Method for reducing the particle size of graphite phase carbon nitride particles

Abstract

The present invention relates mainly to a process for the preparation of sub-micron sized graphite phase carbon nitride comprising the step of milling or ultrasonication of graphite phase carbon nitride. The present invention also relates to a sub-micron sized graphite phase carbon nitride having a size distribution in suspension wherein less than 1 pm of the particle size accounts for more than 50% of the total particle volume by volume.

Description

Technical Field

[0001] This invention primarily relates to a method for reducing the particle size of graphitic carbon nitride particles. This invention also relates to graphitic carbon nitride particles with a reduced particle size. Background Technology

[0002] UV protection is a key factor in cosmetic products. Organic and inorganic UV-filtering compounds (such as TiO2 and ZnO) are widely used to filter radiation in the UV region (wavelengths below 400 nm). Graphitic carbon nitride (an inorganic compound) is known to exhibit UV absorption properties. Several previous reports have been published on graphitic carbon nitride.

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

[0004] In addition, several documents have been published to date regarding technologies for reducing the particle size of carbon materials.

[0005] For example, US7300958B2 discloses a method for manufacturing a hyperdispersion of nanoscale primary carbon particles, the method comprising: applying a wet milling method to an aggregate structure of the nanoscale primary carbon particles to overcome van der Waals forces by which the nanoscale primary carbon particles are held together to form the aggregate structure, wherein the wet milling method is performed using balls as the breaking medium, each ball having a diameter of less than or equal to 0.1 mm.

[0006] In addition, EP3096866A1 discloses a method for removing mercury, which includes injecting activated carbon into flue gas generated from coal combustion, wherein the activated carbon has a d95 particle size distribution ranging from 1 μm to 28 μm and a d95 / d50 ratio ranging from 1.5 to 3, wherein the d95 particle size distribution can be obtained by grinding and air classification.

[0007] In addition, CN103975468A discloses a composite particle comprising: one or more carbon materials selected from the following: (i) fibrous carbon materials, (ii) chain carbon materials, and (iii) carbon materials formed by linking fibrous carbon materials and chain carbon materials together; and a lithium-containing phosphate; and a method for manufacturing the same.

[0008] However, these documents make no mention of graphitic carbon nitride.

[0009] Cosmetic compositions are used to provide a desired color appearance to keratinous substances, such as skin, especially facial skin. There is a need to develop a new method for manufacturing graphitic carbon nitride as an environmentally friendly UV-absorbing material. Summary of the Invention

[0010] One object of the present invention is to provide a method for effectively reducing the particle size of graphitic carbon nitride to obtain submicron-sized graphitic carbon nitride.

[0011] Another object of the present invention is to provide graphitic carbon nitride with reduced particle size, which can exhibit improved UV protection performance and a transparent appearance.

[0012] The above-mentioned objective of the present invention can be achieved by a method for preparing submicron-sized graphitic carbon nitride particles, wherein the graphitic carbon nitride is subjected to a grinding process or an ultrasonic treatment process.

[0013] The grinding step can be a wet grinding step.

[0014] The wet grinding step can be a wet jet grinding step or a wet bead milling step.

[0015] The ultrasonic treatment can be performed using a homogenizer.

[0016] The method may include the steps of grinding or ultrasonically treating graphitic carbon nitride two or more times.

[0017] The method may include an additional step of preparing graphitic carbon nitride by heating at least one precursor compound at a temperature of 450°C or higher for at least 1 minute prior to the step of grinding or ultrasonically treating graphitic carbon nitride.

[0018] The heating can be carried out in the presence of oxygen-containing substances such as O2 (especially using oxygen flux) and / or moisture.

[0019] The present invention also relates to a submicron-sized graphitic carbon nitride having a volume size distribution in which particles smaller than 1 μm account for more than 50% of the total particle volume.

[0020] A suspension of submicron-sized graphitic carbon nitride in water at a concentration of 0.01% by weight can have a turbidity of 300 NTU or less, preferably 200 NTU or less.

[0021] The present invention also relates to the use of submicron-sized graphitic carbon nitride according to the invention as a coating active ingredient, as a pigment, as a filler, especially a plastic filler, or as a cosmetic active ingredient, and particularly as a UV absorber.

[0022] The present invention also relates to a composition comprising submicron-sized graphitic carbon nitride according to the invention, and water and / or at least one organic medium.

[0023] The present invention also relates to a composition, preferably a cosmetic composition for use with keratinous substances such as skin, particularly a sunscreen composition, comprising submicron-sized graphitic carbon nitride according to the present invention. Brief description of the attached diagram Figure 1 The particle size distribution (A) of as-synthesized graphitic carbon nitride powder in suspension, measured by dynamic light scattering, and the particle size distribution (B) of graphitic carbon nitride powder in suspension according to Example 1 are shown.

