A triphenylamine-modified graphitic carbon nitride, its preparation method and application

Abstract

This invention relates to the field of materials preparation technology, specifically disclosing a triphenylamine-modified graphitic carbon nitride, its preparation method, and its applications. The method involves thermally polycondensing at least one carbon nitride precursor and at least one 1,3,5-triazine derivative containing a triphenylamine group to obtain triphenylamine-modified graphitic carbon nitride. This method precisely controls the band structure and photophysical processes of the material at the molecular level by in-situ embedding the triphenylamine group into the conjugated network framework of the graphitic carbon nitride. This effectively solves the technical bottlenecks of existing graphitic carbon nitride modification methods, such as limited redshift, low quantum efficiency, and poor color purity. It achieves efficient, high-color-purity orange-yellow light emission, and the resulting material possesses excellent thermal and photochemical stability, meeting the long-term high-power operation requirements of LED devices. This invention provides a feasible path for the industrial application of novel rare-earth-free, low-cost orange-yellow LED materials and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a triphenylamine group-modified graphitic carbon nitride, its preparation method, and its application. Background Technology

[0002] Light-emitting diodes (LEDs) have been widely used in lighting, displays, and other fields due to their significant advantages such as energy saving, environmental friendliness, small size, and long lifespan. LEDs play an irreplaceable role in scenarios such as traffic signals, landscape lighting, interior decoration, and plant lighting, leading to continuously rising market demand. Currently, orange-yellow light materials for LEDs are mainly divided into two categories: inorganic fluorescent materials and organic fluorescent materials. Inorganic fluorescent materials largely rely on rare-earth element doping, which not only suffers from problems such as scarce rare-earth resources, high synthesis temperatures, and high energy consumption, but also has drawbacks such as insufficient color rendering index and significant thermal quenching, making it difficult to meet the application requirements of high-power, high-performance LED devices. Organic fluorescent materials, on the other hand, have advantages such as strong molecular structure designability, low-temperature preparation, and no rare-earth dependence. However, they generally suffer from problems such as low photoluminescence quantum yield, poor thermal stability, and easy degradation after long-term use, limiting their large-scale application in the LED field.

[0003] Graphitic carbon nitride (g-C3N4), a novel two-dimensional semiconductor material composed of carbon and nitrogen, can be prepared by high-temperature pyrolysis of inexpensive nitrogen-containing precursors such as melamine and urea. It possesses excellent chemical stability, thermal stability, environmental friendliness, and unique optoelectronic properties. Furthermore, its raw materials are widely available, and its preparation cost is low, requiring no precious metals or inert atmospheres, demonstrating enormous application potential in the field of optoelectronic materials. However, intrinsically pure graphitic carbon nitride materials inherently possess several structural and optoelectronic performance defects: pure graphitic carbon nitride has a wide bandgap, extremely high photogenerated carrier recombination rate, extremely low exciton separation efficiency, severe π-π stacking and aggregation between material layers, a relatively small specific surface area, and a limited photoluminescence range, emitting only blue light and completely failing to cover the orange-yellow light emission band, thus directly unsuitable for use as an orange-yellow light-emitting material for LEDs.

[0004] Currently, although researchers have attempted to modify g-C3N4 through methods such as elemental doping and organic functional group modification, efficient orange-yellow light emission has not yet been achieved. Furthermore, existing modification methods are cumbersome and require stringent reaction conditions, making it difficult to effectively improve its luminescence efficiency and stability. Therefore, developing a modified g-C3N4 orange-yellow light material with simple processing and excellent performance has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies that modify g-C3N4 to achieve efficient orange-yellow light emission, and the cumbersome and demanding processes of current modification methods that struggle to balance luminous efficiency and stability, this invention provides a triphenylamine-modified graphitic carbon nitride, its preparation method, and its applications. This material undergoes covalent modification with specific triphenylamine groups, effectively controlling its electronic band structure, significantly promoting photoexciton dissociation, and suppressing non-radiative transitions, thereby achieving efficient and high-purity orange-yellow light emission. Furthermore, its preparation process is simple and highly controllable, requiring no stringent reaction conditions, and the resulting modified material exhibits excellent thermal stability, meeting the industrial production and practical application requirements for orange-yellow light materials in LEDs.

[0006] To solve the above-mentioned technical problems, the technical solution 1 provided by the embodiments of the present invention is: In a first aspect, the present invention provides a method for preparing triphenylamine-modified graphitic carbon nitride, wherein at least one carbon nitride precursor and at least one 1,3,5-triazine derivative containing triphenylamine groups are subjected to a thermal polycondensation reaction to obtain triphenylamine-modified graphitic carbon nitride.

