28-08-2014, 03:52 PM
In the present work, We have synthesized ZIF-8 nanocrystals in completely aqueous medium at room temperature. Study on effect of different reaction parameters such as temperature, pH, rate of mixing and counterions have been attempted. For counterion studies, different zinc sources were used viz., zinc acetate, zinc chloride, zinc nitrate, and zinc sulphate. Rate of mixing of reactants was studied by setting different rpm (300,500, 900 1200 and 1500) for reaction mixture. Similarly, different pH (4, 5, 5.7, 7 and 8.2) and metal ion to imidazole ratios (1:50, 1:70 and 1:100) were set to check the effect of individual parameter on nanpocrystals size of ZIF-8. Subsequently, the optical and structural properties of synthesized nanocrystals were characterized various characterization techniques such as dynamic light scattering measurement (DLS), Fourier Transformed Infrared spectroscopy (FTIR), UV-Vis-NIR spectrophotometer, X-Ray diffraction (XRD), Atomic Force microscopes (AFM), Scanning electron microscopy (SEM), Energy Dispersion X-Ray Spectroscopy (EDS) and Differential scanning c
Inorganic zeolites have been studied as micro-porous materials for application in gas storage, gas separation and heterogeneous catalysis because of their high stability and structure diversity. Porous Metal Organic Framework (MOFs) is a new class like of zeolite-analogous materials that are more desirable in pore size, shape and also wide structural diversity. Zeolitic Imidazolate frameworks (ZIFs) are a important subclass of porous metal-organic frameworks (MOFs). The ZIFs have structural resemblance to Zeolite topologies wherein all tetrahedral atoms are transition metals and are bridged by imidazolate (IM) units. A prototypical member of ZIF family; ZIF-8 shows remarkable properties such as large pore size with small window ideal for gas separation, storage and catalysis, high chemical and thermal stability, and high surface area. By the virtue of these properties, ZIF-8 have shown tremendous potential in wide range of applications.
Recently, nanocrystals of ZIF-8 have gained considerable research interest. The reduction of the particles size from the micrometers to nanometers scale causes changes in the surface properties of the materials, which further enhance the performance of ZIFs in the applications area such as catalysis, gas storage and gas separation. Nanocrystals shows high surface area to volume ratio, thereby enhancing surface dependent applications like gas adsorption, separation, catalysis and most importantly allowing easy fabrication of miniaturized sensors. However, syntheses of uniform, monodispersed ZIF-8 nanocrystals have been a challenge. Most of the synthesis methods reported for ZIF-8 have been carried out using organic solvents such as dimethylformamide (DMF), diethylformamide (DEF) or methanol which are expensive, and can cause pollution as well as risk to human health. In addition they are not scalable for industrial synthesis due to cost factor.
In the present work, We have synthesized ZIF-8 nanocrystals in completely aqueous medium at room temperature. Study on effect of different reaction parameters such as temperature, pH, rate of mixing and counterions have been attempted. For counterion studies, different zinc sources were used viz., zinc acetate, zinc chloride, zinc nitrate, and zinc sulphate. Rate of mixing of reactants was studied by setting different rpm (300,500, 900 1200 and 1500) for reaction mixture. Similarly, different pH (4, 5, 5.7, 7 and 8.2) and metal ion to imidazole ratios (1:50, 1:70 and 1:100) were set to check the effect of individual parameter on nanpocrystals size of ZIF-8. Subsequently, the optical and structural properties of synthesized nanocrystals were characterized various characterization techniques such as dynamic light scattering measurement (DLS), Fourier Transformed Infrared spectroscopy (FTIR), UV-Vis-NIR spectrophotometer, X-Ray diffraction (XRD), Atomic Force microscopes (AFM), Scanning electron microscopy (SEM), Energy Dispersion X-Ray Spectroscopy (EDS) and Differential scanning calorimetry Thermo-gravimetric analysis (DSC-TGA).
The synthesis method we employed here produced pure phase ZIF-8 nanocrystals having sodalite (SOD) type zeolitic topology evident from XRD pattern. The size measurement through DLS, SEM and AFM suggested ZIF-8 nanocrystals of ~100-200 nm size were obtained, wherein zinc acetate produced reproducible and least sized ZIF-8 nanocrytals indicating the effect of counterion on nanocrystals size. Furthermore, pH and metal to ligand ratio also showed effect on size which is accordance with previously reported literature.
Inorganic zeolites have been studied as micro-porous materials for application in gas storage, gas separation and heterogeneous catalysis because of their high stability and structure diversity. Porous Metal Organic Framework (MOFs) is a new class like of zeolite-analogous materials that are more desirable in pore size, shape and also wide structural diversity. Zeolitic Imidazolate frameworks (ZIFs) are a important subclass of porous metal-organic frameworks (MOFs). The ZIFs have structural resemblance to Zeolite topologies wherein all tetrahedral atoms are transition metals and are bridged by imidazolate (IM) units. A prototypical member of ZIF family; ZIF-8 shows remarkable properties such as large pore size with small window ideal for gas separation, storage and catalysis, high chemical and thermal stability, and high surface area. By the virtue of these properties, ZIF-8 have shown tremendous potential in wide range of applications.
Recently, nanocrystals of ZIF-8 have gained considerable research interest. The reduction of the particles size from the micrometers to nanometers scale causes changes in the surface properties of the materials, which further enhance the performance of ZIFs in the applications area such as catalysis, gas storage and gas separation. Nanocrystals shows high surface area to volume ratio, thereby enhancing surface dependent applications like gas adsorption, separation, catalysis and most importantly allowing easy fabrication of miniaturized sensors. However, syntheses of uniform, monodispersed ZIF-8 nanocrystals have been a challenge. Most of the synthesis methods reported for ZIF-8 have been carried out using organic solvents such as dimethylformamide (DMF), diethylformamide (DEF) or methanol which are expensive, and can cause pollution as well as risk to human health. In addition they are not scalable for industrial synthesis due to cost factor.
In the present work, We have synthesized ZIF-8 nanocrystals in completely aqueous medium at room temperature. Study on effect of different reaction parameters such as temperature, pH, rate of mixing and counterions have been attempted. For counterion studies, different zinc sources were used viz., zinc acetate, zinc chloride, zinc nitrate, and zinc sulphate. Rate of mixing of reactants was studied by setting different rpm (300,500, 900 1200 and 1500) for reaction mixture. Similarly, different pH (4, 5, 5.7, 7 and 8.2) and metal ion to imidazole ratios (1:50, 1:70 and 1:100) were set to check the effect of individual parameter on nanpocrystals size of ZIF-8. Subsequently, the optical and structural properties of synthesized nanocrystals were characterized various characterization techniques such as dynamic light scattering measurement (DLS), Fourier Transformed Infrared spectroscopy (FTIR), UV-Vis-NIR spectrophotometer, X-Ray diffraction (XRD), Atomic Force microscopes (AFM), Scanning electron microscopy (SEM), Energy Dispersion X-Ray Spectroscopy (EDS) and Differential scanning calorimetry Thermo-gravimetric analysis (DSC-TGA).
The synthesis method we employed here produced pure phase ZIF-8 nanocrystals having sodalite (SOD) type zeolitic topology evident from XRD pattern. The size measurement through DLS, SEM and AFM suggested ZIF-8 nanocrystals of ~100-200 nm size were obtained, wherein zinc acetate produced reproducible and least sized ZIF-8 nanocrytals indicating the effect of counterion on nanocrystals size. Furthermore, pH and metal to ligand ratio also showed effect on size which is accordance with previously reported literature.