Polyethyleneimine-modified lobster shell biochar for the efficient removal of copper ions in aqueous solution: Response surface method optimization and adsorption mechanism

Abstract

In this study, lobster shells were used as the biomass raw material, and were modified by cross-linking with KOH and polyethyleneimine to obtain amine-functionalized biochar (PBC) for the removal of Cu2+ in polluted water bodies. The biochar was characterized before and after modification. The BoxBehnken design response surface methodology was used to optimize the experimental conditions and to investigate the effects of initial concentration, pH and dosage on Cu2+ removal. Its adsorption performance was evaluated. The results show that PBC has a greater Cu2+ adsorption capacity than other biochars, and the maximum adsorption capacity reached 491.68 mg·g−1. This is mainly because the main inorganic component of lobster shell biochar is CaCO3. polyethyleneimine modification makes a new active functional group -NH2 on the surface of the original biochar (BC) and increases the number of nitrogen-containing groups such as C-N and -NH. The initial concentration had the greatest effect on the removal of Cu2+, and the interaction of pH and initial concentration was the most significant interaction factor throughout the adsorption process. The adsorption of Cu2+ by BC and PBC followed the pseudo-second-order, fractal-like pseudo-first-order, fractal-like pseudo-second-order kinetic equation and Langmuir isothermal adsorption model for chemisorption on a single molecular layer. Cu2+ is mainly removed by complexation, ion exchange, coprecipitation and physical adsorption. Carbonate and nitrogen-containing groups on the surface of PBC are the main adsorption sites for Cu2+. Furthermore, the adsorbent has excellent reusability and practical application potential.