Thermodynamic and Kinetics Aspects of Spherical MnO2 Nanoparticle Synthesis in Isoamyl Alcohol: An Ex Situ Study of Particles to One-Dimensional Shape Transformation

Abstract

Thermodynamically stable and robust α-MnO2 nanowire has been obtained in gram quantity from low cost starting materials KMnO4 and isoamyl alcohol. Here KMnO4 acts as an oxidizing agent and eventually produces the corresponding acid which caps the spherical MnO2 particles. The MnO2 nanoparticle formation is monitored by UV−visible spectrophotometry, and the activation energy of the reaction is reported to be 44−49 kJ mol−1. The particles upon modified hydrothermolysis (MHT) reaction produce nanofibrils and the nanofrabrils finally evolved stable α-MnO2 nanowires by heat treatment. The spherical MnO2 nanoparticles under MHT conditions undergo oriented attachment and result in MnO2 nanofibrils, i.e., the shape transformation takes place from spherical MnO2 nanoparticles to nanofibrils. This has been documented in this study. The nanofibrils, being thermally unstable, upon heat treatment easily change to robust single-crystalline defect-free α-MnO2 nanowires with an exact angle of 90° between (200) and (002) crystal planes.