Simple Solution Plasma Synthesis of Hierarchical Nanoporous MnO2 for Organic Dye Removal

We have demonstrated a simple and green approach to synthesize hierarchical nanoporous MnO2 by applying plasma in a liquid precursor; the approach is named the “solution plasma process (SPP).” Three types of sugar, i.e., glucose, fructose, and sucrose, were used as inducers for the nanoporous MnO2 formation (hereafter called G-MnO2, F-MnO2, and S-MnO2). These were successfully synthesized within a few minutes (7–19 min) under ambient conditions. It was confirmed that the generated numerous reactive species (e.g., electrons, radicals, and ions) accelerated the reduction of MnO4–. The reaction rate as well as the physical and chemical features of resulting products were found to be related to the type of sugars. Their high surface areas (F-MnO2 (169.1 m2·g–1) > G-MnO2 (141.0 m2·g–1) > S-MnO2 (85.5 m2·g–1)) provided efficient capability for the adsorption of cationic dye molecules, i.e., methylene blue. The dye removal efficiencies of all samples were >99% for an initial dye concentration (C0) of 10 mg·L–1 w...