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

such as the binder content, sintering strategy, and powder
characteristics, affecting the geometries and mechanical
properties of the final products . The feeding process of
[87]
SLS is similar to that of binder jetting. SLS employs a laser
which is only sufficiently strong for the fusion of powder
particles. Therefore, the SLS is generally used to print
ceramic materials by coating material with a lower melting
point onto the matrix powder. The coating materials can
be removed later through sintering or left to enhance the
mechanical properties .
[88]
Besides the groups of 3D systems mentioned above,
laminated object manufacturing (LOM) is also a standard
3D printing technique. In the LOM process, the top layer Figure 7. Schematic of binder jetting as a typical powder-based printing
cutting is achieved by a blade or laser cutter, followed by the process.
laminate bonding. Additional machining is often required
to achieve final products in the desired shape. LOM is also
used to produce porous ceramic materials like other 3D
printing systems .
[89]
3. Recent advancements in 3D printing of
zeolitic gas adsorbents
As mentioned in the previous sections, 3D printing is a Figure 8. Scanning electron microscopy images of self-standing
practical approach to fabricating zeolitic adsorbents in 3D-printed zeolite structure with different magnifications. Reprinted
[91]
customized geometry for gas adsorption usage. Both the gas with permission from Thakkar et al. .
adsorption performance and fabrication processes of the framework. It is because that framework determines the
3D-printed zeolitic adsorbents are essential to their practical structural and chemical properties of zeolites, leading to
applications. The recent advances in the development of different selectivity and absorptivity of different gases.
3D-printed zeolitic adsorbents are reviewed and discussed Therefore, the selection of the appropriate framework
in this section. is crucial to the fabrication of zeolitic gas adsorbent for

3.1. Material selection and development targeted gas through 3D printing. As shown in Figure 9,
different zeolite frameworks contain various tiny openings
3D printing has been applied to fabricate porous ceramic or that permit molecules of a specific size to pass through. The
metal support structures such as scaffolds for the growth of size of these pores determines which gas molecules can be
zeolite crystals . However, the non-zeolite layers between absorbed into a zeolitic gas adsorbent. Any molecules that
[90]
the zeolite and the substrate could act as barriers to the are larger than the pore size will be unable to enter and be
reactants, leading to a reduced adsorption rate. Therefore, absorbed by the pores.
recent research has focused on developing a self-standing
zeolite monolith for gas adsorption through 3D printing. For example, LTA zeolites have a narrow pore size
distribution and a high degree of structural order, which
3.1.1. Self-standing type makes them ideal for separating small molecules based
on size and shape. In contrast, faujasite (FAU) zeolites
In 2016, Thakkar et al. first formulated the printable 13X have a larger pore size and a more disordered structure,
and 5A zeolite paste with binding agents for the fabrication which makes them better suited for adsorbing larger
of monoliths through the DIW printing technique. The molecules. Furthermore, smaller pores tend to have
printed products were found to achieve a CO adsorption higher selectivity for specific gases, while larger pores
2
capacity comparable to that of their counterparts in tend to have higher adsorption capacity. Table 3 shows
powder form . Figure 8 reveals that the 3D-printed some common types of zeolite materials, including
[91]
zeolite monoliths can preserve a stable porous network for mordenite framework inverted (MFI) and chabazite
gas adsorption without requiring an additional supporting (CHA) zeolites, that have been applied for the 3D
structure made from a different material. printing of gas adsorbent, where the surface area of
One critical aspect of material selection for the 3D the printed adsorbent structure is determined by the
printing of zeolitic gas adsorbents is the choice of a zeolite Brunauer-Emmett-Teller (BET) test.

Volume 2 Issue 4 (2023) 8 https://doi.org/10.36922/msam.1880