According to Encyclopedia Britannica , zeolites are described as a family of hydrated aluminosilicates that are characterized by their tetrahedral cage-like framework. These molecules are known for their characteristic ion exchange and adsorption properties. An image from the work of Pieter J. Smeets et al titled “Transition-Metal Ions in Zeolites: Coordination and Activation of Oxygen”, which was published in Inorganic Chemistry in 2010 has been included below as a visual of the microporous structure of various zeolites. The specific zeolites displayed are a few that are have current industrial applications. According to the source, the lines of the various structures displayed below are representative of oxygen atoms, and the corners are representative of either aluminum or silicon atoms. The various Roman numerals that can be seen on the structures below indicate various sites on the molecules that allow exchange of cations.
In their work, Smeets et al outline defining structural
characteristics of zeolites and provide functions and reactive behaviors of a
few zeolites in context of their applications. The article states that the size
of the pores, and the structure of a zeolite dictate the function of the
specific molecule. As a general example, various zeolites are used in
separation techniques. These zeolites are chosen based on the size of their
pores, also known as windows. Separation of molecules using these zeolites is
based solely on the sizes of the molecules in a mixture. Molecules that are
small enough to enter the zeolite structure do so and react with the zeolite, whereas,
any molecule too large is kept outside the structure.
Besides the aforementioned
applications, zeolites are being used for numerous practical applications,
ranging from water filters such as for swimming pools to petroleum refining. NASA
briefly explains the use of zeolites for the refinement of petroleum. The
general structure of zeolites is described as a natural sieve which allows for
the certain chemicals to be filtered out of a specific bulk material, a
characteristic that is utilized in petroleum processing. A space application of
these molecules includes the absorption and separation of CO2 and
water for portable life support systems. Other general applications of these
molecules that were mentioned in Britannica were synthetic blood clotting for
medical uses and filtration for the purpose of controlling pollution.
Over the
past years, zeolites have been gaining attention for their abilities to pull
metal ions from water and such materials. Zeolites function as ligands by
binding to metal ions. They make coordinate bonds with the appropriate metal
ions present, and essentially remove the metals from their original
environment. The end result of such an interaction is that the free metal ions
have created neutral complexes with the zeolite, and are no longer reactive
ions.
The chemical capabilities of these
molecules open up ideas for numerous beneficial applications, one being the
handling of nuclear wastes. Nuclear energy has long been known for immense
amounts of energy that can be produced in comparison to traditional methods of
energy production. Those against nuclear power plants and the use of nuclear
energy as a major energy provider for our societies stand on the harmful and
lethal effects of the waste produced as their support. According to “Solid
phase extraction-inductively coupled plasma spectroscopy for adsorption of
Co(II) and Ni(II) from radioactive wastewaters by natural and modified
zeolites,” a article that appeared in a 2011 publication (Vol 288) of Journal of Radioanalytical and Nuclear
Chemistry, Akbar Malekpour et al cited that cobalt (II) and nickel (II) are
two of the heavy-metals that are commonly found in nuclear waste. These heavy
metals carry significantly harmful effects to both the environment and human
health. This research group was successfully able to use clinoptilolite, a naturally
occurring zeolite, to remove these target metals from radioactive wastewater.
They then used a chemically modified version of the same zeolite to run the
same tests. It was concluded that the synthetic zeolite adsorbed the metal ions
even more than the natural one. The fact that clinoptilolite is an effective,
abundant, and low-cost resource that can remove such harmful by-products of
nuclear energy production opens the possibility of nuclear energy as a main
source of energy, making energy cheaper and available to more. Similarly,
Sharma et al outlines the successful extraction of thallium (IV) and europium
(III) using nanocrystalline mordentite (MOR) in the article “Sorption behavior
of nanocrystalline MOR type zeolitefor th(IV) and Eu(III) removal from aqueous
waste by batch treatment,” which was
published in the Journal of Colloid and
Interface Science in 2011. The synthetic MOR zeolite successfully extracted
the metals from solutions in the lab. Overall, the use zeolites will make the safe
production of nuclear energy since safe waste disposal is now possible.
