Manganese oxides are of considerable importance in technological applications, including ion-exchange, molecular adsorption, catalysis, and electrochemical supercapacitors owing to their structural flexibility combined with novel chemical and physical properties. [1][2][3][4][5] Up to now, various nanostructures of MnO 2 , such as nanoparticles, [6] nanorods/-belts/-wires/-tubes/-fibers, [7][8][9][10][11] nanosheets, [12] mesoporous/molecular sieves and branched structures, [13,14] urchins/orchids, and other hierarchical structures [15] have been synthesized by different methods.Over the past years, fabrication of hierarchical hollow nanostructures has attracted significant interest because of their widespread potential applications in catalysis, drug delivery, acoustic insulation, photonic crystals, [16][17][18][19][20] and other areas. Until now, the general approach for preparation of hollow structures has involved the use of various removable or sacrificial templates, referred to as "hard", such as monodispersed silica, [21,22] polymer latex spheres [23] and reducing metal nanoparticles, [24] as well as "soft" ones, for example, emulsion droplets/ micelles [25] and gas bubbles. [26] Furthermore, lots of one-pot template-free methods for generating hollow inorganic microand nanostructures have been developed employing novel mechanisms, including the nanoscale corrosion-based insideout evacuation [27] and Kirkendall effect. [28] Recently, rhombododecahedral silver cages have been prepared by self-assembly coupled with the precursor crystal-templating approach. [29] By treating the external morphologies of hollow structures, unique properties can be obtained. [30] Thus, it is desirable to develop easy methods to control the morphologies of assembled systems with well-defined hierarchical structures. Herein, we report a simple controlled preparation of hierarchical hollow microspheres and microcubes of MnO 2 nanosheets through self-assembly with an intermediate crystaltemplating process. As shown in Figure 1, the synthesis is performed by a three-step process. Particularly, discrete spherical and cubic hollow MnO 2 nanostructures with controlled morphologies can be prepared by changing the morphologies of MnCO 3 precursors, which can be simply obtained by adding the (NH 4 ) 2 SO 4 solution in the reaction system, and the thicknesses of the shells of hierarchical hollow nanostructures can be adjusted easily by the relative quantities of KMnO 4 reacted followed by selective removal of MnCO 3 crystal template with HCl. When used as adsorbent in waste-water treatment, as-prepared MnO 2 with a hierarchical hollow nanostructure exhibited a good ability to remove organic pollutant.Some related chemical reactions are shown as follows. The main chemical reaction (1) can be formulated with two half reactions. On the basis of the value of E°, the standard Gibbs free energy change DG°of reaction (1) could be estimated as -99.0 kJ mol -1 , implying strong tendency for reaction (1) to progress toward the right-hand side. As ...

We report that a single dipeptide (L-Phe-L-Phe, FF), which is probably one of the smallest peptide gelators, can self-assemble into long nanofibrils in organic solvents and entangle further to form gels. The obtained FF gels are responsive to temperature, and the FF sol-gel process is thermoreversible. The formation of such gels may be driven by the hydrogen bond of peptide main chains and the π-π interactions between aromatic residues of the peptide. Lipophilic nanocrystals can be encapsulated into the gel through gelating the organic solution of corresponding nanocrystals using the FF gelator at room temperature. Quantum dots (QDs) are encapsulated into the FF gel by adopting the above method. The resulting gels with the incorporated QDs still remain photoluminescent (PL). It is an effective method to protect QDs from oxidation and improve the stability of the QDs. This strategy is generally suited for encapsulation of lipophilic nanocrystals.