In Situ Growth and Characterization of Metal Oxide Nanoparticles within Polyelectrolyte Membranes

Abstract

This study describes anovel approach for the in situ synthesis of metal oxide-polyelectrolyte nanocomposites formed via impregnation of hydrated polyelectrolyte films with binary water/alcohol solutions of metal salts and consecutive reactions that convert metal cations into oxide nanoparticles embedded within the polymer matrix. The method is demonstrated drawing on the example of Nafion membranes and avariety of metal oxides with an emphasis placed on zinc oxide.T he in situ formation of nanoparticles is controlled by changing the solvent composition and conditions of synthesis that for the first time allows one to tailor not only the size, but also the nanoparticle shape,g iving ap reference to growth of ap articular crystal facet. The high-resolution TEM, SEM/ EDX, UV-vis and XRD studies confirmed the homogeneous distribution of crystalline nanoparticles of circa 4nmand their aggregates of 10-20 nm. The produced nanocomposite films are flexible,m echanically robust and have ap otential to be employed in sensing,o ptoelectronics and catalysis.There is atremendous demand in developing novel polymer composites that contain an inorganic phase with particular interest towards the inclusion of semiconducting metal oxide nanoparticles (MONP). Doing so endears the composite material to applications in heterogeneous catalysis, [1][2][3] sensors [4] for both biological compounds [5] and chemical warfare agents; [6,7] actuators, [8] optoelectronics, [9,10] energy storage, [11] and chemical protection. [12] In this study,w ef abricate MONP-polyelectrolyte nanocomposites and investigate the conditions that lead to the in situ growth of MONP within hydrated polyelectrolyte films impregnated by aqueous solutions of metal salts.B yi nvoking consecutive reaction schemes,the metal cations are converted to MONP within the polyelectrolyte matrix. Nafion serves as the archetype polyelectrolyte,d ue to its commercial availability and widely investigated properties. [13] Its molecular structure is comprised of ahydrophobic fluoroalkene backbone,towhich hydrophilic sulfonated side chains are attached. Upon hydration, Nafion nanosegregates into hydrophobic and hydrophilic subphases. [14] Thel atter represents ac ontinuous 3D network of water domains of the nanometer size. [15,16] An instructive image of nanoscale segregation in amodel Nafion film simulated with the coarse-grained dissipative particle dynamics [14] is given in Scheme 1. Thec ontinuity and restricted geometry of the hydrophilic subphase allows for uniform nucleation and controlled growth of MONP.T his approach, that has been earlier demonstrated with examples of Fe 2 O 3 , [17] ZnO, [18,19] and from zirconium phosphate, [20,21] has particular advantages over other efforts to incorporate MONP into Nafion, which have largely focused on traditional techniques to fabricate the nanoparticles beforehand then incorporating them into the polymer,such as dropcasting with apolymer resin via the doctor blade method [22] or with the use of organic salts as the precursor.T hese tra...