Porous sol gel silica films doped with crystalline NiO nanoparticles for gas sensing applications

A reliable sol gel route to synthesize NiO doped SiO2 films with different NiO content is here described. The films showed detectable and reversible changes in both optical and electrical properties when exposed to some reducing/oxidizing gaseous species at temperatures in the 250◦C–350◦C range. A functional characterization protocol has been designed and some of the sensing properties of the materials have been investigated for detecting NO2, CH4, CO and H2. An optical transmittance increase up to 2% has been detected for 1% CO in dry air atmospheres, while relative resistance response (RR = Rgas/Rair) values up to 4.97 for 850 ppm H2/air mixtures have been registered for conductometric gas sensing. Films at all NiO molar concentrations in the 10% NiO - 40% range showed an optical response to the target gas, while only 30% and 40% NiO films provided a detectable gas induced resistance change.