[0025] Figure 2 The UV-vis absorption spectra of 0.01 wt% of the initially synthesized graphitic carbon nitride powder and the suspension of the graphitic carbon nitride powder according to Example 1 in water / isopropanol (1 wt% isopropanol) are shown.

[0026] Figure 3 The particle size distribution of the initially synthesized graphitic carbon nitride powder in the suspension, as measured by laser diffraction / scattering (A), and the particle size distribution of the graphitic carbon nitride powder in the suspension according to Example 2 (B) are shown.

[0027] Figure 4 The image shows an SEM image (A) of the initially synthesized graphitic carbon nitride and an ADF-STEM image (B) of graphitic carbon nitride with reduced particle size according to Example 2.

[0028] Figure 5 The UV-vis absorption spectra of a suspension of graphitic carbon nitride according to Example 2 at a concentration of 0.1% by weight in water are shown compared to water.

[0029] Figure 6 The particle size distribution of the initially synthesized graphitic carbon nitride powder in the suspension, as measured by dynamic light scattering (A), and the particle size distribution of the graphitic carbon nitride powder in the suspension according to Example 3 (B) are shown.

[0030] Figure 7 The particle size distribution of the initially synthesized graphitic carbon nitride powder in the suspension, as measured by dynamic light scattering (A), and the particle size distribution of the graphitic carbon nitride powder in the suspension according to Example 4 (B) are shown.

[0031] Figure 8The absorption coefficient (A) of the suspension of graphitic carbon nitride according to Example 4 is shown compared to the suspension of newly synthesized graphitic carbon nitride, TiO2 (average primary particle size: 15 nm), and ZnO (average particle size: maximum 200 nm), and the backdiffusion coefficient (B) of the suspension of graphitic carbon nitride according to Example 4 in the UV-Vis wavelength region is shown compared to the suspension of newly synthesized graphitic carbon nitride, TiO2 (average primary particle size: 15 nm), and ZnO (average particle size: maximum 200 nm).

[0032] Best Implementation of the Invention Through diligent research, the inventors have surprisingly discovered that the particle size of graphitic carbon nitride can be reduced by grinding or ultrasonic treatment, resulting in smaller graphitic carbon nitride with improved UV protection and transparency, thus completing this invention.

[0033] Therefore, the present invention mainly relates to a method for preparing submicron-sized graphitic carbon nitride, the method comprising the steps of grinding or ultrasonically treating graphitic carbon nitride.

[0034] The inventors of this invention have surprisingly discovered that manufacturing submicron-sized graphitic carbon nitride provides enhanced UV protection and improved transparency to graphitic carbon nitride.

[0035] Therefore, the method according to the present invention can produce submicron-sized graphitic carbon nitride with enhanced UV protection and improved transparency.

[0036] The invention will now be described in detail.

[0037] [method] This invention relates to a method for preparing submicron-sized graphitic carbon nitride, the method comprising the steps of grinding or ultrasonically treating the graphitic carbon nitride.

[0038] The term "graphite phase" in the context of graphite-phase carbon nitride refers to the carbon nitride having a graphite-like sheet structure. Therefore, the graphite-phase carbon nitride of the present invention can have a layered or sheet-like structure. Graphite-phase carbon nitride is typically a solid at room temperature and is in powder form.

[0039] The term "submicron size" as used herein refers to particles with a size of less than 1 μm. Therefore, the method according to the invention can produce an increased concentration of graphitic carbon nitride particles with a size of less than 1 μm in a suspension. In this 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 (LS 13 320 XR, Beckman Coulter Inc.).

[0040] The submicron-sized carbon nitride of the present invention may have a volume size distribution in which particles smaller than 1 μm account for more than 50%, preferably more than 60%, of the total particle volume. Furthermore, in one embodiment, the submicron-sized carbon nitride of the present invention may have an average particle size greater 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 greater than 0.1 μm.

[0041] The term "average particle size" used in this paper refers to the volume average size and average diameter, which is given by the statistical particle size distribution for half of the population and is called d50. The volume average size, average diameter, and volume size distribution of submicron carbon nitride can be measured, for example, by a dynamic light scattering particle size distribution analyzer.

[0042] Graphitic carbon nitride will be described in more detail in the subsequent entry on “Graphitic Carbon Nitride”.

[0043] The method according to the invention includes at least one step of grinding or ultrasonically treating graphitic carbon nitride. Therefore, the method according to the invention includes at least one step: wherein the graphitic carbon nitride is subjected to a grinding or ultrasonic treatment step to produce submicron-sized graphitic carbon nitride particles.

