Identification of a Slowly Relaxing Paramagnetic Center in Graphene Oxide

Maria A Augustyniak-Jabłokow,Ryhor Fedaruk,Łukasz Majchrzycki,Roman Strzelczyk

doi:10.1007/s00723-018-1058-2

Abstract

We demonstrate the existence of two types of paramagnetic centers in a pure graphene oxide. Saturation features of the electron paramagnetic resonance (EPR) spectrum in the temperature range of 4.2–300 K reveal that one of these centers has the spin–lattice relaxation time longer than 1.6 μs at room temperature. The spectrum of these centers consists of a central line and two satellite lines. The satellite lines result from the forbidden transitions in the hyperfine structure induced by protons in the vicinity of the slowly relaxing centers. The observability of the satellites can be used as a characteristic signature of graphene oxide purity. Since the number of slowly relaxing centers is reduced during chemical reduction of graphene oxide, this type of centers can be attributed to the isolated unfunctionalized carbons in the highly functionalized regions of GO. The second type of paramagnetic centers has shorter relaxation times and dominates in the reduced graphene oxide.

Highlights

Graphene oxide (GO) is a well-known and widely used form of functionalized graphene [1, 2]
We used the rapid passage effects under microwave saturation to identify paramagnetic centers with the spin–lattice relaxation time (T 1 ) longer than 1 μs at room temperature (RT) in GO. Another type of centers with short relaxation times is observed in this material. These fast relaxing centers dominate in reduced graphene oxide (RGO)
The saturation results in the nonlinear dependence of the electron paramagnetic resonance (EPR) signal intensity on the square root of MW power as it is observed for the in-phase and out-of-phase signals of GO (Fig. 2b)

Summary

Introduction

Graphene oxide (GO) is a well-known and widely used form of functionalized graphene [1, 2]. Thermal or chemical removal of functional groups existing on the GO surface produces reduced graphene oxide (RGO), a kind of chemically derived graphene [12, 13]. Such modification extends the range of possible applications of this material [13]. We used the rapid passage effects under microwave saturation to identify paramagnetic centers with the spin–lattice relaxation time (T 1 ) longer than 1 μs at RT in GO Another type of centers with short relaxation times is observed in this material.

Experimental

Results and Discussion

Conclusions