Polyaniline is unique among the family of conducting polymers due to its ease ofsynthesis,environmental stability and simple doping/dedoping chemistry,which hasreceived growing interest in recent years.Nanostructures of polyaniline can lead to betterperformance in the already established areas and create new opportunities.In thisdissertation,on the basis of the review on the properties and preparation of polyaniline andin combination with current ways of synthesizing polyaniline nanomaterials,especiallyfree-template methods to prepare polyaniline nanofibers,a new approach for the synthesisof polyaniline nanostructures (nanofibers and nanowires) under UV light illumination hasbeen developed.This dissertation investigated the effect of various experimentalparameters,such as the kind of oxidants,their concentration,stirring and reactiontemperature et al.on the morphology and the ability of acid doping/dedoping of theproducts from UV illumination and in dark,respectively.The results indicate that thisphoto-assisted method not only is fitted for various oxidants with different oxidationability,but also prepares polyaniline nanofibers on the rigorous conditions,in which thenanofibers can not be obtained by conventional routes in dark.It is interesting thatphoto-assisted method at lower temperature can produce polyaniline nanowires withoutany template.In the consideration on the comparison of the protonation ability of aniline and itspolymer with other conductive polymers,a theoretical model was proposed to explain theformation of polyaniline nanofibers,namelyelectric double layersmodel.Thistheoretical model can better explain why the nanofibers are intrinsic morphology ofpolyaniline.In the presence of chiral CSA,this dissertation studied the effect of variousexperimental parameters on the polyaniline morphology and its optical activity,whichfurther confirms that it is rational forelectric double layersmodel,and found the correlation between polyaniline one-dimensional growth and its optical activity.TiO_2 photocatalytic technology attracts increasingly intesest due to its various merits.Inthe present work,in allusion to the existing problems,we tried to prepare one-dimensionalTiO_2 nanomaterials to enhance the UV photocatalytic activity;on the other hand,wedeveloped TiO_2 visible photocatalysts via the visible light sensitization of polyaniline.Infourth chapter,this dissertation modified alkaline hydrothermal method,salt effecttailoring TiO_2 and titanate nanostructures.We repeated investigating the important role ofNaOH in this alkaline hydrothermal method,and proposed a rational mechanism toexplain the formation of TiO_2 and titanate nanostructures on the basis of the evolutiveregulation of products morphology.In fifth chapter,we successfully synthesized TiO_2/polyaniline nanocomposites viaself-assembling and graft polymerization.The resulted nanocomposites were characterizedby using various measuremental technologies.The results indicated the formation ofself-assembling layer and outside polyaniline,and the better thermal stability of thesenanocomposites.Moreover,these composites showed better photocatalytic activity undersunlight due to the sensitizing effect of polyaniline.We further studied the oxidationcharacteristics of aniline at different concentration on TiO_2 photocatalysts,and proposed away of removing aniline in aqueous systems.Our strategy is to degrade and mineralizelow-level aniline by using a photocatalytic degradation process,and to convert high-levelaniline to TiO_2/polyaniline nanocomposites via a photocatalytic polymerization approach.