Recent Manganese Oxide Octahedral Molecular Sieves (OMS–2) with Isomorphically Substituted Cationic Dopants and Their Catalytic Applications

Abstract

The present report describes the structural and physical–chemical variations of the potassium manganese oxide mineral, α–MnO2, which is a specific manganese octahedral molecular sieve (OMS) named cryptomelane (K–OMS–2), with different transition metal cations. We will describe some frequently used synthesis methods to obtain isomorphic substituted materials [M]–K–OMS–2 by replacing the original manganese cationic species in a controlled way. It is important to note that one of the main effects of doping is related to electronic environmental changes, as well as to an increase of oxygen species mobility, which is ultimately related to the creation of new vacancies. Given the interest and the importance of these materials, here, we collect the most recent advances in [M]–K–OMS–2 oxides (M = Ag, Ce, Mo, V, Nb, W, In, Zr and Ru) that have appeared in the literature during the last ten years, leaving aside other metal–doped [M]–K–OMS–2 oxides that have already been treated in previous reviews. Besides showing the most important structural and physic-chemical features of these oxides, we will highlight their applications in the field of degradation of pollutants, fine chemistry and electrocatalysis, and will suggest potential alternative applications.

Self-assembly of random networks of zirconium-doped manganese oxide nanoribbons and poly(3,4-ethylenedioxythiophene) flakes at the water/chloroform interface

“…17 The most extensively studied OMS material is K-OMS-2 because of its rich porous and tunnel structure. 11 K-OMS-2 has a hollandite 2 × 2 tunnel structure of dimensions 4.6 × 4.6 Å 2 formed by corner and edge sharing [MnO 6 ] units, acquiring a tetragonal I 4/ m crystal structure. 6,11,14 The framework manganese centers are multivalent (4+, 3+, and minor 2+), where the charge neutrality is retained by K + ions occupying the 2 × 2 tunnels.…”

“…9,10 Expeditious efforts have been made to develop MnO x nanostructures, which offer strong redox couples of Mn 2+ /Mn 3+ and Mn 3+ /Mn 4+ associated with the multivalent Mn x + species on the MnO x surface. 11–13 Among the wide varieties of MnO x catalysts, manganese dioxide (MnO 2 ) is identified as the most promising due to its easily reversible multiple oxidation states, 14 low cost, 15 environmentally-benign nature, 16 controllable morphology, 9 and high-level of polymorphism. 11…”

Ni-Ce-OMS-2 material: preparation and preliminary catalytic-study on removing ethanol in the gas phase

“…This material has manganese oxides framework with structural unit of MnO6 octahedra connecting by sharing vertices and edges, creating a tunnel structure. The OMS materials are varied through the arrangement of MnO6 octahedra units that define the tunnel structure with dimensions ranging from (2.3 x 2.3) Å to (4.6 x 11.5) Å [Sabaté et al, 2021]. Manganese oxide octahedral molecular sieve cryptomelane (K-OMS-2) is an one-dimensional manganese oxide, formed a 2 x 2 tunnel structure having dimensions of 4.6 Å with K + ions inside for a charge balance system [Yin et al, 1994].…”

Adsorption of Rutin from Aqueous Solution over an OMS‐2‐Modified ZrO2 Nanocomposite

“…They also used high‐pressure steam heat technology to prepare mesoporous Zr/La hydroxide fibers which were able to adsorb phosphate from aqueous solution [18] . Cryptomelane‐type manganese oxide octahedral molecular sieve (OMS‐2), a type of MnO 2 with alpha crystal phase, is composed of MnO 6 unites in 2x2 tunnel structure [21–23] . It has been applied in catalysis, adsorption, ion‐exchange, battery and semiconductivity since OMS‐2 has mild acid and basic properties, porosity, mixed valence of Mn species and rich surface oxygen vacancies [24–31] .…”

“…[18] Cryptomelane-type manganese oxide octahedral molecular sieve (OMS-2), a type of MnO 2 with alpha crystal phase, is composed of MnO 6 unites in 2x2 tunnel structure. [21][22][23] It has been applied in catalysis, adsorption, ion-exchange, battery and semiconductivity since OMS-2 has mild acid and basic properties, porosity, mixed valence of Mn species and rich surface oxygen vacancies. [24][25][26][27][28][29][30][31] In terms of wastewater treatment, dyes and As(III) in wastewater were usually removed via adsorption over MnO 2 with alpha phase.…”