Peroxydisulfate Research Articles

Enhanced degradation of naphthalene in persulfate-based systems coupled with calcium sulfite: Elucidation of degradation mechanisms and pathways

Na2SO3 and NaHSO3 have been widely used as the source of SO32− to participate in the reproduction of Fe(II) in iron-based advanced oxidation processes. In this work, CaSO3 with low solubility was innovatively introduced and compared with Na2SO3 and NaHSO3 to investigate their effects on naphthalene (NAP) degradation in Fe(II)-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) processes. The results showed that CaSO3 displayed a better performance due to its sustained-release of SO32−, and NAP removal increased from 57.6% and 77.7% to 91.4% and 98.5% in PDS/Fe(II) and PMS/Fe(II) processes, respectively, with the addition of CaSO3. The enhancement mechanisms of CaSO3 were illustrated by measuring the variation of iron and SO32− concentrations and by quantitatively determining the production of reactive oxygen species (ROS). The dominant ROS generated in CaSO3-enhanced systems was confirmed by scavenging tests. Moreover, NAP degradation intermediates and pathways, as well as the toxicological properties of intermediates, were accordingly elucidated. Finally, CaSO3-enhanced systems had a wide application range of pH, and exhibited a great performance on the tolerance of various water matrixes. The significant removal of various contaminants in CaSO3-enhanced processes confirmed that these techniques are suitable for the remediation of organic contaminated groundwater.

Regulating the reactive site density of two-dimensional N self-doped carbon for boosted Fenton-like catalytic ability

The mediocre catalytic ability of metal-free carbon-based catalysts limits its practical application in wastewater treatment. Herein, a facile “steam-etching” method is utilized to boost the catalytic ability of N self-doped carbon (NSDC) catalysts. Compared to the original NSDC catalyst (NSDC-N2), the NSDC-H2O-50 catalyst modified with the water vapor content of 50 % exhibits much better catalytic performance. The pseudo-first-order kinetic rate constant k of NSDC-H2O-50 is 4.88 times that of NSDC-N2. The presence of water vapor can cause a massive vacancy-like defects in the carbon structure, which is conducive to form more edge reactive groups. Pyrrolic N and CN groups are proved to be the reactive sites for the catalytic reaction. Reactive site density can be easily adjusted by changing the water vapor content. The prepared NSDC-H2O catalysts can effectively activate peroxydisulfate (PDS) to degrade various organic pollutants with high efficiency in the pH range of 2.02–10.28. In addition, the NSDC-H2O/PDS system exhibits strong anti-interference ability to common anions and humic acid. The catalytic ability has not been affected in actual water sources. By a simple calcination treatment, most of the catalytic ability can be restored. Therefore, the prepared NSDC-H2O catalysts show strong application potential in organic wastewater treatment. Furthermore, singlet oxygen is proved to be the main active species in the NSDC-H2O/PDS system, and sulfate radical and superoxide radical play an auxiliary role.

Flexible regulation of persulfate activation mechanisms through tuning Cu valence in CuBTC-derived copper oxide catalysts for improved pollutant degradation

Radical and nonradical dominated persulfate activation processes have pros and cons in the degradation of pollutants. It is challenging to flexibly tune the contribution ratios of radicals and nonradicals in a persulfate activation process for improved pollutant degradation. Herein, we successfully synthesize copper oxide catalysts derived from metal-organic frameworks. By varying the annealing temperature, valence states of copper can be regulated in the catalyst, thereby enabling the switching between radical and nonradical mechanisms for persulfate activation. Copper oxides annealed at 300 °C (CuBTC-300) demonstrate high performance in peroxydisulfate (PDS) activation for the degradation of bisphenol A (BPA), with the synergy of radical and nonradical mechanisms. The surface activated PDS-catalyst complex and OH are identified as the reactive oxidative species involved in this process. On one hand, PDS undergoes a one-electron transfer reaction with Cu(I) sites in Cu2O, generating SO4−, which subsequently converts into OH for BPA degradation. On the other hand, the combination of PDS molecules with CuO forms surface-activated complexes, depriving electrons from BPA. The increased content of Cu(II) in the catalyst gradually directs PDS activation towards the nonradical pathway. As the annealing temperature increases from 300 °C to 500 °C, the contribution of nonradical oxidation to BPA degradation increases from 58.65 % to 100 %. This work provides new insights into flexibly regulating persulfate activation mechanisms via rational catalysts design.

