Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

Abstract

Optical and magnetic properties of graphene oxide (GO) have been intensively investigated because of the promising applications of GO-related materials in various technical fields. So far, the optical and magnetic properties of GO have been discussed independently. However, localized electronic states in reduced GO may simultaneously add optical transitions and spin moments in sp 2 nanodomains in GO nanosheets. In the present study, the structural, optical, and magnetic properties of graphene oxide (GO) photoreduced in an aqueous solution are correlated on the basis of experimental and theoretical investigations. Experimental observations show that photoreduction leads to enhancement of visible absorption, quenching of photoluminescence, and emergence of magnetism. Detailed spectroscopic and microscopic characterizations indicate the presence of photoreduction-produced basal plane C-H bonding and carbon vacancies. Ab initio calculations suggest that the presence of these defects in sp 2 nanodomains results in singly occupied molecular orbital levels in the π-π* gap to afford enhanced visible to near infrared (NIR) absorption and emergence of magnetism, which is consistent with the experimentally observed change in the optical and magnetic properties of GO by photoreduction. Enhancement of NIR emissions observed in shortly photoreduced GO and their extinction found in longer photoreduced GO are explained with integrating the theoretical calculations and time-resolved fluorescence measurements. The correlation among structural, optical, and magnetic properties, highlighted for the first time, could help accelerate the development of open-shell nanographene devices with concurrently tunable electrical, optical, magnetic, and electrochemical properties.

Synthesis of Reduced Graphene Oxide with Adjustable Microstructure Using Regioselective Reduction in the Melt of Boric Acid: Relationship Between Structural Properties and Electrochemical Performance

“…Infrared spectroscopy is useful to provide insights into the state of particular functional groups during the GO reduction process [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Figure 2 compares FTIR spectra of GO reduction products and their precursor.…”

Electrochemical Reaction of Graphene Oxide at Au Electrode Surface Monitored by Surface Enhanced Infrared Absorption Spectroscopy

“…The band around 3500 cm −1 corresponds to the stretching band of H 2 O, caused by the adsorption of GO on the electrode surface. Usually the GO contains OH groups in the addition of COOH and C-O-C groups [17], however the observed band here corresponds not to the OH group of GO but the H 2 O molecule at the electrode surface. The change in the enlarged SEIRA spectra in a narrow wavenumber region (1250-1850 cm −1 ) were shown in Fig.…”

“…of the sample injection, clear two bands at 1465 and 1618 cm −1 were observed. Since SEIRAS can detect the vibration mode of perpendicular component to the surface, these two bands correspond to the carboxylic group of the GO at the surface [17]. The SEIRA spectra after 3, 5 (not shown), 10 (not shown), and 20 min.…”

“…In contrast, at −1.0 V, the band almost disappeared. The band at 1250 cm −1 corresponds to the C-O-C vibration band of GO [17]. Therefore, the decrease in the absorbance was caused by the partial reduction of C-O-C of GO and the absorbance at −1.0 V was almost equal to that at OCP.…”

“…† Corresponding author: nisiyama@kumamoto-u.ac.jp the Faradaic electrochemical reaction of the oxygen functional groups, that is, the pseudocapacitive redox reaction [3,[12][13][14][15][16]. In addition, more recently, the correlation of optical and magnetic properties of photoreduced GO has been reported [17].…”