KR20240091470A - A method for designing low-dimensional complex materials using crystalline growth and chemical reaction analysis - Google Patents

Abstract

The present invention is a method of designing new composite materials with different crystal growth and chemical reactions by measuring crystal growth and chemical reactions according to mixing conditions and heat treatment in low-dimensional (0-dimensional, 2-dimensional) mixed materials of different dimensions. It's about.
The present invention includes the steps of “(a) obtaining a mixture of a two-dimensional graphene material and a zero-dimensional metal oxide nanopowder; (b) heat treating the mixture in a non-oxidizing atmosphere; (c) simultaneously measuring the growth rate of each graphene material and metal oxide nanopowder and the mutual chemical reactivity between the materials as a result of heat treatment of the mixture; and (d) designing a graphene-metal oxide composite based on the data measured in step (c); Provides a “low-dimensional composite material design method through crystal growth and chemical reaction analysis, including .”

Description

{A method for designing low-dimensional complex materials using crystalline growth and chemical reaction analysis}

The present invention is a method of designing new composite materials with different crystal growth and chemical reactions by measuring crystal growth and chemical reactions according to mixing conditions and heat treatment in low-dimensional (0-dimensional, 2-dimensional) mixed materials of different dimensions. It's about.

Carbothermal Reduction (CTR) is a method of reducing metal oxides through heat treatment using a carbon-based material as an oxidizing agent.

With the development of graphene manufacturing methods, a method of using graphene as an oxidizing agent instead of existing carbon-based materials has recently been developed, which is called GTR (Graphenothermal Reduction). Results have been published showing that CTR/GTR is important for obtaining pure metals and for energy-related applications [non-patent documents 1 to 3 among prior art documents]. In particular, the nano mixed phase of graphene/NiO is used as a binder-free electrode and lithium ion battery. , can be used in electrochemical catalysts. Most of these CTR/GTR studies focus only on lowering the reaction temperature or applicability to simple mixtures (not highly complex materials) (non-patent documents 1 to 6 among prior art documents).

However, there are few cases where nano-level processes/mechanisms are proposed based on accurate analysis results for GTR, and the possibility of diversified composite material design based on mechanism analysis is not shown. Since this field is still in the early stages of technological development, it is expected that it will be greatly revitalized through the results of this invention.

1. Publication Patent No. 10-2020-0121088 “Method for manufacturing graphene-metal oxide nanoparticle composite material” 2. Registered Patent 10-1595625 “Metal oxide/graphene composite microparticles and anode for lithium secondary battery containing same” 3. Registered Patent 10-1406371 “Three-dimensional metal or metal oxide/graphene nanocomposite and method of manufacturing the same” 4. Registered Patent 10-1622099 “Method for manufacturing graphene-metal oxide nanoparticle hybrid material”

1. S. Vijayan, R. Narasimman, K. Prabhakaran, Mater. Lett. 181 (2016) 268-271. 2. S. Bakhshandeh, N. Setoudeh, M. Ali Askari Zamani, A. Mohassel, J. Min. Metall. Sect. B-Metal 54 (2018) 313-322. 3. H. Pant, S. Petnikota, V.S.S.S. Vadali, ECS J. Solid State Sci. and Technol. 10 (2021) 031002-031007. 4. E.S. Agudosi, E.C. Abdullah, A. Numan, N.M. Mubarak, S.R.Aid.R. Benages-Vilau, P. Gomez-Romero, et al. Nature 10 (2020) 11214. 5. F. Li, X. Jiang, J. Zhao, S. Zhang, Nano Energy 16 (2015) 488. 6. K. Chu, Y-P. Liu, J. Wang, H. Zhang, Appl. Energy Mater. 2 (2019) 2288-2295. 7. S.H. Huh, Physics and Applications of Graphene (INTECH), Chapter 5 (2011) 73-90. 8. H.-M. Ju, S.H. Huh, S.-H. Choi, H.-L. Lee, Mater. Lett. 64 (2010) 357. 9. D. Losic, F. Farivar, P.L. Yap, A. Karami, Anal. Chem. 93 (2021) 11859-11867. 10. F. Farivar, P.L. Yap, K. Hassan, T.T. Tung, D.N.H. Tran, A.J. Pollard, D. Losic, Carbon 179 (2021) 505-513. 11. F. Farivar, P.L. Yap, R.U. Karunagaran, D. Losic, J. Carbon Research C 7 (2021) 41. 12. A.I. Rusanov, Surf. Sci. Rep. 69 (2014) 296. 13. S.H. Huh, Carbon 78 (2014) 617. 14.T.O. Drews, M. Tsapatsis, Microporous and Mesoporous Mater. 101 (2007) 97-107. 15. T.J. Woehl, C. Park, J.E. Evans, I. Arslan, W.D. Ristenanoparticleart, N.D. Browning, Nano Lett. 14 (2014) 373-378. 16. M. Zhang, M.Y. Efremov, F. Schiettekatte, E.A. Olson, A.T. Kwan, S.L. Lai, et al. Phys. Rev. B 62 (2000) 10548.

