Efficient degradation of anthracene in soil by carbon-coated nZVI activated persulfate

Towards advanced removal of organics in persulfate solution by heterogeneous iron-based catalyst: A review

Heterogeneous iron-based catalysts have drawn increasing attention in the advanced oxidation of persulfates due to their abundance in nature, the lack of secondary pollution to the environment, and their low cost over the last a few years. In this paper, the latest progress in the research on the activation of persulfate by heterogeneous iron-based catalysts is reviewed from two aspects, in terms of synthesized catalysts (Fe0, Fe2O3, Fe3O4, FeOOH) and natural iron ore catalysts (pyrite, magnetite, hematite, siderite, goethite, ferrohydrite, ilmenite and lepidocrocite) focusing on efforts made to improve the performance of catalysts. The advantages and disadvantages of the synthesized catalysts and natural iron ore were summarized. Particular interests were paid to the activation mechanisms in the catalyst/PS/pollutant system for removal of organic pollutants. Future research challenges in the context of field application were also discussed.

A sustainable method for oxidizing phenanthrene in tropical soil using natural iron as a catalyst in a slurry phase reactor with persulfate assistance

The presence of impurities is a significant restriction to the use of natural iron minerals as catalysts in the advanced oxidation process (AOP), especially if applied for soil remediation. This study evaluated the catalytic activity of tropical soil, which has relatively low impurities and naturally contains iron, for the remediation of phenanthrene (PHE) contamination. The system showed good performance, and the best result was 81% PHE removal after 24 h under experimental conditions of pH 7, [PHE]0 = 300 mg/50 g soil, temperature 55 °C, air flow = 260 mL min-1, and [persulfate]0 = 20 mg kg-1, while the mineralization was 61%. Nevertheless, certain limitations were noted in the soil matrix following the remediation procedure, including the appearance of cracks in the soil aggregate, reduction in the crystal size of the soil particles, and decline in the iron and aluminium contents. The results confirmed that the radicals play a major role in the remediation process. SO4˙- was more dominant than O2˙-, while HO˙ played a minor role. Additionally, the by-products were detected by gas chromatography-mass spectroscopy (GC-MS), and the degradation pathway of PHE is proposed. Toxicity assessment tests were performed by using a computational method. In spite of the challenges, this research achieved notable progress in soil remediation, taking a significant step forward in implementing the AOP without catalysts to activate oxidants and remove PHE within the soil. Also, this approach supports sustainability by reducing the need for extra materials and providing an environmentally friendly way of soil remediation.

A comprehensive approach for the recycling of anode materials from spent lithium-ion batteries: Separation, lithium recovery, and graphite reutilization as environmental catalyst

The effective recovery of valuables from anodes coming from spent lithium-ion batteries (LIBs) is of great importance to ensure resource supply and reduce the environmental burden for recycling. In this work, a simple and low energy consumption roasting method was proposed by employing low-temperature eutectic NaOH-KOH as reaction medium, in order to simultaneously separate graphite from Cu foils, extract lithium from it and set it up for reuse as environmental catalyst through one-step water washing process. Our results show that polyvinylidene difluoride (PVDF) was effectively deactivated due to dehydrofluorination/carbonization at a relatively low temperature and short time (150 °C, 20 min) when a mass ratio of 1:1 for eutectic NaOH-KOH to spent LIBs anodes was used, yielding 97.3 % of graphite detached. Moreover, a remarkable lithium extraction efficiency of 93.2 % was simultaneously obtained. Afterwards, the reusability of the recycled graphite was tested by employing it as a catalyst for the treatment of a contaminant organic dye (Rhodamine B) in the presence of NaClO. Our results show that a superior NaClO activation was obtained with the addition of recycled graphite, being this fact closely associated to the abundant active sites formed during the long-term charging/discharging cycles in the original battery. The alkaline-mediated roasting process presented in this work presents an energy-saving scheme to efficiently recover useful components from spent anodes, whereas the reusability example highlighted a useful option for repurposing the severely damaged graphite as an environmental catalyst rather than disposing it in landfills, turning waste into a valuable material.

