Oxalic acid sensors based on sol–gel nanostructured TiO₂ films

Titanium (IV) oxide semiconducting layers were prepared by means of the templated sol–gel method and deposited on conductive ITO substrates. The films were described by a series of techniques involving X-ray diffraction (XRD), Raman spectroscopy, X-ray reflectivity (XRR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and ultraviolet–visible spectroscopy (UV–Vis). The photo-excitation properties of the films were characterized by electrochemical tests and evaluated from the obtained polarization curves. The generated photocurrents were measured in the presence of the hole-scavengers—oxalic acid and formic acid in the electrolyte. It was shown that especially in the case of oxalic acid the developed system can be used as an efficient and simpler concentration sensor. The relationship between values of the generated photocurrent and the layers’ thicknesses was also investigated.