A facile approach of developing Al/SnO2 xerogels via epoxide assisted gelation: A highly versatile route for formaldehyde gas sensors

Abstract

A robust synthesis approach to Al/SnO2 based formaldehyde gas sensing xerogels using epoxide assisted sol-gel chemistry is reported. The route utilizes simple tin and aluminum salt precursors in alcohol/water mixture, thus eliminating the need for organometallic precursors. Propylene oxide acts as a proton scavenger and drives metal hydroxide formation and subsequent polycondensation reactions. Al/SnO2 xerogels (with Al doping 1–4 mol%) were aged for 24 h to strengthen the gel network, followed by sintering and screen printed thick films formation. Prior to gas sensing investigations, the physico-chemical properties of the material were analysed using TG-DTA, XRD, FE-SEM, TEM, SAED, EDAX, UV–Visible and FTIR spectroscopic techniques. The developed material showcase tetragonal rutile structure of SnO2 with porous morphology required for effective gas diffusion. Al/SnO2 with 3 mol% doping level exhibited excellent gas sensing ability (Ra/Rg = 15 @ 300 °C operating temperature) towards barely 100 ppm formaldehyde concentration. Not only sensor response was got improved (from Ra/Rg value 5 to 15), but also the operating temperature got reduced from 325 °C to 300 °C). An effect of formaldehyde concentration, the sensor response got increased rapidly up to 100 ppm concentration, thereafter the increase in response was observed almost stagnant. By keeping the measurement parameters as is, the sensor performance was checked six times after the initial measurement with the interval of 10 days, which showed ~89% of its initial sensitivity. The developed material showcase the potentiality of being formaldehyde gas sensor.