Preparation And Photocatalytic Characterization Of Electrospun Silica-doped Titania Fiber

Titania has become research hot spot in recent years because of its chemical stabilityunder UV-vis radiation, biocompatible, free of secondary pollution and efficient in degradingof organic pollutants. However, conventional suspended nano-powder system is prone toagglomerating and hard to recycle, which greatly limits its application in practical waste watertreatment. Therefore, titania photocatalyst immobilization becomes the main trend in thefuture. In this paper, sol-gel method combined with electrospinning were applied to preparetitania self-supported fiber mat, which acted as photocatalytic active component andsupporting material as well. The self-supported photocatalyst has a good application prospectfor its efficiency and facility.In this thesis, tetra-n-butyl titanate and anhydrous acetic acid were used as the startingmaterials for a simple one step sol-gel process. Water molecules generated by in situesterification reaction pushed forward the hydrolysis of titania precursor in a gentle,homogeneous way. Titanium-oxo linear molecules formed and rendered the spinning soladequate spinnability for electrospinning. Tetraethyl orthosilicate was added to the sol at thispoint and spinning sols with vavious silica contents were prepared. A cone and platerheometer was applied to study the rheology of spinning sols with various reacting time at afixed reaction condition, while the morphology of the fibers electrospun from these spinningsols were observed under SEM. The results showed the spinning sol reacted for 84 hours hadthe best spinnablity, where the molar ratio of tetrabutyl titanate and anhydrous acetic acid was1:2.5 and the reacting temperature was 50℃. The effect of the silica doping on thespinnability were studied via SEM and the spun fiber was found to be thinning with theincrease of dopant content from 5% to 20%. The thinning effect of silica dopant, where silicadoping ratio was fixed at 5 mol %, was found to be still working when the feeding rate of thespinning sol was scaled up to twofold, fourfold or even eightfold from 2.33 mL/h, with thediameter decreasing from 3% to30%.The effect of silica doping on crystal phase transformation and grain growth was studied.First, TG-DSC was applied to determine the mass and heat variation during the calcination ofthe titania precursor. The result showed that the removal of the organic component as well as the crystallization were suppressed by the effect of dopant. Then the influence of heating rateand the dopant amount on crystal phase transformation and grain growth was investigated byXRD test. The XRD result showed the phase transformation temperature of titania anatase torutile shifted from 800℃to 900℃. Moreover, the grain growth of anatase or rutile weresharply suppressed by the dopant. Samples calcinated at 600℃were characterized bynitrogen adsorption, wherein 5 mol % Si sample showed the largest BET surface area andwell-developed porous structure.Methylene blue was chosen as the target of photocatalysis measurment, the photocatalyticefficiency of samples with different calcinating temperatures and silica doping amounts werestudied. The pure series showed the best photocatalytic activity when calcinated at 700℃,while the doped series showed the optimum activity at 600℃. The photocatalytic activity oftitania was improved after doping silica and the 5 mol % sample exhibitted the optimumactivity.