Synthesis and characterization of iron and copper doped β-MnO2 nanoparticles

Manganese dioxide (beta-MnO2; Pyrolusite) nanoparticles doped with 1 and 2 mol % of iron and copper oxide contents have been synthesized by sol-gel technique and characterized by XRD, SEM, Raman, FTIR, UV-Vis spectroscopy and Magnetization measurements. The particle size is found to vary from 23 to 15 nm with increase of dopant concentration. The surface morphology of all samples was studied by Scanning Electron Microscopy and shows the small agglomeration. The agglomeration increases with increase in doping concentration may be attributed to the strength of vander Waals forces, changes with particle size leads to increase in surface area of MnO2 nanoparticles. The two main Raman peaks correspond to the stretching mode of MnO6 octahedral, and the peaks at lower wave number are attributed to the deformation modes of the metal-oxygen chain of Mn-O-Mn in MnO2 octahedral lattice. The FTIR spectra of pure and doped Manganese dioxide nanoparticles were recorded in the spectral range 400-4000 cm(-1). The weak absorption peak at 2300 cm(-1) and 2360 cm(-1) may be attributed to alkynes groups. The fundamental absorption peaks at 1620 cm(-1) & 3400 cm(-1) are assigned to the bending and stretching vibrations of O-H group. The optical band gap was determined from UV-Vis absorption spectra and found to increase with decrease in particle size and is attributed to quantum confinement effect. The increase in coercivity (189 kOe to 385.1 kOe) with decrease in particle size also indicates the quantum phenomenon at nanoscale.