Chemical inertness conversion of carbon fraction in coal gangue via N-doping for efficient benzo(a)pyrene degradation

Efficient degradation of organic pollutants in complex media via advanced oxidation processes (AOPs) is still critical and challenging. Herein, nitrogen (N)-doped coal gangue (CG) catalysts (N-CG) with economic competitiveness and environmental friendliness were successfully synthesized to activate peroxymonosulfate (PMS), exhibiting ultrafast degradation performance toward benzo(a)pyrene (BaP) with 100.00 % and 93.21 % in contaminated solution and soil under optimized condition, respectively. In addition, 0.4 N-CG possessed excellent reusability toward BaP degradation with over 80.00 % after five cycles. However, BaP removal efficiency was significantly affected by some co-existing anions (HCO3- and SO42-) and humic acid (HA) in solution and soil, as well as inhibited under alkaline conditions, especially pH ≥ 9. According to the characterizations, N-doping could promote the generation of pyridinic N and graphitic N in N-CG via high-temperature calcination, which was conducive to produce hydroxyl radical (•OH), sulfate radical (SO4•-), superoxide radical (•O2-) and single oxygen (1O2). In 0.4 N-CG/PMS system, 1O2 and •O2- were proved to be the predominant reactive oxygen species (ROSs) in BaP degradation, as well as •OH and SO4•- made certain contributions. To sum up, this work provided a promising strategy for synthesis of CG-based catalysts by chemical inertness conversion of carbon fracture via N-doping for PMS activation and opened a novel perspective for environmental remediation of hydrophobic and hydrophilic contaminants pollution.

Degradation and mechanism of PAHs by Fe-based activated persulfate: Effect of temperature and noble metal

The accumulation of contaminants like PAHs in soil due to industrialization, urbanization, and intensified agriculture poses environmental challenges, owing to their persistence, hydrophobic nature, and toxicity. Thus, the degradation of PAHs has attracted worldwide attention in soil remediation. This study explored the effect of noble metal and temperature on the degradation of various polycyclic aromatic hydrocarbons (PAHs) in soil, as well as the types of reactive radicals generated and mechanism. The Fe-Pd/AC and Fe-Pt/AC activated persulfate exhibited high removal efficiency of 19 kinds of PAHs, about 79.95 % and 83.36 %, respectively. Fe-Pt/AC-activated persulfate exhibits superior degradation efficiency than that on Fe-Pd/AC-activated persulfate, due to the higher specific surface area and dispersity of Pt particles, thereby resulting in increased reactive radicals (·OH, SO4-· and ·OOH). Additionally, thermal activation enhances the degradation of PAHs, with initial efficiencies of 64.20 % and 55.49 % on Fe-Pd/AC- and Fe-Pt/AC-activated persulfate systems respectively, increasing to 76.05 % and 73.14 % with elevated temperatures from 21.5 to 50 °C. Metal and thermal activation facilitate S2O82- activation, generating reactive radicals, crucial for the degradation of PAHs via ring opening and oxygen hydrogenation reactions, yielding low-ring oxygen-containing derivatives such as organic acids, keto compounds, ethers, and esters. Furthermore, understanding the impact of parameters such as activation temperature and the types of noble metals on the degradation of PAHs within the activated persulfate system provides a theoretical foundation for the remediation of PAH-contaminated soil.

Advanced oxidation of polycyclic aromatic hydrocarbons in tropical soil: Self-catalytic utilization of natural iron contents in an oxygenation reactor supported with persulfate

The catalysts derived from natural iron minerals in the advanced oxidation process offer several advantages. However, their utilization in soil remediation is restricted due to the presence of soil impurities, which can inhibit the catalytic activity of these minerals. The soils in tropical regions exhibit lower organic matter content, limited cation exchange capacity, and are non-saline, this enhances the efficiency of utilizing natural iron minerals from tropical soil as a catalyst. In this regard, the catalytic potential of naturally iron-bearing tropical soil was investigated to eliminate phenanthrene (PHE), pyrene (PYR), and benzo[α]pyrene (B[α]P) using an oxygenated reactor supported with persulfate (PS). The system showed an efficient performance, and the removal efficiencies under the optimum conditions were 81 %, 73 %, and 86 % for PHE, PYR, and B[α]P, respectively. This indicated that the catalytic activity of iron was working efficiently. However, there were changes in the soil characteristics after the remediation process such as a significant reduction in iron and aluminum contents. The scavenging experiments demonstrated that HO• had a minor role in the oxidation process, SO4•- and O2•- emerged as the primary reactive species responsible for the effective degradation of the PAHs. Moreover, the by-products were monitored after soil remediation to evaluate their toxicity and to propose degradation pathways. The Mutagenicity test showed that two by-products from each PHE and B[α]P had positive results, while only one by-product of PYR showed positive. The toxicity tests of oral rat LD50 and developmental toxicity tests revealed that certain PAHs by-products could be more toxic from the parent pollutant itself. This study represents a notable progression in soil remediation by providing a step forward in the application of the advanced oxidation process (AOP) without requiring additional catalysts to activate oxidants and degrade pollutant PAHs from the soil.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·- generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

