Design and synthesis of a new coordination polymer of zinc (II): Crystal structure and evaluation for its adsorption studies in removing perilous organic dye pollutants in aqueous medium

Abstract

The contamination of aqueous environments by hazardous organic dye pollutants has become a pressing global concern, necessitating innovative strategies for effective water purification. In this research, we present the design, synthesis, and comprehensive evaluation of a new zinc(II) coordination polymer, formulated as [Zn(HIPA)(HIZ)2]n⋅H2O (CP-1), specifically tailored for adsorption studies aimed at the removal of hazardous organic dye pollutants from aqueous mediums. The CP-1 was effectively synthesized using a hydrothermal synthesis approach and incorporates two distinct organic ligands, namely, 5‑hydroxy isophthalic acid, and imidazole, along with a water molecule within the crystal lattice. The structural and morphological attributes of the synthesized coordination polymer (CP-1) are elucidated through a comprehensive characterization process, including SCXRD, PXRD, FTIR, UV–VIS spectroscopy, TGA, SEM, and BET analysis. Single-crystal diffraction of CP-1 confirms that Zn is coordinated in a tetrahedral environment. The CP-1 was systematically examined for dye adsorption of four hazardous organic dyes namely methylene blue (MB), methyl orange (MO), crystal violet (CV) and congo red (CR). Batch adsorption experiments were conducted, probing the influence of variables such as contact time, pH, temperature, the effect of dosage and initial dye concentration on the adsorption efficiency of CP-1. The CP-1 shows the best adsorption efficiency for MB followed by MO, CV, and CR. The CP-1 exhibits high selectivity and efficient MB and MO dyes adsorption at room temperature and neutral pH. Moreover, three different kinetic models were utilized to attain a deeper comprehension of the reaction mechanism involved in the adsorption of MB and MO. Amongst these models, the pseudo-second-order kinetic model demonstrated the best fit for both cases. Furthermore, the density functional theory with the dispersion correction (Grimme's DFT-D3) was utilized to support the dye's adsorption mechanism with the CP-1. To study this, the dispersion corrected interaction energies were computed for the dye-complex systems at B3LYP-D3/6–31G(d,p)/LANL2DZ level of theory. The efficient adsorption performance, coupled with its structural and chemical stability, suggests that CP-1 holds great potential for practical applications in water treatment processes aimed at addressing the pressing challenge of organic dyes pollutant contamination. Further research and exploration of its adsorption properties can unveil its full potential for future applications as a dye adsorbent.