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.

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.

Removal of ammonium from aqueous solution by ion exchange on natural and modified chabazite.

The ammonium exchange capacity of a natural chabazite was studied in this work. The XRD analysis of the zeolite sample revealed that the main zeolitic phase was chabazite. The textural properties were determined by the N(2)-BET method and the surface morphology and charge were examined using a scanning electron microscope and a zetameter, respectively. The ion exchange equilibrium data were obtained in a batch adsorber and the Langmuir isotherm fitted plausibly well the equilibrium data. The effects of the temperature and pH on the ammonium exchange capacity of chabazite were investigated and the capacity increased augmenting the temperature from 15 to 35 °C and pH from 3 to 6. The natural chabazite was modified by a hydrothermal treatment using NaCl and KCl solutions and it was found that the modification influenced the ammonium exchange capacity of the chabazite. The ammonium capacity of natural chabazite was compared with that of a natural clinoptilolite and it was concluded that the chabazite capacity was 1.43 times higher than that of clinoptilolite.

Comparison of isotherms for the ion exchange of Pb(II) from aqueous solution onto homoionic clinoptilolite.

The ion exchange equilibrium of Pb(II) on clinoptilolite modified with NH(4)Cl and NaCl can be represented by two types of isotherms. The first one is the ion exchange isotherm based upon the constant of thermodynamic equilibrium for the ion exchange reaction; however, the fitting procedure for this isotherm can be very tedious due to all the calculations involved and additional thermodynamic data. The second one is the Langmuir isotherm. The use of the Langmuir isotherm to represent ion exchange equilibrium has increased in recent last years since it adequately fits the equilibrium data and, furthermore, its calculation is much simpler. A comparison between the two isotherms showed that they fitted the experimental data reasonably well, but the Langmuir isotherm is much simpler and easier to use.