Electrochemical-enhanced nanoscale oxygen-vacancy CuFe2O4 to activate persulfate (E/oxygen-vacancy CuFe2O4/PS) for separation of Ebselen from wastewater

To enhance the catalytic activity of CuFe2O4 on PS, a nanoscale oxygen-vacancy CuFe2O4 was prepared by hydrogenation reduction technique to construct an advanced oxidation system of electrochemical-enhanced nanoscale oxygen-vacancy CuFe2O4-activated persulfate. Using Ebselen (EBS) as a model pollutant, the degradation efficiency, activation mechanism and degradation pathway were studied. The oxygen-vacancy CuFe2O4 was characterized and analysed by FESEM, EDS and XPS. The results show that under the optimal reaction conditions (PS = 0.8 g/L, oxygen-vacancy CuFe2O4 = 0.3 g/L, initial pH = 6.5), the removal rate of 20 mg/L EBS can reach 92% after reaction for 60 min, which proves that the formation of oxygen-vacancy changed the catalytic inertness of CuFe2O4 on PS. It is speculated that in the E/oxygen-vacancy CuFe2O4/PS system, the existence of oxygen holes enhances the electron transfer ability and reducibility of the catalyst, so the oxygen-vacancy CuFe2O4 can efficiently activate PS to degrade EBS. The quenching experiments show that both SO 4 ⋅ - and ⋅ OH are involved in the oxidation reaction as reactive radicals in the system, with SO 4 ⋅ - being the main reactive radical. In addition, both dissolved oxygen (DO) and anions in the solution inhibit the oxidative degradation of EBS by oxygen-vacancy CuFe2O4/PS system. Through GC-MS detection, a possible degradation pathway is proposed.

Tropical soil remediation from pyrene: Release the power of natural iron content in soil for the efficient oxidant's activation

Natural soil minerals often contain numerous impurities, resulting in comparatively lower catalytic activity. Tropical soils are viewed as poor from soil organic matter, cations, and anions, which are considered the main impurities in the soil that are restricted to utilizing natural minerals as a catalyst. In this regard, the dissolved iron and hematite crystals that presented naturally in tropical soil were evaluated to activate oxidants and degrade pyrene. The optimum results obtained in this study were 73 %, and the rate constant was 0.0553 h-1 under experimental conditions [pyrene] = 300 mg/50 g, pH = 7, T = 55 °C, airflow = 260 mL/min, [Persulfate (PS)] = 1.0 g/L, and humic acid (HA) ( % w/w) = 0.5 %. The soil characterization analysis after the remediation process showed an increase in moieties and cracks of the soil aggregate, and a decline in the iron and aluminium contents. The scavengers test revealed that both SO4•- and O2•- were responsible for the pyrene degradation, while HO• had a minor role in the degradation process. In addition, the monitoring of by-products, degradation pathways, and toxicity assessment were also investigated. This system is considered an efficient, green method, and could provide a step forward to develop low-cost soil remediation for full-scale implementation.

