Efficient removal of cadmium by salts modified-biochar: Performance assessment, theoretical calculation, and quantitative mechanism analysis

Modified biochar is a feasible adsorbent to solve cadmium pollution in water. However, few studies could elucidate the mechanism of cadmium adsorption by biochar from a molecular perspective. Furthermore, traditional modification methods are costly and have the risk of secondary contamination. Hence, several environmentally friendly sodium salts were used to modify the water chestnut shell-based biochar and employ it in the Cd2+ adsorption in this work. The modification of sodium salt could effectively improve the specific surface area and aromaticity of biochar. Na3PO4 modified biochar exhibited the highest Cd2+ adsorption capacity (112.78 mg/g). The adsorption of Cd2+ onto biochar was an endothermic, monolayer, chemisorption process accompanied by intraparticle diffusion. Microscopically, the enhancement of aromatization after modification made Cd2+ more likely to interact with the regions rich in π electrons and lone pair electrons. This study provided a new research perspective and application guidance for heavy metal adsorption on biochar.