Sulfate Radical-based Advanced Oxidation Research Articles

Towards removal of PPCPs by advanced oxidation processes: A review

The continuous influx of emerging contaminants (ECs) into water bodies poses a significant threat to human health. Among these contaminants, pharmaceuticals and personal care products (PPCPs) are of particular concern due to their potential to exert adverse effects even at low concentrations. Therefore, it is imperative to explore methods for their effective removal or reduction to safeguard both human health and the ecological environment. Advanced oxidation processes (AOPs) have received substantial attention as promising treatment methods. AOPs are capable of efficiently treating water by generating reactive oxygen species (ROS) with potent oxidation properties, which can effectively eliminate various contaminants. This review delves into the diverse range of AOPs available, including ozonation, photocatalytic oxidation, the Fenton process, electrochemical oxidation, sulfate radicals-based advanced oxidation processes (SR-AOPs), and more. It also discusses the respective limitations and future prospects of these processes, aiming to provide insights into their potential for addressing the pressing issue of PPCP contamination in water bodies.

Cobalt oxide functionalized ceramic membrane for 4-hydroxybenzoic acid degradation via peroxymonosulfate activation

Membrane separation and sulfate radicals-based advanced oxidation processes (SR-AOPs) can be combined as an efficient technique for the elimination of organic pollutants. The immobilization of metal oxide catalysts on ceramic membranes can enrich the membrane separation technology with catalytic oxidation avoiding recovering suspended catalysts. Herein, nanostructured Co3O4 ceramic catalytic membranes with different Co loadings were fabricated via a simple ball-milling and calcination process. Uniform distribution of Co3O4 nanoparticles in the membrane provided sufficient active sites for catalytic oxidation of 4-hydroxybenzoic acid (HBA). Mechanistic studies were conducted to determine the reactive radicals and showed that both SO4•− and •OH were present in the catalytic process while SO4•− plays the dominant role. The anti-fouling performance of the composite Co@Al2O3 membranes was also evaluated, showing that a great flux recovery was achieved with the addition of PMS for the fouling caused by humic acid (HA).

Fabrication of CoFe2O4/Mn3O4 decorated ultrathin graphitic carbon nitride nanosheets membrane for persistent organic pollutants removal: Synergistic performance and mechanisms

Integration of sulfate radicals-based advanced oxidation processes (SR-AOPs) with separation membranes has enthralled considerable attentions because it can remove persistent toxic micropollutants in a low-energy and cost-effective manner. However, fabrication of such an integrated membrane simultaneously with excellent self-cleaning property, catalytic capability and long-term durability remains a challenge. Herein, for the first time, CoFe2O4 (CFO) and Mn3O4 (MO) nanoparticles were anchored on ultrathin graphitic carbon nitride (UCN) nanosheets via a solvothermal method to prepare heterogeneous Fenton-like catalysts (MO/CFOUCN). Systematic characterizations demonstrated the successful preparation of powder catalysts with favorable degradation ability. Notably, the optimal composite catalyst possessed satisfactory degradation (94.5 %) and kinetic rate (0.1367 min−1) for norfloxacin (NOR) within 30 min. Thereafter, an integrated MO/CFO/UCN@P membrane was fabricated by vacuum-assisted filtration of the catalyst on a supporting membrane surface. It was interestingly found that, benefiting from the synergistic effect of in-situ oxidation and membrane filtration, activating peroxymonosulfate (PMS) endowed the membrane with high removal rates (over 91.8 % for tetracycline, bisphenol A, humic acid (HA)) and high permeation flux (332.7 L·m−2·h−1) driven solely by gravity. Significantly, the membrane achieved a flux recovery rate of 91.9 % with the assistance of PMS after filtering HA solution. Furthermore, quenching experiments and electron paramagnetic resonance (EPR) tests confirmed that both radical and nonradical pathways contributed to the mineralization of NOR. Based on the detection of intermediates in the degradation process, potential NOR degradation pathways were proposed. Overall, this study provided new ideas about integrating Fenton-like catalysts with membrane technology for removal of persistent organic pollutants.

