Template-free Construction And Characterization Of Alumina And Other Hollow/Porous Metal Oxides

Alumina and other inorganic hollow/porous metal oxides have played crucial roles and potential application prospects in the fields of high-performance catalyst supports,adsorption separation and electrochemistry.Currently,inorganic hollow/porous materials are constructed mainly by using soft or hard template methods.However,there are some bottlenecks in the template preparation of hollow/porous materials,such as complicated operations,difficult large-scale production,high-content impurities,relatively narrow pore size and relatively low pore volume.Herein,the purpose of this dissertation was to develop a batch preparation technology.Without employing additional templates,based on the solubility differences and interface reactions,a series of inorganic hollow/porous materials with adjustable pore volume were prepared using self-assembly method and spray reaction.The research framework and results are as follows:(1)Fabrication of porous alumina and other metal oxides by interfacial self-assembly.The gas produced by the thermal decomposition of ammonium carbonate in a sealed container was diffused to the aluminum or magnesium salts solution,these metal ions can be subjected to acid-base reaction at the gas-liquid interface,and specific precursors can be obtained by self-assembly process.Then porous alumina or MgO can be constructed after subsequent calcination.The effects of reactants and subsequent treatment temperature were investigated.The adsorption properties of the porous alumina and MgO have been evaluated and measured by using the adsorption of macromolecule Congo red as the model.The results showed that the spindle-like aluminas which were rich in macropores can be obtained by using aluminum nitrate as aluminum source in the self-assembly process,and the flower-like porous MgO can be obtained by using magnesium chloride as magnesium source.The as-obtained porous alumina and MgO samples using this self-assembly method had excellent specific surface areas and relatively significant pore volumes.The as-obtained porous alumina and MgO had superior adsorption performances towards the organic dye in aqueous phase:the maximum adsorption capacity of porous alumina was 3284 mg/g,and the adsorption capacity of porous magnesium oxide was more than 5000 mg/g.(2)Preparation of high purity aluminas with large pore volume by a spray hydrolysis reaction.In order to improve the purity and pore volume of alumina,aluminum isopropanol which can be easy to purify by distillation was employed as as aluminium source,ammonium carbonate aqueous solution was employed as hydrolysate.The solution of aluminum isopropoxide was sprayed into the hydrolysate by using a atomizer.The precursor was prepared after aging and separation,and then the porous high-purity alumina can be obtained by calcination.The effects of the precursor preparation conditions and calcination parameters on the pore structure of nanometer alumina have been investigated.The results showed that the pore volume of the alumina(2.95 cm3/g)obtained by atomization feed was larger than that by direct drop feeding(1.35 cm3/g),it was 4 times that of the commercial ?-Al2O3.The specific surface area and the pore volume of the product decreased with the increase of calcining temperature from 300? to 1100?.Among them,the specific surface area of the alumina calcined at 300? was 498 m2/g,and the pore volume was up to 3.14 cm3/g;the specific surface area and the pore volume of the alumina calcined at 1100? were 94 m2/g and 1.25 cm3/g.However,the pore diameter was still concentrated mainly at 56.9-58.2 nm.(3)The construction of hollow/porous alumina and other metal oxides by the spray precipitation method.Based on the above-mentioned self-assembly and spray hydrolysis reaction,without any additional template,a simple,convenient and universal spray precipitation method has been further proposed,which can be used to construct a variety of porous metal oxide hollow spheres without template.The inorganic salt solutions were used as the raw material by this method,the spherical droplets produced by the atomization were added into solution systems specified.Based on the difference of solubility or interfacial acid-base reaction,metal ions can be precipitated,the corresponding hollow structure can be been formed.Hollow metal oxide microspheres can be obtained by subsequent treatment.The effects of aging time and raw materials on the structure of hollow alumina were investigated.The universality of this method for the preparation of a series of hollow/porous materials such as magnesium oxide,nickel oxide,manganese oxide,magnesium oxide/alumina,molybdenum oxide,tungsten oxide and nickel oxide/silver was investigated.The results are as follows:the as-obtained alumina samples possessed high specific surface areas and pore volumes,and the specific surface area and pore volume of the ?-Al2O3 hollow microspheres consisted of nanorods were 360 m2/g and 1.59 cm3/g,respectively.The extension of aging time was beneficial to the formation of hierarchical structures;and the raw materials can change the morphology of the primary particles in the shell structure of alumina.This method had nice universality and can be successfully used to construct various porous metal oxide hollow spheres,indicating that this method is expected to open up an economical and simple way to construct hollow/porous materials.(4)Large-scale construction of hollow/porous alumina.Based on the above-mentioned research results,a set of scalable spray precipitation reaction system which can be employed to manufacture kilogram-scale raw materials has been further designed and built.An industrial ultrasonic atomizing nozzle was employed to spray the aluminum sulfate solution into alkaline ethanol,and then hollow/porous alumina powders can be constructed in batch after the water addition,washing,and calcination.The effects of calcination temperature,raw materials,aging time and aging temperature on the structures of hollow/porous alumina were studied in kilogram-scale experiments.Products were characterized by electron microscopy,nitrogen adsorption and so on.The results showed that the products were hierarchical aluminas with large pore volumes,which can be basically consistent with the results of the gram-scale experiment.?-Al2O3 with a pore volume of 1.56 cm3/g and an average pore size of 18.1 nm was acquired after calcination at 600?,and the pore volume was 2 times as much as that of the commercial ?-Al2O3.The as-prepared hierarchical amorphous alumina powders calcined at 300?,which was composed of rod-like secondary structures,possessed a noteworthy pore volume(2.04 cm3/g)and a nice specific surface area(505 m2/g).Benefiting from their excellent structural and functional properties,these powders presented superior adsorption performance and good recyclability.Moreover,the maximum adsorption capacity of our alumina toward Congo red was 8 times that of the ?-Al2O3 obtained by spray drying.