Highly Efficient Adsorptive Removal of Organic Dyes from Aqueous Solutions Using Polyaromatic Group-Containing Zn(II)-Based Coordination Polymers

In the present study, we have constructed four new Zn(II) coordination polymers (CPs), formulated as [Zn(L1)(DMF)(H2O)(2)](n)center dot n(H2O) (1), [Zn-2(L1)(2)(DMF)(CH3OH)](n) (2), [Zn(L2)(DMF)](n) (3), and [Zn(L2)(4,4'-Bipy)](n) (4), using polyaromatic group-containing carboxylic acid proligands 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H(2)L1) and 5{(pyren-1-ylmethyl) amino}isophthalic acid (H(2)L2) and zinc nitrate under solvothermal conditions. The synthesized proligands were characterized by attenuated total reflectance-infrared Fourier transform infrared (ATR-FT-IR) and NMR techniques. On the other hand, CPs 1-4 were characterized by ATR-FT- IR, thermogravimetry, elemental, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction analyses. Single-crystal analysis revealed that CPs 1 and 2 have one- and two-dimensional structures, respectively, whereas CP 3 possesses a one-dimensional (1D) double-chain and CP 4 has a three-dimensional (3D) assembly. The topological analysis showed that 1 has a uninodal 2-connected net, 2 and 3 have 2,4-connected binodal nets, and 3D polymer 4 has a 2,2,8-connected trinodal net. The synthesized CPs were used for the adsorption of various cationic and anionic organic dyes in aqueous media, which was monitored by UV-vis spectroscopy. Among all of the coordination polymers, CP 1 bearing an anthracene group is the most effective one for the removal of different types of dyes (both cationic and anionic) with a removal efficiency of 96-99%. CP 1 presented a rare example where a single CP can adsorb multiple (at least five) cationic and anionic dyes. The adsorption kinetics, adsorption isotherms, and thermodynamic parameters of CP 1 were also determined, demonstrating that the adsorption kinetics and the adsorption isotherms obey a pseudo-second-order model and the Langmuir model, respectively. However, the pyrene-tagged CPs 3 and 4 can selectively remove (removal efficiency of 97-98%) only the cationic methylene blue (MB) dye from an aqueous solution. In silico studies were performed to understand the mechanism of the removal of the organic dyes. The recyclability tests showed that CP 1 can be recycled at least three times without a marked decrease in its dye removal capacity.

Automated summary

In this study, four new zinc(II) coordination polymers (CPs) were synthesized and characterized. CP 1, with an anthracene group, showed the highest efficiency in removing various cationic and anionic dyes. CPs 3 and 4, tagged with pyrene, selectively removed cationic dyes.