RESUMEN
BACKGROUND AND PURPOSE: Surfactant-assisted soil washing and photocatalysis are well-known remediation processes of environmental concern. The application of photocatalysis to treat soil washing extracts containing 4-methylphenol, 4-ethylphenol and 4-tert-butylphenol in the presence of nonionic (C(12)E(8) and C(12)E(23)) and anionic (SDS) surfactants and some of their binary mixtures was investigated in this work by studying the pollutants degradation in the presence of TiO(2) dispersions irradiated with simulated solar light. MATERIALS AND METHODS: Clean soil samples were spiked with the investigated alkylphenols. Aqueous solutions of the chosen surfactants were placed in contact for some hours with the spiked soil samples in a rotatory mixer. The pollutants recoveries were evaluated via HPLC analysis. Photocatalytic experiments were performed in solarbox on aqueous solutions and on aqueous surfactant solutions containing the pollutants. RESULTS: The pollutants removal from the soil was proven effective using the examined surfactant solutions. The photocatalytic treatment of the wastes was faster using Brij 35, but also SDS and C(12)E(8)-SDS mixtures can be applied. After 2-5 h the complete pollutants abatement was obtained, depending on the surfactant chosen and on the amount of TiO(2) employed. On the contrary, the treatment of wastes containing C(12)E(8) was an extremely slow process. CONCLUSIONS: The photocatalytic approach can be applied to remove the examined aromatic pollutants from the washing wastes, confirming the viable coupling between this advanced oxidation method and the surfactant-based soil remediation treatments. Surfactant adsorption onto TiO(2) and micelles concentration play a dominant role.
Asunto(s)
Fenoles/química , Fotoquímica/métodos , Contaminantes del Suelo/química , Tensoactivos/química , Titanio/química , Catálisis , Concentración de Iones de HidrógenoRESUMEN
High-performance liquid chromatography coupled to ultraviolet diode array detection and electrospray ionization mass spectrometry was applied to monitor the photocatalytic degradation mediated by TiO2 of three sulfonated monoazo dyes (Orange I, Orange II, and Ethylorange) present in aqueous solution. Photobleaching, organic carbon, nitrogen and sulfur evolution were also followed during the process. Delayed carbon mineralization was observed with respect to both dyes disappearance and photobleaching, due to the formation of transient intermediate compounds which were in turn completely degraded. Among the intermediates produced during the initial degradation steps the formation of several hydroxylated derivatives, mostly coloured, was evidenced. The MS(2) spectra allowed one to formulate hypothesis about the OH attack positions; a peculiar reactivity of the azo moiety was shown by Orange I and Orange II.
Asunto(s)
Alcanosulfonatos/química , Cromatografía Líquida de Alta Presión/métodos , Colorantes/química , Espectrometría de Masa por Ionización de Electrospray/métodos , Espectrofotometría Ultravioleta/métodos , Catálisis/efectos de la radiación , Estructura Molecular , FotoquímicaRESUMEN
Nitrobenzene thermal degradation was investigated using the Fenton reagent in different experimental conditions. Reaction products were analyzed by HPLC, GC-MS, LC-MS and IC. The products obtained at different nitrobenzene conversion degrees show that degradation mainly involves successive hydroxylation steps of the aromatic ring and its subsequent opening followed by oxidation of corresponding aliphatic compounds. Our results show as primary reaction products: 4-nitrophenol, 3-nitrophenol, 2-nitrophenol, phenol and 1,3-dinitrobenzene, indicating that both hydroxylation and nitration reactions are involved. The formation of phenolic products can be explained by postulating an initial step of HO() addition to nitrobenzene ring. The mechanisms of primary reaction pathways are discussed and a detailed kinetic analysis to obtain the true primary yields of phenolic products is proposed. The relative yields observed for nitrophenol isomers do not follow the expected orientation according to deactivating characteristics of the nitro group but significantly depend on Fe(+2), Fe(+3), H(2)O(2) and O(2) concentrations. The understanding of the effect of reaction conditions on the relative product distribution benefits the application of Fenton and Fenton-like systems to waste water treatment.
Asunto(s)
Peróxido de Hidrógeno/química , Hierro/química , Nitrobencenos/análisis , Fenoles/análisis , Contaminantes Químicos del Agua/análisis , Purificación del Agua , Modelos Químicos , Nitrobencenos/química , Oxidación-Reducción , Contaminantes Químicos del Agua/química , Purificación del Agua/métodosRESUMEN
The photocatalytic oxidation of methyl-orange (C14H14N3SO3Na) dye was carried out in aqueous suspensions of polycrystalline TiO2 irradiated with artificial light until its complete mineralization was achieved. The performances of two widely used semiconductor powders were studied for comparison purposes. The dependence of dye photo-oxidation rate on various experimental parameters, including substrate concentration, semiconductor amount, and pH was investigated by using both catalysts. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. The two investigated TiO2 powders (Degussa P25 and Merck) showed different photoactivities. TOC analyses confirmed the complete mineralization achievable using both photocatalysts. Three main transient products still maintaining the chromophoric azo group were identified prior to their transformation into other degradation products which are non-absorbing in the visible region.
Asunto(s)
Compuestos Azo/química , Colorantes/química , Titanio/química , Contaminantes Químicos del Agua , Catálisis , Concentración de Iones de Hidrógeno , Cinética , Oxidación-Reducción , Fotólisis , Suspensiones , Industria Textil/métodos , Agua/químicaRESUMEN
The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C14H14N3SO3Na) and orange II (C16H11N2SO4Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO2 irradiated by sunlight. Compound parabolic collectors, installed at the "Plataforma Solar de Almería" (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H2O2, S2O8(2-)) and some ions (Cl-, SO4(2-)) on the process was also studied.