Dual oxidant strategy involving calcium peroxide and peroxydisulfate for waste activated sludge recycling: Removal of sulfamethoxazole and hydrocortisone

In this study, the removal of sulfamethoxazole (SMX) and hydrocortisone (HC) from waste activated sludge (WAS) was explored using a dual oxidant strategy involving calcium peroxide (CaO2) and peroxydisulfate (PDS). Synergistic effects were observed between CaO2 and PDS at 0.1 g/g TS (total solids), leading to 89 % and 54 % removal of SMX and HC, respectively, in 8 min in sludge. Ca2+, Ca(OH)2, H2O2, and SO42– from CaO2 and PDS hydrolysis promoted pollutant removal. SMX removal was mainly driven by 1O2, which had a 78 % contribution to the removal rate, while HC removal was mainly due to OH and SO4–, with an overall 79 % contribution. Furthermore, removal pathways for SMX and HC during CaO2/PDS were proposed. SMX, HC, and their intermediates with high toxicity transformed into less toxic or nontoxic products during CaO2/PDS oxidation. Moreover, the dewatering ability and solubility of sludge increased after CaO2/PDS treatment. Furthermore, the production of volatile fatty acids during anaerobic fermentation of sludge pretreated with CaO2/PDS increased by 1.8 times relative to the control, with a 13 % increase in acetic acid content. The altered relative abundance of Firmicutes and Proteobacteria played a key role in promoting the recovery of carbon sources from the sludge.

Enhancement of peroxydisulfate activation by inherent nature of Fe-N-P/C biochar derived from Capsosiphon fulvescens as a green biomass material for organic pollutants degradation

This study explores the catalytic activity of biochar materials derived from seaweed biomass (Capsosiphon fulvescens) for groundwater treatment. A facile pyrolysis process was utilized to prepare C. fulvescens biochar (CFBCX), where X represents the pyrolysis temperature. The instrumental analysis using surface characterization techniques revealed that CFBC800 inherently contained heteroatoms (N, P) and a trace metal (Fe) in the biochar. The adsorption kinetics and isotherm experiments depicted a mixed mechanism of physical and chemical adsorption of SDZ on CFBC. Consequently, in optimal conditions with 2 mM peroxydisulfate (PDS), 200 mg L−1 CFBC800, and 6.1 initial solution pH, SDZ degradation (>97.2%) is achieved within 60 min. Chemical quenching tests indicate the involvement of radical (O2•– = 41.6%) and non-radical processes, including electron transfer (58.4%), in the PDS/CFBC800 system. The electron spin resonance spectroscopy confirmed the formation of reactive oxygen species (ROS) in the PDS/CFBC800 system, including radical (O2•–, SO4•–, and HO•) and non-radical (1O2) species. Furthermore, electrochemical studies demonstrated the existence of an electron transfer pathway in the non-radical process of the PDS/CFBC800 system. Based on chemical scavenger and ESR analyses, the PDS/CFBC800 system exhibited both radical and non-radical mechanisms, with the electron transfer pathway being more dominant in this catalytic system. The excellent catalytic activity of the PDS/CFBC800 system toward co-existing ions and various organic contaminant degradation is demonstrated. Moreover, the CFBC800-activated PDS system successfully demonstrated catalyst reusability in SDZ degradation. Thus, this study establishes CFBC800 as an ecofriendly catalyst with remarkable catalytic activity for groundwater remediation.

Adsorption and catalytic degradation of phenol in water by a Mn, N co-doped biochar via a non-radical oxidation process

A modified biochar material (Mn/C-KOH) was synthesized from chitosan using KOH and MnCl2 as the activators via a one-pot pyrolysis process. The characterization suggested that the two activators promoted its textural properties, led to a surface area of 1223 m2/g and modified the surface chemical groups. Mn/C-KOH with a Mn-doping dosage of 0.27 wt% was an adsorbent and outstanding catalyst for removing phenol via peroxydisulfate (PDS) activation. A 55% adsorption rate of phenol was achieved within 10 min at a concentration of 30 mg/L. A 95% degradation rate and a 75% mineralization rate of phenol (30 mg/L) were obtained through the activation of PDS (200 mg/L). And, the catalytic degradation system could tolerate a wide pH range from 3 to 9. The intrinsic pyridinic N and CC/CC groups of the chitosan-derived biochar played dominant roles in the adsorption. The simultaneous activation of KOH and MnCl2 enhanced the proportion of CO groups of Mn/C-KOH, and CO groups served as the catalytic active sites for PDS activation. The electron transfer and 1O2-mediated non-radical processes that were induced by the formation of a dioxirane intermediate between Mn/C-KOH and PDS were responsible for the phenol degradation. This work offers a modification for the biomass-derived catalysts and is beneficial to the understanding of non-radical mechanism in AOPs.