The present invention manufactures a composite material by heat-treating a mixture of low-dimensional nanomaterials (2-dimensional graphene material and 0-dimensional metal oxide nanopowder), and determines the dimension by applying precise measurement and evaluation technology regarding crystal growth and chemical reaction. The purpose is to be able to design composite materials according to industrial needs based on change state data for each material condition (material composition, heat treatment temperature, etc.) of different dimensions.

In order to solve the above-mentioned problem, the present invention includes the steps of “(a) obtaining a mixture of a two-dimensional graphene material and a zero-dimensional metal oxide nanopowder; (b) heat treating the mixture in a non-oxidizing atmosphere; (c) simultaneously measuring the growth rate of each graphene material and metal oxide nanopowder and the mutual chemical reactivity between the materials as a result of heat treatment of the mixture; and (d) designing a graphene-metal oxide composite based on the data measured in step (c); Provides a “low-dimensional composite material design method through crystal growth and chemical reaction analysis, including .”

In step (a), RGO (Reduced Graphene Oxide) and NiO nanopowder are mixed, and in step (b), heat treatment can be performed at 380°C or higher.

Accordingly, in step (a), 30 wt% or less (excluding 0 wt%) of NiO nanopowder compared to RGO was mixed, and in step (c), RGO thickness growth, NiO crystal growth, and partial reduction reaction of NiO were measured according to heat treatment. do or,

In step (a), 30 to 75 wt% of NiO nanopowder is mixed with RGO, and in step (c), the RGO thickness reduction, NiO crystal growth, and partial reduction reaction of NiO due to heat treatment are measured, or

In step (a), more than 75 wt% of NiO nanopowder compared to RGO is mixed, and in step (c), the decrease in RGO thickness, decrease in NiO crystal diameter, and amount of reduced Ni produced due to heat treatment can be measured.

In step (c), thermogravimetric analysis (TGA) and XRD analysis can be applied together.

Previously, it was impossible to intentionally design composite materials to express specific physical properties.

According to the present invention, it is possible to design a composite material target tailored to various specifications required in the fields of electrodes, lithium-ion batteries, and electrochemical catalysts.

[Figure 1] shows FE-SEM images of samples before and after heat treatment.
[Figure 2] shows the porous structure and nanoparticles tightly bound to the RGO surface by increasing the magnification of the FE-SEM image of the RGO _II /NiO _II -5 sample.
[Figure 3] shows changes in XRD patterns of samples before and after heat treatment.
[Figure 4] shows the TGA curve and DTA curve according to thermogravimetric analysis (TGA).
[Figure 5] shows XRD data of RGO and NiO according to the weight ratio of NiO to RGO.

The present invention includes the steps of “(a) obtaining a mixture of two-dimensional graphene material and zero-dimensional metal oxide nanopowder; (b) heat treating the mixture in a non-oxidizing atmosphere; (c) simultaneously measuring the growth rate of each graphene material and metal oxide nanopowder and the mutual chemical reactivity between the materials as a result of heat treatment of the mixture; and (d) designing a graphene-metal oxide composite based on the data measured in step (c); Provides a “graphene-metal oxide composite design method including.”

