Order of Photocatalytic Degradation as Ranked by Critical Photonic Times (CPTs) Indicates the Composition of Organic Dye Mixtures: Selectivity of Hydroxyl Radicals

Abstract

A simple critical photonic time (CPT) ranking method for the simultaneous determination of known organic dyes in the industrial wastewater of different concentrations was developed. A kinetic-measure, CPT theory, was developed to discriminate between the dyes in the textile effluent solution. The CPTs were calculated and ranked 1–4 from the smallest to the largest. The ranks indicate the order in which the individual dyes in the effluents were photocatalytically degraded. The described procedure allowed us to monitor the decolorization kinetics of the dyes in mixtures of different concentrations, when subjected to immobilized TiO₂ photocatalysis in the presence of H₂O₂ from the start (H₂O_2FS). The outcome of hydroxyl radical (HO^•) attack was consistently specific and regioselective for the individual dyes in the textile effluent. To explain the effect of HO^•, the order of degradation of Acid Orange 52 < Acid Yellow 36 < Acid Red 17 < Acid Blue 45 < polyvinyl alcohol (PVA) was inferred.

Key Words:

• Textile effluent
• Spectrophotometry
• Critical photonic time (CPT)
• Rank
• Hydroxyl radical attack

ACKNOWLEDGMENTS

We would like to thank Prof. Fuhimide Shiraishi at the Department of Bio-Systems Design, Bio-Architecture Center Kyushu University (Japan) for providing a TiO₂ thin film glass and GL-6 UV lamp; Li Jia, Richard Hirsh, and Liang Zhou for technical analysis. The authors gratefully acknowledge also the financial support for this study, which is part of a Scientific Research Foundation funded for the Returned Overseas Scholars, State Education Ministry.