MOF immobilization on the surface of polymer-cordierite composite monoliths through in-situ crystal growth

Recent Advances in 3D Printing of Structured Materials for Adsorption and Catalysis Applications

Porous solids in the form of adsorbents and catalysts play a crucial role in various industrially important chemical, energy, and environmental processes. Formulating them into structured configurations is a key step toward their scale up and successful implementation at the industrial level. Additive manufacturing, also known as 3D printing, has emerged as an invaluable platform for shape engineering porous solids and fabricating scalable configurations for use in a wide variety of separation and reaction applications. However, formulating porous materials into self-standing configurations can dramatically affect their performance and consequently the efficiency of the process wherein they operate. Toward this end, various research groups around the world have investigated the formulation of porous adsorbents and catalysts into structured scaffolds with complex geometries that not only exhibit comparable or improved performance to that of their powder parents but also address the pressure drop and attrition issues of traditional configurations. In this comprehensive review, we summarize the recent advances and current challenges in the field of adsorption and catalysis to better guide the future directions in shape engineering solid materials with a better control on composition, structure, and properties of 3D-printed adsorbents and catalysts.

Curcumin Delivery on Metal-Organic Frameworks: The Effect of the Metal Center on Pharmacokinetics within the M-MOF-74 Family

Metal-organic frameworks (MOFs) have gained considerable attention as drug delivery platforms over the past decade owing to their tunable physiochemical properties, biodiversity, and capability to encapsulate sizable active compound loadings. Nevertheless, many fundamental properties pertaining to MOFs' pharmacokinetic performances as drug carriers have been poorly investigated. One such property is the relationship between the MOF metal center solubility and drug release rate. In this study, we investigated this relationship within the M-MOF-74 family by impregnating 30 or 50 wt % curcumin on either Mg-, Ni-, Zn-, or Co-MOF-74. The drug delivery performance of the materials was assessed in phosphate buffered saline solution by high-performance liquid chromatography over a time period of 0-24 h. From these experiments, it was determined that the 30 wt % curcumin loading led to increased drug delivery and kinetics compared to the 50 wt % loading regardless of the metal center, as the lower drug concentration did not hinder diffusion from the MOF pores. As such, the optimal curcumin loading within the M-MOF-74 family was concluded to be greater than 30 wt % but less than 50 wt %. These experiments also revealed that using Mg-MOF-74 as a drug carrier produced a twofold enhancement in the release rate from 0.15 to 0.30 h^1/2 compared to the other three metal centers, where Mg-MOF-74's improved pharmacokinetics were attributed to the increased group II Mg solubility compared to Ni, Co, or Zn transition metals. On the basis of these findings, it was concluded that to promote rapid pharmacokinetics, it is essential to use MOFs with more soluble metal centers to promote dissolution of the nanocarrier. While this study focused on M-MOF-74, we expect that this conclusion has implications to other crystallites as well.

Gel-Print-Grow: A New Way of 3D Printing Metal-Organic Frameworks

3D printing offers an attractive means of forming structured metal-organic frameworks (MOFs), as this technique imparts digital geometric tuning to fit any process column. However, 3D-printed MOF structures are usually formed by suspending presynthesized particles into an ink for further processing. This leads to poor rheological properties as MOFs do not bind with inert binders. Herein, we address this problem by coordinating the MOF secondarily by 3D printing its gelated precursors. Specifically, we produced a printable sol-gel containing ∼70 wt % of HKUST-1 precursors and optimized the in situ growth conditions by varying the desolvation temperature and activation solvent. Analysis of the so-called gel-print-grow monoliths' properties as a function of the coordination variables revealed that desolvating at 120 °C produced fully formed MOF particles with comparable diffractive indices to the parent powder regardless of the activation solvent used. Assessment of the samples' textural properties revealed that washing in acetone or methanol produced the highest surface areas, pore volumes, and CO₂ adsorption capacities, however, washing with methanol produced binder swelling and collapse of the printed structure, thereby indicating that washing with acetone was more effective overall. This study represents a promising way of 3D printing MOFs and a breakthrough in additive manufacturing, since the simple, high-throughput, framework detailed herein-whereby the synthesis temperature and washing solvent are varied to optimize MOF coordination-could easily be applied to other crystallites. As such, it is anticipated that this new and exciting method will provide new paths to shape engineer MOFs for applications in energy-intensive fields and beyond.

In Situ Growth of Ca2+-Based Metal-Organic Framework on CaSiO3/ABS/TPU 3D Skeleton for Methylene Blue Removal

The work reports a novel strategy for combining polymers and metal–organic frameworks (MOFs) into composites for adsorption applications. Calcium silicate (CaSiO₃) was introduced into acrylonitrile butadiene styrene/thermoplastic polyurethane (ABS/TPU) alloy, and the CaSiO₃/ABS/TPU skeleton was fabricated by 3D printing technology. The Ca-MOF was directly loaded on the surface of acetone-etched 3D skeleton by in-situ growth method. The obtained 3D skeleton was characterized and the performance of methylene blue (MB) adsorption was determined. It is clear that Ca-MOF is successfully loaded on the surface of 3D skeleton due to the presence of CaSiO₃. The MB adsorption ratios of the solutions with initial concentrations of 50, 100 and 200 mg/L at the equilibrium time (5 h) are 88%, 88% and 80%, respectively, revealing good MB adsorption performance of the 3D skeleton. The MB adsorption ratio remains 70% at six runs of adsorption–desorption experiment, indicating the excellent recovering property of the skeleton. The results show that the prepared CaSiO₃/ABS/TPU 3D skeleton is a candidate adsorbent for printing and dyeing effluent treatment.

