A composite system based on zif-8 modified go and m-cns, a preparation method and application thereof

Abstract

This invention belongs to the field of composite material preparation technology, specifically a ZIF-8 modified GO and M-CNS composite system, its preparation method, and its application. The preparation method includes the following steps: dissolving hexadecyltrimethylammonium bromide in water, adding ammonia to obtain an alkaline solution; adding tetraethyl silicate dropwise to the hexadecyltrimethylammonium bromide alkaline solution, stirring, centrifuging to remove the liquid phase, and calcining to obtain porous silica sol M-CNS; dissolving graphene oxide in methanol solution, dispersing it until the solution is free of agglomeration, adding Zn(NO3)2, stirring, and obtaining graphene oxide and Zn... 2+ The mixture; 2-methylimidazole dissolved in DMF was then added dropwise to the mixture of graphene oxide and Zn. 2+ After reaction in the mixture, ZIF-8 modified GO is obtained through centrifugation and drying. Porous silica sol and ZIF-8 modified GO are then mixed uniformly to obtain a ZIF-8 modified GO / M-CNS composite system. This invention significantly improves the mechanical properties of concrete and substantially reduces the chloride ion diffusion coefficient of concrete.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, specifically a preparation method and application of a ZIF-8 modified GO and M-CNS composite system. Background Technology

[0002] Marine concrete is widely used and indispensable as a key material in major marine engineering projects such as offshore military engineering, artificial islands, cross-sea bridges, and subsea tunnels. Most of these completed, under-construction, or planned marine engineering projects are concrete structures. However, the inherent porous nature of cement concrete and the hydrophilic properties of its hydration products make it unavoidable for water and salt to permeate, posing a significant risk of chloride ionization in seawater. - The rapid transmission channel then reaches the surface of the reinforcing steel, causing corrosion.

[0003] In recent years, nanomaterials have been rapidly developing in various research fields. For concrete structures, significant performance improvements can be achieved through the high density and fine particle size of nanomaterials. Therefore, various materials are being used in concrete in nanoscale form as cementitious materials to improve its microstructure and macroscopic properties. Among these, powdered nano-silica (NS) has become one of the most popular nano-additives for cement concrete due to its nanoscale particle characteristics and high pozzolanic activity. However, because NS has a large specific surface area and high surface energy, it is prone to agglomeration, affecting its effectiveness in cement-based materials. Therefore, researchers changed the preparation method to directly prepare monodisperse silica sol (CNS). Based on the presence of a large number of active groups (-Si-OH) on the surface of silica sol, CNS, like NS, has a theoretical basis for improving the mechanical properties and durability of cement-based materials. Furthermore, it can undergo a pozzolanic reaction with Ca(OH)2, a cement hydration product, transforming the weak Ca(OH)2 in cement-based materials into CSH gel, which contributes to strength, thereby optimizing the pore structure of concrete and demonstrating its potential to improve the mechanical properties and durability of cement-based materials. However, similar to NS, in cement systems, CNS, due to the presence of silanol groups on its surface, will react with Ca in the pore solution... 2+ They combine to form loose aggregates, thereby preventing further dispersion of nanoparticles in CNS.

[0004] Graphene oxide (GO), another commonly used nanomaterial in concrete, exhibits a significant advantage in preventing the propagation of micron-sized cracks in concrete due to its layered structure. However, GO has a low surface roughness and weak bonding with the cement concrete matrix, making it prone to debonding during concrete fracture and failure. This prevents it from fully exerting its reinforcing and toughening effects, greatly limiting its application in cement concrete. Summary of the Invention

[0005] To solve the problem of CNS and Ca in cement systems2+ To address the issue that GO, due to its low roughness, forms loose aggregates and has poor bonding with the concrete matrix, this invention provides a preparation method based on a ZIF-8 modified GO and M-CNS composite system.

