Photodechlorination of PCB's in the Presence of Titanium Dioxide in Aqueous Suspensions


By jpeza - Posted on 09 Julio 2009

Fecha Publicación: 
1 Ene 1976
Datos del paper
Autor Principal: 
John H. Carey
Volumen: 
16
Issue: 
6
Página Inicial: 
967
Página Final: 
701
Abstract: 

In view of their biological and chemical s t a b i l i t y , the

photoreactions of polychlorobiphenyls (PCB's) may be a significant

route for their environmental degradation. Reductive dechlorination

is the main photoreaction of PCB's in solvents such as hexane,

(CROSBY and HAMADMAD, 1971). In more hydroxylic solvents, the rate

of dechlorination is faster and 'polar' products are also formed,

(CROSBY and LEITIS, 1969). The observed PCB photoproducts are all

thought to arise through reaction of the same t r i p l e t excited state

via dechlorination or neucleophilic substitution.

An area which has received very l i t t l e attention has been

the possibility of photointeraction between PCB's and suspended

solids. Absorption of light by metallic oxides can induce reaction

at the oxide surface with molecules in solution or gas phase. For

a recent review see Photo-effects in Adsorbed Species, Faraday Discussions

of the Chemical Society (London) Vol. 58, 1974. This photocatalysis

is particularly pronounced for wide bandgap semiconductors

such as titanium dioxide (rutile) and zinc oxide, but some degree

of photocatalytic behaviour bas been observed for iron oxides and

beach sand, (KINNEY and IVANUSKI, 1969).

MARKHAM and LAIDLER (1963) studied the production of hydrogen

peroxide by zinc oxide slurries under irradiation with 365 nm

light. Organic additives had the effect of increasing the H202

yield indicating that, although they were consumed in the photoreaction,

they were not reacting with this photoproduct. Instead it was

reasoned that the organics reacted at the zinc oxide surface with

oxidizing species produced during the irradiation. The photo-oxidation

of benzene led to trace quantities of phenols, polyphenols and

biphenyl but the major product, thought to be an organic peroxide,

could not be isolated. Chlorobenzene also gave similar products in

trace amounts along with a significant amount of chloride ion.

Since chlorobenzene appeared to be oxidized by the irradiated

s]urry, we hoped that chlorinated biphenyls would exhibit

similar behaviour. Titanium dioxide was chosen as photocatalyst

since it doesn't decompose upon irradiation as does zinc oxide.

Dirección del Autor: 

Water Chemistry Section

Canada Centre for Inland Waters

P.O. Box 5050

Burlington, Ontario

Canada L7R 4A6

Keywords: 
photoreactions of polychlorobiphenyls ; environmental degradation. Reductive dechlorination
Coautores: 

John Lawrence, and Helle M. Tosine

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