A Composite Formation Route to Well‐Crystalline Manganese Oxide Nanocrystals: High Catalytic Activity of Manganate–Alumina Nanocomposites

Abstract

Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a signifi cant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as-prepared manganese oxide-aluminum oxide nanocomposite is X-ray amorphous whereas heat-treatment gives rise to the crystallization of an α α -MnO 2 phase at 600 ° C and Mn 3 O 4 /Mn 2 O 3 and γ -Al 2 O 3 phases at 800 ° ° C. Electron microscopy and N 2 adsorption-desorptionisotherm analysis clearly demonstrate that the as-prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ∼ 20 nm and a surface area of > 410 m 2 g − 1 . Of particular interest is that the small particle size of the as-prepared nanocomposite is well-maintained up to 600 ° C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very-high catalytic activity for the oxidation of cyclohexene with an extremely high conversion effi ciency of > 95% within 15 min. The present results show that the improvement of the crystallinity without signifi cant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals.

Nano “Koosh Balls” of Mesoporous MnO2: Improved Supercapacitor Performance through Superior Ion Transport

“…24–0735), although the product had low crystallinity with short‐range crystallographic arrangement (Figure c) . The Raman spectrum of MnO 2 ‐KBs had a strong peak at 651 nm along with a broad shoulder around 573 nm, which can be attributed to Mn−O lattice vibrations on the basis of literature precedence (Figure S3 c) …”

“…[38,39] The Ramans pectrum of MnO 2 -KBs had as trong peak at 651 nm along with ab road shouldera round5 73 nm, which can be attributed to MnÀOl attice vibrations on the basis of literature precedence ( Figure S3 c). [40][41][42] The N 2 sorption profile of MnO 2 -KBs exhibited at ype-IV adsorption/desorptioni sotherm with H3-hysteresisl oop, suggestive of its mesoporous nature with cylindrical pore geometries ( Figure 1d). [43,44] The BETs urfacea rea of MnO 2 -KBs was 235 m 2 g À1 ,w hich decreasedp rogressively as the Tween 20 concentration was increased.T he BET surfacea reas for the samples prepared at 7 ,1 4 ,a nd 28 CMC of Tween 20 were 267, 235, and 184 m 2 g À1 ,r espectively,( FigureS4i nt he Supporting Information andF igure 1d).…”

Graphene‐Assisted Room‐Temperature Synthesis of 2D Nanostructured Hybrid Electrode Materials: Dramatic Acceleration of the Formation Rate of 2D Metal Oxide Nanoplates Induced by Reduced Graphene Oxide Nanosheets

“…In the course of the reaction, a notable acidification of the reaction media occurs. In the case of the RGO-free reaction, the pH of the solution is decreased from % 6 to % 5 after the reaction for 1 h. The observed pH lowering is attributable to the oxidation reaction of water molecules by the persulfate ions as follows; S 2 2À C) radicals. [37][38][39] This process of radical formation is relatively slow but can be accelerated by several catalysts.…”

“…Over the past decade, low-dimensional nanostructured metal oxides have received a great deal of research activity because of their useful functions as electrodes, catalysts, nanobio materials, and so on. [1][2][3] There are intense research efforts devoted for the exploration of energy-saving and economic synthetic routes to nanostructured metal oxides. [4][5][6][7] Among the developed diverse synthetic methods, solution-based synthesis is quite advantageous in that a large amount of nanostructured metal oxides can be obtained in a single batch.…”

Facile synthesis and magnetic properties of manganese dioxide nanowires

“…Recently, much attention has focused on the synthesis of 1D MnO 2 nanostructures because of its promising applications in catalysis, rechargeable batteries, ion sieves and supercapacitors [24][25][26][27][28][29][30]. Up to now, various methods including sol-gel route, wet chemical method, template-assisted method and hydrothermal route have been developed to synthesise 1-D MnO 2 nanostructures [31][32][33][34][35][36]. Among these methods, the hydrothermal route is the most useful and efficient because the method can control the nanostructures by choosing the reaction temperature, concentration and time.…”