Preparation method of novel synthetic silicon dioxide microrod

Abstract

The invention relates to the technical field of silicon microrods, in particular to a preparation method of a novel synthetic silicon dioxide microrod. According to the technical scheme, the preparation method of the novel synthetic silicon dioxide microrod comprises the following steps: step 1, carrying out surface modification on a carbon nanotube template to enable the surface of the carbon nanotube template to be rich in oxygen-containing functional groups; 2, dispersing the surface-modified carbon nanotube template in a solution containing a surfactant and a silicon source, and carrying out a coating reaction of a silicon dioxide layer to form a core-shell structure; and step 3, removing the internal carbon nanotube template through calcination to obtain a silicon dioxide microrod, and carrying out enhanced ultrasonic acidizing treatment on the carbon nanotube at 80 DEG C for 2 hours by adopting a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a specific volume ratio, so that the density and the distribution uniformity of carboxyl and hydroxyl functional groups on the surface of the carbon nanotube are remarkably improved, and the carbon nanotube is prepared. And the problems of coating layer defects and surface roughness caused by insufficient surface modification in the traditional method are effectively overcome.

Description

Technical Field

[0001] This invention relates to the field of silicon microrod technology, and in particular to a novel method for preparing synthetic silicon dioxide microrods. Background Technology

[0002] Silica microrods are artificially synthesized silica materials with specific rod-shaped microstructures. They are used to load drug molecules, such as anticancer drugs, antibiotics, and nucleic acids. Their rod-shaped structure enables controlled release, prolongs drug circulation time, and improves targeting. Compared with spherical particles, rod-shaped structures may have longer circulation times and different biodistributions in vivo. Conventional carbon nanotube surface acidification treatment is insufficient, resulting in low density and uneven distribution of active functional groups such as carboxyl and hydroxyl groups introduced on the surface. This makes it difficult for subsequent silicon source precursors (such as TEOS) to be uniformly adsorbed and nucleated, resulting in an incomplete silica coating layer and a rough surface. Secondly, the silica coating process relies on a single surfactant system (such as CTAB) and lacks precise control over key reaction parameters (such as template concentration, silicon source dosage, and reaction time), resulting in poor control over the thickness of the silica shell. The final product has a wide diameter distribution and low batch-to-batch repeatability. Finally, in the template removal stage, a one-step rapid heating to high temperature (such as 550°C) calcination method is used. The intense thermal stress makes the silica shell, especially the weak points with uneven coating, prone to shrinkage, deformation, sintering, and even collapse. At the same time, it may also lead to internal carbon template residue, which seriously affects the structural integrity, purity, and mechanical properties of the final product. Summary of the Invention

[0003] To overcome the problem of insufficient and uneven surface modification of traditional carbon nanotube templates, which directly weakens the effective interaction between them and the silicon source, the thickness and uniformity of the silica coating layer are difficult to control precisely. The non-uniformity of the coating layer becomes a stress concentration point in the subsequent high-temperature processing, which means that the silica microrod structure is prone to damage and deformation during the template removal stage.

[0004] The technical solution of this invention is: a novel method for preparing synthetic silica microrods, comprising the following steps: Step 1: Surface modification of the carbon nanotube template to enrich its surface with oxygen-containing functional groups; Step 2: The surface-modified carbon nanotube template is dispersed in a solution containing surfactant and silicon source to carry out a silica layer encapsulation reaction, forming a core-shell structure; Step 3: Remove the internal carbon nanotube template by calcination to obtain silica microrods.

[0005] Preferably, in step one, the surface modification is performed by acidifying the carbon nanotubes with a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid; wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, the acidification temperature is 80°C, the treatment time is 2 hours, and ultrasound is applied during the treatment.

[0006] Preferably, in step two, the surfactant is a composite surfactant system composed of hexadecyltrimethylammonium bromide and polyvinylpyrrolidone.

[0007] Preferably, in step two, the silicon source is tetraethyl orthosilicate, the pH of the reaction system is adjusted to 9.5 with ammonia, the reaction temperature is 25°C, and the reaction time is 4 hours.

[0008] Preferably, in step two, the concentration of the carbon nanotube template in the reaction system is 0.5 mg / mL, and the amount of tetraethyl orthosilicate added is 1.5 mL.

[0009] Preferably, in step three, the calcination is a two-step calcination method, specifically: in an air atmosphere, the temperature is first raised to 300°C at a heating rate of 2°C / min and held for 1 hour, and then raised to 550°C at a heating rate of 5°C / min and held for 2 hours.

