Theoretical and experimental studies to design an ion-imprinted polypyrrole polymer for selective detection of Pb(II) heavy ions

In the present work, density functional theory (DFT) was performed to select the most appropriate chelating agent to design Pb²⁺ imprinted polypyrrole (PPy) polymer. We have therefore selected five molecules able to chelate heavy metal ions: L-Cysteine (L-Cys), glycine (Gly), ethylene glycol dimethacrylate (EGDMA), diethylenetriaminepentaacetic acid (DTPA) and acrylic acid (AA). To approach the polymeric configuration, we investigated the interaction energy between tripyrrole (triPy) and each (chelating agent/Pb²⁺) complex. DFT calculations revealed that the most stable geometry with a minimum interaction energy in the solvent of order of − 230.29 kJ/mol, is [triPy@AA /Pb²⁺]. Based on these results, a surface acoustic wave sensor, functionalized with PPy-AA-IIP was designed. Gravimetric results indicate that the limit of detection of the designed sensor was of order of 0.1 pM. The calibration curve was fitted with a combined “one site binding/Hill” model. The one-site model is related to the degree of affinity between the templates and the imprints, while the Hill one provides more information on the PPy polymeric rearrangement after the recognition of the analytes by the cavities. The corresponding dissociation constants K_d1 and K_d2 were of order of K_d1 = (1.1 ± 0.3)×10⁻¹³ M and K_d2 = (5.9 ± 1.8)×10⁻¹⁰ M respectively. Selectivity tests, investigated by both gravimetry and DFT calculation, indicated that affinity for lead ions is superior to that of other heavy metal interferents.