Overlooked involvement of phosphate radicals in the degradation of the atrazine herbicide by sulfate radical-based advanced oxidation

Overlooked involvement of phosphate radicals in the degradation of the atrazine herbicide by sulfate radical-based advanced oxidation

One-step synthesis of natural montmorillonite/hematite composites with enhanced persulfate catalytic activity for sulfamethoxazole degradation: Efficiency, kinetics, and mechanism

Along with rapid development of sulfate radicals-based advanced oxidation process, efficient, alternatively eco-friendly and cost-effective catalyst is of uppermost priority. However, expensive chemicals are used as source of metal in most of these catalysts, and lose sight of the abundant natural mineral resources on immediate surroundings. In this work, montmorillonite and hematite, two of abundantly natural minerals were utilized to prepare a persulfate catalyst (TMH@M) for sulfamethoxazole (SMX) degradation. The results indicated more than 91% of SMX was removed within 60 min in TMH@M/PS system. The degradation efficiency of SMX of TMH@M/PS combined system was impacted by SMX concentration, PS dosage and natural organic matters, and can remain stable in a certain concentration of HA/chelating agent and a wide pH range (3.01–9.06). Radical scavenging and EPR tests demonstrated 1O2, OH, and SO4- were major reactive oxygen species in the TMH@M/PS system, while the latter seems more important for degradation of SMX. The results of SEM-EDS, XRD and XPS conformed that low valence iron species (Fe0, Fe2+ and Fe3O4) on TMH@M surface are the main driving force behind PS activation to generate reactive species. Furthermore, the iron species on TMH@M surface were transformed during reaction, that in favor of mitigating metal leaching. This work presented a method based on ubiquitous natural minerals to prepare catalyst with excellent PS activate performance for organic wastewater treatment implying a new strategy in minerals utilization deeply and a promisingly alternative process for organic wastewater treatment based on mineral materials.

Persulfate Process Activated by Homogeneous and Heterogeneous Catalysts for Synthetic Olive Mill Wastewater Treatment

Wastewaters from the olive oil industry are a regional environmental problem. Their phenolic content provides inherent toxicity, which reduces the treatment potential of conventional biological systems. In this study, Sulfate Radical based Advanced Oxidation Processes (SRbAOPs) are compared with advanced oxidation processes (namely Fenton’s peroxidation) as a depuration alternative. Synthetic olive mill wastewaters were submitted to homogeneous and heterogeneous SRbAOPs using iron sulfate and solid catalysts (red mud and Fe-Ce-O) as the source of iron (II). The homogenous process was optimized by testing different pH values, as well as iron and persulfate loads. At the best conditions (pH 5, 300 mg/L of iron and 600 mg/L of persulfate), it was possible to achieve 39%, 63% and 37% COD, phenolic compounds and TOC removal, respectively. The catalytic potential of a waste (red mud) and a laboratory material (Fe-Ce-O) was tested using heterogenous SRbAOPs. The best performance was achieved by Fe-Ce-O, with an optimal load of 1600 mg/L. At these conditions, 27%, 55% and 5% COD, phenolic compounds and TOC removal were obtained, respectively. Toxicity tests on A. fischeri and L. sativum showed no improvements in toxicity from the treated solutions when compared with the original one. Thus, SRbAOPs use a suitable technology for synthetic OMW.

Targeted accumulation and spatial confinement effect of Fe(II)-MOFs@MIP for efficiently removing low concentration dibutyl phthalate

Sulfate radicals-based advanced oxidation processes are regarded as effective methods for removing organic contaminants. However, current removal technologies are often unable to achieve satisfactory results due to the low concentrations and high stability that are frequently characteristics for many types of organic contaminants. To improve the efficacy of using sulfate radicals to remove organic contaminants, we designed metal–organic frameworks (Fe(II)-MOFs) modified with enrichment and specific recognition of molecular imprinting layer (Fe(II)-MOFs@MIP). Using dibutyl phthalate (DBP) as the model target contaminant, the selectivity coefficient towards DBP was 7.28 for adsorption and 4.46 for catalytic degradation of Fe(II)-MOFs@MIP, which is excellent for most of the imprinted material. Additionally, we achieved the accurate recognition (169.25 μg × g−1) and efficient degradation (0.071 min−1) of DBP reducing levels to 100 μg × L-1. UV–vis analysis confirmed that specific recognition of DBP was mainly through hydrogen bonding and π-π interaction, while in-situ Raman and radical quenching experiments showed that the imprinting layer could accurately adsorb and produce the spatial confinement effects on target contaminants, thereby reducing the transfer distance of free radicals. As a result, we show that Fe(II)-MOFs@MIP can achieve efficient targeted degradation of DBP, opening up a new avenue for the removal of this and other highly stable organic contaminants present at low concentrations in environmental systems.

