Effect of Low Temperature Gel Aging on Zeolite LTA Particle Size and Morphology in Template-Free Hydrogel Process

Effect of low temperature gel aging on zeolite LTA particle size and morphology in template-free hydrogel process

Afsaneh Khosravi, Julia A. King, Alexander Maltagliati, Tony Nguyen, Mary Laura Lind^*

Arizona State University, Tempe, AZ 85287, USA

* Corresponding author. Tel.: +1 480-727-8613; Fax: +1 480-727-9321

E-mail address: mllind@asu.edu

Decreasing the size of zeolite particles increases the external surface area available for interaction and therefore extensive research has been done to investigate decreasing zeolite size. Template-based syntheses are the most common way to synthesize nanosized zeolites. However, this method has major drawbacks including the use of expensive and environmentally unfriendly organic chemicals as well as irreversible aggregation of particles due to the calcination in the removal of the template. Preliminary heat treatment of gel at temperatures lower than their crystallization temperatures (a process termed ‘aging') can be an effective and environmentally friendly method to produce nanosized zeolite particles with and narrow size distribution. To best of our knowledge, there is no comprehensive report on physical insight and understanding of the effect of aging of zeolite LTA gel at different temperatures and for different times.

In this work, we extensively investigated the effect of different aging temperatures (-8ēC to 40 ēC) and aging times (2 days to 180 days) in a template-free process on crystal size, synthesis yield, and morphology of zeolite LTA by emphasizing the understanding of the physical mechanism of aging. We also report a variety of characterizations of the particles through scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDAX).

Our results show that while two weeks of aging the gel at room temperature decreases the size of particles 52.13% in comparison with non-aged ones, the same gel aging period at -8 ēC decreases the size of particles 93.62% in comparison with non-aged ones. Furthermore, although lengthening the aging time decreases particle size significantly, there is a certain point where increasing the aging time does not have a significant effect on particle size. Very long aging times (more than two months) changes the morphology of the zeolite.