HF‐free synthesis of MIL‐101(Cr) and its hydrogen adsorption studies

Abstract

The present study focused on the hydrofluoric acid (HF) free synthesis of chromium based metal organic framework, MIL‐101(Cr) and its application for hydrogen storage. MIL‐101(Cr) has been synthesized hydrothermally using HF, acetic acid, perfluorobenzoic acid, and without acid. The characterization of the synthesized materials were carried out using powder X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and surface area (BET) by nitrogen adsorption isotherm at 77 K. The results demonstrated that acetic acid mediated synthesized MIL‐101(Cr) exhibited higher surface area and pore volume than those synthesized with other organic acids. This may be due to the enhanced dissolution of terephthalic acid in the presence of acetic acid which facilitates the formation of MIL‐101(Cr) nuclei during the synthesis. A comparison of conventional and HF free‐synthesized MIL‐101(Cr) for hydrogen adsorption capacity determined at 77 K up to 4500 kPa revealed that MIL‐101(Cr) synthesized using acetic acid exhibited higher hydrogen adsorption capacity (5.6 wt %) than the MIL‐101(Cr) synthesized with perfluorobenzoic acid (3.7 wt %) and without acid (4.8%). However, it is slightly less than the H2 adsorption capacity of MIL‐101(Cr) synthesized using HF (6.1 wt %). The higher H2 adsorption capacity of MIL‐101(Cr) synthesized using acetic acid can be attributed to the better terephthalate–chromium interaction which facilitates the formation of more crystalline product thereby creating more unsaturated metal centers in MIL‐101(Cr). The present study suggested that acetic acid may be a suitable alternative for highly corrosive and hazardous HF which led to easier preparation of MIL‐101(Cr) for the large‐scale production and applications. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 461–468, 2016