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 H 2 adsorption capacity of MIL-101(Cr) synthesized using HF (6.1 wt %). The higher H 2 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.

Elimination of 4‐chlorophenol in aqueous solution by the Novel Pd/MIL‐101(Cr)‐Hydrogen‐Accelerated catalytic fenton system

“…MIL‐101(Cr) was prepared via a modification of the procedure reported by Rallapalli et al In a typical synthesis process, Cr (NO 3 ) 3 ·9H 2 O (4 g, purity≥99.0%), terephthalic acid (1.54 g, purity≥99.0%) and sodium acetate solution (0.05 M, 50 ml) was added to 250 ml capacity Teflon lined stainless steel autoclave, sonicated (10 min), then placed in a preheated oven at 220 °C for 12 hr. After it was cooled down to room temperature, the mixture was transferred into a beaker.…”

Structure activity relationships in metal–organic framework catalysts for the continuous flow synthesis of propylene carbonate from CO2and propylene oxide

“…2, the mechanistic role of the co-catalyst is to serve as a nucleophile to ring-open the epoxide once it is activated by coordination to an electrophilic metal center (presumably a metal in the node of the MOF). [31][32][33] Importantly, previous work has shown that, in batch, the yield of PC without co-catalyst is low. 27 However, we hypothesized that the high ratio of MOF catalyst to epoxide in a packed bed ow reactor relative to that in a batch reactor might result in increased reactivity, and that nucleophilic functional groups present at the MOF nodes (e.g., hydroxides, chlorides, uorides, or carboxylates derived from the MOF synthesis) and/or in solution (e.g., water in the solvent) could potentially serve as nucleophiles under these conditions.…”

Molecular Level Understanding of the Free Energy Landscape in Early Stages of Metal–Organic Framework Nucleation

“…Fluoride anions have an affinity to the chromium at the metal center of MOF building units and their interaction assists the stability of the crystal structure 22 . Nevertheless, recent studies [23][24][25][26] have used alternative synthetic methods by replacing fluoride with hydroxide anions using deionized water [23][24][25] . In this work, the self-assembly of MIL-101 (Cr) SBU from its constituent half-SBUs is studied as a prototypical example to highlight the most important stages of nucleation.…”