Aluminum-based Metal-Organic Frameworks And Derivative Alumina

Recently,research on metal–organic frameworks?MOFs?has attracted much attention due to their large surface areas accompanied by uniform pores,and potential applications in gas storage,separation,catalysis,multiferroics,drug delivery and so on.Among them,the trivalent ion aluminum was found to be a good candidate for the generation of three-dimensional networks with noticeable porosity,lightweight,low cost,nontoxic,and most of these materials are stable against hydrolysis.However,more interest has been focused on the synthesis of new Al-MOFs,or control and application of the pores in MOFs,the growth control as well as the application of the secondary building units?SBUs?has received little attention.If the growth control of Al-MOFs could be realized,and the assemble of Al-cluster in the transformation of Al-MOFs could be figure out,it would be meaningful for the development of MOFs.Accordingly,based on the current research,a new method was proposed for the controllable synthesis of MOFs,and the transformation process of Al-MOFs to alumina was investigated.The results are listed below:Four kinds of Al-MOFs,named MIL-53,MIL-96,MIL-100,MIL-110,were synthesized successfully by hydrothermal method,using Al?NO₃?₃·9H₂O and 1,4-benzenedicarboxylic acid or 1,3,5-benzenetricarboxylic acid as reactants.Besides,the synthesis conditions were modified to realize the scale-up fabrication.Based on the characterization,using same aluminium source but different ligand could produce Al-MOFs with different structure and morphology.Even using same aluminum and ligand,the structure and morphology could also be different,since the pH,concentration,and time were changed.All the scale-up products have regular morphology and high porous structure,which is helpful for the following research.Based on the synthesis of MIL-96,the method of dual reactant systems was firstly proposed,which is an efficient method to realize the size and morphology control of MIL-96crystals.By mixing other forms of reactants to replace the coordination modulators or capping agents,the size and morphology of MIL-96 could be selectively varied by simply altering the ratio of dual reactants via their hydrolysis reaction.Although dual aluminium source and ligand can both have effect on the growth control of MIL-96,the mechanism of them is different.The isopropanol produced in the hydrolysis process of aluminum isopropoxide could coordinate competitively with BTC and inhibit the nucleation and growth process of crystals,while the effect of Me₃BTC was derived from the slow hydrolysis rate which limits the release of BTC,as well as the growth of crystals.This method is also useful for the controllable synthesis of MIL-53-Al and MIL-101-Cr,indicating the universality of dual reactant systems for the MOFs using hydrothermal method.Through two-step treatment of MIL-96,microporous alumina was firstly synthesized.High temperature and inert atmosphere could induce the carbonization of ligand in frameworks,then the carbon in the Al₂O₃/carbon composite was removed in air.The effect of temperature,heating rate and time on the microstructure,morphology,surface and acid properties of alumina was investigated,and found that temperature and heating rate could remarkably affect the texture properties and surface of microporous alumina,while time have little effect on the properties of alumina.The as-synthesized four kinds of different Al-MOFs?MIL-53,MIL-96,MIL-100 and MIL-110?were used as precursor to fabricate mesoporous alumina with different morphology and texture structures through thermal treatment method.Results from characterizations showed that alumina products keep the morphology of their precursor,and the thermal treatment conditions have large effect on alumina microstructures;besides,the structure of Al-MOFs and its secondary building units have structure-directed effect in the formation of alumina.