Preparation and catalytic activity of thermosensitive Ga₂O₃ nanorods

Gallium oxide (β-Ga₂O₃) nanorods were prepared by ultrasonic irradiation of molten gallium in warm water to form α-GaO(OH). This precursor was then subjected to calcination in air at 600 °C for 3 h to form β-Ga₂O₃, as confirmed by X-ray diffraction (XRD). Field emission scanning electron microscopy (FE-SEM)/high-resolution transmission electron microscopy (HRTEM) micrographs revealed the formation of well-organized nanotubes/nanorods with homogeneous size distribution. The average length of the β-Ga₂O₃ nanorods was affected by the temperature of the water during sonication, decreasing from 480 to 72 nm with an increase in the temperature from 25 to 50 °C. A sharp decline in the particle size was also observed when the temperature was above 35 °C. The catalytic activity of the β-Ga₂O₃ nanorods was examined, as a model, during the dehydration reaction of xylose to furfural. Furfural is a versatile biomass-derived platform compound used for the synthesis of several strategic chemicals. This nanoscale catalyst has a large surface area, which enhances its catalytic activity and enables it to completely convert xylose to furfural at 150 °C within 12 h without any trace of byproducts, as confirmed by high-performance liquid chromatography (HPLC), ¹³C nuclear magnetic resonance (NMR), and ¹H NMR. The XRD pattern of the used β-Ga₂O₃ nanorods was identical to that of pristine Ga₂O₃, indicating the possible reusability of this catalyst. β-Ga₂O₃ was reused for more reduction cycles, with similar results to the freshly prepared β-Ga₂O₃. HPLC analysis demonstrated that the selectivity of furfural is up to 94% compared to the 30% obtained with GaO(OH) as a catalyst.