Efficient oxidation of bisphenol A with oxysulfur radicals generated by iron-catalyzed autoxidation of sulfite at circumneutral pH under UV irradiation

There is actually a need for efficient methods to clean waters and wastewaters from pollutants such as the bisphenol A endocrine disrupter. Advanced oxidation processes currently use persulfate or peroxymonosulfate to generate sulfate radicals. There are, however, few reports on the use of sulfite to generate sulfate radicals, instead of persulfate or peroxymonosulfate, except for dyes. Here we studied the degradation of the bisphenol A using iron(III) as catalyst and sulfite as precursor of oxysulfur radicals, at initial pH of 6, under UV irradiation at 395 nm. The occurrence of radicals was checked by quenching with tert-butyl alcohol and ethanol. Bisphenol A degradation products were analyzed by liquid chromatography coupled with mass spectrometry (LC–MS). Results reveal that iron(III) or iron(II) have a similar oxidation efficiency. Quenching experiments show that the oxidation rate of bisphenol A is 47.7 % for SO ₄ ^·? , 37.3 % for SO ₅ ^·? and 15 % for HO^·. Bisphenol A degradation products include catechol and quinone derivatives. Overall, our findings show that the photo-iron(III)–sulfite system is efficient for the oxidation of bisphenol A at circumneutral pH.     

Evidence for the involvement of Fe(IV) in water treatment by Fe(III)-activated sulfite

Water contamination by emerging organic pollutants is calling for advanced methods of remediation such as iron-activated sulfite-based advanced oxidation. Sulfate radical, SO₄^??, and hydroxyl radical, ^?OH, are the primary reactive intermediates formed in the Fe(III)/sulfite system, yet the possible involvement of Fe(IV) produced from Fe(II) and persulfates is unclear. Here we explored the role of Fe(IV) in the Fe(III)/sulfite system by methyl phenyl sulfoxide (PMSO) probe assay, electron paramagnetic resonance spectra analysis, alcohol scavenging experiment, and kinetic simulation. Results show that PMSO is partially transformed into methyl phenyl sulfone (PMSO₂), thus evidencing Fe(IV) formation. The remaining degradation of PMSO is due to SO₄^?? and ^?OH. The contribution of Fe(IV) versus free radicals is progressively promoted when the Fe(III)-sulfite reaction proceeds, with an upper limit of 80–90%. The contribution of Fe(IV) versus free radicals increases with Fe(III) and sulfite dosages, and decreases with increasing pH. Overall, our findings demonstrate the involvement of Fe(IV) in the Fe-catalyzed sulfite auto-oxidation process.

     

Reactivity of sulfate radicals with natural organic matters

Advanced oxidation processes based on sulfate radicals (SO ₄ ^·? ) are capable of efficiently degrade organic pollutants from ground, surface and wastewaters. However, this degradation may be limited by aqueous natural organic matter (NOM). Here we measured the absolute rate constants of reaction of SO ₄ ^·? with four types of organic matter: two fulvic acids and two lake organic matter. We used laser flash photolysis technique to monitor the SO ₄ ^·? decay and the formation of the transients from organic matters. Reaction rate constants comprised between 1530 and 3500 s^?1 mgC^?1 L were obtained by numerical analysis of differential equations and the weighted average of the extinction coefficient of the generated organic matters radicals between 400 and 800 M^?1 cm^?1.     

Removal of carbamazepine from urban wastewater by sulfate radical oxidation

The occurrence of bioactive trace pollutants such as pharmaceuticals in natural waters is an emerging issue. Numerous pharmaceuticals are not completely removed in conventional wastewater treatment plants. Advanced oxidation processes may represent an interesting alternative to completely mineralize organic trace pollutants. In this article, we show that sulfate radicals generated from peroxymonosulfate/Co^II are more efficient than hydroxyl radicals generated from the Fenton’s reagent (H₂O₂/Fe^II) for the degradation of the pharmaceutical compound, carbamazepine. The second-order rate constant for the reaction of SO₄ ^·− with carbamazepine is 1.92·10⁹ M⁻¹ s⁻¹. In laboratory grade water and in real urban wastewater, SO₄ ^·− yielded a faster degradation of carbamazepine compared to HO^· . Under strongly oxidizing conditions, a nearly complete mineralization of carbamazepine was achieved, while under mildly oxidizing conditions, several intermediates were identified by LC–MS. These results show for the first time in real urban wastewater that sulfate radicals are more selective than hydroxyl radicals for the oxidation of an organic pollutant and may represent an interesting alternative in advanced oxidation processes.     