[0007] Compared to existing technologies, this invention achieves effective control over band structure and photophysical processes at the molecular level by in-situ embedding triphenylamine groups, which possess strong electron-donating and hole-transporting capabilities, into the conjugated network framework of graphitic carbon nitride. The triphenylamine groups can form an extended conjugated system with the carbon nitride framework, effectively reducing the band gap, promoting photoexciton dissociation, and suppressing nonradiative transitions. This significantly redshifts the emission from the intrinsic blue light band to the orange-yellow light region, fundamentally solving the problems of limited redshift, low quantum efficiency, and accompanying color variations in the emission spectrum associated with existing modification methods. This results in highly efficient and high-purity orange-yellow light emission. Simultaneously, the prepared triphenylamine-modified graphitic carbon nitride exhibits excellent thermal and photochemical stability, fully meeting the application requirements of LED devices under long-term high-power operating conditions. This breakthrough overcomes a key bottleneck in the application of graphitic carbon nitride in the field of orange-yellow light materials for LEDs, demonstrating significant economic value and application prospects.

[0008] Specifically, the thermal polycondensation reaction is carried out using a high-temperature solid-state thermal polymerization method.

[0009] It should be noted that, in this invention, the carbon nitride precursor refers to a nitrogen-containing organic compound that can form a graphitic carbon nitride (g-C3N4) conjugated network structure through thermal polycondensation. During the co-thermal polycondensation process, it provides the carbon and nitrogen sources constituting the main body of the g-C3N4 skeleton, and undergoes in-situ copolymerization with a 1,3,5-triazine derivative containing triphenylamine groups, thereby embedding the triphenylamine groups into the conjugated network of the final product. As an example, the carbon nitride precursors that can be used in this invention include, but are not limited to, melamine, urea, dicyandiamide, thiourea, monocyanamide, ammonium thiocyanate, cyanuric acid, and any combination thereof. Preferably, the carbon nitride precursor is melamine.

[0010] In this invention, 1,3,5-triazine derivatives containing a triphenylamine group refer to compounds whose molecular structure simultaneously contains a 1,3,5-triazine ring and a triphenylamine group, and which are capable of undergoing co-thermal polycondensation with the aforementioned carbon nitride precursor. Suitable 1,3,5-triazine derivatives containing a triphenylamine group include, but are not limited to, 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine, and other derivatives having one or more triphenylamine groups or substituted triphenylamine groups attached to the 1,3,5-triazine ring, and retaining at least two reactive amino groups capable of co-condensation with the carbon nitride precursor. Furthermore, the benzene ring of the triphenylamine group may optionally contain one or more substituents that do not significantly affect its electron-donating properties, such as alkyl, alkoxy, aryl, halogen, etc., to meet the need for fine-tuning specific emission wavelengths.

[0011] Furthermore, the structural formula of the 1,3,5-triazine derivative containing the triphenylamine group is shown in formula (I):

[0012] (I).

[0013] As a specific embodiment of the present invention, the method for preparing the 1,3,5-triazine derivative containing a triphenylamine group includes the following steps: Under organic solvent and alkaline catalyst conditions, 4-(diphenylamino)benzonitrile and dicyandiamide were subjected to a cyclization condensation reaction to obtain the 1,3,5-triazine derivative containing a triphenylamine group as shown in formula (I). The synthetic route is as follows:

[0014] Furthermore, the organic solvent is n-butanol.

[0015] Furthermore, the alkaline catalyst is potassium hydroxide.

[0016] Furthermore, the molar ratio of 4-(diphenylamino)benzonitrile, dicyandiamide and the base catalyst is 1:(1.5~2.5):(1~3).

[0017] Furthermore, the cyclization condensation reaction is carried out at a temperature of 105℃~125℃ for 5h~10h.

[0018] Furthermore, the molar ratio of the carbon nitride precursor to the 1,3,5-triazine derivative containing a triphenylamine group is 10:1 to 20:1.

[0019] Furthermore, the temperature of the thermal polycondensation reaction is 400℃~500℃, and the reaction time is 1.5h~2.5h.

