KR20210081275A - Process for preparing Boron Nitride Nanodisk by exfoliation and cutting of boron nitride with covalent functionalization - Google Patents

Abstract

The present invention relates to a method for preparing boron nitride nanodisks. The method includes the following: a first step of oxidizing hexagonal boron nitride through a modified Hummer's method to prepare -OH-functionalized boron nitride nanodisks; and a second step of treating the -OH-functionalized boron nitride nanodisks obtained from the first step with Fenton's reagent to perform -OH and -OOH functionalization. The present invention also relates to boron nitride nanodisks obtained by the method. According to the method of the present invention, a high ratio of -OH and _OOH groups can be incorporated to a plurality of layers at the edges and basal plane of boron nitride nanodisks (BNND). The resultant OH/OH-boron nitride nanodisks show high long-term dispersibility in ethanol and an E_g reduced by 1.4 times as compared to pure hexagonal boron nitride. Since E_g is reduced after exfoliating and cutting hexagonal boron nitride, application of boron nitride to semiconductor electronics may play an important role in the field of semiconductor electronics.

Description

Method for preparing boron nitride nanodisk by exfoliating and cutting boron nitride through covalent functionalization {Process for preparing Boron Nitride Nanodisk by exfoliation and cutting of boron nitride with covalent functionalization}

The present invention relates to a method for manufacturing a boron nitride nanodisk, comprising: a first step of oxidizing hexagonal-boron nitride through a modified Hummer's method to prepare a -OH functionalized boron nitride nanodisk; and a second step of treating -OH functionalized boron nitride nanodisks obtained in the first step with Fenton's reagent to functionalize them with -OH and -OOH. The present invention also relates to a boron nitride nanodisk manufactured by the above method.

The large-scale production of exfoliated graphene nanosheets has attracted great attention in the past decade, since 2004, when graphene was successfully obtained from graphite. This simultaneously improves the performance of graphene-based devices, including solar cells, supercapacitors, batteries, sensors, etc., due to their excellent physical, mechanical, chemical and electronic properties (the mobility of charge carriers is about 200,000 cm ² V ⁻¹ s ^{−1 ).} make it As graphene's potential applications and improved performance have emerged in numerous technologies, the recent development of graphene-like 2D materials including _{MoS 2} , boron nitride (BN), metal oxides, and graphene carbon nitride (gC ₃ N _{4 )} This is getting a lot of attention.

Among these 2D nanomaterials, hexagonal boron nitride (h-BN), which is called white graphene and has an equivalent structure to graphene, is the first choice to replace graphene. Unlike graphene, carbon atoms are replaced by boron (B) and nitrogen (N) atoms in ^{the sp 2 hybridized 2D layer of hexagonal boron nitride.} In addition, the partial ionic property of the BN bond of hexagonal boron nitride compared to the covalent property of the CC bond of graphene makes the hexagonal boron nitride have a high thermal resistance phase and chemical inertness. Nevertheless, the insulating properties of pure hexagonal boron nitride (bandgap, E _g = 4-6 eV) with high sheet count limit its application in electronic and optoelectronic devices where electrical conductivity and catalytic activity are important. Therefore, single-layered boron nitride (BN) sheets or little-layered boron nitride nanosheets (BNNS), boron nitride nanoplatelets and boron nitride nanodisks ( BNND) is of great importance.

To date, the preparation of boron nitride nanosheets has been extensively studied by exfoliating hexagonal boron nitride using various methods including electrochemical, ion insertion, hydrothermal, modified Hummer's method, and mechanical methods. According to the paper of , a boron nitride nanodisk was prepared by argon plasma treatment. Some of these methods can successfully synthesize boron nitride nanosheets with several or monolayers of boron nitride with different functional groups/heteroatomic dopants (eg -OH, -NH _{2 , C, etc.).} In particular, if -OH is grafted to the base surface or edge of boron nitride, the optical E _g can be reduced, so that boron nitride can be applied to electronic and optoelectronic devices. In addition, -OH functionalization increases the dispersibility of boron nitride in polar solvents, which is important for the preparation of substrates with high homogeneity for reproducible and improved device performance.

Negatively charged hydroxyl ions (-OH) can easily covalently bond to electron-poor B sites at the edge of boron nitride. ^{B radicals (B ●} ) naturally occurring at the defect site of the basal surface of boron nitride can also induce covalent bonding of hydroxyl radicals (HO ^{● ).} These HO ^● can ^{covalently bond to the edge of boron nitride together with B ●} , which can be generated due to balanced decomposition of the BN bond. OH-boron nitride can be directly applied to matrix filling and biological processes. In addition, the -OH functional group can serve as an initiator for further modification of OH-boron nitride, enabling the design and synthesis of complex boron nitride nanosheets or boron nitride nanodisc derivatives.

Therefore, many attempts have been demonstrated for the preparation of OH-boron nitride, including NaOH-assisted ball milling, vapor treatment, and solution-phase methods using organic peroxide and plasma methods. All of these reported methods can successfully functionalize boron nitride with -OH groups. However, most of them are not effective for the preparation of OH-boron nitride having a high proportion of -OH groups. For example, a solution-phase process using NaOH can only produce 6.4 wt % of oxygen in OH-boron nitride. In other words, some of these methods are expensive and require high temperatures, making them unsuitable for large-scale production.