Efficient benzo(a)pyrene degradation by coal gangue-based catalytic material for peroxymonosulfate activation

A low cost and green peroxymonosulfate (PMS) activation catalyst (CG-Ca-N) was successfully prepared with coal gangue (CG), calcium chloride, and melamine as activator. Under the optimal conditions, the CG-Ca-N can remove 100 % for benzo(a)pyrene (Bap) in an aqueous solution after 20 min and 72.06 % in soil slurry medium within 60 min, which also display excellent reuse ability toward Bap after three times. The removal of Bap is significantly decreased when the initial pH value was greater than 9 and obviously inhibited in the presence of HCO3- or SO42-. The characterization results indicated that the addition of calcium chloride could stabilize and increase the content of pyridinic N during thermal annealing, resulting in the production of •OH, SO4•- and 1O2. Based on electron paramagnetic resonance (EPR) and active radical scavenging experiments, 1O2 could be identified to be the dominant role in Bap degradation. Overall, this work opened a new perspective for the low cost and green PMS catalysts and offered great promise in the practical remediation of organic pollution of groundwater and soil.

Activation of persulfate by biochar-supported sulfidized nanoscale zero-valent iron for degradation of ciprofloxacin in aqueous solution: process optimization and degradation pathway

The pollution of antibiotics, specifically ciprofloxacin (CIP), has emerged as a significant issue in the aquatic environment. Advanced oxidation processes (AOPs) are capable of achieving stable and efficient removal of antibiotics from wastewater. In this work, biochar-supported sulfidized nanoscale zero-valent iron (S-nZVI/BC) was adopted to activate persulfate (PS) for the degradation of CIP. The impacts of different influencing factors such as S/Fe molar ratios, BC/S-nZVI mass ratios, PS concentration, S-nZVI/BC dosage, CIP concentration, initial pH, coexisting anions, and humic acid on CIP degradation efficiency were explored by batch experiments. The results demonstrated that the highest degradation ability of S-nZVI/BC was achieved when the S/Fe molar ratio was 0.07 and the BC/S-nZVI mass ratio was 1:1. Under the experimental conditions with 0.6 g/L S-nZVI/BC, 2 mmol/L PS, and 10 mg/L CIP, the degradation rate reached 97.45% after 90 min. The S-nZVI/BC + PS system showed significant degradation in the pH range from 3 to 9. The coexisting anions affected the CIP degradation efficiency in the following order: CO32- > NO3- > SO42- > Cl-. The radical quenching experiments and electron paramagnetic resonance (EPR) revealed that oxidative species, including SO4•-, HO•, •O2-, and 1O2, all contribute to the degradation of CIP, in which •O2- plays a particularly prominent role. Furthermore, the probable degradation pathway of CIP was explored according to the 12 degradation intermediates identified by LC-MS. This study provides a new idea for the activation method of PS and presents a new approach for the treatment of aqueous antibiotics with highly catalytic active nanomaterials.

Effects of electron acceptors and donors on anaerobic biodegradation of PAHs in marine sediments

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants accumulated in the environment. PAHs' bioremediation in sediments can be promoted by adding electron acceptor (EA) and electron donor (ED). Bicarbonate and sulfate were chosen as two EAs, and acetate and lactate were selected as two EDs. Six groups of amendments were added into the sediments to access their role in the anaerobic biodegradation of five PAHs, containing phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene. The concentrations of PAHs, EAs and EDs, electron transport system activity, and microbial diversity were analyzed during 126-day biodegradation in serum bottles. The HA group (bicarbonate and acetate) achieved the maximum PAH degradation efficiency of 89.67 %, followed by the SL group (sulfate and lactate) with 87.10 %. As the main PAHs degrading bacteria, the abundance of Marinobacter in H group was 8.62 %, and the addition of acetate significantly increased the abundance of Marinobacter in the HA group by 75.65 %.

Electrodeposited copper enhanced removal of 2,4-dichlorophenol in batch and flow reaction in Cu@CC-PS-MFC system

