Research On The Preparation Of Polyaniline Nanostructures By High Gravity Chemical Oxidative Polymerization

As a typical intrinsically conducting polymer (ICP), polyaniline (PANI) has attracted intense attention due to easy synthesis, low cost monomer, unique acid/base doping/dedoping and oxidation/reduction chemistry. PANI nanostructures integrate the conductivity of ICP and the unique physical/chemical properties of nanomaterials, e.g. size effect, surface effect and quantum effect. PANI nanostructures have wide application prospect.High gravity technology (Higee) is a novel chemical process intensification technology, which can highly intensify multiphase mass transfer and micromixing. Rotating packed bed (RPB) is a familiar high-gravity apparatus, and it has already been used in the preparation of nanoparticles. RPB has obvious advantages in the production of nanosized powders, such as less reaction time, smaller particle size, and narrower size distribution as well as easier industrialization.In this work, PANI nanoparticles and nanofibers were successfully synthesized by high gravity chemical oxidative polymerization (HGCOP) in RPB for the first time. The synthesis mechanism, influence factors and application of PANI nanostructures were investigated. The main contents of this paper were summarized as follows:1. PANI nanostructures were synthesized by rapid mixing method in stirred tank reactor (STR) and HGCOP in RPB, respectively. Additionally, two kinds of HGCOP processes, including batch process and circulation process, were advocated for the preparation of PANI nanostructures. This study shows that the high-gravity field in RPB is very helpful in the generation of a high level of supersaturation which is necessary to homogeneous nucleation. PANI prepared by HGCOP batch process keeps a morphology of nanofibers (30-50nm) while that prepared by HGCOP circulation process keeps a morphology of nanoparticles. In the HGCOP batch process, PANI grows from nanoparticle to nanofiber. HGCOP is more favorable than the rapid mixing polymerization on the preparation of PANI nanofibers, and its advantage is especially obvious when the polymerization is carried out with a relatively higher aniline concentration (0.5mol/L).2. The influences of operating conditions in HGCOP batch process on the morphology and properties of PANI nanofibers were investigated. The result indicates that PANI nanofibers with diameters of 30-50nm can be successfully obtained in a wide range of aniline concentration (0.1-0.5M) by HGCOP batch process. The diameters of PANI nanofibers decrease as the high-gravity level increased. PANI nanofibers prepared at a higher reaction temperature maintain more regular morphology. PANI nanofibers prepared at lower reaction temperature have better doping level and crystallinity. Nanofibers appear to form no matter what acid dopant (including HC1O4, HC1, H2SO4 and H3PO4) was used in the polymerization. PANI nanofibers synthesized using strong acids are more uniform and smooth than that prepared with relatively weak acids. The suitable range of An:APS in the synthesis of PANI nanofibers is from 4:1 to 2:1. The weight-average molecular weights of the products are higher than 20000. The highest conductivity is exhibited by the sample prepared at 20℃.3. The dispersion stability of PANI nanofibers in different system and the adsorption of Cr(VI) by PANI were studied in this work. The result shows that the dispersion stability of PANI nanofibers in water is better than that in hydrochloric acid (1M HC1) and absolute ethylalcohol. PANI has a strong capability in the the adsorption of Cr(VI). The amount of adsorption reached equilibrium (about 99.7%) within 30min.