[0006] On the one hand, the present invention is achieved through the following technical solution: Step 1: Dissolve hexadecyltrimethylammonium bromide in water, add ammonia water, and prepare an alkaline solution; Step 2: Add tetraethyl silicate dropwise to an alkaline solution of hexadecyltrimethylammonium bromide, stir, centrifuge to remove the liquid phase, and calcine to obtain porous silica sol M-CNS; Step 3: Dissolve graphene oxide in methanol solution, disperse it (preferably by ultrasound) until the solution is free of agglomeration, add Zn(NO3)2, stir, and obtain graphene oxide and Zn 2+ Mixture; Step 4: After dissolving 2-methylimidazole in DMF, it is added dropwise to the mixture of graphene oxide and Zn. 2+ After reaction in the mixture, ZIF-8 modified GO was obtained by centrifugation and drying. Step 5: The porous silica sol and ZIF-8 modified GO are mixed evenly to obtain the ZIF-8 modified GO and M-CNS composite system.

[0007] This invention aims to solve two core durability problems in marine concrete: chloride ion attack and microcrack propagation. Based on the synergistic and complementary effects of M-CNS and ZIF-8 modified GO, a multi-layered protection system is constructed from three levels: physical barrier, chemical adsorption, and mechanical reinforcement.

[0008] The functions of M-CNS are as follows: (1) Pore refinement and structural densification: The nano-silica in M-CNS has a large specific surface area, providing a large number of active sites for reaction with Ca(OH)2. The active components react with the cement hydration product Ca(OH)2 in a secondary pozzolanic reaction to generate more low calcium-silica ratio CSH gel, which effectively fills the capillary pores and transition pores in cement stone, and physically lengthens and tortuouss the migration path of chloride ions. M-CNS can continuously and deeply participate in secondary hydration to generate more and finer CSH gel, which is the fundamental driving force for achieving matrix densification. (2) Anti-calcium ion aggregation stability: M-CNS treated by a specific process reduces the surface susceptibility to Ca ion aggregation. 2+ The number of bound silanol groups (-Si-OH) is increased, thus maintaining better dispersibility in the high-calcium alkaline pore liquid of concrete, avoiding failure due to agglomeration, and ensuring the full utilization of its active function.

[0009] The effects of ZIF-8 on GO modification are as follows: (1) Physical / chemical adsorption of chloride ions: ZIF-8 grown on the GO surface is a metal-organic framework material with a regular porous structure (mainly micropores). Its channels and metal nodes (Zn 2+ (1) It can actively capture and fix invading free Cl⁻ ions through physical adsorption and coordination, significantly reducing the concentration and migration driving force of Cl⁻ in the pore solution. (2) Enhanced interfacial bonding and crack prevention: GO itself has excellent mechanical strength and two-dimensional lamellar structure, making it an ideal reinforcing phase. The in-situ growth of ZIF-8 crystals on the GO surface greatly increases the surface roughness of GO, thereby significantly improving the mechanical interlocking force and interfacial bonding strength between it and cement hydration products, effectively preventing the initiation and propagation of microcracks.

[0010] Synergistic effects of the composite system: The dense matrix created by M-CNS provides a more stable and less defect-prone environment for ZIF-8@GO (ZIF-8 modified GO), resulting in more uniform dispersion and stronger interfacial bonding. While ZIF-8@GO performs its crack-inhibiting and adsorption functions, its layered structure can also guide the growth orientation of cement hydration products, further optimizing the microstructure. The synergy of these two aspects achieves full-range reinforcement and protection from the nanoscale (pore structure) to the microscale (microcracks), jointly constructing a composite defense network against chloride ion erosion and mechanical damage.

[0011] In a further improvement of the present invention, in step 1, the mass-to-volume ratio of hexadecyltrimethylammonium bromide to water (g:mL) is 1.0-1.5:80-100, the temperature is 50-70℃, ammonia water is added, the pH of the alkaline solution is adjusted to 10.3-10.7, and the process is carried out under reflux conditions.

[0012] In a further improvement of the present invention, in step 2, the molar ratio of tetraethyl silicate to hexadecyltrimethylammonium bromide is 4-6:1, and the dropping rate is controlled by an injection pump at 0.3-0.5 mL / min. The solution is added dropwise to the alkaline solution of hexadecyltrimethylammonium bromide at 30-50°C, and the mixture is stirred at a constant temperature for 4-6 h.

