Formation Of Sulfate Radicals Research Articles

Radiation-induced preparation of nanoscale CoO@graphene oxide for activating peroxymonosulfate to degrade emerging organic pollutants

In this study, ionizing radiation was used to induce the in-situ formation of highly dispersed nanosized cobalt oxide on the surface of graphene oxide (R-Co-GO), which was highly effective for activating PMS to degrade sulfamethoxazole (SMX). R-Co-GO had the highest catalytic activity when 150 μL cobalt chloride hexahydrate solution was used in the precursor, and the pseudo first-order kinetic constant of SMX degradation was 0.07 min−1 with high mineralization efficiency (63.1 %) and high PMS utilization efficiency. The sulfate radicals and high-valent cobalt oxo were mainly responsible for SMX degradation. Mechanism analysis showed that cobalt active site dominated in PMS activation, which was responsible for the formation of sulfate radicals and high-valent cobalt oxo; while the carbon framework contributed to the formation of singlet oxygen. The R-Co-GO-150 had good catalytic activity and stability in five cycling experiments, in which SMX was completely degraded and the concentration of dissolved Co was below 0.1 mg/L. In addition, the R-Co-GO-150/PMS system could also degrade phenol, bisphenol A, atrazine and nitrobenzene effectively, confirming its wide applicability. This study provided a facile method to uniformly disperse the metal oxides on the surface of carbon materials, and an effective system for the removal of emerging organic pollutants from the actual wastewater.

Comparative study of reactive oxygen species and tetracycline degradation pathways in catalytic peroxodisulfate activation by asymmetric mesoporous TiO2 and the corresponding controlled-release materials

The removal of trace amounts of antibiotics from water environments while simultaneously avoiding potential environmental hazards during the treatment is still a challenge. In this work, green, harmless, and novel asymmetric mesoporous TiO2 (A-mTiO2) was combined with peroxodisulfate (PDS) as active components in a controlled-release material (CRM) system for the degradation of tetracycline (TC) in the dark. The formation of reactive oxygen species (ROS) and the degradation pathways of TC during catalytic PDS activation by A-mTiO2 powder catalysts and the CRMs were thoroughly studied. Due to its asymmetric mesoporous structure, there were abundant Ti3+/Ti4+ couples and oxygen vacancies in A-mTiO2, resulting in excellent activity in the activation of PDS for TC degradation, with a mineralization rate of 78.6%. In CRMs, ROS could first form during PDS activation by A-mTiO2 and subsequently dissolve from the CRMs to degrade TC in groundwater. Due to the excellent performance and good stability of A-mTiO2, the resulting constructed CRMs could effectively degrade TC in simulated groundwater over a long period (more than 20 days). From electron paramagnetic resonance analysis and TC degradation experiments, it was interesting to find that the ROS formed during PDS activation by A-mTiO2 powder catalysts and CRMs were different, but the degradation pathways for TC were indeed similar in the two systems. In PDS activation by A-mTiO2, besides the free hydroxyl radical (·OH), singlet oxygen (1O2) worked as a major ROS participating in TC degradation. For CRMs, the immobilization of A-mTiO2 inside CRMs made it difficult to capture superoxide radicals (·O2−), and continuously generate 1O2. In addition, the formation of sulfate radicals (·SO4−), and ·OH during the release process of CRMs was consistent with PDS activation by the A-mTiO2 powder catalyst. The eco-friendly CRMs had a promising potential for practical application in the remediation of organic pollutants from groundwater.

