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The influence of the oxidation degree of graphene oxide (GO) on its deoxygenation efficiency via hybrid microwave heating (HWH) method by using graphite powder as the external susceptor was investigated, and the response behavior was compared with the situation when GO is directly submitted to microwave irradiation. In addition, the deoxygenation behavior of mildly reduced GO (VRGO) that was obtained via chemical reduction by Vitamin C was compared with that of GO during above two microwave heating processes. No response of GO to microwave irradiation when GO samples are exposed directly to microwave, no matter how the oxidation degree is. However, the VRGO sample can be heated when it is solely submitted to microwave irradiation. The partial reduction of GO leads to enhancement of the dielectric parameters, and the residual defects and oxygen-containing functional groups not only can improve the impedance matching characteristics, but also produce defects polarization relaxation and dipole polarization relaxation, which are all beneficial to the microwave penetration and absorption. The deoxygenation efficiency of VRGO is lower in comparison with GO under the HWH condition, which should be attributed to higher amount of epoxides in GO samples that can be easily reduced in a mixed heating mode.

The deoxygenation efficiency of graphene oxide (GO) under solid-state microwave irradiation was improved via chemical pre-reduction using different reductants (Vitamin C, hydrazine hydrate and sodium borohydride). The reduced graphene oxide (RGO) samples obtained by reduction of GO via Vitamin C were denoted as VRGO-x (x = 0.33, 1.5 and 5), where x indicates the mass ratio of VC to GO (RVC/GO). And the products fabricated via reduction of GO by hydrazine hydrate and sodium borohydride are recorded as HRGO and SRGO, respectively. It is found that deoxygenation efficiency of RGO samples at the similar initial oxygen concentrations via further microwave irradiation is different. For instance, the oxygen concentration of VRGO-0.33 and SRGO decreases to 10.75% and 19.19%, and the oxygen concentration of VRGO-5 and HRGO decreases to 10.66% and 13.78%, respectively. The real part of complex permittivity (e′) of GO increases from 2.25 to 2.4–2.5 and 2.7–2.8 for VRGO-0.33 and SRGO, VRGO-5 and HRGO, demonstrating the absorption ability of VRGO-0.33 and SRGO, VRGO-5 and HRGO is very close, respectively. Compared with SRGO, the deoxygenation efficiency is higher for VRGO-0.33 that with higher content of carbonyls. This can be explained by that the lower energy is required to remove carbonyls relative to that for the other functional groups. Moreover, because HRGO contains high content of stable oxygen functional groups and some amount of nitrogen-containing groups, which are relatively stable at high temperature, especially for pyrrolic N and graphitic N, the reduction efficiency of HRGO is lower than that of VRGO-5.