Fenton-like Conditions Research Articles

Use of copper sheet in a solar photo-Fenton-like process applied in the treatment of landfill leachate.

It is known that copper can be used as catalyst in photo-Fenton-like process; however, there is a lack of information related with its use in the treatment of landfill leachate (LL) in solar photo-Fenton-like processes. Here, we studied the effect of the mass of a copper sheet, the pH of the solution, and the concentration of LL in the removal of the organic matter present in this water. Before the reaction with landfill leachate, the copper sheet used in the reaction was constituted by Cu+ and Cu2O, respectively. The results showed that in a volume of 0.5 L of a pretreated LL, the higher removal of organic matter resulted using a mass of 2.7g of the copper sheet, a pH of solution of 5, and a concentration of LL of a 10%, obtaining a final value of C/C0of chemical oxygen demand (COD) of 0.34, 0.54, 0.66, and 0.84 for concentrations of 25%, 50%, 75%, and 100%, respectively, and 0.0041, 0.0042, 0.0043, and 0.016 for concentration of 25%, 50%, 75%, and 100%, respectively, of C/C0 of humic acids. The photolysis on LL at its natural pH using solar UV removes very little humic acid and COD, going from 9.4 to 8.5 and 7.7 Abs254 for photolysis and UV + H2O2, obtaining 8.6 and 17.6% of removal, respectively, and 2.01 and 13.04% removal of COD, respectively. Copper sheet applied under Fenton-like conditions results in 65.9% removal and an increase of 0.2% for humic acid and COD, respectively. Removal using only H2O2 for Abs254 and COD was 11.95 and 4.3%, respectively. Raw LL produced a 29.1% inhibition of the biological activated sludge rate after the adjustment to pH 7 and the final process of inhibition was 0.23%.

Plasmalogens: Free Radical Reactivity and Identification of Trans Isomers Relevant to Biological Membranes.

Plasmalogens are membrane phospholipids with two fatty acid hydrocarbon chains linked to L-glycerol, one containing a characteristic cis-vinyl ether function and the other one being a polyunsaturated fatty acid (PUFA) residue linked through an acyl function. All double bonds in these structures display the cis geometrical configuration due to desaturase enzymatic activity and they are known to be involved in the peroxidation process, whereas the reactivity through cis-trans double bond isomerization has not yet been identified. Using 1-(1Z-octadecenyl)-2-arachidonoyl-sn-glycero-3-phosphocholine (C18 plasm-20:4 PC) as a representative molecule, we showed that the cis-trans isomerization can occur at both plasmalogen unsaturated moieties, and the product has characteristic analytical signatures useful for omics applications. Using plasmalogen-containing liposomes and red blood cell (RBC) ghosts under biomimetic Fenton-like conditions, in the presence or absence of thiols, peroxidation, and isomerization processes were found to occur with different reaction outcomes due to the particular liposome compositions. These results allow gaining a full scenario of plasmalogen reactivity under free radical conditions. Moreover, clarification of the plasmalogen reactivity under acidic and alkaline conditions was carried out, identifying the best protocol for RBC membrane fatty acid analysis due to their plasmalogen content of 15-20%. These results are important for lipidomic applications and for achieving a full scenario of radical stress in living organisms.

Thioguanine restoration through type I photosensitization-superoxide oxidation-glutathione reduction cycles.

UVA-induced deleterious effect of thiopurine prodrugs including azathioprine, 6-mercaptopurine and 6-thioguanine (6-TG) increases the risk of cancer development due to the incorporation of 6-TG in patients' DNA. The catalytic mechanism by which thiobases act as a sustained oxidant producer has yet to be explored, especially through the Type I electron transfer pathway that produces superoxide radicals (O2˙-). Under Fenton-like conditions O2˙- radicals convert to extremely reactive hydroxyl radicals (˙OH), thus carrying even higher risk of biological damage than that induced by the well-studied type II reaction. By monitoring 6-TG/UVA-induced photochemistry in mass spectra and superoxide radicals (O2˙-) via nitro blue tetrazolium (NBT) reduction, this work provides two new findings: (1) in the presence of reduced glutathione (GSH), the production of O2˙-via the type I reaction is enhanced 10-fold. 6-TG thiyl radicals are identified as the primary intermediate formed in the reaction of 6-TG with O2˙-. The restoration of 6-TG and concurrent generation of O2˙- occur via a 3-step-cycle: 6-TG type I photosensitization, O2˙- oxidation and GSH reduction. (2) In the absence of GSH, 6-TG thiyl radicals undergo oxygen addition and sulfur dioxide removal to form carbon radicals (C6) which further convert to thioether by reacting with 6-TG molecules. These findings help explain not only thiol-regulation in a biological system but chemoprevention of cancer.