[0020] It should be noted that the above-mentioned 4-(diphenylamino)benzonitrile can be a commercially available product or prepared according to the above method: 4-(diphenylamino)benzaldehyde, concentrated ammonia, and elemental iodine were added to tetrahydrofuran and reacted at room temperature for 7-12 hours to yield 4-(diphenylamino)benzonitrile. The synthetic route is as follows:

[0021] As a specific embodiment of the present invention, the method for preparing triphenylamine-modified graphitic carbon nitride specifically includes the following steps: At least one carbon nitride precursor and at least one 1,3,5-triazine derivative containing a triphenylamine group were mixed and ground, and reacted at 400℃~500℃ for 1.5h~2.5h under an inert atmosphere to obtain triphenylamine-modified graphitic carbon nitride. The schematic diagram of the synthetic route is as follows:

[0022] During the reaction, melamine and triazine derivatives containing triphenylamine groups undergo intermolecular deamination condensation to jointly construct a graphitic carbon nitride network structure with an extended conjugated plane. This allows the triphenylamine groups to be covalently embedded in situ within the carbon nitride framework, fundamentally ensuring the material's luminescent properties and thermal stability. This synthetic route provides a reliable technical approach for the large-scale preparation of high-purity orange-yellow luminescent graphitic carbon nitride materials.

[0023] Secondly, the present invention also provides a triphenylamine-modified graphitic carbon nitride, which is prepared by the method described in any one of the above-mentioned methods for preparing triphenylamine-modified graphitic carbon nitride.

[0024] The triphenylamine-modified graphitic carbon nitride prepared by the above method achieves efficient, high-color-purity redshift emission from blue light to orange-yellow light, and also has excellent thermal and photochemical stability. It is a new type of orange-yellow light emitting material product that is different from existing graphitic carbon nitride materials, and provides a feasible path for the industrial application of new rare-earth-free, low-cost orange-yellow light LED materials.

[0025] Thirdly, the present invention also provides the application of the above-mentioned triphenylamine group-modified graphitic carbon nitride in the preparation of LED devices.

[0026] The triphenylamine-modified graphitic carbon nitride of this invention can be introduced into the device structure in the form of an orange-yellow light fluorescence conversion material through conventional LED packaging processes in the art. As a non-limiting example, this material can be dispersed in an encapsulation matrix such as epoxy resin or silicone, coated onto the surface of a blue LED chip or inside a reflective cavity, and cured to form a fluorescence conversion layer, thereby constituting an LED device. Furthermore, this material can also be used in conjunction with fluorescence conversion materials of other colors to obtain warm white light or lighting sources with specific color temperatures through spectral tuning, further expanding its application scenarios.

[0027] Fourthly, the present invention also provides an LED device in which the light-emitting layer comprises the aforementioned triphenylamine-modified graphitic carbon nitride.

[0028] Specifically, GaN-based blue light chips (λ) for commercial applications are selected. ex,max ≈ 460 nm, LE ≈ 25.00 lm·W -1 LED devices are fabricated using [a certain source] as the excitation source. The specific steps are as follows: The triphenylamine-modified graphitic carbon nitride was added to the epoxy resin and mixed evenly. The mixture was then coated into the reflective cavity of the GaN-based blue LED chip. The coating amount was controlled until it was basically flush with the cavity opening. The device was then placed in a vacuum drying oven for curing to obtain the LED device.

[0029] Specifically, the amount of triphenylamine-modified graphite phase carbon nitride added is 0.5% to 1.0% of the mass of epoxy resin.

[0030] Specifically, the curing temperature is 50℃~60℃, and the curing time is 2h~3h.

[0031] In summary, this invention provides a triphenylamine-modified graphitic carbon nitride, prepared by thermal polycondensation of at least one carbon nitride precursor and at least one 1,3,5-triazine derivative containing a triphenylamine group. This method precisely controls the band structure and photophysical processes at the molecular level by in-situ embedding the triphenylamine group into the conjugated network framework of graphitic carbon nitride. This effectively solves the technical bottlenecks of existing graphitic carbon nitride modification methods, such as limited redshift, low quantum efficiency, and poor color purity, achieving efficient and high-purity orange-yellow light emission. Furthermore, the resulting material exhibits excellent thermal and photochemical stability, meeting the long-term high-power operation requirements of LED devices. This invention successfully overcomes the application bottleneck of graphitic carbon nitride in orange-yellow light-emitting materials, providing a feasible path for the industrial application of novel rare-earth-free, low-cost LED materials, possessing significant economic value and broad application prospects. Attached Figure Description