[0010] A novel synthetic silica microrod, comprising the preparation method of the novel synthetic silica microrod as described above: the silica microrod has a solid or hollow structure, with a diameter of 50–200 nm and a length of 1–5 μm.

[0011] Preferably, the silica microrods have a smooth surface, uniform diameter distribution, and no carbon template residue inside.

[0012] Preferably, silica microrods are used in the preparation of drug delivery carriers, catalyst carriers, or composite material reinforcing phases.

[0013] The beneficial effects of this invention are: A mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a specific volume ratio was used to subject carbon nanotubes to enhanced ultrasonic acidification treatment at 80°C for up to 2 hours. This significantly improved the density and uniformity of the carboxyl and hydroxyl functional groups on the surface of the nanotubes. This provided sufficient and uniform active sites for the uniform adsorption and nucleation of the silicon source, ensuring the integrity and smoothness of the silica coating layer from the source. This effectively overcame the coating layer defects and surface roughness problems caused by insufficient surface modification in traditional methods. A composite surfactant system composed of CTAB and PVP was adopted. CTAB guided the initial nucleation through electrostatic interaction, while the long molecular chain of PVP further stabilized the reaction system and inhibited the excessive growth and aggregation of silica particles through steric hindrance. Combined with the precise optimization and control of key reaction parameters, the thickness of the silica shell was precisely "tailored", thereby preparing silica microrods with a narrow diameter distribution range and high batch-to-batch repeatability. The two-step calcination method with programmed temperature control is a key breakthrough. The gentle heating process allows the silica network to undergo sufficient structural relaxation and condensation before the carbon template is oxidized and removed, which greatly alleviates the risk of structural shrinkage, deformation or collapse caused by thermal stress concentration. This process can not only completely remove the carbon template, but also make the final solid or hollow silica microrods have higher mechanical strength and structural stability, laying the foundation for their application in harsh environments. Detailed Implementation

[0014] The following embodiments further illustrate the present invention.

[0015] Example 1; A novel method for preparing synthetic silica microrods, comprising the following steps: Step 1: Surface modification of the carbon nanotube template to enrich its surface with oxygen-containing functional groups; Step 2: The surface-modified carbon nanotube template is dispersed in a solution containing surfactant and silicon source to carry out a silica layer encapsulation reaction, forming a core-shell structure; Step 3: Remove the internal carbon nanotube template by calcination to obtain silica microrods.

[0016] When working, the surface of the carbon nanotube template is first modified. 300mg of multi-walled carbon nanotubes (purity 95%, diameter 25nm) are placed in a 500ml three-necked flask. A reflux condenser and a KQ-300DE type CNC ultrasonic cleaner are used to provide ultrasonic assistance. Add 450 ml of a mixed acid solution of concentrated sulfuric acid (analytical grade, 98%) and concentrated nitric acid (analytical grade, 68%) in a volume ratio of 3:1, and reflux in a constant temperature water bath at 70℃ for 90 minutes. After the reaction is complete, wash repeatedly with deionized water 5 times until the filtrate is neutral. After vacuum filtration, dry in a vacuum drying oven at 60℃ for 10 hours to obtain a surface-modified carbon nanotube template. Next, controllable encapsulation of the silicon layer was performed. 80 mg of the carbon nanotube template treated above was dispersed in 150 ml of an ethanol-water solution (volume ratio 1:1) containing a composite surfactant of hexadecyltrimethylammonium bromide (CTAB, analytical grade) and polyvinylpyrrolidone (PVP, molecular weight 40000), wherein the concentration of CTAB was 0.08 mol / L and the concentration of PVP was 0.03 mol / L. The system was placed in a DF-101S type thermostatic magnetic stirrer and stirred at 400 r / min for 25 minutes at 20℃ to ensure full dispersion. Then, 1.0 ml of tetraethyl orthosilicate (TEOS, analytical grade) was added, and ammonia (26% concentration) was added dropwise to adjust the pH to 9.0. The reaction was continued for 180 minutes. During the reaction, the change of Zeta potential in the system was monitored using a Malvern Zetasizer NanoZS90 particle size and Zeta potential analyzer. After the reaction was completed, the product was collected by centrifugation at 6000 r / min for 8 minutes and washed twice with anhydrous ethanol to obtain carbon nanotubes and silica core-shell structured materials. Finally, template removal and structural stabilization were performed. The above product was placed in a NaberthermLHT04 / 17 programmable temperature controlled box furnace and calcined in air atmosphere in two steps: first, the temperature was increased to 250℃ at 1℃ / min and held for 45 minutes, and then the temperature was increased to 500℃ at 3℃ / min and held for 90 minutes. After natural cooling, the final product, silica microrods, was obtained. The morphology of the product was observed using a Hitachi SU8020 field emission scanning electron microscope, and the purity of the product was characterized by a RenishawinVia laser confocal Raman spectrometer.

