(14e) 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 (-8ºC to 40 ºC) 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 ºC 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.