RESUMO
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.
Assuntos
Benzopiranos/química , Fracionamento Químico/métodos , Cromatografia em Gel/métodos , Substâncias Húmicas , Lagos , Fotoquímica/métodos , Adsorção , Desinfecção , Alemanha , Halogenação , Peso Molecular , Fotólise , Espectrofotometria Ultravioleta , Luz Solar , Titânio , Raios Ultravioleta , Áreas AlagadasRESUMO
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.
Assuntos
Monitoramento Ambiental , Substâncias Húmicas , Titânio/química , Raios Ultravioleta , Catálise , Monitoramento Ambiental/instrumentação , Monitoramento Ambiental/métodos , Recuperação e Remediação Ambiental , Substâncias Húmicas/análise , Substâncias Húmicas/efeitos da radiação , Processos Fotoquímicos , Espectrometria de Fluorescência , Espectrofotometria UltravioletaRESUMO
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.
Assuntos
Titânio/química , Carbono/análise , Catálise , Cromatografia em Gel , Cristalização , Cinética , Fotoquímica , Espectrometria de Fluorescência , Espectrofotometria Ultravioleta , Luz Solar , Raios UltravioletaRESUMO
Se optimizó la técnica de microextracción en fase sólida acoplada a cromatografía gaseosa con detector de ionización de flama (HS-SPME/GC-FID por su nombre en inglés) para análisis de metanol en agua utilizando diferentes microfibras, una fibra de poliacrilato y una fibra de polidimetilsiloxano y una columna RTX-5. Las variables evaluadas fueron tiempo de absorción del contaminante en la fibra, volumen libre en el vial, tiempo y temperatura de desorción y efecto de la agitación y presencia de sal en el sistema. De acuerdo con los resultados, el tiempo óptimo de absorción es 15 minutos, el volumen de muestra es 5 mL. Se encontró que existe una íntima relación entre la temperatura de desorción y el área del pico cromatográfico, y una correlación R² = 0,99965 para la curva de calibración elaborada en un rango entre 0 y 50%, considerando el origen, con un límite de detección de 0,01% y un límite de cuantificación del 0,04%.
The technique head space-solid phase micro extraction with gaseous chromatography by using flame ionization detector (HS-SPME/GC-FID) for analysis of methanol in water was optimized using different microfibers, a polyacrylate fiber and a polydimethylsiloxane fiber and a RTX-5 column. The evaluated variables were time of absorption of the pollutant on the fiber, free volume in the vial (free space), time and temperature of desorption as well as effect of agitation and presence of salt in the system. According to the results, the optimal absorption time is 15 minutes, the optimal volume of sample is 5 mL. A close relationship between the temperature of desorption and the chromatographic peak area was found, and a correlation R² = 0.99965 was obtained for the calibration curve in a range between 0 and 50%, considering the origin, with a detection limit of 0.01% and a quantification limit of 0.04%.
A técnica microextração em fase sólida acoplada a cromatografia gasosa com detector de ionização de chama (HS-SPME/GC-FID por seu nome em Inglês) foi otimizada para análise de metanol em água através de diferente micro fibra, uma fibra de poliacrilato e uma fibra de polidimetilsiloxano e uma coluna de RTX-5. As variáveis avaliadas foram tempo para absorver o poluente no volume de fibra livre no frasco, tempo e temperatura de dessorção e efeito da agitação e da presença de sal no sistema. De acordo com os resultados, o tempo de absorção ideal é 15 minutos, o volume da amostra é 5 mL. Descobrimos uma íntima relação entre a temperatura de dessorção e área do pico cromatográfico, e uma correlação R2 = 0,99965 para a curva de calibração desenvolvida em uma escala entre 0 e 50%, considerando a origem, com um limite de detecção de 0,01% e um limite de quantificação de 0,04%.