Effect of Au loading on Schottky barrier height in TiO2 + Au plasmonic photocatalysts
Artikel i vetenskaplig tidskrift, 2022
Composites of TiO2 and different amounts of plasmonic noble metal Au (0.25–2 wt%) were synthesized by employing the wet impregnation technique. The results of SEM, TEM, XRD and N2 physisorption analyses reveal that the morphologies of the prepared composites are similar to the morphology of bare TiO2 support and are not influenced by the increasing amount of deposited Au nanoparticles. On the other hand, the size of Au ensembles in the TiO2 + Au composites increased from 27.1 to 54.9 nm with the increasing amount of Au. With the increase of the diameter of Au ensembles, the intensity of the surface plasmon resonance (SPR) effect of Au ensembles in the UV–Vis diffuse reflectance spectra of the composites increased. The X-ray photoelectron spectroscopy (XPS) analysis of the valence band maxima (VBM) of the investigated photocatalysts revealed that the height of the Schottky barrier (SBH) at the Au/TiO2 junction in the investigated TiO2 + Au composites decreased from 0.4 to 0.15 eV with the increasing amount of Au (and their size). Therefore, the visible-light-generated “hot electrons” in Au ensembles of TiO2 + 2% Au composite have to overcome a lower energy barrier during the injection into the conduction band (CB) of the TiO2 support than “hot electrons” in the Au ensembles in the TiO2 + 0.25% Au composite. This makes the “hot electrons” in the TiO2 + 2% Au composite less accessible for the recombination with the visible-light generated holes, as the “hot electrons” do not agglomerate at the Schottky barrier (SB). This phenomenon was well expressed in the results of electrochemical impedance spectroscopy (EIS) analysis: under visible-light illumination, the TiO2 + 2% Au composite generated the highest amount of charge carriers among all investigated photocatalysts. The beneficial effect of the low SBH in the TiO2 + 2% Au solid was also expressed in the photoluminescence (PL) emission spectra, where the TiO2 + 2% Au composite showed the lowest charge carrier recombination rate. Further, the TiO2 + 2% Au composite expressed the highest visible-light triggered photocatalytic activity in the hydroxyl radical (OHÂ·) generation and water-dissolved bisphenol A (BPA) oxidation test.
Schottky barrier height
Plasmonic noble metal