Polyoxotungstates (POTs) are tungsten oxygen anion clusters of nanometric size characterized by a wide variety of structures [1]. Generally speaking, POTs can be divided into two main groups: isopolytungstates, constituted only by W and O atoms, and heteropolytungstates where a heteroatom (X¼Si, P, S, Ge, etc.) different from W and O is also present. The most important isopolytungstate is decatungstate anion that is viewed as the union of two W5O18 units, bonded through shared oxygen in vertices with internal empty space. Each subunit is made up of WO6 octahedra that has sides and oxygen atoms in common. Among heteropolytungstates, Keggin ([XM12O40]n]) and Dawson ([X2M18O62]n]) types represent the most common structures: a central tetrahedric XO4 unit is surrounded by a definite number of WO6 octahedra. POTs exhibit very peculiar structure-dependent chemical and physical properties (acid-base and redox properties) which are thermally and oxidatively stable and undergo photoinduced multielectron transfers without changing their structures. These features make them attractive materials for applications as redox catalysts. Moreover, irradiation with UV and/ or near UV light in the ligand to metal charge transfer band causes an intramolecular charge transfer from O2-based highest occupied molecular orbital (HOMO) to the W6+-based lowest unoccupied molecular orbital (LUMO) leading to the formation of a photoexcited state. The resulting photoexicted POT is highly reactive both in oxidation and reduction reactions and can trigger chemical transformations on organic and inorganic molecules that are transparent in the wavelength range employed. The entire process is truly photocatalytic when the photoexcited POT is regenerated in its initial state at the end of the reaction cycle (as it happens for a thermal catalyst), while the light is a stoichiometric reagent. This is the base of the utilization of POTs as photocatalysts. Also, POTs have been applied to a wide range of new applications [2–5], and most of them have been recently reviewed [6].
Heterogeneous photocatalysts based on iso- and heteropolytungstates
Alessandra Molinari;Michele Mazzanti
2021
Abstract
Polyoxotungstates (POTs) are tungsten oxygen anion clusters of nanometric size characterized by a wide variety of structures [1]. Generally speaking, POTs can be divided into two main groups: isopolytungstates, constituted only by W and O atoms, and heteropolytungstates where a heteroatom (X¼Si, P, S, Ge, etc.) different from W and O is also present. The most important isopolytungstate is decatungstate anion that is viewed as the union of two W5O18 units, bonded through shared oxygen in vertices with internal empty space. Each subunit is made up of WO6 octahedra that has sides and oxygen atoms in common. Among heteropolytungstates, Keggin ([XM12O40]n]) and Dawson ([X2M18O62]n]) types represent the most common structures: a central tetrahedric XO4 unit is surrounded by a definite number of WO6 octahedra. POTs exhibit very peculiar structure-dependent chemical and physical properties (acid-base and redox properties) which are thermally and oxidatively stable and undergo photoinduced multielectron transfers without changing their structures. These features make them attractive materials for applications as redox catalysts. Moreover, irradiation with UV and/ or near UV light in the ligand to metal charge transfer band causes an intramolecular charge transfer from O2-based highest occupied molecular orbital (HOMO) to the W6+-based lowest unoccupied molecular orbital (LUMO) leading to the formation of a photoexcited state. The resulting photoexicted POT is highly reactive both in oxidation and reduction reactions and can trigger chemical transformations on organic and inorganic molecules that are transparent in the wavelength range employed. The entire process is truly photocatalytic when the photoexcited POT is regenerated in its initial state at the end of the reaction cycle (as it happens for a thermal catalyst), while the light is a stoichiometric reagent. This is the base of the utilization of POTs as photocatalysts. Also, POTs have been applied to a wide range of new applications [2–5], and most of them have been recently reviewed [6].I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
