Coupling interaction between porous biochar and nano zero valent iron/nano α-hydroxyl iron oxide improves the remediation efficiency of cadmium in aqueous solution

Abstract Based on the interaction between mesoscopic biochar materials and nanomaterials, the synergistic mechanism of the two materials in the process of cadmium remediation was studied. K2CO3 activated porous biochar (KBC) loaded with nano-zero-valent iron (nZVI)/nano-α-hydroxy-iron oxide (nHIO) was studied. Macroscopically, batch adsorption experiments were carried out to describe the adsorption properties of the composites. Microscopically, the changes of surface chemical states were characterized by electron microscopy, XRD, FTIR and XPS. Combining the macroscopic and microscopic characteristics, the synergistic mechanism between biochar and nZVI/nHIO was comprehensively analyzed. The strong synergistic effects between biochar and nano-zero-valent iron (nZVI)/nano-α-hydroxy-iron oxide (nHIO) were found, which improved the removal efficiency of cadmium (Cd) in aqueous solution. The results showed that the loading of nZVI/nHIO reduced the specific surface area to 178.6 m2 g−1 and 272.2 m2 g−1, respectively, but the adsorption capacity of Cd increased to 22.37 mg g−1 and 26.43 mg g−1, respectively, which was more than three times that of KBC (7.02 mg g−1). The interaction between nZVI/nHIO and Cd was enhanced by the complexation of surface functional groups, but the coupling effects were different. The coupling mechanism of Cd on nZVI@KBC was complexation - reduction. Cd was partly reduced in the removal process. While for nHIO@KBC, the existence of Fe (III) on the surface of biochar increased the number and species of oxygen-containing functional groups and enhanced complexation. The existence of synergistic mechanism will provide theoretical basis for the preparation of high efficient nanocomposites and expand the application of nanomaterials in the field of environment.