Cooperative effect of Au and Pt inside TiO2 matrix for optical hydrogen detection at room temperature using surface plasmon spectroscopy

Metal (Au, Pt, Au@Pt) and metal oxide (TiO2) nanoparticles are synthesized with colloidal techniques and subsequently used as nanocrystal inks for thin films deposition. The optical properties of Au colloids are strongly influenced by both Pt and TiO2 interfaces: while platinum causes a damping and a blue-shift of the Au Surface Plasmon Resonance (SPR) peak as a consequence of the metal-metal interaction, the anatase matrix is responsible for the red shift of the plasmon frequency due to the increased refractive index. By a careful tailoring of the nanoparticles synthesis, high quality, scattering-free films composed of an anatase matrix embedding Au, Pt and Au@Pt colloids are deposited at room temperature and stabilized at 200 °C. Room temperature exposure of these films to hydrogen leads to optical changes. In the case of Au, there is a slow blue shift of the surface plasmon band, resulting in a wavelength dependent optical response. Much faster but smaller optical changes occur for titania films containing Pt. When both metals are present, the optical response of the gold is much faster. This is attributed to spillover of hydrogen atoms from platinum to gold. This synergy enables enhanced optical sensing of hydrogen at room temperature by combining the low temperature dissociation of H2 on Pt with the intensive surface plasmon response of the gold nanocrystals.