Molecular Sieve Based Chemical Sensors

Abstract

Molecular sieves, are attractive materials for discriminating chemical sensors. These microporous metal oxides offer shape selective adsorption as well as chemical and thermal stability. Molecular sieves have shown promise in SAW devices, however, these sensors rely only on a weight change upon adsorption of target molecules. We have developed a molecular sieve based capacitance type chemical sensor. Such a device should discriminate between molecules of similar size and shape because the signature change depends on the polarity of the adsorbate which in turn affects the dielectric properties of the molecular sieve. In this paper we describe the deposition of AIPO4 and MeAPO molecular sieve thin films on titanium nitride coated silicon wafers by laser ablation. A subsequent hydrothermal treatment followed by a Pd/Au coating and standard microlithography techniques generate the capacitors. The results for capacitance measurements in the presence of CO2, CO, NO, N2, O2, H2O and toluene indicate clear differences in selectivity between small, medium and large pore molecular sieves.

Preparation of Oriented Zeolite UTD-1 Membranes via Pulsed Laser Ablation

“…Thin Film Preparation. We have previously reported the laser ablation of various aluminophosphate molecular sieves including AlPO 4 and MeAPO materials (where Me = Co, Fe, Mn, Mg, V) onto different substrates. ,− More recently we extended this method to silicate-based zeolites which turned out to have special requirements (vide infra). The high silica UTD-1 is of particular interest because of the ultra-large pores and good thermal stability.…”

“…Pulsed laser ablation of the UTD-1 target with a laser energy of 100 mJ/pulse and a repetition rate of 10 Hz results in the generation of a bright blue plume. To deposit well-adhered UTD-1 material from this plume the substrate temperature, background pressure, and deposition time must be decreased from that used for the MeAPO systems we previously studied. − Using laser energies similar to that used to deposit the phosphate type molecular sieves results in comparatively faster deposition rates. Additionally, UTD-1 films are adhered with lower substrate temperatures (160 vs >250 °C).…”

“…Whatever the nature of these UTD-1 fragments they can be reorganized, thereby acting as seed layers or nucleation sites for recrystallization of the film. In the case of laser-ablated AlPO 4 and MeAPO materials, a post hydrothermal treatment in a synthesis gel or exposure to vapors of a template solution enhances the crystallinity of the PLD films . Therefore UTD-1 films laser deposited on silicon were placed in a Teflon-lined Parr reactor containing a UTD-1 synthesis gel at 175 °C for 18, 24, and 72 h under static conditions.…”

“…We have reported a method for the preparation of molecular sieve thin films using pulsed laser ablation. − Recently, we obtained for the first time an oriented film of zeolite UTD-1 by this method . In this process a high-intensity excimer laser beam strikes a pressed zeolite pellet that generates a plume comprised of fragments of the target that deposit on a temperature-controlled substrate.…”

Zeolite Coatings on Three-Dimensional Objects via Laser Ablation

“…We have recently shown that pulsed laser deposition (PLD) can be used to generate thin films of zeolite molecular sieves. − In some cases highly oriented zeolite films may be prepared. , The application of such zeolite films as membranes for catalysis or separations might require a nonplanar configuration. However, there are relatively few examples of three-dimensional objects that have been coated with zeolite films.…”