O que é óxido de grafite?

Graphite oxide is an important carbon-based material. It has attracted great attention in many fields such as energy storage, catalysis and composite materials due to its unique structure and properties. The in-depth study of graphite oxide helps to promote technological innovation and progress in related fields. And it will develop materials and products with more performance advantages.

O que é óxido de grafite?

• The physical and chemical properties of graphite oxide

Graphite oxide is a layered compound obtained by oxidizing graphite.

From the physical properties, it usually appears black or dark brown solid powder. Its layered structure gives it a large specific surface area. This is conducive to the adsorption and loading of substances. In terms of density, there is an increase compared to the original graphite. This is due to the introduction of functional groups such as oxygen atoms in the oxidation process.

Chemically speaking, the surface of graphite oxide is rich in oxygen-containing functional groups. Such as hydroxyl (-Oh), epoxy (-O-) and carboxylic (-COOH) groups. The presence of these functional groups gives graphite oxide a good hydrophilicity. So that it can be well dispersed in polar solvents such as aqueous solutions. At the same time, these functional groups also make graphite oxide have certain chemical reactivity. And they can carry out a variety of chemical modifications and functionalization reactions. Such as chemical bonding with organic molecules, metal ions, etc., so as to further expand its application range. For example, through coordination with metal ions, you can prepare graphite oxide matrix composites with catalytic properties. The composite with organic polymer can improve the mechanical properties and thermal stability of the polymer.

• The graphite oxide formula

Graphite oxide does not have a fixed simple chemical formula. This is because graphite oxide is a non-stoichiometric compound with a variety of oxygen-containing functional groups in its structure. In general, it can be roughly represented by a general formula such as C(x)O(y)(OH)(z), where the values of x, y, and z depend on factors such as the degree of oxidation. The oxygen in the graphite oxide structure is mainly in the form of hydroxyl group (-OH), epoxy group (-O-) and carboxylic group (-COOH). For example, in the case of mild oxidation, the oxygen content is relatively low. In the deep oxidation, the proportion of oxygen will increase significantly. And the type and number of functional groups will also change. These changes can result in a difference in the composition represented by its chemical formula.

The use of graphite oxide

Energy storage

In lithium-ion batteries, you can use graphite oxide as a precursor for negative electrode materials. Due to its layered structure and oxygen-containing functional group, it can provide lithium ion embedding and exiting channels. And its electrochemical performance can be further improved by chemical modification. At the same time, in terms of supercapacitors, graphite oxide based electrode materials can achieve rapid charge storage and release. This dues to their high specific surface area and good electrical conductivity, showing high specific capacitance and good cycle stability.

Catálise

You can use graphite oxide as catalyst carrier. The oxygen-containing functional groups on the surface can effectively adsorb the active components such as metal nanoparticles or metal oxides. This prevents their agglomeration, and improves the dispersion and activity of the catalyst. For example, graphite oxide catalysts loaded with platinum nanoparticles show excellent catalytic performance in oxygen reduction reaction of fuel cells. This can improve the energy conversion efficiency of fuel cells. In addition, graphite oxide itself also has a certain catalytic activity. In some organic reactions such as esterification reaction, epoxidation reaction can play a catalytic role.

Composite material field

It is combined with polymers to form high-performance composite materials. Adding graphite oxide to the polymer matrix, such as polyethylene, polypropylene, etc., can significantly improve the mechanical properties of the polymer. Such as tensile strength, bending strength and modulus. This is because the layered structure of graphite oxide can play a role in strengthening and toughening the polymer. And the interface interaction between it and the polymer also contributes to the transfer of stress. In addition, graphite oxide can also improve the thermal stability and barrier properties of composite materials. So in many fields like aerospace, it has a wide range of application prospects.

Graphite oxide price and its influencing factors

The price of graphite oxide varies due to a number of factors. Generally speaking, its market price ranges from a few dollars to tens of dollars per kilogram. Among them, the cost of raw materials is one of the important factors affecting the price. The price of high-quality natural graphite powder is relatively high. And the cost of chemical reagents such as strong oxidants cannot be ignored. In addition, the complexity and cost of the preparation process also have an impact on the price of graphite oxide. The use of more advanced and fine preparation processes, such as the improved Hummers method, although better quality graphite oxide products can be obtained, they often require higher equipment investment and more energy consumption. It results in higher product prices.

The purity and quality of the product are also key factors in determining the price. Graphite oxide products with high purity, uniform particle size, oxygen-containing functional group content and controllable distribution are usually more expensive. Because such products have better performance in high-end applications such as electronic grade materials, high-performance catalysts. And the market demand is relatively large. At the same time, the market supply and demand will also fluctuate on the price of graphite oxide. When the market demand for graphite oxide is strong, and the supply is relatively insufficient, the price tends to rise. On the other hand, when the market is oversupplied, the price may fall.

