Environmentally Friendly gamma-MnO2 Hexagon-Based Nanoarchitectures: Structural Understanding and Their Energy-Saving Applications

Although about 200,000 metric tons of gamma-MnO2 are used annually worldwide for industrial applications, the gamma-MnO2 structure is still known to possess a highly ambiguous crystal lattice. To better understand the gamma-MnO2 atomic structure, hexagon-based nanoarchitectures were successfully synthesized and used to elucidate its internal structure for the present work. The structural analysis results, obtained from the hexagon-based nanoarchitectures, clearly show the coexistence of akhtenskite (epsilon-MnO2), pyrolusite (beta-MnO2), and ramsdellite in the so-called gamma-MnO2 phase and verified the heterogeneous phase assembly of the gamma-MnO2 state. which violates the well-known De Wolff model and derivative models, but partially accords with Heuer's results. Furthermore, heterogeneous gamma-MnO2 assembly was found to be a metastable structure under hydrothermal conditions, and the individual components of the heterogeneous gamma-MnO2 system have structural similarities and a high lattice matches with pyrolusite (beta-MnO2). The as-obtained gamma-MnO2 nanoarchitectures nontoxic and environmentally a re friendly, and the application of such nanoarchitectures as support matrices Successfully mitigates the common problems for phase-change materials of inorganic salts, such as phase separation and supercooling-effects, thereby showing prospect in energy-saving applications in future smart-house systems.