Light-induced formation of 2,5-dihydroxy-p-benzoquinonefrom hydroquinone in photoirradiated silver-loaded zirconium phosphate suspension

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Hirokazu Miyoshi, Hiroki Kourai and Takuya Maeda


Abstract

Silver-loaded zirconium phosphate [Ag1-xHxZr2(PO4)3] has shown photocatalytic activity concerning the generation of OH and the hydroxylation of hydroquinone (HQ) to 2,5-dihydroxy-p-benzoquinone (DHQH2). HQ was initially oxidized to p-benzoquinone (BQ) by Ag+ on the surface of Ag1-xHxZr2(PO4)3 in the dark and by photogenerated OH during visible-light irradiation. As an intermediate, a semiquinone radical BQH was detected by EPR measurements in both cases. Furthermore, under visible-light irradiation, DHQH2 was identified by its absorption spectrum and thin layer chromatography. The amount of DHQH2 increased and BQ decreased with irradiation time. The total amount of BQ and DHQH2 under visible-light irradiation agreed with that of BQ in the dark. Consequently, DHQH2 appeared to form from BQH generated by the oxidation of HQ and the reduction of BQ by photogenerated e-. From the XPS and FT-Raman technique analyses, it was found that the addition of the photogenerated OH to BQH occurred at the surface of Ag1-xHxZr2(PO4)3. This indicated that both the OH and HBQ were stabilized on the surface of Ag1-xHxZr2(PO4)3.


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