Oxidation of sulfonamides by ferrate(VI): Reaction kinetics, transformation byproducts and toxicity assesment.

This study was aimed at the degradation of sulfonamides (SNs) via oxidation with Fe(VI). The reaction kinetics, identification of degradation byproducts and their toxicity were investigated. The pH solution and Fe(VI) loading had significant effects on the degradation of the sulfonamides. The maximum degradation rate occurred at pH 3.0 with a 6:1 ratio Fe(VI): sulfonamide, obtaining 100% degradation of 15 mg L-1 SN within 5 min. Although Fe(VI) also showed an appreciable reactivity towards SNs (kapp = 9.85-19.63 × 102 M-1 s-1) at pH 7. The influence of solution pH on the values of kapp can be explained considering the specific reaction between Fe(VI) and SNs. Degradation rates are also influenced by the presence of inorganic ions in different water matrixes. For this reason, ions present in groundwater enhanced the SNs degradation through a synergistic effect among carbonates, sulfates and Fe(VI). Degradation byproducts identified, through UPLC analysis, allowed us to proposed three degradation pathways depending on pH. At acid pH there is a cleavage of C-S and S-N bonds. At neutral pH nitroso and nitro-derivates are formed. At basic pH hydroxylation is the main reaction. The cytotoxicity assay of HEK-293 and J774 cell lines exposed to Fe(VI) indicated that transformation byproducts had a lower toxicity than SNs as baseline products. Accordingly, this research suggests that Fe(VI) can act as a chemical oxidant to remove SNs antibiotics and it can be used to treat antibiotic pollution in wastewater.

Halide removal from water using silver doped magnetic-microparticles.

This study proposes the use of new materials based on core-shell structure magnetic microparticles with Ag0 (Ag(0)-MPs) on their surface to remove bromides and chlorides from waters intended for human consumption. Hydrogen peroxide was used as oxidizing agent, Ag(0)-MPs is thereby oxidized to Ag (I)-MPs, which, when in contact with Cl- and Br- ions, form the corresponding silver halide (AgCl and AgBr) on the surface of Ag-MPs. The concentration of Cl- and Br- ions was followed by using ion selective electrodes (ISEs). Silver microparticles were characterized by high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy, while the presence of AgCl and AgBr on Ag-MPs was determined by microanalysis. We analyzed the influence of operational variables, including: hydrogen peroxide concentration in Ag-MP system, medium pH, influence of Cl- ions on Br- ion removal, and influence of tannic acid as surrogate of organic matter in the medium. Regarding the influence of pH, Br-and Cl- removal was constant within the pH range studied (3.5-7), being more effective for Br- than for Cl- ions. Accordingly, this research states that the system Ag-MPs/H2O2 can remove up to 67.01% of Br- ions and 56.92% of Cl- ions from water (pH = 7, [Ag-MPs]0 = 100 mg L-1, [H2O2]0 = 0.2 mM); it is reusable, regenerated by radiation and can be easily removed by applying a magnetically assisted chemical separation process.

Photocatalytic oxidation of diuron using nickel organic xerogel under simulated solar irradiation.

In this study, a nickel organic xerogel (X-Ni) was used as semiconductor photocatalyst for the degradation of the herbicide diuron (DRN) in aqueous solution. The main objective of this work was to analyze and compare the effectiveness of solar irradiation to remove DRN from water both by direct photolysis and photocatalytic degradation. We examined the influence of the initial concentration of the herbicide, the solution pH, the presence of different ions in the medium, the chemical composition of the water, and the presence of a photocatalyst, after 240 min of irradiation. Direct photolysis achieved a low percentage of DRN degradation but was favored: i) by a reduction in the initial concentration of the herbicide (from 35.6% to 79.0% for 0.150 × 10-3 mol/L and 0.021 × 10-3 mol/L of DRN, respectively) and ii) at solution pHs at which diuron is positively charged (78.6% for pH 2 and 50.4% for pH 7), as suggested by DFT calculations carried out for DRN and its protonated form (DRN-H+). The corresponding mono-demethylated DRN derivative, 1-(3,4-dichlorophenyl)-3-methylurea (DCPU), was identified as a DRN degradation byproduct. In addition, the presence of certain anions in the medium significantly affected the overall degradation process by direct photolysis, due to the additional generation of HO radicals. We highlight that the presence of X-Ni considerably improved the photodegradation process under solar irradiation. The photocatalytic degradation rate constant was directly proportional to the xerogel concentration, because an increase in catalyst dose produced an increase in surface active sites for the photodegradation of DRN, enhancing the overall efficiency of the process. Thus, when 4167 mg/g of X-Ni was added, the DRN removal rate was 3-fold higher and both percentage of degradation and mineralization increased 88.5% with respect to the results obtained by direct photolysis.

