Homogeneous Precipitation Preparation And Characterizations Of γ-Al₂O₃Nanoparticles

Since porous γ-Al2O3nanoparticles possess the advantages of fine particle sizes and high specific surface area, they can be used for catalyst supports, adsorbents, material coatings and dehydrants. They can be widely applied in fields of petrochemical industry, environmental protection, pharmacy and metallurgy. In addition, they can also find applications in heat insulation, filtration, separation and sound absorption. Therefore, preparation of γ-Al2O3nanoparticles with the characteristics of low cost, high quality and ease to commercialization is of significance.In order to obtain high quality γ-Al2O3nanoparticles, high quality γ-Al2O3precursor nanoparticles must be prepared in advance. In other words, precursor nanoparticles with the features of small particle size, regular morphology, narrow particle size distribution, monodispersity should be prepared firstly. By selecting the appropriate calcination conditions when calcining precursors,γ-Al2O3nanoparticles with the features of small particle size, regular shapes, narrow particle size distribution, monodispersity can be obtained. However, the preparation of the precursors that meets all the above-mentioned requirements is still difficult so far. The preparation methods reported in literature have the disadvantages of high cost, complicated operation or impurity. Therefore, it is significant to develop a low cost preparation method for high quality γ-Al2O3precursor nanoparticles.Based on the above situation and understanding, a simple and low cost preparation method of γ-Al2O3precursor nanoparticles, homogeneous precipitation method, has been chosen through a literature survey and experimental verification. Homogeneous precipitation method has advantages of simple equipment and operation, low cost, easy to commercialization; and prepared nanoparticles have the features of fine particle sizes, regular shapes, a narrow particle size distribution, and good dispersity. In this work, the aluminum basic sulfate nanoparticles with the features of fine particle sizes, regular shapes, a narrow particle size distribution, and no agglomeration have been prepared by homogeneous precipitation method. During the process of preparation, cheap aluminium sulfate octadecahydrate was used as aluminum source, dimethylamine borane (DMAB) was used as a precipitant for the first time. After a calcination at950℃for2h, γ-Al2O3nanoparticles that inherit the shape of aluminum basic sulfate nanoparticles were obtained. According to LaMer’s qualitative explanation for the mechanism of the formation of monodisperse sulfur sols by the decomposition of sodium thiosulfate in acidic solution, the formation process of aluminum basic sulfate nanoparticles has been studied. Furthermore, the major factors that affect the preparation of alumina precursors (different aluminum salt, precipitating agents, aluminum salt, concentration of aluminum salt and precipitant concentration ratio, reaction time, cooling method) were studied. The optimal experimental conditions were obtained by contrastive analyses of the experiment. The main research conclusions are as follows:(1) The optimal preparation condition of alumina precursors is as follows:aluminium sulfate octadecahydrate is used as aluminum source. DMAB is used as a precipitant. The reaction time is1hour. The reaction temperature is80℃. The molar ratio of aluminum salt and precipitant is1:20. The concentration of aluminium ion is0.5mM.(2) The alumina precursors and the product calcined at different temperatures for the holding time of2hours) were analyzed by X-ray diffraction (XRD) and fourier transform infrared (FTIR) spectrometry, it can be clearly concluded that the alumina precursor is a aluminum basic sulfate phase. The product is the mixture of amorphous and y phase when the calcination temperature is800℃. The product is pure y phase when the calcination temperature is950℃. And the product after calcining at1000℃is the mixture of y and a phase. The microstructure of aluminum basic sulfate and γ-Al2O3nanoparticles (obtained by calcining the aluminum basic sulfate particles at950℃for2hours were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). It can be found that the prepared aluminum basic sulfate particles have the features of an average diameter of96run, spherical shape, a narrow size distribution from75to127nm, monodispersity and no agglomeration, and porous structure. The obtained γ-Al2O3nanoparticles have the features of an average diameter of90nm, spherical shape, a narrow size distribution from50to105nm, monodispersity and no agglomeration, porous structure, and polycrystals. γ-Al2O3nanoparticles with an average pore diameter of9nm and a narrow pore size distribution from2to16nm also can be found by the BJH pore size distribution obtained from the absorption branch of the nitrogen isotherms of the γ-Al2O3nanoparticles calcined at950℃for the holding time of2hours. The phase transition process of aluminum basic sulfate nanoparticles is as follows: amorphous Al(SO4)x(OH)yâ†'γ-phaseâ†'α-phase and γ-phase γ-Al2O3nanoparticles inherit the characteristics of spherical shape, monodispersity and porosity of Al(SO4)x(OH)y nanoparticles.