Electrochemical Preparation Of Polypyrrole Micro/Nanostructures Based On The Biomolecule-templates

Polypyrrole (PPy), one of the most important conducting polymers (CPs) with high electrochemical activity and good biocompatibility, has promising applications in various fields such as tissue engineering, drug delivery, anticorrosion, sensors and supercapacitors et al. It has proved that the polymerization of PPy required the incorporation of charged dopants and a number of biomolecules, such as heparin sodium, hyaluronic acid, collagen and enzymes et al, have been incorporated into PPy to increase its bioactivity. Notably, some biomolecules may play the role of template for the preparation of nano-materials. In the past few years, Au, Ag and Te nanowires have been synthesized with the assist of protein, polysaccharide or DNA. However, to the best of our knowledge, there were few reports on the synthesis of CPs nano materials guided by biomolecules. In fact, biomolecules are promising templates for the preparation of PPy nanostructures because it may link the unique properties of CPs nanomaterials with the biological properties of biomolecules. Consequently, this paper mainly pays attention to the electrochemical polymerization of PPy micro- and nanostructures with several linear biomolecules acting as morphology-directing agents. The main research results and contributions are described as follows:PPy nanowires were electrochemically synthesized at room temperature with the assist of biomolecules, including starch, sodium hyaluronate, chitosan and gelatin et al. This method has many advantages such as facile operation, mild (room temperature), short preparation time (30～600 s), controllable diameter, low cost, environmental friendly (near neutral phosphate buffer solutions) and one-step route (needn't removal of template).The influences of experimental conditions, such as concentrations (biomolecules, pyrrole, lithium perchlorate and phosphate), pH of the solutions, preparation methods, electrode materials and polymerization time et al, on the morphologies of PPy were studied. The results indicate that the diameters of the PPy nanowires can vary from 50 nm to 95 nm by changing the concentrations of pyrrole monomer (0.03～0.21 M) and biomolecule (0.002～0.08 wt %). PPy nanowires can grow on various electrodes including tin-doped indium oxide (ITO), titanium, gold, graphite and stainless steel. And various techniques such as galvanostatic method, potentiostatic method and cyclic voltammetry can be adopted. However, only cauliflower-like PPy can be prepared in the absence of biomolecules. Based on the results mentioned above, we proposed the possible preparation mechanism that chain-shaped biomolecules played the template-like role in the formation of PPy nanowires.PPy cone-like tubes were synthesized on the Ti electrode in the presence of starch when the concentration of pyrrole monomer is no less than 0.28M. The cone-like tubes stand upright on the electrode surface. The height and the bottom diameter are about 4～7μm and 1.5μm, respectively. There are obvious holes on the top of cone-like tubes and the diameter is 100～200 nm. The morphologies were influenced by the concentrations of biomolecules and pyrrole monomer, electrode materials, pontential, polymerization time and pH of the solutions et al. The formation of the cone-like tubes maybe explained by the double-template ("gas bubble" and starch) mechanism.