Therefore, it is highly desirable to develop a scalable solution process synthesis method for the production of OH-boron nitride nanosheets and OH-boron nitride nanodisks having a high proportion of -OH functional groups. In addition, the functionalization of boron nitride using hydroperoxyl (-OOH) groups is very important. To operate as a hydroperoxide oxyl radical ^(● OOH) the oxidizing agent in many important biological reactions and because it can protect an organism from oxidative damage. For example, α - tocopherol, the lipid bilayer and highly unsaturated fatty acids plays an ^● OOH scavenger role. In addition, recent studies have shown that boron nitride can be degraded by biological processes under certain conditions and increases prostate cancer cell death by releasing B atoms. Therefore, a drug that acts in a boron nitride nano disc with a suitable boron nitride nanosheets or -OOH group (OOH- boron nitride nanosheet, boron nitride or OOH- nano disk) to a living body extend the application of the boron nitride by the radical OOH ^● It can protect the organism from oxidative damage caused and at the same time protect the organism for the treatment of prostate cancer. These ^● OOH and B can be produced reversibly or irreversibly by the decomposition of OOH-boron nitride through biological processes, so further in-depth investigation is required.

Li L H, Li L, Dai X J and Chen Y 2013 Mater. Lett. 106 409-12

The present invention aims to provide a novel method for exfoliation and covalent functionalization of hexagonal boron nitride (h-BN) to produce boron nitride nanodiscs (BNND) functionalized with -OH and -OOH. To date, no invention has been reported on the large-scale preparation of boron nitride nanodisks with simultaneous functionalization of -OH and hydroperoxyl (-OOH) groups.

According to an aspect of the present invention, as a method for producing a boron nitride nanodisk functionalized with -OH and -OOH, functionalizing hexagonal-boron nitride and performing exfoliation and cutting, a modified Hummer's method A first step of oxidizing hexagonal-boron nitride through -OH to prepare a boron nitride nanodisk, and a first step of treating the -OH functionalized boron nitride nanodisk obtained in the first step with Fenton's reagent There is provided a method of manufacturing a boron nitride nanodisk, comprising two steps.

The exfoliation and functionalization process of the present invention involves a two-step procedure. In the first step, the improved Hummus method is used for exfoliation from hexagonal boron nitride (h-BN) to boron nitride nanodisks (BNND), which leads to functionalization of boron nitride nanodisks with a low proportion of -OH groups. The second step involves further exfoliation and functionalization in which -OH and -OOH groups are functionalized using Fenton's chemistry.

According to an embodiment of the present invention, the first step is

a) mixing the hexagonal-boron nitride with an acid;

b) adding _{KMnO 4} to the resultant of step a); and

c) adding _{H 2} O ₂ to the resultant of step b).

According to an embodiment of the present invention, the acid in step a) may be sulfuric acid.

According to an embodiment of the present invention, the reaction temperature of step c) may be ^{40 ~ 60 o C.}

According to an embodiment of the present invention, centrifugation, filtration and drying steps may be added after step c).

According to an embodiment of the present invention, the Fenton reagent in the second step may be a mixed solution of ^{Fe 2+} and H ₂ O _{2 in water.} The ratio of Fe ²⁺ and H ₂ O ₂ is preferably 1 to 0.5-2.

According to an embodiment of the present invention, the reaction temperature of the Fenton reagent treatment in the second step may be ^{20 ~ 40 o C.} Preferably it is 20-30 ^o C.

According to an embodiment of the present invention, the reaction time of the Fenton reagent treatment in the second step may be 24-96 hours. Preferably it is 36 to 60 hours.

According to another aspect of the present invention, there is provided a boron nitride nanodisk functionalized with -OH and -OOH, prepared by the above manufacturing method.

Through the manufacturing method of the present invention, a high ratio of -OH and -OOH groups at the edge and the basal surface of the boron nitride nanodisk (BNND) can be incorporated into several layers. The resulting OH/OH-boron nitride nanodiscs show a high long-term dispersion capacity in ethanol, which also shows a 1.4-fold reduction in _{E g compared to pure hexagonal boron nitride. Due to the decrease in E g} after exfoliation and cutting of hexagonal boron nitride, the application of boron nitride in the field of semiconductor electronics will play a large role.

1 is (a) Schematic of OH-boron nitride nanodisc synthesis by the improved Hummers method. (b) and (c) show field emission scanning electron microscopy (FE-SEM) images of pure hexagonal boron nitride and OH-boron nitride nanodiscs.
Figure 2 is (a) OH/OOH-boron nitride nanodisk and the corresponding (b) FE-SEM image synthesis circuit diagram. (c) to (e) are EDS elemental mappings of B, N, and O in OH/OOH-boron nitride nanodiscs, respectively. (f) Bar diagrams for elemental weight % of B, N and O in OH/OOH-boron nitride nanodisks measured in EDS spectra.
3 shows (a) XRD patterns of hexagonal boron nitride, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks, and (b) corresponding enlarged XRD patterns in the 2θ range in the range of 24-28. (c) Raman spectra of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks and (d) corresponding enlarged Raman spectra in the range of ^{1300-1450 cm -1 .} (e) Fourier transform infrared (FTIR) spectra of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks.
4 (a) to (c) are HR-TEM images of hexagonal boron nitride, OH-boron nitride nanodisks and OH / OOH-boron nitride nanodisks, respectively ((a) to (c) inserts are Tyndall ) shows the light scattering effect and magnification correction (lattice patterns of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks, respectively). A dispersion of the material was prepared in ethanol for Tyndall light scattering experiments. (d) Cross-sectional HR-TEM image of the OH/OOH-boron nitride nanodisc layer. (e) Selective area diffraction (SAED) pattern of OH/OOH-boron nitride nanodiscs. (f) HR-TEM image of the high-magnification OH/OOH-boron nitride nanodisk and (g) the corresponding schematic of the crystal structure of the OH/OOH-boron nitride nanodisk.
5 is a tap mode AFM image of (a) hexagonal boron nitride, (b) OH-boron nitride nanodisk, and (c) OH/OOH-boron nitride nanodisk, (d) to (f) are the respective height profiles. to be.
6 shows (a) to (c) B 1s, (d) to (f) N 1s and (g) to (i) of hexagonal boron nitride, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks. ) represents the XPS narrow scan spectrum for O 1s. Black circles and shaded areas represent experimental data and fitted data, respectively. All XPS plots were fitted using a Shirley type background correction combining Gaussian (70%) and Lorentzian (30%) (GL30) functions using Fityk software (version 1.3.1).
7 is (a) ultraviolet-visible absorption spectrum (inset Tauc plot) and (b) energy level diagrams of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks.
8 is (a) OH/OOH-boron nitride nanodiscs (1 mg ml ^-1 ) prepared by sonication for 2 hours, suspension photos before and after 1 week, (b) OH/OOH-nitridation dispersed in other solvents Beer-Lambert relationship of boron nanodisks. Plot of maximum dispersibility of OH/OOH-boron nitride nanodisks as a function of surface tension in various solvents. Plots of maximum dispersibility of OH/OOH-boron nitride nanodisks in different solvents for (c) Hansen solubility parameters (d) and surface tension of solvents.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto. Rather, the content introduced herein is thorough and complete, and is provided to sufficiently convey the spirit of the present invention to those of ordinary skill in the art.

