Synthesis and characterization of a surface-grafted Pb(ii)-imprinted polymer based on activated carbon for selective separation and pre-concentration of Pb(ii) ions from environmental water samples

Abstract

Even the lowest concentration level of lead (Pb) in the human body is dangerous to health due to its bioaccumulation and high toxicity. Therefore, it is very important to develop selective and fast adsorption methods for the removal of Pb(ii) from various samples. In this paper, a new Pb(ii) ion-imprinted polymer (Pb(ii)-IIP) was prepared with surface imprinting technology by using lead nitrate as a template, for the solid-phase extraction of trace Pb(ii) ions in environmental water samples. The imprinted polymer was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and N₂ adsorption-desorption isotherms. The separation/pre-concentration conditions for Pb(ii) were investigated, including the effects of pH, shaking time, sample flow rate, elution conditions and interfering ions. Compared with non-imprinted particles, the ion-imprinted polymer had a higher selectivity and adsorption capacity for Pb(ii). The pseudo-second-order kinetics model and Langmuir isotherm model fitted well with the adsorption data. The relative selectivity factor values (α _r) of Pb(ii)/Zn(ii), Pb(ii)/Ni(ii), Pb(ii)/Co(ii) and Pb(ii)/Cu(ii) were 168.20, 192.71, 126.13 and 229.39, respectively, which were all much greater than 1. The prepared Pb(ii)-imprinted polymer was shown to be promising for the separation/pre-concentration of trace Pb(ii) from natural water samples. The adsorption and desorption mechanisms were also proposed.

Fig. 1. Scheme for the preparation of Pb(ii)-IIP.

Fig. 2. FT-IR spectra of AC (a), AC-COOH (b), Pb(ii)-IIP (c) and Pb(ii)-NIP (d).

Fig. 3. Raman spectra of AC, AC-COOH and Pb(ii)-IIP.

Fig. 4. SEM images of AC (a), AC-COOH (b) and Pb(ii)-IIP (c).

Fig. 5. XRD patterns of AC (a) and Pb(ii)-IIP (b).

Fig. 6. Effect of pH on the adsorption of Pb(ii) on Pb(ii)-IIP.

Fig. 7. Effect of shaking time on the adsorption of Pb(ii) on Pb(ii)-IIP. Other conditions: pH 4.0, temperature 25 °C.

Fig. 8. Effect of solution flow rate on the recovery of Pb(ii). Other conditions: volume 50 mL, pH 4.0, temperature 25 °C.

Fig. 9. Effect of initial concentration (C_o) of Pb(ii) on the adsorption quantity (Q) of Pb(ii)-IIP and Pb(ii)-NIP. Other conditions: pH 4.0, temperature 25 °C.

Fig. 10. The linearized form of the Langmuir adsorption isotherm. Other conditions: 30 mg Pb(ii)-IIP, temperature 25 °C, pH 4.0.

Fig. 11. Adsorption capacity of Pb(ii)-IIP after eight cycles.

Fig. 12. Proposed reaction mechanism for Pb(ii)-adsorption.