One-pot mass self-assembly of MnO2 sponge-like hierarchical nanostructures through a limited hydrothermal reaction and their environmental applications

We report an environmentally-responsible limited hydrothermal reaction to construct gram-scale MnO2 sponge-like hierarchical nanostructures composed of ultrathin nanosheets (similar to 5 nm) in one pot. This template-free strategy simultaneously avoids the disposal of toxic materials and provides novel metal oxide nanostructures. As a typical application, the MnO2 hierarchical nanostructures prepared can easily remove positively-charged methylene blue in water with much more adsorption capacity than those of commercial carbon grain and MnO2 microparticles, TiO2 and Fe2O3 nanoparticles. Meanwhile, the solid liquid separation is ready due to higher density resulted from their hierarchical nanostructures. Importantly adsorbed methylene blue can be reclaimed after elution with ethanol. Remarkably, the sponge-like hierarchical nanostructures can be recycled for many times with no obvious loss of adsorption capacity, qualifying them as a great potential application in environmental protection and resource reuse. (C) 2015 Elsevier Inc. All rights reserved.