Method for particle size reduction of graphitic carbon nitride particles

Abstract

To provide a new production method of graphitic carbon nitride as an environmentally friendly UV absorption material.SOLUTION: The present invention relates to a method for preparing submicron-sized graphitic carbon nitride, including a step of subjecting graphitic carbon nitride to milling treatment or ultrasonic treatment. The present invention also relates to submicron-sized graphitic carbon nitride having a volume size distribution in which particle sizes of less than 1 μm account for more than 50% of the volume of all particles in a suspension.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention mainly relates to a method for reducing the particle size of graphitic carbon nitride particles. The present invention also relates to graphitic carbon nitride particles with a reduced particle size.

Background Art

[0002] The UV protection effect is one of the important elements of cosmetics. In order to shield irradiation in the UV range (wavelength less than 400 nm), organic UV shielding compounds and inorganic UV shielding compounds such as TiO2 and ZnO are widely used. Graphitic carbon nitride, which is an inorganic compound, is known to exhibit UV absorption characteristics. Several documents regarding graphitic carbon nitride have already been reported.

[0003] For example, WO2020 / 246715 discloses an ultraviolet absorber containing polymeric carbon nitride having a heterocyclic structure. However, this document does not describe the particle size of graphitic carbon nitride.

[0004] In addition, regarding techniques for reducing the particle size of carbon materials, several documents have already been published so far.

[0005] For example, US7300958B2 is a method for producing an ultradispersion of primary particles of carbon of nanometer size, which includes applying a wet milling treatment method to the aggregate structure of the primary particles of carbon of nanometer size to overcome the van der Waals force that holds the primary particles of carbon of nanometer size together to form the aggregate structure, wherein the wet milling treatment method is carried out using balls as a breaking medium, and each of the balls has a diameter of 0.1 mm or less.

[0006] Also, EP3096866A1 discloses a method for mercury removal, which includes a step of injecting activated carbon into the exhaust gas generated from coal combustion, wherein the activated carbon has a d95 particle size distribution in the range of 1 μm to 28 μm and a d95 / d50 ratio in the range of 1.5 to 3, and the d95 particle size distribution can be obtained by milling treatment and air classification.

[0007] Also, CN103975468A discloses composite particles comprising (i) a fibrous carbon material, (ii) a chain-like carbon material, and (iii) one or more carbon materials selected from the group consisting of a carbon material in which the fibrous carbon material and the chain-like carbon material are bonded to each other, and a lithium-containing phosphate; and a method for producing the same.

[0008] However, these documents do not mention hexagonal boron nitride at all.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0010]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] Makeup compositions are used to provide a desired color appearance to keratinous substances such as the skin, especially facial skin. There is a need to develop a new production method of graphite-like carbon nitride as an environmentally friendly UV absorption material.

Means for Solving the Problems

[0012] An object of the present invention is to provide a method for efficiently reducing the particle size of graphite-like carbon nitride to obtain submicron-scale graphite-like carbon nitride.

[0013] Another object of the present invention is to provide graphite-like carbon nitride having a reduced particle size and capable of exhibiting improved UV protection properties and a transparent appearance.

[0014] The above object of the present invention can be achieved by a method for preparing submicron-scale graphite-like carbon nitride particles, wherein the graphite-like carbon nitride is subjected to a milling process or an ultrasonic treatment process.

[0015] The milling process may be a wet milling process.

[0016] The wet milling process may be a wet jet milling process or a wet bead milling process.

[0017] The ultrasonic treatment may be carried out using a homogenizer.

[0018] The method may include a step of subjecting the graphite-like carbon nitride to milling or ultrasonic treatment two or more times.

[0019] The method may further include a step of preparing graphitic carbon nitride by heating at least one precursor compound at 450 °C or higher for at least 1 minute before the step of milling or sonicating the graphitic carbon nitride.

[0020] The heating can be carried out in the presence of oxygen-containing species such as O2 (especially by an oxygen flux) and / or humidity.

[0021] The present invention also relates to submicron-sized graphitic carbon nitride having a volume size distribution in which the particle size of less than 1 μm occupies more than 50% of the volume of all the particles.

[0022] A suspension of submicron-sized graphitic carbon nitride at a concentration of 0.01% by mass in water can have a turbidity of 300 NTU or less, preferably 200 NTU or less.

[0023] The present invention also relates to the use of the submicron-sized graphitic carbon nitride according to the present invention as a paint active substance, as a pigment, as a filler, especially as a filler for plastics, or as a cosmetic active substance, in particular as a UV absorber.

[0024] The present invention also relates to a composition comprising the submicron-sized graphitic carbon nitride according to the present invention, and water and / or at least one organic medium.

[0025] The present invention also relates to a composition comprising the submicron-sized graphitic carbon nitride according to the present invention, preferably a cosmetic composition for keratinous substances such as the skin, in particular a sunscreen composition.