[0013] In a further improvement of the present invention, in step 2, the centrifugation is performed for 9-12 min, the bottom precipitate is collected, and dried at 50-70℃ for 10-13 h.

[0014] A further improvement to this invention involves a programmed temperature calcination process in step 2. First, the temperature is raised to 280-310°C to decompose cetyltrimethylammonium bromide, held for 1-3 hours, and then raised to 500-580°C, held for 4-6 hours to remove carbon residue. The low-temperature stage removes the template agent CTAB, forming pores; the high-temperature stage thoroughly removes carbon residue, stabilizes the silica network, and reduces surface silanol groups, resulting in highly dispersible, porous M-CNS.

[0015] In a further improvement of the present invention, in step 3, the mass-to-volume ratio of graphene oxide to methanol solution (mg:mL) is 40-50:50-60, the mixture is ultrasonically treated for 20-35 min, Zn(NO3)2 is added, the mass ratio of Zn(NO3)2 to graphene oxide is 10:1 to 20:1, and the mixture is stirred for 30-60 min at 30-45°C.

[0016] A further improvement of the present invention is that, in step 4, 2-methylimidazole is dissolved in DMF and then added dropwise to the graphene oxide and Zn at a rate of 0.2-0.5 mL / min. 2+ In the mixed solution, the isothermal reaction temperature is 25-60℃, and the time is 1-4 h. This parameter affects the integrity of ZIF-8 crystals and the binding strength with GO. Suitable conditions ensure the formation of a structurally stable and firmly bonded modified layer. Centrifuge at 8000-10000 rpm for 5-15 min, collect the bottom precipitate, and dry it at 50-70℃ for 10-13 h.

[0017] Among them, according to the molar ratio Zn 2+ The ratio of 2-methylimidazole is 1:2 to 1:8. This parameter controls the nucleation and growth density and grain size of ZIF-8 crystals on the GO surface. If the ratio is too low, the ZIF-8 coating will be incomplete; if it is too high, free ZIF-8 particles will be generated, affecting the composite efficiency. The mass concentration of 2-methylimidazole in DMF is 0.02 - 0.05 g / mL.

[0018] In a further improvement of the present invention, in step 5, the mass ratio of ZIF-8 modified GO to porous silica sol is 1:1-3, the ball milling mixing time is 10-30 min, and the rotation speed is 200-300 rpm, to ensure that the two materials achieve uniform physical mixing and avoid stratification or agglomeration caused by differences in density and particle size.

[0019] On the other hand, the present invention provides a ZIF-8 modified GO and M-CNS composite system obtained by the above preparation method.

[0020] Furthermore, this invention provides the application of the ZIF-8 modified GO and M-CNS composite system obtained by the above method in marine concrete.

[0021] As can be seen from the above technical solutions, the beneficial effects of the present invention are: (1) The present invention significantly improves the mechanical properties of concrete, which is due to the pozzolanic activity of M-CNS and the excellent reinforcing and toughening effect of ZIF-8 modified GO. At the same time, the composite system of the present invention can significantly reduce the chloride ion diffusion coefficient of concrete, which is due to the dual effect of dense barrier of M-CNS and active adsorption of ZIF-8.

[0022] (2) By modifying CNS (M-CNS) to improve its resistance to calcium ions and by modifying GO with ZIF-8 to increase its surface roughness, the key technical bottleneck of easy agglomeration and weak interface of nanomaterials in concrete is fundamentally solved.

[0023] (3) The composite system has a slow decay of chloride ion resistance, has long-term protection potential, can provide long-term durability guarantee, and can meet the high standard requirements of structural durability in harsh marine environments. Attached Figure Description

[0024] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The average particle size of CNS / M-CNS after being mixed with saturated Ca(OH)2 solution in Example 4 of this invention. Detailed Implementation

[0026] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the embodiments described below are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this patent.

[0027] All raw materials used in the examples can be obtained through market purchase.

