Influence of the hydrodynamic size and ζ potential of manganese ferrite nanozymes as peroxidase‒mimicking catalysts at ph 4 in different buffers

Abstract

Peroxidase-mimicking activity of manganese ferrite nanoparticles was studied, based on the oxidation of TMB (3,3’,5,5’-tetramethylbenzidine) by H2O2 at pH 4 using acetate and citrate buffers. The aim of this study was to examine this reaction not only by enzymology (Michaelis-Menten kinetics model) but also by surface science methods of heterogeneous catalysis. Nanoparticles were characterized by different techniques to determine their phase composition, surface area, surface composition, surface charge, pH at the point of zero charge, magnetization, mean size, and morphology. Results show that the nanozymes are coated with buffer anions that form a shell around them. In addition, the hydrodynamic size and ζ potential of the nanoparticles under reaction conditions play an important role in the proposed Fenton-type oxidation mechanism. A greater amount of Mn ions than Fe ions leaches from the nanozymes during TMB oxidation, likely because Fe is better protected than Mn by the buffer coating the outer surface of the nanoparticles. This shortcoming must be addressed when applying these nanomaterials.