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 C=N and C=H on biochar were involved in the adsorption process, while the coordination between -OH, C-O 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.