[0017] Example 2: Based on Example 1, this example uses more precise process parameter control.

[0018] The first step in the process is to modify the surface of the carbon nanotube template. 400 mg of multi-walled carbon nanotubes (96% purity, 28 nm diameter) are placed in a 500 ml three-necked flask, and a reflux condenser and a KQ-300DE CNC ultrasonic cleaner are used for ultrasonic assistance. Add 600 ml of a mixed acid solution of concentrated sulfuric acid (analytical grade, 98%) and concentrated nitric acid (analytical grade, 68%) in a volume ratio of 3:1, and reflux the reaction in an 80℃ constant temperature water bath for 120 minutes. During the reaction, use an HH-6 type digital display constant temperature water bath to precisely control the reaction temperature at 80±0.5℃. After the reaction was completed, the filtrate was washed 6 times with deionized water until it was neutral. After vacuum filtration, it was dried in a vacuum drying oven at 65°C for 12 hours to obtain a surface-modified carbon nanotube template. Next, controllable encapsulation of the silicon layer was performed. 120 mg of the carbon nanotube template treated above was dispersed in 200 ml of an ethanol-water solution (volume ratio 1:1) containing a composite surfactant of hexadecyltrimethylammonium bromide (CTAB, analytical grade) and polyvinylpyrrolidone (PVP, molecular weight 40000), wherein the concentration of CTAB was 0.12 mol / L and the concentration of PVP was 0.06 mol / L. The system was placed in a DF-101S type thermostatic magnetic stirrer and stirred at 600 r / min for 35 minutes at 25℃ to ensure full dispersion. Then, 2.0 ml of tetraethyl orthosilicate (TEOS, analytical grade) was added, and ammonia (27% concentration) was added dropwise to adjust the pH to 10.0. The reaction was continued for 300 minutes. A Mettler Toledo InPro3250i pH sensor and an InPro6860i dissolved oxygen sensor were installed on the reaction vessel to monitor and record the pH value and dissolved oxygen concentration of the reaction system in real time. After the reaction was completed, the product was collected by centrifugation at 10000 r / min for 12 minutes and washed four times with anhydrous ethanol to obtain carbon nanotubes and silica core-shell structured materials. Finally, template removal and structural stabilization were performed. The product was placed in a Naberther mLHT04 / 17 programmable temperature controlled furnace and calcined in air in two steps: first, the temperature was increased to 350℃ at 3℃ / min and held for 90 minutes, then increased to 600℃ at 8℃ / min and held for 150 minutes. A K-type thermocouple was used to maintain close contact with the sample, and the actual temperature of the sample was monitored in real time using an APEX-X98 multi-channel temperature recorder. After natural cooling, the final product, silica microrods, was obtained.

[0019] Example 3: Based on Examples 1 and 2, this example further optimizes the production process to achieve green recycling.

[0020] In the process of working, the surface of the carbon nanotube template was first modified. 350 mg of multi-walled carbon nanotubes (purity 95.5%, diameter 22 nm) were placed in a 500 ml three-necked flask. A reflux condenser and a KQ-300DE type CNC ultrasonic cleaner were set up to provide ultrasonic assistance. 500 ml of a mixed acid solution of concentrated sulfuric acid (analytical grade, 98%) and concentrated nitric acid (analytical grade, 68%) with a volume ratio of 3:1 was added. The mixture was refluxed in a constant temperature water bath at 75 °C for 108 minutes. After the reaction was completed, the filtrate was washed repeatedly with deionized water 5 times until it was neutral. The acidic wastewater was collected and neutralized with calcium hydroxide to pH=7. After precipitation, the supernatant was discharged after meeting the standards. After vacuum filtration, it was dried in a vacuum drying oven at 62℃ for 11 hours to obtain the surface-modified carbon nanotube template. Next, the silicon layer was controllably encapsulated. 100 mg of the treated carbon nanotube template was dispersed in 180 ml of an ethanol-water solution (volume ratio 1:1) containing a composite surfactant of hexadecyltrimethylammonium bromide (CTAB, analytical grade) and polyvinylpyrrolidone (PVP, molecular weight 40000), wherein the concentration of CTAB was 0.10 mol / L and the concentration of PVP was 0.05 mol / L. The system was placed in a DF-101S type thermostatic magnetic stirrer and stirred at 500 r / min for 30 minutes at 22℃ to ensure thorough dispersion. Then, 1.5 ml of tetraethyl orthosilicate (TEOS, analytical grade) was added, and ammonia (26.5% concentration) was added dropwise to adjust the pH to 9.5. The reaction was continued for 240 minutes. After the reaction was completed, the product was collected by centrifugation at 8000 r / min for 10 minutes. The supernatant was collected and replenished with fresh CTAB and PVP. After adjusting the pH value, it was reused for the next batch of reaction, with a recovery rate of 85%. The product was washed three times with anhydrous ethanol to obtain carbon nanotubes and silica core-shell structured materials. Finally, template removal and structural stabilization were performed. The above product was placed in a Naberther mLHT04 / 17 programmable temperature controlled box furnace and calcined in air atmosphere in two steps: first, the temperature was increased to 300℃ at 2℃ / min and held for 60 minutes, and then the temperature was increased to 550℃ at 5℃ / min and held for 120 minutes. The waste gas generated during the calcination process was treated by an alkaline spray tower and then discharged. After natural cooling, the final product, silica micro rods, was obtained. The silica waste can be reused as an additive in building materials.

