Fig. 2: Reductive immobilization of toxic elements by embedded ZVI.

Removal capacities of engineered biochar and ZVI–based materials for electroplating wastewater with sole toxic elements (removed amount, a) or multiple toxic elements (remaining concentration, b); c, d Reduction of the toxic elements indicated by XPS and XANES analysis; e ZVI content in different engineered biochar and ZVI–based materials; f Electron efficiency of ZVI during the decontamination process; * electron efficiency of FMBCOH–120 might be higher than its actual value as parts of the toxic elements was not reduced; g STEM-EDX analysis of the spent engineered biochar; h Schematic diagram of reductive immobilization induced by the carbon-ZVI and uncovered ZVI. The error bar represents the Standard Deviation (SD) from triplicates.