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Miray Bekbolet - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of humic acid photocatalytic degradation by uv vis and fluorescence spectroscopy
    Catalysis Today, 2005
    Co-Authors: Ceyda Senem Uyguner, Miray Bekbolet
    Abstract:

    Abstract Photodegradation of humic substances causes drastic changes in the UV–vis absorption and fluorescence properties of humic acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of humic acids during photocatalytic oxidation process es and elucidate the effects observed on the Molecular Size Distribution of humic acid focusing on their analysis by UV–vis and fluorescence spectroscopy. As confirmed by the spectroscopic evaluation of the Molecular Size Distribution data, photocatalytic degradation of humic acid leads to the formation of lower Molecular Size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV 254 absorbing moieties in treated humic acid samples become higher than that of raw humic acid designating the generation of new species during photocatalysis. UV–vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated humic acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time.

  • Effects of oxidative treatment techniques on Molecular Size Distribution of humic acids.
    Water Science and Technology, 2004
    Co-Authors: Aslihan Kerc, Miray Bekbolet, A. M. Saatçi
    Abstract:

    In this study ultrafiltration has been used for the fractionation of humic acid samples. Humic acids were treated in a sequential oxidation system in which ozonation was followed by photocatalytic oxidation using TiO 2 . Evaluation of the spectroscopic characteristics of the oxidized and fractionated humic acid samples have shown that Molecular Size Distribution ranges shift to lower Molecular Sizes depending on the oxidation stages. Applied ozone dosage and irradiation time during the photocatalysis stage are the factors affecting the Molecular Size Distribution in the treated humic acid samples. Formation of lower Molecular weight compounds during the ozonation stage resulted in increased degradation rates during the photocatalysis stage.

S Senkavurmaci - One of the best experts on this subject based on the ideXlab platform.

  • the effect of photocatalytic oxidation on Molecular Size Distribution profiles of humic acid
    Photochemical and Photobiological Sciences, 2015
    Co-Authors: M Bekbolet, S Senkavurmaci
    Abstract:

    The influence of photocatalytic degradation on Molecular Size fractionation (0.45 μm filtered, 100 kDa, 30 kDa and 3 kDa) of humic acid as a model compound of natural organic matter was investigated. The results were evaluated using UV-vis parameters, dissolved organic carbon (DOC) and excitation emission matrix (EEM) fluorescence spectral features. EEM fluorescence signatures displayed an irradiation period dependent transformation of humic-like fluorophores to fulvic-like fluorophores in accordance with the photocatalytic mineralization of HA. Molecular Size Distribution profiles expressed the formation of lower Molecular Size (<3 kDa) fractions through oxidative degradation of humic acid of higher Molecular Size fractions (100 kDa and 30 kDa fractions). The fluorescence-derived index (fluorescence intensity (FI), represented by the ratio of the emission intensity at λemis = 450 nm to that at λemis = 500 nm, following the excitation at λexc = 370 nm) was also investigated. The use of EEM features has proven to be a useful tool for monitoring the effect of photocatalytic degradation on the structure and Molecular Size Distribution profile of HA.

Kalevi Pihlaja - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Size Distribution and spectroscopic properties of aquatic humic substances
    Analytica Chimica Acta, 1997
    Co-Authors: Juhani Peuravuori, Kalevi Pihlaja
    Abstract:

    The number- and weight-averaged Molecular weights of different isolated humic fractions and unfractionated organic matter from natural water samples were measured using high-performance Size-exclusion chromatography (HPSEC). The chromatograms obtained, with sodium acetate as the mobile phase on a TSK G3000SW high-speed column, provided illustrative information about the nature of the dissolved organic matter that was not available with phosphate buffer eluents. The calibration of the column system merely with protein standards generated misleading information about the Molecular weight and Size Distribution of humic solutes. Instead, the present results support the utilization of polystyrene-sulphonates (PSS) either alone or together with certain other model compounds for the calibration of HPSEC in studying Molecular weights of humic solutes. The data obtained with the HPSEC system indicate that the average Molecular weight of humic solutes is distinctly lower than is generally assumed. Besides, aquatic humic solutes also contain some very large-Sized though minor constituents, leading to a fairly polydisperse mixture. Number-averaged Molecular weights obtained using the HPSEC system were 4–5-fold greater than those from vapour-pressure osmometry. Bulk spectroscopic properties such as molar absorptivity at 280 nm and the quotient, E2E3, correlated strongly with the total aromaticity and averaged Molecular weights of all the humic solutes. This observation suggests that bulk spectroscopic properties can be applied, as a first approximation, for estimating the Size of humic solutes and their aromaticity in natural surface waters.

M Bekbolet - One of the best experts on this subject based on the ideXlab platform.

