Facile preparation of ZrO2 whiskers by LiF-KCl molten salts synthesis

Monoclinic zirconia (ZrO2) whiskers were made via the molten salt method using zirconyl chloride octahydrate (ZrOCl2 ? 8H2O) as zirconium source, potassium chloride (KCl) as molten salt and lithium fluoride (LiF) as a mineraliser. DSC-TG, XRD, FE-SEM, Raman and TEM were performed to study the effects of heat treatment temperature, holding time and heating rate on the synthesis of zirconia whiskers. The results indicate that zirconia whiskers with diameters of 50-80 nm and aspect ratios of 10-30 can be obtained by heating the precursor at slow rate (3?C/min) to 718?C for 1 h and then at faster rate (7?C/min) to 950?C for 3 h. The whiskers have a smooth surface and grow in [001] direction. The key to the ZrO2 whiskers growth is the controlled dissolution and precipitation of the ZrO2 in a LiF-KCl molten salt solution environment.

An Analysis of the Effect of the Zirconium Precursor of MOF-808 on Its Thermal, Structural, and Surface Properties

<p>Due to their thermal and chemical stability zirconium based Metal-Organic Frameworks (Zr-MOFs) have been extensively studied in the literature. However, many details of the influence of preparation conditions are still unclear. Most papers tend to use one type of metallic precursors for synthesizing Zr-MOFs such as MOF-808. Therefore, as far as we know, a systematic analysis of the effect of the zirconium precursor on the properties of MOF-808 has not been conducted. In this work, three different metallic precursors were employed; namely, zirconium chloride, zirconyl chloride, and zirconyl nitrate for synthesizing MOF-808 keeping all other synthesis conditions constant. The results of the study indicated the following: (i) the nature of the zirconium precursor impacts the crystalline and porous structure of MOF-808. Particularly, the presence of structural water in the precursors causes a detriment in these properties which was reflected in an increase of the relative percentage of amorphicity of the materials as well as on the formation of disorganized mesopores. (ii) In contrast to (i), the surface properties of the materials and their thermal stability under an air atmosphere were not altered by the use of the different precursors. All materials exhibited a surface populated by free and uncoordinated carboxylates as well as inorganic zirconium structures corresponding to uncoordinated oxo-clusters. The ensemble of these findings contributess to a better understanding of the features that make MOFs interesting for diverse applications. Particularly, works on defect engineering may be benefited from the insight on surface chemistry provided in this contribution.</p>

An Analysis of the Effect of the Zirconium Precursor of MOF-808 on Its Thermal, Structural, and Surface Properties

<p>Due to their thermal and chemical stability zirconium based Metal-Organic Frameworks (Zr-MOFs) have been extensively studied in the literature. However, many details of the influence of preparation conditions are still unclear. Most papers tend to use one type of metallic precursors for synthesizing Zr-MOFs such as MOF-808. Therefore, as far as we know, a systematic analysis of the effect of the zirconium precursor on the properties of MOF-808 has not been conducted. In this work, three different metallic precursors were employed; namely, zirconium chloride, zirconyl chloride, and zirconyl nitrate for synthesizing MOF-808 keeping all other synthesis conditions constant. The results of the study indicated the following: (i) the nature of the zirconium precursor impacts the crystalline and porous structure of MOF-808. Particularly, the presence of structural water in the precursors causes a detriment in these properties which was reflected in an increase of the relative percentage of amorphicity of the materials as well as on the formation of disorganized mesopores. (ii) In contrast to (i), the surface properties of the materials and their thermal stability under an air atmosphere were not altered by the use of the different precursors. All materials exhibited a surface populated by free and uncoordinated carboxylates as well as inorganic zirconium structures corresponding to uncoordinated oxo-clusters. The ensemble of these findings contributess to a better understanding of the features that make MOFs interesting for diverse applications. Particularly, works on defect engineering may be benefited from the insight on surface chemistry provided in this contribution.</p>

An Analysis of the Effect of the Zirconium Precursor of MOF-808 on Its Thermal, Structural, and Surface Properties

<p>Due to their thermal and chemical stability zirconium based Metal-Organic Frameworks (Zr-MOFs) have been extensively studied in the literature. However, many details of the influence of preparation conditions are still unclear. Most papers tend to use one type of metallic precursors for synthesizing Zr-MOFs such as MOF-808. Therefore, as far as we know, a systematic analysis of the effect of the zirconium precursor on the properties of MOF-808 has not been conducted. In this work, three different metallic precursors were employed; namely, zirconium chloride, zirconyl chloride, and zirconyl nitrate for synthesizing MOF-808 keeping all other synthesis conditions constant. The results of the study indicated the following: (i) the nature of the zirconium precursor impacts the crystalline and porous structure of MOF-808. Particularly, the presence of structural water in the precursors causes a detriment in these properties which was reflected in an increase of the relative percentage of amorphicity of the materials as well as on the formation of disorganized mesopores. (ii) In contrast to (i), the surface properties of the materials and their thermal stability under an air atmosphere were not altered by the use of the different precursors. All materials exhibited a surface populated by free and uncoordinated carboxylates as well as inorganic zirconium structures corresponding to uncoordinated oxo-clusters. The ensemble of these findings contributess to a better understanding of the features that make MOFs interesting for diverse applications. Particularly, works on defect engineering may be benefited from the insight on surface chemistry provided in this contribution.</p>