Sulfonamides degradation assisted by UV, UV/H2O2 and UV/K2S2O8: Efficiency, mechanism and byproducts cytotoxicity.

The objective of this study was to analyze the effectiveness of UVC, UVC/H2O2 and UVC/K2S2O8 on the degradation of SAs. Rate constant values increased in the order SMZ < SDZ < SML and showed the higher photodegradation of sulfonamides with a penta-heterocycle. Quantum yields were 1.72 × 10-5 mol E-1, 3.02 × 10-5 mol E-1, and 6.32 × 10-5 mol E-1 for SMZ, SDZ and SML, respectively, at 60 min of treatment. R254 values show that the dose habitually utilized for water disinfection is inadequate to remove this type of antibiotic. The initial sulfonamide concentration has a major impact on the degradation rate. The degradation rates were higher at pH 12 for SMZ and SML. SMZ and SML photodegradation kλ values are higher in tap versus distilled water. The presence of radical promoters generates a greater increase in the degradation rate, UVC/K2S2O8 cost less energy, a mechanism was proposed, and the degradation by-products are less toxic than the original product.

Lanthanum-doped silica xerogels for the removal of fluorides from waters.

The objective of this study was to determine the influence of different operational variables on fluoride (F-) removal from waters using lanthanum (La)-doped silica xerogels and the mechanisms involved in this process. Accordingly, four xerogels were synthesized, one acting as blank (X-B), two doped with LaCl3 and dried at different temperatures (X-LaCl and X-LaCl-M), and a fourth doped with La2O3 (X-LaO). The results show that fluorides are only removed when La-doped xerogels are utilized. In addition, X-LaCl yielded the highest adsorption capacity, removing 28.44% of the initial fluoride concentration at a solution pH of 7. Chemical characterization of materials confirmed that fluoride removal from waters is due to the precipitation of LaF3 on the surface of La-doped xerogels. The presence of dissolved organic matter on the aqueous solution also reduce the removal capacity of La xerogels. Finally, analysis of the influence of solution pH revealed that the adsorption capacity of all xerogels was highest at a solution pH of 7.

Halide removal from waters by silver nanoparticles and hydrogen peroxide.

The objective of this study was to remove halides from waters by silver nanoparticles (AgNPs) and hydrogen peroxide (H2O2). The experimental parameters were optimized and the mechanism involved was also determined. The AgNP/H2O2 process proved efficacious for bromide and chloride removal from water through the selective precipitation of AgCl and AgBr on the AgNP surface. The optimal AgNP and H2O2 concentrations to be added to the solution were determined for the halide concentrations under study. The removal of Cl- and Br- anions was more effective at basic pH, reaching values of up to 100% for both ions. The formation of OH, O2-, radicals was detected during the oxidation of Ag(0) into Ag(I), determining the reaction mechanism as a function of solution pH. Moreover, the results obtained show that: i) the efficacy of the oxidation of Ag(0) into Ag(I) is higher at pH11, ii) AgNPs can be generated by the O2- radical formation, and iii) the presence of NaCl and dissolved organic matter (tannic acid [TAN]) on the solution matrix reduces the efficacy of bromide removal from the medium due to: i) precipitation of AgCl on the AgNP surface, and ii) the radical scavenger capacity of TAN. AgNPs exhausted can be regenerated by using UV or solar light, and toxicity test results show that AgNPs inhibit luminescence of Vibrio fischeri bacteria.