Functionalization of Metal-Organic Frameworks To Achieve Controllable Wettability

The overall versatility of a material can be immensely expanded by the ability to controllably tune its hydrophobicity. Herein we took advantage of steric bias to demonstrate that tricarboxylate metal organic frameworks (MOFs) can undergo covalent post synthetic modification to confer various degrees of hydrophobicity. MOF copper 2-aminobenzeue-1,3,5-tricarboxylate was modified with varying-length aliphatic carbon chains. Unmodified Cu-3(NH2BTC)(2) degrades in minutes upon contact with water, whereas modification as low as 14% results in powders that show significantly enhanced hydrophobic character with contact angles up to 147 degrees. The modified material is capable of withstanding direct contact with water for 30 min with no visual evidence of altered surface characteristics. A linear relationship was observed between the length of the tethered chain and the water contact angle. These results reveal a predictable method for achieving a range of desirable sorption rates and highly controllable hydrophobic character. This work thereby expands the possibilities of rationally modifying MOFs for a plethora of target-specific applications.