Controlling ZIF-67 film properties in water-based cathodic electrochemical deposition

One of the main approaches to increase the surface area of a substrate is through depositing films of porous materials such as Zeolite imidazole frameworks (ZIFs). ZIF films have shown surpassing capabilities because of their zeolite-like features, including porosity, homogeneous pore size, structural tunability and remarkable thermal and chemical stability. Many methods have been proposed and tested to form such films. Of the techniques that have been documented is electrosynthesis which is considered to be the most practical, quick, and mildly conditioned. In this study, ZIF-67 films were cathodically electrodeposited on an electrically conductive Indium Tin Oxide (ITO) coated Polyethylene Terephthalate (PET) substrates. Unlike previous reports, in this study, water was used as a solvent. In addition to this, effect of crucial operating parameters such as applied potential, molar ratio of reactants and solution pH, on the formation of ZIF-67, was investigated for the first time. It was found that increasing the applied potential, increased the surface coverage and decreased the formed ZIF-67 crystal size. Changing the molar ratio between the organic ligand and the metal salt had a profound influence on the formed phase and crystal shape. It was also found that at neural and mildly basic solution pH, ZIF-67 could not be formed. Statistical analyses were carried out showing low p-values (<<0.05), expressing strong relation between variables and robustness and reliability of the data collected in this study. Finally, mathematical expressions were fitted to experimental data to reveal the relationship between applied potential, molar ratios of reactants, pH and conductivity of solutions, surface coverage and crystal size. This study revealed that surface coverage, crystal shape and size can be controlled by manipulating operating conditions.