Persulfate Decomposition Research Articles

Relative contribution of ferryl ion species (Fe(IV)) and sulfate radical formed in nanoscale zero valent iron activated peroxydisulfate and peroxymonosulfate processes

Activation of persulfates (i.e., peroxydisulfate (PDS) and peroxymonosulfate (PMS)) by nanoscale zero-valent iron (nZVI) is reported to be effective in oxidative treatment of environmental contaminants. It has been widely accepted in numerous literature that sulfate radical (SO4•-) formed from the decomposition of persulfates activated by aqueous Fe(II) released from nZVI corrosion is responsible for the oxidative performance in nZVI/persulfates systems. In this work, by employing methyl phenyl sulfoxide (PMSO) as a probe, we demonstrated that the activation of persulfates by nZVI through electron transfer led to SO4•- formation, while the homogeneous activation of persulfate by the released Fe(II) resulted in ferryl ion species (Fe(IV)) generation in nZVI/persulfates systems. Similarly, nanoscale zero-valent aluminum (nZVAl) and zinc (nZVZn) were also demonstrated to be able to donate electron to persulfates leading to SO4•- formation. However, the insulative aluminum oxide shell hindered the electron transfer leading to the poor persulfates decomposition, while the conductive iron and zinc oxide shell enabled the electron transfer process resulting in a continuous generation of SO4•-. Further, it was obtained that the relative contribution of SO4•- and Fe(IV) in nZVI/persulfates systems was independent of the initial concentration of nZVI and PDS, but was positively correlated with PMS concentration. In addition, the increase of pH from 3 to 7 led to the decrease of the relative contribution of Fe(IV), which was rationalized by the decrease of availability of aqueous Fe(II) at higher pH. Our findings not only shed lights on the nature of the reactive intermediate formed in the nZVI/persulfates systems, but also unprecedentedly distinguished the surface activation of persulfates from the homogeneous catalysis process.

Degradation of sulfamethazine by persulfate activated with nanosized zero-valent copper in combination with ultrasonic irradiation

Commercial nanosized zero-valent copper (nZVC) was used as persulfate (PS) activator in combination with ultrasonic irradiation (US) for the oxidative degradation of typical antibiotic sulfamethazine (SMZ) in this study. Compared with other processes, the combined nZVC-PS-US process significantly enhanced SMZ removal due to a synergistic interaction between sonolysis and a heterogeneous reaction. Almost complete SMZ removal was achieved within 60 min using a PS dose of 0.5 mM and a nZVC concentration of 64 mg/L at pH 3.06, with US at 0.4 W/mL and 40 kHz. The presence of NO3–, SO42−, HCO3–, Cl− and humic acid demonstrated adverse effects on SMZ degradation. Moreover, the inhibitory effect of different inorganic anions on SMZ degradation followed the sequence of HCO3– > SO42−> NO3– > Cl− > no salt. Electron spin resonance and radical scavenging tests indicate that the primary reactive species was SO4•−, while •OH played a less important role. Cu+ is an active copper species in activating PS. The production of Cu+ and Cu2+ induced by Cu0 and US favored the continuous decomposition of PS as well as the production of SO4•− at the surface of nZVC. Nine intermediates were identified and four oxidation pathways were proposed, the aniline moiety oxidation, SO2 extrusion/smile-type rearrangement and S-N bond cleavage were the major pathways. Practicality and effectiveness of nZVC-PS-US was confirmed when other organic micro-pollutants and SMZ added to raw waters were tested. The findings reported here offer promising implications in developing the utilization of nZVC in advanced oxidation for treatment of wastewater.

