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Materials Science in Additive Manufacturing Emerging 3D-printed zeolitic gas adsorbents

Organic materials are also utilized as binding agents due to binderless NaX zeolite monoliths. However, this technique
their ability of forming strong bonds between zeolite particles was time-consuming and required extensive optimization
and water solubility, allowing for easy binder removal during to coordinate the various components, as shown in
calcination. Methylcellulose is a commonly used organic Figure 10. In addition, it only resulted in a single binderless
[27]
plasticizing binder. It can promote both the gelation and zeolite and has not been applied to other zeolite families .
shear thinning behavior of zeolite mixtures because it can Lawson et al. developed a novel 3D printing approach
form a network of hydrogen bonds in the presence of water. for producing binderless zeolite monoliths with sacrificial
This network can increase the viscosity of the mixture and biopolymers gelatin and pectin. Those biopolymers were
promote gelation. However, under shear stress, the hydrogen found to be fully removed by calcination at high temperatures,
bonds can break, causing the viscosity to decrease and resulting in 100% pure zeolite structures without any
allowing for easier extrusion through the printer nozzle [106] . residual binder material. Moreover, calcining zeolites
Another type of organic material, polyvinyl alcohol (PVA), is alongside gelatin and pectin led to the narrowing of the pore
often added as a co-binder that provides additional binding windows and gave rise to enhanced adsorption capacities.
strength and stability to the printed structure. PVA also has The resulting binderless zeolite monoliths demonstrate a
a high degree of flexibility, which can help to reduce the versatile means of 3D printing binderless zeolites for the first
likelihood of cracking or deformation during the printing time, with several advantages over traditional methods, such
process. In addition to its binding properties, PVA can act as greater geometric control during 3D printing and lower
as a pore-forming agent in the printed structure. Controlling manufacturing costs compared to hydraulic extrusion .
[94]
the concentration and distribution of PVA in the printed
material makes it possible to create specific pore structures 3.1.2. Polymer-based type
within the printed zeolitic gas adsorbents [107] .
Polymer-zeolitic gas adsorbents are composed of a polymer
Recent research has focused on the exploration of matrix with dispersed zeolite particles. Such hybrid materials
alternative additives that can be entirely removed by the combine the properties of both polymers and zeolites,
post-processing treatment for the fabrication of binderless resulting in materials that have enhanced mechanical
zeolitic gas adsorbents. It is because that the additives, such strength. This is because incorporating zeolite particles
as clay binders, cannot be easily removed after printing into the polymer matrix gives the composite adsorbents
because they do not decompose at low temperatures. This a higher surface area for gas adsorption compared to
makes achieving 100% pure zeolite structures difficult, traditional zeolite monoliths [108] . In addition, the polymer
which is necessary for many applications. Wang et al. matrix provides a synergistic effect that enhances the
adopted a solvothermal bridging technique to create adsorption properties of the zeolite particles. This is

Figure 10. Schematic of 3D printing procedure of binderless zeolite. Reprinted with permission from Wang et al. .
[27]

Volume 2 Issue 4 (2023) 10 https://doi.org/10.36922/msam.1880