[0032] Figure 1 The X-ray diffraction (XRD) pattern of g-C3N4-TPA-1-1 prepared in Example 1; Figure 2 g-C3N4-TPA-1-1 prepared in Example 3 13 C solid-state nuclear magnetic resonance (C) 13 CSSNMR resonance spectrum, with the inset showing a representative structural unit of g-C3N4-TPA; Figure 3 Comparison of photoluminescence emission spectra of g-C3N4-TPA-1-1, g-C3N4-TPA-1-2, g-C3N4-TPA-1-3, and g-C3N4-TPA-1-4 prepared with different raw material molar ratios in Example 1; Figure 4 Comparison of photoluminescence emission spectra of g-C3N4-TPA-2-1, g-C3N4-TPA-2-2, and g-C3N4-TPA-2-3 prepared at different reaction temperatures in Example 2; Figure 5 Comparison of photoluminescence emission spectra of g-C3N4-TPA-3-1, g-C3N4-TPA-3-2, and g-C3N4-TPA-3-3 prepared at different reaction times in Example 3; Figure 6 Thermogravimetric (TG) and differential thermogravimetric (DTG) diagrams of g-C3N4-TPA-1-1 prepared in Example 1 are shown. Figure 7 The graph shows the change in PL intensity at the maximum emission wavelength of g-C3N4-TPA-1-1 prepared in Example 1 as a function of temperature. Figure 8The emission spectrum of g-C3N4-TPA-1-1 prepared in Example 1 as a phosphor applied to LEDs; Figure 9 The CIE color coordinate diagram of g-C3N4-TPA-1-1 prepared in Example 1 as a phosphor applied to LEDs. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] To better illustrate the present invention, further examples are provided below.

[0035] The 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine used in the following examples was prepared by the following method: 4-(diphenylamino)benzaldehyde was dissolved in tetrahydrofuran (THF), and then 20-50 molar volumes of concentrated ammonia (25%-28%) and 1-2.5 molar ratio of iodine (I2) catalyst were added. The mixture was stirred at room temperature for 7-12 hours. After the reaction was completed, solid Na2S2O3 was added until the remaining dark brown I2 disappeared. The sample was washed and extracted with water and dichloromethane. The organic phases were collected and combined, and the solvent was removed by rotary evaporation. The residue was separated by silica gel column chromatography using petroleum ether and dichloromethane (volume ratio 5:1). The eluent was dried to give 4-(diphenylamino)benzonitrile, a white solid, with a yield of 89.0%.

[0036] 1 H NMR (400 MHz, CDCl3, ppm, δ ): 7.42 (d, 3 J = 8.88 Hz, 2H, ArH), 7.35-7.31 (m, 4H, ArH), 7.18-7.13 (m, 6H, ArH), 6.96 (d, 3 J = 8.92 Hz, 2H, ArH).

[0037] 4-(diphenylamino)benzonitrile (3.50 g, 15.4 mmol), dicyandiamide (1.56 g, 18.5 mmol), and potassium hydroxide (0.69 g, 12.3 mmol) were added to n-butanol (70 mL). The mixture was heated to reflux under an argon atmosphere and stirred for 7 h. After cooling to room temperature, the precipitate was collected and dried. Separation was then performed by silica gel column chromatography, eluting with dichloromethane and ethyl acetate (5:1 v / v) to give 2.63 g of 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine, a white solid, in a yield of 75.0%.

[0038] 1 H NMR (400 MHz, CDCl3, ppm, δ ): 8.18 (d, 3 J = 8.96 Hz, 2H, ArH), 7.31-7.27 (m, 4H, ArH), 7.15-7.08 (m, 6H, ArH), 7.05 (d, 3 J = 8.92 Hz, 2H, ArH ),5.41 (s, 4H, -NH2).

[0039]

[0040] The proportions of each material, as well as the reaction temperature and time, in the above methods can all be achieved using other conditions specified in this invention. Within the specified range, these conditions will not have a significant impact on the reaction and can all achieve comparable technical effects.

[0041] Example 1 This embodiment provides a method for preparing triphenylamine-modified graphitic carbon nitride, comprising the following steps: Weigh 0.4000g of melamine and 0.0749g of the 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine prepared above (molar ratio 15:1), grind them in an agate mortar for 30min, transfer them to a corundum crucible, seal the mouth of the corundum crucible with high temperature resistant and thermally conductive aluminum foil, and punch 4-5 small holes in the aluminum foil at the mouth of the crucible. Under a nitrogen atmosphere, perform a constant temperature thermal polymerization reaction at 450℃ for 2h to obtain triphenylamine group modified graphite phase carbon nitride, denoted as g-C3N4-TPA-1-1.

