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This study demonstrates, for the first time, the successful fabrication, using binder jetting (a 3D printing process), of monolithic zeolite adsorbents. The characteristics of raw powder (Zeolite 13X), printed samples, and calcined samples at different temperatures were evaluated and compared. The calcined sample at 750°C exhibited a balanced performance between adsorption and mechanical strength. First, this sample retained the granular morphology and crystalline structure of the raw powder as confirmed by scanning electron microscopy and X-ray diffraction analysis. Thermogravimetric analysis validated the effective removal of organic binders in this sample. Compared with the raw powder, nitrogen adsorption showed that this sample had a decrease in specific surface area (from 848 to 383 m2/g) and micropore volume (from 0.3854 to 0.1402 cm3/g), accompanied by an increase in mesopore volume (from 0.0041 to 0.0851 cm3/g). This sample achieved a CO2 adsorption capacity of 2.65 mmol/g at 25°C and 1 bar while maintaining a notable CO2/N2 selectivity of 1390 based on ideal adsorption solution theory under these conditions, which approaches that of the raw powder. Moreover, mechanical testing following ASTM standards showed that this sample exhibited a compressive strength of 0.45 MPa at room temperature, which is expected to suffice certain adsorption applications. Additionally, the successful fabrication of complex geometries highlights the versatility of binder jetting and confirms its feasibility for producing mechanically stable zeolite adsorbents. 

Powder bed compaction can be used to control powder bed density in binder jetting additive manufacturing. Applying a forward-rotating roller to the powder bed is one of the methods for powder bed compaction. Both the compaction rotation speed and compaction thickness are critical parameters affecting the powder packing density and resultant printed sample integrity. However, their joint effects have not been investigated for roller-compaction-assisted binder jetting. This paper reports an experimental study to investigate the effects of the compaction rotation speed and the compaction thickness on powder bed density and the printed sample quality (in terms of distortion and cracks). The experimental results showed that powder bed density was not affected by changing compaction rotation speed but was enhanced by increasing compaction thickness. Small compaction thickness did not cause any observable distortions or cracks in the printed samples at any compaction rotation speed. Large compaction thickness caused printed samples to distort and crack under specific conditions. At large compaction thickness, compaction rotation speed significantly affected both the direction and extent of the printed sample distortion. Samples with improved density and integrity were achieved in the center of the build platform at large compaction thickness and at a compaction circumferential speed larger than the compaction traverse speed. These results can help optimize binder jetting additive manufacturing for printed sample quality. 

One cause of climate change is the increasing amount of carbon dioxide (CO2) in the atmosphere. Substantial research efforts have been directed towards the exploration of solid porous adsorbents for the purpose of capturing CO2. Zeolites have well-defined nanoporous structures, effective in capturing CO2. This review paper summarizes zeolite types reported in the literature on CO2 adsorption capacity. About 106 zeolite types appear in reported studies on CO2 adsorption capacity based on a survey of over 90 journal papers. Activation temperature plays a critical role in enhancing CO2 adsorption capacity of zeolites, yet only 6% of reported zeolite types have been studied regarding the effects of activation temperature on CO2 adsorption capacity. For post-combustion CO2 capture, only 46% of the zeolite types have been evaluated for the effects of temperature and 58% of the zeolite types have been evaluated for the effects of pressure on CO2 adsorption capacity, leaving many zeolite types unexplored regarding the effects of temperature and pressure on CO2 adsorption capacity. For direct air capture, only 18% of zeolite types have been studies regarding the effects of temperature on adsorption capacity. The practical value of this paper lies in its ability to help researchers easily identify gaps in existing studies, guiding them toward unexplored combinations of zeolite types, temperature ranges, and pressure levels for future research. It also supports practitioners by summarizing which zeolite types have demonstrated specific CO2 adsorption capacity values under certain conditions, aiding in the selection of appropriate zeolite types for targeted applications. 

In this work, the effect of printing orientation on the flexural strength of the parts from binder jetting was investigated. Flexural samples were printed with six different orientations using a commercially available alumina powder. The printed samples were then cured, depowdered, debound, and sintered. Afterward, the flexural strength of the samples was measured with three-point bending tests. The results showed that the flexural strength varied significantly from 82.8 ± 5.3 MPa to 151.6 ± 4.0 MPa with different printing orientations. Archimedes method and X-ray computed tomography were then used to evaluate the bulk density and defect distribution of the samples, as an attempt to explain their flexural strengths. The Archimedes method showed there was no considerable difference in the bulk density among samples printed with different orientations. However, the X-ray computed tomography revealed significantly different defect distributions with different printing orientations, which was expected to be the cause for the different flexural strengths. 

This paper reports on a preliminary experimental study on binder jetting 3D printing of biomass–fungi composite materials. Biomass–fungi composite materials have potential applications in the packaging, furniture, and construction industries. Biomass particles (prepared from agricultural residues) act as the substrate of the composite materials. The filamentous roots of fungi intertwine and bind biomass particles together. In this study, the biomass (hemp hurd) powders used had two distinct average particle sizes. The liquid binder used contained fungi (Trametes versicolor) cells. T-shaped samples were printed using a lab-designed binder jetting setup. Printed samples were kept inside an incubator oven for four days to allow fungi to grow. Afterward, loose biomass powder was removed from the T-shaped samples. The samples were then kept inside the incubator oven for eight more days to allow further fungal growth. The samples were subsequently placed in an oven at 120 °C for four hours to terminate all fungal activity in the samples. SEM micrographs were taken of the cross-sectional surfaces of the samples. The micrographs showed a significant presence of fungi hyphae inside the printed samples, providing evidence of the binding of biomass particles by the hyphae.