[0028] Example 1: The preparation method of porous silica sol (M-CNS) in this scheme is as follows: (1) Dissolve hexadecyltrimethylammonium bromide (CTAB) in deionized water at 60°C and stir until transparent. The speed of the magnetic stirrer is 800 rpm. Add ammonia water to obtain an alkaline solution and maintain pH = 10.5. The mass-volume ratio of hexadecyltrimethylammonium bromide to deionized water is 1.2:90 g:mL.

[0029] (2) Tetraethyl silicate (TEOS) was added dropwise to an alkaline solution of hexadecyltrimethylammonium bromide (CTAB) at a rate of 0.4 mL / min using a syringe pump. The mixture was stirred at a constant temperature of 40°C at a speed of 600 rpm for 5 h. The molar ratio of tetraethyl silicate to hexadecyltrimethylammonium bromide was 5:1. The liquid phase was removed by centrifugation at a speed of 10,000 rpm for 10 min. The bottom precipitate was collected, washed three times with ethanol, and dried at 60°C for 12 h. Then, the mixture was calcined using a programmed temperature rise method. The temperature was increased to 300°C at a rate of 2°C per minute and held for 2 h. Then, the temperature was increased to 550°C at a rate of 5°C per minute and held for 5 h to remove carbon residue, thus obtaining porous silica sol (M-CNS).

[0030] Example 2: The preparation method of porous silica sol (M-CNS) in this scheme is as follows: (1) Dissolve hexadecyltrimethylammonium bromide (CTAB) in deionized water at 50°C and stir until transparent. The speed of the magnetic stirrer is 800 rpm. Add ammonia water to prepare an alkaline solution and maintain pH = 10.3. The mass-volume ratio of hexadecyltrimethylammonium bromide to deionized water is 1.0:100 g:mL.

[0031] (2) Tetraethyl silicate (TEOS) was added dropwise to an alkaline solution of hexadecyltrimethylammonium bromide (CTAB) at a rate of 0.3 mL / min using a syringe pump. The mixture was stirred at a constant temperature of 30°C at a speed of 600 rpm for 4 h. The molar ratio of tetraethyl silicate to hexadecyltrimethylammonium bromide was 4:1. The liquid phase was removed by centrifugation at 10,000 rpm for 9 min. The bottom precipitate was collected, washed three times with ethanol, and dried at 70°C for 10 h. Then, the mixture was calcined using a programmed temperature rise method. The temperature was increased to 280°C at a rate of 2°C per minute and held for 3 h. Then, the temperature was increased to 500°C at a rate of 5°C per minute and held for 6 h to remove carbon residue, thus obtaining porous silica sol (M-CNS).

[0032] Example 3: The preparation method of porous silica sol (M-CNS) in this scheme is as follows: (1) Dissolve hexadecyltrimethylammonium bromide (CTAB) in deionized water at 70°C and stir until transparent. The speed of the magnetic stirrer is 800 rpm. Add ammonia water to prepare an alkaline solution and maintain pH = 10.7. The mass-volume ratio of hexadecyltrimethylammonium bromide to deionized water is 1.5:80 (g:mL).

[0033] (2) Tetraethyl silicate (TEOS) was added dropwise to an alkaline solution of hexadecyltrimethylammonium bromide (CTAB) at a rate of 0.5 mL / min using a syringe pump. The mixture was stirred at a constant temperature of 50°C at a speed of 600 rpm for 6 h. The molar ratio of tetraethyl silicate to hexadecyltrimethylammonium bromide was 6:1. The liquid phase was removed by centrifugation at a speed of 10,000 rpm for 12 min. The bottom precipitate was collected, washed three times with ethanol, and dried at 50°C for 13 h. Then, the mixture was calcined using a programmed temperature rise method. The temperature was increased to 310°C at a rate of 2°C per minute and held for 1 h. Then, the temperature was increased to 580°C at a rate of 5°C per minute and held for 4 h to remove carbon residue, thus obtaining porous silica sol (M-CNS).

[0034] Example 4: Silica sol aqueous solutions were prepared according to Examples 1-3. Comparative Example 1 used commercially available CNS aqueous solutions with the same mass fraction.