Activation of persulfate by EDTA-2K-derived nitrogen-doped porous carbons for organic contaminant removal: Radical and non-radical pathways

Nitrogen-doped porous carbons prepared from ethylenediaminetetraacetic acid dipotassium salt (EDTA-2K) were employed in combination with sodium persulfate (PS) for the catalytic removal of sulfamethoxazole (SMX). Almost complete removal (99.5%) of SMX was obtained with the optimum carbon prepared at 800 °C (NC800), which was attributed to its high surface area, good electrical conductivity, rich defects as well as doped carbonyl and nitrogen groups. The reaction mechanism was proposed to be a combination of both radical and non-radical pathways. OH, SO4−, O2− and 1O2 as reactive oxidative species were involved in the reaction process based on quenching tests and electron spin resonance (ESR) measurements, while the non-radical pathway between PS and SMX with the assistance of NC800 also made a significant contribution as indicated from PS decomposition tests and linear sweep voltammetry (LSV) analysis. Adsorption played an important role in the reaction process, and this point was emphasized when interpreting the effects of quenchers and pH values. For potential practical applications of the NC800/PS system, experiments concerning catalyst stability, the catalytic removal of three other organic contaminants and SMX removal in real water matrices were also conducted.

Pyrite enables persulfate activation for efficient atrazine degradation.

Persulfate (PS) is widely used for environmental remediation, but its organic contaminant removal performance strongly depends on its activation. In this study, we demonstrate that pyrite (FeS2) can more effectively activate PS than the commonly used FeSO4 for atrazine degradation. When 3.0mM of PS and 4.2mM of iron salts were used, the atrazine degradation efficiency of FeS2/PS was 1.4 times that of FeSO4/PS, while the amount of consumed PS in case of FeS2 was only 53% of that by FeSO4. The better PS activation performance of FeS2 could be attributed to its slow and sustainable release of dissolved Fe(II), inhibiting the quenching reaction between •SO4-/•OH and Fe(II) ions, and thus producing more reactive oxygen species for the atrazine degradation. More importantly, the surface bound Fe(II) of FeS2 could activate molecular oxygen to generate superoxide radical (•O2-), which could further promote the effective decomposition of PS by accelerating the Fe(III)/Fe(II) redox cycle. This study unravels the roles of dissolved Fe(II) and surface bound Fe(II) on the persulfate activation, and provides a promising heterogeneous persulfate activator for pollutant control and environmental remediation.

Role of surfactants in accelerating or retarding persulfate decomposition

When surfactants are coupled with persulfate-based ISCO (in situ chemical oxidation) to facilitate the remediation of soil-sorbed hydrophobic organic contaminants or non-aqueous phase liquids, surfactant selection is critical in avoiding excessive nonproductive consumption of persulfate and ensuring proper longevity of persulfate. In this study, the kinetics and mechanisms of the decomposition of persulfate in the presence of simple organic compounds containing primary basic building blocks of nonionic and anionic surfactants were first examined to elucidate the impact of individual building blocks to persulfate decomposition. Further kinetic and mechanistic studies were then carried out in the presence of representative surfactants from the four families of surfactants frequently applied in subsurface remediation. The results indicate that alkyl polyoxyethylene nonionic surfactants significantly accelerated initial persulfate decomposition due to radical-chain processes induced by the oxyethylene functional groups, whereas alkylphenol polyoxyethylene nonionic surfactants retarded initial persulfate decomposition by quenching the radical-chain processes by the aromatic rings. On the other hand, alkyl sulfonate anionic surfactants and alkylbenzene sulfonate surfactants retarded initial persulfate decomposition to some extent; Coulomb repulsion of SO4−/S2O82− and surfactant anion/radical, and entry of surfactant radical anion from the pseudo-aqueous phase into the pseudo-micellar phase may contribute to retarding initial persulfate decomposition. Overall, the results offer insightful structure-based guidance in selecting proper surfactants for surfactant-enhanced persulfate-based ISCO.

