Photocatalytic degradation of dichlorvos in aqueous TiO₂ suspensions

Introduction In the present work, we explored the kinetics of dichlorvos (2,2-dichlorvinyl dimethyl phosphate, DDVP) decay through UV-A light-induced TiO₂ photocatalysis at pH 4 and 9, and the formation of degradation intermediates and final products under specific experimental conditions. Experimen...

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Bibliographic Details
Published in:Environmental science and pollution research international 2010-06, Vol.17 (5), p.1158-1166
Main Authors: Oncescu, Tatiana, Stefan, Mihaela I, Oancea, Petruta
Format: Article
Language:English
Subjects:
Adsorption
Aquatic Pollution
Aqueous solutions
Atmospheric Protection/Air Quality Control/Air Pollution
By products
Catalysis - radiation effects
Chlorides - chemistry
Degradation
Dichlorvos
Dichlorvos - chemistry
Dissolved oxygen
Earth and Environmental Science
Ecotoxicology
Environment
Environmental Chemistry
Environmental Health
Environmental monitoring
Environmental protection
Experiments
Flow rates
Formaldehyde - chemistry
Hydrogen-Ion Concentration
Insecticides - chemistry
Intermediates
Irradiation
Kinetics
Mineralization
Organic acids
Oxidation
Oxygen - chemistry
Pesticides
pH effects
Phosphates - chemistry
Photocatalysis
Photochemical Processes - radiation effects
Photodegradation
Reaction mechanism
Research Article
Studies
Suspensions
TiO₂ photocatalysis
Titanium - chemistry
Titanium dioxide
Toxicity
Ultraviolet radiation
Ultraviolet Rays
Waste Disposal, Fluid - methods
Waste Water Technology
Water - chemistry
Water Management
Water Pollutants, Chemical - chemistry
Water pollution
Water Pollution Control
Water treatment
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Summary:Introduction In the present work, we explored the kinetics of dichlorvos (2,2-dichlorvinyl dimethyl phosphate, DDVP) decay through UV-A light-induced TiO₂ photocatalysis at pH 4 and 9, and the formation of degradation intermediates and final products under specific experimental conditions. Experimental observations and theoretical considerations allowed us to suggest the degradation mechanism of DDVP by the UV/TiO₂ process in aqueous solution. Methods The irradiation experiments were carried out in a photoreactor using a 228-W medium-pressure Hg vapor lamp. The concentration of DDVP, phosphate ion and formaldehyde as reaction intermediate, are determined spectrophotometrically. Chloride ion concentration was measured potentiometrically. Results The photocatalytic degradation rate of dichlorvos (DDVP) under UV irradiation (360-380 nm) was optimized with respect to the flow rate of O₂ gas sparged into the solution and photocatalyst concentration for a constant dichlorvos concentration (1.66×10⁻⁴ M) at pH 4. Kinetic data were obtained at pH 4 and pH 9 for dichlorvos and the inorganic species released through its photo-induced degradation. The proposed mechanism which assumes the formation of some toxic intermediates resistant to mineralization is supported by theoretical calculations and the observed inorganic mass balances. Conclusions The calculated pseudo-first-order rate constants were dependent on the dissolved oxygen level at low O₂ flow rate, but somewhat independent on the initial pH. The decrease of pH during the irradiation suggests the formation of organic acids. The presence of organic intermediates was confirmed also by TOC measurements. A plausible reaction mechanism of DDVP degradation through the UV-A/TiO₂ process was proposed.
ISSN:0944-1344
1614-7499
DOI:10.1007/s11356-009-0292-4