Effect of synthesis conditions on the structure and sorption properties of films based on mesoporous tin dioxide

Abstract

We have conducted a comparative study of the synthesis conditions for mesoporous materials and films based on tin dioxide in the presence of different types of templates, and we have studied their thermal stability and sorption properties. We demonstrate the advantage of using alcoholic reaction media and nonionic templates (triblock copolymers to obtain thin films of mesoporous SnO 2 with relatively high parameters for the porous structure (V meso = 0.15 cm 3 /g, S BET = 147 m 2 /g) and cassiterite crystallite sizes down to 2.7 nm, significantly smaller than the thickness of the walls.The increased interest in studying oxide semiconductor materials over the past decade is because of their promising catalytic, photocatalytic, and optical (in particular, luminescent, photochromic, etc.) properties. Tin dioxide is a wide-gap n-type semiconductor and is used mainly as a catalyst for oxidation of organic compounds, the working material for sensitive elements of conductimetric gas sensors mainly based on reducing gases H 2 , CO, and hydrocarbons [1,2], and also is a widely used material for electrodes in rechargeable lithium batteries [3]. Designing tin dioxide-based high-sensitivity materials for chemical sensors requires development and perfecting of reproducible methods for obtaining thermally stable films (thin layers) with an extended surface on different types of substrates. The sol-gel method and also the template synthesis method using surfactants hold a special place among the methods making it possible to substantially increase the specific surface area of tin dioxide. Moreover, synthesis of mesoporous oxides is associated with a number of difficulties connected with too rapid hydrolysis of precursors, crystallization of the oxides themselves (on the walls of mesoporous materials), and consequently breakdown of the mesostructure during detemplating. Among synthetic approaches making it possible to improve the stability and adsorption characteristics of mesoporous materials, we should single out the use of nonaqueous reaction media and inhibition of crystallization by introducing other hydroxides into the gel. The method for synthesizing mesostructural materials from alcoholic media using metal alkoxides makes it possible to obtain multicomponent materials with a homogeneous distribution of components over the entire volume, and to better control the process in the gel formation stage.The aim of this work was to develop and identify the conditions and characteristic features of a reproducible template method for obtaining thermally stable thin films based on mesoporous tin dioxide as working elements of chemical sensors, to determine the effect of various factors (nature of the template, composition of the reaction medium, aging and detemplating conditions, etc.) on their structural and sorption characteristics and thermal stability.As the basis for the method, we chose a procedure similar to that described in [4]. Anhydrous tin chloride was added to a solution of surfactant (Pluronic-127 or Pluronic-123) in...

Engineering metal oxide nanostructures for the fiber optic sensor platform

“…In the wet chemical synthesis of the precursor, Pluronic F-127, a triblock copolymer was used as the structure direct agent for the nano-engineering of SnO 2 [15,[36][37][38]. By controlling its mole fraction, the porosity of the SnO 2 is controlled on the tens-of-nanometers scale to tailor the refractive index of the nano-material.…”

“…The increase of the surface area of metal oxide nanostructures enhances the interactions between the oxide and the target species. The typical width of the gas modulated space charge region is between 1 and 10nm; therefore, nanostructuring on the scale comparable with this width provides high ratios between the modulated and non-modulated regions, allowing more effective utilization of the sensing material in comparison with thin film devices where the interacting volume is just the modulated width of its geometric surface [5,12,14,15]. Lastly, the controlled nanostructuring on the tens of nanometer scale allows the tuning of the dielectric constants of metal oxides at will while maintaining sufficient scale separation between the dimensions of the nano features and the typical operating wavelengths (visible and near infrared, NIR) [13].…”

Effect of synthesis and doping conditions on the physical and chemical properties of mesoporous tin dioxide

“…Inhibition of cassiterite crystallization (which can be tracked based on the change in the half-width of the reflections at 2q = 26.4°, 33.8°, 51.8°, etc. on the diffraction patterns) is a necessary condition for preservation not only of the ordering but also the good adsorption characteristics of such materials [7]. We observed such inhibition to the greatest extent in the case when the materials based on tin oxide were doped with In and Si ions (Fig.…”

“…Layers of mesoporous tin dioxide were formed from a film-forming solution in the presence of a nonionic surfactant, the poly(alkylene oxide) block copolymer Pluronic-127, as follows: the surfactant (8-10 wt.%) was dissolved with stirring in ethanol, anhydrous SnCl 4 was added (template/Sn » 0.008) and homogenized at 30°C [7]. The materials were doped by adding alcohol-soluble compounds ((C 2 H 5 O) 4 Si, InCl 3 , C 12 H 28 O 4 Ti, (NH 4 ) 2 Ce(NO 3 ) 6 , Ce(NO 3 ) 3 ·6H 2 O, FeCl 3 , VCl 3 , as 0.5-30 mole %) to the solution immediately before application of the solution to the substrate.…”

3D sub-wavelength refractive index adjusted metal oxides for applications in optical sensing

“…The surface area of nanostructured films are much higher. And, in general, the sensory modulation depth due to charge transfer interaction are on the order of 1-10nm, therefore structuring on this scale allows for the full or near-full modulation of the sensory material in response to an analyte [2,15,16]. Whereas, in thin film coatings only the geometric surface is modulated.…”