Trace Co2+ coupled with phosphate triggers efficient peroxymonosulfate activation for organic degradation

Cobalt-mediated activation of peroxymonosulfate (PMS) has been widely used to remove the refractory organic pollutants from contaminated waters. However, the residual cobalt usually at a trace level inevitably brings about secondary pollution to be disposed of. In this study we found that the presence of phosphate could trigger a more efficient catalytic activation of PMS at trace Co2+ dosages (0.17–1.7 μM). Fast degradation of atrazine (ATZ) was observed in the Co2+/PMS/phosphate system, with the pseudo first-order kinetic rate constant as high as 5.4 and 15.4 times that in Co2+/PMS and phosphate/PMS systems respectively under otherwise similar conditions. The presence of phosphate promoted the production of sulfate radical (SO4·-), accompanying the enhanced formation of by-product 1O2 simultaneously. Using a competition reaction kinetics approach, the contribution of SO4·- to ATZ oxidation was determined as 96.5%, suggesting that SO4·- was the main reactive species responsible for ATZ removal. Such favorable effect was partially ascribed to the specific ligand structure of six coordination structure between phosphate and cobalt, which facilitated electron transfer in the CoIII/CoII reduction. In addition, it was dependent upon the aqueous phosphate levels, and low level (< 0.5 mM) was insufficient to drive the CoIII/CoII cycle, whereas the higher level (> 15 mM) showed negative effect since the excessive phosphate could quench SO4·- and·OH. This study is believed to advance the fundamental understanding of the ligand effect on the cobalt-mediated sulfate radicals-based advanced oxidation process.

UV light-assisted persulfate activation by Cu0-Cu2O for the degradation of sulfamerazine

Sulfate radicals-based advanced oxidation process (SRAOP) has received increasing attention in the wastewater treatment area because sulfate radicals have high redox potential. The key for SRAOP is to develop high efficient catalysts that can effectively and stably activate persulfate (PS) to produce sulfate radicals. Cu2O is a good activator of PS and photo-catalyst. However, its catalytic activity is relatively low because of the poor stability and the recombination of electron and holes. In theory, Cu0 can reduce Cu2+ to form Cu+, which can decrease the recombination of electron and holes from the Cu2O by the formation of heterojunction. In this study, Cu0-Cu2O was synthesized by a simple ball-milling method. The as-prepared Cu0-Cu2O was characterized and used to activate PS for sulfamerazine (SMZ) degradation by means of UV illumination. In the Cu0-Cu2O/PS/UV system, the removals of 100% SMZ and 30% TOC within 30 min were achieved, respectively, and the removal efficiency of SMZ decreased by only 12.2% after 5 cycles. The high efficiency and good catalytic stability of Cu0-Cu2O for the activation of PS were due to that Cu0 and photo-induced electron of Cu2O promoted the conversion of Cu2+ to Cu+. Quenching experiments demonstrated that the hydroxyl radicals and sulfate radicals contributed to SMZ degradation. However, the concentrations and fractions of radicals was affected by the initial pH of solution. Nine intermediate products were identified, and the degradation pathways were proposed, including the fission of sulfur and nitrogen bond, the oxidation of methyl group and the hydroxylation of benzene ring. The effects of initial pH, PS concentration, Cu0-Cu2O dosage and SMZ initial concentration on the degradation of SMZ were investigated. This study provided an effective catalyst that could simultaneously activate PS and utilize UV to form photo-induced electron, which could enhance the degradation and mineralization of organic pollutants.

Efficient activation of peroxymonosulfate by a novel catalyst prepared directly from electrolytic manganese slag for degradation of recalcitrant organic pollutes

Preparations of catalysts for sulfate radicals-based advanced oxidation (SR-AOPs) are usually time-consuming and costly. This study developed a short-cut method for preparation of AOPs catalyst (MS-N3H) directly from electrolytic manganese slag. MS-N3H/PMS could effectively remove levofloxacin (LVF) from solution. Phase transformation and active sites exposure after modifications facilitated the adsorption and catalysis capacities. Both radical and non-radical pathway contributed to the degradation of LVF, in which abundant Mn and Fe on MS-N3H surface contributed to the generation of SO4−, OH and O2− radicals, and lattice oxygen played a crucial role in non-radical 1O2 production. The MS-N3H/PMS was stable for the degradation of LVF in different water matrixes and kept high recyclability even after four recycles. This study brought underlying insights to develop novel high-efficient and easy-preparing catalysts for the degradation of recalcitrant organic pollutes.

