Exceptional ammonia uptake by a covalent organic framework

Abstract

Covalent organic frameworks (COFs) are porous crystalline materials composed of light elements linked by strong covalent bonds. A number of these materials contain a high density of Lewis acid boron sites that can strongly interact with Lewis basic guests, which makes them ideal for the storage of corrosive chemicals such as ammonia. We found that a member of the covalent organic framework family, COF-10, shows the highest uptake capacity (15 mol kg⁻¹, 298 K, 1 bar) of any porous material, including microporous 13X zeolite (9 mol kg⁻¹), Amberlyst 15 (11 mol kg⁻¹) and mesoporous silica, MCM-41 (7.9 mol kg⁻¹). Notably, ammonia can be removed from the pores of COF-10 by heating samples at 200°C under vacuum. In addition, repeated adsorption of ammonia into COF-10 causes a shift in the interlayer packing, which reduces its apparent surface area to nitrogen. However, owing to the strong Lewis acid-base interactions, the total uptake capacity of ammonia and the structural integrity of the COF are maintained after several cycles of adsorption/desorption.

A Recyclable Metal–Organic Framework as a Dual Detector and Adsorbent for Ammonia

“…[3] NH3 is an important raw material for the manufacturing of large numbers of chemicals including fertilizers, dyes, plastics, and pharmaceuticals, [4] and is considered as a potential carbon-free green fuel due to its high energy density and its lower cost of production, storage, and delivery compared to hydrogen. [5] Both the danger and usefulness of NH3 have motivated researchers to develop economical and responsive materials that can selectively detect and capture NH3; for example, NH3 sensors based on catalytic metals [6] and conducting polymers [7] have been reported, whilst porous materials such as activated carbons, [8] organic polymers, [9] covalent organic frameworks, [10] and MOFs [11] are known as efficient NH3 sorbents. MOFs are crystalline materials prepared by the selfassembly of metal ions or clusters with organic ligands to form porous extended structures.…”

Pore surface engineering in covalent organic frameworks

“…The pore surface forms a microscopic interface with gas or guest molecules, and is an important characteristic that determines the macroscopic nature of these materials in applications such as gas adsorption, molecular separation, catalysis and energy storage. Among these materials, covalent organic frameworks (COFs) are a class of porous materials that feature low-weight elements and strong covalent linkages of their components, and they exhibit high flexibility in their molecular design, which allows the atomically precise integration of their building blocks into porous structures [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] . COFs can be constructed by the reticular design of their components, which, upon undergoing condensation reactions, form a porous skeleton with a precise pore size and specific pore geometry.…”

Facile Uptake and Release of Ammonia by Nickel Halide Ammines

“…After 120 min, the chloride absorbed 42.9 wt % NH 3 (98 % of the theoretical maximum). The uptake thus compares favourably with other metal ammines and also the best porous materials under similar conditions 17, 18. The solids increased in volume dramatically on gas uptake and evolved heat in the process.…”