TiO2/Au/TiO2 Plasmonic Photocatalysts: The Influence of Titania Matrix and Gold Properties

Abstract

Plasmonic photocatalysts have gained more and more attention because of possible applications for solar energy conversion, environmental decontamination, and water treatment. However, the activity under visible light is usually very low, and the property-governed activity as well as the mechanisms are not fully understood yet. Accordingly, this study examines four different titania photocatalysts (anatase and rutile with fine and large crystallites) modified with gold by photodeposition. Three kinds of samples were prepared, as follows: (i) gold-modified titania (Au/TiO2), (ii) physically mixed Au/TiO2 samples (Au/TiO2(1) + Au/TiO2(2)), and (iii) Au/(TiO2(1) + Au/TiO2(2)) samples, prepared by subsequent deposition of gold on the mixture of bare and gold-modified titania. In total, twelve samples were prepared and well characterized, including diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM). The photocatalytic activity was examined in three reaction systems: (i) methanol dehydrogenation during gold photodeposition under UV/vis irradiation, (ii) oxidative decomposition of acetic acid (UV/vis), and (iii) oxidation of 2-propanol to acetone under visible light irradiation (λ > 450 nm). It was found that during subsequent deposition, gold is mainly formed on the surface of pre-deposited Au nanoparticles (NPs), localized on fine titania NPs, through the electrostatic attractions (negatively charged gold resulting from photogenerated electrons’ accumulation). This gold aggregation, though detrimental for UV activity (many “naked” large titania with low activity), is highly beneficial for vis activity because of efficient light harvesting and increased interface between gold and titania (gold deposits surrounded by fine titania NPs). Moreover, it was found that rutile is more active than anatase for plasmonic photocatalysis, probably due to easier electron transfer from gold via titania to adsorbed oxygen (more negative conduction band), which might hinder the back reaction (electron transfer: Au→TiO2→Au).

How much is the plasmonic effect worth in photocatalysis? Mechanisms of photocatalytic activity enhancement in composites with metallic nanostructures

“…S4, S5, and Table S1). † A similar growth pattern was observed by Yoshiiri et al 30 Differences in morphology are also pronounced in the material colour. Gold-modied anatase is light pink to purple depending on the photodeposition time/structure size, while rutile is very light violet to bluish-grey (Fig.…”

“…The SPR band positions correspond clearly with the observed colours of the materials and also with the size and shape of metallic nanostructures as observed by others. 12,30…”

TiO2 Nanowires on TiO2 Nanotubes Arrays (TNWs/TNAs) Decorated with Au Nanoparticles and Au Nanorods for Efficient Photoelectrochemical Water Splitting and Photocatalytic Degradation of Methylene Blue

“…As shown in Figure 6e, the O 1s spectrum is asymmetrical and it has an extending tail towards the higher energy. The O 1s was deconvoluted into three component peaks at 530.0 eV, 531.8 eV, and 533.7 eV, which could be assigned to (i) O 2− in the TiO 2 lattice, (ii) Ti-OH or C=O groups bound to two titanium atoms, (iii) OH groups bound to C and/or Ti, respectively [42,43]. To evaluate the PEC activity of TNWs/TNAs and Au-TNWs/TNAs, linear sweeping voltammetry (LSV) curves were performed using the sample as photoanode, Pt as a counter electrode, and Ag/AgCl as a reference electrode and under the UV-Vis irradiation.…”