Degradation of phenanthrene by peroxymonosulfate activated with bimetallic metal-organic frameworks: Kinetics, mechanisms, and degradation products

In this study, bimetallic metal-organic frameworks (FeCo-BDC) containing the (BDC = 1,4-benzenedicarboxylic acid) metalloligand unit, linked by Fe(II) and Co(II) cations, were synthesized successfully with different stoichiometric ratio of precursors. FeCo-BDC were investigated by XRD, FT-IR, SEM, XPS, ICP-MS, BET, and TEM techniques. Effects of stoichiometric ratio of precursors, peroxymonosulfate (PMS) concentrations, catalyst dosages, and initial pH on the phenanthrene degradation were evaluated. The results indicated that 99.0% of phenanthrene removal efficiency was achieved at pH 3.15, 50 mg/L FeCo-BDC-2, 0.6 mM PMS, 1.0 mg/L phenanthrene and 30 min reaction time. Based on the scavenger experiments and electron paramagnetic resonance (EPR) analyses, SO4−, OH, and O2− were identified as the dominant Reactive Oxygen Species (ROS) and responsible for the phenanthrene degradation. It was interesting to find that the signals of DMPO-OH/SO4− transformed to DMPOX with the addition of tert butyl alcohol (TBA). The intermediate products of phenanthrene were identified by GC–MS and the possible degradation pathway was proposed, whereas two intermediates containing sulfur atom were detected for the first time in the Sulfate Radicals-based Advanced Oxidation Processes (SR-AOPs). These interesting findings will guide the development of metal-organic frameworks as catalysts of PMS and enrich our understanding of the SR-AOPs for wastewater treatment.

Degradation of phenol by coal-based carbon membrane integrating sulfate radicals-based advanced oxidation processes

Phenol, as a representative organic pollutant in aquatic environments, has posed a serious threat to humans and ecosystem. In this work, a novel integration system combined coal-based carbon membrane with sulfate radicals-based advanced oxidation processes (SR-AOPs) was designed for degradation of phenol. The integrated system achieved 100% removal efficiency under the optimal condition (peroxydisulfate dosage is 0.2 g/L, at alkaline condition with 2 mL/min flow velocity). The quenching experiments revealed that the efficient removal of phenol by the integrated system were attributed to the co-existence of radical and nonradical mechanisms. This study proposes a green and efficient technique for the removal of phenol.

Novel NiCo2S4/CS membranes as efficient catalysts for activating persulfate and its high activity for degradation of nimesulide

In recent years, sulfate radicals-based advanced oxidation process becomes an effective and common technique for elimination of emerging organic contaminants. In this study, novel NiCo2S4/CS composite was synthesized through hydrothermal method, with the physicochemical properties being characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microcopy (TEM), Brunauer-Emmett-Teller (BET) and Fourier Transform infrared spectroscopy (FT-IR). Then, NiCo2S4/CS composite acted as catalyst to activate PS for nimesulide degradation. The results showed that NiCo2S4/CS composite owned the highest activity compared with pure NiCo2S4 and carbon sphere (CS), achieving 92% nimesulide degradation in 10 min with 0.1 g/L catalyst and 0.4 g/L persulfate. Furthermore, the NiCo2S4/CS membrane was fabricated by vacuum filtration, and 94% and 80% above nimesulide degradation were realized for the first time and after six times repeated experiment, which demonstrated that the catalyst was convenient to achieve recovery and reusability. In addition, the radical quenching experiment, XPS and the electrochemical methods (LSV and EIS) were measured to investigate the possible mechanism pathway, the results of which showed that both the non-radical pathway and radical pathway might attribute to nimesulide degradation, while the SO4− remained the dominant species. This research provided a novel sulfide NiCo2S4/CS membrane for the oxidative technique for emerging organic contaminants in water treatment.

Metal-Organic Frameworks and Their Derived Materials: Emerging Catalysts for a Sulfate Radicals-Based Advanced Oxidation Process in Water Purification.

With the ever-growing environmental issues, sulfate radical (SO4•- )-based advanced oxidation processes (SR-AOPs) have been attracting widespread attention due to their high selectivity and oxidative potential in water purification. Among various methods generating SO4•- , employing heterogeneous catalysts for activation of peroxymonosulfate or persulfate has been demonstrated as an effective strategy. Therefore, the future advances of SR-AOPs depend on the development of adequate catalysts with high activity and stability. Metal-organic frameworks (MOFs) with large surface area, ultrahigh porosity, and diversity of material design have been extensively used in heterogeneous catalysts, and more recently, enormous effort has been made to utilize MOFs-based materials for SR-AOPs applications. In this work, the state-of-the-art research on pristine MOFs, MOFs composites, and their derivatives, such as oxides, metal/carbon hybrids, and carbon materials for SR-AOPs, is summarized. The mechanisms, including radical and nonradical pathways, are also detailed in the discussion. This work will hopefully promote the future development of MOFs-based materials toward SR-AOPs applications.

