Room temperature toluene gas sensor based on TiO2 nanoparticles decorated 3D graphene-carbon nanotube nanostructures

This work presents a highly sensitive room-temperature gas sensor based on 3D titanium dioxide/graphene-carbon nanotube (3D TiO2/G-CNT) fabricated by chemical vapor deposition and sparking methods. Characterizations by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and Transmission electron microscopy confirmed the formation of 3D graphene-carbon nanotube nanostructures decorated with TiO2 nanoparticles. The toluene detection performances of 3D TiO2/G-CNT structures with varying Ti sparking times were investigated in comparison with 3D G-CNT, TiO2-CNT, graphene and CNTs at room temperature. From result, the optimal sparking time of 60 s led to an optimal sensor response of 42%-500 ppm at room temperature. In addition, the optimal 3D TiO2/G-CNT exhibited substantially higher toluene response, sensitivity and selectivity than 3D G-CNT, TiO2-CNT, graphene and CNTs over a low concentration range of 50-500 ppm. The toluene-sensing mechanisms of 3D titanium dioxide/graphene-carbon nanotube nanostructures were proposed based on the formation of Schottky metal-semiconductor junctions between metallic 3D graphene-carbon nanotube structures and n-type semiconducting titanium dioxide nanoparticles due to the adsorption of toluene molecules via low-temperature reducing reactions or direct charge transfer process.