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 Pihlara
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
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).