Combination of microbial fuel cell (MFC) and advanced oxidation process (AOP) is promising for pollutant removal. In this paper, Cu0-loaded carbon cloth cathode by electrodeposition (Cu@CC-PS-MFC) was applied to enhance 2,4-dichlorophenol (2,4-DCP) degradation based on persulfate (PS) activation in microbial fuel cell. Cu0 exhibited a typical structure of face-centered cubic metal polyhedron on carbon cloth. The removal of 2,4-DCP by Cu@CC-PS-MFC (75.6%) was enhanced by more than 50% compared to CC-PS-MFC (49.2%) after 1 h of reaction. 30 mg/L 2,4-DCP in Cu@CC-PS-MFC was completely removed and achieved a high mineralization (80.6%) after 9 h of reaction under optimized condition with low dissolved copper ion concentration (0.615 mg/L). Meanwhile, more than 90% removal of 2,4-DCP was stably achieved with flow operation condition (hydraulic residence time of 7.2 h). The change of copper valent state Cu0/Cu2O/CuO was the main mechanism of PS activation with main reactive species of O•H and O21. The bioanode of MFC enhanced the in-situ regeneration of ≡Cu+ and ≡Cu0 on the catalyst surface by transporting electrons, which was believed to contribute to good catalyst lifetime and excellent 2,4-DCP removal. Electrodeposited copper contributes to the enhanced degradation of 2,4-DCP with energy recovery at the same time which can further broaden the application MFC.

Recent Advances in Nanoscale Zero-Valent Iron (nZVI)-Based Advanced Oxidation Processes (AOPs): Applications, Mechanisms, and Future Prospects

The fast rise of organic pollution has posed severe health risks to human beings and toxic issues to ecosystems. Proper disposal toward these organic contaminants is significant to maintain a green and sustainable development. Among various techniques for environmental remediation, advanced oxidation processes (AOPs) can non-selectively oxidize and mineralize organic contaminants into CO2, H2O, and inorganic salts using free radicals that are generated from the activation of oxidants, such as persulfate, H2O2, O2, peracetic acid, periodate, percarbonate, etc., while the activation of oxidants using catalysts via Fenton-type reactions is crucial for the production of reactive oxygen species (ROS), i.e., •OH, •SO4-, •O2-, •O3CCH3, •O2CCH3, •IO3, •CO3-, and 1O2. Nanoscale zero-valent iron (nZVI), with a core of Fe0 that performs a sustained activation effect in AOPs by gradually releasing ferrous ions, has been demonstrated as a cost-effective, high reactivity, easy recovery, easy recycling, and environmentally friendly heterogeneous catalyst of AOPs. The combination of nZVI and AOPs, providing an appropriate way for the complete degradation of organic pollutants via indiscriminate oxidation of ROS, is emerging as an important technique for environmental remediation and has received considerable attention in the last decade. The following review comprises a short survey of the most recent reports in the applications of nZVI participating AOPs, their mechanisms, and future prospects. It contains six sections, an introduction into the theme, applications of persulfate, hydrogen peroxide, oxygen, and other oxidants-based AOPs catalyzed with nZVI, and conclusions about the reported research with perspectives for future developments. Elucidation of the applications and mechanisms of nZVI-based AOPs with various oxidants may not only pave the way to more affordable AOP protocols, but may also promote exploration and fabrication of more effective and sustainable nZVI materials applicable in practical applications.

Resource utilization of rice straw to prepare biochar as peroxymonosulfate activator for naphthalene removal: Performances, mechanisms, environmental impact and applicability in groundwater

Herein, biochar was prepared using rice straw, and it served as the peroxymonosulfate (PMS) activator to degrade naphthalene (NAP). The results showed that pyrolysis temperature has played an important role in regulating biochar structure and properties. The biochar prepared at 900°C (BC900) had the best activation capacity and could remove NAP in a wide range of initial pH (5-11). In the system of BC900/PMS, multi-reactive species were produced, in which 1O2 and electron transfer mainly contributed to NAP degradation. In addition, the interference of complex groundwater components on the NAP removal rate must get attention. Cl- had a significant promotional effect but risked the formation of chlorinated disinfection by-products. HCO3-, CO32-, and humic acid (HA) had an inhibitory effect; surfactants had compatibility problems with the BC900/PMS system, which could lead to unproductive consumption of PMS. Significantly, the BC900/PMS system showed satisfactory remediation performance in spiked natural groundwater and soil, and it could solve the problem of persistent groundwater contamination caused by NAP desorption from the soil. Besides, the degradation pathway of NAP was proposed, and the BC900/PMS system could degrade NAP into low or nontoxic products. These suggest that the BC900/PMS system has promising applications in in-situ groundwater remediation.