Brief Description of the Drawings

[0026]

Figure 1

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Embodiments for Carrying Out the Invention

[0027] As a result of intensive studies, the inventors of the present invention have surprisingly found that the particle size of graphitic carbon nitride can be reduced by a milling or ultrasonic treatment process to obtain smaller graphitic carbon nitride with improved UV protection properties and transparency, thus completing the present invention.

[0028] Accordingly, the present invention mainly relates to a method for preparing submicron-scale graphitic carbon nitride, the method comprising a step of subjecting graphitic carbon nitride to a milling or ultrasonic treatment.

[0029] The inventors of the present invention have surprisingly discovered that producing submicron-scale graphitic carbon nitride results in graphitic carbon nitride with enhanced UV protection properties and improved transparency.

[0030] Therefore, by the method according to the present invention, it is possible to produce submicron-sized graphitic carbon nitride with enhanced UV protection properties and improved transparency.

[0031] The present invention will be described in detail below.

[0032] [Method] The present invention relates to a method for preparing submicron-sized graphitic carbon nitride, the method comprising a step of subjecting graphitic carbon nitride to a milling or ultrasonic treatment.

[0033] Here, the term "graphitic" in graphitic carbon nitride means that the carbon nitride has a sheet-like graphite structure. Therefore, the graphitic carbon nitride of the present invention may have a layered or sheet structure. Graphitic carbon nitride is generally solid at room temperature and in powder form.

[0034] Here, the term "submicron-sized" may mean that the particles have a particle size of less than 1 μm. Thus, the method according to the present invention can produce graphite-like carbon nitride having a particle size of less than 1 μm with an increased concentration in the suspension. In the present specification, the particle size in the suspension can be measured, for example, by using dynamic light scattering (DLS; Nanotrac Wave EX, MicrotracBEL Corp.) or laser diffraction / scattering method (LS 13 320 XR, Beckman Coulter Inc.).

[0035] The submicron-sized carbon nitride of the present invention may have a volume size distribution in which the particle size of less than 1 μm occupies more than 50%, preferably more than 60% of the volume of all particles. Also, in one embodiment, the submicron-sized carbon nitride of the present invention may have an average particle size of more than 0.01 μm, preferably 0.05 μm. In another embodiment, the submicron-sized carbon nitride of the present invention may have an average particle size of more than 0.1 μm.

[0036] The term "average particle size" as used herein may represent the average diameter of the volume average size indicated by the statistical particle size distribution of half of the population, called d50. The average diameter of the volume average size and the volume size distribution of the submicron-sized carbon nitride can be measured, for example, by a dynamic light scattering particle size distribution analyzer.

[0037] Graphite-like carbon nitride will be described in more detail in the subsequent section on "Graphite-like Carbon Nitride".

[0038] The method according to the present invention includes at least one step of milling or ultrasonic treating the graphite-like carbon nitride. Thus, the method according to the present invention includes at least one step of subjecting the graphite-like carbon nitride to milling or ultrasonic treatment to produce submicron-sized graphite-like carbon nitride particles.

[0039] Any method including media-free processes such as wet jet milling, thin film spin mixers, and high-speed laminar flow mixers, and media-based processes such as wet and dry bead milling can be used to mill graphitic carbon nitride.

[0040] As the milling methods, wet milling method and dry milling method can be particularly mentioned. As the wet milling method, wet jet milling method and wet bead milling method can be particularly mentioned.

[0041] The media used in the method according to the present invention may include water and / or organic solvents. The organic solvent may be hydrophilic or hydrophobic. Examples of organic solvents include linear or branched alcohols such as ethanol, propanol, butanol, isopropanol, and isobutanol.

[0042] The wet jet milling method is generally classified into two methods; one method is to collide suspensions containing the material to be milled; the other method is to pass the suspension through a nozzle with a narrow gap to cause turbulent flow.

[0043] In the wet jet milling method, the suspension of graphitic carbon nitride is discharged under high pressure. The method for applying pressure is not particularly limited. The pressure applied to the suspension can be in the range of 50 MPa to 300 MPa, and the number of times of passing through the nozzle can be from 1 to 400 times.

[0044] Regarding the wet bead mill treatment method, the peripheral speed can be in the range of 6 m / s to 18 m / s, preferably 10 m / s to 14 m / s, considering actual production. The constituent material of the beads is not limited, and examples include metal oxides such as SiO2, glass, ZrO2, and Y2O3-stabilized ZrO2; metal nitrides such as Si3N4; metal carbides such as WC; and metals and metal alloys such as steel. The diameter size of the beads can be in the range of 0.01 mm to 2 mm, preferably 0.05 mm to 1 mm, considering actual production. As the mill treatment device, any type applicable to the beads of the aforementioned diameter can be used, such as annular type and disk type devices, and their modified examples, and the device is not limited to a specific device.