Comparison of graphite oxide and graphene oxide

Structural features

Graphite oxide retains the layered structure characteristics of graphite. But the layer spacing is increased compared with the original graphite, generally between 0.6-1.2nm. This is because during the oxidation process, oxygen-containing functional groups (such as hydroxyl, epoxy and carboxyl groups, etc.) are introduced into the interlayer and edge of the graphite. And the tightly packed graphite layer is stretched apart. The overall structure still presents a multi-layer stacking state, the number of camadas varies from dozens to hundreds of layers. And the layers are maintained by weak van der Waals forces and the interaction between functional groups.

Graphene oxide is usually a single layer or a few layers (generally less than 10 layers) of two-dimensional sheet structure, the thickness of only a few nanometers. It is the product of graphite oxide after further stripping treatment. And the single layer of graphene oxide has a great aspect ratio, and its plane size can range from hundreds of nanometers to tens of microns. This unique monolayer structure gives it a higher specific surface area and more significant surface effect than graphite oxide.

Physical property

In appearance, graphite oxide is mostly a black or dark brown powder solid. While graphene oxide is relatively light in color due to the small number of layers, often showing brownish yellow or light brown.

From the perspective of solubility, graphite oxide has certain solubility in polar solvents (such as water, alcohols, etc.) due to the existence of more oxygen-containing functional groups between the layers. But the dispersion is relatively poor and agglomeration is easy to occur. Graphene oxide showed good dispersion in a variety of polar solvents and could form a stable colloidal solution. This is because its monolayer structure reduces the tendency to agglomerate. And the abundant functional groups on the surface make it have stronger interactions with solvent molecules.

In terms of electrical properties, both of them exhibit semiconductor properties due to the presence of oxygen-containing functional groups. And their electrical conductivity is relatively low. However, due to its thinner structure and larger specific surface area, graphene oxide has a better degree of recovery and controllability of electrical properties after reduction treatment than graphite oxide. After removing some oxygen-containing functional groups by chemical reduction or thermal reduction, the electrical conductivity of graphene oxide can be significantly improved. Even it close to the level of original graphene, while the electrical performance of graphite oxide is relatively limited.

Chemical property

The oxygen-containing functional groups on the surface of graphite oxide and graphene oxide give them similar chemical reactivity. These functional groups can participate in a variety of chemical reactions. Such as esterification, etherification, amidation, etc., so as to achieve functional modification of materials. For example, by reacting with an organic amine, amino functional groups can be introduced on its surface. This further improves the solubility of the material or its compatibility with other substances.

However, because the monolayer structure of graphene oxide makes its functional groups more fully exposed. It often has higher reaction activity and reaction rate in chemical reactions. When combined with metal ions or metal oxides, graphene oxide can interact more quickly and more uniformly with the active components to form a composite with better performance.

Synthesis of graphite oxide and graphene oxide

The synthesis of graphite oxide mainly adopts chemical oxidation method, such as the classic Hummers method and its improved process. With graphite as raw material, under the action of strong oxidants such as concentrated sulfuric acid and potassium permanganate, the graphite is gradually oxidized and formed by a series of complex steps. Such as low temperature reaction, medium temperature oxidation and high temperature intercalation. The preparation process needs to strictly control the reaction temperature, oxidizer dosage, reaction time and other parameters to ensure the quality and performance of graphite oxide.

The synthesis of graphene oxide is usually a further stripping treatment on the basis of graphite oxide. Common stripping methods include ultrasonic stripping, mechanical stripping and chemical reduction stripping. Ultrasonic stripping method is the use of ultrasonic cavitation, graphite oxide in solvent dispersion and peel into a single layer or a few layers of graphene oxide. Mechanical stripping is achieved by high-speed shear force or friction. In the process of reducing graphite oxide, the chemical reduction stripping method uses the gas generated by the reducing agent or the structural change in the reduction process to promote the stripping of graphite oxide. And at the same time realizes the removal of some oxygen-containing functional groups to obtain reduced graphene oxide with certain conductivity.

Conclusão

Como um carbon-based material with unique structure and properties, graphite oxide shows many characteristics in physical and chemical properties. Its preparation formula is relatively mature. But it still needs fine regulation to obtain high quality products. It is widely used in energy storage, catalysis, composite materials and other fields. And its price is affected by many factors such as raw materials, process, quality and market supply and demand. Compared with graphene oxide, both have advantages and disadvantages. And it can play their respective advantages in different application scenarios.

With the continuous deepening of materials science research and continuous progress of technology, graphite oxide is expected to be applied and developed in more fields. And its performance will continue to be optimized and improved, providing strong support for promoting the development of related industries. In the future research and development, it will be important to further explore the new synthesis methods of graphite oxide. And deeply understand the relationship between its structure and properties, expand its new application fields are also significant.