Efficient metoprolol degradation by heterogeneous copper ferrite/sulfite reaction

Metal/sulfite systems are currently used for SO ₄ ^?? generation and oxidative removal of organic contaminants. However, homogeneous metal/sulfite systems are limited because their working pHs must be acidic and metal ions cannot be separated from the bulk reaction solution. As a consequence, these drawbacks have severely limited the application of metal/sulfite systems in real conditions. To address these issues, we tested the use of copper ferrite (CuFe₂O₄), a ferromagnetic nanoparticle, to catalyze sulfite oxidation for the degradation of the metoprolol drug. The reaction mechanism was investigated by electron spin resonance, X-ray photoelectron spectroscopy, and radical quenching assay. The effects of pH, CuFe₂O₄, and sulfite dosages were also assessed. Results show that SO ₄ ^?? was the primary radical responsible for metoprolol degradation. Higher pHs induced more metoprolol degradation using CuFe₂O₄/sulfite. Moreover, CuFe₂O₄ remained morphologically intact and catalytically active after four batches of recycling. Overall, our findings show that CuFe₂O₄/sulfite can effectively degrade water contaminants in alkali pH and withhold catalyst activity after multiple reuses, therefore addressing the issues associated with homogeneous metal/sulfite systems.     

Removal of toluene from air streams by cobalt-copper bimetallic catalysts supported on sepiolite

Abstract

Oxidative removal of toluene using copper and cobalt bimetallic catalysts with varying molar ratios supported on sepiolite was investigated. The catalysts prepared by a deposition precipitation method and were characterized using X-ray diffraction, nitrogen adsorption-desorption, field emission scanning electron microscopy, H₂-temperature-programmed reduction, transmission electron microscope, and inductive coupled plasma atomic emission spectroscopy. The species supported on sepiolite are Co₃O₄, CuO, and CuCo₂O₄. The activities of the tested catalysts increased in the order 0Co-4Cu/Sep <1Co-3Cu/Sep <4Co-0Cu/Sep <1Co-1Cu/Sep <3Co-1Cu/Sep. The latter exhibiting 90% toluene oxidative degradation at 288?°C within 15?h, having high selectivity towards CO₂, and being stable at 300?°C up to 15?h. In conclusion, this study showed that sepiolite has excellent properties as a support.     

Copper recovery from waste printed circuit boards concentrated metal scraps by electrolysis

Copper recovery is the core of waste printed circuit boards (WPCBs) treatment. In this study, we proposed a feasible and efficient way to recover copper from WPCBs concentrated metal scraps by direct electrolysis and factors that affect copper recovery rate and purity, mainly CuSO₄·5H₂O concentration, NaCl concentration, H₂SO₄ concentration and current density, were discussed in detail. The results indicated that copper recovery rate increased first with the increase of CuSO₄·5H₂O, NaCl, H₂SO₄ and current density and then decreased with further increasing these conditions. NaCl, H₂SO₄ and current density also showed a similar impact on copper purity, which also increased first and then decreased. Copper purity increased with the increase of CuSO₄·5H₂O. When the concentration of CuSO₄·5H₂O, NaCl and H₂SO₄ was respectively 90, 40 and 118 g/L and current density was 80 mA/cm², copper recovery rate and purity was up to 97.32% and 99.86%, respectively. Thus, electrolysis proposes a feasible and prospective approach for waste printed circuit boards recycle, even for e-waste, though more researches are needed for industrial application.