Shaping the Future of Fuel: Monolithic Metal-Organic Frameworks for High-Density Gas Storage

The environmental benefits of cleaner, gaseous fuels such as natural gas and hydrogen are widely reported. Yet, practical usage of these fuels is inhibited by current gas storage technology. Here, we discuss the wide-ranging potential of gas-fuels to revolutionize the energy sector and introduce the limitations of current storage technology that prevent this transition from taking place. The practical capabilities of adsorptive gas storage using porous, crystalline metal-organic frameworks (MOFs) are examined with regard to recent benchmark results and ultimate storage targets in this field. In particular, the industrial limitations of typically powdered MOFs are discussed while recent breakthroughs in MOF processing are highlighted. We offer our perspective on the future of practical, rather than purely academic, MOF developments in the increasingly critical field of environmental fuel storage.

Novel Zeolite-5A@MOF-74 Composite Adsorbents with Core-Shell Structure for H2 Purification

Hydrogen is considered as one of the most important clean and renewable energy sources for a sustainable energy future. However, its efficient and cost-effective purification still remains challenging. In this work, we report the development of novel zeolite@metal-organic framework (MOF) composites comprised of MOF-74 and zeolite-5A with core-shell structure for efficient purification of H₂. The composites were synthesized hydrothermally through the addition of zeolite particles with and without carboxyl functional groups to the MOF synthesis solution. The zeolite/MOF weight ratio was varied systematically to find the optimum composition based on the adsorption performance. The formation of zeolite@MOF composites was confirmed by various characterization techniques. Single-component adsorption isotherms of CO₂, CO, CH₄, N₂, and H₂ over composites were measured at 25 °C to determine their equilibrium adsorption capacity. It was found that the zeolite-5A@MOF-74 with weight ratio of 5:95 exhibited a similar morphology to that of pristine MOF-74, but with higher surface area and total pore volume. Moreover, this composite showed 20-30% increase in CO₂, CO, CH₄, and N₂ uptake than the bare MOF, which could be attributed to the formation of new mesopores at the MOF-zeolite interface. The estimated selectivity values for CO₂/H₂, CO/H₂, CH₄/H₂, and N₂/H₂ were higher than those of the zeolite and/or MOF. Our results also indicated that surface modification of zeolite prior to composite formation does not enhance the adsorption capacities of the composites. Overall, the findings of this study suggest that the zeolite-5A@MOF-74 composites with core-shell structure are promising candidates for industrial H₂ purification processes.

UTSA-16 Growth within 3D-Printed Co-Kaolin Monoliths with High Selectivity for CO2/CH4, CO2/N2, and CO2/H2 Separation

Honeycomb monoliths loaded with metal-organic frameworks (MOFs) are highly desirable adsorption contactors because of their low-pressure drop, rapid mass-transfer kinetics, and high-adsorption capacity. Moreover, three-dimensional (3D)-printing technology renders direct material modification a realistic and economic prospect. In this study, 3D printing was utilized to impregnate kaolin-based monolith with UTSA-16 metal formation precursor (Co), whereupon an internal growth was facilitated via a solvothermal synthesis approach. The cobalt weight loading in the kaolin support was varied systematically to optimize the MOF growth while retaining monolith mechanical integrity. The obtained UTSA-16 monolith with 90 wt % loading exhibited similar textural features and adsorption characteristics to its powder analogue while improving upon structural integrity. In comparison to previously developed 3D-printed UTSA-16 monoliths, the UTSA-16-kaolin monolith not only showed higher MOF loading but also higher compression stress, indicative of its robust structure. Furthermore, the 3D-printed UTSA-16-kaolin monolith displayed a comparable CO₂ adsorption capacity to the UTSA-16 powder (3.1 vs 3.5 mmol/g at 25 °C and 1 bar), which was proportional to its loading. Selectivity values of 49, 238, and 3725 were obtained for CO₂/CH₄, CO₂/N₂, and CO₂/H₂, respectively, demonstrating good separation potential of the 3D-printed MOF monolith for various gas mixtures, as determined by both equilibrium and dynamic adsorption measurements. Overall, this study provides a novel route for the fabrication of UTSA-16-loaded monoliths, which demonstrate both high MOF loading and mechanical integrity that could be readily applied to various CO₂ capture applications.

3D-Printed Metal-Organic Framework Monoliths for Gas Adsorption Processes

Metal-organic frameworks (MOFs) have shown promising performance in separation, adsorption, reaction, and storage of various industrial gases; however, their large-scale applications have been hampered by the lack of a proper strategy to formulate them into scalable gas-solid contactors. Herein, we report the fabrication of MOF monoliths using the 3D printing technique and evaluation of their adsorptive performance in CO₂ removal from air. The 3D-printed MOF-74(Ni) and UTSA-16(Co) monoliths with MOF loadings as high as 80 and 85 wt %, respectively, were developed, and their physical and structural properties were characterized and compared with those of MOF powders. Our adsorption experiments showed that, upon exposure to 5000 ppm (0.5%) CO₂ at 25 °C, the MOF-74(Ni) and UTSA-16(Co) monoliths can adsorb CO₂ with uptake capacities of 1.35 and 1.31 mmol/g, respectively, which are 79% and 87% of the capacities of their MOF analogues under the same conditions. Furthermore, a stable performance was obtained for self-standing 3D-printed monolithic structures with relatively good adsorption kinetics. The preliminary findings reported in this investigation highlight the advantage of the robocasting (3D printing) technique for shaping MOF materials into practical configurations that are suitable for various gas separation applications.