Facile synthesis of oxygen vacancy-rich ZnxCu1-xFe2O4 nano-catalyst to activate peroxydisulfate for the efficient degradation of tetracycline

Introduction of oxygen vacancies (OVs) into the heterogeneous catalysts is an efficient method to improve their catalytic activity for persulfate activation. The OVs-rich ZnxCu1-xFe2O4 nano-catalysts were synthesized by a facile co-precipitation method and analyzed using various characterization techniques (XRD, FE-SEM, EDS, BET surface area and XPS). OVs-rich ZnxCu1-xFe2O4 nano-catalysts exhibited a significantly higher catalytic activity for the removal of tetracycline (TC) by activating peroxydisulfate (PDS) than ZnFe2O4 and CuFe2O4 nano-catalyst. TC degradation efficiency in different ZnxCu1-xFe2O4/PDS systems demonstrated that Zn0.6Cu0.4Fe2O4 showed the best catalytic performance due to its highest OVs content, largest specific surface area and pore volume, and 90.09% of TC (20 mg/L) was degraded by Zn0.6Cu0.4Fe2O4 with PDS after 60 min. Cu in-situ introduction can increase the amount of OVs in ZnFe2O4 and affect the cross-occupancy of Zn and Fe, thus promoting the generation of the reactive oxygen species (ROS) in PDS-activated process; moreover, doped Cu can also act as an activation site for PDS and boost the formation of active Fe(Ⅱ). Mechanism study showed that all of ROS (1O2, O2•−, SO4•− and •OH) generated in ZnxCu1-xFe2O4/PDS system simultaneously engaged in TC elimination, and 1O2 played the main role. The probable TC degradation pathways in Zn0.6Cu0.4Fe2O4/PDS system were proposed. The practical application potential of magnetic Zn0.6Cu0.4Fe2O4 nano-catalyst in the treatment of TC-contaminated wastewater was assessed by investigating the reusability of Zn0.6Cu0.4Fe2O4, the removal of TC in real water matrix and the toxicity of TC degradation intermediates.

Degradation of imidacloprid via the activation of peroxymonosulfate and peroxydisulfate using a Fenton-sludge-derived Fe0/Fe3C composite

The Fenton process is a commonly employed advanced oxidation process for industrial wastewater treatment. However, large volumes of iron-containing sludge are generated in the Fenton reaction, causing secondary pollution. In the present study, we report a Fenton-sludge-derived biochar (FSB) designed to degrade the neonicotinoid pesticide, imidacloprid (IMD) via activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS). The effect of pyrolysis temperature on the transformation of the crystal phase and surface functional groups of samples was monitored using X-ray diffraction, Fourier transformation-infrared spectroscopy, and scanning electron microscopy. The use of FSB treated at 900 °C (FSB 900) containing the iron phase Fe0/Fe3C led to the highest IMD degradation efficiency with both PMS and PDS (92.7 ± 0.5 % and 100.0 ± 0.0 %, respectively; [IMD]0 = 20 mg/L, [persulfate]0 = 2 mM, [FSB]0 = 0.2 g/L, reaction time = 60 min). The main reactive species involved in IMD degradation via PMS and PDS activation using FSB 900 were identified with scavenger tests. The effects of solution pH and the additional anions on the performance of IMD removal efficiency were also investigated. This study provides insights into the recycling of solid waste derived from the Fenton process and the degradation of recalcitrant organic pollutants in wastewater.

