Modifying optical properties of reduced/graphene oxide with controlled ozone and thermal treatment in aqueous suspensions

Abstract

Graphene possesses a number of advantageous properties, however, does not exhibit optical emission, which limits its use in optoelectronics. Unlike graphene, its functional derivative, graphene oxide (GO) exhibits fluorescence emission throughout the visible. Here, we focus on controlled methods for tuning the optical properties of GO. We introduce ozone treatment of reduced graphene oxide (RGO) in order to controllably transform it from non-emissive graphene-like material into GO with a specific fluorescence emission response. Solution-based treatment of RGO for 5-45 min with ∼1.2 g l ozone/oxygen gas mixture yields a drastic color change, bleaching of the absorption in the visible and the stepwise increase in fluorescence intensity and lifetime. This is attributed to the introduction of oxygen-containing functional groups to RGO graphitic platform as detected by the infrared spectroscopy. A reverse process: controllable quenching of this fluorescence is achieved by the thermal treatment of GO in aqueous suspension up to 90 °C. This methodology allows for the wide range alteration of GO optical properties starting from the dark-colored non-emissive RGO material up to nearly transparent highly ozone-oxidized GO showing substantial fluorescence emission. The size of the GO flakes is concomitantly altered by oxidation-induced scission. Semi-empirical PM3 theoretical calculations on HyperChem models are utilized to explore the origins of optical response from GO. Two models are considered, attributing the induced emission either to the localized states produced by oxygen-containing addends or the islands of graphitic carbon enclosed by such addends. Band gap values calculated from the models are in the agreement with experimentally observed transition peak maxima. The controllable variation of GO optical properties in aqueous suspension by ozone and thermal treatments shown in this work provides a route to tune its optical response for particular optoelectronics or biomedical applications.

Optical Band Gap Alteration of Graphene Oxide via Ozone Treatment

“…the types of oxygen-containing functional groups or their arrangements 38–40 . In order to alter the optical band gap, we subject aqueous suspensions of graphene oxide to oxidizing ozone treatment inside the ultrasonic bath for the periods of 0 to 35 minutes which was previously utilized to convert RGO (Reduced Graphene Oxide) into GO 17 . Ultrasonic treatment serves as a means of disaggregation, improving the access of ozone to GO sheets.…”

“…Prolonged ozone treatment is known to induce GO flake scission 17 and, potentially, a decomposition of fluorescing centers causing a decrease in GO emission. Thus, we expect two competing processes to take place: (1) the addition and rearrangement of functional groups on GO surface resulting in a blue shift, increase in the emission intensity and fluorescence quantum yield (Fig.…”

“…In order to measure fluorescence spectra, 400 nm excitation was chosen on the basis of previous works 17 . In PLE experiments, excitation wavelength was scanned from 376 to 476 nm with 2 nm interval.…”

“…In addition to these properties, GO is water-soluble and exhibits fluorescence, which makes it a more attractive candidate than graphene for optoelectronics and biomedical applications 10, 11 . Different GO fabrication methods including Hummers/modified Hummers methods 12, 13 , facile oxidative techniques utilizing benzyl peroxide 14 , and structure-defining synthetic methods 15–17 result in GO materials with different optical and electronic properties that are strictly defined by the synthetic procedure. This restricts potential applications of GO to those fitting with the properties of as-synthesized materials.…”

Intracellular microRNA quantification in intact cells: a novel strategy based on reduced graphene oxide-based fluorescence quenching

“…Single monolayer graphene and graphene oxides posses all these properties. Especially, the wide spectral absorbance of graphene and its derivatives (graphene oxides and reduced graphene oxides) provides opportunity to develop assays based on fluorescence 15 . Several graphene based sensors have been attempted for measuring various biomolecules of cells for diagnostic applications in biomedicine 16, 17 .…”