Persulfate Decomposition Research Articles

Soft hydrogels obtained by photothermal curing of poly(vinylpyrrolidone)/gold nanoparticles dispersions showing anisotropic swelling and photo-activated antimicrobial properties

Poly(vinylpyrrolidone) (PVP) hydrogels were obtained by green light irradiation of aqueous PVP/ammonium persulfate solutions modified with gold nanoparticles (AuNPs). The increase in temperature produced through the activation of the photothermal effect of AuNPs triggers the decomposition of ammonium persulfate producing radicals that, by attacking the polymer main chain and generating macro-radicals, induce the crosslinking of the polymer via recombination paths. Irradiation from the top of the solutions in an open configuration produced water evaporation and a concomitant increase in temperature during curing, giving rise to dry materials with high aspect ratio and moderate swelling anisotropy. Pads that reversibly adhere to different substrates, including human skin, were produced by simple contact of the final materials with water. Impregnation of gauze wound dressings with PVP-Au-ammonium persulfate dispersions, followed by direct “in situ” photothermal crosslinking, enabled the fabrication of supported functional pads with potential applications as reversible adhesive skin wound dressings. Infusion of the hydrogels with Rose Bengal (RB) provides the materials with photosensitizing properties useful for the photodynamic inactivation of Staphylococcus aureus. A decrease in cell viability of 99.9% was attained after 30 min of irradiation with a low-power green LED source, which demonstrates the efficient singlet oxygen production by RB in the hydrogels and paves the way towards the design of new stimulus-activated bactericidal supplies for biomedical uses.

New role of radical-induced polymerization: Base/self-heating synergistically activate persulfate to boost food waste humification

Radical-induced polymerization in persulfate (PS)-based advanced oxidation process (AOP) is attracting attention in water decontamination. Herein, we revealed its new role in rapid recycling of perishable food wastes using KOH activated PS. A glucose (Glu) solution of 250 g C/L was applied to mimic the carbohydrate-rich raw material with 50–60% moisture in conventional composting, wherein boosted humification occurred after addition of solid KOH/PS. Intense heat release (from 25 to 79.4 °C), mainly generated from KOH dissolving and exothermic radical chain polymerization, was observed within 2 min. Solid KOH addition contributed to synergistic PS activation by base and self-heating, realizing complete PS decomposition and fulvic like acid (FLA, 210.8 g C/L) formation within 10 min. Extracted FLA promoted cucumber seed germination and fresh weight of chickweeds by 40.0% and 128.3%, respectively. Identified •OH and SO4•- played primary roles in FLA formation through aromatization, carboxylation, and polymerization, wherein several key reactive intermediates such as 5-hydroxymethylfurfural and aromatic radicals (i.e. 1,2,4-benzenetriol radical) were formed. Moreover, the humification process simultaneously produced K2SO4 (i.e. the end product of PS decomposition) which could be used as a typical K/S fertilizer. Scaling-up humification of waste cooked rice and fertilization results further supported the potential of solid KOH/PS in efficiently converting food wastes into FLA and K+-rich compound fertilizer.

Development of a slow-release CO2 absorbent material for alkaline activation of persulfate oxidation of TCE and CO2 capture

Control of carbon dioxide (CO2) emission during chemical oxidation processes of organic-chemical contaminated sites has become a challenge. In this study, a novel slow-release CO2 absorbent material (SCAM) was developed for a slow release of Ca2+ and OH–, which were used for CO2 capture, pH adjustment, and alkaline activation of persulfate (PS) oxidation for trichloroethylene (TCE) degradation. The SCAM was produced using basic oxygen furnace slag (BOFs) and calcium sulfate hemihydrate (CSH) as the components for granulation and modification. Batch experiments were conducted to determine the optimal mass ratio of BOFs to CSH and evaluate CO2 capture capacity and SCAM performance. An increase in BOFs proportion led to a higher CO2 capture capacity, with the maximum capture amount reaching 156 g CO2/kg SCAM. An excessive addition of BOFs resulted in an overly alkaline pH value (pH = 12.4), causing the diminished PS oxidation efficiency. The optimal mass ratio of BOFs to CSH (1 to 1) could capture produced CO2 after TCE oxidation without inhibiting PS oxidation. The SCAM could serve as the catalyst and activate PS oxidation, resulting in 93.1 % of TCE oxidation (initial TCE concentration = 2.32 mM) and 95.4 % of CO2 emission reduction due to the formation of CaCO3 precipitates under alkaline conditions. Produced sulfate and hydroxyl radicals confirmed the PS oxidation of TCE using SCAM as an activator. The developed SCAM is a green catalyst for PS oxidation and it is also an effective CO2 absorbent. SCAM can reduce CO2 emission due to the formation of CaCO3 precipitates under alkaline conditions. The released OH– could also prevent the acidification problem caused by the production of sulfuric acid through PS decomposition.

