Fabrication of TiO2 nanofibers based sensors for enhanced CH4 performance induced by notable surface area and acid treatment

Abstract

We report on the notable surface area and gas sensing properties of TiO2 nanofibers synthesized following a microwave assisted hydrothermal method followed by washing with various concentrations of Hydrochloric acid (HCl) and distilled water (DW). The sample washed with DW only had narrow nanofibers in diameter. Structural analyses showed that the TiO2 nanofibers were made of 55% of the anatase phase, while the 45% was associated to the rutile phase. Moreover, at higher HCl concentration, an increased crystallite size and nanofibers diameter were observed from the X-ray diffraction and scanning electron microscopy analyses, respectively. A remarkable increase in surface area of 1375.238 m2/g was observed with a change in morphology from nanoparticles to nanofibers (i.e. the sample washed with 1.0 M HCl). The gas sensing properties, such as response, sensitivity and selectivity were tested towards CH4, NH3, CO and NO2 gases at different operating temperatures. The TiO2 nanofibers washed with 1.0 M HCl presented higher selectivity and sensitivity (0.62 ppm−1) towards CH4 gas at 23 °C. This was attributed to the exceptionally high surface area and crystallinity provided by the one dimensional nanofibers. The improved sensitivity and selectivity at room temperature for the 1.0 M HCl treated sample suggested that it could be applied as a low-power consumption CH4 gas sensor. The gas sensing mechanism is also discussed in detail.