TiO2- and BaTiO3-assisted photocatalytic degradation of selected chloroorganic compounds in aqueous medium: correlation of reactivity/orientation effects of substituent groups of the pollutant molecule on the degradation rate.

Investigation of the photocatalytic activity of BaTiO(3), a perovskite wideband gap semiconductor has been done in comparison with a widely used photocatalyst TiO(2) for the degradation of 4-chlorophenol (4-CP), 4-chloroaniline (4-CA), 3,4-dichloronitrobenzene (3,4-DCNB), and 2,4,5-trichlorophenol (2,4,5-TCP). BaTiO(3)/TiO(2) nanoparticles were prepared by gel-to-crystalline conversion method. BaTiO(3) has exhibited better catalytic efficiency and process efficiency compared with TiO(2) in most of the cases. The present research focuses mainly on two aspects: first the photocatalytic activity of BaTiO(3), as there are very few reports in the literature, and second the reactivity/orientation effects of substituent groups of the pollutant molecules on the degradation rate. The above chloroorganic compounds have at least one chlorine substituent in common, along with other functional groups such as -OH, -NH(2), and -NO(2). Furthermore, the effect of electron acceptors and pH on the rate of degradation is presented. The reactions follow first-order kinetics. The degradation reaction was followed by UV-vis, IR, and GC-MS spectroscopic techniques. On the basis of the identification of the intermediates, a probable degradation reaction mechanism has been proposed for each compound.

Heterogeneous photo catalytic degradation of anionic and cationic dyes over TiO(2) and TiO(2) doped with Mo(6+) ions under solar light: Correlation of dye structure and its adsorptive tendency on the degradation rate.

Degradation of synthetic dyes like Methyl Orange (MO), p-amino azo benzene (PAAB), Congo Red (CR), Brilliant Yellow (BY), Rhodamine-B (RB) and Methylene Blue (MB) under solar light were carried out using TiO(2) doped with Mo(6+) ions. The rate constant for the degradation of anionic dyes MO, PAAB, CR and BY was high at pH 5.6, while for cationic dyes the highest rate constant was obtained in the alkaline pH 8.0. These differences can be accounted to their adsorption capacity on the catalyst surface at different pH conditions. Among the photocatalyst used, Mo(6+) (0.06%)-TiO(2) showed enhanced activity due to the effective separation of charge carriers.

TiO(2)/BaTiO(3)-assisted photocatalytic mineralization of diclofop-methyl on UV-light irradiation in the presence of oxidizing agents.

Gas chromatograph-mass spectroscopic identification of intermediate products in the degradation of diclofop-methyl and the kinetics of the reaction has been investigated. Formation of 4-[(2,4-dichlorophenoxy) phenoxy] ethane and (2,4-dichlorophenoxy) phenol was investigated. The other intermediate products are 2,4-dichlorophenol, 2,4-dichlorobenzene, phenol and acetic acid have been ascertained. The decrease in the concentration of the parent/intermediate compounds is followed by UV-vis spectral study and the supportive information on the functional groups in the intermediates has been obtained from IR-spectroscopy. Degradation process proceeds with oxidation-reduction reaction by the attack of OH*, H*, O(2)*(-) free radicals, which are photogenerated on the UV-light illuminated TiO(2)/BaTiO(3) photocatalysts particles in aqueous medium. In this presentation another wide band gap semiconductor BaTiO(3) is shown to have comparable photocatalytic efficiency. The oxidizing agents are added to accelerate the rate of the reaction by enhancing the formation of free radicals. Based on the intermediates formed in the process of degradation, a suitable mechanism has been proposed.

Photo degradation of methyl orange an azo dye by advanced Fenton process using zero valent metallic iron: influence of various reaction parameters and its degradation mechanism.

Advanced Fenton process (AFP) using zero valent metallic iron (ZVMI) is studied as a potential technique to degrade the azo dye in the aqueous medium. The influence of various reaction parameters like effect of iron dosage, concentration of H(2)O(2)/ammonium per sulfate (APS), initial dye concentration, effect of pH and the influence of radical scavenger are studied and optimum conditions are reported. The degradation rate decreased at higher iron dosages and also at higher oxidant concentrations due to the surface precipitation which deactivates the iron surface. The rate constant for the processes Fe(0)/UV and Fe(0)/APS/UV is twice compared to their respective Fe(0)/dark and Fe(0)/APS/dark processes. The rate constant for Fe(0)/H(2)O(2)/UV process is four times higher than Fe(0)/H(2)O(2)/dark process. The increase in the efficiency of Fe(0)/UV process is attributed to the cleavage of stable iron complexes which produces Fe(2+) ions that participates in cyclic Fenton mechanism for the generation of hydroxyl radicals. The increase in the efficiency of Fe(0)/APS/UV or H(2)O(2) compared to dark process is due to continuous generation of hydroxyl radicals and also due to the frequent photo reduction of Fe(3+) ions to Fe(2+) ions. Though H(2)O(2) is a better oxidant than APS in all respects, but it is more susceptible to deactivation by hydroxyl radical scavengers. The decrease in the rate constant in the presence of hydroxyl radical scavenger is more for H(2)O(2) than APS. Iron powder retains its recycling efficiency better in the presence of H(2)O(2) than APS. The decrease in the degradation rate in the presence of APS as an oxidant is due to the fact that generation of free radicals on iron surface is slower compared to H(2)O(2). Also, the excess acidity provided by APS retards the degradation rate as excess H(+) ions acts as hydroxyl radical scavenger. The degradation of Methyl Orange (MO) using Fe(0) is an acid driven process shows higher efficiency at pH 3. The efficiency of various processes for the de colorization of MO dye is of the following order: Fe(0)/H(2)O(2)/UV>Fe(0)/H(2)O(2)/dark>Fe(0)/APS/UV>Fe(0)/UV>Fe(0)/APS/dark>H(2)O(2)/UV approximately Fe(0)/dark>APS/UV. Dye resisted to degradation in the presence of oxidizing agent in dark. The degradation process was followed by UV-vis and GC-MS spectroscopic techniques. Based on the intermediates obtained probable degradation mechanism has been proposed. The result suggests that complete degradation of the dye was achieved in the presence of oxidizing agent when the system was amended with iron powder under UV light illumination. The concentration of Fe(2+) ions leached at the end of the optimized degradation experiment is found to be 2.78 x 10(-3)M. With optimization, the degradation using Fe(0) can be effective way to treat azo dyes in aqueous solution.