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The sulfur cycle of a marine sediment model system

In a laboratory sediment model consisting of sand and chopped Zostera marina leaves, the sulfur cycle and the succession and zonation patterns of sulfur bacteria were studied for a period of 7 months. The pool size of different forms of sulfur was quantified, and the rate of sulfate reduction was measured with an in situ radio-tracer technique at regular intervals. From these data, transfer rates of the sulfur cycle in the system could be calculated for different periods. The rate of sulfate reduction was initially 80 nMS·cm³·day^-1; this decreased to 25 nMS·cm³·day^-1 towards the end of the experiment as the system started to become oxidized. There was a transient accumulation of elemental sulfur in the bacterial plate at the sediment surface. More than 50% of the total mineralization of the organic material was due to sulfate reduction. Comparison with the net oxygen uptake showed that, during the first 2 to 3 months (when the sediment closely resembled a natural, reduced shallow water sediment), SO₄ ^- was equally as important as O₂ for transporting oxidacion equivalents from the water to the sediment.     

Decomposition of perfluorooctanoic acid by microwaveactivated persulfate: Effects of temperature, pH, and chloride ions

Microwave-hydrothermal treatment of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S₂O ₈ ^2? ) has been found effective. However, applications of this process to effectively remediate PFOA pollution require a better understanding on free-radical scavenging reactions that also take place. The objectives of this study were to investigate the effects of pH (pH = 2.5, 6.6, 8.8, and 10.5), chloride concentrations (0.01?C0.15 mol·L^?1), and temperature (60°C, 90°C, and 130°C) on persulfate oxidation of PFOA under microwave irradiation. Maximum PFOA degradation occurred at pH 2.5, while little or no degradation at pH 10.5. Lowering system pH resulted in an increase in PFOA degradation rate. Both high pH and chloride concentrations would result in more scavenging of sulfate free radicals and slow down PFOA degradation. When chloride concentrations were less than 0.04 mol·L^?1 at 90°C and 0.06 mol·L^?1 at 60°C, presence of chloride ions had insignificant impacts on PFOA degradation. However, beyond these concentration levels, PFOA degradation rates reduced significantly with an increase in chloride concentrations, especially under the higher temperature.     

Degradation of carbendazim by UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> investigated by kinetic modelling

The transformation of the fungicide carbendazim (methyl-2 benzimidazole carbamate) induced by hydroxyl radical generated by the UV photolysis of H₂O₂ has been studied in dilute aqueous solution. The efficient reaction of hydroxyl radicals with carbendazim led to the rapid degradation of carbendazim. The study of reaction kinetics yielded a second order rate constant of 2.2±0.3 10⁹ M⁻¹ s⁻¹ for HO^· radicals with carbendazim. This value is in agreement with a high reactivity of HO^· radicals with carbendazim. Most degradation products were identified by high performance liquid chromatography mass spectrometry (HPLC-MS). In the presence of hydrogenocarbonate and carbonate ions, hydroxyl radicals were quenched and in turn carbonate radicals CO₃ ^·− were formed. Carbonate radicals are indeed known to react efficiently with compounds containing electron-rich sites such as nitrogen or sulfur atoms. The use of a kinetic modelling software gave evidence for the occurrence of such reactions with carbendazim. The second order rate constant of carbonate radical with carbendazim was equal to 6±2 10⁶ M⁻¹ s⁻¹. Electronic Publication     

Spectroscopic studies and biological evaluation of some transition metal complexes of a novel Schiff base ligands derived from 5-arylazo-salicyladehyde and o-amino phenol

