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

BRACCO, ESTEFANÍA BELÉN; BUTLER, MATÍAS; CARNELLI, PATRICIO FRANCISCO FLORENCIO; ALFANO, ORLANDO MARIO; CANDAL, ROBERTO JORGE

Ciudad Obregón, Sonora

Simposio; The Sixth International Symposium of Environmental Biotechnology and Engineering; 2018

ITSON

TiO2 is one of the most employed compounds for the treatment of recalcitrant pollutants by heterogeneous photocatalysis. However, TiO2 is only activated by UVA light (around 5% of the solar light), which represents a limitation on its use as photocatalyst. Therefore, a potential alternative to improve its photocatalytic activity is through nonmetals doping, although byproducts and reaction rate may be affected by light wavelength and doping. In this work, sol-gel process coupled with urea coprecipitation was used to prepare nanoparticulated powders of nitrogen doped TiO2 (N-TiO2), since it has been shown as a nontoxic dopant contributing to the activity under visible light. A control sample of pure TiO2 was synthesized in a similar way, except for the addition of urea. Powders were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photocatalysis experiments were performed using salicylic acid as a model contaminant at different initial concentrations (10 -4 M and 2x10-5 M). A homemade photoreactor equipped with two different light sources, UVA (372 nm) and blue led (462 nm), was used for the experiments with each synthesized photocatalyst besides commercial P-25 TiO2 . The evolution of the experiments was followed via the initial and final measurement of temperature, pH and TOC, as well as through the analysis of samples taken at regular times by UV-Vis spectrophotometry and high performance liquid chromatography coupled to mass spectrometry (HPLC-MSn ). The latter was applied to detect the presence of transformation products in the samples via a linear ion trap with electrospray ionization in negative ion mode. The analysis of the results showed a faster decrease in the concentration of salicylic acid when using P-25 TiO2, followed by N-TiO2 and pure TiO2 catalysts under bothlight sources. Accordingly, the calculated quantum yields obeyed the same trend, although N-TiO2 displayed the highest photon absorption efficiencies and photonic efficiencies similar to the quantum yields with both lights. The major differences found in the amount and identity of the transformation products were owed to the different light sources and to a lower extent to the photocatalyst. Further structural characterization of the degradation products was made by mass spectrometry through fragmentation (MSn) and analysis of derivatives.