Synthesis, Characterization, and Application of [Pb(H2btec)(Ben)]·H2O Coordination Polymer for Efficient Removal of Mordant Black 11 Dye from Aqueous Solutions

In this study, a lead(II) coordination compound, [Pb(H2btec)(Ben)]·H₂O, was synthesized via a one-pot solvothermal reaction involving 1,2,4,5-benzenetetracarboxylic acid (H₄BTEC) and benzoic acid (Ben) as organic ligands. The resulting compound was characterized by elemental analysis, Fourier Transform Infrared, and powder X ray diffraction, which confirmed the successful formation of a coordination framework incorporating lead(II) ions and aromatic ligands. The adsorption performance of the compound was evaluated using Mordant Black 11 dye as a model anionic pollutant. Batch adsorption experiments were conducted to investigate the effects of contact time, pH, initial dye concentration, and temperature on the adsorption efficiency. The compound exhibited notable dye removal capacity, with a maximum adsorption capacity of 97.99 mg/g under optimal conditions. Kinetic modeling of the adsorption data demonstrated that the process followed pseudo-second-order (R² = 0.998), indicating that chemisorption was the primary mechanism. Isotherm modelling indicated a better fit to the Langmuir model (Q2 = 86.21 mg/g, R² = 0.8868), suggesting monolayer adsorption on a homogeneous surface. Comparatively, Freundlich and Temkin models showed weaker correlation coefficients. FTIR spectra before and after adsorption revealed noticeable band shifts, the disappearance of existing bands, and the appearance of new bands, particularly new peaks at 1496 cm⁻¹ (N=N) and 1150–1120 cm⁻¹ (S=O), confirming the interaction of Mordant Black 11 dye with the adsorbent surface while maintaining structural integrity. Overall, the synthesized [Pb(H2btec)(Ben)]·H₂O coordination polymer demonstrates promising potential as an effective and reusable adsorbent suitable for the removal of anionic dyes from aqueous systems, offering insights for future design of coordination-based adsorbents for wastewater treatment.