Electrochemistry-Induced Direct Deposition of Nanoscale Thin Zeolitic Imidazolate Framework-8 Films on Insulator Substrates

Electrochemical approaches have been explored as controlledmeansto prepare thin films of metal-organic frameworks (MOFs) onelectrodes but have rarely been used to form insulator films on insulatorsurfaces. Herein, we report an electrochemistry-based approach todirect deposition of a thin film of zeolitic imidazolate framework-8(ZIF-8) onto an insulator surface. The film deposition was inducedby a cathodic reaction at an electrode that was placed above the insulatorwith a separation of & AP;100 & mu;m in a methanol solution containingZnCl(2) and 2-methylimidizole. The effects of the electrodeand insulator material, applied potential, electrode-substratedistance, deposition time, and the number of deposition cycles weresystematically investigated to gain insight into the deposition mechanism.The results of these measurements were consistent with a hypothesizedmechanism involving cathodic base generation at the working electrodefor ligand deprotonation, formation of intermediate species, theirdiffusion toward the substrate, and the formation of ZIF-8 on thesubstrate. Interestingly, the size, shape, and position of the filmon the substrate replicated those of the working electrode, showingthe applicability of this approach to the patterned deposition ofa ZIF-8 film. In addition, film thickness could be easily controlledin the range of tens to hundreds of nanometers by adjusting the potentialapplication conditions. This electrochemistry-induced method willprovide a simple means for the patterned formation of a MOF film ofcontrolled thickness on an insulator without metal precoating andthus will open the possibility of designing unique devices for variousapplications including chemical sensing and separations. This paper reports a new electrochemistry-basedapproachto the controlled formation of a thin ZIF-8 film on the surface ofan insulator (and also a conductor). The film is formed only belowa working electrode, showing its applicability to the patterned depositionof a ZIF-8 film.