1. Experiment

1.1. Substances and reagents

99.0 %), 과산화수소 (H₂O₂) (수_water 중 30 중량%) 및 철(II) 황산7수화물 (FeSO₄)·7H₂O) (순도

99.0 %)는 Sigma-Aldrich (미국 미주리 주 세인트 루이스)에서 구매했다. 모든 화학 물질과 시약은 별도의 추가 정제없이 사용되었다. 실험에 초순수 (18MΩ·cm)가 사용되었으며, 실험은 Millipor Milli-Q Biocell 정수 시스템 (독일 다름슈타트 소재 머크)으로 제작되었다. 이 실험에 사용된 모든 용매는 시약 등급이며 추가 정제없이 사용되었다.Pure hexagonal boron nitride (99.5% purity, ~325 mesh) was purchased from Alfa Aesar (Ward Hill, Massachusetts, USA). sulfuric acid (H ₂ SO ₄ ) (98%), potassium permanganate (KMnO ₄ ) (purity)

99.0 %), hydrogen peroxide (H ₂ O ₂ ) ( _{30% by weight in water} ) and iron(II) sulfate heptahydrate (FeSO ₄ ) 7H ₂ O) (purity)

99.0%) were purchased from Sigma-Aldrich (St. Louis, Missouri, USA). All chemicals and reagents were used without further purification. Ultrapure water (18MΩ·cm) was used in the experiment, and the experiment was manufactured with a Millipor Milli-Q Biocell water purification system (Merck, Darmstadt, Germany). All solvents used in these experiments were reagent grade and were used without further purification.

1.2. equipment

The crystallographic phase of the material was determined by XRD (D8 Advance, Bruker, Germany) with an accelerating voltage of 40 kV Cu K _α was analyzed using radiation (λ = 1.5406 Å). Raman spectra (Horiba Scientific, XploRA PLUS, France) were obtained at ambient temperature with a laser excitation wavelength of 532 nm. FE-SEM (JSM-7610 F/JEOL) combined with EDS (INCAx-sight 7421, Oxford Instruments) was used to characterize the morphology and elements of each sample. In addition, the material morphology and SAED pattern were investigated by HR-TEM (G2 F20, Tecnai, Japan). The topography and thickness of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks were further evaluated using AFM (Nanoscope (R) IIIA) in non-contact mode. The functional groups of the samples were characterized by XPS (Thermo Scientific™, Thermo Fisher Scientific, UK) using _{Al-K α as a monochromatic X-ray source.} TGA (TAN-1000, USA) plots were determined in the temperature range of ^{50-600 o} C at a heating rate of 10 ^o C min ^-1 _{under N 2 atmosphere.} The optical absorption spectrum of the sample was investigated with an ultraviolet-visible photometer (Lambda 35, Perkin Elmer, USA). FTIR spectroscopy (Nicolet iS5) was used to characterize the functional groups of the samples in the wavenumber range of ^{500-4000 cm -1 .}

1.3. Synthesis and functionalization of boron nitride nanodiscs

In the first step, hexagonal boron nitride was exfoliated according to the improved Hummers method. Briefly, _{a suspension of hexagonal-boron nitride (2 g) in H 2} SO ₄ (50 mL) solution was prepared by stirring with a magnetic rod for 2 hours in an ice bath. Then, _{1 g of KMnO 4} was slowly added with stirring, followed by stirring for 12 hours. H ₂ O ₂ (8 mL) was then added to the mixture with stirring. The mixture was ^{further stirred at 50 o} C for 10 hours to form OH-boron nitride nanodiscs. The resulting mixture was centrifuged at 10000 rpm for 15 minutes and centrifuged repeatedly with water until the pH of the water reached 7. The OH-boron nitride nanodisks were collected by filtration and dried in a vacuum oven at 80 ^° C for 24 h.

