Solvent free mechanochemical synthesis of MnO2 for the efficient degradation of Rhodamine-B

Abstract

MnO2 nanorods were synthesized by mechanochemical processing with subsequent heat treatment and their photocatalytic activity was studied on the decolourization of aqueous solution of Rhodamine B at different pH levels. A solid state redox reaction 2KMnO4 + MnCl2 → 3MnO2 + 2KCl + O2 was activated during mechanical milling. Excess KCl salt was added in the starting powder mixture to prevent agglomeration of MnO2 nanoparticles. The milling resulted in the production of amorphous MnO2 nanoparticles with a high surface area of 204m2g−1. Crystalline MnO2 nanorods of diameters about 15–20nm were produced by heating the as-milled powder at 350°C for 1h in air. Amorphous MnO2 nanoparticles showed higher degradation rate of Rhodamine B than crystalline MnO2 nanorods under simulated sunlight. The degradation rate was higher under acidic conditions. This work demonstrates the potential for cost effective, green and scalable synthesis of MnO2 nano-catalysts for environmental applications.