TiO2-Based Nanomaterials for Gas Sensing—Influence of Anatase and Rutile Contributions

Abstract

The paper deals with application of three nanomaterial systems: undoped TiO2, chromium-doped TiO2:Cr and TiO2-SnO2 synthesized by flame spray synthesis (FSS) technique for hydrogen sensing. The emphasis is put on the role of anatase and rutile polymorphic forms of TiO2 in enhancing sensitivity towards reducing gases. Anatase-to-rutile transformation is achieved by annealing of undoped TiO2 in air at 700 °C, specific Cr doping and modification with SnO2. Undoped TiO2 and TiO2-SnO2 exhibit n-type behaviour and while TiO2: 5 at.% Cr is a p-type semiconductor. X-ray diffraction (XRD) has been applied to determine anatase-to-rutile weight ratio as well as anatase and rutile crystal size. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to characterize the structure and morphological parameters. Optical reflectometry enabled to find and compare the band gaps E g of anatase and rutile predominated compositions. Electrical properties, i.e. the electrical conductivity and values of constant phase element (CPE), have been established on the basis of impedance spectroscopy. Dynamic responses of the electrical resistance as a function of hydrogen concentration revealed that predominance of rutile in anatase/rutile mixture is beneficial for gas sensing. Partial transformation to rutile in all three material systems under study resulted in an increased sensitivity towards hydrogen. It is proposed that this effect can be explained in a similar way as in photocatalysis, i.e. by specific band alignment and electron transfer from rutile to anatase to facilitate oxygen preadsorption on the surface of anatase grains.

One-step preparation of TiO2particles with controllable phase and morphology by plasma electrolysis

“…When the concentration is higher than 0.4 mol L À1 , the current density changes violently in the range of 0.85-1.30 A cm À2 . Earlier studies 7,8 have reported that the transformation temperature from anatase to rutile is in the range of 700-900 C. It means that when the supplied energy is high enough, anatase-TiO 2 can be transformed into rutile-TiO 2 . Combining the results of current density-time curves (Fig.…”

“…Rutile is the stable phase, whereas anatase is metastable and tends to transform into rutile upon heating. 7,8 The rutile structure TiO 2 (rutile-TiO 2 ) has even more applications, such as a photocatalytic material, white pigment, in cosmetics and as an electrode material for lithium-ion batteries. [9][10][11] In addition, the mixed phase structures have been researched for some new properties and synergetic effects due to the interface lattice mismatch between the two phases.…”

“…[9][10][11] In addition, the mixed phase structures have been researched for some new properties and synergetic effects due to the interface lattice mismatch between the two phases. 7 In order to further improve the properties of the TiO 2 and broaden the elds of its application, preparation of TiO 2 with nano/micro structure has been received considerable attention especially in recent years. Many methods have been proposed for the synthesis of special structured TiO 2 , such as hydrothermal method, [12][13][14][15] hydrolysis method, 10,16,17 mechanochemical synthesis, 18,19 chemical vapor synthesis 20 and sol-gel method.…”

Component‐Tunable Rutile‐Anatase TiO2/Reduced Graphene Oxide Nanocomposites for Enhancement of Electrocatalytic Oxygen Evolution

“…So, an electron transfer mechanism is suggested (Figure ). The band gap of rutile and anatase TiO 2 is 3.0 eV and 3.2 eV, respectively ,. While, the energy of conduction band (bottom) of rutile is higher than that of anatase.…”

Enhanced photovoltaic properties of perovskite solar cells by TiO 2 homogeneous hybrid structure

“…The peak maximum of TiO 2 NSs films occurs at approximately 370 nm and the films have no significant absorption for visible light due to the large band gap of TiO 2 [22,23]. However, after coating with MAPbI 3 , the TiO 2 NSs/MAPbI 3 films present excellent absorption capacity from 350 to 800 nm, and the absorption intensity increased substantially.…”