Synthesis of TiO2-(B) Nanobelts for Acetone Sensing

Abstract

Titanium dioxide nanobelts were prepared via the alkali-hydrothermal method for application in chemical gas sensing. The formation process of TiO₂-(B) nanobelts and their sensing properties were investigated in detail. FE-SEM was used to study the surface of the obtained structures. The TEM and XRD analyses show that the prepared TiO₂ nanobelts are in the monoclinic phase. Furthermore, TEM shows the formation of porous-like morphology due to crystal defects in the TiO₂-(B) nanobelts. The gas-sensing performance of the structure toward various concentrations of hydrogen, ethanol, acetone, nitrogen dioxide, and methane gases was studied at a temperature range between 100 and 500 °C. The fabricated sensor shows a high response toward acetone at a relatively low working temperature (150 °C), which is important for the development of low-power-consumption functional devices. Moreover, the obtained results indicate that monoclinic TiO₂-B is a promising material for applications in chemo-resistive gas detectors.

Keywords: TiO2 nanobelts; acetone detection; chemical sensing; hydrothermal synthesis.

Figure 1

The crystal structures of TiO₂: (a) anatase, (b) rutile, (c) brookite, and (d) monoclinic. Reprinted with permission from [22].

Figure 2

Schematic of the fabricated conductometric chemical gas sensor and the electrodes.

Figure 3

XRD patterns of samples: (a) intermediate H₂Ti₃O₇, (b) TiO₂-(B), and (c) Raman spectra of the prepared H₂Ti₃O₇ at 200 °C before calcination. B—TiO₂-(B); ✓—H₂Ti₃O₇; ●—Na₂Ti₃O₇; ■—Na₂Ti₄O₉; —Na₂Ti₉O₁₉. The oridinal Ramana spectra is shown in black and the fitted Ramana spectra is shown in Red. Whle other are the peak fitting corresponding to fitted spectra (Red).

Figure 4

Schematic formation of (a) sodium titanate (Na₂Ti₃O₇) nanosheets, (b) hydrogen titanate (H₂Ti₃O₇) nanobelts, and (c) TiO₂ nanobelts.

Figure 5

FE-SEM of (a) H₂Ti₃O₇ prepared in the autoclave at 200 °C, and (b) TiO₂-(B) annealed at 500 °C.

Figure 6

CTEM images: (a) H₂Ti₃O₇, (b) TiO₂-(B), and (e) formation of pore-like structure in TiO₂-(B); (c) HRTEM image of TiO₂-(B) with insert showing (101) planes; and (d) SAED of TiO₂-(B); (f) magnified image of (c).

Figure 7

(a) CTEM of several overlapping TiO₂-(B) nanobelts; EDS analysis of TiO₂-(B) nanobelts. The maps show the (c) O and (d) Ti distribution on the nanobelts corresponding to the HAADF image of (b).

Figure 8

Electrical conductance variation of the fabricated sensors at different working temperatures under 40 RH% conditions.

Figure 9

Response of the TiO₂ nanobelts (TiO₂-8n) to 10 ppm C₃H₆O at different working temperatures in 40% RH conditions.

Figure 10

Dynamic response–recovery plot of the TiO₂-8 sensor toward 10, 25, and 50 ppm of C₃H₆O at the working temperature of 150 °C.

Figure 11

(a) Electrical band bending due to the adsorption of oxygen species to the TiO₂ nanobelt surface (O₂⁻_ads, O⁻_ads, O²⁻_ads), and (b) reduction in the space charge region resulting in a decrement in electrical resistance due to the interaction between acetone molecules and TiO₂ surface. E_c is the conduction band, E_v is the valence band, and E_f is the Fermi level.

Figure 12

Variation in the sensor’s response toward different concentrations of C₃H₆O at the working temperature of 150 °C.

Figure 13

(a) The plot of response vs. concentration value of the sensor (TiO₂-8n) toward C₃H₆O at 150 °C. (b) Selectivity of the TiO₂-8n sensor toward the tested gases (10 ppm C₃H₆O, 10 ppm C₂H₅OH, 100 ppm H₂, 100 ppm CH₄, and 1 ppm NO₂) in 40 RH% humidity air at the operating temperature of 150 °C.