Step (a) is a step of obtaining a mixture of two-dimensional graphene material and zero-dimensional metal oxide nanopowder.

In the present invention, a two-dimensional graphene material refers to a material that forms a plate shape with a small number of graphene layers, and an example may be RGO (Reduced Graphene Oxide) stacked with 10 or less layers. RGO may contain doping elements such as sulfur (S) and nitrogen (N), and the doping elements may include some alkaline ions and anions. The two-dimensional graphene material applied to the present invention may also include graphene material containing the above-described doping elements.

An example of a zero-dimensional metal oxide nanopowder is NiO nanopowder, and various metal oxide nanopowders can be applied to the present invention depending on the required physical properties of the composite to be designed.

The mixing amount of metal oxide nanopowder can be adjusted as needed based on the weight of the two-dimensional graphene material, and conversely, the two-dimensional graphene material can be mixed based on the weight of the metal oxide nanopowder.

Step (b) is a step of heat treating the mixture in a non-oxidizing atmosphere. In this step (b), heat treatment can be carried out by increasing the temperature while blocking oxygen, such as by injecting nitrogen into the reaction chamber. can do. Referring to the general CTR (Cathermal reduction) reaction, the heat treatment temperature can be increased to 1,500°C depending on the type and content of the two-dimensional graphene material and metal oxide nanopowder.

Step (c) is a step of simultaneously measuring the growth rate of each graphene material and metal oxide nanopowder and the mutual chemical reactivity between the materials as the mixture is heat treated. “Growth” in the present invention is a concept that includes both growth and decline.

Growth/decrease of graphene material means growth/decrease in thickness (number of layers), and growth of metal oxide nanopowder means growth/decrease in crystal size (diameter). In this specification, both the thickness of the graphene material and the metal oxide crystal size are expressed as D _size . Depending on the heat treatment temperature and material mixing ratio, the growth rate of the graphene material and the metal oxide and the mutual chemical reactivity between the materials may vary. Depending on the conditions, the thickness of the graphene material may grow or decrease, and the crystal size of the metal oxide nanopowder may grow or decrease. You can.

In this step (c), thermogravimetric analysis (TGA) and XRD analysis can be applied together to simultaneously measure the growth rate and chemical reactivity. Specific details regarding this will be explained along with test examples.

Step (d) is a step of designing a graphene-metal oxide composite based on the data measured in step (c). In step (c) above, the growth rate and chemical reactivity of the mixed materials are measured according to the heat treatment temperature, material mixing ratio, and mutual chemical reaction between materials, and the measured data is used as a reference to determine various physical properties required in the industry such as secondary cells and batteries. A graphene-metal oxide composite can be designed according to this.

As will be described later with specific test data, when mixing 30 wt% or less (excluding 0 wt%) of NiO nanopowder compared to RGO in step (a), heat treatment at 380°C or higher is performed to achieve RGO thickness growth, NiO crystal growth, and NiO A partial reduction reaction occurs, and in step (c), the relevant reference can be obtained by measuring the data.

In addition, when mixing 30 to 75 wt% of NiO nanopowder compared to RGO in step (a), heat treatment at 380 ° C or higher is performed to reduce the thickness of RGO, grow NiO crystals, and partially reduce NiO, and (c) ) step, these data can be measured to obtain relevant references.

In addition, when 75 wt% or more of NiO nanopowder compared to RGO is mixed in step (a), heat treatment at 380°C or higher is performed to reduce the thickness of RGO, reduce NiO crystals, and generate reduced Ni, and in step (c), By measuring their data, relevant references can be obtained.

Hereinafter, the present invention will be described in detail along with specific examples.

1. Sample production

As a two-dimensional graphene material, RGO (Reduced Graphene Oxide) with a thickness of 10 layers or less was used, and as a zero-dimensional metal oxide nanopowder, NiO nanoparticles with a diameter of 50 to 200 nm were used (the diameter is the crystalline size). ) may be different).

