Controllable Preparation And Characterization Of Nanopolyaniline And Its Nanocomposites With Gold

The research on morphological control of micro/nanostructured polyaniline(PANI) and its composite have caused extensive attentions due to the huge impact ofmicrostructure, morphology and size on their physical and chemical porperties.Therefore, controllable design andsynthesis of micro/nanostructured PANI materialsand its composites have become a new hotspot of material scientificresearches.In thiswork, the PANI nanofibers and nanorods have been prepared via a simple chemicalpolymerization reaction of aniline with oxidant carried out in ethylene glycol (EG)medium. The polyaniline/gold nanoparticles (PANI/AuNPs) composite with differentmorphology such as nanofibers, nanospheres and nanoflowers also have been perparedthrough an one-step chemical synthesized method withthe assistance of EGmedium.The relationship between reaction conditions and structures or morphology ofmaterials is analyzed, and the formation mechanisms of nanostructuresarepresented.The main contents are as follow:Firstly, the PANI nanofibers and nanorods with controlled size and morphologyare preapredby the chemical methodin the absences of any templates using ammoniumpersulfate (APS) and hydrogen peroxide (H2O2) as the initiator, respectively. Thismaterialcan be facilely dispersed in a polar solvent such as water or ethanol to formsteadyPANI colloids.Mechanism investigations demonstrate that the existence ofstrong hydrogen bonds between EG and aniline or PANI is the main factor leading tothe one-dimensional orientational growth of PANI. The reaction conditionssignificantly impactthe morphology, size, and performance of PANI.The aspect ratioand conductivity of one-dimensional PANIis decreasedwith the rise of temperature,while the yield is increased.When the mole ratio ofH2O2to aniline is two and APS toaniline is one, respectively, the conductivity of PANI is the best. In addition, theconductivity and morphology of PANI nanofibers can be impacted by theconcentration and type of doping acid, in which the higher concentration of acid isbeneficial for the enhancement of the conductivity and yield, but the PANI nanofibersare unable to obtain when the CSA organic functional acid is used as the doped agent.Itcan be found by comparison that the presence of stirring can improve the doping level,conductivity, degree of oxidation and yield of PANI.Secondly, the one-dimensional morphological PANI/AuNPs composites are prepared by one-step chemical synthesized method in EG solution.The results indicatethat the reaction temperature and oxidant concentration have great influence on themorphologyof composites, and size and distribution of gold nanoparticles. As thetemperature increases, the length of PANI fibers is increased, but the diameter of fiberand size of gold nanoparticle is decreased.The electrochemical experiments show thatthe conductivity and electrical activity of composite as well as the distribution of goldnanoparticles are better when the reaction temperature is10℃.On theother hand, thelength of composite fibers and the diameter of gold nanoparticles is increased with theincreasing concentration of oxidant, but the diameter of fibers is reduced. When themole ratio of oxidant to aniline is1:5, the PANI/AuNPscomposite fibers andmicrospheres both can be observed in the product.In addition, the uniformity of sizeand distribution of gold nanoparticles embedded in the PANI can be improved byintroduction of H2O2, and resulting in the formation of PANI/AuNPs composite fibers.Finally, the PANI/AuNPs flower-shaped composites are also prepared by one-stepchemical synthesized method using sulfuric acid (H2SO4) instead of hydrochloric acid(HCl) as a dopant in the presence of H2O2.The experiments confirm that the chlorideions which come from HCl can inhibit the redox reaction of HAuCl4with aniline, butthe H2SO4is used as dopant can improve the redox reaction speed due to the absenceof chloride ion, which leads to the morphological change of PANI/AuNPs compositesfrom one-dimensional to flower-shaped nanostructure.Subsequently, it is found that theabesence of H2O2also can impact the reaction rate. Therefore, the PANI/AuNPscomposite nanospheres are synthesized in the absence of H2O2at alower temperatuer.Mechanism investigations demonstrate that the continuousaggregated growthofpreformed gold or PANI/AuNPs composite particles and the constantly reduction ofAu3+on bare gold surface are major factors for the formation of compositenanospheres.With the concentration of HAuCl4increase, the diameter of compositenanospheres is decreased and the formation of “thorn sphere” shaped compositespheres with more uniform protruding branches is observed. However, when theoxidant is excess, only the PANI/AuNPs composite fibers are formed, in which the sizeof gold nanoparticles is about5nm. The experimental results indicate thatthe presenceof agitation is beneficial for improving the surface smoothness of compositenanosphere, but not significant effect on their diameter.