Electrodeposition of CoNi alloys in a biocompatible DES and its suitability for activating the formation of sulfate radicals

Building a sustainable future requires new, accessible, economic, and ecological methods of preparing nanostructured materials used in biomedical and environmental applications. In this work, a detailed study on the electrodeposition process of CoNi in a biocompatible deep eutectic solvent (DES) is presented. Alloy plating performed in choline chloride within a urea-based DES allowed us to tailor elemental compositions, morphologies, and size of the deposits based on the plating conditions. Homogeneous, continuous, and needle-shaped deposits were characterized using electrochemical methods and ex-situ characterization techniques. Although the process's electrochemical behavior corresponded to that of normal deposition, applying the most negative potentials produced a co-reduction of the solvent, which favored the incorporation of oxygen species into the deposit. Given the materials’ nature, morphology, and composition tailored to the high active surface, the materials were tested as platforms to activate the formation of sulfate radicals from the peroxomonosulfate salt. Results related to the proposed material and preparation method were promising, as, confirmed by the high effectiveness in degrading the antibiotic tetracycline. Altogether, the work showcases a versatile, environmentally friendly route for electrodepositing CoNi in DESs to yield a proactive tool for developing of platforms with catalytic potential.

In-situ photoelectrocatalytical formation of sulfate radicals on BiPO4 modified carbon paper electrode in sodium sulfate electrolyte for high efficient degradation of pefloxacin

In recent years, advanced oxidation processes (AOP) based on sulfate free radicals (SO4−·) have attracted considerable attention due to the excellent advantages of SO4−· compared with hydroxyl radical (·OH). However, SO4−· generally produced by activating extra persulphates, which causes high cost and risk of secondary pollution. In this work, BiPO4 modified carbon paper electrode (BiPO4/CP) successfully fabricated via simple method can be used as a photocatalyst to effectively activate sulfate originally existed in wastewater to generated sulfate radicals in-situ without adding any extrinsic chemical oxidants. Pefloxacin (PFX) was degraded effectively on BiPO4/CP with the help of applied potential. CP with large surface area and high electrical conductivity as an excellent support for BiPO4 is beneficial to improve the reutilization, electron transfer and photocatalytic performance of BiPO4. Moreover, BiPO4 with large bandgap has sufficient redox capacity to produce not only ·OH, superoxide radical (·O2−), but also SO4−·, which is crucial for photocatalytic pollutant degradation. Detailed characterizations give strong evidences of the successful fabrication of photocatalyst, thermodynamic feasibility of SO4−· in-situ formation, the generation of free radicals, and the possible mechanism. Consequently, under the optimal conditions (pH=5.6, +1.0 V (vs.SCE), [SO42−]=10 mM, 61 μW cm−2 UV light irradiation, 33 mg BiPO4 loaded on CP), the degradation efficiency of PFX (10 mg/L) was 87.8% in 120 min, which was 5.1 ad 8.2 times higher than that in photocatalytic and electrocatalytic system and 3.3 times higher than that without SO42−. Meanwhile, BiPO4/CP maintains high level of degradation efficiency of PFX after 6 cycles under the optimal conditions.

Sulfate radical formation by Cr(III) activation of peroxydisulfate – Diphenylcarbazide spectrophotometric determination of sulfate radical and its scavenging activity

Even though sulfate anion radical (SO4−) is a very reactive oxidant used in advanced oxidation processes, a reliably selective and simple colorimetric method for determining this radical can hardly be found. Peroxydisulfate (S2O82−) or peroxymonosulfate (HSO5−) can be activated with transition metal ions to produce SO4−. We have discovered that Cr(III) can be an activator for persulfate, generating Cr(VI) along with SO4−. By measuring the emerging chromate with diphenyl carbazide (DPC) spectrophotometry at 542 nm, we could measure both the formation of SO4− and its scavenging with antioxidant compounds. We could also investigate a number of UV-absorbing SO4− scavengers which could not be measured with other UV spectrometric methods. In addition to conventional antioxidants (phenolics such as quercetin, catechin, epicatechin, caffeic acid, thiols like cysteine and N-acetyl cysteine, and ascorbid acid), nitro-aromatics (represented by 2,4,6-trinitrophenol and 2,4-dinitrophenol) used in ammunition formulations could also be measured as scavengers. The presence of scavengers caused a reduction in the amount of Cr(VI) generated, where the difference in absorbance (ΔA) of chromate – with respect to the DPC method – in the absence and presence of scavengers was a linear function of SO4− scavenging capacity. Ethanol and tert-butanol were tested as solvents to show the selectivity of the method for SO4−. The method was statistically compared to a suitably modified ABTS/persulfate assay. The efficiency order of sulfate radical scavengers was determined and ranked (Spearman’s test) using both the proposed method and modified ABTS/persulfate method to reveal a moderate correlation.

