The kinetics of gold(III) extraction by pyridine-2-azo-p-dimethylaniline in water and in micellar systems

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Aydinoglu S., Biver T., SECCO F., Venturini M.

COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, vol.481, pp.431-438, 2015 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 481
  • Publication Date: 2015
  • Doi Number: 10.1016/j.colsurfa.2015.05.048
  • Journal Name: COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.431-438
  • Keywords: DTAC, Au(III)-PADA complex, Micellar catalysis, Reaction mechanism, Gold speciation, COMPLEX-FORMATION, PADA, DISSOCIATION, INTERFACES
  • Çukurova University Affiliated: Yes

Abstract

The kinetics of reaction between AuCl4- and the azo-dye pyridine-2-azo-p-dimethylaniline ( PADA) have been investigated in water and in the presence of DTAC micelles, using classical spectrophotometry and the stopped-flow technique. PADA reacts with different chloro/hydroxo gold(III) complexes, in turn formed as the pH and Cl- concentration were changed, according to a network of parallel paths. In aqueous solution, at low pH values, a fast step is observed which is ascribed to the ligand induced expulsion of a labile water molecule from the reacting species Au(H2O)Cl-3 which forms at low pH values. At higher values of pH, the reaction is much slower because, in the key step, PADA has to replace the more inert Cl- ions in the gold coordination shell. In the presence of DTAC a remarkable catalytic effect is observed, owing to the absorption and attraction of the reactants on the micelle surface. Moreover, DTAC favors the formation of aquochloro aurates, thus inducing a change in the gold( III) speciation compared to that in water. The analysis of the data suggests that the aquo species Au(H2O)Cl-3 and Au(H2O)(2)Cl-2(+) play a major role in the reaction mechanism. (C) 2015 Published by Elsevier B.V.