Carboxylic acid-functionalized, core–shell polystyrene@polypyrrole microspheres as platforms for the attachment of CdS nanoparticles

Abstract

Polypyrrole-coated polystyrene latex particles bearing N-carboxyl functional groups (PS@PPyCOOH) were prepared by the in-situ copolymerization of pyrrole (Py) and the active carboxyl-functionalized pyrrole (PyCOOH) in the presence of 390 nm diameter-sized polystyrene (PS) latex particles. Uncoated PS particles were prepared by emulsion polymerization of styrene. The initial comonomer fractions (in mol%) were 25/75, 50/50, 75/25 and 100/0 for pyrrole and PyCOOH, respectively. The PS@PPyCOOH x particles, where x stands for the initial molar fraction of PyCOOH ( x = 0, 25, 50 or 75%), were characterized in terms of particle size, surface morphology, chemical composition and electrochemical redox activity using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), FTIR, TGA and cyclic voltammetry respectively. TEM showed an increase of the latex particle diameter after coating by the conducting polymer layer, from 390 nm for uncoated PS to 430 nm for PS@PPyCOOH 50 particles, allowing an estimation of the PPyCOOH shell thickness to 20 nm. FTIR and XPS detected PyCOOH repeat units at the surface of the latex particles, indicating that this monomer had indeed copolymerized with pyrrole. The core–shell structure of the PS@PPyCOOH x particles was confirmed by etching the polystyrene core in THF, leading to the formation of hollow conducting polymer capsules. Positively charged CdS nanoparticles were electrostatically assembled onto the surface of PS@PPyCOOH 50 particles, as a function of pH. It was found that, contrarily to unfunctionalized PPy-coated latex particles, PS@PPyCOOH 50 particles could be evenly decorated with stabilized CdS nanoparticles, at pH 5. The films of the PS@PPyCOOH@CdS-coated ITO electrodes are shown to be electroactive and electrochemically stable.