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

adsorption process, the adsorbent is regenerated by that are emitted as gases from certain solids or liquids.
increasing the temperature, which causes the adsorbed They can cause a variety of health and environmental
gas to desorb from the surface of the adsorbent. In problems, including respiratory issues and the formation of
contrast, the energy expended is delivered directly to the smog [126,127] . As shown in Figure 12, Wang et al. proposed a
adsorbent during the ESA process, which implies a higher design of the core-shell structure in the 3D-printed zeolite
efficiency and minimization of lost heat [124] . Regufe et al. monoliths to enhance their adsorption and separation
used DIW to print an electrically conductive 3D-printed performance. The core of the monolith was a ZSM-5
zeolitic gas adsorbent for CO capture in the ESA honeycomb structure with high selectivity for VOCs. After
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process [125] . Zeolite 13X was mixed with activated carbon the ZSM-5 core was printed, a hydrophobic silicalite-1 shell
and carboxymethylcellulose to formulate printing ink. was grown on the surface of individual ZSM-5 crystals
At a pressure of 0.15 bar, the CO adsorption capacity of by introducing colloidal silica into the printing inks. The
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the 3D-printed gas adsorbent is 3.49 mol/kg, an increase breakthrough time for toluene removal over one printed
of about 40% from its counterpart fabricated by the sample under dry conditions is reported as 357 s/g, while
traditional die-based extrusion process. under humid conditions, it is slightly longer at 442 s/g .
[97]
4.2. Gas purification As a typical zeolite-like structure, 3D-printed ZIF-8
monoliths have also been adopted for the removal of
There are several high-value purification applications for VOCs. Pellejero et al. formulated the ZIF-8 on ABS
3D-printed zeolite form factors. Specialty gases are one such filament to adopt dimethyl methylphosphonate (DMMP),
area. Contaminant signatures are unique to many specialty a type of VOC used as a simulant for nerve agents in
gases, mainly due to production methods. Still, these research and testing [128] . The formulation involved low-
signatures can also be influenced and even determined by temperature atomic layer deposition of ZnO on the ABS
other factors such as geography and raw materials supply. matrix and subsequent hydrothermal conversion of ZnO
Purification across this gas landscape involves dozens, to ZIF-8 on the ABS support to prepare the filament. The
perhaps hundreds of separations, which are complicated by printed ABS/ZIF-8 fillers were found to have an adsorption
the inherent reactivity of the gas itself and competition of capacity of 20.4 mg of DMMP per gram of ZIF-8 [128] .
contaminants for adsorbent active sites. The semiconductor
industry is a large consumer of ultra-high purity specialty 4.3. Gas storage
gases, where sensitivity to contamination often drives purity The storage of gases such as CH for energy sources is a
needs to 99.999% (5N) or better. Gas-phase processes such key application for 3D-printed ZIF-8 gas adsorbents that
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as deposition, etch, epitaxy, and annealing all consume possess MOFs and zeolites properties. The high porosity
specialty gases through the use of sophisticated process and stability of 3D-printed ZIF-8 gas adsorbents make them
tools. Often, these tools employ many different gases in their suitable for gas storage, as they can provide high storage
operation, and most include small point-of-use purifiers to capacity and stability under a wide range of operating
ensure both stable process yield and protection of critical conditions. Dhainaut et al. studied the formulation of several
components. Considering the physical space constraints, types of MOF inks, including ZIF-8, for 3D printing and
gas velocities, and lifetimes required in these ultra-high the creation of robust microporous solids for high-pressure
purity applications, the purification of specialty gases gas storage. The SEM examination in Figure 13A showed
represents considerable challenges. For the gas purification that the 3D-printed ZIF-8 monoliths contain numerous
technologist, gaining access to the large variety of zeolite pores induced by the rapid drying process, leading to a
structural motifs and other sorbents through 3D printing is compressive strength slightly lower than that of dense ZIF-8
a significant solution enabler. pellets by a factor of 10–100 times. Figure 13B shows that
Although contaminant signatures can be specific to high-pressure CH adsorption/desorption isotherms were
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many process gases, many long-standing purification measured at ambient temperature on 3D-printed ZIF-8
targets are common across the industry. Atmospherics such monoliths up to 55 bars. The results revealed that 3D-printed
as moisture, CO, CO , and NO compounds are ubiquitous monoliths were able to store 59 g/kg of ZIF-8 at 298 K and
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x
contaminants, usually present due to intrusions in handling 30 bars. Such capacity was close to that of commercial
and transportation. Other common contaminants include ZIF-8 powder, which was reported to store 68 g/kg at
the class of volatile organic compounds (VOCs), which can the same temperature and pressure level. It was pointed
be attributed to the atmosphere, lubricants used in various out that further optimization of printing parameters and
processes, or even cleaning residue. Adsorption of VOCs MOF crystal loadings was required to improve mechanical
is an essential application of 3D-printed zeolite structures properties and prevent partial sagging on the edges of the
for gas purification. VOCs are a group of organic chemicals printed monolith for gas storage application [129] .

Volume 2 Issue 4 (2023) 15 https://doi.org/10.36922/msam.1880