Juan Marín

Application of excitation–emission fluorescence matrices and UV/Vis absorption to monitoring the photocatalytic degradation of commercial humic acid

This study reports the use of excitation-emission matrix (EEM) fluorescence and UV/Vis spectroscopy to monitor the changes in the composition and reactivity of Aldrich humic acids (Aldrich HA) as a model compound for natural organic matter (NOM) during photocatalytic degradation. Degussa P-25 titanium dioxide (TiO(2)) and a solar UV-light simulator (a batch reactor) were used. The photocatalysis shifted the fluorescence maxima of EEMs of Aldrich HA toward shorter wavelengths, which implied that the photocatalytic degradation of commercial Aldrich HA caused the breakdown of high molecular weight components and the formation of lower molecular weight fractions. In addition, the fluorescence intensity of fulvic- and humic-like Aldrich HA presented a strong correlation with dissolved organic carbon (DOC), specific UV absorbance (SUVA) parameters, trihalomethane formation potential (THMFP), and organically bound halogens absorbable on activated carbon formation potential (AOXFP). Fluorescence spectroscopy was shown to be a powerful tool for monitoring of the photocatalytic degradation of HA.

Magnetron-sputtered Ag surfaces. New evidence for the nature of the ag ions intervening in bacterial inactivation.

DC-magnetron sputtering with an Ag target on textile surfaces produced Ag particles with sizes approximately 4.7 nm (+/-15%). Sputtering for 15 s led to Ag layers of 15-20 nm. The threshold sputtering time precluding airborne bacterial growth was about 60 s. In this case, the coating was approximately 40-50 nm thick and the cotton Ag loading was 0.0026 wt %. The Ag particle size did not vary significantly with sputtering time between 15 and 600 s. Only coatings above this thickness lead to bacterial inactivation. Ag/Pt targets with sputtering times<60 s did not increase the bactericide performance of the Ag cotton samples with respect to sputtering from an Ag target alone, as expected from the position of Pt respect to Ag in the electrochemical series (Galvanic effect). The Ag cotton deposition led to very thin metallic semitransparent gray color coatings. X-ray of the Ag cotton suggested the presence of amorphous and crystalline Ag species. By X-ray photoelectron spectroscopy (XPS), it was found that the amount of oxidized silver species on the cotton was similar for sputtering times of 60 and 600 s, but the total amount of Ag deposited was almost two times higher after 600 s sputtering. This suggests that the positive silver-ions were located mainly at the silver interface. The type of silver ions produced using the Ag/Pt sputtering was determined to be very similar at 15, 60, and 600 s with the silver ions produced with the Ag target. This explains the lack of an increased inhibitory effect of Pt during the inactivation of airborne bacteria when present in the Pt/Ag target with respect to the Ag target, because in both cases similar silver ionic species were found.

Study of pH effects on the evolution of properties of brown-water natural organic matter as revealed by size-exclusion chromatography during photocatalytic degradation

This study shows the effect of pH on the photocatalytic degradation of natural organic matter (NOM). The experiments were carried out in batch reactor (a solar UV-light simulator) with Degussa P-25 titanium dioxide (TiO2). The NOM degradation was followed by size-exclusion chromatography for dissolved organic carbon (DOC), ultraviolet absorption and fluorescence-detection (SEC-DOC, SEC-UV254 and SEC-Fl254/450). Changes in pH values affected the adsorption of NOM onto TiO2, but did not affect the photodegradation sequence of NOM. For high or low pH values, the degradation of the NOM preferentially removed the larger molecular size fraction in comparison to the middle and small molecular size fractions, resulting in the relative increase of these smaller fractions. This sequence of NOM degradation leads to the evolution of the formation potential for disinfection by-products (DBPs). Specifically, the trihalomethanes and halogenated organic compounds formation potential (THMF and AOXFP) decreased steadily.

Innovative UVC Light (185 nm) and Radio-Frequency-Plasma Pretreatment of Nylon Surfaces at Atmospheric Pressure and Their Implications in Photocatalytic Processes

Innovative pretreatment by UVC light (185 nm) and by radio-frequency (RF) plasma at atmospheric pressure to functionalize the Nylon surface, increasing its bondability toward TiO(2), is reported in this study. In the case of UVC light pretreatment in air, the molar absorption coefficient of O(2)/N(2) at 185 nm is very low and the air in the chamber absorbs very little light from the UVC source before reaching the Nylon sample. Nylon fabrics under RF plasma were also functionalized at atmospheric pressure because of the marked heating effect introduced in the Nylon by the RF plasma. This effect leads to intermolecular bond breaking and oxygenated surface groups in the topmost Nylon layers. Both pretreatments enhanced significantly the photocatalytic discoloration of the red-wine stain in Nylon-TiO(2) compared with samples without pretreatment. The UVC and RF methods in the absence of vacuum imply a considerable cost reduction to functionalize textile surfaces, suggesting a potential industrial application. Red-wine-stain discoloration under simulated sunlight was monitored quantitatively by diffuse-reflectance spectroscopy and by CO(2) evolution. X-ray photoelectron spectroscopy (XPS) was used to monitor the changes of the C, N, and S species on the Nylon topmost layers during the discoloration process. Significant changes in the XPS spectra of Ti 2p peaks were observed during discoloration of the wine spots. Wine stains attenuated the signal of the Ti 2p (458.4 eV) peak in the Nylon-TiO(2)-stained wine sample at time zero (from now on, the time before the discoloration process). Furthermore, a decrease of the wine-related O 1s signal at 529.7 eV and N 1s signal at 399.5 eV was observed during the discoloration process, indicating an efficient catalytic decomposition of the wine pigment on Nylon-TiO(2). X-ray diffraction detected the formation of anatase on the Nylon fibers. High-resolution transmission electron microscopy shows the formation of anatase particles with sizes between 8 and 20 nm.

