Kinetic and mechanistic features on the reaction of stored TiO2 electrons with Hg (II), Pb (II) and Ni (II) in aqueous suspension

Abstract

The reaction of electrons stored on TiO2 nanoparticles with heavy metal ions Hg (II), Ni (II) and Pb (II) has been studied employing steady state and stopped flow spectrophotometric techniques. Prior to kinetic investigation the formation of metal deposits is detected by their surface Plasmon absorbance observed after mixing of their corresponding metal ions with stored electron on TiO2 nanoparticles (eTiO2-). The dynamic of transfer of stored TiO2 electrons to Hg (II), Pb (II) and Ni (II) in water has been investigated after mixing in the stopped flow chamber following the decrease of the absorbance of eTiO2- at 600nm. The results indicate that Hg (II), Pb (II) and Ni (II) ions react readily with eTiO2-. The kinetic parameters of the electron transfer reactions have been obtained by pseudo first order fitting. In the presence of Hg (II) ions, the transients decay followed by a buildup at 380–480nmrange. In the presence of Pb (II) and Ni (II), a concurrent decay of TiO2 electron absorbance and buildup of the absorbance of metal deposits were observed. The rate constants of the electron transfer reactions induced by TiO2 stored electrons to metal ions increase with the driving force of the reaction according to Tafel equation.