Gloria M Restrepo

Evolution of natural organic matter by size exclusion chromatography during photocatalytic degradation by solvothermal-synthesized titanium dioxide

This study shows the effect of different titanium dioxides in transforming the structural properties of natural organic matter (NOM) during photocatalytic degradation with a solar UV light simulator. Titanium dioxide (TiO(2)) synthesized by the sol-gel method coupled with the solvothermal technique and Degussa P-25 TiO(2) were used. The evolution of NOM degradation was followed by size exclusion chromatography with dissolved organic carbon, ultraviolet and fluorescence detection (SEC-DOC, SEC-UV(254) and SEC-Fl(254/450)). For both catalysts, there was a preferential degradation of the larger molecules of NOM into medium and smaller molecular size fractions. However, the synthesized TiO(2) was found to be more efficient than Degussa P-25 TiO(2) for DOC removal, especially UV(254) absorption and Fl(254/450) removal.

XAFS study of TiO2/SiO2 system prepared by sol–gel from inorganic precursors

Abstract The samples of 5%TiO 2 /SiO 2 prepared by sol–gel method from inorganic precursors calcinated at the various temperatures were studied by XAFS spectroscopy at Siberian Synchrotron Radiation Center. It was established that structural lability of this system and the change of symmetry of the oxygen coordination around the Ti(+4) ions depends on the calcination temperature. It seems that the mechanism of dissolution of the Ti(4+) ions in SiO 2 depends on the calcination temperature and consists in the formation of Wadsley defects following the incorporation of SiO 2 in TiO 2 particles.

Efecto del pH en la Degradación Fotocatalítica de Materia Orgánica Natural

Resumen Se ha estudiado el efecto del pH en la degradacion fotocatalitica de materia organica natural del agua de un ecosistema lentico, empleando dioxido de titanio comercial en suspension y un simulador solar UV. Para el seguimiento de la degradacion y la caracterizacion de la materia organica natural se uso cromatografia de exclusion de tamano, con un detector de carbon organico disuelto y un detector ultravioleta a una longitud de onda λ=254 nm, y espectrofotometria UV-Vis. Se encontro que la cinetica de la reaccion es alta a un pH por debajo del punto isoelectrico del fotocatalizador y disminuye a un pH por encima del punto isoelectrico. Ademas, la fotocatalisis se da por la alteracion de la distribucion de las masas moleculares, especialmente por la degradacion de compuestos de alta masa molecular a compuestos de baja masa molecular, antes de su mineralizacion. Palabras clave : materia organica natural, fotocatalisis heterogenea, dioxido de titanio, cromatografia Effect of pH on the Photocatalytic Degradation of Natural Organic Matter

Preparación de Sistemas Óxido de Titanio/Óxido de Silicio (TiO2/SiO2) mediante el Método Solvotérmico para Aplicaciones en Fotocatálisis

Resumen Sistemas Oxido de Titanio/Oxido de Silicio (TiO 2 /SiO 2 ) fueron obtenidos por anclaje de TiO 2 en SiO 2. El fotocatalizador TiO 2 se obtuvo por alcoholisis del TiCl 4 con 2-propanol y posterior cristalizacion a presion autogena a 200 °C, excluyendo etapas de calcinacion a altas temperaturas. Se emplearon diferentes relaciones SiO 2 /TiCl 4 para determinar su influencia en la estabilidad, propiedades y fotoactividad de los sistemas TiO 2 /SiO 2 . La actividad fotocatalitica fue evaluada por la fotodegradacion de metanol en fase gaseosa. El TiO 2 cristalizo como fase anatasa o como una mezcla rutilo/anatasa, dependiendo por la relacion SiO 2 /TiCl 4 inicial. Los resultados muestran que se producen materiales compuestos con alta cristalinidad del TiO 2 . Se encontro tambien que hay una fuerte relacion entre la actividad fotocatalitica con las propiedades fisicoquimicas y de estas con las composiciones iniciales de sintesis. Palabras clave: sistemas TiO 2 /SiO 2 , fotocatalisis, metodo solvotermico, materiales compuestos

Discrepancias en los Cálculos Termodinámicos Relacionados con la Deshidrogenación de Parafinas

In this paper, the differences between the equilibrium constants and conversions, for the dehydrogenation of paraffins, calculated by three methods and the values traditionally accepted in the literature are presented. Usually, it is accepted that the equilibrium conversions, for the dehydrogenation of paraffins, increase with the number of carbons in a monotonous way. However, the conversions calculated in this work for paraffins from C3 to C10, oscillate between 15 and 20%, and only from C11 a similar trend to the traditionally reported values is observed. The trend widely mentioned in the scientific literature shows important differences with the results obtained in this work, concluding that the accepted tendency between equilibrium conversion and number of carbons is not correct.

Dispersión de Contaminantes del Aire (PM10, NO2, CO, COV y HAP) emitidos desde una Estación Modular de Compresión, Tratamiento y Medición de Gas Natural

espanolEste estudio presenta el analisis de la emision, dispersion y concentracion de PM10, CO, NO2, COV y HAP (contaminantes peligroso del aire), emitida desde una estacion modular de compresion, tratamiento y medicion de gas natural, ubicada en la peninsula de La Guajira al norte de Colombia. Se aplico el modelo de dispersion Gaussiana WKBK2 para fuentes puntuales para estimar las concentraciones de los contaminantes. Las emisiones de los contaminantes se estimaron utilizando los factores de emisiones de la Agencia Ambiental de los Estados Unidos USEPA. La aplicacion del modelo fue validado con PM10 y NO2 medido en un sitio cerca de la planta industrial. Las maximas concentraciones ocurren entre 100 a 200 metros de la fuente. Las concentraciones maxima estimadas de PM10 estaria violando el estandar anual de la Organizacion Mundial de la Salud. En las cuatro comunidades indigenas ubicadas en la zona, se estimaron niveles menores a los establecidos en la norma Colombiana. EnglishThis study presents the analysis of the emission, dispersion, and concentration of PM10, CO, NO2, COV y HAP (Hazardous Air Pollutants), emitted from a modular station of compression, processing and measurement of natural gas located on the peninsula of La Guajira in northern Colombia. To estimate the concentrations of pollutants was applied Gaussian dispersion WKBK2 model for point source. Emissions of the pollutants are estimated using the US Environmental Agency emission factor. The application of the model was validated with PM10 and NO2 measured at a site near the Industrial Plant. The maximum concentration occurs between 100 to 200 meters from the source. The maximum concentrations of PM10 exceeded the World Health Organization guideline value of 20 µg/m3. In four indigenous communities located in the area, the levels were lower than those established in the Colombian norm

Predicción y Análisis de la Contribución de PM10 desde Pilas de Carbón en una Mina a Cielo Abierto

The contributions of PM10 to the environment were determined in a mining industrial zone in northern Colombia for activities involved in storing 3.2 Mton of coal. As the main modeling tool the software CALPUFF was used to determine the contribution of PM10 for 10 days modeling during a month period. Ambient concentrations of PM10 in five receivers were measured. Although higher emissions occur during daytime, characterized by high values of wind speed and higher solar radiation, the greater receptivity of PM10 measurements stations occurred during night hours due to the decreasing the mixing height. The modeling results show that the activities involved in carbon storage can provide 14.5% of daily ambient concentrations at receptors located 16.2 km downwind from the source.