Acid-modified red mud biochar for the degradation of tetracycline: Synergistic effect of adsorption and nonradical activation

In this study, a novel acid-modified red mud biochar catalyst (MMBC) was synthesized by industrial waste red mud (RM) and peanut shell (PSL) to activate peroxodisulfate (PDS) for the degradation of TC. Meanwhile, MMBC exhibited remarkable adsorption capacity, reaching a 60% removal ratio of TC within 60 min (equilibrium adsorption capacity = 12 mg/g). After adding PDS, MMBC/PDS system achieved a 93.8% removal ratio of TC within 60 min. Quenching experiments and electron paramagnetic resonance (EPR) results showed that 1O2 played a dominant role in the degradation of TC and O2•− was the mainly precursor for the production of 1O2 in the MMBC/PDS system. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis showed that the surface Fe(II), –OH and –COOH provided the active sites for the activation of PDS by MMBC. In addition, acid modification optimised the surface structure of the catalyst and enhanced the conversion of Fe (mainly Fe(III) to Fe(II)), thereby improving the adsorption and catalytic efficiency of MMBC. This study confirmed that modified red mud biochar is an efficient composite with both adsorption and catalysis, providing new ideas for the practical treatment of antibiotic wastewater and the resource utilization of red mud.

In-Situ photothermal regeneration of fulvic Acid-Saturated Co@NC magnetic nanoparticles via persulfate oxidation

To achieve sustainable adsorbent regeneration in wastewater treatment, a novel in-situ regeneration strategy using photothermally activated peroxydisulfate (PDS) oxidation was developed. Here, magnetic cobalt nanoparticles embedded in nanoporous carbon (Co@NC) were synthesised at different carbonization temperatures, and their potential for removing fulvic acid (FA) were assessed during adsorption-regeneration cycles. The results revealed that Co@NC prepared at 700℃ (Co@NC@700) exhibited excellent adsorption and regeneration capabilities, as well as outstanding photothermal properties. The FA removal rate could reach 90% during the adsorption process, and Co@NC@700 could be efficiently separated from water by magnetic force. Under irradiation equivalent to four suns, the Co@NC@700 system reached 70 °C with a photothermal conversion efficiency of 65%, providing ample thermal energy for PDS activation. Even after seven photothermal regeneration cycles, over 55% of the original adsorption capacity could still be recovered. Compared with direct desorption without degradation, the total organic carbon (TOC) content in the regeneration solution reduced to 18.84 mg/L, achieving a removal rate of 83%. The quenching experiments, electron paramagnetic resonance and electrochemistry tests indicated that both radical and non-radical pathways contributed to the regeneration process. By harnessing renewable solar energy, this study provides a feasible approach for simultaneous in-situ adsorbent regeneration and containment removal.

A novel Co–CoAl2O4/exfoliated montmorillonite composite with improved nanoparticle dispersion for methyl orange removal via coupling peroxydisulfate

The degradation of refractory pollutants via the activation of peroxydisulfate (PDS) by Co-based nanostructures as catalysts has been gaining significant attention. However, most cobalt-based catalysts suffer from severe aggregation and metal ion leakage, resulting in a loss of activity and potential environmental threats. In this study, exfoliated montmorillonite (EMMT) loaded Co–CoAl2O4 composites were elaborately constructed through a facile coprecipitation-reduction method. The effects of the calcination temperature, the EMMT addition content, the pH of the precursor, and the reduction temperature on the microstructure of the Co–CoAl2O4/EMMT composites were investigated, and the optimum synthesis conditions were determined. In the optimal sample, well-crystallized CoAl2O4 nanoparticles were uniformly deposited onto the EMMT nanosheets with a considerably large specific surface area, while ultrafine metallic Co nanoparticles were homogeneously immobilized on the CoAl2O4 surface. This sample exhibited a superior activity (90% within 70 min) and reusability during methyl orange (MO) degradation. In the catalytic reaction, the superior adsorption property of EMMT facilitated the rapid transfer of MO molecules to the catalytically active sites. Moreover, CoAl2O4 acted as a transition layer which provided a cobalt source for the subsequent reduction process and regulated the growth of metallic Co nanoparticles, which increased the number of active sites for catalysis. Simultaneously, the metallic Co can not only activate PDS by being an electron donor, but also initiate the formation of Co-based redox pairs. This study offers new insights into the synthesis of efficient and cost-effective supported Co-based catalysts.