Surfactant enhanced persulfate system for the synergistic oxidation and reduction of mixed chlorinated hydrocarbons

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is widely applied in soil and groundwater remediation. However, the role of surfactants in the reactive species (RSs) transformation remains inadequately explored. This work introduced nonionic surfactant Tween-80 (TW-80) into a nano zero-valent iron (nZVI) activated persulfate (PS) system. The findings indicate that PS/nZVI/TW-80 system can realize the concurrent removal of trichloroethylene (TCE), tetrachloroethene (PCE), and carbon tetrachloride (CT), whereas CT cannot be eliminated without TW-80 presence. Further analysis unveiled that hydroxyl (HO•) and sulfate radicals (SO4－•) were the primary species for TCE and PCE degradation, while CT was reductively eliminated by surfactant radicals generated from TW-80. Moreover, the surfactant radicals were found to accelerate Fe(III)/Fe(II) cycle, reduce the production of iron sludge, and increase PS decomposition. The possible degradation routes of mixed chlorinated hydrocarbons (CHCs) and the decomposition pathways of TW-80 were proposed through the density function theory (DFT) calculation and intermediates analysis. Additionally, the effects of other nonionic surfactants on the simultaneous removal of TCE, PCE, and CT, and the practical applications using the actual contaminated groundwater were also evaluated. This study provides theoretical support for the simultaneous removal of CHCs, particularly those containing perchlorinated contaminants, using the S-ISCO techniques.

Degradation of diazine dye safranin T using potassium persulfate activated by ultrasonic treatment and MnFe2O4 spinel nanoparticles

An advanced oxidation process of ultrasound/MnFe2O4/K2S2O8 was developed for the degradation of diazine dye safranin T, according to which potassium persulfate was co-activated by ultrasonic (US) cavitation and MnFe2O4 spinel nanoparticles synthesized via co-precipitation in the ultrasonic field. A synthesis product annealed at a temperature of 4000C, with an average size of MnFe2O4 crystallites of about 7 nm, was used as a catalyst for the decomposition of potassium persulfate. Based on the results of experimental studies on the influence of various factors on the degree and rate constant of safranin T oxidative degradation, as well as considering energy and resource-saving principles, the rational conditions of oxidative degradation were determined as follows: the reaction medium temperature of 600C, the molar ratio of safranin T:K2S2O8=1:100, the catalyst loading of 0.1 g/l, and the specific power of the ultrasonic cavitation treatment of 51.0 W/l. It was established that under such conditions the oxidative degradation degree of safranin T was equal to 98.3%, and the rate constant was 1.510–3 s–1. The changes in the UV-Vis spectra of safranin T, namely a decrease in the intensity of absorption bands, both in the visible (at a wavelength of 520 nm) and in the UV (at a wavelength of 275 nm) regions of the spectrum, confirmed the degradation of safranin T. In addition, the absence of the appearance of new peaks in the visible and UV regions of the spectrum indicated mineralization of the dye.

Electrochemiluminescence Enhancement and Passivation Mitigation in Carbon Nitride Semiconductors via an Integrated Ternary Heterostructure Strategy.

