Influence of Different Improved Hummers Method Modifications on the Characteristics of Graphite Oxide in Order to Make a More Easily Scalable Method

Abstract

Different samples of graphite oxide (GrO) were prepared by modification of the Improved Hummers Method reported in the literature. Graphite was used as the raw material and KMnO4 and H2SO4 were used as chemical reagents. GrO samples were analyzed by Raman spectroscopy, SEM, TEM, elemental analysis, X-ray diffraction, N2 adsorption–desorption, and thermogravimetric analysis. The results indicate that, after optimizing the synthesis method, the oxidation time was reduced from 12 to 3 h, coagulation step was removed, wash step was halved, use of H3PO4 during the oxidation step was no longer necessary, the production of graphite oxide per batch was increased, and the amount of graphite that could be processed was increased five times. Therefore, synthesis costs were significantly lower than those related to the published Improved Hummers Method. An economic assessment for the industrial scale demonstrated that this process could be viable from the third year after its implementation.

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“…To prepare the synthesized GO, the oxidation step in the 2016 work of M. del P. Lavin-Lopez et al was followed; however, the amount of graphite was reduced to 3 g and the graphite : KMnO 4 mass ratio was maintained at 1 : 3 in order to obtain the same oxidation degree. 22 3 g of graphite powder was mixed with 80 mL of 98% wt/wt H 2 SO 4 and then continuously stirred for 1 h. Next, a strong oxidizing agent (KMnO 4 , 9 g) was gradually dropped into the mixed solution, where the temperature was slowly raised to 45 C in this step because of an exothermic reaction. Then, the mixed solution was heated to 50 C under stirring.…”

“…20 To remedy this problem, the Hummers' method was improved by replacing NaNO 3 with H 2 SO 4 , H 3 PO 4 , and a doubled amount of KMnO 4 ; this technique is sometimes called the "improved Hummers' method" or "Tour method". 21 In 2016, the optimized improved Hummers' method was reported as a novel synthetic method for modied GO by Lavin-Lopez et al; 22 its advantages are low production cost, short reaction time and lack of toxicity. The reaction time decreases from 12 hours to 3 hours because the coagulation step is omitted; the wash step is reduced, the use of H 3 PO 4 is not necessary, the production per batch of GO is increased, and the method is easily scalable.…”

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“…Some difference can be additionally observed in a volume distribution of oxygen as elemental formula is quite different in case of GO I indicating more homogeneous distribution of oxygen in the mass of graphene oxide particles. Concerning literature methods [9,10] of graphite oxidation, products mostly suffer from low quality of carbon layers as they are strongly damaged by harsh oxidizing agents such as potassium manganate or dichromate or sodium nitrite in strongly acidic solutions which are employed. In addition products can be contaminated by impurities in a form of low molecular weight carbon fragments which are formed as by-products during oxidation.…”

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“…Advantages of the modified Hummers reaction are (1) high yield, (2) highly functionalised and therefore flexible product, (3) tuneable reaction variables that can influence product properties, and (4) relatively simple hardware required to perform the reaction. Researchers have achieved a high product yield (in excess of 30 g of GO from 15 g of graphite feedstock) (Zhang et al, 2009;Marcano et al, 2010;Lavin-Lopez et al, 2016). This technique does however have disadvantages, and these are (1) multiple process steps involved in the work-up and (2) single usage of reactants.…”

“…This technique does however have disadvantages, and these are (1) multiple process steps involved in the work-up and (2) single usage of reactants. Work has been done (Lavin-Lopez et al, 2016) to systematically reduce the unit operations from five to three while increasing the reactants to achieve a laboratory scale yield of 34 g/day with no detrimental impact to the product quality. XPS showed a conventional C/O ratio of 0.74; SEM and XRD showed a dry product size of ∼10 µm in diameter and 5 layers.…”