Precise control of iron activating persulfate by current generation in an electrochemical membrane reactor

Activated persulfate (PS) oxidation is promising for contaminant removal but a lack of controllable activation can lead to a loss of reagents and thus low contamination degradation. Herein, we have proposed and investigated an innovative method to control PS activation by introducing ion exchange membrane into electrochemically activated PS. This electrochemical membrane reactor (EMR) could precisely control PS activation by adjusting electrical current for slow release of Fe2+, and also avoid direct contact between PS and a sacrificial anode electrode (iron electrode)/an alkaline cathode solution. It was found that the PS decomposition rate constant was linearly increased by increasing the applied current (R2 = 0.988). The rate of the released Fe2+ also exhibited a linear relationship with the applied current (R2 = 0.995). Compared to one-time dosage of Fe2+, the EMR-based slow-release process had higher contamination degradation and better PS utilization (molar ratio of the decomposed PS to the migrated Fe, 1.04 ± 0.01:1), thereby minimizing the waste of both reaction reagents and generated radicals. The EMR was also employed to degrade a representative dye contaminant in a controllable manner and achieved 95.7 ± 0.7% removal percentage with PS dosage of 3.0 g L−1 within 20 min. This study is among the earliest to explore effective approaches for precisely controlling PS activation and subsequent oxidation of contaminants.

New Insights into the Degradation Mechanism of Perfluorooctanoic Acid by Persulfate from Density Functional Theory and Experimental Data.

Thermally activated persulfate is a promising oxidant for in situ remediation of perfluorooctanoic acid (PFOA), yet a comprehensive understanding of the degradation mechanism is still lacking. In this study, we used density functional theory (DFT) calculations and experimental data to map entire reaction pathways for the degradation of PFOA by persulfate, with specific considerations on the influence of pH. The DFT results showed that the rate-limiting step was the first electron abstraction from PFOA, yet the generation of SO4•- from the decomposition of persulfate contributed a large part of the free energy of activation (ΔG‡) for the overall reaction. The subsequent steps did not contribute to the ΔG‡. For the electron abstraction from PFOA, we investigated reactions using protonated and deprotonated species of PFOA and SO4•- and showed that the reaction of anionic PFOA with HSO4• was most favorable with a ΔG‡ of 7.2 kJ/mol. This explains why low pH (<3.5) is a sine qua non condition for the degradation of PFOA by persulfate. The overall ΔG‡ derived theoretically based on the pathway involved HSO4• was consistent with the ΔG‡ determined experimentally. This study provides valuable insight into remediation strategies that include persulfate as an oxidizing agent for perfluoroalkyl carboxylic acids.

Transformation of persulfate to free sulfate radical over granular activated carbon: Effect of acidic oxygen functional groups

In this research, modification of activated carbon using nitric acid was studied in order to investigate the role of acidic oxygen functional groups on the transformation of persulfate to free sulfate radicals for metronidazole antibiotic removal from an aqueous medium. The physicochemical properties of original and modified activated carbons were characterized by Elemental analysis, nitrogen sorption isotherms, scanning electronic microscope, X-ray photoelectron spectroscopy, Raman spectra, Fourier transform infrared spectra, and Boehm titration. Due to the acid treatment, it was found that modification process generated a large number of acidic oxygen functional groups on the surface of activated carbon, especially carboxylic acid. Also, the increase in nitrogen content of surface was very low compared to oxygen content. After modification, the specific surface area and point of zero charge of modified carbon reduced by 36% and 6.2 unit, respectively. Although the adsorption capacity of the two samples was approximately the same, the increase of persulfate decomposition and metronidazole removal after surface modification of catalyst were related to the increase in acidic oxygen functional groups on the surface. Moreover, the affinity of metronidazole removal to catalyst dosage as well as persulfate concentration was grown after modification. In the optimal condition, about 71% of metronidazole was removed after 60 min and gradually reached 87% at the end of the process. Scavenging study showed that the surface reactive radicals were the main responsible in the redox reaction. The reusability of modified carbon showed no obvious decline in the efficiency of the process which indicated the feasible potential of nitric acid modification for the preparation of high quality granular activated carbon.

