title: Modifying the Size of Ultrasound-Induced Liquid-Phase Exfoliated Graphene: From Nanosheets to Nanodots.
abstract: 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.
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Artur
authors.initials: A
authors.lastname: Ciesielski
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Haar
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Aliprandi
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Mohamed
authors.initials: M
authors.lastname: El Garah
authors.affiliation: Department of Physics and Astronomy (CMMP Group) and London Centre for Nanotechnology, University College London , Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Giulia
authors.initials: G
authors.lastname: Tregnago
authors.affiliation: Department of Physics and Astronomy (CMMP Group) and London Centre for Nanotechnology, University College London , Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Giovanni F
authors.initials: GF
authors.lastname: Cotella
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Mirella
authors.initials: M
authors.lastname: El Gemayel
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Richard
authors.affiliation: Graphene Labs, Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Sun
authors.affiliation: Department of Physics and Astronomy (CMMP Group) and London Centre for Nanotechnology, University College London , Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Franco
authors.initials: F
authors.lastname: Cacialli
authors.affiliation: Graphene Labs, Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Bonaccorso
authors.affiliation: Institut de Science et d'Ingénierie Supramoléculaires (ISIS) and International Center for Frontier Research in Chemistry (icFRC), Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS) , 8 Allée Gaspard Monge, 67000 Strasbourg, France.
authors.forename: Paolo
authors.initials: P
authors.lastname: Samorì
keywords: graphene; liquid-phase exfoliation; nanodots; photoluminescence