Phase change on stainless-steel mesh for promoting sulfate radical formation via peroxymonosulfate oxidation

Surface-etched and N2-annealed stainless-steel mesh (NESS) was fabricated by a chemical etching and annealing treatment under a nitrogen atmosphere of a cheap stainless-steel mesh, and employed to degrade organic pollutants via peroxymonosulfate (PMS) activation. Extensive characterization showed that surface modification could bring about phase change and metal layer generation with a thickness of several nanometers. Excellent electron conductivity and the favorable morphology with coexisting Fe, Ni, and Cr species in NESS make an effective electron transfer between catalysts and PMS. The as-prepared NESS itself can induce the PMS activation, and oxygen vacancies can strengthen chemical bonding with PMS, providing active sites to activate PMS. As a result, NESS possessed a superior activity in PMS activation for mineralization of organic compounds. Electron paramagnetic resonance and quenching experiments demonstrated SO4•−, HO•, O2•− and 1O2 were the dominant reactive species. Considering the procedure simplicity, NESS is an effective and low-cost catalyst for environmental applications.

Novel CuCo2O4 Composite Spinel with a Meso-Macroporous Nanosheet Structure for Sulfate Radical Formation and Benzophenone-4 Degradation: Interface Reaction, Degradation Pathway, and DFT Calculation.

A series of CuCo2O4 composite spinels with an interconnected meso-macroporous nanosheet morphology were synthesized using the hydrothermal method and subsequent calcination treatment to activate peroxymonosulfate (PMS) for benzophenone-4 (BP-4) degradation. As-prepared CuCo2O4 composite spinels, especially CuCo-H3 prepared by adding cetyltrimethylammonium bromide, showed superior reactivity for PMS activation. In a typical reaction, BP-4 (10.0 mg/L) was almost completely degraded in 15 min by the activation of PMS (200.0 mg/L) using CuCo-H3 (100.0 mg/L), with only 9.2 μg/L cobalt leaching detected. Even after being used six times, the performance was not influenced by the lower leaching of ions and surface-absorbed intermediates. The possible interface mechanism of PMS activation by CuCo-H3 was proposed, wherein a unique interconnected meso-macroporous nanosheet structure, strong interactions between copper and cobalt, and cycling of Co(II)/Co(III) and Cu(I)/Cu(II) effectively facilitated PMS activation to generate SO4•- and •OH, which contributed to BP-4 degradation. Furthermore, combined with intermediates detected by liquid chromatography quadrupole time-of-flight mass spectrometry and density functional theory calculation results, the degradation pathway of BP-4 involving hydroxylation and C-C bond cleavage was proposed.

Mechanisms of electro-assisted persulfate/nano-Fe0 oxidation process: Roles of redox mediation by dissolved Fe

Mechanisms involved in an electrochemically assisted oxidation process using persulfate and nanosized zero-valent iron (NZVI) were elucidated. Initially, Fe0 acted as a source of Fe2+ to activate the persulfate, then Fe2+/Fe3+ redox mediation between cathode and persulfate played a decisive role in persulfate activation at a current density low enough not to inhibit Fe0 corrosion. An excessive current density which resulted in a low cathodic potential limited Fe0 corrosion and therefore limited the supply of dissolved Fe to activate the persulfate. Direct oxidation of phenol at the anode therefore became more important under the excessive current density than oxidation by sulfate radicals. At a low current density, Fe0 in the NZVI particles was completely transformed into iron (oxyhydr)oxides such as ferrihydrite, lepidocrocite, and magnetite. Fe0 was transformed into Fe2+ little when the current density was high. Increasing the current density increased the energy cost by increasing the amount of electrical energy dissipated in side reactions that decreased sulfate radical formation. The results indicated that a low current density can generally be used to give a high reaction rate and a high energy efficiency and that a high current density can be used when the NZVI particles need to be preserved.