Magnetized algae catalyst by endogenous N to effectively trigger peroxodisulfate activation for ultrafast degraded sulfathiazole: Radical evolution and electron transfer

An innovative Fe–N co-coupled catalyst MN-2 was prepared from waste spirulina by co-pyrolysis as a highly active carbon-based catalyst for the activation of peroxydisulfate (PDS) for the degradation of sulfathiazole (ST). The protein-rich raw material Spirulina provided sufficient N during the pyrolysis process, thus achieving N doping without an additional nitrogen source, optimizing the interlayer structure of the biochar material and effectively inhibiting the leaching of the ligand metal Fe. MN-2 showed highly efficient catalytic activity for peroxydisulfate (PDS), with a degradation efficiency of 100% for ST within 30 min and a kinetic constant (kobs) reached 0.306 min−1, benefiting from the excellent adsorption ability of MN-2 forming MN-2-PDS* complexes and the electron transfer process generated by Fe3+ and Fe2+ cycling, oxygen-containing functional groups. The effects of PDS dosage, initial pH and coexisting anions on the oxidation process were also investigated. Free radical quenching, electron paramagnetic resonance and electrochemical measurements were employed to explain the hydroxyl (·OH) and sulfate (SO4·−) as the dominant active species and the electron transfer effect on the removal of ST. MN-2 maintained a ST removal rate of 84% after four recycling experiments, showing a high reusability performance. This work provides a simple way to prepare magnetized N-doped biochar, a novel catalyst (MN-2) for efficient activation of PDS for ST degradation, and a feasible method for removing sulfanilamide antibiotics in water environment.

Effects of peroxide types on the removal performance and mechanism of sulfonamide antibiotics using graphene-based catalytic membranes

This study reports in situ catalytic oxidation processes using graphene-based catalytic membranes to activate peroxydisulfate (PDS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2). Sulfonamide antibiotics in water, including sulfamethoxazole (SMX), sulfadiazine (SDZ), sulfamerazine (SMR), and sulfamethazine (SM2), were used as target pollutants. The composites of reduced graphene oxide and nitrogen-doped carbon nanotubes were loaded onto nylon microfiltration membranes at 8 g·m–2 mass dosage. The PDS-based systems exhibited the highest efficiency in removing SDZ (≥ 98%) and SMX (> 93%) during continuous 10 h filtration. In contrast, PMS was more suitable for oxidizing SMR (≥ 99%) and SM2 (≥ 90%) in a single pass. Based on functional group characterization and density functional theory calculations, structural defects and pyridinic/graphitic nitrogen species in carbon mats were identified as the main active centers for peroxide activation. Moreover, PDS, PMS and H2O2 exhibited distinct adsorption behaviors on defective and nitrogen-doped graphitic carbon, influencing the cleavage of peroxide bonds to generate reactive oxygen species. The reaction mechanism was investigated through electron paramagnetic resonance and chemical quenching tests. Surface-active species and singlet oxygen dominated in the PDS- and PMS-based systems, representing non-radical pathways, that selectively oxidize sulfonamides in real water matrices more effectively than the hydroxyl radicals involved in H2O2-based systems. PDS activating exhibited significant performance in organic fouling polishing, lowering the transmembrane pressure during continuous filtration. These findings offer valuable insights into implementing in situ catalytic oxidation processes in actual water purification.

Electron-enriched supramolecular PDI-SiO2 promoting PDS activation for enhanced photocatalytic advanced oxidation

The efficient activation of peroxydisulfate (PDS) for wastewater treatment remains a great challenge. Photocatalysis, which generates highly-reactive electrons and holes, shows great potential in activating PDS for effective degradation and deep mineralization. Herein, an electron-enriched PDI-SiO2 photocatalyst was synthesized by covalently linking 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) onto silicon dioxide (SiO2) to form π-π stacked supramolecular PDI layers for efficient PDS activation. The highly dispersed PDI generates electron-enriched PDI·- under visible light, promoting the rapid activation of PDS for bisphenol A (BPA) degradation. The PDI-SiO2 activated PDS system realized a high BPA degradation rate of 0.100 min−1 and a remarkable mineralization rate of 81%. Moreover, the charge separation efficiency is significantly improved since the electrons of PDI·- are captured by PDS, boosting oxidative degradation and improving the mineralization efficiency. This work developed a novel PDS activation strategy by constructing electron-enriched photocatalyst, and revealed the mechanism of photocatalytic activation and deep mineralization.