In recent years, carbon nitride (CN) has attracted substantial attention in the field of electrochemiluminescence (ECL) applications, owing to its outstanding optical and electronic properties. However, the passivation of CN during the ECL process has contributed to reduced stability and poor repeatability. While some studies have tried to boost ECL performance by altering CN through doping and vacancies, effectively suppressing CN passivation at high potentials continues to be challenge. In this study, the built-in electric field and the Schottky barrier effect is used to expedite the transfer of electrons from CN to the molybdenum disulfide (MoS2) conduction band. This transfer deterred excessive electron injection into the CN band, thus mitigating its electrochemical degradation. Moreover, by introducing nickel nanoparticles (Ni NPs) as catalytic active sites, it is facilitated that the decomposition of potassium persulfate (K2S2O8), thereby enhancing both the stability and intensity of ECL emission. In the end, the application of ternary heterostructure as sensing platform for the cancer biomarker carcinoembryonic antigen (CEA) demonstrated high sensitivity. This research introduces a novel approach to overcome CN passivation, paving the way for more promising applications of CN in energy, environmental, and biosensing fields.

Activation of persulfate for the degradation of ethyl-parathion in soil: Combined effects of microwave with biochar

Sulfate radical (SO4•−), formed by persulfate (PS) activation during advanced oxidation process (AOPs), can be used for the remediation of organic contaminated soil. However, the role of biochar and microwave (MW) in the activation of PS is not fully understood, especially the corresponding mechanism. Herein, biochar combined with MW was used to activate PS for the remediation of ethyl-parathion (PTH)-polluted soil. The dynamic evolutions of PTH under different conditions, such as biochar content, particle size, reaction temperature, and the degradation mechanisms of PTH were also systematically investigated. Significant enhancement performance on PTH removal was observed after adding biochar, which was 88.78% within 80 min. Meanwhile, activating temperature exhibited remarkable abilities to activate PS for PTH removal. The higher content of adsorption sites in nano-biochar facilitated the removal of PTH. Furthermore, chemical probe tests coupled with quenching experiments confirmed that the decomposition of PS into active species, such as SO4•−, •OH, O2•− and 1O2, contributed to the removal of PTH in biochar combined with MW system, which could oxidize PTH into oxidative products, including paraoxon, 4-ethylphenol, and hydroquinone. The results of this study provide valuable insights into the synergistic effects of biochar and MW in the PS activation, which is helpful for the potential application of biochar materials combined with MW-activated PS in the remediation of pesticide-polluted soils.

Ascorbic acid promoted sulfadimidine degradation in the magnetite-activated persulfate system by facilitating the Fe(III)/Fe(II) cycle.

Persulfate (PS) activation technologies were of significant importance to the organic contaminant treatment. In this study, ascorbic acid (AA) was introduced to the traditional PS-activated process by using magnetite (Fe3O4) as the activator; herein, the degradation efficiency of sulfadimidine (SM2) was improved from 30 to 93% within 3h, and the observed removal rate was about 8.0 times higher than that of the Fe3O4/PS system. These improvements were found to be induced by the added AA because it could reduce the surface Fe(III) to Fe(II) on Fe3O4 and thus facilitate the Fe(III)/Fe(II) cycle, which was conducive to producing reactive oxygen species (ROSs) in the oxidation process during PS activation. Meanwhile, AA could also promote the Fe(III)/Fe(II) cycle in the homogeneous solution, further advancing the PS decomposition for SM2 degradation. The ROS trapping experiments indicated that SM2 removal in the Fe3O4/PS/AA system was attributed to •OH and •SO4-, and •SO4- was the dominant ROS. Moreover, the reusability test experiment revealed that magnetite retained good activity after five cycles in the Fe3O4/AA/PS system. This study provides a promising PS activation technology for efficient organics contaminant treatment.

