Assessment of Dye Decolorization Test for the Activity Measurement of Visible Light Photocatalysts

Abstract

MasterVarious photocatalyst modification methods for enhancing visible light activity (i.e. metal doping, surface sensitization, composite semiconductors, etc) are currently under extensive research. Their activities can be tested by the degradation rate of different organic compounds (e.g. 4-chlorophenol, carbon tetrachloride, VOCs, etc). Among these organic substrates, dyes are the most widely used due to their rapid decolorization and simple kinetic analysis. However, an uncertainty on the use of dye absorption spectra is inherently present for the evaluation of photocatalytic activity. Therefore, in this study, diverse photocatalysts (N-TiO¬2, C-TiO2, C60(OH)X/TiO2, Pt/WO3, BaBiO3, Bi2WO3 and P25) were tested for various organic dye degradation (anionic: Acid Orange 7, Indigo Carmine and New Coccinecationic: Methylene Blue and Rhodamine B) to demonstrate some inconsistent correlations between photocatalytic activities and dye degradation kinetics. Removal of dyes was influenced not only by the molecular complexity of dye but also its adsorption extent. Moreover, it is possible that the photocatalytic efficiency is influenced by direct photolysis and dye-sensitization because dye molecules are excited by visible light. In this sense, TOC removal was negligible although dye was completely photobleached, implying that dye molecules might not be further mineralized. This study demonstrates that dyes as test substrates for visible photocatalysts are unsuitable target pollutants