Carbon fiber-carbon quantum dot composite material based on surface modification and chemical crosslinking as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a carbon fiber-iodine doped carbon quantum dot composite material based on surface modification and chemical crosslinking, and belongs to the technical field of nano composite materials. The material is prepared by carrying out surface treatment on carbon fibers to introduce functional groups, carrying out iodine doping on carbon quantum dots, and directionally connecting complementary functional groups of the carbon fibers and the carbon quantum dots by adopting a bifunctional crosslinking agent (such as 1-ethyl-3-(3-dimethyl propyl) carbodiimide (EDC) / N-hydroxysuccinimide (NHS), glutaraldehyde, hexamethylene diisocyanate and toluene diisocyanate). A stable composite interface is formed through covalent bonds. According to the method, the high CT contrast ratio of the iodine-doped carbon quantum dots is utilized, and in the using process of the carbon fiber, damage and defects in the carbon fiber structure can be detected through a CT imaging method.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanocomposite materials, and specifically relates to a composite material comprising carbon fibers (CF) and iodine-doped carbon quantum dots (I-CQDs) connected by surface modification and a chemical crosslinking agent, and a preparation method thereof, for improving the CT imaging contrast of the carbon fibers. Background Art

[0002] Carbon fiber, due to its exceptional strength-to-weight ratio, high modulus, and lightweight properties, has been widely used in aerospace, wind turbine blades, and automotive lightweighting. However, in practical applications, carbon fiber is susceptible to microscopic damage caused by fatigue, impact, porosity, and fiber misalignment. These microscopic damages are highly concealed and difficult to detect early. These microscopic damages can lead to gradual degradation of the carbon fiber's structural properties or even sudden failure, seriously threatening engineering safety. The mechanisms underlying these microscopic damages remain unclear, and exploring these mechanisms has become a key focus of carbon fiber development. Currently, the main methods used for carbon fiber damage detection have limitations. For example, ultrasonic testing (UT) requires a contact probe, which is poorly suited for complex components and lacks real-time monitoring capabilities. Acoustic emission technology can only capture dynamic signals as damage occurs and cannot locate static defects. These methods suffer from insufficient sensitivity, poor real-time performance, and strong equipment dependence, making them difficult to meet the requirements for carbon fiber damage monitoring in practical applications. Industrial CT, as a core non-destructive testing method, is facing a critical bottleneck. The difference in X-ray absorption rate between carbon fiber and resin matrix is ​​extremely low, resulting in insufficient CT imaging contrast and a minor damage missed detection rate of >35%. Therefore, improving the contrast of carbon fiber has become the key.

[0003] As a novel nanomaterial, carbon quantum dots (CQDs) offer high nanoscale spatial resolution. CQDs with a particle size of 2-10 nm can penetrate microcracks or interfacial debonding areas in carbon fiber composites. Furthermore, an iodine source can be added during the synthesis process, enabling the loading of iodine without affecting the carbon fiber's properties, thereby enhancing CT imaging contrast and facilitating carbon fiber damage detection. However, existing techniques for combining carbon fibers with CQDs often employ physical coating or blending. For example, Chen Yifeng et al. reported in the Chemical Engineering Journal (2023) that CQDs were loaded onto carbon fiber surfaces using electrospinning. These physical bonding methods suffer from weak interfacial bonding, are prone to failure, and cannot stably localize damage. Therefore, by leveraging the multifunctional surface modification of CQDs—the CQDs surface can chemically bond to carbon fibers through functional groups such as amino (-NH2) and carboxyl (-COOH) groups—we can achieve high-contrast CT imaging of carbon fibers under stable chemical bonding conditions. Summary of the Invention

[0004] The present invention proposes a carbon fiber-iodine-doped carbon quantum dot composite material that can be used to improve CT imaging contrast. Surface modification and chemical cross-linking are used to achieve covalent bonding between the carbon fiber and the iodine-doped carbon quantum dots. The high CT performance of iodine and the nano-properties of carbon quantum dots are utilized to identify damage to the carbon fiber material and assist in analyzing the causes of damage.

[0005] The specific steps include:

[0006] Step 1: Carboxyl (-COOH) / amino (-NH2) / hydroxyl (-OH) functionalization modification is performed on the CF surface.

[0007] In step 2, I-CQDs were synthesized by a hydrothermal method using citric acid (CA), ethylenediamine (EDA), and potassium iodide (KI) as raw materials.

[0008] Step 3: Add the I-CQDs prepared in step 2 into deionized water or an organic solvent for ultrasonic dispersion.

[0009] In step 4, the modified CF in step 1 is immersed in the dispersion obtained in step 3, a chemical crosslinking agent is added, the reaction conditions are adjusted, and the reaction is promoted by stirring or ultrasound.

