TiO2 and N-TiO2-photocatalytic degradation of salicylic acid in water: characterization of transformation products by mass spectrometry

The aim of this work is to study the byproducts formed as a result of the photocatalytic process under different conditions of light wavelength and photocatalyst doping, rendering valuable information about the fate of pollutants for water treatment applications. Salicylic acid was selected as a model emerging pollutant and powders of nitrogen-doped titanium dioxide (N-TiO2) and TiO2 were prepared by the sol-gel process, using TiO2 P-25 Degussa as benchmark. Two light sources, UVA fluorescent tubes (372 nm) and blue LEDs (462 nm), were employed for photolysis and photocatalysis experiments. Transformation products formed during the process were studied by high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS). Major differences were found in the amount and identity of the transformation products due to the different light sources, detecting similar transformation products among the studied catalysts. Under UVA light, hydroxylated and carbonylated byproducts were the first intermediates to reach maximum abundances whereas presumed ring opening products were the last ones. On the other hand, under blue LED illumination byproducts accumulated with decreased mineralization. Photocatalytic degradation pathways were proposed based on the findings.Fil: Bracco, Estefania Belen. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Butler, Matias. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Carnelli, Patricio Francisco Florencio. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Candal, Roberto Jorge. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentin

Degradation of oxytetracycline and characterization of byproducts generated by Fenton or photo-Fenton like processes after adsorption on natural and iron(III)-modified montmorillonite clays

The combination of adsorption with advanced oxidation is presented as an alternative to remove antibiotics in water, particularly using clays as cheap adsorbents. However, little is known about the evolution of the reaction in a heterogeneous phase, the formation of byproducts and their persistence. In this work oxytetracycline (OTC), raw (MMT) and iron modified montmorillonite (Fe-MMT), and Fenton (F) or photo-Fenton (phF) like reactions were employed as model antibiotic, adsorbents, and oxidation treatments, respectively. Homogeneous F and phF experiments for OTC degradation were also performed. Adsorption experiments demonstrated that incorporation of Fe(III) to MMT increased OTC adsorption at both studied pHs (3.0 and 7.0), due to the formation of OTC-Fe(III) complexes. MMT or Fe-MMT containing adsorbed OTC (OTC-MMT or OTC-Fe-MMT) exposed to F or phF like processes at pH 3.0 or 7.0 released solely OTC oxidation byproducts. Mineralization was only observed for OTC-Fe-MMT at both pH values, after a maximum TOC was attained, being more marked for phF than for F like processes. The structures of transformation products were proposed based on HPLC-MSn analysis of withdrawn samples from solution. Similar intermediates were identified in homogeneous and heterogeneous oxidation processes although the total number was lower for the latter. OTC degradation occurred by several pathways including oxidations by hydrogen abstraction and hydroxyl addition, as well as ring contractions and losses of water, carbonyl and carboxamide moieties. The performance and outcomes of phF like process applied to OTC-Fe-MMT at initial pH 3.0 and 7.0 were comparable to homogeneous phF at pH 3.0.Fil: Bracco, Estefania Belen. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Marco Brown, José Luis. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Butler, Matias. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Candal, Roberto Jorge. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; Argentin