Ortho-N-S/N-O dual-site synergistic COF for efficient selective removal and highly sensitive detection of hydrated lead ions

Lead ions (Pb(II)) in industrial wastewater pose a serious threat to the ecological environment and human health due to their toxicity and persistence. Traditional treatment methods often struggle to achieve both efficient capture and sensitive detection of Pb(II). In this study, a novel bifunctional covalent organic framework (BTT-DHBD-COF) with ortho N-S/N-O dual sites was innovatively designed to enable highly selective adsorption and ultrasensitive detection of Pb(II). Adsorption studies revealed that the BTT-DHBD-COF exhibits a high adsorption capacity for Pb(II) (570.7 mg/g at pH 5) and rapid kinetics (equilibrium reached in 10 min). The BTT-DHBD-COF/GCE sensor demonstrated a wide linear detection range (0.0001–0.5 μM) and an ultralow detection limit (0.03 nM). In real water samples (lake water and tap water), it achieved high recovery rates of 96–108 % with relative standard deviations (RSDs) of 2.5–3.45 %. Experimental results and theoretical calculations confirmed that the N-S/N-O dual sites significantly enhance Pb(II) capture and detection through strong coordination (with Pb transferring 0.46 and 0.44 electrons to the N-S and N-O sites, respectively) and efficient electron conduction via the π-conjugated framework. Compared to single binding sites (S: 0.42 e, O: 0.40 e, N: 0.37 e), the significant charge transfer of the dual site highlights its key role. This work presents an innovative bifunctional “adsorption-detection” strategy for the remediation of Pb(II) pollution in industrial wastewater.