Textile dye removal in wastewater by peroxymonosulfate (PMS) activation on a zero-valent iron nanoparticle-modified ultrafiltration catalytic membrane (nZVI@PES)

The use of the nano zero-valent iron (nZVI) nanoparticle-based advanced oxidation systems in conjunction with an activator such as peroxymonosulfate (PMS) to generate hydroxyl and sulfate radicals for the degradation of organic pollutants has been extensively used in recent studies. In this study, a nZVI-modified polyethersulfone (PES) membrane (nZVI@PES) was produced successfully by attaching the nZVI catalytic nanoparticles on the surface of a commercial microporous polymeric membrane material using a simple and easy filter press coating method. The presence of nZVI nanoparticles on the nZVI@PES membrane was confirmed by XRD, SEM, and EDS analyses. The nZVI@PES membrane was applied in the dead-end filtration system in the presence of the PMS activator to treat the reactive black 5 (RB5) dye solution. The effect of catalyst loading, RB5 dye concentration, PMS dosage, and pH level on the nZVI@PES membrane/PMS system was investigated. Quenching experiments were carried out to identify the reactive species responsible, and reusability tests were conducted on the membrane. The highest decolorization efficiency (96.8%) was obtained at 20 mg/L RB5 dye solution, initial pH of 3, the nZVI loading of 5 mg/cm2, and the PMS dosage of 300 mg/L at the end of a reaction time of 30 min. The formation of HO•, [Formula: see text], [Formula: see text] and, 1O2 was confirmed by quenching experiments. The results indicate that the nZVI@PES membrane/PMS system could successfully treat wastewater contaminated with an organic dye.

Removal of antibiotic resistant bacteria and genes by nanoscale zero-valent iron activated persulfate: Implication for the contribution of pH decrease

The mechanism of removing antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) by persulfate was attributed to the generation of reactive oxygen species (ROS). However, the potential contribution of decreased pH in persulfate system to ARB and ARGs removal has rarely been reported. Here, the efficiency and mechanism of removing ARB and ARGs by nanoscale zero-valent iron activated persulfate (nZVI/PS) were investigated. Results showed that the ARB (2 × 10⁸ CFU/mL) could be completely inactivated within 5 min, and the removal efficiencies of sul1 and intI1 were 98.95% and 99.64% by nZVI/20 mM PS, respectively. Investigation of mechanism revealed that hydroxyl radicals was the dominant ROS of nZVI/PS in removing ARB and ARGs. Importantly, the pH of nZVI/PS system was greatly decreased, even to 2.9 in nZVI/20 mM PS system. Impressively, when the pH of the bacterial suspension was adjusted to 2.9, the removal efficiency of ARB, sul1 and intI1 were 60.33%, 73.76% and 71.51% within 30 min, respectively. Further excitation-emission-matrix analysis confirmed that decreased pH contributed to ARB damage. The above results on the effect of pH indicated that the decreased pH of nZVI/PS system also made an important contribution for the removal of ARB and ARGs.

The debatable role of singlet oxygen in persulfate-based advanced oxidation processes

Singlet oxygen (¹O₂) attracts much attention in persulfate-based advanced oxidation processes (PS-AOPs), because of its wide pH tolerance and high selectivity toward electron-rich organics. However, there are conflicts about the ¹O₂ role in PS-AOPs on several aspects, including the formation of different key reactive oxygen species (ROS) at similar active sites, pH dependence, broad-spectrum activity, and selectivity in the elimination of organic pollutants. To a large degree, these conflicts root in the drawbacks of the methods to identify and evaluate the role of ¹O₂. For example, the quenchers of ¹O₂ have high reactivity to other ROS and persulfate as well. In addition, electron transfer process (ETP) also selectively oxidizes organics, having a misleading effect on the identification of ¹O₂. Therefore, in this review, we summarized and discussed some basic properties of ¹O₂, the debatable role of ¹O₂ in PS-AOPs on multiple aspects, and the methods and their drawbacks to identify and evaluate the role of ¹O₂. On the whole, this review aims to better understand the role of ¹O₂ in PS-AOPs and further help with its reasonable utilization.

