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

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.