Operating Temperature, Repeatability, and Selectivity of TiO 2 Nanotube-Based Acetone Sensor: Influence of Pd and Ni Nanoparticle Modifications

This paper concerns the tuning of the operating temperatures, selectivity, and repeatability of a resistive acetone sensor based on TiO 2 nanotubes (NTs) through surface modifications (of NTs) using Pd and Ni nanoparticles. Three sets of sensor devices, which employ unmodified, Ni-modified, and Pd-modified TiO 2 NT arrays as the sensing layer, were tested for acetone detection in the temperature range of 50 °C-250 °C, targeting 10-1000 ppm. It was found that both the modified (Pd and Ni) sensors offered a lower optimum operating temperature (100 °C) compared with its unmodified counterpart (150 °C), possibly owing to the requirement of lower activation energy in the case of modified systems. The cross sensitivity toward other interfering species, viz., ethanol, methanol, 2-butanone, and toluene, was investigated. Both the modified sensors were found to offer better selectivity toward acetone than the unmodified sensor. However, the response and selectivity improvement of the modified sensors was achieved at the expense of poor repeatability. Possibly owing to the increased structural defects and the nonidentical oxygen spill over in the repeated cycles, the modified sensors offered relatively poor repeatability. Among the two types of modifications, the Pd-modified sensor offered better response magnitude and transient characteristics (the response time and the recovery time) than the Ni-modified sensor. The underlying mechanism for such improvement has been also highlighted.