Could the porous chitosan-based composite materials have a chance to a "NEW LIFE" after Cu(II) ion binding?

Currently, biosorption is considered a leading-edge environmentally-friendly method for the low-cost remediation of wastewaters contaminated with metal ions. However, the safe disposal of metal-loaded biosorbents is still a challenging issue. In this context, our major objective was to explore the possibility of "waste minimization" by reusing the metal-loaded biosorbents in further environmental applications, particularly into the oxidative catalysis of dyes. Thus, the decolourisation efficiency (DE) of Methyl Orange (MO) in aqueous solutions under ambient light using copper-imprinted chitosan-based composites in comparison to non-imprinted ones was investigated in this work. The MO degradation was established first in the absence of any co-catalyst, when a DE value of 95.3% was achieved by the ion-imprinted catalysts within 360 min of reaction, compared to only 67.4% attained by the non-imprinted ones. Under Fenton-like conditions, the apparent degradation rate constant was seventy times higher, the DE increasing within 40 min to about 98.6%, and 70.5% respectively, whereas the content of co-catalyst (H2O2) was significantly lowered compared to other reported studies. The straightforward preparation of copper-loaded composites, along with their excellent stability and high efficiency even after four consecutive reaction runs support our ion-imprinted systems as potential catalysts for dye removal by oxidative decolourisation treatments.

Ferrosilicate-Based Heterogeneous Fenton Catalysts: Influence of Crystallinity, Porosity, and Iron Speciation

Different ferrosilicate samples have been prepared with varying degrees of crystallinity, porous texture, and speciation of the Fe sites by both hydrothermal and sol–gel procedures: Fe-silicalite-1 with microcrystals (2–10 µm) and nanocrystals (180 nm), Fe-containing composite material consisting of silicalite-1 and amorphous silica, and two samples of mesoporous Fe-containing amorphous silica Fe–SiO2. The resulting solids have been tested for their potential as organic pollutants removal under Fenton-like conditions in heterogeneous catalytic wet peroxide oxidation of phenol and clarithromycin lactobionate. Our results indicate that the three aforementioned parameters show a strong interplay towards the abatement of pollutants in liquid phase. Thus, samples with high crystallinity show an improved performance in the oxidation of organic contaminants over amorphous samples in which the Fe speciation is very well controlled.

Comparison of organic peracids in wastewater treatment: Disinfection, oxidation and corrosion

The use of organic peracids in wastewater treatment is attracting increasing interest. The common beneficial features of peracids are effective anti-microbial properties, lack of harmful disinfection by-products and high oxidation power. In this study performic (PFA), peracetic (PAA) and perpropionic acids (PPA) were synthesized and compared in laboratory batch experiments for the inactivation of Escherichia coli and enterococci in tertiary wastewater, oxidation of bisphenol-A and for corrosive properties. Disinfection tests revealed PFA to be a more potent disinfectant than PAA or PPA. 1.5 mg L−1 dose and 2 min of contact time already resulted in 3.0 log E. coli and 1.2 log enterococci reduction. Operational costs of disinfection were estimated to be 0.0114, 0.0261 and 0.0207 €/m3 for PFA, PAA and PPA, respectively. Disinfection followed the first order kinetics (Hom model or S-model) with all studied peracids. However, in the bisphenol-A oxidation experiments involving Fenton-like conditions (pH = 3.5, Fe2+ or Cu2+ = 0.4 mM) peracids brought no additional improvement to traditionally used and lower cost hydrogen peroxide. Corrosion measurements showed peracids to cause only a negligible corrosion rate (<6 μm year−1) on stainless steel 316L while corrosion rates on the carbon steel sample were significantly higher (<500 μm year−1).

