High Gravimetric and Volumetric Ammonia Capacities in Robust Metal–Organic Frameworks Prepared via Double Postsynthetic Modification

Abstract

Ammonia is a promising energy vector that can store the high energy density of hydrogen. For this reason, numerous adsorbents have been investigated as ammonia storage materials, but ammonia adsorbents with a high gravimetric/volumetric ammonia capacity that can be simultaneously regenerated in an energy-efficient manner remain underdeveloped, which hampers their practical implementation. Herein, we report Ni_acryl_TMA (TMA = thiomallic acid), an acidic group-functionalized metal–organic framework prepared via successive postsynthetic modifications of mesoporous Ni2Cl2BTDD (BTDD = bis­(1H-1,2,3,-triazolo [4,5-b],-[4′,5′-i]) dibenzo­[1,4]­dioxin). By virtue of the densely located acid groups, Ni_acryl_TMA exhibited a top-tier gravimetric ammonia capacity of 23.5 mmol g–1 and the highest ammonia storage of 0.39 g cm–3 at 1 bar and 298 K. The structural integrity and ammonia storage capacity of Ni_acryl_TMA were maintained after ammonia adsorption–desorption tests over five cycles. Temperature-programmed desorption analysis revealed that the moderate strength of the interaction between the functional groups and ammonia significantly reduced the desorption temperature compared to that of the pristine framework with open metal sites. The structures of the postsynthetic modified analogues were elucidated based on Pawley/Rietveld refinement of the synchrotron powder X-ray diffraction patterns and van der Waals (vdW)-corrected density functional theory (DFT) calculations. Furthermore, the ammonia adsorption mechanism was investigated via in situ infrared and vdW-corrected DFT calculations, revealing an atypical guest-induced binding mode transformation of the integrated carboxylate. Dynamic breakthrough tests showed that Ni_acryl_TMA can selectively capture traces of ammonia under both dry and wet conditions (80% relative humidity). These results demonstrate that Ni_acryl_TMA is a superior ammonia storage/capture material.

Defects in a Metal–Organic Framework Fabricated by Carboxy-Functionalized Ionic Liquids for Enhancing NH3 Uptake

“…Metal–organic frameworks (MOFs) are a new class of porous materials linked by metal clusters and organic ligands through coordination bonds. − The high specific surface area, intrinsic porosity, and designable chemical structure endow them with great potential for gas capture and separation. − Especially, as a kind of solid adsorbent for NH 3 adsorption, MOFs have received unprecedented attention over the years, and some important results have been reported. − At present, it is generally accepted that coordinating interaction of NH 3 to metal nodes of the frameworks cannot be very strong. If not, NH 3 desorption is always difficult, and MOF regeneration is also an energy-intensive process.…”

Anchoring LiCl in the Nanopores of Metal–Organic Frameworks for Ultra‐High Uptake and Selective Separation of Ammonia

“…Such a high capacity far exceeds the current record of MOF‐ and COF‐based sorption materials (24.1 and 26.5 mmol g −1 ) under the same conditions [8b, 17] . In addition, the volumetric NH 3 capacity was calculated to be 47.22 mmol cm −3 (Table S3) from the gravimetric capacity and crystal density [10c] data (see details in Supporting Information), which is 2.1 times that of the highest capacity reported among metal–organic frameworks so far [18] …”

“…[8b, 17] In addition, the volumetric NH 3 capacity was calculated to be 47.22 mmol cm À 3 (Table S3) from the gravimetric capacity and crystal density [10c] data (see details in Supporting Information), which is 2.1 times that of the highest capacity reported among metal-organic frameworks so far. [18] Another important feature is that the composites exhibited an excellent adsorption capacity at low pressure. For example, the micropore filling effect allows the NH 3 adsorption capacity to reach 11.3 mmol g À 1 at 0.1 bar, then the adsorption exhibits a short plateau at 0.1-0.16 p/p 0 .…”

Adenine-based bio-MOFs with high water and acid–base stability for ammonia capture

“…Porous MOF materials incorporating special functional groups with high specific surface area and larger pore volume are often superior to others. 30,52,55,56 For example, the presence of acidic functional groups and open metal sites can significantly enhance NH 3 uptake. 53 Therefore, we believe that such an abundant free -NH 2 group in the channel of these two MOFs is beneficial to NH 3 uptake.…”