Degradation of organochlorinated pollutants in water by catalytic hydrodechlorination and photocatalysis (original) (raw)
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Research on Chemical Intermediates, 2000
Homogeneous aqueous solutions of organochlorine pesticides and chlorophenols, namely, lindane, hexachlorobenzene and 2,4-dichlorophenol (2,4DCP), undergo effective photodegradation upon photolysis with UV and near visible light in the presence of a characteristic polyoxometallate catalyst PW12O403−. These substrates remained, practically, intact (lindane, HCB) or underwent minor degradation under similar conditions in absence of catalyst. The main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometallate with H2O. The system compares with the widely published TiO2. Chlorohydroquinone (ClHQ), hydroquinone (HQ), chlorobenzoquinone (ClBQ), benzoquinone (BQ), 3,5-dichlorocatechol (3,5DCC) and 4-chlorocatechol (4CC), among others, were identified as the main aromatic intermediates in the photodegradation of 2,4DCP. Acetic acid was detected as ring cleavage product. In all cases the final photodegradation leads to complete mineralization of substrates to CO2 and HCl.
photocatalytic degradation of chlorophenol in water
This work aims to study the photocatalytic degradation of chlorophenols. They belong to a notable group of pollutants because of their high toxicity, and hardly biodegradable, and are difficult to remove from the environment. Photocatalytic degradation of chlorophenols using UV light was investigated over mesoporous catalysts. Ti-MCM-41(20), Ti-MCM-41(10), TiO2/MCM-41, Fe-Ti-MCM-41, TiO2/Fe-MCM-41 and TiO2/SBA-15 catalysts were prepared from the corresponding metal salts by the sol-gel technique. The catalyst were investigated using X-ray diffraction (XRD), FT-IR spectroscopes, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface areas of the samples were determined using the nitrogen adsorption and desorption isotherms. 100 ppm was used as model pollutants. High purity 2,4,6-trichlorophenol and 4-chlorophenol solutions individually and 0.1 g/L of each catalyst was tested at different irradiation times. At each interval time 10 ml of irradiated solution was taken and analyzed by High Performance Liquid Chromatography (HPLC), Ion Chromatography (IC). Aromatic intermediates, organic acid and chloride ions were detected. The reaction mechanism has been proposed.
Indonesian Journal of Chemistry
To shorten the biological treating time and to examine the effect of electrolytes in a model water on the photocatalytic treatment, the combined biological-photocatalytic treatment was evaluated for removal of a mixture (total: 100 mg L-1, each: 25 mg L-1) of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,5-trichlorophenol (2,4,5-TCP), and pentachlorophenol (PCP) in tap water. The mineralization of the four phenols was performed by a flow (biological treatment)-circulative flow (photocatalytic treatment) operation under black light and sunlight irradiations. After a large portion of biodegradable 2-CP and 2,4-DCP, and around half amount of slightly biodegradable 2,4,5-TCP were removed by the biological treatment, the remained three chlorophenols, biorecalcitrant PCP, and biodegradation products were completely removed by the subsequent photocatalytic treatment. The combined treatment significantly shortened the degradation time only the biotreatment. High circulative flow...
Photocatalytic Oxidation in Drinking Water Treatment Using Hypochlorite and Titanium Dioxide
2013
The main focus of this thesis is to study the advanced oxidation processes (AOPs) of water pollutants via UV/hypochlorite (homogeneous AOPs), and UV solar light/TiO2 (heterogeneous AOPs) in which the highly oxidative hydroxyl radicals (OH) are produced. These radicals are capable of destructing the emerging organic pollutants in water. The combined action of both OH and Cl that are produced during the NaOCl/UV processes increased the chlorination potential of humic acids (HA). In addition, at a high free-radical dose, such as in swimming pool water recirculation systems, the equal levels of adsorbable organic halogens (AOX) and CHCl3 are formed with both low pressure (LP) and medium pressure (MP), respectively. CHCl3, once formed, is not degraded with either LP or MP. Moreover, the photo-degradation of HA in LPUV/NaOCl process is higher than that for the MPUV/NaOCl process, which results in a higher initial rate of AOX and CHCl3 formation. This raised the attention to the risk of...
Photocatalytic degradation of 3,4-dichlorophenol using TiO2 in a shallow pond slurry reactor
Indian Journal of Chemical Technology, 2005
In the present study, the TiO2 mediated photocatalytic degradation of 3,4-dichlorophenol, as a model compound, has been investigated using a low cost non-concentrating shallow pond slurry reactor at laboratory scale under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV-spectroscopic analysis, decrease in COD values and increase in chloride formation as a function of irradiation time. The effect of pH, catalyst loading, substrate concentration, UV intensity, aperture to volume ratio of the reactor and presence of electron acceptors such as hydrogen peroxide besides molecular oxygen, on degradation, was studied. The degradation rates were strongly influenced by some of these parameters. The optimum parameters for maximum degradation were determined. The degradation of 3,4-dichlorophenol can be emulated in sunlight using a similar large-scale shallow pond reactor for the solar detoxification in open atmosphere.