Two highly stable inorganic–organic hybrid 3D frameworks based on Cu–Ln incorporated polyoxometalates for selective dye removal and proton conduction

Abstract

Two novel inorganic–organic hybrid 3D TM–Ln incorporated POM-based frameworks, H₂[Cu₂OL₃(H₂O)₂][Ce(L)(H₂O)₃(PW₁₁O₃₉)]·17H₂O (1) and H₄[CuL₃]₂[Ln(H₂O)₃(PW₁₁O₃₉)]₂·28H₂O (2) (L = 4,4′-bipyridine), were hydrothermally synthesized at different temperatures. Structural analysis reveals that both compounds are constructed from [Ln(PW₁₁O₃₉)]⁴⁻ polyoxoanions and different copper complexes. Interestingly, in compound 1, 2D copper complex layers and 1D chain [Ln(PW₁₁O₃₉)]⁴⁻ polyoxoanions interconnect to form a 3D framework. In contrast, in compound 2, 1D copper complex chains join the 2D [Ln(PW₁₁O₃₉)]⁴⁻ layers to give rise to a 3D framework. Both compounds exhibit excellent chemical stability. Furthermore, the dye adsorption and proton conduction properties of both compounds were also investigated. The conductivities of 1 and 2 are 3.175 × 10⁻⁴ S cm⁻¹ and 1.750 × 10⁻⁴ S cm⁻¹ at 85 °C and 98% RH, respectively. Dye adsorption studies indicate that they can selectively adsorb cationic dyes MB, CV and BR over anionic dyes MO, AO and large cationic RhB.