The OH-boron nitride nanodiscs (1 g) prepared in the second step of the synthesis were ^{mixed with 25 mL Fenton's reagent (Fe 2+} in water : H ₂ O ₂ =1:1) in a flask. The mixture ^{was stirred at 25 °} C for 48 h. This enabled the functionalization of boron nitride nanodisks with -OH and -OOH groups. The mixture was then transferred to a separatory funnel, repeatedly washed with water and centrifuged until the solution reached pH 7. The precipitate was collected by filtration and dried in ^{vacuo at 80 °C.}

2. Results

= 0.037 nm) 에 비해 육방정 질화붕소층 사이의 층간 거리(0.33 nm)가 훨씬 더 높기 때문일 수 있다. 이를 통해 육방정 질화붕소 층의 확장이 가능했고 더 큰 SO₄ ^2- 이온(

= 0.258 nm)의 삽입이 가능해졌다. 삽입된 H⁺ 및 SO₄ ^2-는 KMnO₄ 를 추가한 후 육방정 질화붕소층으로 K ⁺ (

= 0.138 nm) 및 MnO₄ ^- (

= 0.229 nm)의 삽입을 촉진한다. 이온 삽입 외에도 KMnO₄는 H₂SO₄ 와 쉽게 반응하여 O₂ 가스의 발생으로 MnO₂ 를 형성하여 반응 1을 유발할 수 있다: Figure 1 (a) shows a schematic diagram of the synthesis and exfoliation mechanism of hexagonal boron nitride into OH-boron nitride nanodisks by the improved Hummers method. After adding H ₂ SO ₄ ^{, H +} can be easily inserted into the hexagonal boron nitride layer through coordination interactions with single pair electrons of N atoms in the hexagonal boron nitride. The ^{easy insertion of H +} into the hexagonal boron nitride layer is due to the hydrogen ion's ionic radius (r) (

= 0.037 nm), which may be because the interlayer distance (0.33 nm) between the hexagonal boron nitride layers is much higher. This allowed the expansion of the hexagonal boron nitride layer and the larger SO ₄ ^2- ion (

= 0.258 nm). The intercalated H ⁺ and SO ₄ ^2- are added to the hexagonal boron nitride layer after adding _{KMnO 4} K ⁺ (

= 0.138 nm) and MnO ₄ ^- (

= 0.229 nm). In addition to ion insertion, KMnO ₄ can readily react with _{H 2} SO _{4 to form MnO 2} with the generation of _{O 2} gas to trigger Reaction 1:

Reaction 1: 2H ₂ SO ₄ + 4 KMnO ₄ = 2K ₂ SO ₄ + 4 MnO ₂ + 3O ₂ + 2 H ₂ O

The formation of MnO ₂ is evident in the color change of the hexagonal boron nitride from white to dark gray [S1 (available online at stacks.iop.org/NANO/31/425604/mmedia)], which is consistent with previous reports. . _{When MnO 2} is formed in the hexagonal boron nitride layer, the re-stacking of the hexagonal boron nitride layer may be prevented and boron nitride nanodisks having a small number of disk layers may be formed. Moreover, _{the evolution of O 2} gas may induce an outward repulsive force, which may possibly accelerate further exfoliation of the hexagonal boron nitride. _{Separation and decomposition of MnO 2} from boron nitride nanodisks induced by H ₂ O ₂ can occur according to Reaction 2:

Reaction 2: MnO ₂ + 2H ⁺ + H ₂ O ₂ = 2H ₂ O + Mn ²⁺ + O ₂

While removing MnO _{2 with H 2} O ₂ ^{at 50 o} C with stirring, H ₂ O ₂ may be partially decomposed to form radicals. These reactive radicals can easily attack the B atom in the BN combined at the edge of the boron nitride nano disk, which leads to degradation of uniform BN bonds and N ^● It can form B-OH covalent bonds with radicals. This can open the hexagonal ring of the boron nitride nanodisk, so additional HO at the B site ^● -OH functionalization promoted by attack simultaneously facilitates cleavage of the boron nitride nanodisc layer. HO ^●, while in the B position of the BN bond N formed after the attack ^● As soon as silver is formed in aqueous solution, it can be easily deactivated by binding with ^{H + .} Naturally Occurring Freedom B ^● is also present at the defect site (basal plane) of the boron nitride nanodisk. Therefore, HO ^● Is B ^● in deficient sites of boron nitride nano disc plane may be covalently bound to This facilitates further cleavage of the layer induced by further free radical attack of the B site in the plane near the free B ^●. Functionalization of boron nitride nanodisks according to this improved Hummers method is not expected to be effective in incorporating a significantly high proportion of -OH functional groups at the edges or planes. This is because most H ₂ O ₂ can be used for MnO _{2 decomposition.} Therefore, a small amount of HO ^● may be involved in functionalization.

FE-SEM images of hexagonal boron nitride and OH-boron nitride nanodisks are shown in Figs. 1 (b) and (c), respectively. This indicates that hexagonal boron nitride has a relatively large white point, and the size of the OH-boron nitride nanodisk is significantly reduced after exfoliation. This shows the successful exfoliation of hexagonal boron nitride reduced to an average nanodisk size in the range of about 200 to 550 nm. Energy dispersive X-ray spectroscopy (EDS) spectra and elemental mapping (S2) of B (39.11 wt %), N (47.46 wt %) and O (13.42 wt %) were improved by MHM method for nitration with -OH functional groups This is due to the functionalization of boron nanodisks. Further -OH functionalization along with the incorporation of the -OOH functional group was generated by Fenton reagent (FR). Further -OH functionalization along with the incorporation of the -OOH functional group was generated by the Fenton reagent (FR). The ^{redox reaction of Fe 2+} induced by _{H 2} O ₂ in FR is OH-, HO ^● , HOO ^● On the other hand, and that can easily generate a proton _{^{(H +), H 2 O}} 2 is HO, as described in reaction 3-4 ^● and HOO ^● It can produce radicals disproportionately. In addition the presence of agitated when Fe ²⁺ / Fe ³⁺ according to the reaction H ₂ O is 6 HO ^● and H ^● It can be decomposed into ^{H +} , OH ^- , H ₂ and O ₂ gases together with the associated radicals.

