Metal-organic frameworks (MOFs) are a class of functional solid-state materials with potential for use in hydrogen storage, gas separation, carbon dioxide capture, and drug release. Porous MOFs could offer solutions for the safe storage and efficient use of H2 in mobile applications.
Mohamed Eddaoudi, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia, and colleagues studied ways of improving the H2 and CH4 binding affinity to the walls of a MOF. They constructed the MOF [Pb2(C14H8O6S)2] via a solvothermal reaction of Pb(NO3)2 and 4,4’-sulfonyldibenzoic acid in N,N-dimethylformamide (DMF). The framework has a molecular square geometry. Four benzene rings interact simultaneously with a single H2 molecule residing in the center of the square.
The square-like channels in the MOF structure have a periodic array of aromatic rings with a relatively short distance between opposing rings. This makes H2 and CH4 adsorption easier. There is a particularly the sharp H2 adsorption isotherm at 77 K. This sharp step in H2 adsorption could be attributed to the equal distribution of H2 sorption sites with uniform binding affinities within the framework. These sites are most probably located on the surfaces of aromatic rings present in the MOF. Similar uniform interactions were also observed for methane adsorption.
According to the researchers, the new MOF material could be a model for studying the interplay between porosity/storage capacity and the strength of host-guest interactions.
- Metal–organic frameworks for H2 and CH4 storage: insights on the pore geometry–sorption energetics relationship,
Mohamed H. Alkordi, Youssef Belmabkhout, Amy Cairns, Mohamed Eddaoudi,
IUCrJ 2017, 4, 131–135.