[0045] Examples of the dry mill treatment method include a high-energy dry jet mill treatment method such as a steam jet mill treatment method.

[0046] As the ultrasonic treatment method, any device for ultrasonic treatment irradiation can be used. In one embodiment, the ultrasonic treatment is carried out using a homogenizer. The output of the ultrasonic treatment is not particularly limited, but can be in the range of 5 to 5,000 W, preferably 10 to 1,000 W. The time of the ultrasonic treatment is not particularly limited, but can be up to 200 hours. The temperature of the ultrasonic treatment is not particularly limited, but generally, the ultrasonic treatment is carried out at a temperature in the range of 25°C to 80°C.

[0047] The method according to the present invention may include a step of subjecting the graphitic carbon nitride to mill treatment or ultrasonic treatment one or two or more times.

[0048] For example, the bead mill treatment method may include a single step or multiple steps. However, a multi-step bead mill treatment such as a two-step mill treatment can efficiently produce submicron-sized graphitic carbon nitride. An example of a two-step mill treatment is, for the first step, milling using beads having a diameter in the range of 0.3 to 2 mm, for example, beads having a diameter of 0.3 mm or 0.5 mm, and then, for the second step, milling using beads having a diameter of less than 0.3 mm, for example, beads having a diameter of 0.1 mm.

[0049] In one embodiment of the present invention, the method according to the present invention may include a further step of preparing graphitic carbon nitride to be milled or ultrasonically treated as a starting material of the method before the step of milling or ultrasonically treating the graphitic carbon nitride. The preparation of graphitic carbon nitride can be synthesized by heating at least one precursor compound.

[0050] Therefore, the method according to the present invention is a method for preparing submicron-sized graphitic carbon nitride, i) a step of preparing graphitic carbon nitride by heating at least one precursor compound at 450 °C or higher for at least 1 minute; ii) a step of milling or ultrasonically treating the graphitic carbon nitride to produce submicron-sized graphitic carbon nitride may be a method including.

[0051] In the preparation of as-synthesized graphitic carbon nitride, one precursor compound may be used, or two or more precursor compounds may be used in combination.

[0052] The precursor compound can be selected from precursors known to those skilled in the art, such as urea, thiourea, melamine, guanidine, arginine, cyanamide, dicyandiamide and their salts, and combinations thereof (Chem. Rev. 2016, 116, 7159 - 7329, Ong, W.J.; Tan, L.L.; Ng, Y.H.; Yong, S.T.; Chai, S.P., Catalysts 2019, 9(10), 805, Seong Jun Mun and Soo-Jin Park; https: / / doi.org / 10.3390 / catal9100805). Preferably, the precursor compound is selected from urea, melamine, guanidine, arginine and their salts, and combinations thereof.

[0053] The salt of the precursor compound is not particularly limited, and examples thereof include inorganic acids such as carbonic acid and HalH (where Hal represents a halogen atom, such as chloride (hydrochloric acid)).

[0054] In a preferred embodiment of the present invention, only one precursor compound is used for the preparation of graphite-like carbon nitride.

[0055] The temperature for heating at least one precursor compound is at least 450 °C. Preferably, the heating is carried out at 500 °C or higher, more preferably 525 °C or higher.

[0056] The time for heating at least one precursor compound is at least 1 minute. Preferably, the heating time is at least 10 minutes, more preferably at least 20 minutes, and / or within 30 hours, more preferably within 25 hours.

[0057] The heating of the precursor compound can be carried out in air, in a noble gas such as argon or helium, or in an inert gas such as nitrogen. In a preferred embodiment of the present invention, the heating of the precursor compound is carried out in air or in argon.

[0058] In a preferred embodiment, the heating process can be carried out in the presence of an oxygen-containing species as an oxidizing agent, such as O2, humidity, O3, atomic O, and / or oxygen ions. Without wishing to be bound by theory, it is believed that when heating is carried out in the presence of an oxygen-containing species, more porous graphite-like carbon nitride can be obtained. In a preferred embodiment, the heating is carried out in air or in a noble gas or inert gas containing an oxygen-containing species.

[0059] In a preferred embodiment, in addition to oxygen in air, the heating step is carried out in the presence of an oxygen-containing species as an oxidizing agent, such as O2, humidity, ozone O3, O atoms, and / or oxygen ions.

[0060] In a preferred embodiment, the heating step is carried out in the presence of an oxygen-containing species of O2, particularly an oxygen flux and / or humidity. The term "oxygen flux" can mean an oxygen flow herein.

[0061] Preferably, the oxidizing agent used during the heating step is in gaseous form.

[0062] According to one embodiment, the oxygen source is neither derived from permanganate nor from hydrogen peroxide.

