A dual-function schiff base ligand: Fluorescent probe and high sustainable adsorption via PVC immobilized for Cd(II) and Pb(II): Experiments, DFT calculations and cost analysis

A novel facial Schiff base (LH) was used as a fluorescent sensor that turns on–off for cadmium and lead, respectively, with a high level of sensitivity with a detection limit of 2.67 × 10⁻⁷ M for Cd(II) and 1.75 × 10⁻⁷ M for Pb(II), followed by immobilization with polyvinyl chloride (PVC). The fabricated LH-PVC (PVCX) adsorbent was characterized using FTIR, SEM, XRD, BET, and TGA analysis, validating the incorporation and effective immobilization of LH onto PVC with a strong hydrogen bonding. The impact of PVC3 on the adsorption of Cd(II) and Pb(II) was assessed under various adsorption conditions, including solution pH, isotherm, kinetics, thermodynamics, adsorbent dosage, and the adsorption mechanism. The PVC3 adsorbent showed a significant binding affinity for Cd(II) and Pb(II) at pH 5 with a maximum adsorption capacity of 507.217 mg·g⁻¹ and 409.325 mg·g⁻¹, respectively, at 318 K. Kinetic studies revealed that the adsorption process followed pseudo-second-order kinetics, while adsorption isotherms were in agreement with the Langmuir isotherm model, suggesting monomolecular layer adsorption. The evaluation of thermodynamics indicates that the adsorption process is an endothermic spontaneous process. Moreover, a DFT study was conducted to further understand the responsive and adsorptive mechanism. The PVC3 adsorbent demonstrated exceptional reusability, maintaining its high adsorption effectiveness even after multiple cycles of adsorption and desorption. A cost-effective analysis was conducted, revealing a very low final reusability cost. This finding reveals that it might be utilized in water treatment, which provides a potential method to reduce heavy metal pollution and safeguard aquatic ecosystems.