[0035] After the above solution was added to a saturated Ca(OH)2 solution and allowed to stand for 1, 10, 30, 60, 90 and 120 min, the average particle size of the precipitate and the Zeta potential of the supernatant were measured.

[0036] The average particle size of the precipitate is as follows Figure 1 As shown, the particle size of Comparative Example 1 increases rapidly, while that of Comparative Examples 1-3 increases very slowly, reaching only 80-90 nm after 1 minute and only about 155 nm after 120 minutes. At this point, the particle size of Comparative Example 1 has exceeded 1000 nm.

[0037] Regarding the Zeta potential, Comparative Example 1 showed a gradual decrease in absolute value from approximately -35 mV to -20 mV, indicating reduced stability. Examples 1-3 initially showed a decrease from approximately -40 mV to -45 mV, with a slow decrease over time, remaining above -30 mV after 120 min.

[0038] This is mainly because M-CNS undergoes modification to form a porous structure, and the surface silanol groups (Si-OH) are transformed into siloxane structures (Si-O-Si), thus avoiding the problems caused by Ca in ordinary CNS. 2+ The strong agglomeration caused by specific adsorption and bridging results in more stable dispersion in Ca(OH)2 solution, slow particle size growth, and a high negative Zeta potential, indicating that the anti-agglomeration ability is significantly better than that of traditional CNS.

[0039] Example 5: The preparation method of ZIF-8 modified GO in this scheme is as follows: (1) Graphene oxide was dissolved in methanol solution with a mass-to-volume ratio of graphene oxide to methanol solution of 45:55 (mg:mL). The solution was ultrasonically treated for 30 min (30 kHz, 200 W) until no agglomeration occurred. Zn(NO3)2 was then added with a mass ratio of Zn(NO3)2 to graphene oxide of 15:1. The mixture was stirred at 40 °C for 40 min to obtain graphene oxide and Zn(NO3)2. 2+ Mixture; (2) After 2-methylimidazole was dissolved in DMF, it was added dropwise to graphene oxide and Zn at a rate of 0.3 mL / min. 2+ In the mixed solution, the reaction was carried out at a constant temperature of 40℃ for 3 h, followed by centrifugation at 9000 rpm for 10 min. The liquid phase was removed, and the bottom precipitate was collected and dried at 60℃ for 12 h to obtain ZIF-8 modified GO. The Zn molar ratio was [not specified in the original text]. 2+ : 2-Methylimidazole = 1:4, the mass concentration of 2-methylimidazole in DMF is 0.04 g / mL.

[0040] Example 6: The preparation method of ZIF-8 modified GO in this scheme is as follows: (1) Graphene oxide was dissolved in methanol solution with a mass-to-volume ratio of graphene oxide to methanol solution of 40:60 mg:mL. The solution was ultrasonically treated for 20 min (30 kHz, 200 W) until no agglomeration occurred. Zn(NO3)2 was then added with a mass ratio of Zn(NO3)2 to graphene oxide of 10:1. The mixture was stirred at 30 °C for 60 min to obtain graphene oxide and Zn(NO3)2. 2+ Mixture; (2) After 2-methylimidazole was dissolved in DMF, it was added dropwise to graphene oxide and Zn at a rate of 0.2 mL / min. 2+ In the mixed solution, the reaction was carried out at a constant temperature of 25℃ for 4 h, followed by centrifugation at 8000 rpm for 15 min. The liquid phase was removed, and the bottom precipitate was collected and dried at 50℃ for 13 h to obtain ZIF-8 modified GO. The molar ratio of Zn... 2+ : 2-Methylimidazole = 1:2, the mass concentration of 2-methylimidazole in DMF is 0.02- g / mL.

