Why is my graphene oxide not turning yellow instead it stays green black?

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Balamurugan Thangavel

In the hummers method, oxidation of graphite into graphite oxide is to be carryout. In this, acidified KMnO4 oxidizes the graphite and after the addition of H2O2, the GO solution should be turn yellowish-brown which indicates that the reaction is completed. If you add additional H2O2, you are oxidizing the Mn present in the system. This might be the reason that the blue/ violet color appearance. After washing the product u may see the GO color as brown.

Selva Kumar

If you keep it long time, the graphene oxide will convert to graphite itself. So better graphene oxide convert to reduced graphene oxide the stability might increase and the expect results you may get

Arnab Mukherjee

Thank you Balamurugan Thangavel for this informative statement.

Hi Nhlanhla Matsenjwa

Oxidation of graphite into graphite oxide is carried out in Hummer's method. The oxidation is done using KMnO4, H2O2, in a concentrated H2SO4 medium. When the solution turned yellowish-brown the reaction is completed. If there is some unreacted KMnO4 the color may be the greenish-black as stated by you. This I can suggest from my side.

Regards

Santosh K. Tiwari

If your graphene oxide sample is staying green-black instead of turning yellow, it could be due to following reasons:

The color of GO is influenced by the extent of oxidation. If your GO sample has a lower degree of oxidation, it may appear greener or darker in color instead of turning yellow. The color can vary based on the ratio of carbon-to-oxygen atoms and the distribution of functional groups on the graphene oxide surface.

The processing conditions during the synthesis or purification of GO can influence its color. Factors such as reaction temperature, reaction time, and pH can impact the oxidation state and the resulting color of the GO sample.

The presence of impurities, such as residual reducing agents or organic contaminants, can affect the color of GO. These impurities can alter the electronic structure or interfere with the oxidation state of the graphene oxide, resulting in a different color appearance.

Graphene oxide samples can undergo changes over time due to exposure to air, moisture, or other environmental factors. The aging process can lead to modifications in the structure and oxidation state of GO, resulting in a darker color.