Biquaternary ammonium salt modified silica sol as well as preparation method and application thereof

Abstract

According to the biquaternary ammonium salt modified silica sol and the preparation method and application thereof, the triple targets of stability improvement, broad-spectrum efficient bacteriostasis and catalyst crystallinity breakthrough are achieved through the modification effect of biquaternary ammonium salt, the requirements for long-period use of the catalyst, bacteriostasis in complex scenes and efficient dispersion of active components are met, the crystallinity of the supported catalyst reaches 92% or above, and the service life of the supported catalyst is prolonged. Inactive impurities are reduced, and the catalytic performance is improved.

Description

Biquaternary ammonium salt modified silica sol, its preparation method and application Technical Field

[0001] This invention relates to the field of silica sol technology, specifically to bisquaternary ammonium salt modified silica sol, its preparation method, and its application. Background Technology

[0002] Silica sol, as a nano-silica gel solution, is widely used in catalysts (supports, silicon sources, binders), water treatment, coatings, and other industries due to its high specific surface area, good compatibility, and chemical inertness. However, existing technologies suffer from three major drawbacks: 1. Insufficient stability: Unmodified silica sol has a highly polar surface and is prone to aggregation, especially under acidic conditions (most catalytic reaction systems are acidic); while traditional amino and monoquaternary ammonium salt modified silica sols offer slight improvement, their storage life at 60℃ is mostly no more than 12-18 months, failing to meet the requirements for long-term catalyst use; 2. Limited functionality and antibacterial properties: Existing modified silica sols lack broad-spectrum and highly efficient antibacterial properties, making catalysts susceptible to microbial contamination in wastewater treatment, biocatalysis, and other scenarios, leading to reduced activity. 3. Low crystallinity of catalyst: After modification with traditional silica sol, the active component of the catalyst (metal or metal oxide) is prone to form an amorphous or low crystallinity phase, with a crystallinity of less than 65%. Low crystallinity leads to irregular structure of active sites, poor catalytic selectivity (often ≤85%), and easy sintering and deactivation in high-temperature reactions, which seriously limits the application of catalysts in high-end catalytic scenarios (such as selective hydrogenation in fine chemicals).

[0003] Therefore, it is necessary to propose a new modified silica sol to meet the performance requirements in applications. Summary of the Invention

[0004] This invention proposes a bis-quaternary ammonium salt modified silica sol to meet the performance requirements of at least one existing application.

[0005] The technical solution of the present invention is implemented as follows: The first aspect of the present invention is to provide a bis-quaternary ammonium salt modified silica sol, which is obtained by fully reacting a silica sol dispersion with a bis-quaternary ammonium salt hydrolysate solution under stirring, wherein the bis-quaternary ammonium salt hydrolysate solution is added dropwise; wherein the bis-quaternary ammonium salt hydrolysate solution is obtained by hydrolyzing a bis-quaternary ammonium salt in a weakly acidic alcohol aqueous solution.

[0006] Furthermore, the quaternary ammonium salt is selected from trimethyl-(3-trimethylammoniumpropyl)ammonium dihalide, hexamethylammonium halide, or 1,3-bis(trimethylammoniumpropyl)propane dihalide.

[0007] Furthermore, the pH value of the weakly acidic alcohol aqueous solution is 3 to 5.5; and / or, the hydrolysis of the bisquaternary ammonium salt is carried out under ultrasonic conditions; and / or, the hydrolysis time of the bisquaternary ammonium salt is 1.5 to 2.5 h.

[0008] Further, the mass ratio of the bisquaternary ammonium salt to the alcohol-water solvent is 1:(6~12); and / or, the mass ratio of alcohol to water in the alcohol-water solvent is 1:(2~4); and / or, the alcohol is selected from at least one of ethanol and isopropanol.

[0009] Furthermore, the silica sol dispersion is obtained by dispersing silica sol under the condition of a dispersant, wherein the dispersant is selected from anionic dispersants and nonionic dispersants.

[0010] Preferably, the mass ratio of the dispersant to the silica sol is (0.1~1):100.

[0011] Further, the mass ratio of the quaternary ammonium salt hydrolysate to the silica sol dispersion is 1:(8~15); and / or, the dropping rate of the quaternary ammonium salt hydrolysate is 10~25 ml / min; and / or, the reaction temperature of the silica sol dispersion and the quaternary ammonium salt hydrolysate is 10~25℃, and the reaction time is 3~5 h.

