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.
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