[0063] In one embodiment of the present invention, the heating process includes at least two heating steps at the same or different temperatures. In other words, the heating process can include a post-heating step. Thus, in one embodiment, the heating process may include a first heating step of at least one precursor compound at 450 °C or higher for at least 1 minute, and then a second heating step of at least one precursor compound at 450 °C or higher for at least 1 minute. The temperature of the first heating step and the temperature of the second heating step may be the same or different, but generally, the temperature of the second heating step is equal to or higher than the temperature of the first heating step. The temperature and time of the first and second heating steps are as described above.

[0064] In one embodiment of the present invention, a cooling step exists during the heating step. Thus, in one embodiment, the cooling step is included between the first heating step and the second heating step. The temperature of the cooling step is not particularly limited. For example, the temperature is cooled to room temperature (about 25°C). The time of the cooling step is not particularly limited. For example, it is about 1 minute to 24 hours.

[0065] In another embodiment of the present invention, the method according to the present invention may include at least one pre-grinding process before the step of milling or sonicating graphitic carbon nitride. The pre-grinding process may include not only a wet milling process but also a dry grinding process using a dry bead milling process, a dry ball milling process, and a dry jet milling process.

[0066] When a suspension of submicron-sized graphitic carbon nitride is obtained by the method according to the present invention, the method may include a further step of drying the suspension to obtain dried submicron-sized graphitic carbon nitride. The drying method is not particularly limited and may include freeze-drying, spray-drying, and medium slurry drying. The dried submicron-sized particles can be resuspended in a liquid.

[0067] [Graphitic carbon nitride] The present invention also relates to graphitic carbon nitride particles, particularly submicron-sized graphitic carbon nitride particles. The submicron-sized graphitic carbon nitride particles can be prepared by the method according to the present invention as described above.

[0068] Here, the term "submicron-sized" may mean particles having an average particle diameter of less than 1 μm. Thus, the submicron-sized graphitic carbon nitride according to the present invention has an average particle diameter of less than 1 μm. In the present specification, the particle diameter can be measured, for example, by using dynamic light scattering (DLS; Nanotrac Wave EX, MicrotracBEL Corp.) or laser diffraction / scattering method (LS 13 320 XR, Beckman Coulter Inc.).

[0069] The submicron-sized graphitic carbon nitride of the present invention may contain at least one heptazine unit in its structure. As used herein, a heptazine unit means a hetero-condensed ring composed of three heterocycles consisting of C atoms and N atoms, represented by C6N7. Therefore, the graphitic carbon nitride of the present invention may have a heptazine-based monolayer structure. The graphitic carbon nitride of the present invention may contain at least one heptazine unit, at least one triazine unit, and combinations thereof. The presence of the heptazine unit can be determined by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR) analysis, and nuclear magnetic resonance spectroscopy (NMR) analysis.

[0070] The submicron-sized graphitic carbon nitride of the present invention may have a porous structure. More specifically, the graphitic carbon nitride of the present invention may have a nanoporous structure. The pores may be present in the layers of graphitic carbon nitride between the heptazine units and the triazine units.

[0071] The heptazine unit is preferably of formula (I), its salts and its solvates, such as hydrates:

[0072]

Chemical formula

[0073] (In formula (I), R 1 , R 2 , and R 3 are the same or different, i) a hydrogen atom, ii) a halogen atom, iii) an oxygen-containing group such as a carboxy, nitro, or nitroso group, iv) a saturated or unsaturated, acyclic straight-chain or branched, and / or cyclic, aromatic or non-aromatic hydrocarbon chain containing 1 to 10 carbon atoms, said hydrocarbon chain being potentially interrupted by one or more heteroatoms, such as O, S, N, or N(O); v) hydroxy, vi) amino R 4 R 5 N- (wherein R 4and R 5 are the same or different and are a hydrogen atom, a (C1-C6) alkyl group, or another monovalent heptazine group, preferably a monovalent heptazine group (II)

[0074]

Chemical formula

[0075] (wherein R 1 and R 2 are as defined previously herein); vii) R 4 R 5 N(O)-(R 4 and R 5 are the same or different and are as defined previously herein); and viii) R 4 -N(O)-(wherein R 4 is as defined previously herein) represents, -R 1 、R 2 or R 3 at least one of the groups represents a hydroxyl group in v), more preferably, R1 represents a hydroxyl group in v), and R 2 and R 3 are the same or different, preferably the same, and represent a group selected from iii), vi) to viii), more preferably the nitroso group in viii), It is understood that one or more nitrogens in the cycle may be oxidized (N-oxide or N-OH).

[0076] ii) The halogen may be selected from Cl and Br.

