic matter accompanied with detaching metals from microplastic surface, also would keep the role for re-adsorption of the released metals and separation from aqueous phase by magnetic force. The influences of natural environmental factors including salinity, common matrix species, and temperature on the performance of PGMB/PS system for metal removal from microplastics were discussed to illustrate the universality of the scheme in saline or organic-rich waters. The results of this study provided underlying insights for removing metals from microplastic surface, and decreasing the harm risks in the co-contamination of microplastics and hazardous substances.

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This study explores the enhancement of UV-C tertiary treatment by sulfate radical based Advanced Oxidation Processes (SR-AOPs), including photolytic activation of peroxymonosulfate (PMS) and persulfate (PS) and their photocatalytic activation using Fe(II). Their efficiency was assessed both for the inactivation of microorganisms and the removal or micropollutants (MPs) in real wastewater treatment plant effluents. Under the studied experimental range (UV-C dose 5.7-57 J/L; UV-C contact time 3 to 28 s), the photolysis of PMS and PS (0.01 mM) increased up to 25% the bacterial removal regarding to UV-C system. The photolytic activation of PMS led to the total inactivation of bacteria (≈ 5.70 log) with the highest UV-C dose (57 J/L). However, these conditions were insufficient to remove the MPs, being required oxidant's dosages of 5 mM to remove above 90% of carbamazepine, diclofenac, atenolol and triclosan. The best efficiencies were achieved by the combination of PMS or PS with Fe(II), leading to the total removal of the MPs using a low UV-C dosage (19 J/L), UV-C contact time (9 s) and reagent's dosages (0.5 mM). Finally, high mineralization was reached (>50%) with photocatalytic activation of PMS and PS even with low reagent's dosages.

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Algal extracellular organic matter (EOM) released from Microcystis aeruginosa can cause severe membrane fouling during algae-laden water treatment. To solve this problem, three typical sulfate radical-based advanced oxidation processes (SR-AOPs), i.e., ferrous iron/peroxymonosulfate (Fe(II)/PMS), UV/PMS and UV/Fe(II)/PMS, were employed as membrane pretreatment strategies. Their performance on mitigating EOM fouling of a ceramic UF membrane was systematically investigated and compared in the present study. The results indicated that SR-AOPs pretreatments could promote the reduction of DOC and UV254, and the removal performance showed an apparent regularity of UV/Fe(II)/PMS > Fe(II)/PMS > UV/PMS. The pretreatments were very effective for decomposing high-MW biopolymers (>20,000 Da) into low-MW humic substances (1000-20,000 Da), thus reducing the accumulation of high-MW biopolymers on membrane surface. With respect to membrane fouling control, Fe(II)/PMS significantly mitigated both reversible and irreversible membrane fouling, whereas UV/PMS only reduced reversible fouling, and exhibited little effect on irreversible fouling. By contrast, UV/Fe(II)/PMS showed the best performance for fouling reduction due to the synergistic effect of UV and Fe(II) for PMS activation. The dominating fouling mechanism was governed by both pore blockage and cake filtration, likely due to the bimodal MW distribution of EOM, and SR-AOPs pretreatments delayed the transition from pore blockage to cake filtration. In addition, SR-AOPs prior to UF membrane were also very effective to improve the removal of micropollutants (i.e., ATZ, SMT and p-CNB). These results demonstrate the potential application of SR-AOPs as pretreatment for membrane fouling control during algae-laden water treatment.

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