Multifunctional Nanostructured Materials for Oxidation of Methanol

Abstract

Herein, we report on our investigation on the use of the aqueous solution of the phosphotungstate heteropolyblue as a reducing agent and stabilizer for the synthesis of gold nanoparticles deposited on multiwalled carbon nanotubes and functionalized with CO-type surface groups. Chemical reduction method allowed producing multi-walled carbon nanotube-supported gold (Au/MWCNTs) catalysts with high dispersion and loading of Au up to 5 wt%. The average diameter of Au nanoparticles on MWCNTs was 2.0-4.5 nm. The resulting gold nanoparticles were subsequently cleaned from their inorganic capping agents (PW12O40 3-) by converting to alkaline medium (NaOHaq). The high dispersion of gold nanoparticles at MWCNTs (pretreated with HCl, HNO3 and H3PMo12O40) was attributed to the presence of a high density of active sites for nucleation created during the functionalization procedure. The nanocomposite system based on multi-walled carbon nanotubes decorated with gold nanoparticles was probed towards electrocatalytic oxidation of methanol in alkaline medium under voltammetric conditions. The existence of mesopores created at the surfaces of multi-walled carbon nanotubes originated from an easy accessibility of the OH- groups and methanol molecules at the electrocatalytic interface. The chemical functionalization of the open ends and the side walls of MWCNTs played a vital role in tailoring their electrochemical properties. Electrochemical studies demonstrated the promotional effect of quick pseudofaradaic reactions of surface polar groups created on carbon nanotubes during the methanol electrooxidation process.