Fabrication of one-dimensional porous p-type Co3O4 rods-based sensors for ultra-high sensitivity and selectivity towards benzene vapour
Rethabile Makole, Zamaswazi P. Tshabalala, H.C. Swart, Liza Coetsee-Hugo, Nompumelelo Leshabane, David E. Motaung
Abstract
This study reports on the noble gas sensing properties of Co3O4 nanostructures for the detection of benzene vapour at a low functional temperature of 75 ˚C. The Co3O4 nanostructures were synthesized hydrothermally at different reaction temperatures ranging from 120 ˚C to 220 ˚C. Surface morphology analysis of the nanostructures revealed the formation of 1-D mesoporous nanorods at lower reaction temperatures, i.e., 120 ˚C and 140 ˚C, while synthesis at higher temperatures disintegrated the nanorods and formation of agglomerated plate-like and block-like nanostructures was observed. Among the Co3O4 nanostructures, 1-D nanorods synthesized at 140 ˚C demonstrated a notable response of 361 towards 5 ppm benzene at 75 ˚C. In addition, the lowest theoretical detection limit of 1.9 ppb and sensitivity of 92 ppm-1 were observed for 1-D mesoporous nanorods. The reported ultra-sensitivity of the 1-D mesoporous nanorods is attributed to the porous surface that supplied numerous sites for adsorption/desorption of O2- ions and benzene molecules, the rod-like configuration of its crystallites that provided connecting pathways for efficient charge transportation and the catalytic oxidation of Co3O4 to benzene. Further analyses of the long-term stability of the sensor stored for 304 days and tested in dry air and under relative humidity were discussed in detail as well as the sensing mechanism induced by surface oxygen and benzene gas adsorption.