RESUMO
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.
Assuntos
Poluentes Químicos da Água , Purificação da Água , Células HEK293 , Humanos , Concentração de Íons de Hidrogênio , Ferro , Cinética , Oxirredução , SulfonamidasRESUMO
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.
Assuntos
Fluoretos/isolamento & purificação , Lantânio , Purificação da Água , Adsorção , Fluoretos/química , Concentração de Íons de Hidrogênio , Dióxido de Silício , Poluentes Químicos da ÁguaRESUMO
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.