[0077] (iv) The hydrocarbon chain may be saturated or unsaturated, preferably saturated, acyclic straight-chain or branched, preferably acyclic straight-chain hydrocarbon chain. (iv) The hydrocarbon chain may contain 1 to 6, preferably 1 to 4 carbons. Therefore, (iv) the hydrocarbon chain may be a saturated and acyclic straight-chain hydrocarbon chain containing 1 to 6, preferably 1 to 4 carbons, which may be interrupted by one or more heteroatoms such as O, S, N or N(O).

[0078] Submicron-sized graphitic carbon nitride may be suspendable in water and organic media such as polar oils including diisopropyl sebacate. Without wishing to be bound by theory, the reason that the graphitic carbon nitride of the present invention may be dispersible in both water and oil is that the graphitic carbon nitride contains a relatively large amount of functional groups generated by separation and / or cracking occurring in the structure, particularly in the heptazine units, which is thought to contribute to surface polarity, for example, changes in hydrophilicity and hydrophobicity on the surface of the graphitic carbon nitride. Also, the amount of functional groups can be increased by reducing the size of the graphitic carbon nitride, presumably because it can cause separation and / or cracking in the structure of the graphitic carbon nitride.

[0079] The submicron-sized graphitic carbon nitride of the present invention may exhibit improved UV absorption characteristics. Preferably, the graphitic carbon nitride has an absorption effect on both the UV-B and UV-A light regions. Here, UV-B light means UV light having a wavelength between 280 and 320 nm. Here, UV-A light means UV light having a wavelength between 320 and 400 nm. Absorption curves in the ultraviolet and visible light ranges can be measured, for example, by ultraviolet-visible (UV-vis) absorption spectroscopy and diffuse reflectance spectroscopy.

[0080] The inventors of the present invention have surprisingly discovered that by making graphitic carbon nitride into submicron-sized particles, the UV absorption characteristics of the suspension can be enhanced due to improved dispersibility. Further, the inventors of the present invention have surprisingly discovered that by making graphitic carbon nitride into submicron-sized particles, the opacity caused by the presence of large-sized particles of graphitic carbon nitride can be suppressed.

[0081] Therefore, the suspension of submicron-sized graphitic carbon nitride of the present invention exhibits low turbidity. For example, suspensions with a concentration of 0.01% by mass in water can be 300 NTU or less, preferably 200 NTU or less; suspensions with a concentration of 0.005% by mass in water can be 200 NTU or less, preferably 150 NTU or less; suspensions with a concentration of 0.001% by mass in water can be 50 NTU or less, preferably 30 NTU or less. Turbidity can be measured, for example, by using a 2100Q Portable Turbidimeter (HACH).

[0082] [Use] The present invention may relate to the use of the submicron-sized graphitic carbon nitride of the present invention as a UV absorber for protecting products from damage caused by UV irradiation, particularly as a UV A and / or B absorber. For example, the UV absorber of the present invention can be used in paints, coatings, and cosmetics.

[0083] Since the submicron-sized graphitic carbon nitride of the present invention exhibits improved UV protection characteristics, the use of the present invention can provide an improved protection effect to the products to be used. In addition, the graphitic carbon nitride of the present invention can exhibit a transparent appearance in a liquid and can be used in a wide range of applications.

[0084] [Composition] The present invention also relates to a composition comprising the submicron-sized graphitic carbon nitride of the present invention. Preferably, the composition according to the present invention is a cosmetic composition, in particular a cosmetic composition for keratinous substances such as the skin. In a preferred embodiment, the composition according to the present invention is a sunscreen composition.

[0085] In addition, the composition according to the present invention can be used as a paint active substance, a pigment, a filler for plastics, a cosmetic active substance, and / or a sunscreen, for example, a UVA and / or B absorber.

[0086] The composition according to the present invention preferably does not contain TiO2 or ZnO. In another embodiment, the composition according to the present invention contains TiO2 and / or ZnO in an amount of 5% by mass or less, more preferably 1% by mass or less, based on the total mass of the composition. The graphitic carbon nitride of the present invention can be used in the composition in place of TiO2 and ZnO, which are known as traditional inorganic UV blockers.

[0087] Since the submicron-sized graphitic carbon nitride of the present invention can exhibit improved UV blocking properties, the composition of the present invention can exhibit an improved UV protection effect.

Examples

[0088] The present invention will be described in more detail by way of examples. However, these examples should not be construed as limiting the scope of the present invention.

[0089] [Evaluation] The following evaluations were performed on the graphitic carbon nitride powder samples.

[0090] (Morphology analysis) The morphology of the graphitic carbon nitride in the suspension was observed via an annular dark field scanning transmission electron microscope (ADF-STEM) using a liquid cell.