[0044] Any method, including media-free processes (such as wet jet milling, thin-film cyclone mixers, and high-speed laminar flow mixers) and media-based processes (such as wet bead milling and dry bead milling), can be used to grind graphitic carbon nitride.

[0045] As grinding methods, wet grinding and dry grinding methods can be specifically mentioned. Among wet grinding methods, wet jet grinding and wet bead milling methods can be specifically mentioned.

[0046] The medium used in the method according to the invention may include water and / or an organic solvent. The organic solvent may be hydrophilic or hydrophobic. Examples of organic solvents include straight-chain or branched alcohols, such as ethanol, propanol, butanol, isopropanol, and isobutanol.

[0047] Wet jet milling methods are generally divided into two types: one is to cause the suspension containing the material to be ground to collide; the other is to pass the suspension through a nozzle with a narrow gap to induce turbulence.

[0048] In wet jet milling, a suspension of graphitic carbon nitride is discharged under high pressure. There are no particular limitations on the method of applying pressure. The pressure applied to the suspension can range from 50 MPa to 300 MPa, and the number of passes through the nozzle can range from 1 to 400.

[0049] For wet bead milling methods, considering practical production, the circumferential speed can range from 6 m / s to 18 m / s, preferably from 10 m / s to 14 m / s. The constituent materials of the beads are not limited, but for example, metal oxides such as SiO2, glass, ZrO2, and Y2O3-stabilized ZrO2 can be mentioned; metal nitrides such as Si3N4; metal carbides such as WC; and metals and metal alloys such as steel. Considering practical production, the bead diameter can range from 0.01 mm to 2 mm, preferably from 0.05 mm to 1 mm. The grinding equipment includes any type of equipment suitable for beads with the above-mentioned diameters, such as ring-type and disc-type equipment and their derivatives, wherein said equipment is not limited to the specified equipment.

[0050] As a dry grinding method, high-energy dry jet grinding methods, such as steam jet grinding, can be mentioned.

[0051] As an ultrasonic treatment method, any equipment used for irradiation ultrasonic treatment can be used. In one embodiment, ultrasonic treatment is performed using a homogenizer. The output power of the ultrasonic treatment is not particularly limited, but can range from 5 to 5,000 W, preferably from 10 to 1,000 W. The duration 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, and generally, ultrasonic treatment is performed at a temperature ranging from 25°C to 80°C.

[0052] The method according to the invention may include the steps of grinding or ultrasonically treating the graphitic carbon nitride once, twice or more.

[0053] For example, bead milling methods may include a single step or multiple steps, while multi-step bead milling, such as two-step milling, can effectively produce submicron-sized graphitic carbon nitride. An example of two-step milling is to first mill using beads with a diameter ranging from 0.3 to 2 mm (e.g., 0.3 mm or 0.5 mm diameter), and then milling in a second step using beads with a diameter less than 0.3 mm (e.g., 0.1 mm diameter).

[0054] In one embodiment of the invention, the method according to the invention may include an additional step of preparing the graphitic carbon nitride to be ground or ultrasonicated as a starting material for the method prior to the step of grinding or ultrasonicating the graphitic carbon nitride. The graphitic carbon nitride can be prepared by heating at least one precursor compound.

[0055] Therefore, the method according to the present invention can be a method for preparing submicron-sized graphitic carbon nitride, the method comprising: i) Preparing graphitic carbon nitride by heating at least one precursor compound at a temperature of 450°C or higher for at least 1 minute; and ii) Grinding or ultrasonicating the graphitic carbon nitride to produce submicron-sized graphitic carbon nitride.

[0056] In the preparation of the initially synthesized graphitic carbon nitride, one precursor compound can be used, or two or more precursor compounds can be used in combination.

[0057] The precursor compound may be selected from precursors known to those skilled in the art, such as urea, thiourea, melamine, guanidine, arginine, cyanamide, dicyandiamide and its salts, and combinations thereof. Chem. Rev. 2016, 116, 7159–7329, Ong, WJ;Tan, LL; Ng, YH; Yong, ST; Chai, SP, Catalysts 2019, 9(10), 805, SeongJun Mun and Soo-Jin Park; https: / / doi.org / 10.3390 / catal9100805). Preferably, the precursor compound is selected from urea, melamine, guanidine, arginine, salts thereof, and combinations thereof.

[0058] There are no particular restrictions on the salts of the precursor compounds, but salts with inorganic acids, such as carbonic acid and HalH, may be mentioned, where Hal represents a halogen atom, such as chlorine (hydrochloric acid).

[0059] In a preferred embodiment of the invention, only one precursor compound is used to prepare graphitic carbon nitride.

