Method for obtaining graphite from cast iron for the synthesis of graphene oxide

Abstract

The starting material, cast iron with at least 5.0% by weight of carbon, is cast and subjected to slow cooling, producing graphite with a minimum size of 1 mm, to be ground and dissolved by acid corrosion. The graphite oxide particles are filtered and dried, forming a solution with a dose of H2SO4 and kept agitated for 10 to 20 minutes at a temperature below 10ºC, then, while still being agitated, the potassium permanganate reagent is added, forming a new solution which is left to rest for at least 3 hours before being diluted in distilled water and having the excess oxidant removed by adding H2O2, left to rest again for 20 to 30 hours and then washed, producing graphene oxide, which is diluted and exfoliated in an ultrasonic bath, in order to obtain reduced graphene oxide.

Description

“PROCESS FOR OBTAINING GRAPHITE FROM CAST IRON FOR SYNTHESIS OF GRAPHENE OXIDE” Field of the invention

[0001] The present invention relates to a process that defines a simple, scalable and sustainable synthetic route for obtaining high-quality graphite from cast iron, to be used in the synthesis of graphene oxide species (oxidized and reduced), presenting high yield and leading to high-quality graphene oxides and applicable in the development of various products, such as filter membranes for the retention of pesticides, bacteria, viruses, endocrine disruptors and for effluent treatment, water purification, retention of gases and (micro / nano) particles from combustion.

[0002] Due to the route used to obtain it, the graphene oxide species produced can also be applied in the development of (bio)sensors, catalysts, and materials for the sports, automotive, textile, construction, and medical equipment industries, among other diverse applications in which the use of graphene oxide, although desirable, is generally impractical due to the production costs involved. Background of the invention

[0003] Although the concept of obtaining graphene oxide from carbon-containing metal alloys, such as cast iron, is well-known, the routes suggested so far for extracting graphite from the metal matrix utilize more complex and costly procedures. Known solutions, which suggest extracting graphite from a metallic matrix containing carbon, are not capable of producing high-quality graphite from a low-cost material, as is the case with gray cast iron slag, using a sustainable, environmentally friendly route that does not require sophisticated equipment.

[0004] Document CN108796176A describes a method for inducing ductile iron to synthesize graphene in situ, using a magnetic field and electricity to achieve a desired degree of graphene synthesis from ductile iron. This previous method does not achieve high graphite growth through the use of a furnace, but rather through the insertion of electrons, which compromises the quality of the extracted graphite and also the sustainability and industrial viability of this route, due to the environmental implications and operational costs involved.

[0005] Document CN105016329A describes a method for obtaining graphene, not graphene oxide, from carbon-containing alloys, making no suggestion regarding the production of graphene oxide from a low-cost material, such as cast iron, or the possible sustainable and environmentally friendly procedures that would have to be used to make this route viable. Summary of the invention

[0006] Considering the limitations of the known processes for obtaining graphene oxide, as briefly discussed above, the present invention aims to provide a process that allows obtaining high-quality graphite from cast iron, to be used in the synthesis of graphene oxide species. high quality, through simple, sustainable, environmentally friendly, relatively low-cost, and high-yield synthetic procedures, in which the extracted graphite will have a substantially increased size, from a starting material comprising gray cast iron. Description of the invention

[0007] As previously mentioned, the process of the invention proposes a new route for obtaining high-quality graphite, for the production of graphene oxide, starting from a material with a substantially reduced cost and basically defined by gray cast iron, generally available in the form of polluting industrial slag.

[0008] The starting material considered in the process in question is defined as gray cast iron preferably comprising 5.0% to 6.0% carbon, 1.9% to 2.10% silicon, and 0.60% to 0.80% manganese. Other cast iron compositions may be used as the starting material, provided they contain a minimum percentage of carbon in the metal matrix or may have this minimum carbon percentage of 5.0%, preferably 5.5% by weight, easily achieved through changes in the composition of the metal matrix, which may contain pig iron, steel scrap, returned cast iron, graphite, ferrosilicon, and ferromanganese.

[0009] The minimum percentage of carbon (graphite), present in the starting material defined by the metallic matrix, is that considered adequate to obtain an industrially acceptable yield for the production of a graphite with a minimum dimension.

[0010] According to the process, the starting material is subjected to heating in the range of 1200°C to 1500°C, in an induction furnace, and maintained in this condition until the components of the metal matrix to be used as starting material are completely melted.

[0011] The molten starting material, poured from the casting furnace to form molds containing at least 5.0% carbon, is cooled slowly, at a rate of 5 to 10°C / hour, until it reaches an ambient temperature in the solidification range, to allow the graphite to grow to a minimum dimension of 1 mm in length.

[0012] Once the starting material has been obtained, already cooled, in the form of ingots of the metal matrix, containing at least 5.0% carbon, it is ground to present itself in the form of particles with an average dimension in the range of 0.5 mm.

[0013] The ground starting material is then subjected to a stage of dissolution of the metallic components, through deep acid corrosion, using aqua regia, defined by a mixture of 1 part of concentrated nitric acid, to 4 parts of hydrochloric acid (v / v), diluted in ethyl alcohol.

[0014] The dissolution step of the metallic components, which define the already ground starting material, is carried out in batches, with the amounts of starting material varying according to the capacity of the reaction medium. This special procedure results in the formation of oxidized graphite (graphite oxide).

[0015] Once the dissolution stage of the metallic components of the starting material is completed, the mixture is subjected to a filtration step that is preferably carried out in a conventional filter with filter paper with a filtration structure designed to retain graphite oxide particles.