Synthesis of Magnetic CoFe₂O₄ Nanoparticles and Their Efficient Degradation of Diclofenac by Activating Persulfate via Formation of Sulfate Radicals.

In this study, magnetic CoFe2O4 nanoparticles were synthesized by hydrothermal method by using ferric nitrate and cobalt nitrate as raw materials. Subsequently, physicochemical properties of the resulting CoFe2O4 nanoparticles were systematically studied by scanning electron microscope, X-ray diffraction, N2 adsorption/desorption, Fourier transformation infrared spectroscopy and Vibration sample magnetometer measurement. Results indicated that CoFe2O4 nanoparticles with cubic spinel structure possessed an average diameter of 6.9 nm, specific surface area of 103.48 m2 · g-1, saturation magnetization of 54.65 A · m2(emu · g-1) and coercivity of 1.76×104 A · m-1. Furthermore, scavenging experiments revealed that sulfate radicals (.SO-4) was the main active species derived from persulfates, in which 72.3% of diclofenac could be degraded within 30 min treatment. This study provides a promising strategy to synthesize versatile catalyst which would be potentially applied in pharmaceutical wastewater purification.

Understanding Electrochemically Activated Persulfate and Its Application to Ciprofloxacin Abatement.

This study offers insight into the roles anodic and cathodic processes play in electrochemically activated persulfate (EAP) and screens EAP as a viable technique for ciprofloxacin degradation in wastewater. Sulfate radical formation at a boron-doped diamond (BDD) anode and persulfate activation at a graphite cathode were experimentally elucidated using different electrolytes and electrochemical setups. Rapid ciprofloxacin transformation occurred via pseudo-first-order mechanisms with respect to ciprofloxacin in persulfate electrolyte, reaching 84% removal in 120 min using EAP. Transformation pathways were compared to those in nitrate and sulfate electrolytes. Ciprofloxacin removal rates in the electrochemical system were 88% and 33% faster in persulfate than nitrate and sulfate electrolytes, respectively. Total organic carbon removal rates were 93% and 48% faster in persulfate than nitrate and sulfate, respectively. Use of sulfate electrolyte resulted in removal rates 6-7 times faster than those in nitrate solution. Accelerated removal in sulfate was attributed to anodic sulfate radical formation, while enhanced removal in persulfate was associated with cathodic persulfate activation and nonradical persulfate activation at the BDD anode. Quenching experiments indicated both sulfate radicals and hydroxyl radicals contributed to degradation. Comparisons between platinum and graphite cathodes showed similar cathodic persulfate activation and ciprofloxacin degradation.

Fabrication of magnetic Co/BiFeO 3 composite and its advanced treatment of pharmaceutical waste water by activation of peroxysulphate

Abstract In the present study, cobalt-doped bismuth ferrite (Co/BiFeO3) composite was fabricated by sol-gel method, followed by annealing treatment. Afterwards, physicochemical properties of the resulting composite were systematically studied by scanning electron microscope, X-ray diffraction, transmission electron microscope, N2 physical adsorption/desorption and vibration magnetometer measurements. Results indicated that after doping with Co species, average diameter of BiFeO3 distinctly reduced, accordingly, specific surface area increased, in which Co element existed in the form of Co3O4. In addition, Co/BiFeO3 displayed superior magnetic recovery characteristics. Furthermore, Co/BiFeO3 composite was applied to decompose tetracycline in water by activation of persulfate (PS, S2O82−) via the formation of sulfate radicals. It was found that Co/BiFeO3 exhibited high efficiency for removal of tetracycline, in which 81.09% of tetracycline could be decomposed. This study provides a versatile strategy to fabricate high-efficient recyclable catalysts which would be applied in advanced pharmaceutical waste water treatment.