[0060] The temperature at which at least one precursor compound is heated is at least 450°C. Preferably, the heating is carried out at a temperature of 500°C or higher, and more preferably at a temperature of 525°C or higher.

[0061] The heating time for 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, and more preferably within 25 hours.

[0062] The heating of the precursor compound can be carried out in air, in a rare gas such as argon or helium, or in an inert gas such as nitrogen. In a preferred embodiment of the invention, the heating of the precursor compound is carried out in air or in argon.

[0063] In a preferred embodiment, the heating process can be carried out in the presence of oxygen-containing compounds as oxidants, such as O2, moisture, O3, atomic O, and / or ionic oxygen. While not necessarily bound by theory, it is believed that more porous graphitic carbon nitride can be obtained when heating is carried out in the presence of oxygen-containing compounds. In a preferred embodiment, heating is carried out in air or in a rare or inert gas containing oxygen-containing compounds.

[0064] In a preferred embodiment, in addition to oxygen in the air, the heating process is also carried out in the presence of oxygen-containing substances such as O2, moisture, ozone O3, oxygen atoms and / or ionic oxygen as oxidants.

[0065] In a preferred embodiment, the heating process is carried out in the presence of oxygen-containing substances such as O2 (especially an oxygen flow) and / or moisture. In this specification, the term "oxygen flow" may refer to an oxygen stream.

[0066] Preferably, the oxidant used during the heating step is in gaseous form.

[0067] According to one implementation plan, the oxygen source is neither from permanganate nor from hydrogen peroxide.

[0068] In one embodiment of the invention, the heating process includes at least two heating steps at the same or different temperatures. In other words, the heating process may include a post-heating step. Therefore, in one embodiment, the heating process may include a first heating step of heating at least one precursor compound at a temperature of 450°C or higher for at least 1 minute, and a second heating step of heating at least one precursor compound at a temperature of 450°C or higher for at least 1 minute. The temperatures of the first heating step and 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 temperatures and times of the first and second heating steps are as explained above.

[0069] In one embodiment of the invention, a cooling step is included between the heating steps. Therefore, 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, but for example, it is cooled to room temperature (about 25°C). The duration of the cooling step is not particularly limited, but for example, it ranges from about 1 minute to 24 hours.

[0070] In another embodiment of the invention, the method according to the invention may include at least one pre-grinding process prior to the step of grinding or ultrasonically treating graphitic carbon nitride. The pre-grinding process may include not only wet grinding processes, but also dry grinding processes using dry bead milling, dry ball milling, and dry jet milling.

[0071] In obtaining a suspension of submicron-sized graphitic carbon nitride using the method according to the invention, the method may include an additional 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 media slurry drying. The dried submicron-sized particles may be resuspended in the liquid.

[0072] [Graphite-phase carbon nitride] The present invention also relates to graphitic carbon nitride particles, particularly submicron-sized graphitic carbon nitride particles. Submicron-sized graphitic carbon nitride particles can be prepared by the method according to the present invention as explained above.

[0073] The term "submicron size" as used herein can refer to particles having an average particle size of less than 1 μm. Therefore, the submicron-sized graphitic carbon nitride according to the present invention has an average particle size of less than 1 μm. In this specification, particle size can be measured, for example, by using dynamic light scattering (DLS; Nanotrac Wave EX, MicrotracBEL Corp.) or laser diffraction / scattering (LS 13 320 XR, Beckman Coulter Inc.).

[0074] The submicron-sized graphitic carbon nitride of the present invention may contain at least one heptaazine unit in its structure. In this specification, a heptaazine unit refers to a heterofused ring composed of three heterocycles (composed of C and N atoms), denoted as C6N7. Therefore, the graphitic carbon nitride of the present invention may have a heptaazine-based monolayer structure. The graphitic carbon nitride of the present invention may contain at least one heptaazine unit, at least one triazine unit, or combinations thereof. The presence of the heptaazine unit can be determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance spectroscopy (NMR).

[0075] The submicron-sized graphitic carbon nitride of the present invention can have a porous structure. More specifically, the graphitic carbon nitride of the present invention can have a nanoporous structure. Pores can exist on the layers of graphitic carbon nitride, located between heptaazine units and triazine units.