The RGO was manufactured by chemically reducing graphene oxide (GO), and was dispersed in isopropyl alcohol by ZrO ₂ -ball milling. Afterwards, the NiO nanoparticles were mixed and dispersed in the RGO dispersion and sonicated for 0.5 hours.

To monitor crystal growth and chemical reduction reactions by pure thermochemical reactions, no dispersants or surfactants were used. However, after the exact mechanism of crystal growth and chemical reduction reaction is identified, dispersants, surfactants, other additives, and solvents can be added or changed to improve dispersibility.

Samples as shown in [Table 1] below were produced according to the weight ratio of RGO and NiO.

The sample group before heat treatment was the sonicated dispersion as described above and vacuum-dried at 30°C for 10 hours, and the sample after heat treatment was heated to 600°C in a non-oxidizing atmosphere. The TGA analyzer for thermogravimetric analysis (TGA) is equipped with a derivative TG (DTG) analysis function, and nitrogen gas was administered at 20 ml per minute to create a non-oxidizing atmosphere. The temperature increase rate was set at 10°C per minute. Each sample before and after heat treatment was analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and X-ray dispersive spectroscopy (EDS).

2. FE-SEM and EDS analysis

[Figure 1] shows FE-SEM images of samples before and after heat treatment.

Increasing the amount of NiO nanoparticles promotes aggregation. The state of NiO nanoparticle aggregation can be confirmed at the part indicated by the arrow in [Figure 1].

The samples before heat treatment, RGO _I and RGO _I /NiO _I -1, show a flat shape, while wrinkles are observed in the corresponding samples after heat treatment, RGO _Ⅱ and RGO _Ⅱ /NiO _Ⅱ -1.

Meanwhile, the observation results according to EDS showed that the molar content of oxygen decreased from 8.6% (RGO _I : C _91.4 O _8.6 ) before heat treatment to 3.3% (RGO _II : C _96.7 O _3.3 ) after heat treatment. This is because residual oxygen functional groups are removed from RGO following heat treatment.

[Figure 2] is an increased magnification of the FE-SEM image of the RGO _Ⅱ /NiO _Ⅱ -5 sample, showing the porous structure formed by the release of CO and CO ₂ gases and the nanoparticles tightly bound to the RGO surface through rapid chemical reaction.

3. XRD pattern analysis

[Figure 2] shows the change in XRD patterns of samples before and after heat treatment.

After heating, the RGO _I and NiO _I peaks shift to higher 2θ values due to crystal growth by annealing, and the full width at half maximum (FWHM) shows a narrowed form.

In RGO _II /NiO _II -5, a newly formed Ni metal peak is observed.

4. TGA and DTA curves

[Figure 3] shows the weight loss rate and DTA curve according to thermogravimetric analysis (TGA).

When the RGO _I sample is heat treated to become RGO _II , the weight loss rate is 9.4%, while RGO _I /NiO _I -1 to RGO _I /NiO _I -5 are heat treated to become RGO _Ⅱ /NiO _Ⅱ -1 to RGO _Ⅱ /NiO _Ⅱ The weight loss rates at -5 were 19.5%, 20.5%, 21%, 20%, and 25.4%, respectively.

The DTG curve of RGO shows two characterized peaks (P ₁ , P ₂ ) corresponding to the removal of residual oxygen functional groups and unstable carbon species in the 180–200°C region and 380–460°C region. The S ₁ peak in the 45~100℃ sphere appears due to evaporation of residual solvent.

When RGO is mixed with NiO, an additional peak (P ₃ ) is observed in the range of 460 to 585 ℃, and in the process of heat treating the RGO _I /NiO _I -5 sample to become RGO _Ⅱ /NiO _Ⅱ -5, the peak is observed in the range below 568.4 ℃. A unique sharp peak (P ₄ ) appears.