Efficient activation of persulfate by metallic sulfide mineral for the efficient removal of pesticides: Performance, radical generation and mechanism

In current years, the harm of pesticide residual pollution to environmental ecology and human health has obtained increasing attention. Hydroxylamine (HA) promoted activation of persulfate (PS) by the natural metallic sulfide mineral chalcopyrite (CuFeS2) for the removal of pesticide chlorpyrifos (CPF) and imidacloprid (IMP) in water had been systematically investigated in this study. Experimental results showed that HA could greatly accelerate the regeneration of Cu2+ and Fe3+ in solutions for PS decomposition. Nearly 99% of CPF removal by CuFeS2/PS/HA process was achieved within 80 min under optimal conditions. The decomposition of PS in the CuFeS2/PS/HA process was higher than that in the CuFeS2/PS process. Several coexisting cations (ie., Ca2+, Mg2+ and Al3+) and anions (ie., HCO3− and HPO42−) presented different levels of negative effects on CPF removal. Both HO• and SO4•− were generated in the CuFeS2/PS/HA process, and HO• might be the main reactive species responsible for the removal of CPF. The synchronized removal of CPF and IMP by CuFeS2/PS/HA process had been successfully achieved under certain conditions. The possible pathways of CPF degradation and enhanced mechanism for both CPF and IMP removal by CuFeS2/PS/HA process were thereby proposed. This study highlights the applications of CuFeS2/PS/HA process for the remediation of multiple pesticides-polluted wastewaters.

Self-adhesive frost-resistant conductive hydrogel electrolytes based on TA@WSCA-Zn autocatalytic system for flexible and foldable solid-state capacitors

In this study, we have successfully prepared a freeze-resistant conductive hydrogel with a fast polymerization rate and excellent mechanical and adhesive properties. In this paper, hydrogels capable of rapid polymerization in a short time were prepared based on the TA@WSCA-Zn (WSCA, water-soluble cellulose acetate; TA@WSCA, tannic acid-coated WSCA suspension; TA@WSCA-Zn, a certain amount of zinc chloride (ZnCl2) was added to TA@WSCA suspension;) autocatalytic system at room temperature or low temperature. TA@WSCA-Zn forms a stable reversible quinone-catechol redox reaction to activate the decomposition of ammonium persulfate (APS, initiator) to produce SO4−· radicals, which triggers the ultra-fast polymerization of amphoteric ([2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl), SBMA) and acrylic monomers (AA). To improve the frost resistance and electrical conductivity of the hydrogels, we also introduced amphoteric ions, which can provide migration channels for Zn2+ and greatly increase the migration rate. The TA@WSCA-7.5/PSA hydrogel (PSA, hydrogel prepared by polymerization of acrylic acid and SBMA as monomers;) can achieve tensile strength and toughness of 1.33 MPa and 4.89 MJ m−3. It can provide excellent electrical conductivity and interfacial adhesion over a temperature range of 25 to −60 °C. In addition, the supercapacitor assembled from the TA@WSCA-7.5/PSA hydrogel electrolyte still has good capacitance characteristics after folding and 10,000 charge/discharge cycles, with a capacitance retention of 93.33 % and an excellent cycle life. This autocatalytic system provides a new strategy and approach for the preparation of freeze-resistant conductive hydrogel electrolytes.

Screening analysis: An alternative for real-time analysis and greener microwave-assisted persulfate decomposition of flavored beverages

The proposed procedure aims to generate information about the decomposition efficiency of organic matter before the instrumental determination of elements and real-time decision-making. In the presence of organic compounds samples, the irradiation time was consistently higher (at least 20 s or more) than that observed for the appearance of MnO4– in organic matter-free solutions (10±1 s, n = 6). Moreover, RCC values ≤14% were determined for all solutions independent of the target compound observed. Total carbon was determined in samples before and after persulfate decomposition, with a 95% reduction in the carbon content, except for grape-flavored waters (RCC = 85%). The microwave-assisted S2O82−/Mn2+ system allowed a fast, clean and effortless approach leading to material, energy, and time-saving method for mineralizing beverages.

