p-/n-Type Switching in the Ag/BTO/TiO₂ Nanocomposite as a Gas Sensor toward Ethanol, Liquefied Petroleum Gas, and Ammonia

Abstract

A novel Ag/BTO/TiO 2 nanocomposite was prepared using chemical reduction and sol−gel techniques followed by sintering at ∼950 °C to grow rutile TiO 2 and remove organic materials and hydroxyl groups. The structural, optical, morphological, dielectric, and gas-sensing properties were investigated using X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet−visible spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and inductance, capacitance, and resistance meter, respectively. The surface plasmon resonance peak of Ag was observed at 428 nm, and the absorption edge of the Ag/BTO/TiO 2 nanocomposite was observed at 235 nm, with an energy bandgap of 5.42 eV. The dielectric constant is lower at 25 °C and becomes highest at 350 °C and low frequency. The percentage response is better toward ammonia than ethanol and liquefied petroleum gas (LPG) at 25 °C, while it is greater, ∼87%, for LPG at a higher temperature. The p-/n-type switching and vice versa were recorded in the whole gas-sensing measurement. During response− recovery time, the device performed as n type for ethanol and ammonia and p type for LPG, with a very fast response time of ∼4 s for all gases. The recovery time for ethanol was achieved at 20−25 s, while for LPG and ammonia, it was ∼60 s. Moreover, the negative and positive activation energies also confirm the switching behavior in the novel Ag/BTO/TiO 2 nanocomposite.

Selectivity of an Ag/BTO-Based Nanocomposite as a Gas Sensor Between NO2 and SO2 Gases

“…The structural properties of the Ag/BTO/TiO 2 nanocomposites were characterized and analyzed by Paul et al using X-ray diffraction, as shown in Figure , by comparing the visible peaks with the corresponding JCPDS files of anatase TiO 2 (21-1272), rutile TiO 2 (21-1276), brookite TiO 2 (29-1360), Ag (04-0783), BTO (05-0626), and BaTi 5 O 11 (35-0805).…”

“…■ EXPERIMENTAL SECTION Synthesis of Ag/BTO/TiO 2 Nanocomposites. The Ag/BTO/ TiO 2 nanocomposite was prepared by Paul et al 22 Ag nanoparticles as a colloidal solution was prepared by chemical reduction using tyrosine as a capping agent. 23,24 The colloidal solution was then added along with commercial grade BTO from Sigma-Aldrich during the sol−gel synthesis of TiO 2 .…”

“…Device Fabrication. The as-prepared Ag/BTO/TiO 2 nanocomposite from Paul et al 22 was utilized for this experiment. The parallel plate capacitor device, as illustrated in Figure 1(a), was prepared from the Ag/BTO/TiO 2 nanocomposite pressed into a 0.4 mm thick pellet using a hydraulic press under 1000 psi for 5 min, painted with silver paste on both faces and with copper wires attached to both.…”

“…■ RESULTS AND DISCUSSION Structural Properties. The structural properties of the Ag/BTO/TiO 2 nanocomposites were characterized and analyzed by Paul et al 22 Morphological Properties. Surface morphology was analyzed from scanning electron microscopy, as shown in Figure 3(a), at 2080× magnification and the inset (b) at 22,100× magnification of Ag/BTO/TiO 2 , where crystal growth of TiO 2 and BTO was observed.…”

“…Studies by Zeng et al, Thangamani et al, and Izu et al have been done on various TiO 2 nanomaterials for SO 2 gas sensing, and Zhang et al tested for selectivity of SO 2 among other gases like SOF 2 , SO 2 F 2 , and SF 6 . Comprehensive studies on diverse TiO 2 and BaTiO 3 (BTO) configurations, including single/multiphase forms, thin film composites, core–shell designs, nanocomposites, nanorods, nanofibers, and nanobelts, to discern their gas-sensing potential were conducted on both reductive and oxidative gases, enriching gas-sensing technology insights. − Paul et al prepared a novel Ag/BTO/TiO 2 nanocomposite using sol–gel synthesis and characterized its structural properties using X-ray diffraction (XRD), morphological and elemental properties using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy, and optical properties using ultraviolet–visible (UV–visible) and Fourier transform infrared (FTIR) spectroscopies. In this article, sensitivity and selectivity toward NO 2 and SO 2 for the Ag/BTO/TiO 2 nanocomposite were explored by the authors.…”