The difference can be clearly visible from characterization techniques such as Raman and XPS. The peak intensity of the D and G band tells a lot about whether it is GO or rGO in Raman. Hope the below article helps you.
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As per my opinion you can use Fourier Transform Infrared Spectroscopy (FTIR) to analyze or differentiate Graphene Oxide (GO) and Reduced Graphene Oxide (rGO)
There are many papers on the synthesis of rGO from GO. You can compare your sample with the reported information start with the simplest method, such as FTIR.
If you want confirm the whether rGO or GO in the prepared composites. Raman spectroscopy is most effective techniques for all the carbon based materials, where you can find the D and G bands, the D band is indicates disorder or defect ( broke the sp2 bond or due to attachment oxide functional group in edge centre carbon of outplane vibration) while G band due to in plane vibration of sp2 bond. Then calculated the ID/IG ratio, D peaks is higher which means more sp3 bonds and sp2 to sp3. The oxygen or defect more in carbon materials in your prepared composites
You can differentiate between GO and rGO by different analytical techniques like XRD, FTIR, Raman, and XPS and also with 13C solid state NMR
From Raman, u can find the sp2 to sp3 bond by ID/IG ratio, and from FTIR u can see the functionality in the material, further from the XPS we can see the chemical state of that material and from 13C CPMAS sp2 to sp3 carbon and other functional groups.
Ref:
1. Impact of graphene oxide and highly reduced graphene oxide on cement-based composite
2. The role of sp 2 /sp 3 hybrid carbon regulation in the nonlinear optical properties of graphene oxide materials
Spectrum can be observed to assess the variation between rGO vs GO. From the peak diffractions the rGO and GO in composite can be effectively differentiated. Your studies can be compared with past researches such as :Article Fourier transform infrared (FTIR) spectroscopy