SBA-15 and TiO2-SBA-15 silicas as supports of gold and gold/copper nanoparticles for the photodegradation of methylene blue

SBA-15 and TiO2-SBA-15 (Si/Ti = 3) ordered mesoporous materials [1] have been used to support Au (1.5 wt%) and AuCu alloy (Au:Cu=1, 2.0 wt%) nanoparticles to evaluate the photocatalytic performance in the degradation of methylene blue (MB) under UV light irradiation. The influence of the addition of copper, as a second metal, forming an alloy with gold, has been studied in order to investigate possible synergistic effects of this bimetallic system in the MB photodegradation in aqueous suspension. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2-adsorption-desorption at -196°C, X-ray photoelectron spectroscopy (XPS) and DRUV–vis spectroscopy. The AuCu-based photocatalysts attained very high MB degradation values, in particular AuCu/TiO2-SBA-15 sample reached 100% of dye oxidation after the monitored reaction period (120 minutes). The presence of ordered channels of the mesoporous silica and titania-silica matrixes has led to an effective control of the growth of Au and AuCu NPs, keeping their size within the support pore diameters (< 5 nm). In particular, alloying gold with copper seems to improve the dispersion with the formation of smaller nanoparticles, which other authors have reported to be a critical parameter in photocatalysis [2]. Such small Au and AuCu alloy NPs act as an electron relay able to improve the MB photo-oxidation, due to the surface plasmon resonance. When the NPs are in contact with TiO2, a Schottky barrier is formed between them, playing a paramount role in enhancing the photoactivity of the reaction. AuCu alloyed nanoparticles deposited and incorporated inside the ordered pore channels of a SBA-15 mesoporous silica and titania-silica can be considered very effective as photocatalysts for the oxidation of cationic organic dyes, such as methylene blue.