Degradation of organic pollutants by Co3O4-mediated peroxymonosulfate oxidation: Roles of high-energy {0 0 1}-exposed TiO2 support

Co3O4-mediated heterogeneous activation of peroxymonosulfate (PMS) is an efficient strategy to generate sulfate radicals for environmental pollutants degradation. The rate-limiting step is CoOH− complex formation, and it highly depends on the thermodynamic capacity of water dissociation to generate surface hydroxyl groups. Herein, for efficient PMS activation and pollutants degradation, the water dissociation capacity of TiO2, a promising Co3O4 support, was facilely refined by its shape-tailored synthesis with dominant high-energy {0 0 1} facet. The polar {0 0 1} facet is characterized by a high density of atomic steps, edges and kinks of the low-coordinate surface atoms with a large number of dangling bonds, all of which can serve as reactive sites for water adsorption and dissociation and thus improve CoOH− complex formation dynamics in sulfate radical formation. Co3O4 deposited on TiO2-{0 0 1} exhibited a much higher PMS activation capacity and pollutants degradation efficiency, i.e. p-nitrophenol and rhodamine B, and a much lower Co2+ leaching. This superiority could be mainly attributed to the strong Ti5c-centered water adsorption and dissociation, the high density of surface hydroxyl groups, the robust CoOH− complex generation and the intimate catalyst-support interactions. Our findings might provide a new chance to refine Co-mediated sulfate radical generation and other Fenton-like systems for advanced water treatment with reduced secondary pollution.

Degradation of Acid Orange 7 by an ultrasound/ZnO-GAC/persulfate process

Abstract Granular activated carbon (GAC) supported ZnO catalyst (ZnO-GAC) was prepared to activate persulfate (PS) for the decolorization of Acid Orange 7 (AO7) in the presence of ultrasonic irradiation (US). The effects of initial pH, PS concentration, catalyst dosage, initial dye concentration, and reaction temperature were investigated. The results showed that the decolorization efficiency increased with the increase of catalyst dosage and temperature, but decreased with the increase of initial dye concentration and initial pH, and the optimal PS concentration for color removal was 0.5 g L−1. Radical quenching tests were performed by using ethanol, tert-butanol and phenol to verify the formation of sulfate radicals and hydroxyl radicals in the US/ZnO-GAC/PS process. Under the optimal conditions, 91.2% of decolorization was achieved and 83.1% of TOC was removed after 60 min treatment. Activated sludge inhibition tests were carried out to monitor the change of toxicity during the treatment of AO7 solution.

Degradation of Acid Orange 7 using peroxymonosulfate catalyzed by granulated activated carbon and enhanced by electrolysis

Electrochemistry coupled with granulated activated carbon catalysis of peroxymonosulfate (electro/GAC/PMS) as a novel wastewater treatment process was performed for the degradation of Acid Orange 7 (AO7) in aqueous solution. The decolorization of AO7 was compared under different permutations and combinations of electro-oxidation, GAC and PMS. It showed that the electro/GAC/PMS process was the most effective and the decolorization of AO7 followed pseudo-first order kinetics. The surface chemistry of GAC samples was analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Compared with the fresh samples, π-electron density and hydroxyl group content decreased under the GAC/PMS system, but kept the similar values under the electro/GAC/PMS system. Electron paramagnetic resonance and radical scavenger studies were used to verify the formation of sulfate radicals (SO4−) and hydroxyl radicals (OH). The optimized conditions were found to be: current density 8 mA cm−2; PMS concentration 5 mM; GAC dosage 0.5 g L−1; and initial pH value 5.0. GAC recycling experiments over 4 runs showed some decrease in reactivity. Overall, the results indicate that 100% color removal was readily achieved and 50.4% of TOC was removed which shows high efficiency of the electro/GAC/PMS process.

