Spectrophotometric analysis: Challenge for a reliable evaluation of photocatalytic activity under visible light irradiation

Abstract

Even though dyes have often been used as a model pollutant in photocatalytic degradation tests, their utilization as a substrate might cause unreliable results. Under visible-light (vis) irradiation, dye absorbs light and might sensitize wide-bandgap photocatalyst, which usually is only active under UV. Consequently, dye-decoloration analysis should not be used in the evaluation of photocatalytic activity under vis. To obtain reliable data, colorless compounds are commonly considered as much better substrates for photocatalytic activity testing since they do not absorb vis. However, more expensive analytic methods (e.g., gas and liquid chromatography) than simple UV/vis spectrophotometry (or even spectrometry) must be used for estimation of their concentration. Moreover, colorless compounds might also interact with UV-active photocatalyst, e.g., via molecule to band charge transfer (MBCT), causing photoinduced activity under vis irradiation. Accordingly, this review presents possible prospective methods for reliable but also inexpensive testing of photocatalytic activity under vis irradiation