Polyethyleneimine Modified Activated Carbon for Adsorption of Cd(II) in Aqueous Solution

Abstract Activated carbon (AC) was modified by linear polyethyleneimine (PEI) to prepare polyethyleneimine modified activated carbon (PEI/AC) adsorbent, which was applied in the cadmium ions adsorption in wastewater. The results showed that PEI was successfully loaded on the AC surface, and the specific surface area decreased from 305.8 to 113.3 m²/g on the PEI/AC with 10 wt% PEI loading amounts. The positively charged amine group on the PEI molecule changed the surface ζ-potential from –38.3 to 11.1 mV. XPS analysis demonstrated that the adsorption mainly occurred on the –NH and –NH2 groups on the PEI/AC surface. The adsorption results showed that the adsorption capacity of PEI/AC for Cd(II) was greatly enhanced by the PEI loading, and compared with unmodified activated carbon, the adsorption amount of Cd(II) on the PEI/AC increased four times from 11 to 45 mg/g. The adsorption of Cd(II) by PEI/AC was a pH-dependent process with a maximum adsorption capacity of 45 mg/g at an initial solution pH of 6–7. The adsorption process was fitted with a Langmuir isotherm adsorption model and a pseudo-second-order kinetic equation, indicating the Cd(II) adsorption on PEI/AC was monolayer coverage, and the adsorption process was controlled by a chemical process. After five adsorption-desorption cycles, PEI/AC still exhibited a high adsorption capacity for Cd(II), indicating the adsorbent has good regeneration ability and could be recycled.