Controllable Acid/Base Propriety of Sulfate Modified Mixed Metal Oxide Derived from Hydrotalcite for Synthesis of Propylene Carbonate

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; 5; 7), were investigated in this research. The resulted materials were characterized by XRD, SEM, FT-IR spectra, Py-IR spectra, XPS, Hammett indicator, CO2-TPD, as well as NH3-TPD. Furthermore, the acid-base property of the sample surface was determined by inverse gas chromatography measurements (IGC). Among all the obtained outcomes, the target SMgAlO-5 demonstrated the maximal Ka/Kb value, and it presented the highest activity as a catalyst in the synthesis of propylene carbonate (PC) through 1,2-propylene glycol and urea, giving the yield of 97.2% at the optimized reaction condition, which indicated that the PC yield counted on the synergic effect of the acidity and basicity on catalysts.

Efficient activation of persulfate decomposition by Cu2FeSnS4 nanomaterial for bisphenol A degradation: Kinetics, performance and mechanism studies

In this study, a flower-like Cu2FeSnS4 (CFTS) nanomaterial was applied to the activation of persulfate (PS) for the degradation of bisphenol A (BPA) in model industrial wastewater. The efficiency of PS decomposition by CFTS, and the mechanism of contaminant degradation by SO4− were investigated. The results revealed that CFTS catalyzes PS decomposition more efficiently than the monometallic Cu/Fe/Sn sulfides and exhibits activity over a wide pH range. Electron spin resonance spectroscopy, X-ray photoelectron spectroscopy, and free radical quenching experiments revealed a tandem synergistic effect between Cu, Fe, and Sn in their quaternary chalcogenide systems upon PS activation. The intrinsic electron transfer between Cu, Fe and Sn, especially the Fe(II)* species formed upon the complexation of Fe(II) by S on the surface of the CFTS, overcomes the inhibition of the M(n+1)+/Mn+ redox cycle. CFTS shows promise as a catalyst for wastewater treatment.

Confining Free Radicals in Close Vicinity to Contaminants Enables Ultrafast Fenton-like Processes in the Interspacing of MoS2 Membranes.

Heterogenous Fenton-like reactions are frequently proposed for treating persistent pollutants through the generation of reactive radicals. Despite great efforts to optimize catalyst activity, their broad application in practical settings has been restricted by the low efficiency of hydrogen peroxide or persulfate decomposition as well as ultrafast self-quenching of the activated radicals. Theoretical calculations predicted that two-dimensional (2D) metallic 1T phase MoS2 materials with exposed (001) surfaces and (100) edges should have remarkable affinity towards crucial intermediates in the peroxymonosulfate (PMS) activation process. X-ray photoelectron spectroscopy and in situ Raman spectroscopy were used to show that the exposed metallic Mo sites accelerate the rate-limiting step of electron transfer. A lamellar membrane made from a stack of 2D MoS2 with tunable interspacing was then designed as the catalyst. The non-linear transport between the MoS2 nanolayers leads to high water diffusivity so that the short-lived reactive radicals efficiently oxidize contaminants.

Confining Free Radicals in Close Vicinity to Contaminants Enables Ultrafast Fenton‐like Processes in the Interspacing of MoS2 Membranes

AbstractHeterogenous Fenton‐like reactions are frequently proposed for treating persistent pollutants through the generation of reactive radicals. Despite great efforts to optimize catalyst activity, their broad application in practical settings has been restricted by the low efficiency of hydrogen peroxide or persulfate decomposition as well as ultrafast self‐quenching of the activated radicals. Theoretical calculations predicted that two‐dimensional (2D) metallic 1T phase MoS2 materials with exposed (001) surfaces and (100) edges should have remarkable affinity towards crucial intermediates in the peroxymonosulfate (PMS) activation process. X‐ray photoelectron spectroscopy and in situ Raman spectroscopy were used to show that the exposed metallic Mo sites accelerate the rate‐limiting step of electron transfer. A lamellar membrane made from a stack of 2D MoS2 with tunable interspacing was then designed as the catalyst. The non‐linear transport between the MoS2 nanolayers leads to high water diffusivity so that the short‐lived reactive radicals efficiently oxidize contaminants.