New Insights on the Kinetics of Persulfate‐Initiated Itaconic Acid Free‐Radical Polymerization

AbstractA mathematical model is proposed that couples the decomposition kinetics of persulfate (S2O82−) and the free radical polymerization kinetics of itaconic acid (IA); the results are compared with experimental data reported in the literature. It is found that the former is highly affected by the acidification of the aqueous medium which is caused by the equilibrium dissociation of IA but mainly by HSO4− produced by side reactions of the S2O82− decomposition. This qualitatively explains the dependence of d[S2O82−]/dt with [IA] and the initial concentration of persulfate ([S2O82−]0), reported in the literature. According to the model results, temperature overshoots are very likely to occur in the experiments so there is doubt whether the reaction order >1 with respect to [IA] that is sometimes reported in the literature for the rate of polymerization (Rp) is an artifact related to an imprecise temperature (T) control or is due to a more complex mechanism. Due to the higher activation energy of the persulfate decomposition compared to the propagation reaction, small variations of T can lead to significant variations of d[S2O82−]/dt but to an almost imperceptible effect on Rp. Recommendations for future experimental work and refinement of the kinetic model are provided.

New insights into persulfate decomposition by soil minerals: radical and non-radical pathways

Persulfate (PS)-based in situ chemical oxidation (ISCO) has been widely used for pollutant remediation in soil and groundwater. However, the underlying mechanism of interactions between mineral and PS was not fully explored. In this study, several soil model minerals including goethite, hematite, magnetite, pyrolusite, kaolin, montmorillonite, and nontronite were selected to investigate their potential effects on PS decomposition and free radical evolution. It was found the decomposition efficiency of PS by these minerals varied significantly, and both the radical and non-radical decomposition processes were included. Pyrolusite has the highest reactivity for PS decomposition. However, PS decomposition is prone to form SO42- through non-radical pathway, and thus, the amounts of free radicals (e.g., •OH and SO4•-) produced are relatively limited. However, PS mainly decomposed to produce free radicals in the presence of goethite and hematite. In the presence of magnetite, kaolin, montmorillonite, and nontronite, PS both decomposed to produce SO42- and free radicals. Furthermore, the radical process exhibited the high degradation performance for model pollutant such as phenol with relatively high utilization efficiency of PS, while non-radical decomposition has limited contribution to phenol degradation with extremely low utilization efficiency of PS. This study deepened the understanding of interactions between PS and minerals during the PS-based ISCO in soil remediation.

Enhanced mechanism of carbamazepine degradation by electrochemical activation of persulfate in flow-through system

Degradation of carbamazepine (CBZ) was first conducted by electrochemical activation of persulfate (PS) in flow-through system using boron and cobalt co-doped TiO2 nanotubes (B, Co-TNT) as the anode and carbon felt (CF) as the cathode, achieving a higher removal efficiency than that in beaker mode ascribed to the higher PS decomposition for OH production. Different operating parameters including applied current, initial pH, PS concentration and flow rate were explored, supporting that high current, acidic condition, lofty PS concentration and flow rate were beneficial for the removal of CBZ. The mechanisms of CBZ degradation by electrochemical activation of persulfate in flow-through system were the comprehensive effect of OH, SO4− and 1O2, and the possible CBZ degradation pathway was proposed. In summary, B, Co-TNT anode coupled with CF cathode in flow-through system by electrochemical activation of persulfate was an effective method for contaminants degradation.

Toluene NAPL Oxidation by Ferrous Activated Persulfate in a Fractured Rock Glass Replica

AbstractNon‐aqueous phase liquids (NAPLs), such as toluene, often contaminate the subsurface. In this study, we focus on the transformation of toluene NAPL trapped in a single glass replica of a rock fracture via in situ chemical oxidation (ISCO) with ferrous activated persulfate. The trapped toluene consisted of a main trapped blob surrounded by smaller blobs. Over 53 days, successive persulfate injections into the fracture were interspersed with periods of water flushing. During persulfate injections, effluent toluene concentrations were below 0.04 mM. The rebound toluene concentrations during intervening water flushing periods decreased from 0.9 to 0.3 mM over the study. The smaller toluene blobs were removed by dissolution and partial oxidation. The main toluene blob was reduced in area by 35.5% and in volume by 37.3% due to dissolution and partial oxidation. The main blob changed in shape with reduction in size and there was also formation of an oxidation by‐product zone around the blob. The reduction in toluene effluent concentrations with time over successive persulfate injections and periods of water flushing was attributed to reductions in the NAPL‐water interfacial area of the blob and the formation of the by‐product zone surrounding the blob, which resulted in limited toluene dissolution. Analysis of by‐products of toluene oxidation by ferrous activated persulfate suggests that oligomers were part of the by‐product zone formed in the fracture. Gas bubbles were also observed in the fracture and may have formed from toluene oxidation and persulfate decomposition.