P ₃ can be interpreted as appearing due to weight loss occurring in the carbon of RGO and the oxygen portion of NiO, and P ₄ appears due to rapid weight loss and Ni formation as confirmed in the XRD pattern in [Figure 3]. It can be interpreted as

The peak (P ₅ ) observed in the 300-360°C section in (f) of [Figure 4] can be explained by the influence of the GTR process of P ₁ . In the present invention, the GTR temperature (568.4°C) is relatively much lower than the general temperature. [Figure 4] shows that a similar reaction can occur in NiO when the P ₂ reaction occurs. The starting point of P ₂ is 380℃, and as the temperature gradually increases, 460℃, where P ₂ ends and P ₃ begins, is the starting point for the full-scale GTR reaction. In other words, the start of the GTR reaction is above 380°C, but the activation temperature is above 460°C. The maximum temperature range is 900~1,500℃ when applying general CTR temperature.

5. Changes according to XRD data and composition

For detailed mechanism analysis of the GTR process from the XRD peak, the 2θ value, d value, FWHM, and grain size (D _size ) were obtained by fitting the Lorentzian function. The number of layers (number of layers: N _RGO ) related to RGO thickness was calculated by applying [Equation 1] below.

[Equation 1] N _RGO = D ₀₀₂ /d ₀₀₂

D ₀₀₂ : RGO thickness, d ₀₀₂ : Spacing between floors

The obtained XRD data values are summarized in [Table 2], and the XRD data according to the weight ratio of NiO to RGO are shown in [Figure 5].

When the RGO/NiO sample group is heated to 600°C, the d value of RGO decreases significantly from 3.678 Å to 3.406 Å to 454 Å (see (a) in Figure 5), and the FWHM decreases from 3.96° to 1.25° to l. It decreases significantly to 69° (see (b) in [Figure 5]). Additionally, the N _RGO value increases from 5.5 to 13.8 to 18.9, showing a graphite growth pattern (see (c) in [Figure 5]).

After heating, the d value of NiO slightly decreased from 2.089 Å to 2.081 Å to 2.083 Å (see (d) in Figure 4), and the FWHM was 1.12 except for the RGO _II /NIO _II -5 sample, which was 1.153°. ° decreased from 0.46° to 0.49° (see (e) in [Figure 4]). The D _size of NiO increases from 172.6 Å to 183.9 Å upon heating at 75.5 Å, but the D _size of the RGO _Ⅱ /NiO _Ⅱ -5 sample decreases significantly to 73.5 Å (see (f) in Figure 5).

Crystalline RGO grew during heat treatment regardless of NiO content, which resulted from improved interfacial contact promoted by the removal of residual oxygen and unstable carbon species (nonbasal carbon or dangling carbon).

When the NiO content for RGO is greater than 25 wt%, the increased amount of NiO placed between individual graphene layers hinders RGO growth, and the thickness (D _size ) of RGO decreases as the NiO content increases. As shown in (f) of [Figure 5], heat treatment induces crystal growth of NiO, but factors indicating crystallinity such as 2θ, d, FWHM, and D _size change when the NiO content for RGO is greater than 75 wt%. It suddenly changes. When the NiO content increases from 75 wt% to 100 wt%, the D _size of NiO rapidly decreases from 183.9 Å to 73.5 Å.

The XRD pattern of the RGO _II /NiO _II -5 sample additionally shows peaks of Ni metal (111, 200 shown in (l) of Figure 3) newly generated through chemical reaction. A higher ratio of NiO content increases the number of contacts between NiO, a zero-dimensional material, and allows NiO nanoparticles to aggregate and grow into larger crystals.

As shown in [Table 2] above, the D _size of Ni is 292.9 Å, which is 1.6 times larger than the largest D _size of NiO, which is 183.9 Å. Therefore, it can be seen that a large number of NiO nanoparticles are required to form one Ni particle, and if complete GTR occurs in a single NiO particle, smaller-sized Ni particles are formed, which is thermodynamically unfavorable. This means that Ni formation is possible when the NiO content is higher than the critical value. In theory, the weight ratio of NiO to Ni nanoparticles is 1:0.78, the volumes of NiO and Ni are 6.67 g/cm ³ _and 8.91 g/cm ³ , respectively, and the volume ratio of nanoparticles is 1:0.59. Therefore, in order to form one Ni nanoparticle (292.9 Å) under the above conditions, at least 6.6 NiO nanoparticles (75.5 Å) are required.

