A comparative study of several transition metals in Fenton-like reaction systems at circum-neutral pH

Abstract

The N, N'-(5-nitro-1,3-phenylene) bisglutaramide hydroxylation assay for spectrophotometric determination of the rate of oxidising species generation in Fenton-like systems was used to obtain comparative data for Cd(II), Co(II), Cr(III), Cu(II), Fe( III), Mn(II), Ni(II), and Zn(II). The pH range of interest was 5.5- 9.5 and was controlled by addition of an appropriate phosphate buffer. The temperature of the reaction mixture was controlled in the range 25-80 degreesC. The rates of production of oxidising species at pH 7 decrease in the following order: Cu(II) > Cr(III) > Co(II) > Fe(III) > Mn(II) > Ni(II), while Cd(II) and Zn( II) did not exhibit any catalytic activity and Ni( II) only led to a significant production of oxidising species at pH > 7.5. In mixtures of Cu( II) and Fe( III) the rate of oxidising species production may be considered as the sum of contributions of individual metals. This was not the case of a mixture containing additional small amounts of Zn( II), Co( II) and Mn( II). The later two had strong pro-oxidative effects, the addition of Zn( II) had an anti-oxidative effect. Apparent activation energies for oxidising species generation are in the range 75- 110 kJ mol(-1), and decrease in the following order: Cu( II) > Ni( II) > Mn( II) > Fe( III) > Co( II).