Modifying the Size of Ultrasound-Induced Liquid-Phase Exfoliated Graphene: From Nanosheets to Nanodots

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• 作者：Artur Ciesielski ; Sébastien Haar ; Alessandro Aliprandi ; Mohamed El Garah ; Giulia Tregnago ; Giovanni F. Cotella ; Mirella El Gemayel ; Fanny Richard ; Haiyan Sun ; Franco Cacialli ; Francesco Bonaccorso ; Paolo Samorì
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：December 27, 2016
• 年：2016
• 卷：10
• 期：12
• 页码：10768-10777
• 全文大小：556K
• ISSN：1936-086X

文摘

Ultrasound-induced liquid-phase exfoliation (UILPE) is an established method to produce single- (SLG) and few-layer (FLG) graphene nanosheets starting from graphite as a precursor. In this paper we investigate the effect of the ultrasonication power in the UILPE process carried out in either N-methyl-2-pyrrolidone (NMP) or ortho-dichlorobenzene (o-DCB). Our experimental results reveal that while the SLGs/FLGs concentration of the NMP dispersions is independent of the power of the ultrasonic bath during the UILPE process, in o-DCB it decreases as the ultrasonication power increases. Moreover, the ultrasonication power has a strong influence on the lateral size of the exfoliated SLGs/FLGs nanosheets in o-DCB. In particular, when UILPE is carried out at ∼600 W, we obtain dispersions composed of graphene nanosheets with a lateral size of 180 nm, whereas at higher power (∼1000 W) we produce graphene nanodots (GNDs) with an average diameter of ∼17 nm. The latter nanostructures exhibit a strong and almost excitation-independent photoluminescence emission in the UV/deep-blue region of the electromagnetic spectrum arising from the GNDs’ intrinsic states and a less intense (and strongly excitation wavelength dependent) emission in the green/red region attributed to defect states. Notably, we also observe visible emission with near-infrared excitation at 850 and 900 nm, a fingerprint of the presence of up-conversion processes. Overall, our results highlight the crucial importance of the solvent choice for the UILPE process, which under controlled experimental conditions allows the fine-tuning of the morphological properties, such as lateral size and thickness, of the graphene nanosheets toward the realization of luminescent GNDs.