Enhanced removal of lomefloxacin based on peroxymonosulfate activation by Co3O4/δ-FeOOH composite

In the present study, a novel Co3O4/δ-FeOOH composite was successfully fabricated. Subsequently, we measured its crystal structure, morphology, and surface area. After this, the Co3O4/δ-FeOOH composite was applied to activate peroxymonosulfate (PMS) for lomefloxacin (LOM, a type of fluoroquinolones) degradation. Compared with pure Co3O4 and δ-FeOOH, Co3O4/δ-FeOOH composite exhibited the best efficiency towards LOM degradation, in which the removal of LOM (>82%) and first order reaction kinetic rate constant (kapp = 0.064 min−1) were achieved after 25 min reaction with 0.25 g·L−1 Co3O4/δ-FeOOH, 0.49 mM PMS, and 10 mg·L−1 (28.5 μM) LOM at initial pH 6.08. Next, we considered the concentration of catalyst, PMS and the effect of pH on LOM degradation. The results showed that the increase of PMS and catalyst was beneficial for the degradation of LOM. Moreover, the highest degradation efficiency of LOM was achieved under neutral conditions, which was due to the minimum repulsive force between the PMS and the catalyst. In addition, active radical scavenging experiment was performed and it was found that the contribution of hydroxyl radicals was greater than that of sulfate radicals. Subsequently, possible reaction mechanism was proposed. What’s more, possible degradation intermediates in Co3O4/δ-FeOOH system were determined and five decomposition pathways were proposed. Meanwhile, activated sludge inhibition experiment was carried out to evaluate the variation of toxicity of the LOM and its degradation intermediates in the oxidation process. Overall, this work provided a new strategy for the practical application of sulfate radicals-based advanced oxidation processes (SR-AOPs) in wastewater treatment.

Treatment of bitumen post oxidative effluents by sulfate radicals based advanced oxidation processes (S-AOPs) under alkaline pH conditions

Abstract Sulfate radicals based Advanced Oxidation Processes (S-AOPs), namely Persulfate and peroxymonosulfate, were used for the treatment of post oxidative effluents from a production of petroleum bitumens under alkaline pH. Studies on the identification and monitoring of the volatile organic compounds (VOCs) along with COD, BOD and sulfide ions reduction were performed. Persulfate with a ratio between the oxygen from the oxidant and the COD in the effluents (rox) of 1.28 at 60 °C achieved 33% and 55% reduction of COD and BOD respectively. Peroxymonosulfate with a rox of 1.43 at 60 °C was the most effective S-AOP studied with 43% COD and BOD reduction. Sulfide ions were effectively oxidized in both technologies. Persulfate at lower rox 0.41 at 40 °C was the best process to treat VOCs. A detailed analysis of the effluents composition after treatment revealed VOCs by-product formation. Economical evaluation revealed that persulfate based processes were cheaper. Activation of PS and PMS by heat can occur but effectiveness of this method of activation is low. S-AOPs revealed to be effective as a pre-treatment method in terms of VOCs degradation. These studies also proved that a secondary treatment is mandatory for a cleaner production of petroleum bitumens.

Intensification of UV-C tertiary treatment: Disinfection and removal of micropollutants by sulfate radical based Advanced Oxidation Processes.

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.

Thermally activated persulfate (TAP) oxidation of antiepileptic drug carbamazepine in water

Sulfate radicals-based advanced oxidation processes have been applied in water treatment and in situ chemical oxidation. Batch experiments were conducted to investigate the influencing factors including persulfate dosage, initial carbamazepine (CBZ) concentrations, solution pH, coexisting inorganic anions and cations on the decomposition of CBZ using thermally activated persulfate (TAP) technology. The results showed that TAP oxidation was efficient process for the CBZ degradation in water. The generation of sulfate radicals was accounted for the CBZ degradation in TAP system. The CBZ degradation rate constant increased as persulfate dosage increased and decreased as the initial CBZ concentrations increased. The CBZ decomposition rate decreased with the increasing pH and the best degradation occurred at pH 3. The exception was the strong alkaline condition under which a higher CBZ degradation performance was achieved. Coexisting inorganic anions slowed down the CBZ degradation to different degrees and the inhibiting effect abided by the following order: CO32->HCO3->Cl->SO42->NO3-. In contrast, coexisting cations could significantly enhance the CBZ degradation, and the promoting effect was in the order of Fe2+>Cu2+>Fe3+. In this study, six major intermediate products were generated during the TAP oxidation.