  • the effect of photocatalytic oxidation on Molecular Size Distribution profiles of humic acid
    Photochemical and Photobiological Sciences, 2015
    Co-Authors: M Bekbolet, S Senkavurmaci
    Abstract:

    The influence of photocatalytic degradation on Molecular Size fractionation (0.45 μm filtered, 100 kDa, 30 kDa and 3 kDa) of humic acid as a model compound of natural organic matter was investigated. The results were evaluated using UV-vis parameters, dissolved organic carbon (DOC) and excitation emission matrix (EEM) fluorescence spectral features. EEM fluorescence signatures displayed an irradiation period dependent transformation of humic-like fluorophores to fulvic-like fluorophores in accordance with the photocatalytic mineralization of HA. Molecular Size Distribution profiles expressed the formation of lower Molecular Size (<3 kDa) fractions through oxidative degradation of humic acid of higher Molecular Size fractions (100 kDa and 30 kDa fractions). The fluorescence-derived index (fluorescence intensity (FI), represented by the ratio of the emission intensity at λemis = 450 nm to that at λemis = 500 nm, following the excitation at λexc = 370 nm) was also investigated. The use of EEM features has proven to be a useful tool for monitoring the effect of photocatalytic degradation on the structure and Molecular Size Distribution profile of HA.

  • The effect of photocatalytic oxidation on Molecular Size Distribution profiles of humic acid.
    Photochemical & Photobiological Sciences, 2015
    Co-Authors: M Bekbolet, S. Sen-kavurmaci
    Abstract:

    The influence of photocatalytic degradation on Molecular Size fractionation (0.45 μm filtered, 100 kDa, 30 kDa and 3 kDa) of humic acid as a model compound of natural organic matter was investigated. The results were evaluated using UV-vis parameters, dissolved organic carbon (DOC) and excitation emission matrix (EEM) fluorescence spectral features. EEM fluorescence signatures displayed an irradiation period dependent transformation of humic-like fluorophores to fulvic-like fluorophores in accordance with the photocatalytic mineralization of HA. Molecular Size Distribution profiles expressed the formation of lower Molecular Size (

R L Mcreynolds - One of the best experts on this subject based on the ideXlab platform.

  • INTERRELATIONSHIP BETWEEN PERFORMANCE-RELATED PROPERTIES OF ASPHALT CEMENT AND THEIR CORRELATION WITH Molecular Size Distribution
    Transportation Research Record, 1991
    Co-Authors: Safwat W Bishara, R L Mcreynolds, E R Lewis
    Abstract:

    Rheological parameters, Corbett analysis, colloidal instability, and Molecular Size Distribution (MSD) were applied to investigate relationships between several physicochemical parameters. Emphasis is on the correlation between MSD and viscosity at 60 deg C, viscosity at 135 deg C, viscosity ratio at 60 deg C (after and before thin film oven test), penetration at 25 deg C, viscosity-temperature susceptibility (VTS), penetration-viscosity number (PVN) at 60 deg C and 135 deg C, colloidal instability (I sub c), and asphaltene content. The MSD was obtained using a semipreparative column and a gravimetric finish. The 20 virgin asphalts studied cover a wide viscosity range and were supplied over 7 years by 14 refineries. Virgin asphalts were laboratory-aged; field cores for seven were extracted. For virgin asphalts, viscosity at 60 deg C correlates strongly with each of viscosity at 135 deg C and penetration at 25 deg C. The MSD showed a strong correlation with viscosity at 135 deg C, PVN at 135 deg C, VTS, I sub c, and asphaltene content, and a weak correlation with viscosity ratio. The direction (sign) of association demonstrates that a high PVN and a low VTS (i.e., low temperature susceptibility), a low viscosity ratio (i.e., high resistance to aging), a low I sub c, and a low asphaltene content are all favored by high large Molecular Size (LMS), low medium Molecular Size (MMS), and low small Molecular Size percentages. Asphalts with high LMS/MMS ratios demonstrated common parameters.

  • use of hpgpc with uv detection for determination of Molecular Size Distribution of apshalt cement after quantitative corrections for molar absorptivity variation and saturated oils
    Transportation Research Record, 1990
    Co-Authors: Safwat W Bishara, R L Mcreynolds
    Abstract:

    A method is described for calculating Molecular Size Distribution (MSD) of asphalt cement using ultraviolet (UV) detection. A 5-microm, 500 Angstrom phenogel column is used to fractionate a known amount of a whole asphalt sample. Tetrahydrofuran:pyridine (95:5) serves as mobile phase. After passing through the UV detector at 345 nm, the eluent is fractionated at arbitrarily selected intervals. The fractions are collected in weighed petri dishes and left to dry. A computer generates a slice report showing percent material eluting at successive retention times. The injection is repeated and eluting fractions collected in volumetric flasks. After removing the column, a known volume of a given fraction is injected and the maximum absorbance reading for each fraction is recorded. The second set of fractions is then poured into the petri dishes containing the fractions from the first injection. Then, the molar absorptivity "a" is calculated. Using ASTM Method D4124-86(B), the percent saturates is determined. The saturates are injected, a differential refractive index detector is used to get an MSD value, and a computer generates a slice report. The data generated for the whole asphalt sample are treated mathematically, first, to account for variation of "a" and, second, for undetectability of saturates by UV. For six samples, comparison of data readily available from the slice report with those obtained after treatment reveals differences of up to 65% for some fractions. Reproducibility of the system and of the proposed method proved satisfactory. Excluding the separation of saturates, the proposed method consumes 7 to 8 hr; in series less than 4 hr.