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)(mu-OH)(mu-SnR(H2O))}(2)(P8W48O184)]center dot 59H(2)O (abbreviated as Sn-6-P8W48). Based on this, the transition metal (TM) was further introduced into the Sn-6-P8W48 system, self-assembling three other wheel-like POMs with the general formula KxNayH26 - x - y[{TM(H2O)(3)(SnR(H2O))(2)(mu-OH)(mu-SnR(H2O))}(2)(P8W48O184)]center dot nH(2)O (abbreviated as TM2-Sn-6-P8W48, 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, Sn-119 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-P8W48, TM2-Sn-6-P8W48, 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.