[0076] The heptaazine unit is preferably represented by formula (I), its salt, and its solvates (e.g., hydrates): (I) Equation (I), where the same or different R 1 R 2 and R 3 express: i) Hydrogen atom, ii) Halogen atoms, iii) Oxygen-containing groups, such as carboxyl, nitro, or nitroso groups. iv) A saturated or unsaturated, acyclic, straight or branched, and / or cyclic, aromatic or non-aromatic hydrocarbon chain containing 1 to 10 carbon atoms, said hydrocarbon chain may be interrupted by one or more heteroatoms (e.g., O, S, N or N(O)). v) hydroxyl group, vi) Amino R 4 R 5 N-, where the same or different R 4 and R 5 This indicates a hydrogen atom, a (C1-C6) alkyl group, or another monovalent heptaazinyl group, preferably a monovalent heptaazinyl(II). Where R 1 and R 2 As defined above; vii) R 4 R 5 N(O)-, where the same or different R 4 and R 5 As defined above; and viii) R 4 -N(O)- or; where R 4 As defined above.

[0077] It needs to be understood that: - Group R 1 R 2 or R 3 At least one of them represents a hydroxyl group, more preferably R 1 (v) hydroxyl groups, and the same or different, preferably the same R 2 and R 3 iii) Nitrosyl, selected from vi) to viii), more preferably viii), and One or more nitrogen atoms in the ring can be oxidized (N-oxide, or N-OH).

[0078] ii) Halogens can be selected from Cl and Br.

[0079] iv) The hydrocarbon chain may be saturated or unsaturated, preferably saturated, and acyclic straight-chain or branched, preferably acyclic straight-chain. iv) The hydrocarbon chain may contain 1 to 6, preferably 1 to 4, carbon atoms. Therefore, iv) the hydrocarbon chain may be a saturated and acyclic straight-chain hydrocarbon chain containing 1 to 6, preferably 1 to 4, carbon atoms, which may be interrupted by one or more heteroatoms (e.g., O, S, N, or N(O)).

[0080] Submicron-sized graphitic carbon nitride can be suspended in water and in organic media (e.g., polar oils, including diisopropyl sebacate). While not intended to be theoretically constrained, it is believed that the graphitic carbon nitride of the present invention can be dispersed in both water and oil because it contains a relatively large number of functional groups resulting from discretization and / or cracking in its structure (particularly in heptaazine units), which can contribute to altering surface polarity, such as the hydrophilicity and hydrophobicity of the graphitic carbon nitride surface. It is also believed that the amount of functional groups increases by reducing the size of the graphitic carbon nitride, as this can cause discretization and / or cracking in the structure of the graphitic carbon nitride.

[0081] The submicron-sized graphitic carbon nitride of the present invention exhibits improved UV absorption performance. Preferably, the graphitic carbon nitride has absorption effects in both the UV-B and UV-A ray regions. Here, UV-B rays refer to ultraviolet light with wavelengths between 280 and 320 nm. Here, UV-A rays refer to ultraviolet light with wavelengths 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.

[0082] The inventors of this invention have surprisingly discovered that manufacturing graphitic carbon nitride into submicron-sized particles enhances the UV absorption properties of suspensions due to improved dispersibility. Furthermore, the inventors have surprisingly discovered that manufacturing graphitic carbon nitride into submicron-sized particles can suppress opacity caused by the presence of large-sized graphitic carbon nitride particles.

[0083] Therefore, the submicron-sized graphitic carbon nitride suspension of the present invention exhibits low turbidity. For example, a suspension with a concentration of 0.01% by weight in water can be 300 NTU or less, preferably 200 NTU or less; a suspension with a concentration of 0.005% by weight in water can be 200 NTU or less, preferably 150 NTU or less; and a suspension with a concentration of 0.001% by weight in water can be 50 NTU or less, preferably 30 NTU or less. Turbidity can be measured, for example, using a 2100Q portable turbidimeter (HACH).

[0084] [use] This invention relates to the use of submicron-sized graphitic carbon nitride as a UV absorber, particularly a UV A and / or UV B absorber, to protect products from damage caused by UV radiation. For example, the UV absorbers of this invention can be used in coatings, paints, and cosmetics.

[0085] Because the submicron-sized graphitic carbon nitride of the present invention exhibits improved UV protection performance, its use can provide improved protection for products intended for use. Furthermore, because the graphitic carbon nitride of the present invention can be transparent in liquids, it can be used in a wide range of applications.

[0086] [Composition] The present invention also relates to a composition comprising submicron-sized graphitic carbon nitride of the present invention. Preferably, the composition according to the invention is a cosmetic composition, particularly a cosmetic composition for keratinous substances such as skin. In a preferred embodiment, the composition according to the invention is a sunscreen composition.

[0087] Furthermore, the compositions according to the invention can be used as coating actives, pigments, plastic fillers, cosmetic actives, and / or sunscreens such as UVA and / or UVB absorbers.

[0088] The compositions according to the invention preferably do not contain TiO2 or ZnO. In another embodiment, the compositions contain TiO2 and / or ZnO in an amount of 5% by weight or less, more preferably 1% by weight or less, relative to the total weight of the compositions according to the invention. The graphitic carbon nitride of the invention can be used in this composition instead of TiO2 and ZnO, which are known as conventional inorganic UV filters.

