Carboxyltin‐Functionalized Keggin Sandwich–Type Tungstosilicates With Enhanced Visible‐Light Photocatalytic Performance for Organic Dye Degradation

ABSTRACT Four isomorphic sandwich–type tungstosilicates modified by carboxyethyltin, with the general formula [C(NH 2 ) 3 ] 10 H 2 [(SnRCOO) 2 (TM) 2 (SiW 9 O 34 ) 2 ]·nH 2 O ( SiW 9 ‐TM‐SnRCOO , TM = Mn, Co, Cu, Zn; R = CH 2 CH 2 ; n = 5, 6, 8, 7), were synthesized in aqueous solutions and characterized by single crystal X‐ray diffraction and other physical and spectroscopic methods, marking the first introduction of open‐chain carboxyltin into Si‐polyoxometalate (Si‐POM) system. Notably, as homogeneous visible‐light photocatalysts used for the catalytic degradation of rhodamine B (RhB), the catalytic activity of these POM‐based organic–inorganic hybrids was significantly superior to that of their parent compounds. The reusability of the photocatalysts was studied through the process of “reduce‐reuse‐recycle” in the cyclic experimental system without separating the catalyst. After five repeated uses, the degradation efficiency of RhB was still above 90% within 180 min. With the extension of time, the dye catalyzed by the four catalysts all ultimately degraded nearly 100%. The degradation process involved the removal of RhB and its N ‐deethylated compounds. The trapping experiment indicated that the main active species were holes (h + ) and superoxide radicals (·O 2 − ), and the number of active species h + and ·O 2 − increased with cycling, effectively maintained the activity of the catalysts.