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

Abstract

Abstract Two water stable metal–organic frameworks (MOFs) [M4(ᴅ-cam)4(bpzpip)3(H2O)]·DMAc·3H2O (1, M = Ni; 2, M = Co) were hydro(solvo)thermally prepared from the reactions of MCl2·6H2O (M = Ni, Co), ᴅ-camphoric acid (ᴅ-H2cam), and N,N′-bis(pyraz-2-yl)piperazine (bpzpip) in N,Nʹ-dimethylacetamide (DMAc)–H2O at 150 °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 (42.52.72)(42.57.65.8) 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.