Mechanistic investigation of Pb²⁺ adsorption on biochar modified with sodium alginate composite zeolitic imidazolate framework-8

For the serious situation of heavy metal pollution, the use of cheap, clean, and efficient biochar to immobilize heavy metals is a good treatment method. In this paper, SA@ZIF-8/BC was prepared for the adsorption of Pb²⁺ in solution using sodium alginate (SA) and zeolitic imidazolate framework-8 (ZIF-8) modified corn cob biochar. The results showed that the specific surface area of modified biochar was greatly improved, with good adsorption capacity for Pb²⁺, strong anti-interference ability, and good economy. At the optimal adsorption pH of 5, the adsorption model of Pb²⁺ by SA@ZIF-8/BC was more consistent with the pseudo-second-order kinetic model and Langmuir isotherm model. This indicates that the adsorption of Pb²⁺ by SA@ZIF-8/BC is chemisorption and monolayer adsorption. The maximum adsorption of modified biochar was 300 mg g⁻¹, which was 2.38 times higher than that of before modified BC (126 mg g⁻¹). The shift in binding energy of functional groups before and after adsorption of SA@ZIF-8/BC was studied by XPS, and it was found that hydroxyl and carboxyl groups played an important role in the adsorption of Pb²⁺. It was demonstrated that this novel adsorbent can be effectively used for the treatment of Pb pollution in wastewater.