Highly efficient adsorption of Pb (II) by Cucurbit[7]uril-modified amino-expanded graphite: Experiments, synthetic modelling optimisation and DFT calculations

• CB[7]-modified amino-expanded graphite was successfully prepared for the capture of Pb(II). • Optimal synthetic ratios were obtained by response surface methodology optimisation. • The adsorption process is well fitted to the quasi-second-order kinetic model and the Langmuir model. • Synthesised materials for efficient capture of Pb(II) with excellent stability. Conventional Pb(II) adsorbents suffer from a slow adsorption process, low adsorption capacity, and low removal rates in low concentration. To address these limitations, in this study, Cucurbit[7]uril (CB[7]) modified amino expanded graphite (EG) adsorbent (CB-EG) was prepared by hydrothermal method, and the synthesis was optimized using the response surface methodology. Meanwhile, DFT calculations were performed for mechanism analysis, and the best removal rate of lead ion (Pb(II)) at the optimum ratio was 99.02 %. The DFT-calculated adsorption energy of CB-EG was −739 kJ/mol, which was much higher than that of EG. By complexing CB [7] ports, the ability of CB-EG to capture Pb(II) under actual aqueous environment and low concentration of Pb(II) was increased by 4.25-fold compared to that of EG. The adsorption experiments showed that the adsorption process was spontaneously exothermic, and the adsorption process could be well fitted to the quasi-secondary kinetic model and Langmuir models. The effects of different pH, adsorbent dosage, metal ion concentration and temperature on the adsorption process were investigated. The adsorption reached equilibrium within 60 min, and the maximum Pb(II) adsorption capacity was 268.6 mg/g under the optimum environment (pH = 7, T = 323 K, adsorbent dosage = 0.05 g), which is superior to that of similar adsorbents. In addition, CB-EG has excellent recycling performance, with an adsorption capacity of 85 % of the initial capacity after seven recycling experiments. CB-EG maintained excellent adsorption performance (R%>90 %) in low-concentration and real aqueous environments. The introduction of CB[7] enabled EG to have more adsorption sites and superior Pb(II) adsorption capacity, which improved the disadvantage of EG’s low adsorption capacity in real aqueous environments and low concentration, making it a promising Pb(II) adsorbent.