Electron transfer route tuning caused by photo-irradiation: Stability enhancement of N-doped carbon materials in Fenton-like reactions

Improving the stability of N-doped carbon materials is still a great challenge in Fenton-like reactions. Herein, a hollow structure with TiO2 nanoparticles supported on the inner surface of N-doped carbon spheres (H-TiO2 @NC) is designed for peroxydisulfate (PDS)-based Fenton-like reactions with photo-irradiation. Impressively, the stability of H-TiO2 @NC is greatly enhanced with photo-irradiation. The degradation rate constant of bisphenol A (BPA) with photo-irradiation is ∼61 times larger than dark condition after four runs. The photovoltage enables more electrons to be transferred from BPA to PDS via active carbons. Less electrons from the carbon framework are expended, thus inhibiting the oxidation and deactivation of H-TiO2 @NC effectively. Additionally, the direct electron transfer (DET) process is improved due to conductivity enhancement, which also weakens the oxidation of carbon skeleton. This work provides a reliable method to enhance the stability of N-doped carbon materials. And giving some new insights into the mechanism of stability enhancement.

Electrochemical activation of peroxydisulfate using an IrO2 electrode for the efficient degradation of acid orange 74: Mechanisms of different activation methods

Electrochemical activation of persulfate is an efficient and green technology. In this study, the differences in the pollutant degradation efficiency and peroxydisulfate (PDS) activation mechanism were compared via electrochemical activation of PDS using only an IrO2 anode, an IrO2 cathode, and both an IrO2 anode and stainless steel (SS) cathode. In these methods, the degradation of acid orange (AO) 74 conformed to the pseudo-first-order kinetic degradation model. The electrochemical activation of PDS using an IrO2 anode resulted in the highest AO 74 degradation efficiency of 81.7 % with a degradation rate constant of 0.58 h−1. The results of radical quenching and cyclic voltammetry indicated that during the electrochemical activation of PDS using an IrO2 anode, direct electron transfer and nonradical oxidation contributed to AO 74 degradation. Using an IrO2 cathode, the contribution to AO 74 degradation was mainly OH, while using an IrO2 anode and SS cathode, the contribution was the joint action of the nonradical and radical oxidation. Furthermore, during the electrochemical activation of PDS using an IrO2 anode, the degradation rate exhibited a good linear relationship with the current density and PDS concentration. The addition of Cl− considerably enhanced AO 74 degradation.

Elucidating diatomic catalysis for contaminants degradation: Role of multi-functional Fe/Co sites in peroxydisulfate activation

The application of catalysts with highly available active sites, such as single-atom catalysts (SACs), is a growing trend in peroxysulfate activation for organic contaminant degradation. However, the single functional active site of SACs limits its performance in such reactions involving multiple steps or reactants. For this issue, a Fe-Co diatomic catalyst (FeCo-N-C) with multi-functional active sites is synthesized to abate bisphenol A (BPA) using peroxydisulfate (PDS) as an oxidant. X-ray Absorption Fine Structure (XAFS) measurement confirms the successful construction of diatomic Fe-N4/Co-N4 sites. The FeCo-N-C exhibits a higher normalized reaction rate (2.07 × 105 min−1 mol−1) in BPA removal than previously reported SACs. Low-temperature electron paramagnetic resonance analysis reveals that Fe-N4 and Co-N4 process different intrinsic properties (spin states), which may lead to their diverse functions in the PDS activation process. The Co sites can significantly accelerate electron transfer and enhance the PDS adsorption abilities. As a complement, Fe sites perform better in the electrostatic interaction and destabilization of PDS. This study not only explains the synergy of multi-functional diatomic sites from the whole PDS activation process but provides a reliable reference for the elimination of emerging organic contaminants.

