Synthesis, characterization, and use of magnesium-activated biochar for nitrate removal from aqueous solutions

Eutrophication and algal blooms are serious issues plaguing the environment. Modified pine-derived biochar can be used as an innovative sorbent to address this problem by removing NO ₃ ⁻ from aqueous solutions. In this study, pine nuggets were impregnated by Magnesium Chloride and subsequently pyrolyzed at 600 ⁰C. The physicochemical characteristics of this modified biochar (MB) were characterized by wet chemistry, thermal, spectral, and microscopic methods like acid value, point of zero charge, elemental analysis, specific surface area, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photon spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), elemental mapping by scanning transmission electron microscopy (STEM), and time of flight-secondary ion mass spectrometry (ToF-SIMS) and compared to that of the pristine form. The data validated the successful impregnation of the biochar and revealed that most of the Mg in MB was distributed in the form of MgO-flakes. In addition, MB was used to carry out batch adsorption of NO ₃ ⁻ from the aqueous solution, and the experimental data were fitted to different adsorption isotherm models (Langmuir, Freundlich, and Sips) and adsorption kinetic models (pseudo-first order and pseudo-second order). The results suggest a maximum NO ₃ ⁻ adsorption capacity of 14.40 mg/g suggesting monolayer adsorption as described by the Langmuir model. Additionally, the spent biochar after nitrate adsorption was analyzed by XPS, FTIR, and ToF-SIMS to validate the successful adsorption of NO ₃ ⁻ from the aqueous solution.