Synthesis and characterization of Cu(II), Ni(II), and Zn(II) Schiff bases complexes resulted from the condensation of salicylaldehyde derivatives with o-amino phenol were discussed using elemental analysis (carbon, hydrogen, and nitrogen), molar conductance, magnetic measurements, mass spectra, and electronic spectra. The essential bands of infrared, ¹HNMR, and UV-Vis spectra as well as thermogravimetric analysis corresponding to the active groups within the three ligands and their complexes were interpreted. The dehydration and decomposition processes of the [Cu(H₂L₁)(H₂O)](OAc)₂, [Ni(H₂L₁)(H₂O)]SO₄ · H₂O, [Zn(H₂L₁)(H₂O)]SO₄ · H₂O, [Cu(H₂L₂)(H₂O)](OAc)₂, [Ni(H₂L₂)(H₂O)]SO₄ · H₂O, [Zn(H₂L₂)(H₂O)]SO₄ · 2H₂O, [Cu(H₂L₃)(H₂O)](OAc)₂ · H₂O, [Ni(H₂L₃)(H₂O)]SO₄ · 2H₂O, [Zn(H₂L₃)(H₂O)]SO₄ complexes were studied thermodynamically using the integral method applying the Coats–Redfern and Horowitz–Metzger equations and the thermodynamic parameters were calculated. It was found from the elemental analysis and the thermal studies, that the ligand behaves as tridentate ligand forming chelates with 1 : 1 (metal : ligand) stoichiometrically. The molar conductance measurements of the complexes in dimethyl sulfoxide solvent indicate that the complexes have an electrolytic nature. The biological activities of the three ligands in comparison with metal(II) complexes were studied against different Gram positive and Gram negative bacteria.     

Evaluation of acidity in late Permian outcrop coals and its association with endemic fluorosis in the border area of Yunnan,Guizhou, and Sichuan in China

The junction area of Yunnan, Guizhou, and Sichuan provinces is the heaviest coal-burning endemic fluorosis zones in China. To better understand the pathogenicity of endemic fluorosis in this area, 87 coal samples from the late Permian outcrop or semi-outcrop coal seams were collected in eight counties of the junction area of Yunnan, Guizhou, and Sichuan provinces. The total fluorine and sulfate content, etc. in the coal was determined using combustion-hydrolysis/fluoride-ion-selective electrode method and ion chromatography, respectively. The results show that the total fluorine concentrations in the samples ranged from 44 to 382 µg g^?1, with an average of 127 µg g^?1. The average pH of the coals is 5.03 (1.86–8.62), and the sulfate content varied from 249 to 64,706 µg g^?1 (average 7127 µg g^?1). In addition, the coals were medium- and high-sulfur coals, with sulfur mass fraction ranging from 0.08 to 13.41%. By heating the outcrop coals, HF release from the coal was verified quantitatively without exception, while simulated combustion directly confirmed the release of sulfuric acid (H₂SO₄). The acid in coal may be in the form of acidic sulfate (\({\text{HSO}}_{4}^{ - }\)/H₂SO₄) because of a positive relationship between pH and \(p\left( {{\text{SO}}_{4}^{2 - } } \right)\) in the acidic coal. The possible reaction mechanism would be that a chemical reaction between the acid (H₂SO₄ or \({\text{HSO}}_{4}^{ - }\)) and fluorine in the coal occurred, thereby producing hydrogen fluoride (HF), which would be the chemical form of fluorine released from coal under relatively mild conditions. The unique chemical and physical property of HF may bring new insight into the pathogenic mechanism of coal-burning endemic fluorosis. The phenomenon of coal-burning fluorosis is not limited to the study area, but is common in southwest China and elsewhere. Further investigation is needed to determine whether other endemic fluorosis areas are affected by this phenomenon.     

