For study of photodegradation, an excilamp on working molecules KrCl with λrad = 222 nm, developed at the Institute of High Current Electronics of the SB RAS, was used as source of UV radiation. The results of direct photolysis of phenoxyacetic acids herbicides in aqueous solutions are discussed. The phototransformation occurs more slowly when the herbicides concentration increases. The use of the flow-through reactor is more effective than operation in the stationary conditions. The prospect of using a wide range of excilamps with different characteristics for solving environmental problems is highlighted.
The effect of UV radiation on the efficiency phototransformation BPA in water in the presence of polypropylene superfine microfibers. The absorption and fluorescence spectra of the investigated substance with three types of PPM of various properties were obtained. After excitation with an excilamp, the main photoproduct BPA fluoresces in the region of 405 ÷410 nm. With an increase in the irradiation time from 0 to 10 minutes, an increase in the fluorescence intensity of this BPA photoproduct was recorded. This indicates that in the course of irradiation, effective photodegradation of the initial toxicant occurs and a photoproduct is formed. In the course of irradiation, the degradation of the resulting photoproducts occurs, which is associated with their adsorption on the surface of the PPM.
The study of short-lived induced (singlet-singlet) and long-lived induced (in particular, triplet-triplet) absorption capacity of crystal violet (CV) in various solvents was carried out by the pump-probe method. Water, dimethyl sulfoxide, isopropyl alcohol, and ethyl alcohol were selected as solvents. The formation of triplet states in various CV solvents was revealed upon excitation by nanosecond radiation of the 4th harmonic of a Nd: YAG laser (wavelength 266 nm, average power – 25.5 mV, repetition frequency – 3 Hz, pulse duration – 10 ns, peak power – 10-12 MW/cm2). It is shown that the spectrum of the induced CV absorption in ethanol contains two closely spaced bands at 400 and 485 nm. Short-lived and long-lived induced CV absorption in isopropanol at room temperature (λmax=400 nm) was recorded. Keywords: crystal violet (CV), induced absorption spectra, spectroscopy, pump-probe method.
In the modern world, it is worth seriously thinking about the quality of food consumed. Eating livestock products, we often do not think about such things as the presence of antibiotics in them. However, this can have serious consequences for the body. That is why the sanitary services of all countries pay such attention to the definition of antibiotics. Somewhere very strict standards are set on them. This article is an overview of such antibiotics as sulfaguanidine, benzylpenicillin and chloramphenicol, we also discussed the methods for the determination of antibiotics, methods of fluorescence analysis and quantum chemistry, which we will use in future studies.
The influence of irradiation wavelength on the degradation of Bisphenol A (BPA) in water under the action of KrCl and XeBr excilamp radiation in a photoreactor is investigated. Fluorescent photoproducts of photodegradation of the investigated molecule is constructed. In the work fluorescent photoproducts are defined. In an excited state BPA exists in a dimeric form at a concentration above 0.1 mM. After excitation by an excilamp the main BPA photoproduct fluoresces in the region of 420 nm. This behavior is explained by the fact that the action of 222 nm radiation leads to accumulation of a stable photoproduct. This product is destroyed as well as BPA after 120 minutes of exposure. Under the action of XeBr excilamp radiation a very stable product is formed with fluorescence at 380 nm. In order to establish the mechanism of BPA photolysis the product using chromatomass spectrometryfurther research is needed.
Depending on their origin and structure, humic acids (HAs) have a remarkable ability to absorb light and transfer this energy to other substrates and in some cases strongly affect photolysis of xenobiotics. This search exhibits several examples of spectral and fluorescent study of humics acids with different genesis. The group of studied HAs was isolated from an unditourified high-moor peat with different humidity in the Mezensky District of the Arkhangelsk Region. The standard commercial preparation of humic acids Aldrich was also studied. For photochemical studies, an excilamp on working molecules KrCl with λrad = 222 nm, developed at the Institute of High Current Electronics of the SB RAS, was used as sources of UV radiation. The results of direct and sensitized (in the presence of HAs) photolysis are discussed. For samples of HAs from the Arkhangelsk region, the dependence of the absorption spectra and fluorescence on the duration of drying and the depth of occurrence was found. The longer is the duration of drying of the samples, the lower is the optical density of the absorption spectra. In the process of humification and with the duration of peat drying, the fluorescence intensity of the HAs increases. The dependence of the fluorescence spectra of the studied samples on the wavelength of fluorescence excitation was found.
Results of theoretical research for two psoralen molecules: 8-methoxypsoralen and khellin are presented. Schemes of photophysical processes in psoralens based on quantum chemical calculation by the INDO method are analyzed. The rate constants of intersystem and internal conversions are calculated. We obtained rather high intersystem conversion constant that influences on the fluorescent yield of 8-methoxypsoralen (107 s-1) and an insignificant constant of intersystem conversion for khellin (103 s-1).
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 КSV decrease. This is due not only to structural changes in HA after the mechanic activation, but also to the nature of metal ions.
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 influence of Н2О2 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 Н2О2 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.
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.
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.
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/cm2. 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.
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