Evaluations of the TiO2/simulated solar UV degradations of XAD fractions of natural organic matter from a bog lake using size-exclusion chromatography.

This work reports on the changes in compositions of humic acids (HAs) and fulvic acids (FAs) during photocatalytic degradation. The HAs and FAs were obtained from the XAD-resin fractionation of natural-organic matter (NOM) from a bog lake (Lake Hohloh, Black Forest, Germany). Degussa P-25 titanium dioxide (TiO2) in a suspension and a solar UV simulator (batch reactor) were used in the experiments. The photocatalytic degradation of the HAs and FAs were monitored using size-exclusion chromatography (SEC) equipped with dissolved organic carbon (DOC) and ultraviolet (UV254) detection (SEC-DOC and SEC-UV254) and UV-Vis spectrophotometry. The evolutions of the photocatalytic degradations of the HA and FA fractions were selective. The photocatalytic degradation started with the degradations of high molecular weight compounds with relatively high UV254 absorbances in the HA and FA fractions to yield low molecular weight compounds showing less specific UV254 absorbances. Observance of the same tendency for the original NOM from Lake Hohloh indicates that these XAD-fractions still having complex compound mixtures. However, the larger molecular weight fractions of the FAs showed higher preferential adsorptions onto TiO2, which caused their faster degradation rates. Furthermore, FAs showed a greater reduction of the total THM formation potential (TTHMFP) and the organic halogen compounds adsorbable on activated carbon formation potential (AOXFP), in comparison with the HAs.

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.

Soporte de Nuevas Películas de TiO2 y TiO2/SiO2 sobre Gránulos de Poliéster para Aplicación en Fotocatálisis

Peliculas de TiO2 o TiO2/SiO2 fueron soportadas sobre granulos de poliester usando mecanismos de difusion y posterior tratamiento termico a 100oC. Se emplearon dos clases de geles. El primero fue preparado usando diferentes cantidades de TiO2, cloruro de metileno y silicona liquida. El segundo fue obtenido por medio del metodo sol-gel, empleado para producir una matriz de silice a partir de la hidrolisis el tetraetilo ortosilicato, en un medio organico de 2-propanol, en el cual se disperso el fotocatalizador. Los precursores de cada sistema fueron agregados en diferentes relaciones para determinar su influencia en la estabilidad, propiedades y fotoactividad de las peliculas. La actividad fotocatalitica fue evaluada en la fotodegradacion de metanol en fase gaseosa. Los resultados muestran la produccion de materiales con alta resistencia, funcionalidad y actividad asi como una fuerte relacion entre la actividad fotocatalitica con las propiedades fisicoquimicas.

Oxidación Electroquímica y Ozonización Aplicadas al Tratamiento de Aguas de Lavado de la Producción de Biodiesel

Non-photochemical advanced oxidation technologies, ozonation and electrochemical oxidation, as alternative technologies to treat wastewaters from biodiesel production were applied. The physicochemical characterization of the wastewaters showed high levels in biochemical and chemical oxygen demand, total organic carbon and residual methanol. Both technologies increased the wastewater biodegradability and showed similar efficiencies in the reduction of the organic loads, with chemical oxygen demand removal between 5 and 9 % and total organic carbon removal between 9 and 11 %. However the ozonation showed to be a more versatile technology to be implemented on a larger scale as a system for treatment alone or coupled to biological processes that are typically used in treating waters with high organic load.

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

Fotocatálisis Heterogénea y Foto-Fenton Aplicadas al Tratamiento de Aguas de Lavado de la Producción de Biodiesel

Advanced oxidation technologies, heterogeneous photocatalysis and photo-Fenton, were applied to verify its feasibility in the treatment of wastewater from the washing process of biodiesel production. These waters showed high levels of chemical oxygen demand, total organic carbon and methanol, suggesting the need to implement subsequent treatment processes. The results show that heterogeneous photocatalysis is not an appropriate technology due to high organic loads, while the photo-Fenton has high values of removal. It is concluded that this is a viable technology that could be implemented at industrial scale.