[0091] The IR spectrum of the graphite-like carbon nitride powder was obtained using the attenuated total reflection (ATR) method. The suspension sample was lyophilized for analysis. The peak assigned to the heptazine unit appeared at 804 cm -1 and this is at a higher wavenumber than the wavenumbers of the triazine units by Nan Liu et al. (ACS Omega, 2020, Vol. 5, pp. 12557 - 12567) (814 cm -1 for melamine, 808 cm -1 for melam).

[0092] (Particle size analysis) The particle size distribution in the suspension of graphite-like carbon nitride was evaluated using dynamic light scattering (DLS; Nanotrac Wave EX, MicrotracBEL Corp.) or laser diffraction / scattering method (LS 13 320 XR, Beckman Coulter Inc.).

[0093] (UV absorption characteristics) The UV-vis absorption spectrum of graphite-like carbon nitride suspended in a liquid was collected using a UV-visible spectrophotometer (V750, Jasco Inc.) connected to an integrating sphere in a fine quartz cell (two transparent sides, 2 mm (optical path length) × 10 mm × H45 mm, Tokyo Garasu Kikai Co., Ltd.). The suspension sample was sonicated before measurement using an ultrasonic cleaner (ASU-3M, AS ONE Corporation).

[0094] (Absorption and backscattering coefficients) The transmission and reflection spectra of graphite-like carbon nitride suspended in a liquid at three different concentrations were measured in the wavelength range of 250 nm to 780 nm using a spectral curve and converted to the absorption coefficient (μa) and backscattering coefficient (μs'). The backscattering coefficient in the visible wavelength range greater than 400 nm represents the opacity.

[0095] (Turbidity) The turbidity in nephelometric turbidity units (NTU) was evaluated using a 2100Q Portable Turbidimeter (HACH).

[0096] (Color appearance) The color appearance of each of the graphitic carbon nitrides was evaluated by visually observing the samples.

[0097] [Preparation] The graphitic carbon nitride according to the present invention was prepared in the following Examples 1 to 4 and evaluated as follows.

[0098] (Example 1) 5 g of melamine powder as a precursor compound was heated in air at 550 °C for 2 hours to prepare as-synthesized graphitic carbon nitride.

[0099] The as-synthesized graphitic carbon nitride was suspended in a mixture of water / isopropanol (volume ratio: 99 / 1) at a concentration of 0.1 mass%. Then, using a jet mill at 70 MPa, the suspension was subjected to one jet milling treatment. Then, the suspension was diluted to 0.01 mass% graphitic carbon nitride by the addition of a mixture of water / isopropanol (volume ratio: 99 / 1). After dilution, jet milling treatment at 70 MPa under the same conditions as above was performed again on the suspension to produce a suspension of graphitic carbon nitride according to Example 1.

[0100] Figure 1(A) shows the particle size distribution of the as-synthesized graphitic carbon nitride powder in the suspension measured by dynamic light scattering, and Figure 1(B) shows the particle size distribution of the graphitic carbon nitride powder in the suspension according to Example 1. As can be seen from Figure 1(B), a peak with d50 of 0.24 μm and d90 of 0.41 μm appeared in the range of 0.07 μm to 0.82 μm with a frequency of 100%. Therefore, submicron-sized graphitic carbon nitride having a volume size distribution in which particle sizes less than 1 μm occupy approximately 100% of the volume of all particles was obtained in Example 1.

[0101] The UV-vis absorption of a suspension containing 0.01% by mass of as-synthesized graphitic carbon nitride powder and the graphitic carbon nitride powder according to Example 1 in water / isopropanol (1% by mass isopropanol) is shown in Fig. 2. The suspensions of both samples showed absorption in the UV wavelength region below 400 nm, while the sample according to Example 1 showed higher absorption due to the improved dispersibility.

[0102] (Example 2) As-synthesized graphitic carbon nitride was suspended in a mixture of water / isopropanol (mass ratio: 99 / 1) at a concentration of 0.1% by mass. Then, using a jet mill at 200 MPa, the suspension was subjected to jet milling treatment through circulation equivalent to 300 passes over a continuous time to obtain jet-milled graphitic carbon nitride according to Example 2. Then, the suspension was subjected to freeze-drying to remove the suspension medium and obtain dried and milled graphitic carbon nitride. Then, the dried and milled graphitic carbon nitride was resuspended in water at 0.1% by mass by ultrasonic treatment for 20 minutes.

[0103] Fig. 3(A) shows the particle size distribution of as-synthesized graphitic carbon nitride powder in the suspension measured by the laser diffraction / scattering method, and Fig. 3(B) shows the particle size distribution of graphitic carbon nitride powder in the suspension according to Example 2. 67% of the detected size of the graphitic carbon nitride powder in the suspension according to Example 2 was in the range of 0.13 μm to 0.17 μm with respect to the differential volume. Therefore, submicron-sized graphitic carbon nitride having a particle size with a volume size distribution in which particle sizes less than 1 μm occupy about 67% of the volume of all particles was obtained in Example 2.