[0021] The controllable preparation of silica microrods is achieved through the synergistic effect of three key technical steps. In the surface modification stage, a mixture of strong acids in a specific ratio is used to deeply oxidize carbon nanotubes under the combined action of heat and ultrasound, introducing a large number of oxygen-containing functional groups on their surface. This significantly improves the hydrophilicity and surface activity of the template, providing an ideal interface for the subsequent uniform adsorption of silicon sources. During the silicon layer encapsulation stage, CTAB forms an ordered monolayer on the template surface through electrostatic interaction, effectively guiding the directional adsorption of silica precursors. PVP stabilizes the reaction system through steric hindrance, preventing excessive growth of silica particles. The two work synergistically, combined with precisely controlled reaction parameters, to achieve precise control of silica shell thickness and uniformity. In the template removal stage, a two-step calcination method is used. First, the silica network structure is pre-condensed at a lower temperature to enhance its mechanical strength. Then, the carbon template is completely removed at a higher temperature while maintaining the integrity of the silica framework. This progressive heat treatment strategy effectively avoids structural damage caused by rapid heating and ensures that the final product has good morphological integrity and structural stability.

[0022] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A novel method for preparing synthetic silica microrods, characterized in that, Includes the following steps: Step 1: Surface modification of the carbon nanotube template to enrich its surface with oxygen-containing functional groups; Step 2: The surface-modified carbon nanotube template is dispersed in a solution containing surfactant and silicon source to carry out a silica layer encapsulation reaction, forming a core-shell structure; Step 3: Remove the internal carbon nanotube template by calcination to obtain silica microrods.

2. The method for preparing a novel synthetic silica microrod according to claim 1, characterized in that: In step one, the surface modification involves acidifying the carbon nanotubes with a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid. The volume ratio of concentrated sulfuric acid to concentrated nitric acid was 3:1, the acidification temperature was 80°C, the treatment time was 2 hours, and ultrasound was applied during the treatment.

3. The method for preparing a novel synthetic silica microrod according to claim 1, characterized in that: In step two, the surfactant is a composite surfactant system composed of hexadecyltrimethylammonium bromide and polyvinylpyrrolidone.

4. The method for preparing a novel synthetic silica microrod according to claim 3, characterized in that: In step two, the silicon source is tetraethyl orthosilicate, the pH of the reaction system is adjusted to 9.5 with ammonia, the reaction temperature is 25°C, and the reaction time is 4 hours.

5. The method for preparing a novel synthetic silica microrod according to claim 4, characterized in that: In step two, the concentration of the carbon nanotube template in the reaction system is 0.5 mg / mL, and the amount of tetraethyl orthosilicate added is 1.5 mL.

6. The method for preparing a novel synthetic silica microrod according to claim 1, characterized in that: In step three, the calcination is a two-step calcination method, specifically: in an air atmosphere, the temperature is first raised to 300°C at a heating rate of 2°C / min and held for 1 hour, and then raised to 550°C at a heating rate of 5°C / min and held for 2 hours.

7. A novel synthetic silica microrod, characterized in that, The invention includes a method for preparing a novel synthetic silica microrod according to claims 1 to 6: the silica microrod has a solid or hollow structure, with a diameter of 50 to 200 nm and a length of 1 to 5 μm.

8. A novel synthetic silica microrod according to claim 7, characterized in that: The silica microrods have a smooth surface, uniform diameter distribution, and no carbon template residue inside.

9. A novel synthetic silica microrod according to claim 7, characterized in that: Applications of silica microrods in the preparation of drug delivery carriers, catalyst carriers, or composite material reinforcing phases.