The methods of wastewater treatment from heavy metal ions and dyes are analyzed, and the key advantages of powdered magnetically sensitive carbon nanocomposites as adsorbents are shown. Methods for selecting and preparing raw materials and activators for the synthesis of such nanocomposites are considered, and methods for synthesizing nanocomposites are analyzed. The properties, modeling of adsorption kinetics and isotherms, and efficiency of magnetic carbon nanocomposites for wastewater treatment from dyes and heavy metals are described.

A two-step method for the synthesis of C/Ni/N nanocomposites based on hydrolysis lignin from wood chemical processing waste is proposed. These nanocomposites were found to have a well-developed porous structure with a wide pore size distribution. It was shown that doping hydrolysis lignin with urea-derived nitrogen leads to the appearance of ferromagnetic behavior in the carbon material. When nickel chloride was added during pyrolysis, the magnetic behavior of the C/Ni/N composite was provided by superparamagnetic Ni particles less than 30 nm in size and the magnetism of the carbon matrix. The addition of urea during the synthesis of the nanocomposite further promotes better integration of nickel into the carbon structure. According to the results of magnetic studies, the nickel content in the C/Ni/N nanocomposite was 19 wt.% compared to 15 wt.% in the C/Ni nanocomposite. The synthesized nanocomposite was demonstrated to have no residual magnetization, so its particles do not agglomerate after the external magnetic field is removed. Due to this property and the well-developed porous structure, C/Ni/N composites have the potential to be used as catalysts, active electrode materials for autonomous energy sources, and in environmental technologies as magnetically sensitive adsorbents.

This study presents the synthesis of carbon composites based on iron powder and hydrolysis lignin, both with and without the addition of oleic acid. The synthesized composites were characterized using X-ray diffraction, gas adsorption-desorption porosimetry, and magnetometry. In addition, the adsorption performance of the composites toward methylene blue and congo red dyes from aqueous solutions was investigated. It was found that the addition of oleic acid does not significantly alter the structural or magnetic properties of the synthesized composite. However, it does affect the composition of oxygen-containing surface groups on the carbon. Analysis of the adsorption isotherms revealed that the carbon composite synthesized with oleic acid is nearly equally effective in adsorbing both methylene blue and congo red dyes. Isotherm modeling demonstrated that the synthesized composites adsorb both dyes via a physisorption mechanism.

In this work, Ni/C/N nanocomposites were synthesized from wheat straw and sugar beet pulp by two-stage direct pyrolysis using nickel chloride and urea as activating agents. It was demonstrated that nitrogen doping of the precursor, achieved using urea as the nitrogen source, induces ferromagnetic behavior in the carbon material. Upon additional activation with nickel chloride, the magnetic behavior of the C/Ni/N composites is governed by both Ni nanoparticles with an average size of approximately 100 nm and the magnetism of the nitrogen-doped carbon matrix. Wheat-straw-derived composites exhibited predominantly microporous structures with larger BET surface areas, whereas sugar-beet-pulp-derived samples contained a higher proportion of mesopores. Although the latter possessed lower specific surface areas, they demonstrated superior adsorption capacities toward Congo Red owing to improved accessibility of adsorption sites for large dye molecules. The adsorption process was best described by the Langmuir model, while the Dubinin–Radushkevich model suggested strong specific physicochemical interactions between dye molecules and the adsorbent surface. The results demonstrate that the adsorption efficiency of biomass-derived Ni/C/N nanocomposites is governed not only by the total surface area but also by pore architecture and surface chemistry.

The adsorption properties of carbon nanocomposites synthesized from wheat straw were investigated. The synthesis was performed using one-step and two-step procedures with FeCl ₃ and ZnCl ₂ as activating agents. The adsorption isotherms of the dyes methylene blue and Congo red revealed that the nanocomposites synthesized via the two-step method exhibit significantly higher adsorption capacities compared to those prepared in a single step. The adsorption isotherms were modeled using the Langmuir, Freundlich, and Dubinin–Radushkevich equations. The parameters of these models indicate favorable adsorption of both dyes by the synthesized nanocomposites. Based on the Dubinin–Radushkevich model, the mean adsorption energy values were estimated, and the nature of the interactions between the adsorbate molecules and the active adsorption sites in the nanocomposites was analyzed. It was found that the pseudo-first-order kinetic equation best describes the adsorption kinetics of dyes on nanocomposites synthesized via the two-step method, while the pseudo-second-order model provides a better fit for the adsorption kinetics of dyes on nanocomposites synthesized via the one-step procedure.