[0104] The turbidity of each of the suspensions containing 0.1% by mass of as-synthesized graphitic carbon nitride and the graphitic carbon nitride according to Example 2 was measured. By adding the aforementioned suspension to water, the suspension sample was diluted before measurement to obtain suspensions with concentrations of 0.01% by mass, 0.005% by mass, and 0.001% by mass. The turbidity of the suspensions of as-synthesized graphitic carbon nitride with concentrations of 0.01% by mass, 0.005% by mass, and 0.001% by mass was 549 NTU, 299 NTU, and 57 NTU, respectively, while the turbidity of the suspensions of graphitic carbon nitride according to Example 2 with concentrations of 0.01% by mass, 0.005% by mass, and 0.001% by mass was 176 NTU, 103 NTU, and 26 NTU, respectively.

[0105] According to the morphology of the graphitic carbon nitride in the suspension according to Example 2 via ADF-STEM, it was confirmed that the graphitic carbon nitride has submicron-sized pores and fibrous chain-like structures. FIG. 4(A) shows the SEM image of the as-synthesized graphitic carbon nitride, and FIG. 4(B) shows the ADF-STEM image of the graphitic carbon nitride according to Example 2 with reduced particle size in a mixture of water / isopropanol (mass ratio: 99 / 1). It is confirmed that the method according to the present invention can make the large-sized particles of the aggregates of the as-synthesized graphitic carbon nitride into submicron-sized particles.

[0106] In the IR analysis of the graphitic carbon nitride according to Example 2, a peak appeared at 806 cm -1 , which is located between the peak of the heptazine unit at 804 cm -1 for melamine and the peak of the triazine unit at 808 cm -1 . This result indicates that the graphitic carbon nitride according to Example 2 has both heptazine units and triazine units.

[0107] The UV-vis absorption spectrum of the suspension of the graphitic carbon nitride according to Example 2 with a concentration of 0.1% by mass in water compared to water is shown in FIG. 5. The suspension showed absorption in the UV wavelength region of less than 400 nm.

[0108] (Example 3) The as-synthesized graphitic carbon nitride used in Example 1 was used in Example 3. The as-synthesized graphitic carbon nitride was suspended in water at a concentration of 1% by mass. Then, the suspension was subjected to bead mill treatment including the following two steps: Step 1 (beads: Φ0.3 mm, peripheral speed: 10 m / s, then 12 m / s after 10 minutes, duration: 60 minutes), and then Step 2 (beads: Φ0.1 mm, peripheral speed: 14 m / s, duration: 120 minutes) to obtain the bead mill-treated graphitic carbon nitride according to Example 3.

[0109] Figure 6(A) shows the particle size distribution of the as-synthesized graphitic carbon nitride powder in the suspension measured by dynamic light scattering, and Figure 6(B) shows the particle size distribution of the graphitic carbon nitride powder in the suspension according to Example 3. The particles of micrometer size decreased after the wet bead mill treatment, and the particles of submicron size increased.

[0110] (Example 4) The same as-synthesized graphitic carbon nitride particles were suspended in a mixture of water / propylene glycol (mass ratio: 50 / 50) at a concentration of 0.1% by mass. Then, using a jet mill at 70 MPa, the suspension was subjected to jet mill treatment three times to obtain the jet mill-treated graphitic carbon nitride according to Example 4. Then, polyoxyethylene sorbitan monolaurate (Tween 20) was added at a concentration of 0.3% by mass.

[0111] Figure 7(A) shows the particle size distribution of the as-synthesized graphitic carbon nitride powder in the suspension measured by dynamic light scattering, and Figure 7(B) shows the particle size distribution of the graphitic carbon nitride powder in the suspension according to Example 4. The particles of micrometer size decreased after the jet mill treatment, and the particles of submicron size increased.

[0112] Figure 8(A) shows the absorption coefficient of the suspension of graphitic carbon nitride according to Example 4, compared with the suspensions of as-synthesized graphitic carbon nitride, TiO2 (average primary particle size: 15 nm), and ZnO (average particle size: up to 200 nm). The graphitic carbon nitride according to Example 4 was able to exhibit the highest UV absorption characteristics in the UV-B region and showed good UV-A absorption characteristics in the UV-A region. In addition, an increase in the UV absorption characteristics by milling the graphitic carbon nitride was confirmed.

