In this study, carbonaceous and hybrid adsorbents were synthesized from waste flax fibers and fly ash, integrating two abundant waste streams into a single functional material. Materials were thermally modified and activated with NaOH at 500 °C in a nitrogen atmosphere. The prepared adsorbents exhibit high efficiency for scandium ion removal, with the hybrid systems significantly outperforming the individual components. The obtained Langmuir maximum adsorption capacities for the adsorption of scandium onto hybrid adsorbents were 18.28 and 32.32 mg/g, depending on the flax fibers/fly ash ratio. The contrasting thermodynamic behavior between hybrid adsorbents of different composition highlights the significant influence of material structure on the adsorption mechanism. The results demonstrate that the synergistic integration of waste flax fibers and fly ash in hybrid materials produces efficient and environmentally sustainable adsorbents, offering a novel approach for REE recovery from aqueous systems.

This study aimed to investigate the kinetic properties of methylene blue adsorption on carbon cryogel samples and nitrogen-doped and nitrogen-and-sulfur-co-doped carbon cryogel. Nitrogen and sulfur were incorporated into the carbon structure to enhance surface, electronic and textural properties. Methylene blue, a widely utilized dye in the textile industry, has become one of the most commonly detected substances in water systems. Experimental data were fitted with four kinetic models and showed excellent fits with the linear pseudo-second-order model. The results indicated that doping with nitrogen and sulfur did not significantly affect the adsorption of methylene blue.