SPECTROSCOPIC STUDIES ON UVC-INDUCED PHOTODEGRADATION OF HUMIC ACIDS
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ABSTRACT The effect of UV radiation on absorption, fluorescence spectra and dynamics of phototransformation of five different humic acids (HA) of natural and synthetic origin were investigated. Two types of synthetic HA were prepared: one containing only C, H and O atoms, and another with content of C, H, O and N atoms. Natural HA were also diversified with respect to their origin. We used UV-C radiation (predominantly the wavelength of 254 nm) to provide a wide spectrum of photochemical mechanisms. Fluorescence spectroscopy measurements revealed similar chromophoric centers in different types of HA: at short wavelength (Imax,em at λ = 450 nm for excitation λex from 260 - 350 nm) and at longer wavelength ( Imax,em at λ = 510 nm for excitation λex from 440 - 460 nm). The maximum emission Imax,em was always higher for excitation at λex 260-350 nm than for λex 440-460 nm. Dynamics of fluorescence intensity accompanying UV-C-induced degradation appeared to be different for both chromophori
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ABSTRACT The effect of UV radiation on absorption, fluorescence spectra and dynamics of phototransformation of five different humic acids (HA) of natural and synthetic origin were investigated. Two types of synthetic HA were prepared: one containing only C, H and O atoms, and another with content of C, H, O and N atoms. Natural HA were also diversified with respect to their origin. We used UV-C radiation (predominantly the wavelength of 254 nm) to provide a wide spectrum of photochemical mechanisms. Fluorescence spectroscopy measurements revealed similar chromophoric centers in different types of HA: at short wavelength (Imax,em at λ = 450 nm for excitation λex from 260 - 350 nm) and at longer wavelength ( Imax,em at λ = 510 nm for excitation λex from 440 - 460 nm). The maximum emission Imax,em was always higher for excitation at λex 260-350 nm than for λex 440-460 nm. Dynamics of fluorescence intensity accompanying UV-C-induced degradation appeared to be different for both chromophori
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