Sir,

Graphene oxide can be synthesized by modern Hummer's method, but the size controlling GO formed can be attained by longer oxidation times and more oxidants that can be used,to reduce the mean size of the GO particles from um to nm.

Thank you Anupma Thakur

Dear Syed Asad A Zaidi,

I prepared GO using the following procedure: 

Graphite flakes-500 mesh (2g) and NaNO3 (1g) were mixed  in 250 ml volumetric flaks and kept  at ice bath (0-5◦C) with continuous stirring for 15 min then (50 ml) of H2SO4 (98%) with kept temperature below ( 5◦C) . The mixture was stirred for 30 min at this temperature then the ice bath was removed and potassium permanganate (7/3g) was added to the suspension very slowly (for 4 hour).

The rate of addition was carefully controlled to keep the reaction temperature 35° C under water bath and the mixture was stirred at 35°C for 2 hour until it became dark green. After this stage the water bath was removed and Deionized water (48.3 ml ) was added with continuous stirring for 1 hour at temperature 35◦C, 1hour at 50◦C, 1 hour at 60◦C and 1 hour at 70◦C and the color of mixture changed to brown color. Finally, the solution is treated with H2O2 30% (2.3ml) to terminate the reaction by appearance of yellow color. The mixture was centrifuged and washed with HCl 3% and then deionized (DI) water several times until pH of mixture = 6-7 and dried at 50◦C for 48 hour.

Thank you @Mohamed Bayati and @Amer Sakran

The crucial condition is the size distribution of initial graphite! It corresponds to the size of GO in output (big graphite particles = big GO flakes). People use even nanorods to get finest GO.

could you clarify the expression "GO nanoparticles"?

Anyway,the quality and quantity of GO sheets or flakes are strongly depend on the the quality of graphite powder you use, the oxidation procedure (there are a lot of modified Hummer methods are mentioned in the literature) and the time of oxidation as well. 

The lateral sheet dimension of GO (after oxidation and exfoliation) can not be any larger than the size of the sheets in the graphite starting material.

In our published work on GO as a colloidal stabilizer we use graphite nanofibres with < 200 nm width (commercially available) as this means the GO sheets will be no larger than this across the basal plane.

Dear Syed Asad A Zaidi,

I prepared GO:

In a typical procedure 1.0 g of graphite was mixed with 23 mL of conc. H2SO4 that had been cooled to 0 °C, and 3.0 g of KMnO4 was then added with vigorous stirring. The

mixture was cooled uninterruptedly without allowing the temperature to rise above 20 °C. After mixing the mixture was kept at 35 °C for 25-30 min. Then 46 mL of distilled water was added, and the mixture was kept at 96-98 °C for 15-20 min. The reaction of the graphite with the oxidizing agent was then stopped by the further addition of 140 mL of water and 10 mL of 30% aqueous H2O2 solution to the mixture. The precipitate was separated by filtration, washed repeatedly with a 5% solution of HCl, water, and acetone, and dried in air at 50-60 °C.

To obtain the GO colloids the graphite oxide powder was mixed with an aliquot portion of distilled water or an aqueous solution of SPP and subjected to ultrasonic treatment for 20-25 min.

Dear Syed, 

I have used the following procedure for synthesis of GO:

In a stepwise preparation, 1 g natural graphite powder was added into 50 mL H2SO4. After stirring at room temperature for 2 h, 6 g KMnO4 was added very slowly to the suspension cooled with an ice-bath to keep the reaction temperature below 15 °C. Subsequently, the ice bath was removed and the mixture was stirred continuously in water bath at 35 °C for 1 day. It is then diluted with slow addition of 150 mL deionized (DI) water and the oxidation reaction was terminated by pouring 50 mL H2O2 solution (30%). For purification, the mixture was washed by HCl and DI water several times to remove residual acids and salts. The oxidized solid was subsequently suspended in DI and exfoliated by high-energy sonication to yield GO; it should be mentioned that every 1 g of derived graphite oxide was dispersed in 1 L DI. 

Dear Syed,

Please check pdf attached here that includes Hummer's method and modified Hummer's method for GO synthesis. I have followed same protocol in my lab. Hope it will work in your case too.

Goodluck !!!

Smriti

Thanks alot @ Smriti Gupta

I have liquid graphene oxide that is micrometer scaled size. I want to prepare nanosized graphene oxide from microsized graphene. Does anybody know the exact process for converting microsized to nanosized graphene oxide.