Selective Removal of BTEX and Emulsified Gasoline Hydrocarbons from Water Using Carbonized Biomass-Derived Sorbents

Contamination of water bodies by emulsified gasoline hydrocarbons, particularly BTEX compounds (benzene, toluene, ethylbenzene, and xylenes), represents a critical environmental challenge due to their toxicity and resistance to conventional treatment methods. In this study, carbonized biosorbents derived from rice husk (CRH) and walnut shell (CWS) were developed for efficient removal of emulsified gasoline from water. The materials were prepared via carbonization under CO₂ atmosphere (300–800 °C), enabling simultaneous carbonization and activation. Structural and surface properties were characterized using Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray fluorescence spectroscopy (XRF). The results demonstrated a strong dependence of adsorption performance on carbonization temperature, with maximum removal efficiencies of 90.2% (CRH-600) and 96.5% (CWS-700). The superior performance of CWS-700 was associated with its highly developed hierarchical pore structure (up to 670 m² g⁻¹), increased carbon content, and enhanced hydrophobicity. Kinetic studies revealed pseudo-second-order behavior, with equilibrium achieved within 25–30 min at near-neutral pH. Gas chromatographic analysis confirmed the complete removal of BTEX and light hydrocarbons (C1–C9) using CWS-700, highlighting its high selectivity toward aromatic compounds. The adsorption mechanism was attributed to the synergistic effect of micropore filling, hydrophobic interactions, and π-π interactions with aromatic hydrocarbons. The obtained results demonstrate that biomass-derived carbon materials, particularly walnut shell-based sorbents, are promising low-cost candidates for the treatment of complex water systems contaminated with emulsified petroleum hydrocarbons.