A comparative study of SEVERAL TRANSITION METALS in Fenton-like reaction systems at circum-neutral pH

Matija Strlič,*^a Jana Kolar,^b Vid-Simon Šelih,^a Drago Kočar,^a and Boris Pihlar^a

^a Faculty of Chemistry and Chemical Technology, University of Ljubljana,

Aškerčeva 5, SI-1000 Ljubljana, Slovenia

^b National and University Library, Turjaška 1, SI-1000 Ljubljana, Slovenia

^* matija.strlic@uni-lj.si

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 ^oC. 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).