Preparation of magnetic hydrochar derived from iron-rich Phytolacca acinosa Roxb. for Cd removal.

Considering that hyperaccumulators can accumulate high concentrations of iron salt, they can successfully obtain magnetic hydrochar from iron-rich hyperaccumulators. In this study, iron-rich biomass was obtained by irrigating Phytolacca acinosa Roxb. using iron salt. Magnetic nano-Fe3O4 hydrochar was prepared from iron-rich Phytolacca acinosa Roxb. via hydrothermal carbonization to remove Cd. The characterization results showed that the synthesized magnetic nanoparticles had an average size of 2.62 ± 0.56 nm and N elements were doped into magnetic nano-Fe3O4 hydrochar with abundant oxygenic groups. Cd adsorption on magnetic nano-Fe3O4 hydrochar was better fitted using the Langmuir isotherm and the pseudo-second-order kinetic model. The maximum adsorption capacity was 246.6 mg g-1 of Cd. The research confirmed that Cd adsorption was controlled by multiple mechanisms from the jar test, transmission electron microscopy mapping, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. CdCO3 crystals can be formed after adsorption, indicating that surface precipitation played an important role in Cd adsorption. The abundance of O atoms and the doping of N atoms on the hydrochar surface were conducive to Cd adsorption, indicating that the mechanisms were related to surface complexation and electrostatic attraction. In addition, the significant decrease in Na+ content after Cd adsorption illustrated that ion exchange had a non-negligible effect on Cd adsorption. This study not only provides a strategy for preparing magnetic nano-Fe3O4 hydrochar derived from iron-rich plants but also verifies multiple Cd adsorption mechanisms using magnetic nano-Fe3O4 hydrochar.