Insight into the influence of framework metal ion of analogous metal-organic frameworks on the adsorptive removal performances of dyes from water

Two water stable metal-organic frameworks (MOFs) [M-4(D-cam)(4)(bPzPiP)(3)(H2O)]center dot DMAc center dot 3H(2)O (1, M =Ni; 2, M = Co) were hydro(solvo)thermally prepared from the reactions of MCl2.6H(2)O (M = Ni, Co), D-camphoric acid (D-H(2)cam), and N,N'-bis(pyraz-2-yl)piperazine (bpzpip) in N,N'-dimethylacetamide (DMAc)-H2O at 150 degrees C. Ni MOF 1 and Co MOF 2 are isomorphous and isostructural, both of which adopt a three-dimensional (3D) (4,6)-connected framework with (4(2).5(2).7(2))(4(2).5(7).6(5).8) topology. Dye removal properties of 1 and 2 toward methyl orange (MO), malachite green (MG), and methyl blue (MyB) showed that 1 selectively adsorbed only MyB from water with saturated adsorption capacity of 216 mg/g, while 2 selectively captured MyB and MG from water with saturated adsorption capacities of 671 and 405 mg/g, respectively, in several adsorption-desorption cycles. The Langmuir isotherm model and the pseudo-second-order kinetics model have interpreted the adsorption isotherm and adsorption kinetics, respectively, very well. Most importantly, this study figures out the specific influence of framework metal ion (Ni2+ and Co2+) on the crystal surface charge (zeta potential = -1.67 mV for 1 versus -5.81 mV for 2) that greatly affects the dye removal properties including adsorption rate and capacity as well as adsorbate from water. (C) 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.