LTA Zeolite Monolayers via the Langmuir-Blodgett Technique

Zeolite thin films and membranes are currently a promising technology for pervaporation, gas separation and water purification. The main drawback with these technologies is that the synthesis is not consistent leading to varied and unreproducible results. The Langmuir-Blodgett technique is a robust method for transferring monolayers of molecules or crystals to a solid substrate. By measuring the surface pressure and controlling the area, reliable results can be achieved by transferring monolayers to different solid substrates. It has been shown previously that various types of zeolites can be functionalized and dispersed on the top of water. This is done by using an alcohol to form a hydrophobic coating on the surface of zeolite. The Langmuir-Blodgett can be used to create thin, compact films of zeolites for synthesizing and growing zeolite films. For the first reported time, cubic LTA Zeolites monolayers have been assembled with the Langmuir-Blodgett technique with multiple solvents and different sizes of zeolites. These films were characterized with Scanning Electron Microscopy and Pressure-Area Isotherms generated from the Langmuir-Blodgett. It was found that linoleic acid is a required addition to the zeolite dispersions to protect the mechanical stability during agitation. Without this addition, the LTA zeolites are broken apart and lose their characteristic cubic structure. This effect is discussed and a theory is presented that the interparticle interactions of the long alkane chain of the linoleic acid help reduce the shear stress on the individual zeolite particles, thus preventing them from being broken. The effect of size of the zeolites on the monolayer formation was also discussed. There seemed to be little correlation between the monolayer quality and formation as size was changed. However, to optimize the process, different concentrations and target pressures are needed. Lastly, the effect of the solvent was explored and it was found that there is a different between monolayer formations for different solvents likely due to differing interparticle interactions. Overall, LTA zeolites were successfully fabricated and the important factors to consider are the zeolite size, the solvent, and the amount of surfactant stabilizer added.