山西工矿区土壤二氧化硫与多环芳烃复合污染对小麦种子萌发和幼苗生长的影响

以小麦为供试植物,山西工矿区生黄土为供试土壤,进行了土壤中二氧化硫(SO2)与多环芳烃(PAHs)单一及复合污染对小麦种子萌发率及小麦幼苗株高、根伸长和地下生物量影响的研究,以期考察复合污染的生态毒性效应。结果表明,小麦种子萌发对SO2与PAHs单一及复合污染均不敏感;SO2和PAHs单一污染时,小麦幼苗的株高与根伸长均受到一定程度的影响,低浓度SO2或PAHs处理对小麦生长起促进作用,高浓度则为抑制作用;小麦幼苗株高与SO2浓度呈显著负相关(r=-0.954,P<0.05),但与PAHs浓度的相关性不显著;SO2与PAHs复合污染条件下,对小麦幼苗株高或根伸长的联合作用多体现为协同作用,在低浓度情况下(SO2<500mg·kg-1)表现为协同促进;当SO2达到500～1000mg·kg-1时,对小麦幼苗株高或根伸长的联合作用均体现为协同抑制。SO2和PAHs单一污染时,小麦幼苗地下生物量与SO2、PAHs浓度均为显著负相关(rPAHs=-0.953,rSO2=-0.916,P<0.05);复合污染条件下,在SO2浓度为10mg·kg-1时,对地下生物量的联合作用多体现协同促进作用;而在SO2浓度为1000mg·kg-1,PAHs为50～100mg·kg-1时,对地下生物量的联合作用均体现为协同抑制作用。多元逐步回归分析进一步表明,SO2与PAHs复合污染条件下,小麦幼苗株高、根伸长都受到了SO2及PAHs的共同影响,而SO2是影响小麦幼苗地下生物量的主要因素。     

Photochemical reaction of peroxynitrite and carbon dioxide could account for up to 15 % of carbonate radicals generation in surface waters

The carbonate radical (CO ₃ ^?· ) is a photoinduced transient species occurring in surface waters. The carbonate radical can transform both natural compounds and xenobiotics. For instance, it can react with electron-rich substrates such as anilines, phenols and organic sulfur compounds. Here we used the APEX software to assess photochemical reactions, including the formation rates of transient species, based on water chemistry and depth, under summertime irradiation conditions. We found that the reaction between peroxynitrite and carbon dioxide is a potentially significant source of CO ₃ ^?· in sunlit surface waters, and could account for up to 10–15 % of the total CO ₃ ^?· formation. The peroxynitrite pathway to CO ₃ ^?· would be most significant at pH 7–8 and would be enhanced in waters with elevated nitrate and low alkalinity. Therefore, the proposed process could add to the known photochemical sources of CO ₃ ^?· in surface-water environments.     

NO oxidation over Co-La catalysts and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> reduction in compact SCR

A series of Co-La catalysts were prepared using the wet impregnation method and the synthesis of catalysts were modified by controlling pH with the addition of ammonium hydroxide or oxalic solution. All the catalysts were systematically investigated for NO oxidation and SO₂ resistance in a fixed bed reactor and were characterized by Brunanuer–Emmett–Teller (BET) method, Fourier Transform infrared spectroscopy (FTIR), X–ray diffraction (XRD), Thermogravimetric (TG) and Ion Chromatography (IC). Among the catalysts, the one synthesized at pH = 1 exhibited the maximum NO conversion of 43% at 180°C. The activity of the catalyst was significantly suppressed by the existence of SO₂ (300 ppm) at 220°C. Deactivation may have been associated with the generation of cobalt sulfate, and the SO₂ adsorption quantity of the catalyst might also have effected sulfur resistance. In the case of the compact selective catalytic reduction (SCR), the activity increased from 74% to 91% at the highest gas hourly space velocity (GHSV) of 300000 h^–1 when the NO catalyst maintained the highest activity, in excess of 50% more than that of the standard SCR.

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Simulating the dynamics of sulfur species and zinc in wetland sediments

In situ measurements comparing vertical SO₄²⁻ profiles in vegetated and non-vegetated sediments showed that SO₄²⁻ concentrations in vegetated sediments increased significantly at the beginning of the growing season and then gradually decreased during the rest of the growing season. Throughout the growing season, SO₄²⁻ concentrations remained higher in the vegetated sediments than in the sediments without plants. The higher SO₄²⁻ concentrations in the vegetated sediments indicate that oxygen release from roots and evapotranspiration-induced advection by plants play an important role in the dynamics of sulfur species in sediments. Since the total pool of solid-phase sulfide is relatively large compared to the mass of SO₄²⁻ in the sediments, the gradual decrease of SO₄²⁻ concentrations may result from limitation of the solid-phase sulfide that is in direct contact with or very close to the roots and rhizomes. This would mean that the main pool of solid-phase sulfide and associated trace metals are not affected by the oxygen release from roots, and the associated trace metals will not become bioavailable during the growing season.     

