Synthesis Of ZIF-8 Film And Study Of Its Adsorption Behavior To Guest Molecules Under Applied Electric Field

Metal-organic frameworks(MOFs) are a class of porous crystalline materials consisting of metal ions or clusters and organic ligands connected by coordination bonds.MOFs have attracted lots of attention in fields such as gas adsorption,separation,heterogeneous catalysis due to their high surface area,regular and tunable pore size,structural tailorability,and thermal stability.In the last decade,MOF films have shown great advantages in the field of chemical sensors and electronic devices.It is important to develop suitable preparing methods for high quality MOFs for their further development in these fields.Recently,two promising fabrication methods based on cathodic deposition and conversion of oxides start to receive more attraction.But there still exist some problems,such as undesirable plating of metal during cathodic deposition and the using of solvents during transformation of oxides to MOF.Therefore,we developed two synthesis methods,oxygen-assisted cathodic deposition and vapor phase conversion of oxides to MOF films,to solved the above problems.Besides the preparing methods,it is also extremely important to tune the interactions between MOFs and guest molecules for their applications.The main approach is usually to change chemical structure,but the synthesis is commonly a tough task and the change of chemical structure is irreversible.To avoid these problems,we proposed a reversible way to tune the interactions between MOFs and guest molecules by applying an external electric field,and studied the adsorption behavior of guest molecules in MOFs.ZIF-8,one of typical MOFs,was chosen as a study object in our research.The main contents of this paper include:1.ZIF films(ZIF-8,ZIF-67) with high tunable thickness were prepared by oxygen-assisted cathodic deposition without the plating of metal,and the reaction mechanism as well as the growth kinetics were investigated.Based on this controllable cathodic deposition,large area(?5×7 cm~2) ZIF-8/ZIF-67 hybrid films were prepared and the ordered mesopores were introduced into the microporous ZIF-8 films.2.By vapor phase conversion,the solvent-free transformation from ZnO to ZIF-8 thin film was successfully realized.The problem of carbonization of the ligand was solved by introducing vacuum condition during the transformation of Zn O.The introduce of flowing ligand vapor phase allows for complete conversion of Zn O films with thickness from 10 nm to 160 nm to the dense and smooth ZIF-8 films.3.ZIF-8 thin film interference device and ZIF-8/Pd one-dimensional(1D) photonic crystal device were constructed.We found that sputtering of Pd decreased resistance of ZIF-8/Pd 1D photonic crystal device,which limited the applying of external electric field.Therefore,thin film interference device was chosen to study the adsorption behavior of methanol vapor in ZIF-8 under an external electric field and with UV-vis reflection spectrum as the output signal.In saturated methanol vapor,the decrease of reflectivity and blue-shift of reflection peak of ZIF-8 were observed under an external electric field,which were respectively attributed to the orientation polarization of methanol and the reduction of the adsorption of methanol in the polarized ZIF-8 with decreased pore size and stiffened lattice.