Synthesis Of SiO₂and Al₂O₃Nanofibers With Controlled Diameters Via Electrospinning Method

Electrospinning is a fast emerging, cost-effective, simple and versatile technique for producing ultrafine fibers with size ranging from submicron to nanometer by utilizing electrostatic repulsive forces. Due to the excellent properties, inorganic nanofibers are widely used as catalyst carrier, heat-resisting materials, and high temperature reinforcing materials. Synthesis of inorganic nanofibers with superior performance is of importance for practical applications. In this study, the pristine polymer-supported fiber precursors were prepared by hydrolysis reaction of the inorganic salt in the acidic condition. The precursor solutions were transformed into SiO2and Al2O3nanofibers, and SiO2/Al2O3composite nanofibers with different diameters using electrospinning method.Firstly, silica nanofibers were synthesized by electrospinning method using PVA as the polymer additive and TEOS as the silica source. The PVA was dissolved in water and TEOS was added into the solution under the condition of acid hydrolysis. The solution as precursor was prepared into the PVA/SiO2composite fibers, and then the composite fibers were calcined at high temperature in air to remove PVA. The obtained inorganic products can retain fiber morphology, and show fiber diameters about1.02μm and good flexibility. With decreasing the polymer and inorganic salt concentration, the diameters of fibers can be prepared as ca.260nm.Secondly, Al2O3fibers were fabricated by using PVP as the polymer additive and the aluminium isopropoxide as the precursor. PVP, as the polymer additive, was dissolved in ethanol. Aluminium isopropoxide was added into the solution under the condition of acid hydrolysis. The solution as precursor was prepared into the PVP/AlOOH composite fibers, and then the composite fibers were calcined at high temperature in air to remove PVP. The resultant Al2O3fibers can retain fiber morphology, and show fiber diameters about720nm and good flexibility. By decreasing the polymer concentration, the fibers can be prepared with a diameter about120nm, while by decreasing the inorganic salt concentration, fibers can have a diameter of-180nm.Finally, we investigated the possibility of preparation of SiO2/Al2O3composite nanofibers. PVA, as the polymer additive, was dissolved in the mixture of ethanol and water. Aluminium isopropoxide and TEOS were added into the solution under the condition of acid hydrolysis. The solution as precursor was prepared into the PVA/SiO2/AIOOH composite fibers and then the composite fibers were calcined at high temperature in air to remove PVA. After calcination, the fiber morphology was retained. The mass ratio of SiO2to Al2O3in the final fibers were1:1,1:2and2:1and their diameters were310nm,340nm and280nm, respectively. With the increase in the amount of silica used, the surface of the fibers is getting smooth.