A new strategy towards electroactive polymer–inorganic nanostructure composites. Silver nanoparticles inside polypyrrole matrix with pendant titanocene dichloride complexes

Abstract

Proposed synthesis route is oriented towards hybrid materials, in which inorganic nanoparticles are distributed mostly inside the film of a polymer with conjugated chain far away from its external surface in contact with solution. Its principal idea is to perform the electrodeposition of these particles from a solute precursor in conditions where the electronic transport across the film is so slow that it represents a rate-determining step of the process and the reduction of precursor molecules takes place deeply inside the pores of the film. Such situation is realized in conjugated polymers functionalized by pendant redox-active centers, if the deposition process occurs in the potential range of their redox activity. Important advantage of this procedure consists in the absence of any additional surface-active or stabilizing agent which has to be used if the nanoparticles are incorporated into the growing film from their solubilized colloidal solution. Sizes of these particles may be varied in a controllable manner by the duration of the process and other parameters of the system. This approach has been successfully realized for deposition of silver nanoparticles inside the polymer with polypyrrole matrix and titanocene dichloride ( TcCl 2 ) complex attached to each monomer unit, poly(titanocene-propyl-pyrrole), p(Tc3Py). Redox transformation of these TcCl 2 centers in contact with acetonitrile (AN) solution takes place in the negative potential range (starting at about −0.9 V vs. Ag/0.01 M Ag + in AN) separated from the interval of the matrix conductivity by broad non-electroactivity potential range. To prevent the reduction of silver cation in the range of the polymer conductivity, i.e. to shift the silver deposition potential strongly in the negative direction, 0.1 M TEACl solution in AN was used as electrolyte in addition to silver cation. Excess of chloride ions results in complete transformation of solute silver into soluble complex anion, AgCl 2 - , whose reduction wave at the polymer-coated electrode overlaps with the wave due to reduction of pendant TcCl 2 centers. Presence of chloride anions in solution results also in reversible type of the redox transformation of titanium, Ti(IV)/Ti(III), inside TcCl 2 complexes, that is a prerequisite for the electronic transport across the film via hopping mechanism. Process of AgCl 2 - complex ion electroreduction at the p(Tc3Py) modified electrode has been studied by means of electrochemical methods and EQCM. Synthesized composite material: electroactive polymer–nanoparticles has been characterized by SEM-EDX, AFM and TEM-SAED-EDS. Nanoparticles are composed of Ag(0), their crystallography demonstrating the bulk-metal fcc state and the one with fivefold symmetry (isohedral structure).