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 {[Cu-9(OH)(6)Cl-2(itp)(6)(1,4-bdc)(3)](NO3)(2)(OH)(2)center dot 20H(2)O}(n) (1-NO3-OH center dot 20H(2)O) 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 center dot 20H(2)O, three [Cu-3(mu(3)-OH)(mu(2)-OH)] trimeric clusters are bridged by two mu(3)-Cl and form a [Cu-9(mu(3)-OH)(3)(mu(2)-OH) 3(mu(3)-Cl)(2)] cluster. Such a nonanuclear copper(II) cluster [Cu-9(mu(3)-OH)(3)(mu(2)-OH)(3)(mu(3)-Cl)(2)] has not been reported till now, at least to the best of our knowledge. 1-NO3-OH center dot 20H(2)O showed a 6-connected 2D 3(6)-hxl net based on a nonanuclear copper(II) cluster [Cu-9(mu(3)-OH)(3)(mu(2)-OH)(3)(mu(3)-Cl)(2)]. 1-NO3-OH center dot 20H(2)O is also the first 2D 3(6)-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 x 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-NO3OH 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 center dot 20H(2)O 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.