[0042] By replacing the molar ratio of melamine and 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine with 10:1, 20:1 and 5:1 respectively, g-C3N4-TPA-1-2, g-C3N4-TPA-1-3 and g-C3N4-TPA-1-4 were prepared.

[0043] The XRD pattern of g-C3N4-TPA-1-1 prepared in this embodiment is shown below. Figure 1 As shown in the figure, two characteristic diffraction peaks are observed at 13.2° and 27.7°, corresponding to the (100) and (002) crystal plane diffraction of graphitic carbon nitride, respectively. The diffraction peak at 13.2° is attributed to the porous structure resulting from the in-plane ordered arrangement of heptaazine ring structural units bridged by N atoms, reflecting the periodicity of the material's in-plane orientation. The diffraction peak at 27.7° is attributed to the interlayer gap structure formed by π-π stacking between two-dimensional sheets, reflecting the interlayer spacing characteristics of graphite-like layered stacking. This indicates that the introduction of triphenylamine groups did not disrupt the two-dimensional layered stacked framework structure of graphitic carbon nitride, and the resulting g-C3N4-TPA-1-1 still uses heptaazine rings as basic building blocks, maintaining the graphite-like two-dimensional stacked morphology.

[0044] The g-C3N4-TPA-1-1 prepared in this embodiment 13 C solid-state nuclear magnetic resonance (C) 13 (C SSNMR) diagram as shown Figure 2 As shown in the figure, the spectrum reveals two types of characteristic carbon signals. Two strong resonance signal peaks with chemical shifts of approximately 170–150 ppm are attributed to two non-equivalent carbon atoms on the graphitic carbon nitride heptaazine ring skeleton (corresponding to atoms a and b in the inset structural formula). Simultaneously, two new resonance signal sets appear in the aromatic carbon characteristic region: one signal peak at approximately 148.5 ppm corresponds to the aromatic carbon atom directly bonded to the nitrogen atom in the triphenylamine group (corresponding to atom c in the inset structural formula); the other signal peak in the 115.1–135.0 ppm range corresponds to the remaining aromatic carbon atoms in the triphenylamine group (corresponding to atom d in the inset structural formula). The presence of the characteristic carbon signal of the triphenylamine group, and its coexistence with the carbon signal of the heptaazine ring skeleton in the same spectrum, proves that during the co-thermal polycondensation process, the 1,3,5-triazine derivative containing the triphenylamine group has copolymerized with the carbon nitride precursor through covalent bonds. The triphenylamine group has been successfully incorporated into the heptaazine ring conjugated network of graphitic carbon nitride, rather than existing in the form of physical adsorption or simple mixing.

[0045] To investigate the effect of raw material ratio on the luminescence properties of the product, a series of samples g-C3N4-TPA-1-1 to g-C3N4-TPA-1-4 were prepared under different molar ratios. Their photoluminescence emission spectra are shown below. Figure 3 As shown in the figure, the emission wavelengths of the four samples are mainly located in the range of 500-710 nm, all exhibiting a broad-spectrum emission characteristic with a significant redshift. Among them, the g-C3N4-TPA-1-1 sample has the highest luminescence intensity, with a maximum emission wavelength of 596 nm, which is 145 nm redshifted compared to the bulk g-C3N4, falling into the typical orange-yellow light region. This indicates that the covalent intercalation of the triphenylamine group successfully achieved the emission band transition from blue light to orange-yellow light. The photoluminescence quantum yield (PLQY) of this sample reaches 25.3%, and the average fluorescence lifetime is 2.85 ns. This nanosecond-level short fluorescence lifetime characteristic indicates that the radiative recombination process in g-C3N4-TPA is fast and efficient, and non-radiative energy loss is effectively suppressed. This characteristic makes it highly suitable for everyday light-emitting devices (such as LED lighting and display devices) that require fast response and high luminous efficiency.

[0046] The photoluminescent quantum yields (PLQY) of the g-C3N4-TPA-1-2, g-C3N4-TPA-1-3, and g-C3N4-TPA-1-4 samples were 24.5%, 23.2%, and 14.5%, respectively.

[0047] Example 2 This embodiment provides a method for preparing triphenylamine-modified graphitic carbon nitride, comprising the following steps: Weigh 0.4000g of melamine and 0.0749g of the 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine prepared above (molar ratio 15:1), grind them in an agate mortar for 30min, transfer them to a corundum crucible, seal the mouth of the corundum crucible with high temperature resistant and thermally conductive aluminum foil, and punch 4-5 small holes in the aluminum foil at the mouth of the crucible. Under a nitrogen atmosphere, perform a constant temperature thermal polymerization reaction at 400℃ for 2h to obtain triphenylamine group modified graphite phase carbon nitride, denoted as g-C3N4-TPA-2-1.

