Recent studies on the chemical synthesis of graphene oxide reported in the literature.

Materials used	Duration	Temperature	Specifications	Reference
K2FeO4, H2SO4, and graphite flakes	1 h	Room temperature	Used strng green oxidant, K2FeO4, avoided the use of polluting heavy metal like manganese and toxic gases in the preparation, enables the recycling of H2SO4 and elimination of the pollutants.	119
KMnO4, NaNO3, and H2SO4	16 h	10 °C	Formation of high quality r(GO) was formed reorganizing the carbon framework efficiently by controlling the reaction temperature upto 10 °C during successive oxidation steps; thereby preventing over-oxidation of graphene layers. reduction of graphene oxide to graphene at higher temperature than 1500 °C would cause the complete degradation of GO.	120
KMnO4, NaNO3, and H2SO4	<2 h	35 °C	Reaction time was found short, purification procedure reported in the work eliminated oxidative impurities, thereby, decreasing the thickness of nanoplatelets, similar oxidation degree of graphite oxide was observed as reported by chemical reduction technique.	121
H2SO4, KMnO4, and H3PO4	12 h	50 °C	Exclusion of NaNO3, resulted in the reduction of toxicity, improved efficiency of oxidation process was observed by increasing the concentration of KMnO4 and 9 : 1 mixture of H2SO4/H3PO4, current modified method provided a greater amount of hydrophilic oxidized graphene material as compared to Hummer's method or Hummer's method with additional KMnO4.	122
HNO3	2 h	Room temperature	Oxidation of graphite to graphitic oxide was accomplished by treating graphite with essentially a water-free mixture of concentrated sulfuric acid, sodium nitrate and potassium permanganate, entire process required less than two hours for completion at temperatures below 45 °C. Temperature limitations and safely was successfully maintained.	123