Remediation of polybrominated diphenyl ethers contaminated soil in the e-waste disposal site by ball milling modified zero valent iron activated persulfate

Hydrophobic organic compounds (HOCs) in e-waste disposal sites are difficult to remove effectively. There is little reported about zero valent iron (ZVI) coupled with persulfate (PS) to achieve the removal of decabromodiphenyl ether (BDE209) from soil. In this work, we have prepared the flake submicron zero valent iron by ball milling with boric acid (B-mZVI^bm) at a low cost. Sacrifice experiments results showed that 56.6% of BDE209 was removed in 72 h with PS/B-mZVI^bm, which was 2.12 times than that of micron zero valent iron (mZVI). The morphology, crystal form, atomic valence, composition, and functional group of B-mZVI^bm were determined by SEM, XRD, XPS, and FTIR, and the results indicated that the oxide layer on the surface of mZVI is replaced by borides. The results of EPR indicated that hydroxyl radical and sulfate radical played the dominant role in the degradation of BDE209. The degradation products of BDE209 were determined by gas chromatography-mass spectrometry (GC-MS), accordingly, the possible degradation pathway was further proposed. The research suggested that ball milling with mZVI and boric acid is a low-cost means of preparing highly active zero valent iron materials. And the mZVI^bm has promising applications in improving the activation efficiency of PS and enhancing the removal of the contaminant.

Activation of sulfite by micron-scale iron-carbon composite for metronidazole degradation: Theoretical and experimental studies

In recent years, sulfite (S(Ⅳ)), as an alternative to persulfates, has played a crucial role in eliminating antibiotics in wastewater, so there is an urgent need to develop a cheap, environmentally friendly, and effective catalyst. Zero-valent iron (ZVI) has great potential for activated S(Ⅳ) removal of organic pollutants, but its reactivity in water is reduced due to passivation. In this study, a micron-scale iron-carbon composite(mZVI@C-800) prepared via high-temperature calcination was coupled with S(Ⅳ) to degrade metronidazole (MNZ). Under the optimized reaction conditions of mZVI@C-800 dosage of 0.2 g/L and S(Ⅳ) concentration of 0.1 g/L, the MNZ removal rate was up to 81.5 % in acidic and neutral environments. The surface chemical properties of the catalysts were characterized by different analytical techniques, and the corresponding catalytic mechanism was analyzed based on these analytical results. As a result, Fe²⁺ is the main active site, and ^·OH and SO₄^·- were the dominant active species. The increase in efficiency was attributed to the introduction of carbon to enhance the corrosion of mZVI further releasing more Fe²⁺. Additionally proposed were the potential response mechanism, the degradation path, and the toxicity change rule. These results demonstrate that the catalytic breakdown of antibiotics in wastewater treatment can be accelerated by the use of the outstanding catalytic material mZVI@C-800.

Efficient removal of uranium(VI) from aqueous solution by a novel phosphate-modified biochar supporting zero-valent iron composite

Uranium (U) is an important strategic resource as well as a heavy metal element with both chemical and radiotoxicity. At present, the rapid and efficient removal of uranium from wastewater remains a huge challenge for environmental protection and ecological security. In this paper, phosphate-modified biochar supporting nano zero-valent iron (PBC/nZVI) was triumphantly prepared and fully characterized. The introduction of polyphosphate can greatly increase the specific surface area of biochar pores, and then the zero-valent iron can be evenly distributed on the surface of material, thus leading to excellent removal performance of the PBC/nZVI for U(VI). The theoretical maximum U(VI) removal capacity of PBC/nZVI was up to 967.53 mg/g at pH 5. The results of adsorption kinetics, isotherm, and thermodynamics showed that the adsorption of uranium by PBC/nZVI was a monolayer physical adsorption and endothermic reaction. And the PBC/nZVI has favorable selectivity toward uranium against the interference of coexisting metal ions. Further mechanism studies show that the excellent uranium removal performance of PBC/nZVI is mainly attributed to the synergistic effect of physical adsorption and chemical reduction. This work proves that the PBC/nZVI has a wide application prospect in the field of uranium wastewater treatment.

