In-situ fabricated gas sensors based on one dimensional core-shell TiO2-Al2O3 nanostructures

Abstract

A novel in-situ sensor fabrication method consisting of one dimensional (1-D) core-shell TiO2-Al2O3 nanostructures is reported. The 1-D nanostructures were synthesized on Ti-6Al-4V (Ti64) particles by a robust, simple, inexpensive and highly scalable route based on thermal oxidation. The in-situ fabricated sensors were tested in various reducing and oxidizing gases including hydrogen (H2), hydrogen sulfide (H2S), carbon monoxide (CO), methane (CH4), methanol (CH3OH), ethanol (C2H5OH), ethylene (C2H4), nitrogen dioxide (NO2) and oxygen (O2). The selectivity, sensitivity, optimum operating temperature, response time and recovery time of the sensors were examined. Results reveal that the as-grown 1-D nanostructures are 1–5 µm long with diameter of 30–100 nm. The core and shell of the 1-D nanostructures consist of rutile-TiO2 and corundum-Al2O3, respectively. The growth direction of TiO2 and Al2O3 are <002> and <110>, respectively. The sensors consisting of 1-D core-shell TiO2-Al2O3 nanostructures show n-type sensing behavior. Selective sensitivity is seen towards H2S, CH3OH and C2H5OH in N2 background with response values of 38.7, 349.6 and 1108.9, respectively. The response time of the sensors decreases and recovery time increases with increasing the concentration of target gases. An electron tunneling assisted surface depletion model is proposed to explain the sensing mechanism of these sensors. © 2016 Elsevier B.V.