Temperature-dependent microwave absorption properties of low-defect graphene oxide

Low-defect graphene oxide (GO) was synthesized at low temperature (0 °C) by applying a modified Hummers' method. X-ray diffraction (XRD) and Raman spectroscopy demonstrated the feasibility of low temperature oxidation in a mixed acid system of H₃PO₄ and H₂SO₄. The higher degree of oxidation corresponds to lower defects and further demonstrates that low temperature oxidation can effectively prevent defects (CO₂ formation) during the preparation process. X-ray photoelectron spectroscope (XPS) showed that the C–O content of the as-obtained GO was increased by 10% compared with the conventional method. The microwave absorption capability of GO was investigated by measuring the dielectric properties from room temperature to ∼800 °C at 2.45 Hz. The dielectric constant (ε _r′) and dielectric loss factor (ε _r″) increase slowly from room temperature to 150 °C. In the temperature range 150 °C ∼ 450 °C for GO, ε _r′ increases rapidly from 2.04 to 39.92, but ε _r″ rapidly increases to 4.54 at 250 °C and remains relatively stable. As the temperature increases further, ε _r′ and ε _r″ slowly increase to 52.22 and 8.32, respectively. The theoretical reflection loss (RL) of the sample suggest that the maximum microwave absorption with the reflection losses of −16.72 dB can be obtained for the GO having thicknesses of 1 to 10 mm at 2.45 GHz. The calculation of microwave penetration depth (Dp) shows that the microwave absorption capability of GO can be improved at high temperatures. This work reveals the relationship between the temperature and dielectric properties of GO, which may contribute to the correct understanding for the design and modification of graphene-based materials through microwave irradiation. (paper)