Suppression of inhibition of substrate photodegradation by scavengers of hydroxyl radicals: the solvent-cage effect of bromide on nitrate photolysis

In this paper we show that bromide scavenges the ^·OH radicals formed upon photolysis of nitrate, before they leave the solvent cage. Bromide can thus inhibit the in-cage recombination between ^·OH and ^·NO₂. The consequence is an increased generation of ^·NO₂ and nitrite and of Br₂ ^?· + ^·OH, compared to ^·OH alone in the absence of bromide. We show that this effect compensates for the lower reactivity of Br ₂ ^?· compared to ^·OH toward certain organic substrates, e.g. phenol and tryptophan. Our findings could lead to a deep revision of the present views of the role of bromide in saltwater photochemistry.     

Characterization and performance of V2O5/CeO2 for NH3-SCR of NO at low temperatures

A series of CeO₂ supported V₂O₅ catalysts with various loadings were prepared with different calcination temperatures by the incipient impregnation. The catalysts were evaluated for low temperature selective catalytic reduction (SCR) of NO with ammonia (NH₃). The effects of O₂ and SO₂ on catalytic activity were also studied. The catalysts were characterized by specific surface areas (S_BET) and X-ray diffraction (XRD) methods. The experimental results showed that NO conversion changed significantly with the different V₂O₅ loading and calcination temperature. With the V₂O₅ loading increasing from 0 to 10 wt%, NO conversion increased significantly, but decreased at higher loading. The optimum calcination temperature was 400°C. The best catalyst yielded above 80% NO conversion in the reaction temperature range of 160°C–300°C. The formation of CeVO₄ on the surface of catalysts caused the decrease of redox ability.     

Degradation of carbon tetrachloride in thermally activated persulfate system in the presence of formic acid

The thermally activated persulfate (PS) degradation of carbon tetrachloride (CT) in the presence of formic acid (FA) was investigated. The results indicated that CT degradation followed a zero order kinetic model, and CO ₂ ^– · was responsible for the degradation of CT confirmed by radical scavenger tests. CT degradation rate increased with increasing PS or FA dosage, and the initial CT had no effect on CT degradation rate. However, the initial solution pH had effect on the degradation of CT, and the best CT degradation occurred at initial pH 6. Cl^– had a negative effect on CT degradation, and high concentration of Cl^– displayed much strong inhibition. Ten mmol·L^–1HCO ₃ ^– promoted CT degradation, while 100 mmol·L^–1NO ₃ ^– inhibited the degradation of CT, but SO ₄ ^2– promoted CT degradation in the presence of FA. The measured Cl–concentration released into solution along with CT degradation was 75.8% of the total theoretical dechlorination yield, but no chlorinated intermediates were detected. The split of C-Cl was proposed as the possible reaction pathways in CT degradation. In conclusion, this study strongly demonstrated that the thermally activated PS system in the presence of FA is a promising technique in in situ chemical oxidation (ISCO) remediation for CT contaminated site.     

Metal-free oxidation of aldehydes to acids using the 4Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O<Subscript>2</Subscript>·NaCl adduct

Oxidation of aldehydes to carboxylic acids is a major reaction. Conventionally, this reaction is carried out with oxidants and metal catalysts, thus producing unwanted metal waste. Recently, aqueous media have been used as an alternative for toxic organic solvents. Here, we tested the clathrate-structured, neutral hydrogen peroxide adduct 4Na₂SO₄·2H₂O₂·NaCl for the oxidation of aldehydes to acids in aqueous solution. We found that various aromatic, heteroaromatic and aliphatic aldehydes were selectively oxidized to corresponding acids in 70–98% yields. This simple acid–base treatment allows to separate easily the acid product in high purity without any organic solvent. Moreover, the adduct is produced using 25% H₂O₂, with inexpensive sodium sulphate, Na₂SO₄, and sodium chloride, NaCl. The adduct is a non-toxic white crystalline solid, readily soluble in water, and easy to handle.