One-step synthesis of two Wells–Dawson arsenotungstate hybrids via M–O–M bridges for efficient adsorption and selective separation of organic pollutants

Abstract

Two unique hybrids based on Wells–Dawson polyoxometalates, [Cu(en)₂(OH₂)]₂[{Cu(en)₂}{As₂W^V₂W^VI₁₆O₆₁}]·6H₂O (1) and (H₂dap)[Cu(H₂dap)(H₂O)₂][{Cu(dap)(H₂O)₂}{As₂W₁₇CuO₆₁}]·5H₂O (2) (en = ethylenediamine and 1,2-dap = 1,2-diaminopropane), have been synthesized hydrothermally by reaction of Na₂WO₄, NaAsO₂ and CuCl₂ with 1,2-dap or en, and further characterized by elemental analysis, infrared radiation (IR) spectrophotometry, ultraviolet (UV) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and single crystal X-ray diffraction. In compounds 1 and 2, the emerging building blocks link into new one-dimensional (1D) chain-like Wells–Dawson architectures via two M–O–M (M = Cu/W) and O–Cu–O bridges, which are rarely observed among this arsenotungstate class. The 1D chain-like architectures further extend into 3D supramolecular frameworks through hydrogen bond interactions. They represent the first family of Dawson-type double-bridge arsenotungstate chains built from M–O–M and Cu–L linkers. Compounds 1 and 2 have exhibited electrocatalytic activity toward the reduction of nitrite. Adsorption experiments show that the compounds have the ability to selectively adsorb MB from binary mixed dye solutions (MB and MO and MB and RhB). These compounds still maintain their excellent stability and adsorption properties after several cycles.