Research on Fe-loaded ZSM-5 molecular sieve catalyst in high-concentration aniline wastewater treatment

Fe-ZSM-5 molecular sieve catalysts were fabricated and characterized through scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. Researches were developed within a heterogeneous Fenton-like catalysis system established with Fe-ZSM-5 molecular sieve catalyst and H2O2, with regard to the effects of pH, H2O2 dosage, inlet concentration of aniline, and catalyst dosage on extent of removal and reaction rate, and preliminarily revealed the mechanisms of degradation in aniline wastewater. Outcomes have demonstrated that Fenton-like Fe-ZSM-5 molecular sieve catalysts are functionally stable and recyclable in which the extents of removal of aniline, CODCr and TOC are 96.4, 92.5, and 72.5%, respectively; with 3 g catalyst dosed into 500 mL aniline wastewater of 200 mg L−1 in concentration, pH 4, and H2O2 of 0.5Qth (0.31 mL L−1), the Fenton-like conditions could not only break up the inner structures of aniline, but also catalyze the products in further mineralization to CO2 and H2O.

Model reactions and natural occurrence of furans from hypersaline environments

Abstract. Volatile organic compounds like furan and its derivatives are important for atmospheric properties and reactions. In this work the known abiotic formation of furan from catechol under Fenton-like conditions with Fe3+ sulfate was revised by the use of a bispidine Fe2+ complex as a model compound for iron with well-known characteristics. While total yields were comparable to those with the Fe3+ salt, the bispidine Fe2+ complex is a better catalyst as the turnover numbers of the active iron species were higher. Additionally, the role of iron and pH is discussed in relation to furan formation from model compounds and in natural sediment and water samples collected from the Dead Sea and several salt lakes in Western Australia. Various alkylated furans and even traces of halogenated furans (3-chlorofuran and 3-bromofuran) were found in some Australian samples. 3-chlorofuran was found in three sediments and four water samples, whereas 3-bromofuran was detected in three water samples. Further, the emission of furans is compared to the abundance of several possible precursors such as isoprene and aromatic hydrocarbons as well as to the related thiophenes. It is deduced that the emissions of volatile organic compounds such as furans contribute to the formation of ultra-fine particles in the vicinity of salt lakes and are important for the local climate.

Natural Abiotic Formation of Oxalic Acid in Soils: Results from Aromatic Model Compounds and Soil Samples

Oxalic acid is the smallest dicarboxylic acid and plays an important role in soil processes (e.g., mineral weathering and metal detoxification in plants). We have first proven its abiotic formation in soils and investigated natural abiotic degradation processes based on the oxidation of soil organic matter, enhanced by Fe(3+) and H(2)O(2) as hydroxyl radical suppliers. Experiments with the model compound catechol and further hydroxylated benzenes were performed to examine a common degradation pathway and to presume a general formation mechanism of oxalic acid. Two soil samples were tested for the release of oxalic acid and the potential effects of various soil parameters on oxalic acid formation. Additionally, the soil samples were treated with different soil sterilization methods to prove the oxalic acid formation under abiotic soil conditions. Different series of model experiments were conducted to determine a range of factors including Fe(3+), H(2)O(2), reaction time, pH, and chloride concentration on oxalic acid formation. Under certain conditions, catechol is degraded up to 65.6% to oxalic acid referring to carbon. In serial experiments with two soil samples, oxalic acid was produced, and the obtained results are suggestive of an abiotic degradation process. In conclusion, Fenton-like conditions with low Fe(3+) concentrations and an excess of H(2)O(2) as well as acidic conditions were required for an optimal oxalic acid formation. The presence of chloride reduced oxalic acid formation.

Synthesis and Radioprotective Properties of Pulvinic Acid Derivatives

A high-throughput screening method has highlighted the marked antioxidant activity of some pulvinic acid derivatives (PADs) towards oxidation of thymidine, under γ and UV irradiation, and Fenton-like conditions. Here, we report the synthesis of a series of new hydrophilic PADs and the evaluation of their radioprotective efficacy in cell culture. Using a cell-based fluorescent assay, we show that some of these compounds have a pronounced ability to prevent cell death caused by radiation and to allow the subsequent resumption of proliferation. Thus, PADs may be considered as a novel class of radioprotective agents.

