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Colloidal stabilization of LTA type zeolites in ethanolwater mixtures

Gözcü, Oğuz
Zeolites are promising materials for various applications because of their uniform pores at the nano- and micron- scales as well as their chemical and surface properties. In recent years, fabrication of the complex shape zeolites and nano-sized zeolites has been attracting attention to increase the efficiency in zeolite applications. Since conventional zeolite production techniques are not suitable for the fabrication of such zeolites, the use of techniques such as electrospinning, electrophoretic deposition, and robocasting has been suggested. Those techniques generally require storage, transportation, or dispersion of the zeolite powders in a pure or mixed liquid media often with a carrier polymer, so the dispersion characteristics of zeolites in liquid media are critical for such processes. However, there are only a few studies in literature discussing the stabilization of zeolite powders. Besides, the stabilization of zeolites in mixed solvents and the presence of polymers is not a trivial task. The aim of this study is, therefore, to investigate the dispersion characteristic of zeolites in mixed solvents and discuss the applicability of the available stabilization techniques for zeolite powders in mixed solvents with various concentrations, and in the presence of polymeric carriers. To this end, common LTA zeolites were used, and its dispersion behavior was investigated in ethanol-water mixtures with various concentrations (30:70, 40:60, and 50:50 wt%). Even though zeolite powders were stable in water-rich solutions, increasing ethanol concentrations required the use of additives for dispersion of zeolite powders. Applicability of electrostatic and steric/electrosteric stabilization mechanisms was discussed, and the use of steric/electrosteric stabilization with non-ionic additives was preferred in order to prevent the changes in the chemical structure of zeolites in ionic solutions. The effects of various additives were investigated using a sedimentation test, zeta potential measurements, and ATR-FTIR analysis. High molecular weight PVP was used as a carrier polymer, which worsened the stability of zeolite powders. The rate of LTA zeolite sedimentation in the presence of carrier polymer was slowed down using dispersants. The effect of such an improvement was also demonstrated with the change in dispersion quality of zeolite films produced by spin coating of PVP containing mixed solvent zeolite suspensions.