Controlled Preparation of MnO₂ Hierarchical Hollow Nanostructures and Their Application in Water Treatment

Abstract

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 ...

Porous boron nitride nanosheets for effective water cleaning

“…4c) fitted by the Langmuir model gives a maximum adsorption capacity Q m of 782 mg g À 1 , corresponding to complete monolayer coverage. This capacity is significantly higher than those from most adsorbent nanomaterials reported previously [31][32][33][34] . The versatility of porous BN nanosheets for targeting a wide range of organic wastes has been assessed by testing other dyes with opposite charges commonly used in the textile industry, such as the cationic dyes methylene blue (MB) (Fig.…”

LiMn2O4 microspheres: Synthesis, characterization and use as a cathode in lithium ion batteries

“…As shown in Fig. 1, MnCO 3 solid microspheres and MnO2 hollow microspheres as precursors were synthesized based on a modified version of a previous method [8,9]. They were subsequently transformed into LiMn 2 O 4 solid and hollow microspheres respectively.…”

Sintesis MnO2 Lapisan Nipis Poros menggunakan Templat Silika Alumina-Aptes: Aplikasi Penjerapan Pewarna

“…Keputusan daripada ulasan tersebut menunjukkan kemampanan teknik penjerapan sebagai satu kaedah yang dikaji dalam menyingkirkan bahan pencemar daripada efluen. Penjerapan pewarna dengan menggunakan penjerap logam oksida telah banyak dilakukan dan keputusan kajian menunjukkan keberkesanan yang tinggi bagi logam oksida (CuO, MnO 2 , Mn 2 O 3 , MnOOH) sebagai penjerap terhadap pewarna yang berbeza (Abdullah & Wong 2010;Cao et al 2011;Chen & He 2008;Chen et al 2013;Cui et al 2015;Fei et al 2008;Ge & Qu 2003). Jenis kristal logam oksida dan pH larutan memainkan peranan dalam aktiviti penjerapan pewarna oleh penjerap dengan kumpulan Cui et al (2015) Ujian penjerapan dilakukan dengan menggunakan tiga jenis pewarna berbeza yang terdiri daripada kumpulan anionik iaitu pewarna remazol merah (reaktif), eriokrom hitam (asid) dan kationik iaitu metilena biru (bes) menggunakan kaedah kelompok.…”