A bifunctional cationic metal–organic framework based on unprecedented nonanuclear copper(ii) cluster for high dichromate and chromate trapping and highly efficient photocatalytic degradation of organic dyes under visible light irradiation

Abstract

A bifunctional cationic metal–organic framework {[Cu₉(OH)₆Cl₂(itp)₆(1,4-bdc)₃](NO₃)₂(OH)₂·20H₂O}_n (1-NO₃-OH·20H₂O) was synthesized and characterized (itp = 1-imidazol-1-yl-3-(1,2,4-triazol-4-yl)propane, 1,4-bdc = 1,4-benzenedicarboxylate). In 1-NO₃-OH·20H₂O, three [Cu₃(μ₃-OH)(μ₂-OH)] trimeric clusters are bridged by two μ₃-Cl and form a [Cu₉(μ₃-OH)₃(μ₂-OH)₃(μ₃-Cl)₂] cluster. Such a nonanuclear copper(II) cluster [Cu₉(μ₃-OH)₃(μ₂-OH)₃(μ₃-Cl)₂] has not been reported till now, at least to the best of our knowledge. 1-NO₃-OH·20H₂O showed a 6-connected 2D 3⁶-hxl net based on a nonanuclear copper(II) cluster [Cu₉(μ₃-OH)₃(μ₂-OH)₃(μ₃-Cl)₂]. 1-NO₃-OH·20H₂O is also the first 2D 3⁶-hxl net-based nonanuclear cluster. 1-NO₃-OH (guest-free phase) showed fast and highly efficient Cr₂O₇²⁻ and CrO₄²⁻ trapping, and good recyclability for capturing Cr₂O₇²⁻ and CrO₄²⁻. The adsorption capacities of 1-NO₃-OH to capture Cr₂O₇²⁻ and CrO₄²⁻ were 1.762 mol mol⁻¹ (154.8 mg g⁻¹) and 1.896 mol mol⁻¹ (89.5 mg g⁻¹), respectively, at a molar ratio of 1 : 2 (1-NO₃-OH to 2.5 × 10⁻³ mol L⁻¹ Cr₂O₇²⁻ or CrO₄²⁻). 1-NO₃-OH exhibited the selective sorption of Cr₂O₇²⁻ or CrO₄²⁻ from a solution containing a mixture of Cr₂O₇²⁻ or CrO₄²⁻ and a ten-fold molar amount of ClO₄⁻, NO₃⁻, Cl⁻, BF₄⁻ or a five-fold molar amount of mol L⁻¹ SO₄²⁻. 1-NO₃-OH could capture 87.9% dilute Cr₂O₇²⁻ or 91.8% dilute CrO₄²⁻ at an equimolar 1-NO₃-OH to 20 ppm Cr₂O₇²⁻ or CrO₄²⁻. 1-NO₃-OH·20H₂O exhibited a highly efficient photocatalytic degradation of the cationic organic dyes methylene blue (MB) and rhodamine B (RhB) under visible light irradiation, and was shown to be a good photocatalyst for photocatalytic degradation of the cationic organic dyes.