The role of sulfate radicals and pH in the decomposition of persulfate in aqueous medium: A step towards prediction

The decomposition of persulfate (S2O42−) is a relevant part of free-radical polymerizations in aqueous media, advanced oxidation processes and nanocellulose production. For the first time, dispersed information reported in the literature about the different reactions that occur in the process were consistently integrated into a kinetic model. A sequence of calculations is proposed to evaluate some unknown rate coefficients mainly at 50°C using experimental kinetic data reported in the literature. It is proposed that the decomposition of persulfate occurs by a set of (at least) four parallel reactions one of which is first order (the thermal path) and the others second order. According to the model results, the predominance of each of them depends on the pH except for the thermal path that is present at any pH. Under strong acid and alkaline conditions at constant pH, first-order/pseudo first-order kinetics is obtained (the observable rate coefficient kd0 is constant). At intermediate pHs, where the concentration of sulfate radicals [SO4*−] is maximized, the second order character of the reaction between S2O42− and SO4*− and the autocatalytic-like behavior of the latter become evident (kd0 decrease with time). Notwithstanding the differences between theory and experiment for certain conditions observed in this work, the proposed mathematical model is able to describe the overall kinetic features of the process under study, at least at 50°C. Recommendations are provided so that future experimental work carried out in different laboratories, is comparable.

Oxidation of bromide by heat-activated persulfate – Effects of temperature and the organic matter surrogate phenol on kinetics and stoichiometry

• Oxidation of persulfate by sulfate radical affects persulfate decomposition kinetics. • Bromide oxidation to bromate was hindered by phenol. • Sulfate radicals reacting with Br-species decreased at higher temperature. • Insoluble phenol oxidation byproducts formation is favored at high temperature. Reaction mechanisms of sulfate radical with bromide and organic substances can be largely altered at elevated temperature in heat-activated persulfate process due to different activation energies. This study investigated kinetics and stoichiometry of bromide oxidation in the heat-activated persulfate process. We postulated that reaction of sulfate radical with persulfate, which has relatively low reaction rate (6.3 × 10 5 M −1 s −1 ), may become an important reaction at elevated temperatures. Persulfate decomposition was inhibited in the presence of sulfate radical scavenger phenol at low temperature (40 °C) whereas phenol affected persulfate decomposition only at < 50 °C but not at higher temperatures. This was because the second order reaction rate constant of sulfate radical with persulfate became higher (assumed as 10 10 M −1 s −1 ) than with phenol at a temperature > 50 °C, which can be explained by a high activation energy (estimated activation energy: 311 kJ/mol). Bromate formation was inhibited in the presence of phenol. However, phenol oxidation was not affected by the presence of Br − , even though Br − reacts faster with sulfate radicals than phenol and was present in excess. This indicated that formed reactive bromine species such as Br and Br 2 − oxidize phenol under reformation of bromide. Formation of insoluble products was also observed indicating polymerization of phenol. This can be explained by lack of dissolved oxygen under conditions of heat-activation.

Structural dependent persulfate activation by coke powder for aniline degradation