The chemical reaction and crystal growth of graphene composites depending on NiO content is a complex phenomenon related to low-dimensional shape and reactivity, but can be simplified using a nanocontact model. To promote the chemical reaction of low-dimensional graphene/NiO mixtures, the number of 2D/0D face-to-point contacts must be increased. Therefore, a large number of NiO nanoparticles (0D) should be well dispersed in 2D RGO. However, at the same time, to form larger Ni nanoparticles, NiO nanoparticles must be closely aggregated with each other (0D/0D point-to-point contact). In terms of crystal growth, the 2D/2D interface contact decreases as the NiO content increases (0D/0D contact increases). As heat treatment is performed in a non-oxidizing atmosphere, the competitive and contradictory situation between crystal growth and chemical reactions between different low-dimensional materials is bound to appear in the following three concentration-dependent properties.

(1) NiO content 30 wt% or less compared to graphene material: Graphene, NiO crystal growth and partial GTR reaction (no change in crystal structure)

(2) NiO content 30-75 wt% compared to graphene material: Inhibition of graphene crystal growth, NiO crystal growth, partial GTR (no change in crystal structure)

(3) NiO content greater than 75 wt% compared to graphene material: Inhibition of graphene and NiO crystal growth, GTR reaction (Ni formation)

Although there may be differences in the degree of crystal growth/crystal growth inhibition/chemical reaction/concentration dependence and reaction temperature in the GTR process with different dimensions between various low-dimensional materials, that is, a mixture of 2-dimensional graphene material and 0-dimensional metal oxide, The basic principles of the invention can be applied as is.

The minimum range in which the growth rate of each graphene material and metal oxide nanopowder and the mutual chemical reaction between the materials can be examined through XRD and thermal analysis is a relative weight ratio of metal oxide to graphene material of 1 wt% to 10,000 wt%.

Above, the present invention was examined in detail along with specific test examples. However, the present invention is not limited to the above examples and may be modified and modified without departing from the gist of the present invention. Accordingly, the scope of the claims of the present invention includes such modifications and variations.

Not applicable

Claims (6)

(a) obtaining a mixture of two-dimensional graphene material and zero-dimensional metal oxide nanopowder;
(b) heat treating the mixture in a non-oxidizing atmosphere;
(c) simultaneously measuring the growth rate of each graphene material and metal oxide nanopowder and the mutual chemical reactivity between the materials as a result of heat treatment of the mixture; and
(d) designing a graphene-metal oxide composite based on the data measured in step (c); Low-dimensional composite material design method through crystal growth and chemical reaction analysis, including.
In paragraph 1:
In step (a), RGO (Reduced Graphene Oxide) and NiO nanopowder are mixed,
In step (b), a low-dimensional composite material design method through crystal growth and chemical reaction analysis, characterized by heat treatment at 380 ℃ or higher.
In paragraph 2,
In step (a), 30 wt% or less (excluding 0 wt%) of NiO nanopowder compared to RGO is mixed,
In step (c), a low-dimensional composite material design method through crystal growth and chemical reaction analysis is characterized by measuring RGO thickness growth, NiO crystal growth, and partial reduction reaction of NiO according to heat treatment.
In paragraph 2,
In step (a), 30 to 75 wt% of NiO nanopowder compared to RGO is mixed,
In step (c), a low-dimensional composite material design method through crystal growth and chemical reaction analysis is characterized by measuring the RGO thickness reduction, NiO crystal growth, and partial reduction reaction of NiO due to heat treatment.
In paragraph 2,
In step (a), more than 75 wt% of NiO nanopowder compared to RGO is mixed,
In step (c), a low-dimensional composite material design method through crystal growth and chemical reaction analysis is characterized by measuring the RGO thickness reduction, NiO crystal diameter reduction, and reduced Ni production amount due to heat treatment.
In any one of paragraphs 1 to 5,
In step (c), a low-dimensional composite material design method through crystal growth and chemical reaction analysis is characterized by applying thermogravimetric analysis (TGA) and XRD analysis together.