An alkaline one-pot metathesis reaction to give a [Cu3(BTC)2] MOF at r.t., with free Cu coordination sites and enhanced hydrogen uptake properties

Abstract

A one-pot metathesis reaction between trimesic acid sodium salt and Cu(NO₃)₂ to yield [Cu₃(BTC)₂] (HKUST-1) in moderate to good yields, even at room temperature (r.t.) is presented, herein, for the first time. To determine if the basic nature of the metathesis reaction afforded any new physicochemical properties to HKUST-1, three variables were monitored: a) the energy source either from i) ultrasound (US), ii) stirring at room temperature (SRT) or iii) solvothermal (ST) treatment, b) the reaction solvent and c) the reaction time. The metathesis reaction provided DMF·H₂O, EtOH·H₂O or MeOH·H₂O solvates. The compounds were thoroughly characterized by FTIR, XRD, nitrogen adsorption BET surface areas and TGA/DSC data, which indicated the formation of [Cu₃(BTC)₂] MOFs in eight out of ten synthetic entries. Low-pressure hydrogen uptake experiments revealed values as high as 2.44 wt% for the [Cu₃(BTC)₂] EtOH·H₂O solvates. The [Cu₃(BTC)₂] MeOH·H₂O and [Cu₃(BTC)₂] EtOH·H₂O solvates possess high surface areas, the latter being the metathesis prepared MOF with the least H₂O→Cu coordination according to TGA, DSC and a thermal desorption gas chromatography–mass spectrometry (GC-MS) coupled technique. This resulted in a material with less chemisorbed H₂O and better H₂ adsorption capability.