Electrochemical Characterisation of the Photoanode Containing TiO2 and SnS2 in the Presence of Various Pharmaceuticals

Abstract

In this work, the behaviour of photoanodes made of TiO2, SnS2 and TiO2/SnS2 was examined in the presence and absence of pharmaceuticals diclofenac (DCF), memantine hydrochloride (MEM) and salicylic acid (SA). The focus of the current research is on the following photoelectrochemical (PEC) characterisation methods: linear polarisation, electrochemical impedance spectroscopy (EIS), and open circuit potential (OCP) monitoring. Linear polarisation and EIS provided useful information about the interaction between the pharmaceuticals and the photocatalytic materials. The presence of the selected pharmaceuticals affects the OCP value, mainly due to the pH change. The results obtained by PEC characterisation were compared to the photocatalytic (PC) efficiency of pharmaceutical degradation. In addition to the photocurrent response, the linear voltammogram indicates the electrochemical oxidation of DCF and SA. Geometry optimizations using density functional theory (DFT) showed that the HOMO orbitals’ position of DCF and SA are above the position of the TiO2 HOMO level and below the position of the SnS2 HOMO level. Due to this, the characteristic current peak for DCF and SA was registered, but only for TiO2 and TiO2/SnS2 photoanodes. The oxidation current peak was not registered for MEM, although h+ scavenging properties were noticed for TiO2 in the presence of MEM. Apparently, this is an interplay between the protonated and non-protonated forms of MEM and the differences in their HOMO positions.