From metal–organic framework powders to shaped solids: recent developments and challenges

Abstract

Metal-organic frameworks represent a class of porous materials which developed considerably over the past few years. Their porous structure makes them outperforming conventional adsorbents in hot topics such as dihydrogen...

Binding Materials for MOF Monolith Shaping Processes: A Review towards Real Life Application

“…Polymer binders (e.g., PVA, PVB, MC) and inorganic binders (e.g., ρ-alumina, silica) are two suitable categories of adhesive agents that are used in either pressurized or non-pressurized processes to form a MOF into a pellet, a granule, or a monolith. As noted in other works [5,8,22,114] and also depicted in this study, polymer-type binders have lower weights compared to inorganic binders, which enhances the performance of the structure. These binders are more well-studied and are easier to handle, but on the other hand, there is an increased possibility of pore blockage and reduction of the specific surface area of the MOF, and subsequently, its uptake capacity to gases.…”

“…Good mechanical strength is necessary for withstanding the pressure exerted by a reactor or column in which the gas flow takes place for gas absorption or separation, catalysis, and similar applications [8,21]. However, MOFs in powder form are not suitable for such applications due to poor mechanical performance, and therefore, they need to be shaped with respect to the desired applications and their process conditions [22,23]. Apart from the mechanical properties, the shaped MOF should have a sufficient size for maintaining the diffusion effect among particles and should maintain as much as possible the porosity and crystallinity of the powder form [5].…”

Shaping MOF oxime oxidation catalysts as three-dimensional porous aerogels through structure-directing growth inside chitosan microspheres

“…13,14 To circumvent these drawbacks, efforts focused on shaping MOF powder using conventional strategies, with limitations related to the fragility of their structure, compared to conventional inorganic zeolites, metal oxide ceramics, and activated carbons. 15 In fact, conventional methods such as pelletization and granulation severely impact the textural properties of the parent MOFs as the applied pressure reduces the interparticular voids, leads to amorphization in some cases and can even collapse the frameworks, while the use of binders leads to dramatic pore blocking. 16,17 Alternatively, a nascent field originated where MOF particulates are hybridized with other substructures including synthetic polymers and natural biopolymers, 18,19 ceramics, 20 carbon particles, 21 among others.…”

“…Additional limitations are that granulated MOFs lose above 90% of their surface area when up to 30 wt% binder loading is engaged. 15 To cope with some challenging aspects of shaping such extended metal-coordinated polymers, we envisioned their simultaneous structure-directing growth and configuration using degradable polysaccharide microspheres. Alginate is one of the most widely used biopolymer binders owing to the possible gelation of its network through cross-linking with divalent cations (Ca 2+ and Ba 2+ ) among others, giving rise to the socalled egg-box structure.…”

“…Additional limitations are that granulated MOFs lose above 90% of their surface area when up to 30 wt% binder loading is engaged. 15…”