Immobilized hybrids between nitrogen-doped carbon and stainless steel derived Fe3O4 used as a heterogeneous activator of persulfate during the treatment of aqueous carbamazepine

Immobilized activators of persulfate (PS) with high activity and stability are highly desirable from an industrial and environmental point of view. In this work, nitrogen-doped carbon (CNx) was successfully hybridized with stainless steel (SS) derived Fe3O4 to construct a SS supported CNx/Fe3O4 heterogeneous catalyst (CNx/Fe3O4/SS). When used in a sulfate radical (SO4−)-based advanced oxidation process (SR-AOP), CNx/Fe3O4/SS displayed significantly higher activity towards the degradation of aqueous carbamazepine (CBZ) when compared to the single Fe3O4 and CNx activators. The removal of CBZ had the most rapid progression, with an initial pH of 3.5, a temperature of 35 °C, an initially added PS concentration of 250 mg L−1 and an added amount of CNx/Fe3O4/SS of 0.30 g. The removal efficiency of CBZ was ∼100% after 35 min of SR-AOPs. In addition, the CNx/Fe3O4/SS catalyst was stable, as demonstrated by six successive cycling experiments. The results obtained from the electron paramagnetic resonance (EPR) spectra and radical quenching experiments indicated that both SO4− and HO contributed to the CBZ oxidation process. On the basis of X-ray photoelectron spectroscopy (XPS) and Fermi level analyses, it can be concluded that SO4− and HO originated from the Fe3O4 catalyzed decomposition of aqueous PS. CNx facilitated the redox cycle of Fe(III)/Fe(II) in Fe3O4. This study demonstrated the potential application of SR-AOPs to efficiently degrade organic contaminants.

Remediation of soil co-contaminated with decabromodiphenyl ether (BDE-209) and copper by enhanced electrokinetics-persulfate process

This work investigated the influences of citric acid and methyl-β-cyclodextrin (MCD) as enhancing agents during the electrokinetics (EK)-persulfate process on the remediation of soil artificially contaminated with decabromodiphenyl ether (BDE-209) and copper (Cu) with an initial concentration of 50 and 1000 mg/kg, respectively. The results clearly demonstrate the efficiency of the process while at the same time, the distribution of the residual contaminants in soil and the EK parameters were greatly influenced by the presence of persulfate, MCD and citric acid. The results show that there was significant removal of BDE-209 and Cu from the soil. MCD-assisted process gave the highest BDE-209 removal (88.6%) and the third largest Cu removal (54.3%) from the soil. Comparatively, the highest Cu removal (92.5%) and the second largest BDE-209 removal (85.6%) were achieved by the joint application of MCD and citric acid in anolyte during the EK-persulfate treatment. MCD and citric acid could increase soil electrical current and electroosmotic flow during EK. The alkalization of soil near cathode was alleviated by the acidic byproducts of persulfate decomposition which could be transported to the soil by electroosmosis and electromigration. This integration process may provide a green efficient technology for remediating co-contaminated soil.

Mechanisms of Interaction between Persulfate and Soil Constituents: Activation, Free Radical Formation, Conversion, and Identification.

Persulfate-based in situ chemical oxidation (ISCO) for soil remediation has received great attention in recent years. However, the mechanisms of interaction between persulfate (PS) and soil constituents are not fully understood. In this study, PS decomposition, activation, free radical formation and conversion processes in 10 different soils were examined. The results showed that soil organic matter (SOM) was the dominant factor affecting PS decomposition in soil, but Fe/Mn-oxides were mainly responsible for PS decomposition when SOM was removed. Electron paramagnetic resonance (EPR) spectroscopy analysis showed that sulfate radicals (SO4•-) and hydroxyl radicals (•OH) generated from PS decomposition subsequently react with SOM to produce alkyl-like radicals (R•), and this process is dependent on SOM content. R• and SO4•-/•OH radicals predominated in soil with high and low SOM, respectively, and all three radicals coexist in soil with medium SOM. Chemical probe analysis further identified the types of radicals, and R• can reductively degrade hexachloroethane in high SOM soil, while SO4•- and •OH oxidatively degrade phenol in low SOM soil. These findings provide valuable information for PS-ISCO, and new insight into the role of SOM in the remediation of contaminated soil.

