Photocatalytic degradation of phthalic acid on TiO2 nanoparticles

Department of Chemistry, National Research Council of Argentina, University of Mar del Plata, P.O. Box 422, 7600 Mar del Plata, Argentina
Applied Catalysis A General (Impact Factor: 3.67). 06/2001; 208:419-426. DOI: 10.1016/S0926-860X(00)00727-4

ABSTRACT The photocatalytic oxidation of phthalic acid was studied in aerated sols of TiO2 nanoparticles under monochromatic irradiation at pH=4.25. We report initial quantum efficiencies for phthalate degradation, ΦPHT0, as a function of phthalate concentration and quantitative yields of the primary products. Formation rates of the hydroxyl radical adduct (DMPO-OH) from the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were determined at various initial concentrations of phthalate. Kinetic analysis of the spin-trapping experiments indicates that phthalate is oxidized by a dual hole-radical mechanism. The effect of added phosphate on phthalate photocatalytic degradation is examined in detail. Dark-adsorption of phthalate on TiO2 particles is significantly inhibited by the presence of phosphate, however, ΦPHT0 is almost independent of phosphate concentration.

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    ABSTRACT: The optimization of operational parameters for enhanced phthalic acid photocatalytic mineralization by TiO2/UV system was conducted using factorial experimental design and analysis. Response surface methodology (RSM) was adopted to investigate the optimum value of the selected factors for achieving maximum photocatalytic mineralization. The main factors studied were the initial concentration of phthalic acid, TiO2 dosage, volume of the solution, and agitation speed. The parameters coded as X 1, X 2, X 3, and X 4, consecutively, and were investigated at two levels (−1 and + 1). The effects of individual variables and their interaction effects for dependent variables, namely, the quantity of CO2 formed after 60 min of irradiation were determined. Experimental results showed that TiO2 dosage had significant influence on the photocatalytic mineralization. The optimum quantity of CO2 formed after 60 min of irradiation was 0.08513 mmol, when the operational parameters were phthalic acid concentration of 1 mmol/L, TiO2 dosage of 2,000 mg, volume of the solution of 1 L, and agitation speed of 1,100 rpm. The excellent correlation between predicted and measured values further confirmed the validity and practicability of adopted model.
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    ABSTRACT: The radical intermediates formed upon UVA irradiation of titanium dioxide suspensions in aqueous and non-aqueous environments were investigated applying the EPR spin trapping technique. The results showed that the generation of reactive species and their consecutive reactions are influenced by the solvent properties (e.g., polarity, solubility of molecular oxygen, rate constant for the reaction of hydroxyl radicals with the solvent). The formation of hydroxyl radicals, evidenced as the corresponding spin-adducts, dominated in the irradiated TiO2 aqueous suspensions. The addition of 17O-enriched water caused changes in the EPR spectra reflecting the interaction of an unpaired electron with the 17O nucleus. The photoexcitation of TiO2 in non-aqueous solvents (dimethylsulfoxide, acetonitrile, methanol and ethanol) in the presence of 5,5-dimethyl-1-pyrroline N-oxide spin trap displayed a stabilization of the superoxide radical anions generated via electron transfer reaction to molecular oxygen, and various oxygen- and carbon-centered radicals from the solvents were generated. The character and origin of the carbon-centered spin-adducts was confirmed using nitroso spin trapping agents.
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    ABSTRACT: TiO2 catalyst was prepared by two kinds of different methods. The photocatalytic activity of TiO2 prepared by the hydrothermal method is 2.5 times higher than that by sol-gel in degradation dimethyl phthalate (DMP). The combined photocatalysis with UV irradiation and ozonation (TiO2/UV/O3) process considerably improved mineralization and degradation of dibutyl phthalate compared to combined photocatalysis with UV irradiation (TiO2/UV) process, combined ozonation with UV irradiation (UV/O3) process and ozonation alone (O3) process. DMP can be quickly mineralized in TiO2/UV/O3, its mineralization process followed Langmuir-Hinshelwood model. Its rate constant k is 0.42 mg/ (L·min) and Langmuir adsorption coefficient K is 0.0417 L/mg.


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