Copper-Caffeic Acid Paddlewheel Structure-Based Coordination Polymer for Efficient Adsorption of Atrazine and Metribuzin Herbicides

The contamination of aquatic systems with pesticides poses serious environmental and health risks, necessitating efficient removal strategies. Here, a copper–caffeic acid-based coordination polymer (CuCA-CP) was synthesized hydrothermally for the adsorption of the triazine herbicides atrazine and metribuzin. Structural, morphological, and thermal stability were confirmed by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The Brunauer–Emmett–Teller (BET) surface area of the coordination polymer (CP) was 279 m2 g–1, with a point of zero charge (pHpzc) of 5.53. At optimal conditions (10 mg adsorbent, 10 ppm pesticide conc., 120 min contact time, pH 7), removal efficiencies reached 95% for atrazine and 89% for metribuzin, with similar results in real water samples. Adsorption followed the Langmuir isotherm and pseudo-second-order kinetics, with maximum capacities of 121.65 and 94.25 mg/g, respectively. Thermodynamic analysis showed spontaneous, exothermic processes, and the CuCA-CP maintained performance over three regeneration cycles. Density functional theory (DFT) calculations performed in an aqueous medium revealed distinct mechanisms in the caffeate-bridged [Cu2(Caff)4] paddlewheel: atrazine via multisite π–π stacking (adsorption energy, Eads = −0.33 eV) and metribuzin via carboxylate hydrogen bonding (Eads = −0.29 eV). Experimental enthalpies (−81.3 and −68.1 kJ/mol) confirm the presence of strong but reversible noncovalent interactions, providing design principles for CuCA-CP-based pesticide removal.