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Open AccessArticle

Structural and Electrical Studies for Birnessite-Type Materials Synthesized by Solid-State Reactions

1,2, 1,3,4,5,6 and 1,3,5,*
1
Grupo de Investigación en Procesos Químicos, Catalíticos y Biotecnológicos, Universidad Nacional de Colombia-Sede Manizales, Kilometro 9 vía al aeropuerto, La Nubia, Manizales 170003, Colombia
2
Facultad de Ciencias e Ingeniería, Universidad de Boyacá, Carrera 2ª Este No. 64–169, Tunja 15001, Boyacá, Colombia
3
Laboratorio de Materiales Nanoestructurados y Funcionales, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia-Sede Manizales, Kilometro 9 vía al aeropuerto, La Nubia, Manizales 170003, Colombia
4
Departamento de Ingeniería Química, Facultad de Ingeniería y Arquitectura, Universidad Nacional de Colombia-Sede Manizales, Kilometro 9 vía al aeropuerto, La Nubia, Manizales 170003, Colombia
5
Departamento de Física y Química, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia-Sede Manizales, Kilometro 9 vía al aeropuerto, La Nubia, Manizales 170003, Colombia
6
Departamento de Química, Universidad de Caldas, Calle 65 No 26-10, Manizales 17001, Colombia
*
Author to whom correspondence should be addressed.
Nanomaterials 2019, 9(8), 1156; https://doi.org/10.3390/nano9081156
Received: 14 July 2019 / Revised: 7 August 2019 / Accepted: 8 August 2019 / Published: 12 August 2019
(This article belongs to the Special Issue Functional Nanoporous Materials)
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Abstract

The focus of this paper is centered on the thermal reduction of KMnO4 at controlled temperatures of 400 and 800 °C. The materials under study were characterized by atomic absorption spectroscopy, thermogravimetric analysis, average oxidation state of manganese, nitrogen adsorption–desorption, and impedance spectroscopy. The structural formulas, found as a result of these analyses, were K 0.29 + ( M n 0.84 4 + M n 0.16 3 + ) O 2.07 · 0.61 H 2 O and K 0.48 + ( M n 0.64 4 + M n 0.36 3 + ) O 2.06 · 0.50 H 2 O . The N2 adsorption–desorption isotherms show the microporous and mesoporous nature of the structure. Structural analysis showed that synthesis temperature affects the crystal size and symmetry, varying their electrical properties. Impedance spectroscopy (IS) was used to measure the electrical properties of these materials. The measurements attained, as a result of IS, show that these materials have both electronic and ionic conductivity. The conductivity values obtained at 10 Hz were 4.1250 × 10−6 and 1.6870 × 10−4−1cm−1 for Mn4 at 298 and 423 K respectively. For Mn8, the conductivity values at this frequency were 3.7074 × 10−7 (298) and 3.9866 × 10−5−1cm−1 (423 K). The electrical behavior was associated with electron hopping at high frequencies, and protonic conduction and ionic movement of the K+ species, in the interlayer region at low frequencies. View Full-Text
Keywords: Birnessite; nanoporous metal oxides; impedance spectroscopy Birnessite; nanoporous metal oxides; impedance spectroscopy
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Arias, N.P.; Becerra, M.E.; Giraldo, O. Structural and Electrical Studies for Birnessite-Type Materials Synthesized by Solid-State Reactions. Nanomaterials 2019, 9, 1156.

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