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Supermolecular Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Shangbin Jin, Jiang He, Qingmin Ji, Jonathan P. Hill, Katsuhiko Ariga
Polyoxometalates (POMs) are a class of inorganic cage complexes with very interesting properties, which render them attractive for catalysis application. The catalytic properties of dendritic POM hybrids were based on electrostatic bonding between POMs (the most frequent one is Venturello ion [PO4{WO(O2)2}4]3−) paired with dendritic cations. Dendritic POMs bearing Venturello ion exhibited good catalytic activity and recoverability in the oxidation of organic substrates such as alkenes, alcohols, and sulfides [169, 170]. Kortz and Nlate et al. used zirconium-peroxo-based dendritic POMs as efficient and recoverable sulfide oxidation catalysts [171]. The dendritic POMs are prepared by coupling zirconium-peroxotungstosilicate [Zr2(O2)2(SiW11O39)2]12− with ammonium dendrons by electrostatic bonding. In contrast to the potassium salt of [Zr2(O2)2(SiW11O39)2]12−, the dendritic counterparts are soluble in common organic solvents, which is an important feature for the use of dendritic hybrids in homogeneous catalysis. The oxidation of sulfides to the corresponding sulfoxides and sulfones by these dendritic catalysts showed good to excellent conversion. They are also stable and recoverable without any appreciable loss of activity.
Nanosized metal oxides (NMOs) and polyoxometalates (POMs) for antibacterial water treatment
Published in Alberto Figoli, Jan Hoinkis, Sacide Alsoy Altinkaya, Jochen Bundschuh, Application of Nanotechnology in Membranes for Water Treatment, 2017
Giulia Fiorani, Gloria Modugno, Marcella Bonchio, Mauro Carraro
The term polyoxometalates (POMs) refers to polyanionic and molecular oxides of early series transition metals. Their chemical composition is essentially represented by two types of general formula: [MmOy]p− and [XxMmOy]q−, where M is the main transition metal constituent (the addenda atom: typically W, Mo or V in their highest oxidation state), O is the oxygen atom and X (the heteroatom) can be a non-metal – another element of the p-block – or a different transition metal. In the case of the first formula type, POMs are called isopolyanions, while in the second case they are known as heteropolyanions.
Mesoporous Materials in Heterogeneous Catalysis
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Meenal Batra, Ashutosh Sharan Singh
Polyoxometalates (POMs) anions are another example of an excellent catalyst widely used for variety of catalytic applications. Its excellent redox properties, high acidity, good thermal as well as chemical stabilities drag scientists’ attention towards catalysis. The necessary requirement is to disperse on solid support because of their very low surface areas. Agglomeration, non-uniform distribution, leaching of POM on traditional supports like activated carbon, silicas are drawbacks for its practical applications. To resolve this issue, the first example reported by Férey and co-workers is to use meso-MOFs like MIL-101 as support to load POM anions [59]. Recently, encapsulation of POM anions inside meso-MOF as host has been reported [110] in MIL-100(Fe).
The TiO2 films with sandwich-type polyoxometalates in dye sensitized solar cells with electron recombination decreasing and dye adsorption increasing
Published in Journal of Coordination Chemistry, 2022
Tuo Ji, Di Wu, Xiaowen Zhang, Yue Zhao, Kaicheng Xu
Polyoxometalates (POMs) are discrete anionic metal oxides with high charge density and ability to accept multiple electrons, so they are good electron acceptor materials. Therefore, POMs can be doped into semiconductor materials as electron-transfer materials to accept photogenerated electrons in the conduction band of a semiconductor, used as a bridge for electron transmission to anode conductive materials and external circuits [29]. They can improve the electron-transfer rate of TiO2 and decrease recombination of electrons, improving the utilization of electrons and the overall efficiency of the battery [29]. Among POMs, sandwich-type POMs have good activity, stable structure, and variable element composition, and are the largest subgroup of vacancy Keggin type POMs [30, 31]. Vacancies in POMs provide more reactive sites, allowing the introduction of a variety of transition metals and other elements [32, 33]. Sandwich-type POMs are formed by two vacancy POMs linked with metal ions. The introduction of transition metals in the sandwich-type POMs, which have excellent performance in optical absorbing, can extend the absorption spectrum from UV- to vis-light, achieving full spectrum absorption.
Electrocatalytic detection of l -cysteine using molybdenum POM doped-HKUST-1 metal organic frameworks
Published in Journal of Coordination Chemistry, 2021
Tafadzwa W. Murinzi, Gareth M. Watkins, Munyaradzi Shumba, Tebello Nyokong
HKUST-1 (Cu3(BTC)2(H2O)n) is an example of a MOF with most of these desirable properties. It has a Brunauer-Emmett Teller (BET) specific surface area of 1055 m2/g and a pore size of 9 Å × 9 Å [13–15]; because of the latter, it has been employed as a matrix for other materials. For example, HKUST-1 has been used as a matrix to synthesize CuO and CuO-CeO2 nanoparticle catalysts for CO oxidation [16]. It has also been used for encapsulation of Fe3O4 nanocomposites for oxidation of benzylic C–H bonds [17] and for storage of gases (H2, N2) [18]. In addition to their matrix applications, when combined with other metals MOFs create synergistic effects on the properties of the resulting product, making them highly sought after candidates especially as catalysts [7]. Carbon functionalized MOF Nafion composites have been used for dopamine sensing [19]. Polyoxometallates (POMs) have been used as electrocatalysts due to the high oxidation states of the metals [20]. The combination of Cu and Mo centers in an electrocatalyst for reduction of nitrate has been successful for a small polyoxomolybdate (Mo2) [7]. Based on their previous successes, HKUST-1 was selected for this work to exploit its stability as a matrix and Mo POMs were selected for their catalytic potential creating Mo POM-HKUST-1 hybrid materials.
Synthesis, structure, and antimicrobial properties of mixed-metal organometallic polyoxometalates [Cp*2M5VO17]− (M = Mo, W)
Published in Journal of Coordination Chemistry, 2021
Hülya Avcı Özbek, Emre Erden Kopar, Funda Demirhan
Polyoxometalates (POMs) are molecular metal-oxygen clusters that contain transition metal ions, such as Mo, W, V, Nb, and Ta. Generally, POMs can be classified as either an isopolyanion [MmOy]q− containing only a metal “M” and oxygen, or a heteropolyanion [XrMmOy]q− which also has a heteroelement “X”. They have been extensively studied for their remarkable chemical and physical properties in many applications such as catalysis [1–3], photochemistry [4, 5], electrochemistry [6, 7], medicine [8, 9], macromolecular crystallography [10, 11], materials science [12], and magnetism [13]. Also, in recent years, they have attracted the attention of researchers in the field of green chemistry as environmentally friendly catalysts [14–17]. The observed wide range of POMs applications is due to redox activities; since their electron transport and release capacities are high, they are considered to have electron storage capabilities [18].