The mistake is in the final stages of your oxidation process: the H2O2 needs to be added to complete the redox reaction, and then your solution has to turn yellow.

Only after your finish your reaction, then you can start your washing/filtering process with DI water and HCl (and if you want ethanol as well). Do not use H2O2 in your washing procedure!

For more info, check this conference paper:

Conference Paper Graphite Oxide Post-Synthesis Processing Protocols

The mistake is in the final stages of your oxidation process: the H2O2 needs to be added to complete the redox reaction, and then your solution has to turn yellow.

Only after your finish your reaction, then you can start your washing/filtering process with DI water and HCl (and if you want ethanol as well). Do not use H2O2 in your washing procedure!

For more info, check this conference paper:

Conference Paper Graphite Oxide Post-Synthesis Processing Protocols

Please check your condition of H2O2, this is very important to get yellow-brown color of your GO. We also happening same thing like you before. After using new H2O2 solution, we got yellow-brown. It is better to use H2O2 within one month after opening bottle.

Here the problem is usage of HCL before reduction reaction completed by H2O2 , use H2O2 first to complete the reaction and use HCL and DI water for washing until the pH of the filtrate is neutral. And also use fresh H2O2