Preparation of N-doped porous biochar with high specific surface area and its efficient adsorption for mercury ion...

Herein, a new type of super active nitrogen-doped biochar sheet (SNBC) was prepared by two-step pyrolysis and KOH chemical activation with melamine and cherry kernel powder as precursors of nitrogen and carbon source for removing Hg²⁺ from wastewater. The N₂ adsorption/desorption and scanning electron microscope characterization revealed that the resulted SNBC under 600 °C calcination owned huge specific surface area of 2828 m²/g and plenty of well-developed micropores, and X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy analysis testified the existence of functional groups containing N and O, which could provide adsorption sites for Hg²⁺. The SNBC-600 showed high adsorption capacity for Hg²⁺ even at low pH, and interfering cations had little effect on the adsorption. The adsorption process was rapid and dynamic data fit the pseudo-second-order dynamic model well. The maximum adsorption capacity of Hg²⁺ on SNBC-600 calculated by Langmuir model was 230 mg/g. After six times of reuse, the adsorption capacity still exceeded 200 mg/g, exhibiting good reusability. The designed microfiltration membrane device base on SNBC-600 could remove low concentration of Hg²⁺ effectively from solution. This study provided a simple and environment-friendly method for manufacturing nitrogen-doped biochar sheet, which was of great significance in the practical application of Hg²⁺ pollution treatment.