Hierarchical porous adsorbent from asphaltenes fibers and its application for methyl orange removal

This study explores the preparation of hierarchical porous adsorbent starting from asphaltenes fibers. Solid or aqueous KOH, Fe(NO₃)₃, and Al(NO₃)₃ activation agents were mixed with the fibers followed by treatment at 573 K for 24 h under air atmosphere. The resulting structures were characterized and assessed as adsorbents for methyl orange from aqueous solutions. Asphaltenes fibers modified with solid Al(NO₃)₃ exhibited the highest adsorption capacity (6.32 mg g^-1) and removal efficiency (79%) at 298 K and pH = 3. The intraparticle diffusion kinetic model fitted the experimental data across two time zones corresponding to initial diffusion into the mesopores followed by diffusion into micropores. The second zone could equally be modeled by a pseudo-second order model corresponding to chemisorption onto active sites. The equilibrium uptake was best described by Langmuir isotherm, indicating monolayer chemisorption of endothermic nature (ΔH ⁰ = 8.41 kJ mol^-1). The modified fibers retained significant adsorption capacity with 76.22% of initial adsorption capacity over five cycles, demonstrating their stability and reusability. This study highlights the potential of chemically activated asphaltenes fibers as effective adsorbents for wastewater treatment.