Reaction 3: Fe ²⁺ (aq.) + H ₂ O ₂ (aq.) → Fe ³⁺ (aq.) + HO ^● + OH ^-

Reaction 4: Fe ³⁺ (aq.) + H ₂ O ₂ (aq.) → Fe ²⁺ (aq.) + HOO ^● + H ⁺

Reaction 5: 2 H ₂ O ₂ (aq.) → HO ^● + HOO ^● + H ₂ O

Reaction 6: H ₂ O → H ⁺ + OH ^- + H ₂ + O ₂ + HO ^● + ^● H

Figure 2(a) shows a schematic diagram of further -OH and -OOH functionalization and cleavage of OH-boron nitride nanodisks into smaller nanodisks using FR. After addition of Fenton's reagent, OH ^- ions react mainly with electron-poor B atoms through coordinating covalent interactions and can attach to the edge of OH ^- boron nitride N, and OH - OH - minor cleavage of OH-boron nitride nanodisks Since it can induce a reaction, it is advantageous to obtain a smaller-sized OH-boron nitride nanodisk. In addition, existing in the HO B ^{● ● ●} and B atoms in the HOO BN combination in both edge and basal plane defect of OH- boron nitride nano disc generated by the Fenton's reagent can react with HO ^● and HOO ^{● radicals attacking the existing B ●} in the defect site of the basal surface can be directly attached through a covalent bond.

On the other hand, free radicals attacking at the edge induce homogeneous decomposition of the BN bond and form B-OH and B-OOH bonds together with ^{the N ● radical.} It can be easily inactivated by binding with ^{H +} or H ^● in Fenton's reagent. Homogeneous dissociation of the BN bond could further open the hexagonal ring of the OH-boron nitride nanodisk, while at the same time OH-boron nitride nanodisk through -OH and -OOH functionalization induced by additional free radical attack at the inner B position. further cleavage of

At the same time, the size and number of disk layers of the OH/OOH-boron nitride nanodisks decreased and the average size was about 200 nm, evident in the FE-SEM image (Fig. 2(b)). Figures 2(c)-(e) show the EDS elemental mapping of B, N and O in OH/OOH-boron nitride nanodisks with atomic weights (%) of 34.35%, 35.15% and 30.51%, respectively (Fig. 2). (f)). The corresponding EDS spectrum is shown in S3. In the case of OH/OOH-boron nitride nanodisks, the color of OH-boron nitride nanodisks changes from white to pale yellow, suggesting successful synthesis of OH/OOH-boron nitride nanodisks (S1).

3 (a) is 20 ^o ~ 80 ^o 2 θ angle range indicates in the hexagonal boron nitride, x-ray diffraction (XRD) pattern of nano-OH- boron nitride disk and the OH / OOH- boron nitride nano disc of FIG. 3 (b) shows the XRD pattern from the angle θ 2 in a range 24 ^o ~ 28 ^o. Hexagonal boron nitride is 41.64 ^o , 50.10 ^o and At 2 θ angle of 55.15 ^o with different characteristic diffraction peaks shows the main characteristic XRD peaks at 2 θ of 26.78 ^o. They can be assigned to the (002), (100), (102) and (004) crystal planes of hexagonal boron nitride, respectively. Hexagonal boron nitride and then the peeling and OH- functionalized with boron nitride nano disc (002) crystal face diffraction of the characteristic was shifted to a low angle of 2 θ angle of 26.62 ^o.

This shift of the XRD peak can be attributed to the increase in lattice parameters/unit cell volume induced by -OH functionalization at the edge and defect sites of the basal plane of OH-boron nitride nanodiscs. The diffraction peak is OH / OOH- boron nitride nano for disk 2 θ angle is further moved to the 26.27 ^o a low angle to OH / OOH- to improve the formation and functionalization of the boron nitride nano disk lattice parameter / unit cell volume is showed a further increase. The overall width of the maximum half (FWHM) of the hexagonal boron nitride (002) diffraction plane increased to about 0.43 ^{o and to about 0.68 o} for the OH-boron nitride nanodisk, reducing the thickness of the hexagonal boron nitride and OH-nitriding. The formation of boron nanodisc nanostructures is shown. A further increase in FWHM for OH/OOH-boron nitride nanodisks (about 0.87 ^o ) indicates further delamination of OH-boron nitride nanodisks with a decrease in the number of layers. The XRD patterns of OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks did not show additional peaks, indicating that the synthesis was successful with high purity.

As shown in Fig. 3 (c), the crystal structures and functional groups of hexagonal boron nitride nanodisks, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks were further analyzed by Raman spectroscopy at 500-1800 ^{cm - 1} did. Fig. 3(d) shows the enlarged Raman spectrum in the wavenumber range of ^{1300-1450 cm - 1.} _{All materials exhibit E 2g} phonon mode due to BN coupling vibration and phonon dispersion in the plane of high intensity. This indicates that all materials have high crystallinity. Hexagonal E _2g band defined boron nitride is about 1382.70 ^cm-1 was located in, around 1377.15 cm For OH- boron nitride nano disc ^were red-shift to ^1. This shows the reduction of the interlayer interaction of boron nitride and the shortening of the BN bond induced by the exfoliation of hexagonal boron nitride into OH-boron nitride nanodisks. More -OH and -OOH functionalized by Fenton reagent is about 1372.20 cm ^- shows an In ¹ induces additional red-shift of the E _2g band OH- boron nitride layer can be more reduced due to sharing of the oxygen functional group to the nano-bonded disk. E _2g FWHM of hexagonal boron nitride to the phonon modes of about 13.8 cm ^- increased by ^{1 - 1,} OH- boron nitride nano disk and respectively 14.2 and 14.8 cm for the OH / OOH- boron nitride nano disc. This is also due to the reduced interlayer interactions of exfoliated OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks induced by the formation of few-layer boron nitride nanodisks. On the other hand, the Raman spectrum of the OH / OOH- boron nitride nano disc is approximately 580, 685, 945, 1088 and 1225 cm ^- additional Raman bands is shown in ^Fig. This is because the OH-boron nitride nanodisc and OOH-boron nitride nanodisk bands are associated with B-OH and B-OOH functional groups. The Raman spectrum of OH-boron nitride nanodisks does not show this type of additional Raman band, which may be due to the low -OH functionalization ratio of OH-boron nitride nanodisks.

