Grafting of hydrophilic ethylene glycols or ethylenediamine on coordinatively unsaturated metal sites in MIL-100(Cr) for improved water adsorption characteristics

• Easy grafting of ethylene glycols or ethylenediamine on vacant Cr(III) sites.
• Unchanged water uptake despite halved BET surface area in grafted MIL-100(Cr).
• Favored water uptake through ethylene glycol or diamine grafting of MIL-100(Cr).
• Favored water uptake by increased hydrophilicity and smaller pores of grafted MOF.
• Ethylenediamine shows more stable binding to Cr(III) over alcohol ligands.

Grafting of activated MIL-100(Cr) with EG (ethylene glycol), DEG (diethylene glycol), TEG (triethylene glycol) and EN (ethylenediamine) leads to a decrease of the BET surface area and pore volume. Yet, water adsorption isotherms of the modified compounds MIL-100(Cr)-EG, MIL-100(Cr)-DEG and MIL-100(Cr)-EN show a favored uptake of water at lower partial pressures and no loss of total water uptake capacity compared to non-modified MIL-100(Cr). The reduction in surface area is offset by an increased hydrophilicity and an advantageous smaller pore size for the adsorption of water. MIL-100(Cr) is therefore very promising as a water sorption material, e.g., for heat-transformation applications.

Large pores are not necessarily better – increased hydrophilicity and smaller pores of a grafted MOF material are advantageous for earlier water adsorption and condensation.Figure optionsDownload as PowerPoint slide