Electrospun Alumina Fibers And Their Potential Use In Environmental Areas

Recently, Environment problems such as water pollution and air pollution are more and more serious, which did increase the harm to our health. So it is meaningful to doing studies on simple and efficient methods for preparation of new materials which contribute to environment protection. Electrospinning technique, which has feature of simple equipment, easy operation, environment friendly, low cost and wide applications, can be used to prepare a variety of nanofibers. Al2O3 is an important functional material with advantages of fine thermostability, corrosion resistant, low density and low thermal conductivity. This work made progress in the field of Al2O3 nanofiber’s preparation by electrospinning and its applications in environment area, which includes the preparation of mesoporous Al2O3 fibers, SiO2-Al2O3 core-shell fibrous membranes and flexible Al2O3 fibrous membrane. Their applications in sewage disposal and fine particulate filtration areas are also discussed in the dissertation.1. Electrospinning preparation and adsorption property of mesoporous alumina fibersMesoporous alumina fibers were successfully synthesized via electrospinning technique combined with sol-gel method in the presence of triblock copolymer as structure directing agent. The sol was prepared with Al(NO3)3·9H2O and AICl3·6H2O as acidic alumina sources, isopropanol aluminium (Al(O-i-Pr)3 and alumina powder as basic alumina sources, HNO3 as catalyst, and deionized water as solvent. The mixture was stirred and refluxed at 80℃to form a transparent sol. The copolymer P123 was used as pore-structure directing agent, and the polymer PEO was used as spinning additive. The sol was electrospun to form the xerogel fibers, and after calcinations, the xerogel fibers transferred to mesoporous alumina fibers. The amorphous alumina fibers derived from the electrospun xerogel fibers after calcinations at 450℃and γ-Al2O3 fibers obtained after the xerogel fibers calcined at 700℃exhibit uniform mesopores with fiber diameters of 130-200 nm, and the BET surface areas are up to 264.1 m2g-1 and 242.6 m2g-1, respectively. After the xerogel fibers calcined at 1100℃, with the transformation from γ-Al2O3 to α-Al2O3, the significant grain growth occurs and the mesopores disappear. Further investigation indicates that the γ-AlO3 fibers have good adsorption property toward Congo red with the maximum adsorption capacity of 781.25 mg g-1 for the sample obtained at 700℃. In addition, the fibers show good stability in acidic conditions and good stability during reuse process, which makes its potential applications in adsorption as well as the related areas such as catalysis and catalyst support.2. Electrospun flexible self-standing silica/mesoporous alumina core-shell fibrous membranes as adsorbent toward Congo redFlexible core-shell fibrous membranes for mesoporous alumina based adsorbent have been fabricated via the one-step coaxial electrospinning, which is accomplished by electrospinning silica as the core phase and mesoporous alumina as the shell phase. The core-shell fibers could be directly electrospun in the form of membranes. After calcinations, the mesoporous alumina shell was formed to give a high adsorption capacity, and the core fibers were dense to provide the good mechanical property of the membrane. The membranes exhibit good adsorption property toward Congo red and can keep the membrane form during the cyclic test, which is easy to handle and retrieve. The adsorption capacity for the core-shell membranes after calcinations at 700℃ was 115 mg g-1 with the adsorption time of 48 h. The good adsorption performance, high mechanical property, easily recover and reuse characteristic of the fibrous membranes, as well as the simple fabrication process facilitate their practical application in environmental remediation.3. Electrospun flexible self-standing y-alumina fibrous membranes and their potential as high efficiency fine particulate filtration mediaNovel self-standing y-alumina fibrous membranes with good flexibility have been successfully fabricated by electrospinning technique for the first time. The sol was prepared by the reaction of alumina powder and carboxylic acid. PEO was added into the sol to adjust the viscosity of the sol. The sol was electrospun to form the alumina xerogel fibrous membranes, and after calcinations, the γ-Al2O3 fibrous membranes were formed. The y-alumina membranes were composed of randomly arranged nanofibers with high aspect ratio and small diameters (ca.230 nm). The tensile strength (2.98 MPa) and thermal stability (up to 900℃) of the y-alumina membranes are excellent, which favors its applications in high temperature conditions. Furthermore, the γ-alumina membranes exhibit good filtration performance for 300 nm dioctyl phthalate fine particulate gas filtration. The filtration efficiency is 99.848% and the pressure drop is 239.12 Pa for the membrane calcined at 700℃ with a basis weight of 9.28 g m-2; And the filtration efficiency could be over 99.97% when the basis weight is over 11.36 g m-2, suggesting that the γ-alumina fibrous membrane is a promising candidate for high temperature, fine particulate filtration applications. This work also provides a novel insight into the electrospinning of flexible self-standing inorganic membranes for applications in the separations field.