Natural Abiotic Formation of Furans in Soil

Furan and its derivates are a potentially important, and little studied, class of volatile organic compounds of relevance to atmospheric chemistry. The emission of these reactive compounds has been attributed previously to biomass burning processes and biogenic sources. This paper investigates the natural abiotic formation of furans in soils, induced by the oxidation of organic matter by iron(III) and hydrogen peroxide. Several model compounds like catechol, substituted catechols, and phenols as well as different organic-rich soil samples were investigated for the release of furans. The measurements were performed with a purge and trap GC/MS system and the influence of hydrogen peroxide, reaction temperature, iron(III), pH, and reaction time on furan yield was determined. The optimal reaction turnover obtained with catechol was 2.33 microg of furan from 0.36 mg of carbon. Results presented in this paper show that a cleavage of catechol into a C2- and a C4-fragment occurs, in which the C4-fragment forms furan by integrating an oxygen atom stemming from H2O2. Furthermore, phenols could be transformed into catecholic structures under these Fenton-like conditions and also display the formation of furans. In conclusion, catalytic amounts of iron(III), the presence of hydrogen peroxide, and acidic conditions can be seen as the most important parameters required for an optimized furan formation.

Identification of leucine‐enkephalin radical oxidation products by liquid chromatography tandem mass spectrometry

The oxidation of the peptide leucine-enkephalin (YGGFL) induced by the hydroxyl radical (HO*), formed under Fenton-like conditions [Cu (II)/H(2)O(2)], was studied and monitored by LC-MS. The oxidation products identified included products resultant from (a) the insertion of oxygen atoms (1-5), (b) peptide backbone cleavage (short-chain products formed by diamide pathway) and (c) radical-radical crosslinking reactions. In order to identify the modified residues, LC-MS/MS spectra were obtained. The insertion of oxygen atoms into the peptide originated hydroxide, di-hydroxide and/or hydroperoxide derivatives. In addition it was found that the aromatic amino acids are most susceptible to being hydroxylated, while the aliphatic amino acids are more prone to forming hydroperoxides. Oxidation products with double bonds were also identified. The short chain products resulted from the alpha-carbon radical of terminal amino acids (Tyr and Leu). Products resulting from cross-linking reactions between intact carbon-centered peptide radical (with and without one HO group) and a side chain radical (*C(7)H(7)O) were identified. It was found that, although all amino acids residues of the peptide undergo modifications, the N-terminal seems to be prone to oxidative modifications under these conditions.

Mineralization of sorbed and NAPL-phase hexadecane by catalyzed hydrogen peroxide

The oxidation and mineralization of hexadecane in silica sand slurries was investigated using aggressive Fenton-like reactions [high concentrations of hydrogen peroxide and an iron (II) catalyst]. When spiked with 0.1 mmol kg −1 hexadecane, 56% of the hydrocarbon was sorbed to the silica sand and most of the remaining hexadecane was found as nonaqueous phase liquid (NAPL). Gas-purge methodology documented that hexadecane desorption from the silica sand slurries was negligible over 72 h. Three process variables [hydrogen peroxide concentration, slurry volume and soluble iron (II) amendment] were studied to determine their effects on hexadecane oxidation. A central composite rotatable experimental design was used to determine the most effective oxidation conditions as well as possible interactions between variables. In addition to investigating the oxidation of the parent compound, parallel experiments were conducted using 14C-hexadecane to evaluate its mineralization. The recovery of 14C-CO 2 confirmed that under the most effective conditions (high concentrations of hydrogen peroxide and low slurry volumes), 83% of the sorbed and NAPL-phase hexadecane was mineralized to CO 2 and H 2O. The iron (II) concentration had a negligible effect on parent compound degradation within the range investigated (5 to 25 mM) but was a significant variable in promoting the mineralization of hexadecane. The results show that under aggressive Fenton-like conditions, even a highly hydrophobic compound that is sorbed and in a NAPL-phase can be oxidized to its thermodynamic endpoints.