Effect of switching ultrasonic amplitude in preparing a hybrid of fullerene (C) and gallium oxide (GaO).

In this study, we proposed 'switching ultrasonic amplitude' as a new strategy of applying ultrasonic energy to prepare a hybrid of buckminsterfullerene (C) and gallium oxide (GaO), C/GaO. In the proposed method, we switched the ultrasonic amplitude from 25% to 50% (by 5% amplitude per 10 min, within 1 h of ultrasonic irradiation) for the sonochemical treatment of a heterogeneous aqueous mixture of C and GaO by a probe-type ultrasonic horn operating at 20 kHz. We found that compared to the conventional techniques associated with high amplitude oriented ultrasonic preparation of functional materials, switching ultrasonic amplitude can better perform in preparing C/GaO with respect to avoiding titanium (Ti) as an impurity generating from the tip erosion of a probe-type ultrasonic horn during high amplitude ultrasonic irradiation in an aqueous medium. Based on SEM/EDX analysis, the quantity of Ti (wt.%) in C/GaO prepared by the proposed technique of switching ultrasonic amplitude was found to be 1.7% less than that prepared at 50% amplitude of ultrasonic irradiation. The particles of C/GaO prepared by different modes of amplitude formed large (2-12 μm) aggregates in their solid phase.Whereas, in the aqueous medium, they were found to disperse in their nano sizes. The minimum particle size of the as-synthesized C/GaO in an aqueous medium prepared by the proposed method of switching ultrasonic amplitude reached to approximately 467 nm. Comparatively, the minimum particle sizes were approximately 658 nm and 144 nm, using 25% and 50% amplitude, respectively. Additionally, GaO went under hydration during ultrasonic irradiation. Moreover, due to the electron cloud interference from C in the hybrid structure of C/GaO, the vibrational modes of GaO were Raman inactive in C/GaO.