[0089] Since the submicron-sized graphitic carbon nitride of the present invention exhibits improved UV filtration performance, the compositions of the present invention can exhibit improved UV protection.

[0090] Example The invention will be described in more detail by way of example. However, these embodiments should not be construed as limiting the scope of the invention.

[0091] [Evaluate] The following evaluation was performed on the graphitic carbon nitride powder sample.

[0092] (Morphological Analysis) The morphology of graphitic carbon nitride in suspension was observed using a liquid cell annular dark field scanning transmission electron microscope (ADF-STEM).

[0093] The IR spectra of graphitic carbon nitride powder were obtained using attenuated total reflectance (ATR) spectroscopy. The suspension samples were freeze-dried for analysis. According to Nan Liu et al. (ACS Omega, 2020, Vol. 5, 12557-12567), the peak attributed to the heptaazine unit appeared at 804 cm⁻¹. -1 At this location, the wavenumber is higher than that of the triazine unit (for melamine: 814 cm⁻¹). -1For melamine: 808 cm -1 ).

[0094] (Particle size analysis) The particle size distribution in suspensions of graphitic carbon nitride was assessed using dynamic light scattering (DLS; Nanotrac Wave EX, MicrotracBEL Corp.) or laser diffraction / scattering (LS 13 320 XR, Beckman Coulter Inc.).

[0095] (UV absorption properties) UV-Vis absorption spectra of graphitic carbon nitride suspended in liquid in a fine quartz cell (transparent on both sides, 2 mm (optical path length) × 10 mm × H45 mm, Tokyo Garasu Kikai Co., Ltd.) coupled with an integrating sphere were collected using a UV-Vis spectrophotometer (V750, Jasco Inc.). The suspension samples were sonicated using an ultrasonic cleaner (ASU-3M, AS ONE Corporation) prior to measurement.

[0096] (Absorption and Backdiffusion Coefficients) The transmission and reflection spectra of graphitic carbon nitride suspended in liquid at three different concentrations were measured using spectral curves in the wavelength range of 250 nm to 780 nm, and then converted into absorption coefficient (µa) and backdiffusion coefficient (µs'). The backdiffusion coefficient in the visible light wavelength range greater than 400 nm represents the degree of opacity.

[0097] (Turbidity) Turbidity in NTUs was assessed using a 2100Q portable turbidimeter (HACH).

[0098] (Color and appearance) The color appearance of each graphitic carbon nitride was evaluated by visually inspecting the samples.

[0099] [preparation] The graphitic carbon nitride according to the present invention was prepared in the following Examples 1 to 4 and evaluated as follows.

[0100] Example 1 5 g of melamine powder was used as a precursor compound and heated in air at 550°C for 2 hours to prepare a pre-synthesized graphitic carbon nitride.

[0101] The initially synthesized graphitic carbon nitride was suspended at a concentration of 0.1% by weight in a water / isopropanol (volume ratio: 99 / 1) mixture. The suspension was then subjected to a single jet milling process at 70 MPa. The suspension was then diluted to 0.01% by weight of graphitic carbon nitride by adding the water / isopropanol (volume ratio: 99 / 1) mixture. After dilution, the suspension was jet milled again at 70 MPa under the same conditions as described above to produce a suspension of graphitic carbon nitride according to Example 1.

[0102] Figure 1 (A) shows the particle size distribution of the initially synthesized graphitic carbon nitride powder in suspension, as measured by dynamic light scattering. Figure 1 (B) shows the particle size distribution of graphitic carbon nitride powder in the suspension according to Example 1, measured by dynamic light scattering. Figure 1 As can be seen in (B), the peak with d50 of 0.24 μm and d90 of 0.41 μm appears in the range of 0.07 μm to 0.82 μm, with a frequency of 100%. Therefore, submicron-sized graphitic carbon nitride with a volume size distribution in which particles smaller than 1 μm account for about 100% of the total particle volume was obtained in Example 1.

[0103] Figure 2 The UV-vis absorption spectra of 0.01 wt% of the initially synthesized graphitic carbon nitride powder and the graphitic carbon nitride powder according to Example 1 in a suspension in water / isopropanol (1 wt% isopropanol) are shown. 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 improved dispersibility.

[0104] Example 2 The initially synthesized graphitic carbon nitride was suspended at a concentration of 0.1% by weight in a water / isopropanol (weight ratio: 99 / 1). The suspension was then subjected to wet jet milling at 200 MPa for a duration equivalent to 300 passes to obtain milled graphitic carbon nitride according to Example 2. The suspension was then freeze-dried to remove the suspending medium and obtain dried milled graphitic carbon nitride. The dried milled graphitic carbon nitride was then resuspended in water at 0.1% by weight by ultrasonic treatment for 20 minutes.

