title: High quality reduced graphene oxide flakes by fast kinetically controlled and clean indirect UV-induced radical reduction.
abstract: This work highlights a surprisingly simple and kinetically controlled highly efficient indirect method for the production of high quality reduced graphene oxide (rGO) flakes via UV irradiation of aqueous dispersions of graphene oxide (GO), in which the GO is not excited directly. While the direct photoexcitation of aqueous GO (when GO is the only light-absorbing component) takes several hours of reaction time at ambient temperature (4 h) leading only to a partial GO reduction, the addition of small amounts of isopropanol and acetone (2% and 1%) leads to a dramatically shortened reaction time by more than two orders of magnitude (2 min) and a very efficient and soft reduction of graphene oxide. This method avoids the formation of non-volatile species and in turn contamination of the produced rGO and it is based on the highly efficient generation of reducing carbon centered isopropanol radicals via the reaction of triplet acetone with isopropanol. While the direct photolysis of GO dispersions easily leads to degradation of the carbon lattice of GO and thus to a relatively low electric conductivity of the films of flakes, our indirect photoreduction of GO instead largely avoids the formation of defects, keeping the carbon lattice intact. Mechanisms of the direct and indirect photoreduction of GO have been elucidated and compared. Raman spectroscopy, XPS and conductivity measurements prove the efficiency of the indirect photoreduction in comparison with the state-of-the-art reduction method for GO (hydriodic acid/trifluoroacetic acid). The rapid reduction times and water solvent containing only small amounts of isopropanol and acetone may allow easy process up-scaling for technical applications and low-energy consumption.
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, D-04303 Leipzig, Germany. roman.flyunt@iom-leipzig.de bernd.abel@iom-leipzig.de.
authors.forename: Roman
authors.initials: R
authors.lastname: Flyunt
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, D-04303 Leipzig, Germany. roman.flyunt@iom-leipzig.de bernd.abel@iom-leipzig.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Knolle
authors.affiliation: Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Kahnt
authors.affiliation: Department of Chemistry and Pharmacy & Central Institute for New Materials and Processing Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 90762 Fürth, Germany.
authors.forename: Christian E
authors.initials: CE
authors.lastname: Halbig
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, D-04303 Leipzig, Germany. roman.flyunt@iom-leipzig.de bernd.abel@iom-leipzig.de.
authors.forename: Andriy
authors.initials: A
authors.lastname: Lotnyk
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, D-04303 Leipzig, Germany. roman.flyunt@iom-leipzig.de bernd.abel@iom-leipzig.de.
authors.forename: Tilmann
authors.initials: T
authors.lastname: Häupl
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, D-04303 Leipzig, Germany. roman.flyunt@iom-leipzig.de bernd.abel@iom-leipzig.de.
authors.forename: Andrea
authors.initials: A
authors.lastname: Prager
authors.affiliation: Department of Chemistry and Pharmacy & Central Institute for New Materials and Processing Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 90762 Fürth, Germany and Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41258 Göteborg, Sweden.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Eigler
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, D-04303 Leipzig, Germany. roman.flyunt@iom-leipzig.de bernd.abel@iom-leipzig.de.
authors.forename: Bernd
authors.initials: B
authors.lastname: Abel