[0048] By replacing the temperature of the above thermal polymerization reaction with 500℃ and 550℃ respectively, g-C3N4-TPA-2-2 and g-C3N4-TPA-2-3 were prepared accordingly.

[0049] The photoluminescence emission spectra of the three samples prepared in this embodiment are as follows: Figure 4As shown in the figure, the maximum emission wavelengths of g-C3N4-TPA-2-1, C3N4-TPA-2-2, and g-C3N4-TPA-2-3 are 586nm, 604nm, and 611nm, respectively, with corresponding PLQY values ​​of 21.0%, 15.4%, and 7.3%.

[0050] Example 3 This embodiment provides a method for preparing triphenylamine-modified graphitic carbon nitride, comprising the following steps: Weigh 0.4000g of melamine and 0.0749g of the 6-(4-(diphenylamino)phenyl)-1,3,5-triazine-2,4-diamine prepared above (molar ratio 15:1), grind them in an agate mortar for 30min, transfer them to a corundum crucible, seal the mouth of the corundum crucible with high temperature resistant and thermally conductive aluminum foil, and punch 4-5 small holes in the aluminum foil at the mouth of the crucible. Under a nitrogen atmosphere, perform a constant temperature thermal polymerization reaction at 400℃ for 1.5h to obtain triphenylamine group modified graphite phase carbon nitride, denoted as g-C3N4-TPA-3-1.

[0051] By replacing the above thermal polymerization reaction time with 2.5 h and 3 h respectively, g-C3N4-TPA-3-2 and g-C3N4-TPA-3-3 were prepared accordingly.

[0052] The photoluminescence emission spectra of the three samples prepared in this embodiment are as follows: Figure 5 As shown in the figure, the maximum emission wavelengths of g-C3N4-TPA-3-1, C3N4-TPA-3-2, and g-C3N4-TPA-3-3 are 591nm, 600nm, and 605nm, respectively, with corresponding PLQY values ​​of 21.5%, 23.1%, and 20.7%. With the extension of the polymerization reaction time, the emission wavelength of g-C3N4-TPA-3-3 exhibits a red shift, the emission color changes from orange-yellow to orange-red, and the PLQY decreases.

[0053] Thermal stability test Figure 6The TG and DTG curves of g-C3N4-TPA-1-1 prepared in Example 1, heated from 30℃ to 800℃, are shown in the figure. As can be seen from the figure, the entire thermogravimetric process of the sample can be divided into three main stages. The first stage occurs from 30 to 482℃, with a weight loss rate of approximately 9.5%. This stage of weight loss is mainly attributed to the removal of physically adsorbed water on the material surface and the volatilization of small molecules adsorbed in the internal interlayer or pores, which is a physical desorption process. The second stage occurs from 482 to 590℃, with a weight loss rate of approximately 14.5%. This stage of weight loss mainly corresponds to the thermal decomposition of the triphenylamine group. Since the triphenylamine group is covalently anchored in the carbon nitride conjugated skeleton, its thermal decomposition temperature is significantly higher than that of the free triphenylamine small molecule, reflecting the enhancing effect of covalent intercalation on the thermal stability of the functional group. The third stage occurs after 590℃. This stage of weight loss is mainly attributed to the thermal oxidative decomposition of the heptaazine ring skeleton and its derivatives, marking the gradual destruction of the main structure of the material.

[0054] The above analysis shows that g-C3N4-TPA-1-1 only undergoes surface adsorbate desorption and side group decomposition below 590℃, while the main framework remains intact. Therefore, 590℃ can be considered the thermal decomposition temperature (T0) of this material. d This thermal decomposition temperature is much higher than the lower limit of the temperature required for the phosphor conversion material in LED devices (typically requiring T). d The temperature exceeds 150℃, which fully demonstrates that g-C3N4-TPA-1-1 has excellent thermal stability and can fully withstand the heat load generated by LED devices under high power and long-term operation conditions, meeting the stringent requirements of material reliability in practical applications.

