Al(NO3)3/SiO2 Synthesized from Rice Husk Ash Increases Isomer Separation Efficiency of Natural Beta-Caryophyllene

Beta-caryophyllene is a sesquiterpene found in almost all plant essential oils that provide spacious biological activities. However, this compound is generally mixed with its isomers, leading to decreased caryophyllene purity. Rice husk offers a sustainable source of silica that can be doped with metal ions to increase the separation efficiency. This study aimed to synthesize metal ion-modified silica from rice husk and evaluate its effectiveness in separating beta-caryophyllene from its isomers. Silica was extracted and modified with metal ions (Al(NO3)3, CuSO4, FeNO3, and ZnNO3) using sol-gel and reflux methods. The resulting materials were characterized by XRD, FTIR, and SEM-EDX. XRD analysis confirmed the amorphous nature of the silica, indicated by the presence of a peak at 2theta 20-25°, while FTIR spectroscopy revealed the presence of characteristic silanol (O-H) and siloxane (Si-O-Si) groups. SEM-EDX analysis demonstrated successful metal ion doping and provided insights into the morphology and elemental composition of the modified silica, which indicated the presence of Al, Cu, Fe, and Zn with a round-ball form. The separation efficiency of the metal ion-modified silica was assessed using thin-layer chromatography (TLC) and gas chromatography-mass spectrometry (GC-MS). Al(NO₃)₃-modified silica showed the most promising results as a stationary phase for beta-caryophyllene purification. Column chromatography using this material achieved a 99% purity of beta-caryophyllene, as confirmed by GC-MS analysis. This study demonstrates the potential of metal ion-modified silica derived from rice husk as an effective and sustainable material for the separation of natural product isomers.