Surface-modification of SnO2 nanoparticles by incorporation of Al for the detection of combustible gases in a humid atmosphere

Abstract

Inhibition of hydroxyl poisoning of SnO₂ nanoparticles is important to develop a highly sensitive combustible gas sensor that functions in a humid atmosphere. For this purpose, we incorporated Al into SnO₂ nanoparticles (Al-doped SnO₂) by a precipitation method, and fabricated a thick-film-type sensor using a screen printing method. Bare SnO₂ nanoparticles and Al₂O₃-loaded SnO₂ nanoparticles were also prepared for comparison. The oxygen adsorption amount clearly decreased after Al doping and Al₂O₃ loading, according to temperature programmed desorption measurements. Al doping enhanced the sensor response (sensitivity) to H₂, CO and C₂H₅OH in a humid atmosphere by almost five to ten times. Al₂O₃ loading also slightly increased the sensor response to each gas in a humid atmosphere. The enhancement of the sensor response was attributed to both Al and Al₂O₃ acting as hydroxyl absorbers on the surface of the nanoparticles, thereby providing an oxygen adsorption site for surface combustion reactions in a humid atmosphere. Based on the relationship between the sensor response and C₂H₅OH concentration, it was estimated that Al-doped SnO₂ can detect less than one ppm C₂H₅OH in a humid atmosphere. Therefore, doping with Al, which protects and holds the adsorbed oxygen on the surface of the SnO₂, is important as a surface modification to obtain humidity-tolerant semiconductor gas sensors.