[0055] Thermal quenching performance test To evaluate the luminescence stability of g-C3N4-TPA-1-1 under thermal stress conditions, variable-temperature photoluminescence spectroscopy was performed on the sample obtained in Example 3. The test method was as follows: g-C3N4-TPA-1-1 powder was uniformly spread on the surface of a heating stage, and the temperature was gradually increased at a rate of 10℃ / min within the range of 30~210℃. The photoluminescence emission spectra at each temperature point were collected simultaneously, and then the sample was allowed to cool naturally and the spectral recovery was detected. Figure 7 The curves show the variation of the PL integrated intensity of the sample at the maximum emission wavelength at various test temperatures.

[0056] like Figure 7As shown, with the PL emission intensity at 30℃ as the baseline (100%), the relative luminous intensities of the sample at other temperature points are as follows: 98.8% (50℃), 93.8% (70℃), 92.7% (90℃), 91.2% (110℃), 90.0% (130℃), 88.5% (150℃), 88.2% (170℃), 87.6% (190℃), and 85.5% (210℃). These data show that the intensity loss of this material at 110℃ is less than 8.8%, and even at 150℃ (a typical high-temperature reference point for the harsh operating conditions of LED devices), its intensity loss is only 11.5%, exhibiting a low luminous intensity decay. This indicates that g-C3N4-TPA-1-1 has significantly better thermal quenching suppression capabilities than many traditional LED phosphors.

[0057] More importantly, when the sample was cooled from 210℃ to 30℃, its PL emission spectrum and intensity almost completely recovered to the initial level (recovery rate close to 100%). This indicates that within the stated temperature range, g-C3N4-TPA-1-1 did not undergo irreversible structural damage or chemical changes. The decrease in its luminescence intensity was purely due to enhanced thermally activated nonradiative transitions, and it recovered instantly once the thermal stress was relieved. This excellent thermally reversible luminescence characteristic fully demonstrates that g-C3N4-TPA-1-1 can maintain stable orange-yellow light output during long-term operation of high-temperature, high-power LED devices, fully meeting the stringent requirements of practical applications for the thermal quenching resistance of fluorescent conversion materials.

[0058] Application Examples of g-C3N4-TPA-based LEDs To verify the application effect of g-C3N4-TPA-1-1 prepared in Example 1 of this invention as an orange-yellow light fluorescence conversion material in actual LED devices, g-C3N4-TPA-based LED devices were prepared by doping it with epoxy resin encapsulant at different mass concentrations, and the photoelectric performance of the devices was systematically evaluated.

[0059] Device fabrication: Commercially available GaN-based blue LED chips were selected as the excitation source. Their main technical parameters are: peak emission wavelength λex,max ≈ 460 nm, luminous efficiency LE ≈ 25.00 lm·W. -1The g-C3N4-TPA-1-1 powder prepared in Example 1 was used as a phosphor and doped into epoxy resin at different mass concentrations. After thorough stirring and vacuum degassing, the powder was coated into the reflective cavity of a blue LED chip. The coating amount was controlled until the surface of the colloid was flush with the cavity opening. After coating, the device was placed in a vacuum drying oven and cured at 50°C for 2 hours to obtain the g-C3N4-TPA-based LED device. The phosphor doping concentrations for each example and comparative example are as follows: Application Example 1: The doping concentration of g-C3N4-TPA-1-1 is 0.5%; Application Example 2: The doping concentration of g-C3N4-TPA-1-1 is 0.75%; Application Example 3: The doping concentration of g-C3N4-TPA-1-1 is 1.00%; Comparative Example 1: g-C3N4-TPA-1-1 has a doping concentration of 0.25%; Comparative Example 2: g-C3N4-TPA-1-1 has a doping mass concentration of 1.25%.

[0060] The luminescence performance of each device was tested using a spectral analysis system (Hangzhou Yuanfang Optoelectronic Information Co., Ltd., PMS-50 model). All devices were driven under a forward voltage of 3.0V and a forward current of 20mA, and light signals were collected using an integrating sphere to obtain key performance parameters such as the electroluminescence spectrum, color coordinates, color rendering index (CRI), luminous efficacy (LE), and correlated color temperature (CCT). The electroluminescence emission spectra of each device are shown below. Figure 8 As shown, CIE color coordinates are as follows Figure 9 As shown in Table 1, the maximum emission wavelength of the GaN-based blue LED chip is 461 nm, while that of the g-C3N4-TPA-based LED device is 571 nm. The performance test results for each device are shown in Table 1.

