Two Transition Metal Coordination Polymers: Potential Adsorbents for Contaminant Removal and Photoluminescent Properties

Methylene blue (MB) contamination has become a significant environmental issue due to its widespread presence in industrial effluents, posing serious threats to ecosystems and human health. As a result, there is an urgent need for the development of novel adsorbent materials that can effectively remove these pollutants from water sources. In this context, the present study focuses on the design and synthesis of two coordination polymers (CPs) containing Zn(II) and Mn(II), namely, {[Mn₃(L)₂(tib)₂]·4H₂O}_n (1) and [Zn(L)(3,5-bibp)]_n (2), using a combined-ligand approach under solvothermal conditions. The ligands, H₃L is 4-(3,5-dicarboxylatobenzyloxy)benzoic acid), 1,3,5-tris(1-imidazolyl)benzene and 3,5-bibp is 3,5-bis(imidazol-1-yl)biphenyl), were carefully selected to enhance the properties of the resulting polymers. These CPs were thoroughly characterized using a variety of techniques, including IR spectroscopy, elemental analysis (EA), single-crystal X-ray diffraction, thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). Both CPs demonstrated ligand-dependent blue fluorescence emissions, suggesting their potential for use as photoluminescent materials in various applications. Furthermore, the adsorption capabilities of CP1 and CP2 for methylene blue (MB) were evaluated. The results revealed that both CPs exhibited excellent adsorption efficiencies, with CP1 achieving a 77.6% adsorption efficiency within 1 h and completely removing 20 mg/L of MB within 6 h. These findings highlight the significant potential of CP1 as a highly effective adsorbent for organic dyes, particularly for environmental remediation applications. The ability of these coordination polymers to adsorb MB efficiently underscores the urgent need for the development of innovative and efficient materials to address the growing challenges of water pollution.