• Structural dependent PS activation by CP is investigated. • CP holds excellent activity for PS activation over a wide pH range. • Dissolved oxygen plays an insignificant role in ROS generation. • The carbonaceous component on CP involves in PS activation but ash does not. • PFRs, OFGs, sp 2 -hybridized carbon and defects contribute to persulfate activation. Coke powder (CP), the by-product of coal carbonization, its activity of persulfate (PS) activation was systematically investigated. Structural dependent organic pollutant degradation performances and the related mechanisms were discussed in detail. The structural characteristics of CP were studied using X-ray diffraction, Raman, Fourier transform infrared spectra, X-ray photoelectron spectra, and electron paramagnetic resonance (EPR) etc. Characterization results indicate that CP contains ∼ 78% carbon and presents highly disordered amorphous structures with abundant oxygenated functional groups (OFGs) and persistent free radicals (PRFs). The catalytic application reveals that CP held excellent activity for PS activation across a wide pH range from 3 − 11. In the presence of 0.5 g/L CP, 0.25 mM PS and 0.021 mM aniline (pH 7 ± 0.2), >99% aniline was degraded within 40 min. Under the interference of inorganic anions (Cl − , HCO 3 − and SO 4 2− ), 98% aniline degradation efficiency still could be achieved. Meanwhile, quenching tests and EPR demonstrated that the superoxide anion radical (O 2 − ) was responsible for aniline degradation in CP/PS system, and its generation was independent of dissolved oxygen. The outstanding performance of aniline degradation and ROS generation were attributed to the existence of PRFs, sp 2 -hybridized carbon, OFGs and defects on CP inducing O–O bonding homolytic cleavage of PS into sulfate radicals. Besides, the OFGs including C–OH and –COOH as electron donors facilitated PS decomposition to generate O 2 − . The findings imply that CP is an excellent PS activator, and clarify the development of remediation materials by using by-products of coking process for wastewater treatment.

Efficiency of the heterogeneous catalyst from electrocoagulation sludge for the removal of methylene blue in the presence of persulfate

Persulfate activation by heterogeneous catalysts based on transition metals is of interest in textile effluent treatment processes. Thus, iron-rich electrocoagulation sludge has been thermally treated to obtain new catalysts. The characterization of this catalyst by X-ray diffraction revealed the presence of FeAl2O4 nanoparticles active in the decomposition of persulfate into sulfate radicals (SO4 •−). The efficiency of catalyst/persulfate was monitored during the methylene blue (MB) solution discoloration. The effects of temperature, pH, initial MB concentration, catalyst dose and persulfate dose were also studied. MB removal catalytic activity showed around 94% discoloration and 45.7% TOC reduction after 180 minutes batch reaction at pH = 4.0 (catalyst dose: 0.5 g/L, persulfate dose: 1 g/L; initial MB concentration: 20 mg/L). This catalyst reuse further confirmed its catalytic potential as a discoloration rate of about 82.45% was obtained after five cycles. The biodegradability monitoring measured by the carbon oxidation state (COS) has revealed a remarkable and continuous degradation of organic compounds. The EPR tests revealed that this catalytic reaction generates the radical species responsible for the degradation of MB. Finally, these results show that this catalyst from the thermal activation of electrocoagulation sludge is capable of decomposing persulfate to degrade bioresistant compounds such as textile dyes.

Catalytic effects of activated-carbon particle size on the oxidative degradation mechanisms of a pharmaceutical

The effects of the size of activated carbon (AC) on the catalytic degradation of organic micropollutants was investigated by the removal of a pharmaceutical (acetaminophen, ACT) using persulfate (PS). The removal of ACT, either by adsorption or oxidative degradation, and PS decomposition were enhanced by decreasing the size of the AC. The smallest AC particle (AC1) showed higher specific surface area, pore volume, macropores, and fractions of sp2-C and CO, but lower ID/IG, I2D/IG, and fractions of sp3-C and of O-CO, compared with the largest AC particle (AC6). Electron paramagnetic spectroscopy revealed a strong SO4•− signal for AC1, but the signal for AC6 appeared weaker after 30 min of reaction time. Decomposition of PS and peroxymonosulfate (PMS) was significantly enhanced by increasing the concentration of the electron donor (ACT) when AC1 was used, but it was not affected when AC6 was used. In addition, degradation of micropollutants and PS decomposition were seriously affected by their ionization potential when AC1 was used, and less affected when AC6 was used. These results suggest that the degradation of organic pollutants by AC1 + PS and AC6 + PS can be attributed primarily to the non-radical and radical pathways, respectively. Meanwhile, the catalytic activity was decreased as AC1 and AC6 were reused because of deactivation process. This indicates that the size of AC is a powerful determinant of the characteristics and can be optimized for the catalytic degradation of organic micropollutants.