[0113] Figure 8(B) shows the backscattering coefficient in the UV-Vis wavelength region of the suspension of graphitic carbon nitride according to Example 4, compared with the suspensions of as-synthesized graphitic carbon nitride, TiO2 (average primary particle size: 15 nm), and ZnO (average particle size: up to 200 nm). The graphitic carbon nitride according to Example 4 was able to exhibit the highest diffusion characteristics in the UV region. In addition, the graphitic carbon nitride according to Example 4 showed suppression of the diffusion characteristics in the visible light region, which was almost the same as that of TiO2 and ZnO. This means that the graphitic carbon nitride according to Example 4 exhibits improved transparency. On the other hand, the as-synthesized graphitic carbon nitride showed high diffusion characteristics in the visible light region, which indicates that the as-synthesized graphitic carbon nitride has high opacity.

[0114] (Example 5) The same as-synthesized graphitic carbon nitride as in Example 1 was used in Example 5. The as-synthesized graphitic carbon nitride was suspended in water at a concentration of 0.05 mass%. The suspension was subjected to ultrasonic treatment using a homogenizer (VIOLAMO SONICSTAR 85, manufactured by AS ONE Corporation) at 20 W for 7 hours to obtain the ultrasonically treated graphitic carbon nitride according to Example 5.

[0115] While the color appearance of the as-synthesized graphite-like carbon nitride suspension was yellow, the graphite-like carbon nitride suspension according to Example 5 showed a white appearance and better dispersibility in the suspension. This indicates that the particle size of the graphite-like carbon nitride was reduced by ultrasonic treatment. This result shows that it is possible to obtain a suspension composed of submicron-sized graphite-like carbon nitride by ultrasonic treatment using a homogenizer.

[0116] As can be understood from the results of the examples, the method according to the present invention was able to efficiently produce submicron-sized graphite-like carbon nitride. In addition, the submicron-sized graphite-like carbon nitride according to the examples showed an improved UV shielding effect (absorption and diffusion) and an improved transparency.

[0117] Therefore, it can be concluded that the method according to the present invention is very useful for producing submicron-sized graphite-like carbon nitride, which is a new environmentally friendly UV shielding material. In addition, the submicron-sized graphite-like carbon nitride of the present invention can provide an improved UV protection effect to products, and since it does not color the products, it is very useful as a UV absorber for various products. In particular, the submicron-sized graphite-like carbon nitride of the present invention can provide an improved UV protection effect to keratin substances such as the skin, and since it is transparent in a liquid, it is very useful as a UV absorber for cosmetics.

Claims

1. A method for preparing submicron-sized graphitic carbon nitride, the method comprising the step of subjecting graphitic carbon nitride to milling or ultrasonic treatment.

2. The method according to claim 1, wherein the milling step is a wet milling step.

3. The method according to claim 2, wherein the wet milling step is a wet jet milling step or a wet bead milling step.

4. The method according to claim 1, wherein the ultrasonic treatment is carried out using a homogenizer.

5. The method according to any one of claims 1 to 4, comprising the step of subjecting graphitic carbon nitride to milling or ultrasonic treatment two or more times.

6. The method according to any one of claims 1 to 5, further comprising the step of preparing graphitic carbon nitride by heating at least one precursor compound at 450 °C or higher for at least 1 minute before the step of subjecting graphitic carbon nitride to milling or ultrasonic treatment.

7. The heating step is carried out in the presence of an oxygen-containing species as an oxidizing agent, for example, O 2 , humidity, O 3 , O atoms and / or oxygen ions, and preferably, the oxidizing agent used during the heating step is in gaseous form; more preferably, the oxygen-containing species is neither permanganate nor hydrogen peroxide, the method according to claim 6.

8. The method according to any one of claims 1 to 7, further comprising the step of evaporating the suspension medium from the suspension to obtain dried graphitic carbon nitride after the step of subjecting graphitic carbon nitride to milling or ultrasonic treatment.

9. The method according to claim 8, wherein the evaporation is carried out by freeze-drying.

10. The method according to claim 8 or 9, further comprising the step of resuspending the dried graphitic carbon nitride in a medium after the step of drying the medium.

11. Submicron-sized graphitic carbon nitride having a volume size distribution in which a particle size of less than 1 μm occupies more than 50% of the volume of all particles.

12. The submicron-sized graphitic carbon nitride according to claim 11, wherein a suspension of submicron-sized graphitic carbon nitride having a concentration of 0.01% by mass in water has a turbidity of 300 NTU or less, preferably 200 NTU or less.

13. Use of the submicron-sized graphitic carbon nitride according to claim 11 or 12 as a paint active substance, as a pigment, as a filler, especially as a filler for plastics, or as a cosmetic active substance.

14. Use of the submicron-sized graphitic carbon nitride according to claim 11 or 12 as a UV absorber.

15. A composition comprising the submicron-sized graphitic carbon nitride according to claim 11 or 12, and water and / or at least one organic medium.

16. The composition containing submicron-sized graphite-like carbon nitride according to Embodiment 11 or 12, preferably a cosmetic composition for keratin substances such as skin.

17. The composition according to claim 16, which is a sunscreen composition.

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