H2O/D2O exchange in the presence of CO over SnO2nanomaterials: operando DRIFTS and resistance study for gas sensor applications

Abstract

Modulation excitation diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) together with resistance measurements has been carried out to study water isotopic exchange on undoped SnO 2 materials as a function of CO concentration. We compare two materials synthesized via hydrothermal treatment and different only in their precursors: SnO 2 Ac synthesized from tin(IV) hydroxide acetate and SnO 2 Cl from tin(IV) chloride pentahydrate. DRIFTS and resistance measurements were performed simultaneously in an environmental chamber at 300 oC and in a flow of humid air. The annealed materials were found to have similar particle sizes (16±7 nm), crystallite sizes (12±2 nm) and pore size distribution (9±1 nm). However, sensor tests showed notably higher responses to CO in the presence of water vapor for SnO 2 Ac. Electronic effect of CO chemisorption quantitatively correlates with consumption of bridging hydroxyls on the latter surface upon increasing concentration of CO from 0 to 500 ppm in humid air. No such correlation was found for SnO 2 Cl. Water desorption kinetics was found to be slower for the latter by ca. 30 % with respect to SnO 2 Ac. Low activity of surface OH groups and consequently low sensor signals of SnO 2 Cl were proposed to originate from traces of Cl ions found in the material after the synthesis despite negative Cl test before the hydrothermal treatment.