[0041] Example 7: The preparation method of ZIF-8 modified GO in this scheme is as follows: (1) Graphene oxide was dissolved in methanol solution with a mass-to-volume ratio of graphene oxide to methanol solution of 50:50 (mg:mL). The solution was ultrasonically treated for 35 min (30 kHz, 200 W) until no agglomeration occurred. Zn(NO3)2 was then added with a mass ratio of Zn(NO3)2 to graphene oxide of 20:1. The mixture was stirred at 45 °C for 30 min to obtain graphene oxide and Zn(NO3)2. 2+ Mixture; (2) After dissolving 2-methylimidazole in DMF, it was added dropwise to graphene oxide and Zn at a rate of 0.5 mL / min. 2+ In the mixed solution, the reaction was carried out at a constant temperature of 60℃ for 1 hour, followed by centrifugation at 10,000 rpm for 5 minutes. The liquid phase was removed, and the bottom precipitate was collected and dried at 70℃ for 10 hours to obtain ZIF-8 modified GO. The molar ratio of Zn... 2+ The ratio of 2-methylimidazole to DMF is 1:8, and the mass concentration of 2-methylimidazole in DMF is 0.05 g / mL.

[0042] Comparative Example 2: The preparation method of ZIF-8 is as follows: A volume of methanol equal to that in Example 5 was measured and added to a volume of Zn(NO3)2 equal to that in Example 5. Zn was obtained by stirring at 40°C for 40 min. 2+ Solution.

[0043] 2-Methylimidazole was dissolved in DMF and then added dropwise to Zn at a rate of 0.3 mL / min. 2+ In solution, the reaction was carried out at a constant temperature of 40℃ for 3 h, followed by centrifugation at 9000 rpm for 10 min. The liquid phase was removed, and the bottom precipitate was collected and dried at 60℃ for 12 h to obtain ZIF-8. The molar ratio of Zn... 2+ : 2-Methylimidazole = 1:4, the mass concentration of 2-methylimidazole in DMF is 0.04 g / mL.

[0044] Example 8: The pore structures of the products prepared in Examples 5-7 and Comparative Example 2 were determined using an ASAP2460 surface area and porosity analyzer, and the results are shown in Table 1.

[0045] Table 1 The results show that ZIF-8-modified GO has a higher specific surface area and pore volume compared to pure ZIF-8. This is because the GO sheets provide a carrier for ZIF-8 growth, forming more mesoporous and microporous structures. Simultaneously, the growth of ZIF-8 crystals on the GO sheets acts like inserting nano-spacers between the sheets, effectively preventing the tight stacking of GO and exposing parts of the GO surface that were previously obscured, which is also a factor contributing to the increased specific surface area. Furthermore, the experiments show that reaction conditions also affect the structural morphology. Example 7, due to its more vigorous reaction conditions, formed more ZIF-8 crystals, further increasing the specific surface area and pore size distribution.

[0046] Example 9 The porous silica sol (M-CNS) prepared in Example 1 and the ZIF-8 modified GO prepared in Example 5 were mixed evenly in a ball mill at a mass ratio of 2:1. The ball milling rate was 300 rpm and the time was 30 min to obtain the ZIF-8 modified GO and M-CNS composite system.

[0047] The ZIF-8 modified GO and M-CNS composite system was incorporated into marine concrete. The marine concrete, by weight, included 260 parts cement, 70 parts fly ash, 40 parts recycled micro powder, 30 parts ZIF-8 modified GO and M-CNS composite system, 800 parts manufactured sand, 950 parts ordinary crushed stone, 150 parts water, and 5 parts water-reducing agent.

[0048] Example 10 Unlike Example 9, the marine concrete did not incorporate the ZIF-8 modified GO and M-CNS composite system, and the other components were evenly distributed according to their respective weights.

[0049] Example 11 The difference from Example 9 is that the ZIF-8 modified GO and M-CNS composite system is changed to 30 parts by mass of M-CNS.

[0050] Example 12 The difference from Example 9 is that the ZIF-8 modified GO and M-CNS composite system is changed to 30 parts by mass of ZIF-8 modified GO.

[0051] Example 13 The difference from Example 9 is that the ZIF-8 modified GO and M-CNS composite system is changed to 30 parts by mass of GO.

[0052] Example 14 The difference from Example 9 is that the ZIF-8 modified GO and M-CNS composite system is changed to 30 parts by mass of CNS.

