Decomposition-Reassembly Synthesis of a Silverton-Type Polyoxometalate 3D Framework: Semiconducting Properties and Photocatalytic Applications.

Polyoxometalate-based all-inorganic three-dimensional (3D) frameworks have recently attracted attention as a unique class of materials due to their unique physicochemical properties and a wide field of application with excellent prospects. We herein synthesized a novel all-inorganic 3D framework material based on cobalt-substituted Silverton-type polyoxometalate, H6{Co6W10O42[Co(H2O)4]3}·2H2O (Co9W10), which was successfully constructed using Na12[WCo3II(H2O)2(CoIIW9O34)2]·46-48H2O (Co5W19) and Co(NO3)2·6H2O as starting materials in a hydrothermal reaction via a decomposition-reassembly route together with the rational adjustment of pH values. Co9W10 has been structurally characterized using single-crystal X-ray diffraction. Photocurrent response, band-gap (Eg) value, and the VB-XPS spectrum have been measured to reveal the semiconducting property of Co9W10. Furthermore, we synthesized x% PTh/Co9W10 composites (PTh = polythiophene, x = 0.5, 1, 2, 5) for photodegradation of tetracycline hydrochloride (TH) to evaluate the photocatalytic activities of title composites. Due to the optimal molar ratio of hybrids and matching energy levels, 2% PTh/Co9W10 composites show the best photocatalytic activities among these composites.

pH-Controlled assembly of [ZnW12O40]6--based hybrids from a 0D dimer to a 2D network: synthesis, crystal structure, and photocatalytic performance in transformation of toluene into benzaldehyde.

Polyoxometalate-based organic-inorganic hybrids have attracted considerable attention due to their fascinating structures and wide application prospects. In this work, using the same building blocks, ligands and metal ions (ZnW12O406-(ZnW12), 2,2'-bipyridine (2,2'-bipy), and Cu2+), we synthesized three new POM-based hybrids by controlling the pH values of the reaction systems. These three compounds {(Zn0.6(H2)0.4W12O40)[Cu(2,2'-bipy)(H2O)][Cu(2,2'-bipy)(H2O)2][Cu(2,2'-bipy)(H2O)3]}2·6H2O (1), (Me4N)2{ZnW12O40[Cu(2,2'-bipy)(H2O)][Cu(2,2'-bipy)(H2O)3]}·5H2O (2), and {(Zn0.5(H2)0.5W12O40)[Cu(2,2'-bipy)][Cu(2,2'-bipy)(H2O)][Cu(2,2'-bipy)(H2O)2]}·5H2O (3) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a dimeric cluster structure, while compounds 2 and 3 appear as a 1D chain structure and a 2D network, respectively. The semiconducting properties of compounds 1-3 are different, which was demonstrated by band gap (Eg) and photocurrent response measurements. Compound 3 can efficiently catalyze the photooxidation of toluene to benzaldehyde with high selectivity using molecular oxygen as the oxidant component. Moreover, compound 3 was recycled and reused three times without significant degradation in conversion and selectivity. In addition, the mechanism of the photocatalytic reaction was also investigated.

An unprecedented polyoxometalate-based 1D double chain compound with opposite charges enables conductivity improvement.

A POM-based one-dimensional (1D) chain compound, {BW12O40[Cu(2,2'-bipy)2]2[Cu(2,2'-bipy)(H2O)]}{BW12O40[Cu(2,2'-bipy)2][Cu(2,2'-bipy)(H2O)2]}·7H2O, has been synthesized and structurally characterized, which represents an unprecedented 1D double chain structure with opposite charges. In contrast to common POMs, this compound exhibits a relatively high electrical conductivity of 1.17 × 10-9 S cm-1 at 25 °C. In addition, its semiconducting properties have also been investigated by application of photoelectrochemical sensing of H2O2.