Enhanced Degradation of Aniline by PS Oxidation in the Presence of UV and Ferric Oxalate

Oxidative degradation of aniline by Sodium Persulfate (PS) activated with UV-ferric oxalate[UV-Fe(C2O4)33-] was studied. The effects of Fe(C2O4)33- concentration, PS concentration, and pH on PS activation and aniline degradation were investigated. Results showed that Fe(C2O4)33- concentration and pH determined the reduction process of Fe3+ into Fe2+, which had significant effects on the oxidative degradation of aniline by PS. With an increase in Fe(C2O4)33- concentration, PS decomposition increased; however, when concentrations were>0.75 mmol·L-1, aniline degradation efficiency decreased due to competition with oxalate ions (C2O42-) for SO4·-. Aniline degradation efficiency in processes with different initial Fe(C2O4)33- concentrations followed the sequence:5 mmol·L-1 < 0.25 mmol·L-1 < 0.5 mmol·L-1 < 1 mmol·L-1 < 0.75 mmol·L-1. Neutral and alkaline conditions were not conducive to Fe2+ formation via photochemical reaction. However, with initial pH values of 7 and 9, PS activation efficiency reached 74% and 67% respectively after 300 min due to pH decline during the reaction; aniline removal efficiency was as high as 91% and 97%, respectively, higher than under initial acidic conditions. Furthermore, increased PS concentration was conducive to improvement of aniline degradation efficiency, but when PS concentration was>10 mmol·L-1, the aniline degradation process followed the pseudo first-order reaction kinetics model instead of the second-order reaction kinetics model. PS efficiency for aniline degradation decreased significantly due to the reaction between excessive PS and sulfate radicals.

Degradation of atrazine by persulfate activation with copper sulfide (CuS): Kinetics study, degradation pathways and mechanism

In this study, copper sulfide (CuS) was used as a catalyst to activate persulfate (PS) for atrazine (ATZ) degradation. A new method called one-eight-lives was proposed to investigate the kinetic parameters (i.e., atrazine concentration, CuS dosage, PS dosage). The t1/8 was calculated to analyze ATZ decay and degradation rate of ATZ, which could be expressed by the kinetic rate equation: −d[ATZ]/dt = (2.985 × 10−4 mmol L−1 min−1) [ATZ]0.023[PS]0.76318[CuS]0.80801. Besides, effects of the initial solution pH and the coexisting inorganic anions (i.e., nitrate ions (NO32−), chloride ions (Cl−), bicarbonate (HCO3−) and phosphate (HPO42−)) on ATZ degradation were also evaluated during the experiments. Also, the intermediate products were identified by ultrahigh performance liquid chromatograph-mass spectrometry (UPLC-MS). Based on the detected intermediates, possible reaction pathways were proposed. The stability and reusability of the CuS was investigated after three consecutive experiments. Characteristics of the fresh and used CuS were analyzed via SEM, EDS, XRD and XPS techniques. Furthermore, the different systems were set up to investigate the performance of CuS under the same experimental conditions. In addition, the radical scavengers (e.g., methanol, tert-butyl alcohol and phenol) experiences and PS decomposition study revealed that PS activation process occurred on the surface of CuS, and sulfate and hydroxyl radicals were the dominant active species for the ATZ degradation. The generation of sulfate and hydroxyl radicals was further confirmed by electron spin resonance (ESR). Besides, the generation of HO during the reaction process in CuS/PS system was quantified indirectly by HPLC. Finally, the possible reaction mechanism of CuS/PS system was proposed according to the comprehensive analysis. The findings of this study provided useful information for the application of CuS in recalcitrant organic contaminants degradation.

