Two New Sandwich‐Type Phosphomolybdates: Thermal Decomposition and Photocatalytic Degradation Behavior of a UV‐Excited Solid‐Phase Fenton Catalyst

Although classical homogeneous Fenton reaction systems (Fe II + H 2 O 2 ) are widely used for organic pollutant degradation, this technology has important shortcomings such as waste generation and difficult Fe 2+ recycling. These shortcomings originate secondary pollution issues and make it difficult to control the reactions. Polyoxometalates (POMs) are characterized by bearing large electron‐donating conjugate systems able to stabilize Fe 2+ . To explore a new kind of heterogeneous Fenton reagent, we prepared a new‐type of stable heterogeneous Fenton reagent, (H 3 O) 3.5 (H 3 DETA) 3.5 {Fe II [H 4 Mo V 6 O 15 (PO 4 ) 4 ] 2 } (DETA = diethylenetriamine) ( 1 ) by inserting Fe II into the POMs. The sandwich‐type 1 was excited by ultraviolet (UV) light, showed high efficiency as a solid‐phase Fenton catalyst, and can be potentially recycled to control the reactions. The coordinating reaction mechanisms for the catalytic degradation of methyl orange (MO) over the 1 + H 2 O 2 reaction system was studied, including photocatalysis and Fenton oxidation effects. As a contrast, another new phosphomolybdate, (H 3 DETA) 4 {Zn II [H 5 Mo V 6 O 15 (PO 4 ) 4 ] 2 } · 7.5H 2 O ( 2 ), which has the same sandwich‐type polyanion but Zn II acting as the sandwich‐atom, has also been synthesized, characterized. The comparative study of photocatalytically degrading MO has also been carried out. In addition, by studying the thermal decomposition behavior of 1 , we revealed, for the first time, the presence of Mo 4 P 3 as a decomposition residue of 1 .