Influence of methanol when used as a water-miscible carrier of pharmaceuticals in TiO2 photocatalytic degradation experiments

Research on the use of titanium dioxide (TiO2) for water treatment has expanded to include the degradation of pharmaceuticals and personal care products (PPCPs). PPCPs are typically introduced in aqueous solutions during TiO2 photocatalysis experiments using a water-miscible carrier solvent (e.g. methanol) to improve their solubility; however, carrier solvents may be detrimental to photocatalysis due to their scavenging effect. Although it is advisable to maintain the solvent at low concentrations, the influence of elevated concentrations of methanol or other solvents on photocatalysis has not been carefully explored. In this study, we examined the impacts of different methanol concentrations (0–0.2% v/v) on photocatalysis using P25 (commercial TiO2) and TiO2 nanomaterial synthesized via thermal and chemical oxidation (TCO). Scavenging of hydroxyl radicals by methanol was evident for both P25 and TCO but the effect was more prominent on TCO. Also, the photodegradation of some compounds using P25 were enhanced at low levels of methanol. Overall, this study highlights that trace amounts of methanol used as a carrier solvent can affect photocatalysis, especially in TiO2 nanomaterials with low reactivity. This should be considered carefully in future experiments so that the results are not biased by the introduction of carrier solvents.