[0053] Example 15 The difference from Example 9 is that the ZIF-8 modified GO and M-CNS composite system has a mass fraction of 20 parts.

[0054] Example 16 The difference from Example 9 is that the ZIF-8 modified GO and M-CNS composite system has a mass fraction of 40 parts.

[0055] Example 17 For Examples 9-16, the compressive strength was tested according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GBT50081-2019), and the rapid chloride ion diffusion coefficient of concrete was tested according to the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T 50082-2024). The results are shown in Table 2 below.

[0056] Table 2 Compared to Example 10, it can be seen from the single-component addition groups (Examples 11-14) that: (1) Adding only M-CNS (Example 11): The strength is significantly improved. The active SiO2 in M-CNS reacts with the cement hydration product Ca(OH)2 in a pozzolanic reaction to generate more CSH gel, which refines the pores and improves the density. Chloride ion permeability is improved, and the refinement of pores hinders ion migration channels, but does not provide active adsorption of Cl. - The ability.

[0057] (2) Adding only ZIF 8@GO (Example 12): The strength improvement is moderate. The two-dimensional lamellar structure of GO plays a role in physical crack resistance and stress transfer. ZIF 8 particles increase the surface roughness of GO, enhancing the interfacial bonding with the cement matrix. The improvement in chloride ion permeability is limited. The porous structure of ZIF-8 can physically adsorb some Cl. - However, it has poor dispersibility when used alone and is not as effective as M-CNS in improving pore structure.

[0058] (3) Adding only GO (Example 13) Unmodified GO has a smooth surface, weak bonding with cement matrix, and is easy to debond; and it is easy to agglomerate in a high calcium alkaline environment, which limits its reinforcing effect.

[0059] (4) The performance of ordinary CNS (Example 14) is inferior to that of M-CNS: the silanol groups (-Si-OH) on the surface of ordinary CNS are easily reacted with Ca 2+ It aggregates but has poor dispersibility and its activity is not fully realized.

[0060] For the composite system groups (Examples 9, 15, and 16), it can be seen that: M-CNS, as a microstructure optimizer, fills nano- and micro-sized pores through a pozzolanic reaction, reducing porosity. In ZIF-8@GO, GO sheets bridge microcracks and prevent their propagation. The ZIF-8 modification layer improves GO roughness and enhances interfacial mechanical bonding; its porous structure (especially micropores) can selectively adsorb and immobilize Cl. - Zn in ZIF-8 reduces the concentration of free chloride ions; 2+ With Cl - It forms coordination or precipitation, providing chemical anchoring.

[0061] Furthermore, the dense matrix created by M-CNS provides a more stable dispersion environment for ZIF-8@GO; while ZIF-8@GO further inhibits the cracking and adsorption of Cl. - This makes up for the shortcomings of M-CNS, which can only physically block.

[0062] Comparing Examples 15, 9, and 16 reveals that the present invention has universality. Example 18: Durability Test According to the proportions and process of Example 9, multiple sets of concrete cube specimens with dimensions of 100 mm × 100 mm × 100 mm and cylindrical specimens with dimensions of 100 mm × 50 mm were prepared.

[0063] After 28 days of standard curing (temperature 20±2°C, relative humidity ≥95%), remove and dry in a 60°C oven for 48 hours. Cool to room temperature and seal all surfaces except the two opposite sides with epoxy resin.

[0064] The soaking solution used was a 3.5 wt% NaCl solution. The sealed specimens were completely immersed in the solution and placed in a constant temperature environment (high temperature for acceleration, 40±2°C). The solution was changed periodically to maintain a constant concentration. Control settings: Example 10 (blank group) was set synchronously, with soaking time points set at 28 days, 90 days, and 180 days.

[0065] The results showed that: Example 9 had a chloride ion diffusion coefficient of (×10) over 90 days. -12 m 2 / s) is 1.6; the chloride ion diffusion coefficient (×10) over 180 days is -12 m 2 The strength is 1.8 (s / s), and the compressive strength is 75 MPa after 180 days.

