ZVI/biochar derived from amino-modified corncob and its phosphate removal properties in aqueous solution

In this study, waste corn cobs were oxidized and grafted with diethylenetriamine (DETA), which chelates a large amount of Fe3+. Then, nitrogen-doped zero-valent iron/biochar (ZVI/BC-N) was prepared using a simple carbothermal reduction method. ZVI/BC-N had a larger specific surface area and porous structure due to the irregular folding phenomenon on its surface caused by Fe and N codoping. At the same time, ZVI/BC-N contained more ZVI reactive crystals due to DETA chelation. The pseudo-second-order and Elovich models better describe the behavior of ZVI/BC and ZVI/BC-N in phosphorus adsorption, where the adsorption process was controlled by a combination of the reaction rate and diffusion. The isotherm and thermodynamic fitting results showed that the adsorption of phosphorus by ZVI/BC was a single-molecular-layer physical adsorption process, while ZVI/BC-N exhibited multimolecular layer chemisorption, and the maximum amounts of phosphorus adsorbed by ZVI/BC and ZVI/BC-N were 17.93 and 82.78 mg·g−1, respectively. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy showed that both CN and CH on biochar were involved in the adsorption process, while the coordination between OH, CO and phosphate, the adsorption of ZVI and chemical processes were the main mechanisms of phosphorus removal. The stronger adsorption performance of ZVI/BC-N compared to ZVI/BC might be related to its high ZVI content and rich surface structure. This study aims to provide a method for the preparation of biochar composites with a high ZVI content through simple modifications and provide a new approach for the efficient removal of phosphorus from water.