Pyrolytic behavior of a zero-valent iron biochar composite and its Cu(ii) removal mechanism

The reduction behavior of Fe(3+) during the preparation of a zero-valent iron cocoanut biochar (ZBC8-3) by the carbothermic reduction method was analyzed. Fe(3+) was first converted into Fe(3)O(4), which was subsequently decomposed into FeO, and finally reduced to Fe(0). A minor amount of γ-Fe(2)O(3) was produced in the process. The isothermal thermodynamic data for the removal of Cu(ii) over ZBC8-3 followed a Langmuir model. The Langmuir equation revealed a maximum removal capacity of 169.49 mg g(−1) at pH = 5 for ZBC8-3. The removal of Cu(ii) over ZBC8-3 fitted well to a pseudo-first-order equation, which suggested that the rate limiting step of the process was diffusion. The Cu(ii) removal mechanism on ZBC8-3 involved the reduction of Cu(ii) by Fe(0) to produce Cu(0) and Cu(2)O, while C[double bond, length as m-dash]C, C–O–, and –O–H formed a complex with Cu(ii).