Two novel Zn (II)​-based metal–organic frameworks for rapidly selective adsorption and efficient photocatalytic degradation of hazardous aromatic dyes in aqueous phase

Two novel Zn-MOFs constructed from 5-hydroxy-2-nitroisophthalic acid (H2DIPA) and 5-(4-carboxy-2-nitrophenoxy)-2-nitroisophthalic acid (H3BPPA), namely: {[Zn2(DIPA)2(bimp)5]·DMF·2H2O}n (Zn-MOF 1), {[Zn2(HBPPA)2(bibp)2]·2H2O}n (Zn-MOF 2) (bimp = 1,4-di(1H-imidazol-1-yl)butane, bibp = 4,4′-bis(imidazolyl) biphenyl), have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG). The single-crystal X-ray diffraction analysis indicates that Zn-MOF 1 exhibits an uncommon 3-nodal framework with a (4·6·8)(4·63·82)(66) topology, whereas Zn-MOF 1 exhibits an uninodal 4-connected framework with a (44·62) topology. Moreover, both of the two Zn-MOFs exhibit exceptional dye adsorption capacities towards the organic dyes with high adsorption rates and excellent adsorption amounts. Particularly, Zn-MOF 1 can selectively adsorb the cationic dye malachite green (MG) whereas Zn-MOF 2 adsorb the anionic dye methyl orange (MO) when there exists another kind of dye in the system. The adsorption process can be illustrated by pseudo-second order kinetic and Langmuir isotherm, and the feasible adsorption mechanism could be the electrostatical interactions, hydrogen bonding between the MOFs and the dyes. Meanwhile, the two Zn-MOFs also show good photocatalytic degradation capabilities toward MB/MV dyes under UV irradiation, and the mechanism studies demonstrate that the main active species are ·OH radicals. Therefore, this functional MOF materials can be treated as a convenient and cost-efficient solution for the sewage handling and environmental protection.