I am currently preparing graphene oxide from sub bituminous and bituminous coals by improved hummers method. I have prepared it from different samples, by changing different parameters of hummers method in all the samples systematically. I have achieved all the visible stages of color changes associated with the method in all the samples. But in one sample (bituminous coal), on increasing stirring time, the solution went through a greenish yellow stage before reaching the final yellowish solution color, unlike other samples. The color of GO powder obtained was brown for all the samples (as the literature suggests), except for that sample with increased stirring and stay time. It also formed jelly-like brown-to-black suspension during the washing stage (by centrifuge). The obtained powder is greyish brown and its texture is different from the powders obtained from other samples. GO powder is usually pasty or adherent in nature (to my knowledge based on literature as well as observations of my samples), it adheres to the petri dish and form a layered structure on drying. But in the sample I discussed above, the layer is thin but swollen (mild cake-like appearance) and on touch it breaks just like a dry plant leaf (photo attached). I am wondering if this is something that usually happens with GO or the increased stay time of solution during preparation method has something to do with it?
Your Source of Carbon is bituminous coal. That's why such greyish black material produced. Nothing to do worried. You should washes frequently and few more times with DI water and with 0.1M HCL/Ethanol for washedvout impurities. Washing and maintained pH at 7.. bcz, during chemical synthesis (adopted Hummer's Method)we were using conc. H2SO4, NaNO3 and for oxidation using KMnO4.. all these chemical reagents are highly acidic in nature.. So, we should cleaned and washed our supernatant (that brown/blakish padte)after centrifugation..
Then u should kept the semiliquid paste into a vacuum oven for over n8.. then u dried it in a oven/air heater at 65 degree celsius until complete drying..
Then u found a powered materials or something hard crystalline materials (sometimes )and crushed orvgrind by using a ball mill.
Then ur graphene is now ready..for characterization..
After RAMAN, ftir and XRD, u can recognized its physical characteristics and after BET, Surface area analysis and layer formation (single layer/double/triple /more(not graphene)...
Regards,
Osim, India
Ariha Shahi
Apparently your precursor (coal of this sample) contains more bitumen or asphaltene impurities. Stirring and drying will always have a secondary effect than impurities.
Your Source of Carbon is bituminous coal. That's why such greyish black material produced. Nothing to do worried. You should washes frequently and few more times with DI water and with 0.1M HCL/Ethanol for washedvout impurities. Washing and maintained pH at 7.. bcz, during chemical synthesis (adopted Hummer's Method)we were using conc. H2SO4, NaNO3 and for oxidation using KMnO4.. all these chemical reagents are highly acidic in nature.. So, we should cleaned and washed our supernatant (that brown/blakish padte)after centrifugation..
Then u should kept the semiliquid paste into a vacuum oven for over n8.. then u dried it in a oven/air heater at 65 degree celsius until complete drying..
Then u found a powered materials or something hard crystalline materials (sometimes )and crushed orvgrind by using a ball mill.
Then ur graphene is now ready..for characterization..
After RAMAN, ftir and XRD, u can recognized its physical characteristics and after BET, Surface area analysis and layer formation (single layer/double/triple /more(not graphene)...
Regards,
Osim, India
Prof. Yuri Mirgorod , thank you for your valuable answer. As much as your answer makes sense considering the blackish appearance and adhesive properties of my final product, I am still confused because I have used this same coal sample before (only with different parameters) and have gotten the brown powder.
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