Homogeneous photo-oxidation of phenols: influence of metals

Photochemical treatment of 2-chlorophenol aqueous solutions using ultraviolet radiation, hydrogen peroxide and photo-Fenton reaction

In the present work, the photochemical oxidation of 2-chlorophenol aqueous solutions in a batch recycle photochemical reactor using ultraviolet irradiation and hydrogen peroxide was studied. Specifically, the effect of hydrogen peroxide initial concentration (0-10316 mg L(-1)) and 2-chlorophenol initial concentration (150-3000 mg L(-1)) was examined. The process was attended via total organic carbon (TOC), 2-chlorophenol, chloride ion, acetic acid, formic acid and pH measurements. The conversion of 2-chlorophenol observed was always much higher than the corresponding total organic carbon removal, whereas the increase in hydrogen peroxide amount in the solution led to higher values of 2-chlorophenol conversion and total organic carbon removal. Finally, the photo-Fenton reaction was applied to the oxidation of 2-chlorophenol, leading to a higher degree of mineralization of the parent compound.

Photochemical degradation of 1,3-dichloro-2-propanol aqueous solutions

The photochemical oxidation of 1,3-dichloro-2-propanol (1,3-DCP) was studied by following the target compound degradation, the total carbon removal rate by a total organic carbon (TOC) analyzer and by identifying the oxidation products by gas chromatography-mass spectrometry (GC-MS). The reaction was performed in a batch recycle reactor, at room temperature, using UV radiation provided by a low pressure 12W Hg lamp and H(2)O(2) as oxidant. Chloride ions, formic, acetic and chloroacetic acid were measured by ion chromatography. Apart from the chloride ions and the organic acids, the presence of 1,3-dichloro-2-propanone and chloroacetyl chloride was also detected and a possible pathway is proposed for the degradation of the parent compound. Complete degradation of 1,3-dichloro-2-propanol was achieved and the TOC removal reached as much as 80% at the end of the reaction time. The effect of the initial concentration of hydrogen peroxide was investigated and it was established that higher concentrations of H(2)O(2) slow down the reaction rate. Finally, the effect of the initial concentration of 1,3-DCP was investigated.

Treatment of saline wastewater contaminated with hydrocarbons by the photo-Fenton process

The application of the photo-Fenton process to the treatment of saline wastewater contaminated with hydrocarbons is investigated. Aqueous saline solutions containing raw gasoline were used as a model oil-field-produced water. The dependence on concentrations of the following reagents has been appropriately evaluated: hydrogen peroxide (100-200 mM), iron ions (0.5-1 mM), and sodium chloride (200-2000 ppm). The reactions were monitored by measurement of the absorption spectra and total organic carbon (TOC). Experimental results demonstrate that the photo-Fenton process is feasible for the treatment of wastewaters containing hydrocarbons, even in the presence of high concentrations of salt. The effect of the salt in this process is described through a series of reactions. A simple feedforward neural network model was found to correlate well the observed data for the degradation process.

Photocatalytic detoxification of microcystins combined with ferrate pretreatment

This work focuses on the development and evaluation of a combined technique including ferrate oxidation and photocatalytic detoxification of microcystins. Greater removal efficiency of the microcystins-LR (MLR) can be achieved using the combined process. The experimental result demonstrates that the residual Fe after ferrate oxidation can enhance the efficiency of photocatalytic reaction. The optimal dosage of ferrate 20 mg/l was determined by studying the degradations of total organic carbon (TOC) and MLR at different concentrations of residual Fe. As expected, pH had a remarkable influence on the reaction rate of detoxification of MLR and a low pH was beneficial to the reaction.

Photosensitization of crystalline and amorphous titanium dioxide by platinum(IV) chloride surface complexes

Anatase, rutile, and amorphous titania powders were surface-modified by grinding with PtCl4 and H2[PtCl6]. Only the anatase modification afforded hybrid photocatalysts capable of degradation of 4-chlorophenol (4-CP) with visible light, with sufficient stability towards decomplexation. Grinding with K2[PtCl4] produced materials of only low photocatalytic activity. Most efficient photocatalysts contained up to 2 wt% of PtIV. At higher surface loading the excess fraction of the complex is desorbed into the aqueous solution. Scavenging experiments with benzoic acid and tetranitromethane revealed that hydroxyl radicals are produced by the primary reduction of oxygen by conduction band electrons generated through electron injection from a postulated surface platinum(III) complex. It is proposed that the latter is formed from a charge-transfer ligand-to-metal (CTLM) excited state through homolysis of the Pt-Cl bond. Accordingly. the primary oxidation of 4-CP may occur by adsorbed chlorine atoms, the intermediary existence of which was demonstrated by scavenging experiments with phenol.