Synthesis and Catalase Mimic Activity of MnO2 Nano Powder Prepared by Hydrothermal Process

Abstract

Manganese dioxide (MnO2) nanopowder has been synthesized by hydrothermal method. MnO2 was annealed at different temperatures (250, 400, 550, 700˚C). The crystal structure and surface morphology of these nanostructures were characterized by X-ray diffraction (XRD), Atomic Force Microscope (AFM) and Scanning Electron Microscopy (SEM). The catalase mimic activity (catalytic activity) of MnO2 against hydrogen peroxide (H2O2) was studied by using new method and found that 400˚C is the best annealing temperature. 1. Introduction For many years, manganese dioxide with diverse crystal morphologies are attracting a lot of attention, because of their outstanding structural flexibility combined with novel physical and chemical properties, which are of interest for the following applications, for example, molecular sieves, supercapacitors, catalysts and biosensors [1]. It is n-type semiconductor material [2]. Manganese dioxide exists in various polymorphic forms including α-, β-, γ- and δ-MnO2 which are different in the arrangement of basic octahedral [MnO6] units [3]. The hydrothermal method is a powerful synthesis approach for synthesizing various forms of manganese oxides because of the choice of precursors that can be used and control of reaction time, pH, and temperature and it is a simple and inexpensive technique [4]. The catalytic (catalase) activity can be measured by determining the decrease of H2O2 absorption (at 240 nm)[5,6]. The difficulties associated to this method, due to using high levels of substrate approximately (5-50 mM) to get acceptable absorbance [7]. Moreover, the high levels of H2O2 lead to formation of bubbles in the test cell which cause mistake measurements [8]. Catalase (catalytic) activity can be determined in other methods such as by titrimetric determination of H2O2 concentration, determination of oxygen production from decomposition of H2O2 by oxygen electrode [9,10]. There are simple colorimetric methods such as by Goth [11] for catalase, by measuring of hydrogen peroxide (unreacted) spectrophotometrically by a complex reaction with ammonium molybdate. Sinha and Hadwan [12,13] use another simple method, in which the decomposition of hydrogen peroxide determined spectrophotometrically by a complex reaction with dichromate/acetic acid reagent. Another method for catalase activity measurement is the titration method, which is used when high (UV) absorption pigmentation or precipitation of the sample does not allow the use of the spectrophotometric method [8]. Our work is new modified method which use spectrophotometric assay to determination of H2O2 by potassium permanganate in acidic solution.