[0016] The graphite oxide particles, retained in the filtering stage, are then subjected to a drying stage in a muffle furnace with a temperature ranging from 80 to 110 o W.

[0017] Once high-quality graphite oxide has been obtained, with a minimum dimension of 1 mm, already separated from the starting metallic material and subjected to the drying stage, it is subjected to a synthesis stage, for its conversion into graphene oxide (GO) and subsequently into reduced graphene oxide (rGO), using the modified Hummers method.

[0018] In the synthesis stage, graphite oxide, with a minimum dimension of 1 mm, receives a charge of 60 to 80 mL of H2SO4 for 1 g of graphite to form a solution that is kept, for a period of 10 to 20 minutes, generally 15 minutes, under constant stirring and in an ice bath at a temperature below 10°C.

[0019] After the stirring stage of the graphite oxide and H2SO solution 4,it receives the addition, with constant stirring, of the reagent potassium permanganate (KMnO4) until it reaches a concentration of 0.02 to 0.03 mol / L for 10 to 20 minutes, generally 15 minutes, and the new solution is left to rest for a period of at least 3 hours, generally 3.5 to 4.5 hours, without an ice bath.

[0020] Once the reaction time is over, the new solution formed by the initial mixture of 60 to 80 mL of H2SO4 / 1g of graphite is diluted with 200 mL of distilled H2O / 1g of graphite and the excess oxidant (Mn2O7) is eliminated by adding 10 to 20 mL of H2O2 / 1g of graphite . The new solution, diluted and without the oxidant, is left to rest for a period of 20 to 30 hours, usually 24 hours, after which it is transferred to a Büchner funnel with a quantitative paper filter, mounted on a kitassaco and connected to a vacuum pump, to be washed with 25% of 10% HCl solution, 25% of ethanol (EtOH) and 50% of distilled H2O.

[0021] The graphene oxide (GO) obtained is collected and stored with ethanol (EtOH-95%) or in deionized water, to be subsequently diluted and exfoliated in an ultrasound bath for a period of 8 to 12 minutes, generally 10 minutes, allowing the obtaining of reduced graphene oxide (rGO).

Claims

1 / 3 CLAIMS 1. Process for obtaining graphite from cast iron for the synthesis of graphene oxide, the cast iron having a carbon content of at least 5.0% by weight of the starting material, characterized in that it comprises the steps of: - heating the starting material until complete fusion of its metallic components is obtained; - pouring the starting material to form inguts and cooling it at a rate of 5 to 10°C / hour, until room temperature is reached, producing the growth of graphite to a minimum dimension of 1 mm; - grinding the cooled starting material, to obtain particles with an average dimension of 0.5 mm to facilitate acid attack.- dissolve the metallic components of the ground starting material by means of its deep acid corrosion with aqua regia; - subject the dissolved mixture to a stage of filtration of graphite oxide particles; - dry the filtered graphite oxide particles; - form a solution of filtered and dried graphite oxide particles with a load of 60 to 80 mL of H2SO4 / 1 g of graphite and maintain said solution for 10 to 20 minutes, with constant stirring and in an ice bath at a temperature below 10°C; - add to the solution of graphite oxides and H2SO. 4, the potassium permanganate reagent (KMnO4) until reaching a concentration between 0.022 and 0.03 mol / L, for 10 to 20 minutes, with constant stirring, and leave the new solution to rest 2 / 3 for at least 3 hours; - dilute the new solution 200 mL of distilled H2O / 1g of graphite and eliminate the excess oxidant (Mn2O7) by adding 10 to 20 mL of H2O2 / 1g of graphite ;- keep the new solution, diluted and without the oxidant, at rest for a period of 20 to 30 hours; - wash the new solution, diluted and without the oxidant, with 25% 10% HCl solution, 25% ethanol (EtOH) and 50% distilled H2O; - collect the graphene oxide (GO) obtained and store it in ethanol (EtOH-95%) or in deionized water; and - dilute and exfoliate the graphene oxide (GO), in an ultrasound bath, for a period of 8 to 12 minutes, obtaining reduced graphene oxide (rGO).

2. Process, according to claim 1, characterized by the fact that the starting material is defined by gray cast iron with minimum contents of 5.0% carbon, 1.5% silicon and 0.50% manganese.

3. Process according to claim 1, characterized in that the starting material is defined by gray cast iron comprising from 5.0% to 6% carbon, 1.9% to 2.10% silicon and from 0.60% to 0.80% manganese. 4.Process according to any one of claims 1 to 3, characterized in that the starting material is ground to obtain particles with an average dimension of 0.5 mm.

5. Process according to any one of claims 1 to 4, characterized in that the graphite oxide particles are subjected to drying at a temperature of 80 to 110°C. 3 / 3 6. Process according to any one of claims 1 to 5, characterized in that the graphite oxide and H2SO4 solution is left to stand for a period of 3.5 to 4.5 hours, without an ice bath.

7. Process according to any one of claims 1 to 6, characterized in that the deep acid corrosion of the metallic components of the ground starting material is obtained with an aqua regia in a ratio (v / v) of 1:4 of concentrated nitric acid and concentrated hydrochloric acid diluted in ethyl alcohol.

8. Process according to any one of claims 1 to 7, characterized in that the dissolution step of the metallic components, defining the already ground starting material, is carried out in batches, with quantities of starting material varying according to the capacity of the reaction medium.