SrTiO₃–TiO₂ Heterostructured Nanotube Arrays for Ultrafast Ethanol Sensing

Abstract

Diverse metal oxide semiconductors have bloomed in chemical sensing applications providing opportunities and challenges. In this work, SrTiO 3 −TiO 2 heterostructured nanotube arrays were well designed via the electrochemical synthesis of TiO 2 nanotubes, followed by a facile one-step hydrothermal route by varying the amount of Sr(OH) 2 •8H 2 O precursor (0.25−25 mM) to grow different quantities of SrTiO 3 on TiO 2 nanotubes. The crystalline nature, morphology, and synthesis mechanism of the nanotube array were fully elucidated. Vertically aligned SrTiO 3 − TiO 2 heterostructured nanotube arrays were then sandwiched between the Ti bottom electrode (substrate as well) and Au top electrode to fabricate the metal−insulator−metal type sensors. SrTiO 3 −TiO 2 nanotube sensors exhibited ethanol-selective behavior where the highly defective SrTiO 3 layer acted as the main sensitive material that interacted with target species like ethanol. The SrTiO 3 −TiO 2 heterostructured nanotube array sensor synthesized with 0.25 mM Sr(OH) 2 precursor exhibited an excellent response magnitude (R a /R g ) of ∼556 with an ultrafast response time of 0.4 s toward 50 ppm ethanol at an operating temperature of 150 °C. Moreover, the sensor exhibits excellent stability, a low detection limit of 2.94 ppb, and good selectivity. All the SrTiO 3 −TiO 2 heterostructured nanotube array sensors showed promising humidity-tolerant behavior, and negligible change in response was obtained in the presence of 80% humid ambient air. The mechanism behind the modulated VOC sensing characteristics was explained with the comprehensive effects of the larger specific surface area, high surface defects, and modulated oxygen vacancies coming from the SrTiO 3 modification in the nanotube structures.

Nanostructural evolution of hydrothermally grown SrTiO3 perovskite and its implementation in gaseous phase detection of ethanol

“…Consequently, as the reaction time was increased from S1 to S4 samples more substitution of the ions was taken place due to the formation of more SrTiO 3 (XRD in figure 5(a)) leading towards higher number of defects in the resulting samples. A relatively higher concentration of oxygen vacancies in SrTiO 3 (XPS results in figure 5(d)) compared to TiO 2 helps in more gaseous interaction [19,21]. So, the overall VOC sensing properties were improved in SrTiO 3 as compared to the mixed phase TiO 2 .…”

“…The hydrothermal route is one of the best suitable alternatives which provides SrTiO 3 nanoforms with high specific surface area, improved crystallinity and controlled morphology [10,16,17]. Hydrothermal SrTiO 3 is usually prepared by reacting TiO 2 powder (rutile or anatase or amorphous titania) with a soluble Sr salt (SrCl 2 , Sr(NO 3 ) 2, Sr(OH) 2 ) [16][17][18][19][20][21]. The controlled morphology is achieved by modulating the temperature, reaction time, nature and concentration of the precursor and by changing the mineralizers or surfactants [1,7,10,16,21].…”

“…The functionality and reactivity of nanomaterials are highly dependent on their different dimensions. A wide variety of morphologies of SrTiO 3 like nanocubes, nanoparticles, nanosphere, nanofiber, nanotubes, etc are developed by hydrothermal treatment and employed in various applications such as solid oxide fuel cells, multiferroic materials, water splitting, catalysts, medical devices, and photonic devices [6,7,[18][19][20][21]. Ha et al reported morphology-controlled SrTiO 3 /TiO 2 nanocube, nanoparticle, nanosphere, and nanofiber like heterostructures, by facile hydrothermal process and examined for photocatalytic performance.…”

Polar Perturbations in Functional Oxide Heterostructures

“…[406] In addition, various types of chemical sensors based on complex oxide heterostructures have been reported including pH sensors, [407] ozone sensors, [408] and ethanol sensors. [409] Chemical reactions and the linked charge transfer mechanisms have been widely used for conventional sensing applications. To achieve high sensitivity, the sensing materials have been designed to represent rough surface or 3D structures with a large surface-to-volume ratio.…”

“…[ 406 ] In addition, various types of chemical sensors based on complex oxide heterostructures have been reported including pH sensors, [ 407 ] ozone sensors, [ 408 ] and ethanol sensors. [ 409 ]…”