Indirect electrochemical oxidation of 2,4-dichlorophenoxyacetic acid using electrochemically-generated persulfate

This research investigated persulfate electrosynthesis using a boron-doped diamond anode and a chemical reaction of persulfate in its activated form with an herbicide, 2,4-Dichlorophenoxyacetic acid (2,4-D). The first part of this research is dedicated to the influence of the applied current density on the electrosynthesis of persulfate. The first part shows that for a 2 M sulfuric acid, the current efficiency reached 96% for 5 mA/cm2 and dropped to 52% for a higher current density (100 mA cm−2). This fall cannot be explained by mass transfer limitations: an increase in temperature (from 9 to 30 °C) during electrolysis leads to the decomposition of 23% of the persulfate. The second part of this research shows that a quasi-complete degradation of the target herbicide can be reached under controlled operating conditions: (i) a high ratio of initial concentrations [Persulfate]/[2,4-D], (ii) a minimum temperature of 60 °C that produces sulfate radicals by heat decomposition of persulfate, and (iii) a sufficient contact time between reactants is required under dynamic conditions.

Advanced treatment of biologically treated coking wastewater by persulfate oxidation with magnetic activated carbon composite as a catalyst.

Advanced treatment of biologically treated coking wastewater (BTCW) using persulfate (PS) oxidation with magnetic activated carbon composite (CuFe2O4:AC w/w ratio of 1:1.5, denoted as 1.5-MACC) as a green catalyst was evaluated at ambient temperature (30 °C). Effects of PS (K2S2O8) and 1.5-MACC doses on PS decomposition and total organic carbon (TOC) removal in BTCW were also studied during 360 min. The results showed that the 1.5-MACC/PS system has a much better performance on TOC removal in BTCW than only 1.5-MACC or PS system. PS decomposition and TOC removal follow first-order kinetics in the 1.5-MACC/PS system. The optimum condition of the 1.5-MACC/PS system to treat BTCW is with a K2S2O8 dose of 4 g L-1 and 1.5-MACC dose of 5 g L-1. Under this condition, TOC in the PS oxidation effluent is 20.4 mg L-1 with a removal efficiency of 85.4%. TOC removal is a synergistic effect of adsorption and oxidation. TOC oxidation is due to the generation of ·SO4- via the activation of PS by CuFe2O4 impregnated AC. The gas chromatography-mass spectrometry (GC-MS) analysis revealed that phenol compounds and esters were removed significantly by the 1.5-MACC/PS system. When 1.5-MACC was used for the fourth time in the 1.5-MACC/PS system, the removal ratio of TOC was still over 62.2% in 360 min reaction. Thus, the 1.5-MACC/PS system has a potential practical application in treatment of BTCW.

Heterogeneously degradation of aniline in aqueous solution using persulfate catalyzed by magnetic BiFeO3 nanoparticles

In this study, magnetic BiFeO3 nanoparticles (BFO MNPs) were successfully synthesized by simple sole-gel method. The BFO MNPs catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) techniques. The prepared catalyst was used to activate persulfate (PS) to generate sulfate radicals (SO4−) for the enhanced degradation of aniline from aqueous solution. It was found that BFO MNPs showed high catalytic activity toward PS decomposition for the degradation of aniline. The degradation efficiency of aniline (0.5 mM) was 100% within 120 min using initial dosage of 0.5 g/L BFO MNPs and concentration of 5 mM persulfate. Even at neutral pH (7.0), aniline was efficiently degraded in BFO MNPs /PS system. The effects of reaction parameters such as initial pH, PS concentration and dosage of BFO MNPs were investigated. The radical scavenging and electron paramagnetic resonance (EPR) results showed that sulfate radicals (SO4−) and hydroxyl radicals (OH) were generated by the activation of PS with BFO MNPs for the degradation of aniline. The stability of catalyst was tested by means of successive reuse cycles. The results revealed that BiFeO3 catalyst exhibited high reusability and stability in degrading aniline through PS activation.