Insights to PFOS elimination with peroxydisulfate activation mediated by boron modified Fe/C catalysts: Enhancing mechanism of boron and PFOS degradation pathway

In this study, the boron-doped iron-carbon composite (Fe@B/C-2) was prepared via a simple solvothermal and secondary calcination process by using iron metal–organic frameworks (Fe-MOFs) as precursor. The obtained Fe@B/C-2 possessed abundant active sites and low iron ion leaching, and exhibited excellent performance on peroxydisulfate (PDS) activation for efficient PFOS (10 mg/L) degradation (94 %) in 60 min, with 0.2 g/L of catalyst dosage, 1.0 g/L of PDS dosage and at 5.0 of initial pH. The radical scavenging and electron paramagnetic resonance (EPR) tests demonstrated that SO4·− and ·OH were the primary active species during PFOS elimination. Under the attack of these species, PFOS was first transformed into PFOA, followed by a sequential defluorination process, and lastly mineralized into CO2 and F−. Notably, DFT results revealed that Fe species, -BC3/-BC2O structures on the carbon matrix performed crucial roles in PDS activation. The extraordinary catalytic activity of Fe@B/C-2 was attributable to the synergistic effects of Fe nanoparticles and the B-doped on carbon matrix. The doped B not only could activate the inert carbon skeleton and provided more catalytic centers, but also could accelerate the electron transfer efficiency, leading to a boost in PDS decomposition.

Efficient activation of peroxydisulfate by 3D flower spherical-like Fe–NC for organic contaminant removal: Fe(IV)=O as a dominant species

The high-valent iron-oxo species (Fe(IV)O) exhibit great prospects for the removal of organic contaminants in iron-mediated persulfate activation. Nevertheless, an adequate research of the mechanisms involved in Fe(IV)-based activation processes and organic degradation remains elusive. Here, an Fe encapsulated in N-doped carbons catalyst (2Fe–NC) with three-dimensional flower shape and mesoporous structure was developed, which can 100 % remove various organic pollutants such as chloramphenicol (CAP), sulfamethoxazole, amoxicillin, benzoic acid, and bisphenol A within 30 min by peroxydisulfate (PDS) activation. In the oxidation system, 2Fe–NC as an electron transfer medium was critical to mediate electron transfer from organic compound to PDS, accompanied by the redox cycle of Fe(IV)/Fe(II) and Fe(IV)/Fe(III). Multiple experiments reveal that the oxidation mechanism of 2Fe–NC@PDS system is similar to the dioxygen activation mechanism of binuclear active sites, which activates PDS to form surface-active Fe(IV)O species without producing radicals. The two pathways of CAP degradation simulated by density functional theory calculations release 6.92 and 4.23 eV, respectively, which is thermodynamically favorable. Overall, the new insights gained in this work offer a significant route to design more effective advanced oxidation processes for refractory contaminant treatment.

Degradation of 1,2,3-trichloropropane using peroxydisulfate activation by green tea iron nanoparticles

The pollution of groundwater with 1,2,3-Trichloropropane (TCP) has raised significant concerns due to its toxicity and resistance to degradation. In this study, the degradation of TCP using peroxydisulfate (PDS) activation by green tea iron nanoparticles (G-INPs) was investigated and compared with traditional PDS oxidation activated by citric acid-Fe2＋(CA-Fe), which was commonly used as an effective PDS activator. Oxidation experiments and theoretical analysis were conducted to reveal the degradation efficiency and mechanism. The results showed that the TCP degradation efficiency was significantly enhanced in the G-INPs/PDS oxidation system compared to CA-Fe/PDS oxidation. The degradation efficiency was more than 77% after 48 hours (h) in G-INPs/PDS oxidation (0.625 mM Fe, 25 mM PDS, and 25°C with no pH adjustment) at an initial TCP concentration of 100 mg/L. In contrast, only 59% of TCP was degraded by CA-Fe/PDS using the same ferrous ion (Fe2＋) amount. The addition of G-INPs promoted the generation of hydroxyl radical (OH⋅ ), sulfate radical (SO4−⋅ ), and superoxide radical (O2-⋅ ), among which OH⋅ played a crucial role in the degradation process. The concentration of Fe2＋ in the G-INPs/PDS system after 48 h was twice as high as that in the Fe2＋/PDS system. The increased Fe2＋ content in the system facilitated the production of radicals, leading to improved degradation efficiency of TCP. Reaction product analysis further demonstrated that carbon dioxide (CO2) and hydrochloric acid (HCl) were the oxidation products of TCP degraded by G-INPs/PDS, and only a tiny amount (<5.5 wt%) of less toxic organic by-products were generated, including 1,3-dichloro-2-acetone, 1,2-dichloroethane and 1,1,2-trichloroethane. Conclusively, the G-INPs/PDS oxidation method seems to be a promising technology for removing high TCP contamination from wastewater or polluted groundwater.