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

Abstract

A new, fast, one-pot synthesis of SnO 2 and Pt-doped SnO 2 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 (∼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 SnO 2 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 SnO 2 inverted opal film is indicative of a regular microstructure of SnO 2 nanoparticles.

Macroporous WO3 Thin Films Active in NH3 Sensing: Role of the Hosted Cr Isolated Centers and Pt Nanoclusters

“…This is in agreement with the relatively regular array of WO 3 nanocrystals found in the inverse opal structure (see TEM micrographs, Figure 4a,b) and can be associated with a surface reactivity similar to that described for SnO 2 materials. 23 Differently, Pt-doped WO 3 sensors show β values as always higher than 0.5 ( Figure 9B); this can be reasonably ascribed to the presence of Pt nanoclusters which may induce disordered zones in the inverse opal structure and give rise to a different sensing mechanism at the microscale level.…”

“…We also suggested that, in the presence of doping metal centers, the doping transition metal decreases its positive oxidation state by trapping the electrons given through reactions (6AÀ6C): 21,23 …”

“…The resulting colloidal suspensions of PMMA spheres was finally filtered through a glass wool plug to remove large agglomerates and stored in PET bottles for later use. 23 using the dip-coating method. Suprasil quartz slides (20 Â 20 mm, 0.25 mm thickness) were used as the substrates.…”

“…23 The procedure enables the self-assembled formation of the closely packed polystyrene (PS) microsphere array and the simultaneous infiltration of the precursors into the voids of the structure. Thus, the oxide solid skeleton around the spheres was obtained in one-step, unlike the conventional Received: October 22, 2010 ABSTRACT: Macroporous WO 3 films with inverted opal structure were synthesized by one-step procedure, which involves the self-assembly of the spherical templating agents and the simultaneous solÀgel condensation of the semiconductor alkoxide precursor.…”

Sol–gel derived mesoporous Pt and Cr-doped WO3 thin films: the role played by mesoporosity and metal doping in enhancing the gas sensing properties

“…The mechanism of the metal-oxide sensors is based on the change of electrical conductance in response to the introduction of a small concentration of reducing gas, which reacts with the oxygen species at the oxide surface [1,4,5]. Many extensive studies, mainly concerning SnO 2 , widely investigate the dependence of the electrical response on both the electronic and morphological properties of the semiconductor [9][10][11][12][13][14][15]. The sensing mechanism towards different gases, H 2 [16], CO [17] and NO 2 [18] was also suggested.…”