3(e) shows the FTIR spectra of the received hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks. All materials showed strong absorption bands at about 1372 and 817 cm ^{-1 .} The former can be attributed to BN stretching due to in-plane ring vibration (E _1u mode) and the latter can be considered as BN bending due to _{out-of-plane vibration (A 2u mode).} This means that the exfoliation and functionalization process maintained the structural integrity of the OH-boron nitride nanodisk and OH/OOH-boron nitride nanodisk lattice similar to the hexagonal boron nitride lattice. In addition to boron nitride, nano-OH- disk, while the absorption band low OH / OOH- boron nitride nano disc is about 3410 cm ^- shows a strong absorption band in the ^first. This can be attributed to the occurrence of stretching bands of OH in both OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks originating from oxygen functional groups. Further OH / OOH- boron nitride nano-discs 1085 cm ^- show an additional weak absorption band at ^1, BO represents a strain occurring in the -OH and -OOH group. This shows the successful functionalization of boron nitride nanodisks with -OH and -OOH groups. The exfoliation and functionalization of the boron nitride nanodisks was further confirmed by the weight loss observed in thermogravimetric analysis (TGA) as in S4.

4 (a) to (c) show high-resolution transmission electron microscope (HR-TEM) images of hexagonal boron nitride, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks, respectively. The dark field TEM image of hexagonal boron nitride shows low transmittance to the electron beam, which is due to the high thickness of hexagonal boron nitride due to the large number of sheets. The translucency of the OH-boron nitride nanodisks to the electron beam shows a decrease in the number of layers with a decrease in size due to exfoliation and cleavage of the hexagonal boron nitride. The transparency of the OH/OOH-boron nitride nanodiscs was further increased, which may be due to the further decrease in the number of layers and the size. The number of boron nitride nanodisk layers in the OH/OOH-boron nitride nanodisk was observed in the range of about 6-11. An HR-TEM image with 7 layers is shown in Fig. 4(d), indicated by parallel lines near the edges. 6 and 11 HR-TEM images are shown in S5. The formation of nanostructured OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks reduces the number of disk layers induced by exfoliation and cleavage of hexagonal boron nitride, as shown in Figs. It was further evaluated by Tyndall light scattering experiments as indicated in the inset. The order of the light scattering intensity is consistent with the reduction in size by decreasing the number of disk layers as observed in FE-SEM and HR-TEM analysis Hexagonal boron nitride < OH-boron nitride nanodisks < OH/OOH-boron nitride It was a nanodisc.

4 (a) to (c) insets show the magnification corrected lattice spacing of hexagonal boron nitride nanodisks, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks, respectively. The interplanar spacing of the hexagonal boron nitride with respect to the (002) crystal plane was about 0.334 nm, whereas that of the OH-boron nitride nanodisk was about 0.350 nm. This increase in interplanar spacing can be attributed to the expansion of lattice parameters/unit cell volume induced by -OH functional groups. The interplanar spacing of this (002) plane increased to about 0.373 in OH/OOH-boron nitride nanodisks. This further increase in interplanar spacing shows a further expansion of the lattice parameters/unit cell volume induced by the -OH and -OOH functionalization groups, which is in good agreement with the shift of the XRD peak. These results suggest the successful functionalization and formation of OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks.

The SAED pattern of OH/OOH-boron nitride nanodisks shows bright spots in the (002) and (100) planes, which show that the functionalized boron nitride nanodisks are in a hexagonal phase with high crystallinity (Fig. 4(e)). ). This is in good agreement with the XRD results. A high-magnification HR-TEM image of the OH/OOH-boron nitride nanodisk is shown in Fig. 4(f). A uniformly distributed small bright spot can be seen in the OH/OOH-boron nitride nanodisk, which shows the central position of the hexagonal ring of B. The images also show the presence of high-density defect sites in the plane of the OH/OOH-boron nitride nanodisc, which can be formed by the covalent functionalization of -OH and -OOH. Therefore, it can be concluded that -OH and -OOH can be covalently attached to the boron nitride nanodisks at the edges as well as at the plane defect sites. Topographical maps of hexagonal boron nitride, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks were shown in atomic force microscopy (AFM) as shown in Figs. (d) to (f)) were analyzed together. AFM images show the size and thickness reduction of hexagonal boron nitride upon exfoliation, cleavage and functionalization. The average thicknesses of the hexagonal boron nitride, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks in the examined line profiles were about 44.90, 12.80, and 4.75 nm, respectively. This decrease in thickness with decreasing disk layer size is in good agreement with FE-SEM and TEM observations. XPS analysis was used to determine the amount of functional groups in OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks. X-ray photoelectron spectroscopy (XPS) spectra of hexagonal boron nitride were also measured for comparison.

