Micro- and nanocellulose-based silica hybrid nanocomposites as eco-sorbents for efficient oil removal

The synthesis of hydrophobic cellulose–silica composites was accomplished via a sol–gel route. Cellulose obtained from industrial licorice-root waste, an inexpensive raw material, was used as a renewable precursor in its microcrystalline (MCC) and nanocrystalline (NCC) forms. Methyltrimethoxysilane (MTMS) was employed as the silicon source as well as the hydrophobic modifying agent. During the study, the effects of the MCC and NCC/MTMS molar ratio, reaction temperature, and reaction time on composite formation were systematically investigated. The results showed that a molar ratio of MCC and NCC/MTMS of 1:1.8, a reaction temperature of 80–100°C, and a reaction duration of 60 minutes represented the optimal conditions for composite formation. The composites synthesized under these optimized parameters exhibited pronounced hydrophobic properties. The water contact angles of pristine microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC) were determined to be 15° ± 1°, indicating their intrinsically hydrophilic nature. In contrast, after silica modification, the water contact angle increased significantly to 120° ± 1° for the MCC–(CH₃SiO₁.₅)ₙ composite and to 136° ± 1° for the NCC–(CH₃SiO₁.₅)ₙ composite, confirming the successful formation of hydrophobic surfaces. Furthermore, benzene adsorption isotherms were investigated to evaluate the adsorption performance of the materials. At a relative pressure of P/P₀ = 1, the adsorption capacity of pristine MCC and NCC was found to be 0.88 cm³/g and 0.26 cm³/g, respectively. After composite formation, these values increased markedly to 5.3 cm³/g for the MCC–(CH₃SiO₁.₅)ₙ composite and 1.8 cm³/g for the NCC–(CH₃SiO₁.₅)ₙ composite, demonstrating a substantial enhancement in adsorption capacity as a result of silica incorporation and surface hydrophobization. The structural and thermal properties were evaluated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). Additionally, the hydrophobicity and oil/grease adsorption efficiency were assessed. The resulting materials exhibited enhanced water repellency, high thermal stability, and superior adsorption capacity for oil and grease. The utilization of cellulose–silica composites as sustainable adsorbents for the remediation of hydrocarbon-based pollutants is a promising avenue for environmental restoration. These composites are notable for their eco-friendly origin and demonstrated efficacy, which underscores their significant potential in addressing environmental concerns.