[0105] Figure 3 (A) shows the particle size distribution of the initially synthesized graphitic carbon nitride powder in suspension, as measured by laser diffraction / scattering. Figure 3(B) shows the particle size distribution of graphitic carbon nitride powder in the suspension according to Example 2, measured by dynamic light scattering. For differential volume, 67% of the detected size of the graphitic carbon nitride powder in the suspension according to Example 2 is in the range of 0.13 μm to 0.17 μm. Therefore, submicron-sized graphitic carbon nitride was obtained in Example 2, with a volumetric size distribution in which particles smaller than 1 μm account for approximately 67% of the total particle volume.

[0106] The turbidity of each suspension containing 0.1 wt% of the initially synthesized graphitic carbon nitride and the graphitic carbon nitride according to Example 2 was measured. The suspension samples were diluted with water before measurement to obtain suspensions with concentrations of 0.01 wt%, 0.005 wt%, and 0.001 wt%. The turbidities of the suspensions containing 0.01 wt%, 0.005 wt%, and 0.001 wt% of the initially synthesized graphitic carbon nitride were 549 NTU, 299 NTU, and 57 NTU, respectively, while the turbidities of the suspensions containing 0.01 wt%, 0.005 wt%, and 0.001 wt% of the graphitic carbon nitride according to Example 2 were 176 NTU, 103 NTU, and 26 NTU, respectively.

[0107] The morphology of graphitic carbon nitride in the suspension according to Example 2, obtained by ADF-STEM, confirmed that the graphitic carbon nitride has submicron-sized pores and a fibrous chain-like structure. Figure 4 (A) shows a SEM image of the initially synthesized graphitic carbon nitride, while Figure 4 (B) shows an ADF-STEM image of graphitic carbon nitride according to Example 2 with reduced particle size in a water / isopropanol (weight ratio: 99 / 1) mixture. This confirms that the method according to the invention can transform large particles of initially synthesized graphitic carbon nitride agglomerates into submicron-sized particles.

[0108] In the IR analysis of the graphitic carbon nitride according to Example 2, at 806 cm⁻¹ -1 A peak appeared at 804 cm⁻¹, located in the heptaazine unit. -1 The peak of melamine triazine unit is at 808 cm⁻¹ -1 The peak is in the middle. This result indicates that the graphitic carbon nitride according to Example 2 possesses both heptaazine and triazine units.

[0109] Figure 5 The UV-vis absorption spectrum of a suspension of graphitic carbon nitride according to Example 2 at a concentration of 0.1% by weight in water is shown, compared to water. This suspension exhibits absorption in the UV wavelength region below 400 nm.

[0110] Example 3 In Example 3, the same pre-synthesized graphitic carbon nitride as in Example 1 was used. This pre-synthesized graphitic carbon nitride was suspended in water at a concentration of 1% by weight. The suspension was then subjected to bead milling, comprising two steps: Step 1 (beads: Φ 0.3 mm, circumferential speed: 10 m / s, then 12 m / s after 10 minutes, duration: 60 minutes), followed by Step 2 (beads: Φ 0.1 mm, circumferential speed: 14 m / s, duration: 120 minutes), to obtain the milled graphitic carbon nitride according to Example 3.

[0111] Figure 6 (A) shows the particle size distribution of the initially synthesized graphitic carbon nitride powder in suspension, as measured by dynamic light scattering. Figure 6 (B) shows the particle size distribution of graphitic carbon nitride powder in the suspension according to Example 3, as measured by dynamic light scattering. Micrometer-sized particles decreased and submicrometer-sized particles increased after wet bead milling.

[0112] Example 4 The same initially synthesized graphitic carbon nitride powder was suspended at a concentration of 0.1% by weight in a mixture of water / propylene glycol (weight ratio: 50 / 50). The suspension was then subjected to wet jet milling three times at 70 MPa using a jet mill to obtain the milled graphitic carbon nitride according to Example 4. Polyoxyethylene dehydrated sorbitan monolaurate (Tween 20) was then added at a concentration of 0.3% by weight.

[0113] Figure 7 (A) shows the particle size distribution of the initially synthesized graphitic carbon nitride powder in suspension, as measured by dynamic light scattering. Figure 7 (B) shows the particle size distribution of graphitic carbon nitride powder in the suspension according to Example 4, measured by dynamic light scattering. Micrometer-sized particles decreased and submicrometer-sized particles increased after jet milling.

