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Deposition of two natural clays on a Pt surface using potentiostatic and spin-coating techniques: a comparative study

Department of Chemistry, College of Science, Hashemite University, P.O. Box 330001, Zarka 13133, Jordan

^* E-mail: aymani{at}hu.edu.jo

(Received 16 October 2007; revised 2 April 2008)

Two natural clays (kaolinite and montmorillonite) were deposited onto a platinum electrode surface using two deposition techniques and under different experimental variables. For both clays, the percentages of surface coverage (% ) were optimized in the 75–96% range. A greater surface coverage was observed at higher temperatures for both clays, which confirms the endothermic nature of the deposition process. The maximum surface coverage (96%) was achieved for kaolinite. The surface coverage of kaolinite on a platinum electrode was constant for deposition times between 6 and 20 h. A surface coverage of 91% with montmorillonite particles was achieved. There was a very small increase in surface coverage by increasing the concentration of clay in the modified solution. The maximum surface coverage was observed under acidic conditions and smaller coverage values were reported for neutral and basic solutions. For both clays, a complete surface coverage for the electrode surface was achieved using the spin-coating technique. The experimental variables that affect the deposition of the clay, such as the stoichiometric ratio of clay/PVC and centrifugation speed and time, were studied and optimized to obtain full surface coverage. The spin-coating method achieved the required durability and stability for the modified-electrode. The characterization showed that the metallic surface chemistry of the platinum electrode was totally suppressed. Both modified electrodes were found to be useful for determination of Ag(I) ion with a detection limit as small as 1.00 x 10^–10 M. The analytical precision was also satisfactory (RSD <5.0%).

KEYWORDS: natural clay, potentiostatic deposition, spin-coating deposition, electrochemical analysis, clay-modified electrodes