Facile Synthesis of Titania Nanowires via a Hot Filament Method and Conductometric Measurement of Their Response to Hydrogen Sulfide Gas

Abstract

Titania nanostructures are of increasing interest for a variety of applications, including photovoltaics, water splitting, and chemical sensing. Because of the photocatalytical properties of TiO₂, chemical processes that occur at its surface can be exploited for highly efficient nanodevices. A facile and fast synthesis route has been explored that is free of catalysts or templates. An environmental scanning electron microscopy (ESEM) system was employed to grow titania nanowires (NWs) in a water vapor atmosphere (∼1 mbar) and to monitor the growth in situ. In addition, the growth process was also demonstrated using a simple vacuum chamber. In both processes, a titanium filament was heated via the Joule effect and NWs were found to grow on its surface, as a result of thermal oxidation processes. A variety of nanostructures were observed across the filament, with morphologies changing with the wire temperature from the center to the end points. The longest NWs were obtained for temperatures between ∼730 °C and 810 °C. Typically, they have an approximate thickness of ∼300 nm and lengths of up to a few micrometers. Cross sections prepared by focused-ion-beam milling revealed the presence of a porous layer beneath the NW clusters. This indicates that the growth of NWs is driven by oxidation-induced stresses in the subsurface region of the Ti filament and by enhanced diffusion along grain boundaries. To demonstrate the potential of titania NWs grown via the hot filament method, single NW devices were fabricated and used for conductometric sensing of hydrogen sulfide (H₂S) gas. The NW electric resistance was found to decrease in the presence of H₂S. Its variation can be explained in terms of the surface depletion model.

Selective, sensitive, and reversible detection of H2S using Mo-doped ZnO nanowire network sensors

“…Various metal oxide semiconductors such as SnO 2 , Fe 2 O 3 , In 2 O 3 , Cu 2 O, WO 3 , TiO 2 have been previously explored as sensing materials for the detection of H 2 S. [9][10][11][12][38][39][40][41][42] Numerous published papers have reported incomplete recovery when purging with air aer H 2 S sensing, and hence, additional procedures such as UV irradiation or heating have been suggested to increase the recovery of the sensor. 43,44 This lack of recovery has also been a key issue in several ZnO gas sensors, which is again conrmed by the present results of a pure ZnO NW sensor.…”

Exploiting Free-Standing p-CuO/n-TiO2 Nanochannels as a Flexible Gas Sensor with High Sensitivity for H2S at Room Temperature

“…Table S1 shows the response of the CuO/TiO 2 nanochannel structure and a comparison with other high-temperature gas sensors based on other TiO 2 nanostructures, i.e., nanotubes, 38 nanoplates, 39 nanowires, 40 films, 41 and core−shell nanoparticles. 42 Benefitting from the both-end-open nanochannel structure and CuO/TiO 2 interfaces, the as-proposed sensing device in this study exhibits a satisfactory sensing response at room temperature, and its sensing performance is comparable to that of sensing devices operating at high temperatures.…”

A highly selective fluorescent probe for sulfide ions based on aggregation of Cu nanocluster induced emission enhancement

“…11 It occurs naturally in crude petroleum, coal mines, and natural gas industries; in addition, H 2 S is generated by human activities, such as sewage plants and petroleum refining. 12 Excessive exposure to H 2 S can lead to blood poisoning and even death. 13 Accordingly, to ensure the safety of persons, it is highly desirable to develop selective and sensitive analytical methods for detecting H 2 S in various systems.…”