Anion adsorption on an Au colloid monolayer based cysteamine-modified gold electrode

Anion adsorption behavior on Au colloid surface was investigated in virture of depositing monolayers of Au colloid on the self-assembled monolayers of cysteamine on a gold electrode. Potential-dependent anion adsorption-desorption waves via the nonfaradaic current were obtained by means of cyclic voltammetry at Au colloid-modified gold electrodes in the potential range of -200-600 mV. The adsorption sequence in the order of adsorption peak potentials(E-pa) is OH-> citrate(3-)>H2PO4-> Cl-> SO42-> ClO4-> NO3-. Among them, citrate(3-) exhibited an entirely irreversible adsorption. A rise in temperature can increase the rates of adsorption-desorption and improve the reversibility of the adsorption-desorption of Cl-, SO42-, ClO4-, NO3- and H2PO4-. The adsorption peak potentials shifted more negatively for ca. 63 mV as the anion concentrations were increased by a decade factor. The change of pH from 7 to 1 slightly affected the adsorption peak potentials of Cl- and NOB. Au colloids with a smaller size((16) nm) gave rise to a better reversibility of the adsorption-desorption process and lower adsorption currents. The experimental results of citrate ions adsorption on Au colloid surface show that Au colloids with a smaller size prepared by sodium citrate method exhibited a higher stability in the solution in comparison to those with larger sizes because of its higher ratio of charge/mass. In other words, the smaller gold nanoparticles are covered with citrate ions monolayer that can also be formed at larger gold nanoparticles by means of electrochemical scan.