Polymer-Metal Complexes in Polyelectrolyte Multilayer Films as Catalysts for Oxidation of Toluene

We report on the binding of metal ions (Me2+; Co2+ and Cu2+) with weak polyelectrolyte multilayers (PEMs), as well as on catalytic activity of PEM-Me2+ films for oxidation of toluene. Using several types of PEM films constructed using branched polyethyleneimine (BPEI) or quaterinized poly-4-vinylpyridines (QPVPs) as polycations and poly(acrylic acid) (PAA) or poly(styrene sulfonate) (PSS) as polyanions, we found that binding of Co2+ and Cu2+ ions with a PEM matrix can occur both through coordination to polycationic amino groups and/or ionic binding to polyacid groups. The amount of metal ions loaded within the film increased linearly with film thickness and was strongly dependent on polyelectrolyte type, film assembly pH, and fraction of permanent charge in polymer chains. Among various PEM Me2+ systems, BPEI/PAA-Co2+ films assembled at pH 8.5 show the best catalytic performance, probably because of the preservation of high mobility of Co2+ ions coordinated to amino groups of BPEI in these films. With BPEI/PAA-Co2+ films, we demonstrated that films were highly permeable to reagents and reaction products within hundreds of nanometers of the film bulk; i.e., film catalytic activity increased linearly with layer number up to 30 bilayers and slowed for thicker films.