One-Step Preparation of SnO2 and Pt-Doped SnO2 As Inverse Opal Thin Films for Gas Sensing

A new, fast, one-pot synthesis of SnO2 and Pt-doped SnO2 inverted opal thin films, to be used as materials for gas sensing, was carried out. Films were built from crystalline cassiterite nanoparticles, uniform in size (similar to 5 nm), resulting in a well-organized hierarchical structure of macro- and mesopores. The noble metal was homogeneously dispersed into the sensing layer of the oxide and the doping centers were present as Pt(IV) and Pt(II) species, partially reduced to Pt(0) after the interaction with the reducing gas (CO). The values of the electrical sensitivity under CO/Air atmosphere demonstrated that the response of Pt-doped films is higher than that of bare SnO2 films, and that the response of inverted opal films is higher compared to that of the sol-gel films. The regular array of cassiterite nanoparticles, strongly interconnected and ordered as close-packed hollow spheres, promotes the effective gas diffusion through the oxide layer and, along with the electron acceptor ability of Pt(IV) doping centers, significantly contributes to enhancing the electrical sensitivity. The conductance regime of the Pt-doped SnO2 inverted opal film is indicative of a regular microstructure of SnO2 nanoparticles.