posted on 2001-04-18, 00:00authored byRoshan H. Kore, Jaideep S. Kulkarni, Santosh K. Haram
The effect of nonionic surfactants on the disproportion kinetics of copper sulfide nanoparticles (aqueous sols) from the golden brown, copper-rich phase (Q-Cu2S) to the green
covellite phase (Q-CuS) has been presented. The transformation follows a first-order rate
law. There is a substantial decrease in the rate of transformation in the presence of nonionic
surfactants, viz. TX-100, NP-9.5, and NP-40. An attempt has been made to explain the
phenomenon based on a surface state catalyzed transformation that is sensitive to the
adsorption. The surface coverage (θ), estimated from the dependence of the rate constant
on surfactant concentration, fitted the Langmuir adsorption isotherm. From these, the
equilibrium constants and standard Gibbs free energy change of adsorption
have
been estimated.