Abstract
The isothermal kinetics of fullerene polyhydroxylation under ultrasonic field was investigated. The isothermal kinetic curves of fullerene polyhydroxylation at different temperatures ranging from 293 K to 313 K were determined. By application of the isoconversion method it was established that the reaction of fullerene polyhydroxylation with sodium hydroxide and cetyl trimethyl ammonium bromide as phase transfer catalyst was kinetically an elementary reaction. The model-fitting method confirmed that the kinetics model of first-order chemical reaction best described the kinetics of fullerene polyhydroxylation under ultrasonic field and the kinetics parameters of fullerene polyhydroxylation were determined (Ea,= 29 kJ/mol and lnA=9.4 min-1). It was established that the reaction rate of fullerene polyhydroxylation under ultrasonic field is higher from 1.5 times to 2.2 times than the rate of comparative reaction under the conventional heating. The activation energy is 28% lower than the value of activation energy determined under the conventional heating, whereas the value of pre-exponential factor is 40 times higher. The decreased value of activation energy (Ea,) and pre-exponential factor (lnA) in the ultrasonic field is explained with the increase in the value of ground energy level of the resonant vibration mode (? = 500 cm-1) of C60 molecule (Ag(1) vibrational mode) and toluene molecule (out-of plane bending C-C-C vibration) and with the decreased value of anharmonicity factor.
Highlights
The most representative fullerene, C60, have unique chemical and physical properties due to its unusual structure and extended π -electron system [1]
From the VIS spectra obtained during C60 polyhydroxylation it can be seen that the intensity of the absorption peaks at λ1 = 535 nm and λ2 = 592 nm, which are proportional to the concentration of fullerene in the organic phase, decreases and at the very end of reaction completely disappeared
Using the data of decreasing C60 concentration in the toluene solution and applying Eq (9) we can calculate the degree of C60 polyhydroxylation
Summary
The most representative fullerene, C60, have unique chemical and physical properties due to its unusual structure and extended π -electron system [1]. The pristine C60 is insoluble in water [2]. Numerous methods were developed to overcome the insolubility of C60, while retaining its unique inherent properties, through surface derivatization. Polyhydroxylated C60 fullerenes (fullerols) are derivatives of C60 with hydroxyl group formed by chemical modification of covalent C-O bond on their surfaces. The chemical modification of fullerenes by incorporating OH groups on their carbon surface yields a variety of C60(OH)n, (2≤n≤44) exhibiting different degrees of solubility in water [3]. M. Gigov et al /Science of Sintering, 48 (2016) 259-272
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