Primordial Krebs-cycle-like non-enzymatic reactions detected by mass spectrometry and nuclear magnetic resonance

Background: Metabolism is the process of nutrient uptake and conversion, and executed by the metabolic network. Its evolutionary precursors most likely originated in non-enzymatic chemistry. To be exploitable in a Darwinian process that forms a metabolic pathway, non-enzymatic reactions need to form a chemical network that produces advantage-providing metabolites in a single, life compatible condition. In a hypothesis-generating, large-scale experiment, we recently screened iron and sulfur-rich solutions, and report that upon the formation of sulfate radicals, Krebs cycle intermediates establish metabolism-like non-enzymatic reactivity. A challenge to our results claims that the results obtained by liquid chromatography-selective reaction monitoring (LC-SRM) would not be reproducible by nuclear magnetic resonance spectroscopy (1H-NMR). Methods: This study compared the application of the two techniques to the relevant samples. Results: We detect hundred- to thousand-fold differences in the specific limits of detection between LC-SRM and 1H-NMR to detect Krebs cycle intermediates. Further, the use of 1H-NMR was found generally problematic to characterize early metabolic reactions, as Archean-sediment typical iron concentrations cause paramagnetic signal suppression. Consequently, we selected non-enzymatic Krebs cycle reactions that fall within the determined technical limits. We confirm that these proceed unequivocally as evidenced by both LC-SRM and 1H-NMR. Conclusions: These results strengthen our previous conclusions about the existence of unifying reaction conditions that enables a series of co-occurring metabolism-like non-enzymatic Krebs cycle reactions. We further discuss why constraints applying to metabolism disentangle concentration from importance of any reaction intermediates, and why evolutionary precursors to metabolic pathways must have had much lower metabolite concentrations compared to modern metabolic networks. Research into the chemical origins of life will hence miss out on the chemistry relevant for metabolism if its focus is restricted solely to highly abundant and unreactive metabolites, including when it ignores life-compatibility of the reaction conditions as an essential constraint in enzyme evolution.

Degradation of highly consumed fluoroquinolones, penicillins and cephalosporins in distilled water and simulated hospital wastewater by UV254 and UV254/persulfate processes

In this work, three penicillins (ampicillin “AMP”, oxacillin “OXA” and cloxacillin “CLO”), two cephalosporins (cephalexin “CPX” and cephadroxyl “CPD”) and three fluoroquinolones (levofloxacin “LEV”, norfloxacin “NOR” and ciprofloxacin “CIP”) were initially treated by UV254 and persulfate activated by UV254 (UV/PS). Significant differences in degradation kinetics under UV254 irradiation were found. Photodegradation followed the order: OXA > CPX > CPD > CLO > CIP > NOR > AMP ≫ LEV. Then, in order to study the participation of direct photolysis and reactive oxygen species (ROS) in photodegradation a model antibiotic of each class (OXA, CPX and CIP) was considered. OXA and CPX were mainly degraded by direct photolysis, whereas the CIP removal involved ROS and photolysis. On the other hand, the persulfate addition (UV/PS process) improved the removals due to sulfate radical formation, especially, in the case of antibiotics with lower photodegradation levels (i.e. LEV, AMP and NOR). Computational calculations on the representative antibiotics were applied to determine the regions susceptible to electrophilic attacks by degrading agents. The functional groups of OXA and CPX followed the reactivity order: thioether ≫ β-lactam ring > benzene ring. For CIP, the piperazyl moiety presented higher reactivity than the quinolone ring. Also, the antimicrobial activity (AA) evolution during the treatments was tested. In the cases of CPX and CIP, both UV254 and UV/PS removed the AA; which were associated with structural changes in their reactive moieties: β-lactam ring and piperazyl ring, respectively. However, in the case of OXA only the UV/PS system decreased AA, which was attributed to transformations in its penicillin electron-rich nucleus (thioether + β-lactam). Finally, the applicability of UV254 and UV/PS was assessed using synthetic hospital wastewater (HWW). The processes comparison showed that for practical purposes, OXA and CIP in HWW should be treated by UV/PS, while CPX in HWW could be treated by both UV254 and UV/PS.

