Photochemical Behavior of Carbon Monoxidein Aqueous Suspension of ZnO ZnO
 

Printed in the Republic of Korea

ZnO
    

^† 
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   (2003. 4. 4 )

Photochemical Behavior of Carbon Monoxide in Aqueous Suspension of ZnO

Chul-Ho Park^†, Woo-Suk Chang, Yong-Sung Kim, and Hyoung-Ryun Park* Department of Chemistry, Chonnam National University, Kwangju 500-757, korea

†Department of Health and Environment, Chunnam Techno College, Koksung 516-911, Korea (Received April 4, 2003)

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ABSTRACT. The photochemical transformation of carbon monoxide in aqueous solution has been investigated at 25±0.1^oC using ZnO as a photocatalyst. After irradiation of 253.7 nm UV light in the solution, carboxylation and car- bonylation processes were carried out, and the formation of formic acid, oxalic acid, glyoxylic acid, formaldehyde and glyoxal was observed. The formation of the products depended on the pH values in the solution. The yield of form- aldehyde and glyoxal increased in acidic solution whereas it decreased in basic solution. When the pH values in the solu- tion increased above 11.5, the yield of formic acid increased rapidly. The initial quantum yields of the products were determined and the probable mechanisms for the reactions were presented on the basis of the products analysis.

Keywords: Carbon Monoxide, Zincoxide, Photocatalyst, Photochemical Reaction Mechanism



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Fig. 1. Formation of carboxylic acids after irradiation of aqueous carbon monoxide containing ZnO (0.4 mg/mL) as a function of the number of quanta; () is formic acid, () is glyoxylic acid, ( ) is oxalic acid.

Fig. 2. Formation of aldehydes after irradiation of aqueous carbon monoxide containing ZnO (0.4 mg/mL) as a function of the number of quanta; () is formaldehyde, () is glyoxal.

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Products Qi of the products ( X 10⁴) at pH

1.6 2.1 3.2 4.5 7.0 9.6 10.3 11.6 12.3

Formic acid 2.25 2.28 2.32 2.34 2.41 2.87 3.35 5.37 10.3

Oxalic acid 0.073 0.081 0.087 0.101 0.109 0.115 0.118 0.121 0.123

Glyoxylic acid 1.23 1.22 1.24 1.31 1.34 0.93 0.34 0.21 0.02

Formaldehyde 3.87 3.78 3.81 2.86 1.91 1.25 0.45 0.18 0.03

Glyoxal 0.198 0.198 0.196 0.165 0.136 0.072 0.031 0.014 0.008

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C·

C· C· Fig. 3. Formation of formaldehyde after irradiation of aque-

ous carbon monoxide containing ZnO (0.4 mg/mL) at pH 2.1() and pH 7.0 () as a function of the number of quanta

Fig. 4. Initial quantum yields (Qi) of the products after irra- diation of the aqueous carbon monoxide containing ZnO (0.4 mg/mL) as a function of the pH values in the solution; () is formic acid, () is formaldehyde, ( ) is glyoxylic acid.

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