ZnO as an Efficient Nucleating Agent for Rapid, Room Temperature Synthesis and Patterning of Zn-Based Metal-Organic Frameworks

The use of ZnO particles as efficient agents for seeding, growing, and precisely positioning metalorganic frameworks (MOFs) is described. Ceramic seeds have been successfully used for the preparation of Zn-based MOFs with a number of different carboxylic acids: terephthalic acid, 2-aminoterephthalic acid, 1,3,5-benzenetricarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. In situ synchrotron small-angle X-ray scattering and electron microscopy experiments were employed to determine the effect of the concentration of ZnO nanoparticles, temperature, and time on MOF growth. Under optimized conditions, MOF crystals were found to form in several minutes. This unprecedented capacity to seed MOF formation was used to control the growth of crystals in precise locations. Accordingly, we employed this seeding technique to position porous MOF crystals on paper strips (lateral flow), or within glass and PDMS microchannels (120 mu m width and 100 mu m height). These data demonstrate that ZnO nanoparticles are versatile seeding agents for the growth of porous crystals in a number of different microfluidic platforms.