Spectroscopy and photochemistry of humic acids are discussed. The samples of HAs fractions were obtained from Fluka Chemical Co and prepared from peat of Western Siberia region. The comparative analysis of these acids with the sample of humic acids allocated from brown coal is carried out. A specific feature of the reactor is the use of barrier discharge excilamp (KrCl) with radiation wavelength λ = 222 nm. Influence of the received humic acids on process of photodegradation of herbicide - 2.4-dichlorophenoxyacetic acid is considered.
The interaction of humic acids (HA) isolated from oxidized and brown coals with copper, nickel, and cadmium ions is investigated. The complexation constant of HA with heavy metal ions is determined using the fluorescence quenching method. It is shown that preliminary mechanic activation of humic-containing substances increases the binding coefficients of HA with copper and nickel ions in 1.5 to 3.5 times, as compared to cadmium ions, for which the values of the fluorescence quenching constant К<sub>SV</sub> decrease. This is due not only to structural changes in HA after the mechanic activation, but also to the nature of metal ions.
The influence of Н<sub>2</sub>О<sub>2</sub> on the degradation of 8-methoxypsoralen (8-MOP) in water-ethanol solutions under the action of KrCl and XeBr excilamp radiation in a photoreactor is investigated. A kinematic model of photodegradation of the investigated molecule is constructed. In water-ethanol solutions the addition of Н<sub>2</sub>О<sub>2</sub> altered the mechanism of decay of 8-MOP under the action of a KrCl excilamp in comparison with irradiation by a XeBr excilamp. This behavior is explained by the fact that the action of 283 nm radiation leads to accumulation of a stable photoproduct. In order to establish the toxicity of this product further research is needed.
Dissolved organic matter plays an important role in pollution migration from human waste to aquatic environments. In this study, the effect of humic acid (HA) on the photo-chemical transformation of naphthalene by irradiation model solar and UV light was reported using fluorescence quenching titrations. It was calculated the interactions between naphthalene and humic acids. It is found that the molecular complex of humic acid and naphthalene is more stable to UV irradiation, compared with the model solar radiation. The application of molecular fluorescence spectrometry is a useful sensitive tool evaluate intermolecular HA and naphthalene interactions.
The paper describes an analysis of possible ways of deactivation of electronically excited states of 4-hydroxy- 3-methoxy-benzoic acid (vanillic acid) and its protolytic forms with the use of quantum-chemical methods INDO/S (intermediate neglect of differential overlap with a spectroscopic parameterization) and MEP (molecular electrostatic potential). The ratio of radiative and non-radiative deactivation channels of the electronic excitation energy is established. The rate constants of photophysical processes (internal and intercombination conversions) occurring after the absorption of light in these forms are evaluated.
Currently, the study of the photochemistry of natural phenols is relevant as it has a fundamental and a practical importance. The optical properties of natural phenols are studied: 3-methoxy-4-hydroxybenzaldehyde (vanillin) and 3- hydroxy-4-methoxybenzaldehyde (isovanillin), 4-hydroxy-3-methoxybenzoic acid (vanillic acid). The processes of proton transfer in the investigated molecules in ground and excited states under exposure to lamp and laser emissions are presented using the methods of electron spectroscopy and quantum chemistry.
Upon exposure to radiation in the presence of humic substances, phenol can be transformed by the mechanisms of direct and indirect photolysis. The addition of the humic fraction containing humic and fulvic acids to the aqueous phenol solution causes the efficiency of phenol degradation to decrease. The most efficient phenol degradation in the aqueous solution upon exposure to radiation at 222 nm is observed in the presence of fulvic acid.
It is well known that pH value and excitation energy have a directly impact on photolysis rate of phenols under Hg-lamp irradiation and oxidation process. The purpose of the current study is the research of o-cresol and para-cresol photolysis in acidic medium under various spontaneous radiation sources irradiation. Photochemical degradation was carried out through a high pressure mercury lamp OΚH-11M, and also with a new capacitive discharge excilamps on working molecules KrCl* (λ~222 nm) and XeBr* (λ~283 nm). Exposure time was varied from 1 to 40 minutes that corresponds radiation doses from 0.5 to 20 J/cm<sup>2</sup>. A comparison between phototransformations under different light excitation shows that cresol aqueous solutions acidation leads to increase of phototransformations efficiency. It was been found that both in neutral, and in acidic medium the photodecomposition of cresols is carried out more effectively under KrCl-excilamp irradiation.
A study of the phenol, 4-chlorophenol and 4-bromophenol aqueous solutions, photolysis under UV-irradiation from capacitive discharge KrCl- and XeBr-excilamps at different wavelengths have been undertaken. To specify photolysis efficiency the irradiated solutions have been investigated by spectroscopic methods. To account for obtained results, the quantum-mechanical computation has been invoked.
Phenol and 4-chlorophenol water solutions photolysis under UV-excitation from KrCl-laser and capacitive discharge KrCl- excilamp are presented. The irradiated solutions have been investigated by spectroscopic methods. The comparison of the KrCl-excilamp and KrCl-laser irradiation effects has been realized for the first time.
Phenols are the most widespread pollutants of the environment in the world. Investigations of phenol photolysis are of great importance as concerning the phenol removal from water. The experiments have been performed to study phenol phototransformations in aqueous solution at various pH of the samples under UV irradiation. The fluorescence and absorption spectra were recorded. The spectra analysis shows that phenol molecule changes its ionic form under the irradiation. The phenol dimers and other products of photolysis are produced. Strong dependence of phenol photoprocesses on pH was also noticed.