title: Ultrasound assisted reduction of graphene oxide to graphene in L-ascorbic acid aqueous solutions: kinetics and effects of various factors on the rate of graphene formation.
abstract: The reduction of graphene oxide (GO) to graphene (rGO) was achieved by using 20 kHz ultrasound in L-ascorbic acid (L-AA, reducing agent) aqueous solutions under various experimental conditions. The effects of ultrasound power, ultrasound pulse mode, reaction temperature, pH value and L-AA amount on the rates of rGO formation from GO reduction were investigated. The rates of rGO formation were found to be enhanced under the following conditions: high ultrasound power, long pulse mode, high temperature, high pH value and large amount of L-AA. It was also found that the rGO formation under ultrasound treatment was accelerated in comparison with a conventional mechanical mixing treatment. The pseudo rate and pseudo activation energy (Ea) of rGO formation were determined to discuss the reaction kinetics under both treatment. The Ea value of rGO formation under ultrasound treatment was clearly lower than that obtained under mechanical mixing treatment at the same condition. We proposed that physical effects such as shear forces, microjets and shock waves during acoustic cavitation enhanced the mass transfer and reaction of L-AA with GO to form rGO as well as the change in the surface morphology of GO. In addition, the rates of rGO formation were suggested to be affected by local high temperatures of cavitation bubbles.
authors.affiliation: Graduate School of Engineering, Osaka Prefecture University, Osaka 599-8531, Japan; State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China; College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, PR China.
authors.forename: Abulikemu
authors.initials: A
authors.lastname: Abulizi
authors.affiliation: Graduate School of Engineering, Osaka Prefecture University, Osaka 599-8531, Japan. Electronic address: okitsu@mtr.osakafu-u.ac.jp.
authors.forename: Kenji
authors.initials: K
authors.lastname: Okitsu
authors.affiliation: State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China. Electronic address: jjzhu@nju.edu.cn.
authors.forename: Jun-Jie
authors.initials: JJ
authors.lastname: Zhu
keywords: Graphene; Graphene oxide; Kinetics; Reduction; Ultrasound