In S6, XPS irradiation spectra of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks are shown. High-resolution, narrow-scan XPS spectra of B1 s for hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks are shown in FIGS. 6(a) to 6(c), respectively. 6 (d) to (f) show a narrow scan spectrum of N 1s, and FIGS. 6 (g) to (i) are hexagonal boron nitride, OH-boron nitride nanodisk, and OH/OOH-boron nitride nanodisk, respectively. shows the narrow scan spectrum of O1. The elemental binding energy was calibrated to a reference binding energy of C 1s (284.5 eV). All samples show BN binding at binding energies of about 190.0 and 398.0 eV in the narrow scan spectra of B 1s and N 1s, respectively. Both values agree well with those reported for single-layered hexagonal boron nitride. Both the OH-boron nitride nanodisks and the OH/OOH-boron nitride nanodisks exhibited additional peaks in the B 1s spectrum at binding energies of about 190.90 and 190.70 eV, respectively. This may be due to the BO bonding that occurs in the co-grafting of oxygen functional groups to the boron nitride nanodisk.

The low BO bond peak intensity of OH-boron nitride nanodisks suggests that the improved Hummus method is not an effective method to functionalize boron nitride nanodisks with a high proportion of -OH groups. The N 1s spectra of OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks show additional peaks at about 399.30 and 399.10 eV, respectively, which can be regarded as NH bonds. The presence of such a bond NH OH- boron nitride nano disc with OH / OOH- boron nitride nano discs HO ^● in the B site of the boron nitride nano disc and HOO ^● N formed after radical attack ^● Indicates radical inactivation. Similar to the BO bond strength, it is much higher for OH/OOH-boron nitride nanodisks compared to NH bond OH-boron nitride nanodisks, further showing that FR is highly effective for covalent functionalization of boron nitride. The BO peak does not appear in the O 1s spectrum of h-boron nitride, whereas both the OH-boron nitride nanodisk and the OH/OOH-boron nitride nanodisk show a high-intensity peak of BO at a binding energy of about 531.0 eV. However, the intensity of the BO peak is much higher in the OH/OH-boron nitride nanodisks than in the OH/OH-boron nitride nanodisks. In addition, the OH/OH-boron nitride nanodisks show two additional peaks at about 529.10 and 532.85 eV. The former peak may be due to the bonding of B-OH, whereas the latter may be due to the presence of B-OH in the OH/OH-boron nitride nanodisk.

On the other hand, the OH-boron nitride nanodisc shows only a low intensity B-OH peak with a low ratio of -OH functional groups consistent with the FTIR results. The elemental composition of hexagonal boron nitride was about 49.67%, 49.39%, and 0.93% for B, N and O, respectively, whereas it was about 46.15%, 46.95% and 6.90% for OH-boron nitride nanodisks, respectively. In the OH/OOH-boron nitride nanodisc, the atomic percentages of B, N and O were about 41.60%, 41.15%, and 17.25%, respectively. The very high oxygen ratio in the OH/OOH-boron nitride nanodisks suggests that the boron nitride nanodisks are effectively functionalized with -OH and -OOH by the combination of the improved Hummers method and the Fenton reaction. This is the highest value reported to date. Therefore, it can be concluded that the combination of the improved Hummus method and the Fenton reaction is a useful method for the functionalization of boron nitride nanodisks with a high proportion of -OH and -OOH functional groups.

Ultraviolet-visible absorption spectroscopy measurements were performed to analyze the electronic properties of hexagonal boron nitride, OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks. Fig. 7(a) shows the ultraviolet-visible light absorption spectrum and the inset shows the corresponding Tauc plot. The optical bandgap (Eg) of the sample was calculated using the Tauc relationship. where hν, α, B and n (n=1/2) are the photon energy, absorption coefficient, proportionality constant and electron transition parameters, respectively. The Eg of the sample was calculated by extrapolating the hv plot against (α hv ) 2 . Pure hexagonal boron nitride shows only a single absorption maximum (λ _{max1 ) at about 204.0 nm with E g} = 5.10 eV and shows the insulating properties of hexagonal boron nitride. _{Upon exfoliation and functionalization, λ max1} for OH-boron nitride nanodisks and OH/OOH-boron nitride nanodisks shifted red at 212.0 nm and 216.0 nm, respectively, and the absorption intensity decreased. OH-boron nitride nanodisks display one additional low-intensity absorption maxima (λ _max2 ) (about 244.50 nm), whereas this λ _{max2 for OH/OOH-boron nitride nanodisks exhibits a} similar wavelength (λ max2 ) with high absorption intensity. 244.60 nm). The absorption intensity of λ _max1 decreased in the order of hexagonal boron nitride < OH-boron nitride nanodisks < OH/OOH-boron nitride _nanodisks , whereas the intensity of λ max2 decreased from OH-boron nitride nanodisks to OH/OOH-boron nitride nanodisks. increased to This could lead to a change in electron cloud density distribution for adjacent BN bonds due to covalent functionalization of boron nitride nanodisks with polar -OH groups. This can reduce the electronegativity value of the BN bond.

Thus, functionalization can create two electron environments in the hexagonal boron nitride, resulting in two absorption maxima in the absorption spectrum. The shift in absorption maxima and its intensity are in good agreement with the oxygen functionalization rate as observed in the XPS results. In addition, the OH/OOH-boron nitride nanodisc exhibits an additional absorption maximum (λ _max3 ) at about 290.91 nm with low absorption intensity. This may be because -OOH functionalization of boron nitride nanodisks causes the electron cloud density distribution to further shift with adjacent BN bonds. low intensity of λ _max3 than λ _max2 is and suggest that low relative to the -OH -OH functionalized ratio OH / OOH- boron nitride nano disk, HO ^● Compared to HOO ^● consistent with the long half-life of _{Therefore, the E g} of the OH-boron nitride nanodisk and the OH/OOH-boron nitride nanodisk were about 3.75 and 3.58 eV, respectively (FIG. 7(b)). _{Therefore, increasing the electrical conductivity of hexagonal boron nitride by reducing E g} according to exfoliation and functionalization can broaden the scope of new research on the application of boron nitride to various electroanalysis and electrocatalytic devices.

