Abstract
Graphene oxide (GO) is a graphene derivative that emits fluorescence, which makes GO an attractive material for optoelectronics and biotechnology. In this work, we utilize ozone treatment to controllably tune the band gap of GO, which can significantly enhance its applications. Ozone treatment in aqueous GO suspensions yields the addition/rearrangement of oxygen-containing functional groups suggested by the increase in vibrational transitions of C-O and C=O moieties. Concomitantly it leads to an initial increase in GO fluorescence intensity and significant (100 nm) blue shifts in emission maxima. Based on the model of GO fluorescence originating from sp2 graphitic islands confined by oxygenated addends, we propose that ozone-induced functionalization decreases the size of graphitic islands affecting the GO band gap and emission energies. TEM analyses of GO flakes confirm the size decrease of ordered sp2 domains with ozone treatment, whereas semi-empirical PM3 calculations on model addend-confined graphitic clusters predict the inverse dependence of the band gap energies on sp2 cluster size. This model explains ozone-induced increase in emission energies yielding fluorescence blue shifts and helps develop an understanding of the origins of GO fluorescence emission. Furthermore, ozone treatment provides a versatile approach to controllably alter GO band gap for optoelectronics and bio-sensing applications.
Highlights
Due to its growing role in industry a functional derivative of graphene, graphene oxide (GO) has become a subject of active scientific inquiry
For the first time, we report controllable ozone-induced modification of Graphene oxide (GO) band gap in aqueous suspension
Absorption features show little change with continuous ozone treatment, a gradual increase in emission intensity and substantial blue shifts in fluorescence spectra are observed. These optical changes suggest an alteration of the band gap in GO due to structural modifications introduced by the addition and/or rearrangement of functional groups
Summary
Due to its growing role in industry a functional derivative of graphene, graphene oxide (GO) has become a subject of active scientific inquiry. A number of techniques such as chemical modification[10, 21, 22], infrared irradiation[23], thermal exfoliation[24], exfoliation of GO using focused solar radiation[25], photoreduction[26], photothermal deoxygenation[27], flash reduction[28], laser-induced reduction[29, 30], photocatalytic reduction[31] and mechanical compressive strain processing[32] are known to alter GO band structure Many of those methods are difficult to control due to their complexity, and do not allow the fine tuning of the gap energy for specific applications. This model, supported by FTIR and TEM analysis of GO flake composition, provides an insight into the structural origins of GO fluorescence and allows for optical characterization of GO structure
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