SnS 2 Nanosheets as a Template for 2D SnO 2 Sensitive Material: Nanostructure and Surface Composition Effects.

Two-dimensional nanosheets of semiconductor metal oxides are considered as promising for use in gas sensors, because of the combination of a large surface-area, high thermal stability and high sensitivity, due to the chemisorption mechanism of gas detection. In this work, 2D SnO 2 nanosheets were synthesized via the oxidation of template SnS 2 nanosheets obtained by surfactant-assisted one-pot solution synthesis. The 2D SnO 2 was characterized using transmission and scanning electron microscopy (TEM, SEM), X-ray diffraction (XRD), low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and IR spectroscopy. The sensor characteristics were studied when detecting model gases CO and NH 3 in dry (RH 25 = 0%) and humid (RH 25 = 30%) air. The combination of high specific-surface-area and increased surface acidity caused by the presence of residual sulfate anions provides a high 2D SnO 2 sensor's signal towards NH 3 at a low temperature of 200 °C in dry air, but at the same time causes an inversion of the sensor response when detecting NH 3 in a humid atmosphere. To reveal the processes responsible for sensor-response inversion, the interaction of 2D SnO 2 with ammonia was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in dry and humid air at temperatures corresponding to the maximum "positive" and maximum "negative" sensor response.