Removal of pendimethalin from soil washing effluents using electrolytic and electro-irradiated technologies based on diamond anodes

This work describes the treatment of soil polluted with the herbicide pendimethalin by the combination of surfactant-aided soil-washing (SASW) and electrochemical advanced oxidation processes. Results show that it is possible to completely extract the herbicide from soil using SDS (sodium dodecyl sulfate) solutions as soil washing fluid (SWF) and ratios SWF/soil higher than 10dm3kg−1. Soil washing effluents obtained after the application of the SASW consisted of a mixture of surfactant (high concentration) and pesticide (low concentration) and their degradation by electrolysis, photo-assisted electrolysis (photoelectrolysis) and sonoelectrolysis with diamond anodes has been compared with that obtained by the application of single photolysis and sonolysis. Opposite to photolysis and sonolysis, the different electrolytic techniques allow decreasing the concentration of herbicide and surfactant in the effluents. Competition between the surfactant and the herbicide oxidation is important and irradiation of high-frequency ultrasound or UV light do not seem to outperform very importantly the results obtained by single electrolysis in the effluents of the SASW obtained with low SDS/soil ratios. Opposite, photoelectrolysis becomes the most efficient technology for the treatment of SWF obtained at high SDS/soil ratios (those required for an efficient SASW). Catalytic effect of the sulfate released during the degradation of SDS (in particular the formation of sulfate radicals) can help to explain the differences observed. The removal efficiency is higher during sonoelectrolysis, reaching a final removal of the pesticide after 8h of treatment of 86.22%. Photoelectrolysis (57.59%) shows higher efficiencies for the removal of SDS followed by sonoelectrolysis (52.64%) and, finally, electrolysis (48.29%), after 8h of treatment.

Enhanced formation of sulfate radicals by metal-doped BiFeO3 under visible light for improving photo-Fenton catalytic degradation of 2-chlorophenol

Three metal doped BiFeO3 magnetic nanoparticles (BFO MNPs), namely Bi1−xBaxFeO3 (x=0.03), BiFe1−yCuyO3 (y=0.1) and Bi1−xBaxFe1−yCuyO3 (x=0.03, y=0.1), were successfully prepared by a novel and simple sol-gel method. Then, iron and iron-copper heterogeneous Fenton-like photocatalysts were applied to activate H2O2 to hydroxyl radicals (OH) and persulfate (S2O82−) to sulfate radical anions (SO4-) for enhanced degradation of 2-chlorophenol (2-CP) from aqueous solution. Both Fe3+/Fe2+ and Cu+/Cu2+ pairs in the BFO MNPs systems effectively decomposed H2O2 to OH and S2O82− to SO4-. After only 70min of visible light irradiation, Cu-doped BFO (BiFe1−yCuyO3) and Ba-Cu co-doped BFO (Bi1−xBaxFe1−yCuyO3) almost completely degraded 2-CP with reductions in total organic carbon (TOC) of 68 and 73%, respectively, which were much higher than that achieved with BFO and Ba-doped BFO, due to the formation of OH in the Cu2+/Fe2+/H2O2/visible light couple. However, 2-CP was completely degraded with Cu-doped BFO and Ba-Cu co-doped BFO in less than 30min, due to the effective formation of SO4- in the Cu2+/Fe2+/S2O82−/visible light couple. Cu2+ or Fe2+ ions in H2O2/visible light or S2O82−/visible light couples are important species in the improved degradation of 2-CP in the photo-Fenton catalytic reaction. However, the photo-Fenton catalytic degradation of 2-CP was greatly reduced in the absence of any species of Cu2+ or Fe2+ ions, H2O2, S2O82−, and visible light irradiation.