[0114] Figure 8 (A) shows the absorption coefficient of the suspension of graphitic carbon nitride according to Example 4 compared to a suspension of initially synthesized graphitic carbon nitride, TiO2 (average primary particle size: 15 nm), and ZnO (average particle size: maximum 200 nm). The graphitic carbon nitride according to Example 4 exhibits the highest UV absorption performance in the UV-B region and good UV-A absorption performance in the UV-A region. Furthermore, it can be confirmed that grinding the graphitic carbon nitride improves the UV absorption performance.

[0115] Figure 8(B) shows the backdiffusion coefficient of the suspension of graphitic carbon nitride according to Example 4 in the UV-Vis wavelength region compared to suspensions of newly synthesized graphitic carbon nitride, TiO2 (average primary particle size: 15 nm), and ZnO (average particle size: maximum 200 nm). The graphitic carbon nitride according to Example 4 exhibits the highest diffusion performance in the UV region. Furthermore, the graphitic carbon nitride according to Example 4 exhibits suppressed diffusion performance in the visible light region, which is almost identical to that of TiO2 and ZnO. This implies that the graphitic carbon nitride according to Example 4 exhibits improved transparency. On the other hand, the newly synthesized graphitic carbon nitride exhibits high diffusion performance in the visible light region, indicating its high opacity.

[0116] Example 5 In Example 5, the same pre-synthesized graphitic carbon nitride as in Example 1 was used. This pre-synthesized graphitic carbon nitride was suspended in water at a concentration of 0.05% by weight. The suspension was subjected to ultrasonic treatment at 20 W for 7 hours using a homogenizer (VIOLAMO SONICSTAR 85, AS ONE Corporation) to obtain the ultrasonically treated graphitic carbon nitride according to Example 5.

[0117] The initially synthesized suspension of graphitic carbon nitride was yellow in color, while the suspension of graphitic carbon nitride according to Example 5 exhibited a white appearance and better dispersibility in suspension. This indicates that ultrasonic treatment reduced the particle size of the graphitic carbon nitride. This result demonstrates that it is possible to obtain a suspension containing submicron-sized graphitic carbon nitride by using a homogenizer for ultrasonic treatment.

[0118] As can be understood from the results of the embodiments, the method according to the invention can effectively produce submicron-sized graphitic carbon nitride. Furthermore, the submicron-sized graphitic carbon nitride according to the embodiments exhibits improved UV filtering (absorption and diffusion) and improved transparency.

[0119] Therefore, it can be concluded that the method according to the invention is very useful for producing submicron-sized graphitic carbon nitride as a novel environmentally friendly UV filter material. Furthermore, the submicron-sized graphitic carbon nitride of the present invention is very useful as a UV absorber for various products because it can provide improved UV protection without discoloring the product. In particular, the submicron-sized graphitic carbon nitride of the present invention is very useful as a UV absorber for cosmetic products because it can provide improved UV protection for keratinous substances, such as skin, while remaining transparent in liquid.

Claims

1. A method for preparing submicron-sized graphitic carbon nitride, comprising the steps of grinding or ultrasonically treating the graphitic carbon nitride.

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

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

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

5. The method according to any one of the preceding claims, comprising the step of grinding or ultrasonically treating the graphitic carbon nitride two or more times.

6. The method according to any one of the preceding claims, comprising, prior to the step of grinding or ultrasonically treating the graphitic carbon nitride, an additional step of preparing the graphitic carbon nitride by heating at least one precursor compound at a temperature of 450°C or higher for at least 1 minute.

7. The method according to claim 6, wherein the heating is carried out in the presence of an oxygen-containing compound as an oxidant, such as O2, moisture, O3, atomic oxygen and / or ionic oxygen, preferably, the oxidant used during the heating step is in gaseous form; more preferably, the oxygen-containing compound is neither derived from permanganate nor from hydrogen peroxide.

8. The method according to any one of the preceding claims, further comprising, after the step of grinding or ultrasonically treating the graphitic carbon nitride, an additional step of evaporating the suspension medium from the suspension to obtain dry graphitic carbon nitride.

9. The method of claim 8, wherein the evaporation is performed by freeze drying.

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

11. A submicron-sized graphitic carbon nitride having a volumetric size distribution in which particles smaller than 1 μm account for more than 50% of the total particle volume.

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

13. Use of submicron-sized graphitic carbon nitride according to claim 11 or 12 as a coating active ingredient, as a pigment, as a filler, especially a plastic filler, or as a cosmetic active ingredient.

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

15. A composition comprising submicron-sized graphitic carbon nitride as described in claim 11 or 12 and water and / or at least one organic medium.

16. A composition, preferably a cosmetic composition for use with keratinous substances such as skin, comprising submicron-sized graphitic carbon nitride as claimed in claim 11 or 12.

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

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