A Simple and Green Procedure to Prepare Efficient Manganese Oxide Nanopowder for the Low Temperature Removal of Formaldehyde

Activated reactive synthesis, as a top-down synthesis approach, is proposed for the production of a nanocrystalline, high surface area, manganese (IV) oxide starting from commercial micrometric alpha-MnO2. The developed approach consists of two-steps: 1) high energy ball milling (HEBM) produces a nanosized material, 2) low energy ball milling (LEBM) improves textural properties. During the HEBM step, elementary crystals are observed to evolve from several hundred elongated cylindrical particles to short length cylinders and pseudo spherical particles. Despite fractioning of the elementary crystals, surface area remains low over the HEBM derived solid. The LEBM step, achieves crystal shape modification, giving rise to only pseudo-spherical nanometric particles and significantly increasing the surface area to approximately 60-80 m(2)g(-1). Catalytic activity of alpha-MnO2 powder is affected by the grinding process. Activity is similar to the fresh commercial MnO2 after HEBM, and increases upon LEBM reaching a maximum for LEBM time of 1 h. Thereafter, activity remains constant despite the further increase in surface area upon prolonged LEBM. The presence of an optimal activity after limited LEBM time is paralleled with the increase of the iron contamination occurring after prolonged LEBM time which impacts manganese reducibility and results in less reactive surface.