tannins and gold-tetrachloride--acid

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl4, and the electrochemical reduction of HAuCl4 to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl4 along with FeCl3 and/or CuCl2, the NCPF remained selective toward the electrochemical reduction of HAuCl4 into the metallic state. The chemical reduction of HAuCl4 into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29±1.45 mg g(-1) at 60°C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.

Topics: Chlorides; Copper; Electrochemical Techniques; Electrodes; Ferric Compounds; Gold; Gold Compounds; Oxidation-Reduction; Tannins

Colloidal gold probes have become widely used for immunocytochemical staining at the electron microscopic level. Gold sols are producing by boiling a solution of tetrachloroauric acid with a reducing agent. The type of reducing agent and the concentration of components determine the final particle size. Gold sols that have a particle size ranging from 2 to 40 nm can be made in the laboratory, depending on the type and concentration of the reducing agent. This chapter details methods for producing various sizes of gold. The methods are relatively simple and very reproducible from batch to batch.

Topics: Chlorides; Citrates; Gold Colloid; Gold Compounds; Particle Size; Reducing Agents; Tannins; Thiocyanates