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 postsynthetic modification to confer various degrees of hydrophobicity. MOF copper 2-aminobenzene-1,3,5-tricarboxylate was modified with varying-length aliphatic carbon chains. Unmodified Cu3(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°. 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.