Synthesis and Catalytic Activity of Cryptomelane-Type Manganese Dioxide Nanomaterials Produced by a Novel Solvent-Free Method

Abstract

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Synthesis and Characterization of Manganese Oxide Catalysts for the Total Oxidation of Ethyl Acetate

“…Fibers or needle-like particles, typical of cryptomelane [11,20], are observed in samples synthesized under different pH with KMnO 4 (samples Mn1 to Mn4). In all cases considered, the nanofibers have very long lengths that vary from a few hundred nanometers to a few micrometers, and widths in the middle varying from 10 to 30 nm, characteristic of the method used [19]. However, it seems that the materials prepared with nitric acid have small fiber widths compared to those prepared with the buffer solution, which is consistent with the XRD results.…”

“…Since the splitting depends on the d configuration, the manganese valency can be estimated. According to this and to the relationship between DEs and the average oxidation state (AOS) reported by Galakhov et al [23], the AOS of all materials were calculated using the formula AOS ¼ 8:956 À 1:126 DE s ðeVÞ: Table 3 shows that all cryptomelane materials prepared at pH 4.5, 3.5 and 3.0 have an AOS between 3.8 and 3.9, which is in agreement with the mixed state of manganese in the framework of cryptomelane (coexistence of Mn(IV) and a minor amount of Mn(III)) [6,19]. …”

“…The open tunnel structure and mixed valences of OMS-2 make this material very attractive for oxidation catalysis and, therefore, the synthesis of OMS-2 material with high purities, small particle size, high surface areas, and high yield has been a challenge in recent years. Various synthetic routes have been explored [13], including thermal and hydrothermal treatment of layered birnessite [14], redox precipitation under reflux [7,15], microwave heating [16], sol-gel methods [17,18] and a solvent free procedure [19]. The reflux method, involving the oxidation of Mn 2?…”

Manganese cryptomelane-type oxides: A thermo-kinetic and morphological study

“…Two samples were prepared as follows: the first sample, a cryptomelane oxide denoted as PAM, was prepared by using the process reported by [8]. A solid-solid mixture of KMnO 4 and Mn(CH 3 COO) 2 , in the absence of solvents, was prepared by mixing weighted amounts of both solids (0.06 mol KMnO 4 and 0.09 mol Mn(CH 3 COO) 2 ), guaranteeing a stoichiometric ratio of 2/3.…”

Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO2 electrochemical capacitor electrodes

“…Manganese oxides are multifunctional materials that display a myriad of applications in advanced catalysis, 1 Li-ion rechargeable batteries, 2,3 microbial fuel cells, 4,5 and electrochemical capacitors. 6,7 They have been produced by a variety of chemical and physical methods such as hydrothermal synthesis, 8 sol-gel process, 9 physical vapor deposition (PVD), 10 chemical vapor deposition (CVD), 11 and electrodeposition.…”