Efficient electrochemical synthesis of a manganese-based metal–organic framework for H2 and CO2 uptake†
In this study Mn–DABDC (DABDC = diaminobenzenedicarboxylate, or 2,5-diaminoterephthalate) MOF was synthesised both via an electrochemical method, to make Mn–DABDC(ES), and via a conventional solvothermal approach, to make Mn–DABDC(ST). A Mn–BDC (BDC = benzenedicarboxylate) MOF was also prepared by a conventional solvothermal method for gas uptake capacity comparison. Investigation of the electrochemical synthesis parameters demonstrated that current density, electrolyte amount and reaction time were the most significant factors affecting crystal synthesis and product yield. The best conditions found for obtaining a crystalline MOF with high yield (93%) were 70 mA current, electrolyte 2.7 mmol/30 ml DMF and 2 h of reaction time. These optimized electrochemical conditions allow for a relatively fast MOF synthesis, important for reducing synthesis cost compared with conventional hydrothermal and solvothermal methods. The Mn–DABDC(ES) MOF sample was fully characterized to analyse its structure, thermal stability and surface area. The electrochemically synthesized MOF has high carbon dioxide uptake (92.4 wt% at 15 bar and 273 K) and hydrogen uptake (12.3 wt% at 80 bar and 77 K). This is the first amine-based manganese MOF synthesized electrochemically, and the method has excellent potential for reducing large-scale MOF production costs.