Polyoxometalates and Their Composites as Photocatalysts for Organic Pollutants Degradation in Aqueous Media—A Review

Abstract

Polyoxometalates (POMs), eco‐friendly solid acids, are polyatomic anions containing transition metal (group 5 or group 6) oxyanions linked together through shared oxygen atoms. First, the structure, classification, synthesis, non‐photocatalytic applications, and their photocatalytic properties and applications are presented. POMs are very interesting due to their unique and remarkable characteristics. One of the most attractive characteristics of POMs is their activity as an electron relay, that is, they can undergo stepwise multi‐electron redox reactions while their construction remains intact. Based on this characteristic, POMs have been widely used as photooxidation catalysts for organic and inorganic contaminants removal. According to the literature, POMs are useful homogeneous photocatalysts for the mineralization of dyes, phenol and its derivatives, chloroacetic acids, and pesticides and wood pulp bleaching. Applications of POMs have been limited because of their high solubility in water. Immobilization and solidification of POMs using different methods and various supports for making them reusable are studied in this review. Varieties of composites of POMs are synthesized to make them photorespond to the visible light region.

Photocatalytic Degradation of Organic Dyes with Magnetically Separable PANI/Fe3O4 Composite under Both UV and Visible‐light Irradiation

“…As the HOMO level of MG is situated lower than the oxidation potential of H 2 O/ * OH (+ 2.32 V), H 2 O receives a hole from the HOMO level of MG* to create * OH directly. [55,56] Based on our experimental results and the literature discussions above, the mechanism of photocatalytic degradation of MG dye on the Fe 3 O 4 \PANI catalyst has been proposed, as expressed in reactions from 3 to 14.…”

The Intrinsic Charge Carrier Behaviors and Applications of Polyoxometalate Clusters Based Materials

“…Photogenerated oxo-centered radicals are capable of initiating numerous chemical reactions, including the oxidation of alcohols into aldehydes [77] and ketones, [78,79] the functionalization of alkanes into ketones, [80] the epoxidation of various olefins, [81] and degradation of organic pollutants [82][83][84][85][86][87][88][89] etc. For example, alkylammonium polymolybdates(VI) would oxidize water to form OH▪ with an accompanying reduction of Mo VI into Mo V under photoexcitation.…”

MOF/POM hybrids as catalysts for organic transformations

“…49 The common structures of POMs include Keggin, Wells–Dawson, Anderson, Waugh, Silverton, and Lindqvist. 50 POM anions are a very well-defined electron pool of inorganic building blocks with Lewis and Brønsted acidity that can also be utilised as solid catalysts in multiple organic transformations. 51 However, due to their low specific surface area and stability, their use is limited.…”