التخليق الأخضر لجزيئات أوكسيد السيريوم النانوية باستخدام مستخلص قشور النارنج وتطبيقه في دراسة الامتزاز

Green synthesis of Cerium Oxide Nanoparticles using peels extract of Citrus aurantium and applied in adsorption study

Abstract
This study consisted of four main stages.
In the first stage, bioactive compounds were extracted from Citrus aurantium peels using a Soxhlet apparatus with both a polar solvent (ethanol) and a non-polar solvent (n-hexane). The extracted compounds were identified and characterized using Gas Chromatography–Mass Spectrometry (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR). Among the most important compounds obtained from the ethanol extract of Citrus aurantium peels are naringin, naringenin, hesperidin, Auraptenol, hexamethoxyflavone, and other bioactive compounds. In addition, several active constituents were also identified in the hexane extract of the peels, including limonene, β-pinene, myrcene, linalool, and others.
The second stage involved the synthesis of cerium oxide (CeO₂) nanoparticles using three different methods:
• A conventional chemical method using cerium chloride with cationic surfactant (cetyltri methyl ammonium bromide – CTAB) as a stabilizing agent.
• A green synthesis method using the ethanolic extract of Citrus aurantium Peels
• green synthesis method using the hexane extract of Citrus aurantium Peels
The second and third methods are considered eco-friendly, utilizing the natural extracts as reducing, capping, and stabilizing agents.
The third stage focused on characterizing the synthesized nanoparticles using FTIR, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and nitrogen adsorption–desorption (BET) analysis.
FTIR spectra revealed characteristic peaks in the range of 490–600 cm⁻¹ confirming the formation of CeO₂ nanoparticles. XRD analysis indicated a fluorite cubic crystalline structure with an average crystallite size ranging from 12 to 19 nm. SEM images showed sand-like particles in the chemically synthesized sample, rose Perry-like shapes in the ethanolic extract-based sample, and truffle-like shapes in the hexane extract-based sample. The specific surface area (BET) for the three samples was found to be 116.68cm2/g, 95.87cm2/g, and 87.3 cm²/g, respectively.
In the fourth stage, the synthesized nanoparticles were applied as adsorbents for the removal of Eosin dye from aqueous solutions. The optimal adsorption conditions for all samples were: dye concentration of 10 ppm, adsorbent dosage of 0.025 g, contact time of 90 minutes, and pH 6. However, the optimal temperature was 10°C for the chemically synthesized sample and 25°C for the green-synthesized samples. Thermodynamic studies revealed that the adsorption process was exothermic in the chemical method and endothermic in the green methods. Kinetic studies confirmed that the adsorption followed a pseudo-second-order kinetic model in all cases. The reusability of the synthesized nanoparticles was also tested, and they showed efficient performance over three consecutive cycles.