Electrochemically active mercury nanodroplets trapped in a carbon nanoparticle - chitosan matrix

A thin composite film of carbon nanoparticles (ca. 8 nm diameter) and chitosan biopolymer (poly-D-glucosamine, from chitin, 75-85% deacetylated) was prepared by evaporation from aqueous dispersion onto glassy carbon electrode surfaces. The amine groups in the chitosan biopolymer were used to effectively bind Hg(II) ions from an aqueous pH 5 KCl solution. During redox cycling voltammetric responses for bound mercury are readily observed and mercury nanodroplets (ca. 5.4 (± 1.0) nm diameter based on SAXS measurements) are formed in the film by applying a negative potential. The binding of Hg(II) ions to the chitosan-carbon nanoparticle film occurs with an approximate Langmuirian constant of 2.7 × 10⁴ mol^-1dm³ and the process is dependent on (i) the chitosan content in the film, (ii) the Hg ²⁺ concentration, and (iii) the immobilization time. The immobilized mercury nanodroplets within the carbon nanoparticle - chitosan film are electrochemically active and allow the co-deposition of other metals in the form of amalgams. Preliminary experiments for the anodic stripping voltammetry for Pb²⁺ and for Cu²⁺ are demonstrated. Mercury nanodroplet modified chitosan - carbon nanoparticle film electrodes represent a novel electroanalytical tool.