[0061] Table 1

[0062] As can be seen from the above data, with the gradual increase of the doping concentration of g-C3N4-TPA-1-1, the emission color of the device exhibits a systematic shift from a cool tone to a warm tone. Under low doping concentration (Comparative Example 1, 0.25%), the transmitted light ratio of the blue chip is relatively high, causing the CIE color coordinates to fall into the cool white region (0.22, 0.18), the CCT to be as high as 100,000 K, the overall light color to be bluish, and the color rendering index to be low. As the doping concentration increases to 0.75% (Application Example 2), the orange-yellow light conversion becomes more complete, the device's CIE color coordinates reach (0.33, 0.32), which is very close to the standard white light color coordinates (0.3333, 0.3333), the CCT drops to 5490 K, and the color rendering index and luminous efficiency also remain at a high level. When the doping concentration was further increased to 1.25% (Comparative Example 2), although the orange-yellow light emission was further enhanced, the luminous efficiency decreased due to the concentration quenching effect and excessive absorption, and the CCT was too low, resulting in a warmer light color.

[0063] A comprehensive comparison shows that Application Example 2 achieves the best balance among various performance indicators, with a CRI of 77.5 and an LE of 46.71 mW. -1 With a CCT of 5490K and CIE color coordinates (0.33, 0.32) that almost coincide with the standard white light coordinates, it exhibits the most ideal comprehensive optoelectronic performance, fully demonstrating the practical application value of g-C3N4-TPA-1-1 as an orange-yellow light fluorescence conversion material in LED devices.

[0064] g-C3N4-TPA-1-2, g-C3N4-TPA-1-3, g-C3N4-TPA-2-1, C3N4-TPA-2-2, g-C3N4-TPA-3-1, and C3N4-TPA-3-2, when applied to g-C3N4-TPA-based LED devices, can achieve technical effects essentially equivalent to those of g-C3N4-TPA-1-1.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing triphenylamine-modified graphitic carbon nitride, characterized in that, At least one carbon nitride precursor and at least one 1,3,5-triazine derivative containing a triphenylamine group are subjected to thermal polycondensation to obtain triphenylamine-modified graphitic carbon nitride.

2. The method for preparing triphenylamine-modified graphitic carbon nitride as described in claim 1, characterized in that, The structural formula of the 1,3,5-triazine derivative containing the triphenylamine group is shown in Formula (I): （Ⅰ）。 3. The method for preparing triphenylamine-modified graphitic carbon nitride as described in claim 2, characterized in that, The method for preparing the 1,3,5-triazine derivative containing a triphenylamine group includes the following steps: Under organic solvent and alkaline catalyst conditions, 4-(diphenylamino)benzonitrile and dicyandiamide were subjected to a cyclization condensation reaction to obtain a 1,3,5-triazine derivative containing a triphenylamine group as shown in formula (Ⅰ).

4. The method for preparing triphenylamine-modified graphitic carbon nitride as described in claim 3, characterized in that, The organic solvent is n-butanol; and / or The alkaline catalyst is potassium hydroxide; and / or The molar ratio of 4-(diphenylamino)benzonitrile, dicyandiamide, and the base catalyst is 1:(1.5~2.5):(1~3); and / or The cyclization condensation reaction is carried out at a temperature of 105℃~125℃ for 5h~10h.

5. The method for preparing triphenylamine-modified graphitic carbon nitride as described in claim 1, characterized in that, The carbon nitride precursor is melamine.

6. The method for preparing triphenylamine-modified graphitic carbon nitride as described in claim 1, characterized in that, The molar ratio of the carbon nitride precursor to the 1,3,5-triazine derivative containing a triphenylamine group is 10:1 to 20:1; and / or The temperature of the thermal polycondensation reaction is 400℃~500℃, and the reaction time is 1.5h~2.5h.

7. The method for preparing triphenylamine-modified graphitic carbon nitride according to any one of claims 1 to 6, characterized in that, Specifically, the steps include the following: At least one carbon nitride precursor and at least one 1,3,5-triazine derivative containing a triphenylamine group are mixed and ground, and reacted at 400℃~500℃ for 1.5h~2.5h under an inert atmosphere to obtain triphenylamine group modified graphitic carbon nitride.

8. A triphenylamine-modified graphitic carbon nitride, characterized in that, It is prepared by the method for preparing triphenylamine-modified graphitic carbon nitride according to any one of claims 1 to 7.

9. The application of the triphenylamine group-modified graphitic carbon nitride according to claim 8 in the preparation of LED devices.

10. An LED device, characterized in that, Its luminescent layer comprises triphenylamine-modified graphitic carbon nitride as described in claim 8.

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