Zeolite coated ATR crystals for new applications in FTIR-ATR spectroscopy

Abstract

Thin silicalite-1 films were grown on ATR crystals and used for detection of low amounts of organic molecules in a gas flow by FTIR spectroscopy.Molecular sieves have a number of unique properties that make them interesting in various application areas. 1,2 They are inorganic, microporous materials with large surface areas and well-defined channel systems due to the fact that they are crystalline. 3 Molecular sieves are currently used in large quantities as shape-selective catalysts, adsorbents and ion-exchangers. Selective and strong adsorption render molecular sieves interesting in sensors for detection of low concentrations of molecules in gas or liquid phase. A limitation in novel as well as in several of the established applications of molecular sieves is the lack of knowledge of the adsorption and transport phenomena determining the performance of the materials. Despite the fact that the number of studies devoted to the adsorption of various molecules in zeolites is numerous, few investigations exist where competitive adsorption from mixtures has been studied. Moreover, the reports focusing on kinetic aspects of adsorption, particularly competitive adsorption, are few. This is obviously related to the fact that such studies require well-defined materials, but also to a lack of simple analytical techniques making such studies possible.In the last decade total internal reflection (TIR) spectroscopy using optical fibers and ATR (Attenuated Total Reflection) elements has become one of the fastest growing sensor applications within modern analytical chemistry. [4][5][6] In the ATR technique, the IR beam is totally reflected inside a waveguide. At each reflection an evanescent field is created at the surface of the waveguide. This field is used in ATR spectroscopy to probe the near vicinity of the waveguide. The ATR-technique is useful for investigation of interfacial phenomena in situ. Coated internal reflection elements (IRE) are especially interesting and have been used in various applications. 7,8 A number of studies report the use of polymer coated IREs for detection of organic pollutants and in particular chlorinated hydrocarbons in water. [9][10][11] It has been demonstrated that the thin film serves as an extractor phase enriching the analyte in close vicinity to the sensor surface. Such studies also suggest that the use of a solid film with high surface area, with maximum adsorbent/IRE contact, is vital. However, applications for various film/IRE combinations are really limited by the ability of depositing a thin, uniform, self-supporting film upon the IRE.A method employing seeding has been developed in our laboratory for the synthesis of ultrathin as well as thick zeolite films. 12 The method is very flexible, not very surface sensitive, and allows for reproducible preparation of films of desired thickness and crystal orientation using a number of zeolite-substrate combinations. [13][14][15] The objective of the work described in the present communication is to synthesize and characterize thin silical...

Nanozeolites: Synthesis, Crystallization Mechanism, and Applications

“…A silicon internal reflection element was coated with a silicalite-1 film using nanosized seeds and tested in the detection of organic molecules in a gas flow. 197 The promising results suggest that new applications in FTIR-ATR spectroscopy of zeolite-modified ATR elements can be envisaged.…”

Attenuated Total ReflectionFourier Transform Infrared Spectroscopy

“…(59) Zeolites have been shown to allow the detection of gaseous analytes using the ATR technique. (60,61) Encyclopedia of Analytical Chemistry, Online …”

Advances in Infrared Spectroscopy of Catalytic Solid–Liquid Interfaces: The Case of Selective Alcohol Oxidation

“…Classic experiments of for example CO [20] and pyridine [21,22] adsorption can be then performed in a similar way to more common parent transmission and diffuse reflectance adsorption studies. The advantage of this geometry is that the particulate film will sensibly enhance the density of molecules at the interface which can be probed by the infrared radiation [23]. This is extremely important for studies of solid catalysts.…”