[0010] Step 5: After washing the CF after the reaction in step 4, vacuum drying for a period of time is performed to obtain the CF with the surface modified by I-CQDs.

[0011] Preferably, the method for introducing carboxyl groups (-COOH) in step 1 is to immerse the substrate in concentrated HNO3 / H2SO4 with a volume ratio of 1:3 to 3:1, at a reaction temperature of 50-90°C for 1-5 hours. The method for introducing amino groups (-NH2) is to treat the substrate in an Ar / NH3 mixed atmosphere at 200-400W for 5-30 minutes. The method for introducing hydroxyl groups (-OH) is to immerse the substrate in a 10% NaOH solution at 60-80°C for 1-2 hours.

[0012] Preferably, in step 2, the molar ratio of CA to EDA is 1:1 to 1:2, the molar ratio of KI to CA is 0.1:1 to 1:1, the solvent is deionized water, the pH is 8 to 9, the reaction temperature is 160 to 200° C., and the reaction time is 4 to 8 hours.

[0013] Preferably, the pH of the dispersion in step 3 is neutral and the concentration is 0.1-10 mg / mL.

[0014] Preferably, the cross-linking agent used in step 4 is one or a combination of 1-ethyl-3-(3-dimethylpropyl)carbodiimide (EDC) / N-hydroxysuccinimide (NHS), glutaraldehyde, hexamethylene diisocyanate (HDI), and toluene diisocyanate (TDI).

[0015] Preferably, the vacuum drying temperature in step 5 is 40-80° C. and the time is 2-12 h.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] (1) The present invention improves the CT imaging effect of CF by combining the high CT contrast characteristics of I-CQDs on CF.

[0018] (2) By adopting the present invention, an iodine source is added during the synthesis of CQDs, thereby enriching the functions of CQDs.

[0019] (3) According to the present invention, chemical cross-linking agents are used to connect CF and CQDs, and the covalent bonding has higher bonding strength and bonding stability.

[0020] (4) By adopting the present invention, chemical cross-linking enhances the interface bonding between CF and CQDs, avoiding the performance loss caused by traditional physical mixing. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below with reference to the embodiments.

[0022] Example 1

[0023] Step 1: Take 5 cm long polyacrylonitrile-based carbon fiber T300, immerse it in acetone and ultrasonically clean it for 20 minutes, repeat the cleaning three times to obtain carbon fiber with the surface coating removed.

[0024] Step 2: Take 15 mL of concentrated sulfuric acid and slowly add it into 5 mL of concentrated nitric acid to obtain a mixed solution.

[0025] Step 3: Immerse the CF obtained in step 1 in the strong acid mixture obtained in step 2 and heat at 70° C. for 3 h to obtain a CF with carboxyl groups (-COOH) introduced on the surface.

[0026] Step 4: Using 2 g of citric acid, 1 mL of ethylenediamine, and 0.2 g of potassium iodide as raw materials, hydrothermal reaction was performed at 200 °C for 6 h to obtain I-CQDs.

[0027] Step 5: The I-CQDs obtained in step 4 were dispersed in PBS buffer with a pH of 6.5 and a concentration of 2 mg / mL.

[0028] In step 6, the CF obtained in step 3 was immersed in the dispersion obtained in step 5, 5 mg / mL of EDC and 2.5 mg / mL of NHS were added, and the mixture was stirred at 37°C for 8 h to obtain a CF with a surface modified by I-CQDs.

[0029] In step 7, the CF with the surface modified with I-CQDs in step 6 was washed three times with PBS and dried in a vacuum drying oven at 60°C for 4 h.

[0030] Example 2

[0031] Step 1: Take a 5 cm long polyacrylonitrile-based carbon fiber T300, place it in an atmosphere with an NH3 / Ar volume ratio of 1:4, and treat it with 200-400W plasma for 15 minutes to obtain CF with amino groups (-NH2) introduced on the surface.

[0032] Step 2 is the same as step 4 in Example 1 to obtain I-CQDs.

[0033] Step 3: Disperse the I-CQDs prepared in step 2 in deionized water at a concentration of 1.5 mg / mL.

[0034] In step 4, the CF obtained in step 1 was immersed in the dispersion obtained in step 3, 5% glutaraldehyde (v / v) was added, the pH was 7.5, and the mixture was shaken at room temperature for 4 h to obtain a CF with a surface modified by I-CQDs.

[0035] Step 5: The CF with the surface modified by I-CQDs in step 4 was washed with ethanol three times and dried in a vacuum drying oven at 40°C for 4 h.