Removal of iopamidol, an iodinated X-ray contrast medium, by zero-valent aluminum-activated H2O2 and S2O82−

Activation of H2O2 (HP) and S2O82− (PS) with zero valent aluminum (ZVA, 1g/L) nanoparticles was investigated for the treatment of the X-ray contrast medium and micropollutant iopamidol (IOPA; C17H22I3N3O8; ≈777g/mol) at pH 3. IOPA (2.6μM) degradation was followed in different water matrices (distilled water, tap water, raw surface water and tertiary treated sewage effluent). Both oxidants could be activated with ZVA resulting in a dramatic enhancement of IOPA degradation due to accelerated hydroxyl and sulfate radical formation. The ZVA/PS (0.5mM) treatment was more effective than ZVA/HP (0.25mM) oxidation resulting in 95% IOPA removal after 120min. IOPA and dissolved organic carbon (DOC) abatements were inhibited when IOPA was treated in real water and wastewater. After 120min treatment, IOPA removals decreased from 95% (PS/ZVA) and 41% (HP/ZVA) in distilled water to 29% (PS/ZVA) and 13% (HP/ZVA) in surface water, respectively. IOPA could not be removed with the PS/ZVA process in treated sewage, although DOC removal was still substantial (28%). For the HP/ZVA combination, 24% DOC accompanied with 20% IOPA removal was achieved after 120min in the same wastewater sample. Changes in acute toxicity were followed during PS/ZVA treatment of IOPA in distilled and surface water. These results exhibited a fluctuating trend depending on the sensitivity of the test organism (Vibrio fischeri and Pseudokirchneriella subcapitata) and water matrix. A genotoxic activity analysis was also conducted and the UmuChromo assay indicated that the original and treated IOPA solutions were not genotoxic but cytotoxic. The potentials and differences of PS/ZVA and HP/ZVA treatment of an iodinated contrast medium could be demonstrated in this study.

Sono-activated persulfate oxidation of bisphenol A: Kinetics, pathways and the controversial role of temperature

The sonochemical degradation of bisphenol A (BPA) in the presence of sodium persulfate (SPS) was investigated at 20kHz. Experiments were performed at 110–450μg/L BPA and 1–100mg/L SPS concentration and an ultrasound power density between 4 and 60W/L. The liquid bulk temperature was either kept constant at 30°C or left uncontrolled and gradually increased up to 80°C. BPA degradation occurs due to the combined action of hydroxyl radicals generated by the ultrasound and sulfate radicals generated by SPS sonolysis and this was confirmed with experiments with methanol and t-butanol as radical scavengers. Considerable thermal SPS activation can also occur at increased temperatures (60–80°C) although the enhanced formation of sulfate radicals is compensated by a decrease in sonochemical activity. Kinetics can be approached by a pseudo-first order expression with the apparent rate constant decreasing with increasing BPA concentration; this implies that the actual order is below first. The rate increases with increasing power density and SPS concentration and decreases at alkaline conditions (i.e. pH=9) and in the presence of inorganic and organic constituents (e.g. bicarbonate, humic acid etc) typically found in environmental matrices.Liquid chromatography time of flight mass spectrometry (LC–TOF–MS) analysis revealed the formation of twelve transformation by-products that accompany BPA sonodegradation in the presence of SPS. Based on their evolution profiles, a reaction mechanism is proposed consisting of two major pathways: (i) hydroxylation that can occur mainly in the aromatic ring through HO, SO4− radical attack and to a lesser extent in methyl groups, through hydrogen abstraction by HO radicals, with subsequent O2 addition, and (ii) scission of the bond between the isopropylidene carbon and the phenyl group.