[0066] Chloride ion diffusion coefficient (×10) over 90 days in Example 10 -12 m 2 The chloride ion diffusion coefficient ( / s) is 10.1; the chloride ion diffusion coefficient (×10) over 180 days is 10.1.-12 m 2 The strength is 11.2 (s / s), and the compressive strength after 180 days is 45 MPa.

[0067] In Example 9, the chloride ion diffusion coefficient remained significantly lower than that in Example 10 throughout the entire soaking cycle. This is attributed to the continued effectiveness of the M-CNS-optimized dense microstructure and the ability of the ZIF-8 porous framework to maintain most of its structural integrity in a long-term alkaline environment, continuously adsorbing and immobilizing Cl. - This slows down its inward diffusion. In Example 9, the intensity still increased slightly after 180 days, thanks to the continued volcanic ash reaction of M-CNS, which further filled the pores. In contrast, in Example 10, the intensity stagnated due to early micro-corrosion caused by a small amount of chloride ion intrusion, while the chloride ion diffusion coefficient increased rapidly.

[0068] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a ZIF-8 modified GO and M-CNS composite system, characterized in that, Includes the following steps: Step 1: Dissolve hexadecyltrimethylammonium bromide in water, add ammonia water, and prepare an alkaline solution; Step 2: Add tetraethyl silicate dropwise to an alkaline solution of hexadecyltrimethylammonium bromide, stir, centrifuge to remove the liquid phase, and calcine to obtain porous silica sol M-CNS; Step 3: Dissolve graphene oxide in methanol solution, disperse until no agglomeration occurs, add Zn(NO3)2, stir, and obtain graphene oxide and Zn2. 2+ Mixture; Step 4: After dissolving 2-methylimidazole in DMF, it is added dropwise to the mixture of graphene oxide and Zn. 2+ After reaction in the mixture, ZIF-8 modified GO was obtained by centrifugation and drying. Step 5: The porous silica sol and ZIF-8 modified GO are mixed evenly to obtain the ZIF-8 modified GO and M-CNS composite system.

2. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 1, the mass-to-volume ratio of hexadecyltrimethylammonium bromide to water (g:mL) is 1.0-1.5:80-100, the temperature is 50-70℃, ammonia water is added, and the pH of the alkaline solution is adjusted to 10.3-10.

7.

3. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 2, the molar ratio of tetraethyl silicate to hexadecyltrimethylammonium bromide is 4-6:

1. The dropping rate is controlled by an injection pump at 0.3-0.5 mL / min. The solution is added dropwise to the alkaline hexadecyltrimethylammonium bromide solution at 30-50℃ and stirred at a constant temperature for 4-6 h.

4. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 2, centrifuge for 9-12 min, collect the bottom precipitate, and dry it at 50-70℃ for 10-13 h.

5. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 2, the calcination is carried out by first raising the temperature to 280-310℃ and holding it for 1-3 hours, then raising the temperature to 500-580℃ and holding it for 4-6 hours.

6. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 3, the mass-to-volume ratio of graphene oxide to methanol solution (mg:mL) is 40-50:50-60. Zn(NO3)2 is added, and the mass ratio of Zn(NO3)2 to graphene oxide is 10:1 to 20:

1.

7. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 4, 2-methylimidazole is dissolved in DMF and then added dropwise to the graphene oxide and Zn group at a rate of 0.2-0.5 mL / min. 2+ In the mixture, the constant temperature reaction is 25-60℃ for 1-4 hours; wherein the molar ratio of Zn is... 2+ : 2-Methylimidazole = 1:2-1:8, the mass concentration of 2-methylimidazole in DMF is 0.02-0.05 g / mL.

8. The preparation method of the ZIF-8 modified GO and M-CNS composite system according to claim 1, characterized in that: In step 5, the mass ratio of ZIF-8 modified GO to porous silica sol is 1:1-3, the ball milling time is 10-30 min, and the rotation speed is 200-300 rpm.

9. The ZIF-8 modified GO and M-CNS composite system obtained by the method according to any one of claims 1-8.

10. The application of the ZIF-8 modified GO and M-CNS composite system obtained by the method according to claim 9 in marine concrete.

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