[0036] Example 3

[0037] Step 1: Take 5 cm long polyacrylonitrile-based carbon fiber T300, immerse it in 10% NaOH solution, and treat it at 80° C. for 2 h to obtain CF with hydroxyl groups (-OH) introduced on the surface.

[0038] Step 2 is the same as step 4 in Example 1 to obtain I-CQDs.

[0039] Step 3: The I-CQDs prepared in step 2 were dispersed in anhydrous tetrahydrofuran (THF) at a concentration of 4 mg / mL.

[0040] In step 4, the CF obtained in step 1 was immersed in the dispersion obtained in step 3, 3% HDI (v / v) was added, and the mixture was reacted at 60° C. under nitrogen protection for 8 h to obtain a CF with a surface modified by I-CQDs.

[0041] Step 5: The CF with I-CQDs surface modified in step 4 was washed with THF three times and dried under vacuum at 80 °C for 12 h.

[0042] Comparative Example 1

[0043] This comparative example is substantially the same as Example 1, except that step 3 is not performed.

[0044] The results show that the CF with the surface modified by I-CQDs prepared in this comparative example has a lower I-CQDs loading and a poor CT imaging effect compared with that prepared in Example 1.

[0045] Comparative Example 2

[0046] This comparative example is basically the same as Example 1, except that the EDC / NHS cross-linking agent is not added in step 6.

[0047] The results show that the I-CQDs loading on the CF with the surface modified by I-CQDs prepared in this comparative example is low, and the carbon quantum dots are easy to fall off and have poor stability compared with the one prepared in Example 1.

[0048] Comparative Example 3

[0049] This comparative example is substantially the same as Example 1, except that vacuum drying is not performed in step 7.

[0050] The results show that the mechanical strength of the CF with the surface modified by I-CQDs prepared in this comparative example decreases, the defects increase, the long-term storage stability decreases compared with the one prepared in Example 1, and the material life is shortened.

Claims

1. A method for improving CT imaging contrast of carbon fibers by surface modification of carbon fibers with iodine-doped carbon quantum dots, characterized in that: The following steps are involved: In step 1, the carbon fiber (CF) surface is chemically modified to introduce different functional groups. Step 2: Add an iodine source to the carbon source and nitrogen source as raw materials, and synthesize iodine-doped carbon quantum dots (I-CQDs) by hydrothermal method. Step 3: Disperse the I-CQDs obtained in step 2 in a buffer solution, and adjust the pH and the concentration of the I-CQDs. In step 4, the CF prepared in step 1 is immersed in the I-CQDs dispersion prepared in step 3, and a bifunctional crosslinking agent is added to carry out a crosslinking reaction. In step 5, the obtained product was washed and dried under vacuum to obtain a stable CF with surface modified by I-CQDs.

2. The CF with chemically modified surface as claimed in claim 1, characterized in that: The introduced functional group is at least one of a carboxyl group (-COOH), a hydroxyl group (-OH), and an amino group (-NH2).

3. The hydrothermal method according to claim 1, wherein: The molar ratio of the carbon source to the nitrogen source is 1:1 to 1:2, the molar ratio of the iodine source to the carbon source is 0.1:1 to 1:1, and the iodine source is one of potassium iodide (KI), sodium iodide (NaI), or seaweed extract. The solvent is deionized water, the pH is 8 to 9, the reaction temperature is 160 to 220°C, and the reaction time is 4 to 12 hours.

4. The I-CQDs dispersion according to claim 1, characterized in that , pH is neutral, and the concentration of I-CQDs is 0.1~10mg / mL.

5. The bifunctional crosslinking agent according to claim 1, wherein According to the different functional groups introduced on CF, it is one or a combination of 1-ethyl-3-(3-dimethylpropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS), glutaraldehyde, toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI).

6. The cross-linking reaction according to claim 1, wherein The reaction temperature is 20-60°C, and the reaction time is 4-12 hours.

7. The vacuum drying according to claim 1, wherein The temperature is 40-80℃ and the time is 2-12h.

8. The carbon fiber with surface modified by I-CQDs prepared by the method according to any one of claims 1 to 8, characterized in that: The iodine doping amount of the iodine-doped carbon quantum dots is 5-20 wt %, and the particle size is 2-10 nm; the I-CQDs coverage rate on the modified carbon fiber surface is 20% to 80%; Its CT value under X-ray energy of 80-140 kVp is increased by 30% to 90% compared with unmodified carbon fiber.

9. A method for improving the contrast of carbon fiber CT imaging, characterized in that: After the carbon fiber whose surface is modified with I-CQDs as described in claim 8 is compounded with a resin matrix, the type and density of its internal defects can be analyzed by CT imaging.