Enhanced catalytic activity and stability of composite of cellulose film and nano zero-valent iron on Juncus effusus for activating peroxydisulfate to degrade Rhodamine B dye

In this study, a novel peroxydisulfate (PDS) activator (CF-nZVI-JE) was prepared via in-situ loading nano zero-valent iron (nZVI) on Juncus effusus (JE) followed with wrapping a layer of cellulose film (CF). The CF-nZVI-JE had the same 3D structure as the JE, being easy to separate from aqueous solution. The loaded nZVI existed single nanoparticles with a size of 60-100 nm except chain-type agglomeration of nanoparticles due to the stabilization of JE fibers. The activation performance of the CF-nZVI-JE for PDS was evaluated with Rhodamine B (Rh B) as a representative pollutant. Under the optimal activating conditions, the degradation rate of Rh B reached 99% within 30 min in the CF-nZVI-JE/PDS system. After five cycles, the degradation rate of Rh B was still over 85%, suggesting that the CF-nZVI-JE had good reusability. More interestingly, SO₄^·- and ·OH radicals were simultaneously detected in the CF-nZVI-JE/PDS system, but only SO₄^·- existed in the JE-ZVI/PDS system, suggesting the different activation mechanism. Meanwhile, the introduction of CF not only facilitated to the mineralization of Rh B but also significantly reduced the release amount of iron ions. Hence, the CF-nZVI-JE can be employed as a promising PDS activator for the treatment of organic wastewater.

Electrochemical-enhanced MoS2/Fe3O4 peroxymonosulfate (E/ MoS2/Fe3O4/PMS) for degradation of sulfamerazine

Seeking effective methods to degrade organic pollutants has always been a hot research field. In this work, MoS₂/Fe₃O₄ catalyst was synthesized by hydrothermal method with MoS₂ as carrier to construct an advanced oxidation system of electrochemical enhanced MoS₂/Fe₃O₄-activated peroxymonosulfate (E/MoS₂/Fe₃O₄/PMS). The materials were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The degradation efficiency of sulfamerazine (SM1) by E/MoS₂/Fe₃O₄/PMS system was investigated and reaction mechanism was explored. The results showed that the removal rates of SM1 within 30 min were 31%, 20% and 89% with Fe₃O₄, MoS₂ and MoS₂/Fe₃O₄ as catalysts, respectively. The characterization results revealed that Fe(III) on the surface of Fe₃O₄ was reduced to Fe(II) and Mo(IV) was oxidized to Mo(VI) in the presence of MoS₂. The synergistic effect between Fe₃O₄ and MoS₂ enhanced the PMS decomposition and improved the SM1 removal efficiency. Free radical quenching experiments showed that SO₄^-⋅, ·OH, O₂· and ¹O₂ were all involved in the degradation of SM1, and the effect of ¹O₂ was more significant than other active substances. Low concentrations of Cl^- and humic acid (HA) had no significant inhibitory effect on the degradation of SM1, while HCO₃^- had a significant inhibitory effect on the E/MoS₂/Fe₃O₄/PMS system. In addition, catalyst cycling experiments showed that MoS₂/Fe₃O₄ maintained good stability before and after the catalytic reaction process.

Efficient degradation of imidacloprid in soil by thermally activated persulfate process: Performance, kinetics, and mechanisms

Imidacloprid (IMI) as a first-generation commercial neonicotinoid has been frequently detected in the environment in recent years. In this study, the efficient degradation of IMI in soil by a thermally activated persulfate (PS) process was investigated. The degradation efficiencies of IMI were in the range of 82-97% with the PS dosage of 10 mM, when the initial concentrations of IMI were 5-50 mg/kg in the soil. Degradation of the IMI was fitted with a pseudo-first-order kinetic model under different reaction temperatures. Inhibition effects of the common inorganic anions on the IMI degradation in the system followed the order Cl^- > HCO₃^- > H₂PO₄^- > NO₃^-. Soil pH and soil organic matter were also main factors affecting the degradation of IMI. The degradation efficiencies (64-97%) of three other typical neonicotinoids (acetamiprid, clothianidin, and dinotefuran) indicated that the thermally activated persulfate process could be used for remediation of neonicotinoid-contaminated soil. Quenching experiments indicated that the major reactive species in IMI degradation were SO₄^•-, O₂^•-, and •OH. Six degradation intermediates of IMI were inferred in the soil, and degradation pathways of IMI included hydroxylation, denitrification, C-N bond break and further oxidation.