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

Abstract MnO 2 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 2KMnO 4 + MnCl 2 → 3MnO 2 + 2KCl + O 2 was activated during mechanical milling. Excess KCl salt was added in the starting powder mixture to prevent agglomeration of MnO 2 nanoparticles. The milling resulted in the production of amorphous MnO 2 nanoparticles with a high surface area of 204 m 2  g −1 . Crystalline MnO 2 nanorods of diameters about 15–20 nm were produced by heating the as-milled powder at 350 °C for 1 h in air. Amorphous MnO 2 nanoparticles showed higher degradation rate of Rhodamine B than crystalline MnO 2 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 MnO 2 nano-catalysts for environmental applications.