For device fabrication using OH/OOH-boron nitride nanodisks, it is very important to disperse them in various solvents. This is because a high ratio of good dispersion can facilitate substrate fabrication or modification by OH/OOH-boron nitride nanodisks with improved homogeneity, and at the same time improve device performance with high reproducibility. The dispersion properties were evaluated by varying the concentration of OH/OOH-boron nitride nanodisc (0.10~1 mg mL ^{-1 ) in different solvents.}

Figure 8 (a) shows a photograph of dispersion of OH/OOH-boron nitride nanodiscs (1 mg mL ^{-1 ) in different solvents after 1 week.} After one week, the actual concentration of dispersed OH/OOH-boron nitride nanodiscs was measured according to the reported procedure. Fig. 8(b) shows the actual dispersion concentration versus absorbance (A/l) of OH/OOH-boron nitride nanodisks in different solvents at an excitation wavelength of about 245 nm. All plots fit well with Beer-Lambert's response. The slope of the straight line indicates that the dispersibility of OH/OOH-boron nitride nanodiscs is much higher in ethanol, isopropyl alcohol (IPA), and chloroform, while the dispersibility of DMF and water is much lower. Therefore, the dispersibility of OH/OOH-boron nitride nanodisks depends not only on the polarity of the solvent, but also on other physical properties (eg surface tension (γ) and Hansen solubility parameters) along with the range of -OH and -OOH functional groups.

In order to verify this, the maximum dispersion concentration of OH/OOH-boron nitride nanodisks and the polar cohesive force of the solvent (δ _p ) and the hydrogen bond cohesion force (δ) against the surface tension (γ) as shown in FIGS. _h ) were plotted. The maximum dispersion concentrations of OH/OOH-boron nitride nanodisks in IPA and ethanol were about 0.445 and 0.435 mg mL ^-1 , respectively, which were higher than the concentrations of OH-boron nitride nanodisks prepared by ball milling. It was observed that the dispersion concentration was maximized for solvents with γ values in the range of ^{20-30 mJ m -2,} which are in good agreement with the previous report. It was also reported that the dispersion of boron nitride was highest in solvents with the sum of _{δ p} and δ _h in the range of 8 to 20.

In this study, we observed that OH/OOH-boron nitride nanodisks not only showed good dispersibility within this reported range, but were well dispersed when the sum of _{δ p} and δ _{h was greater than 20.} This high OH/OOH-boron nitride nanodisc dispersibility is because -OH and -OOH groups were exposed at the edges and basal surfaces of the boron nitride nanodisk, enabling OH/OOH-boron nitride nanodisk dispersion in various solvents. The long-term dispersion stability of boron nitride, OH-boron nitride nanodisks, and OH/OOH-boron nitride nanodisks (each 0.2 mg mL ⁻¹ ) was investigated in IPA for more than 8 months as in S7.

OH/OOH-boron nitride nanodisks show the highest long-term stability compared to others, further suggesting that the combination of MHM and FR is an effective strategy for OH/OOH-boron nitride nanodisks with high -OH and -OOH ratios. .

3. Conclusion

Combining the improved Hummus method with Fenton chemistry, we developed a novel solution process yielding high proportions of -OH and -OOH functionalized boron nitride nanodisks at the edges and basal surfaces. Synthesis of boron nitride nano disc using an improved method hummus homogeneous decomposition of H ₂ O ₂ was ^● to produce OH radicals leads to functionalization of the boron nitride nano -OH disk to a low rate. The size and number of disk layers could be further reduced using the Fenton reaction with improved -OH and -OOH functionalization. At the same time, the electrical properties of adiabatic hexagonal boron nitride (E _g = 5.10 eV) are transformed into semiconductor behavior with E _g = 3.58 eV for OH/OOH-boron nitride nanodisks. The covalent functionalization of boron nitride nanodisks with high -OH and -OOH ratios was confirmed by XPS, Raman, FTIR and ultraviolet-visible spectroscopic analysis. As a result, OH/OOH-boron nitride nanodiscs showed high long-term dispersion stability in IPA with a ^{maximum dispersion of 0.445 mg mL - 1.} The high dispersion and long-term stability of OH/OOH-boron nitride nanodisks with semiconducting properties are advantageous for the development of electronic and optoelectronic devices. This approach is also promising for large-scale production of OH/OOH-boron nitride nanodisks and can be extended for the scalable production of other functional layered nanomaterials.

Claims (8)

A method for producing a boron nitride nanodisk in which hexagonal-boron nitride is functionalized with -OH and -OOH, and exfoliation and cutting are performed,
A first step of preparing a -OH functionalized boron nitride nanodisk by oxidizing hexagonal-boron nitride through a modified Hummer's method, and
A second step of treating the -OH functionalized boron nitride nanodisk obtained in the first step with Fenton's reagent
A method of manufacturing a boron nitride nanodisk comprising a.
According to claim 1, wherein the first step
a) mixing the hexagonal-boron nitride with an acid;
b) adding _{KMnO 4} to the resultant of step a); and
c) The method for producing a boron nitride nanodisk comprising the step of adding _{H 2} O ₂ to the resultant of step b).
The method of claim 2, wherein the acid in step a) is sulfuric acid.
The method of claim 2, wherein the reaction temperature of step c) is 40 to 60 ^o C.
The method of claim 1, wherein the Fenton reagent in the second step is a mixture of ^{Fe 2+} and H ₂ O _{2 in water.}
The method of claim 5, wherein the reaction temperature of the Fenton reagent treatment in the second step is 20 to 40 ^o C.
The method of claim 5, wherein the reaction time of the Fenton reagent treatment in the second step is 24-96 hours.
A boron nitride nanodisk functionalized with -OH and -OOH, prepared by the method of any one of claims 1 to 7.

Images