Construction and visible-light photocatalytic performance of carboxyethyltin/transition metal–functionalized wheel-like tungstophosphates

The wheel-like tungstophosphate (P₈W₄₈O₁₈₄]^40?, abbreviated as P₈W₄₈) reacted with estertin trichloride (Cl₃SnRCH₃, R = CH₂CH₂COO) in aqueous solution, resulting in a new wheel-like polyoxometalate (POM) containing six SnR fragments, formulated as K₆Na₂₄{(SnR(H₂O))₂(μ-OH)(μ-SnR(H₂O))}₂(P₈W₄₈O₁₈₄)]·59H₂O (abbreviated as Sn ₆ - P ₈ W ₄₈ ). Based on this, the transition metal (TM) was further introduced into the Sn ₆ - P ₈ W ₄₈ system, self-assembling three other wheel-like POMs with the general formula K_xNa_yH_{26 ? x ? y}{TM(H₂O)₃(SnR(H₂O))₂(μ-OH)(μ-SnR(H₂O))}₂(P₈W₄₈O₁₈₄)]·nH₂O (abbreviated as TM ₂ - Sn ₆ - P ₈ W ₄₈ , TM = Mn, Co, Ni; x = 0, 1, 2; y = 19, 22, 15; n = 72, 85, 75, respectively). The structures of these new organometal and TM co-modified compounds were characterized using infrared, UV–Vis. spectroscopy, ¹¹⁹Sn NMR, and powder- and single-crystal X-ray diffraction analysis. The estertin precursor hydrolyzed into carboxyethyltin (SnR) fragment in these crystalline POM materials, which can improve their adhesion to titanium dioxide (TiO₂). The photocatalytic performance of Sn ₆ - P ₈ W ₄₈ , TM ₂ - Sn ₆ - P ₈ W ₄₈ , and their TiO₂ composites was examined by studying the degradation of a model dye pollutant Rhodamine B (RhB) under visible-light irradiation without adding hydrogen peroxide (H₂O₂), and the photocatalytic mechanism was also discussed. The experimental results show that the title compounds exhibit a quicker and better photocatalytic degradation effect on RhB compared with their parent compound, indicating that the introduced organotin groups play a significant role. Moreover, it was found that H₂O₂ was produced after illumination pretreatment for POM solution, promoting the photocatalytic reaction.