[0012] Furthermore, the silica sol satisfies at least one of the following conditions: solid content of 15-50%, pH value of 2-10, particle size of 5-100 nm, PDI of less than 0.2, and specific surface area of ​​20-400 m² / g.

[0013] The second aspect of this invention is to provide applications of the quaternary ammonium salt modified silica sol described in the first aspect above, the applications including at least one of the following: heavy metal ion adsorption in the field of water treatment, substrate modification of antibacterial coatings, functional modification of adsorption materials, catalyst carrier, catalyst molding binder for catalytic hydrogenation, catalytic oxidation of VOCs and catalytic degradation of wastewater.

[0014] In the above applications, when the bisquaternary ammonium salt modified silica sol is used as a catalyst support or catalyst forming binder, the prepared catalyst preferably satisfies the following condition: XRD crystallinity ≥ 85%.

[0015] Compared to existing technologies, the beneficial effects of this invention include, but are not limited to: the modified silica sol provided by this invention is modified by using a quaternary ammonium salt hydrolysate with quaternary ammonium functional groups, the quaternary ammonium salt hydrolysate generates hydroxyl (C-OH) and double positively charged (N) groups. + The active intermediate of the intermediate has the following functions: a) Bonding: The C-OH of the intermediate forms a CO-Si covalent bond with the -Si-OH on the surface of the silica sol, firmly grafting it onto the silica sol surface; b) Electrostatic stabilization: The double N +The silica sol particles are densely positively charged, which repel each other and prevents aggregation. They can also adsorb metal catalysts and destroy bacterial cell membranes; c) steric hindrance: the connecting chains of the bisquaternary ammonium salt form a physical barrier, further preventing particles from approaching and improving stability.

[0016] Through the above effects, the three goals of "stability improvement + broad-spectrum and efficient antibacterial + breakthrough in catalyst crystallinity" are achieved, which meets the needs of long-term use of catalysts, antibacterial in complex scenarios and efficient dispersion of active components, so that the crystallinity of supported catalysts reaches more than 92%, reducing inactive impurities and improving catalytic performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0018] Figure 1 shows the X-ray photoelectron spectra of the silica sols prepared in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] In one embodiment, a method for preparing a bis-quaternary ammonium salt modified silica sol is provided, comprising the steps of: 1) hydrolyzing a bis-quaternary ammonium salt in a weakly acidic aqueous alcohol solution to obtain solution A; 2) adding a dispersant to the silica sol and stirring until the dispersant is completely dissolved to obtain solution B; 3) adding solution A dropwise to solution B while stirring, and then reacting fully to obtain the bis-quaternary ammonium salt modified silica sol.

[0021] In the above embodiments, the bis-quaternary ammonium salt possesses a double positive charge and hydrolyzes to generate a hydroxyl-containing active intermediate. This intermediate can inhibit the aggregation of silica sol particles through strong electrostatic repulsion, significantly improving storage stability under acidic / neutral conditions. Furthermore, the double positive charge can disrupt bacterial cell membranes through "double charge attack," resulting in a broader antibacterial spectrum and higher efficiency. More importantly, the bipolar groups in the bis-quaternary ammonium salt molecule can form a synergistic adsorption effect with the metal active component, preventing metal particle aggregation and simultaneously enhancing the binding force between the silica sol and the catalyst matrix. This characteristic provides possibilities for innovative applications in the field of catalysts. Currently, there are no reports on technologies using this bis-quaternary ammonium salt to modify silica sol and specifically optimize catalyst application performance; therefore, developing related products has significant industrial value.

[0022] In the above embodiments, the following specific properties can be achieved through quaternary ammonium salt modification: 1. Significantly improved stability: For example, the double positive charge of trimethyl-(3-trimethylammoniumpropyl)ammonium dibromide forms a "double electrostatic repulsion," inhibiting particle aggregation—it does not gel after 24 months in a 60℃ oven (6 months longer than single quaternary ammonium salt modification), and the particle size variation coefficient under acidic conditions (pH=2) is ≤5% (≥15% for single quaternary ammonium salt modification), meeting the requirements for long-term storage and use of catalysts; 2. Broad-spectrum and highly efficient antibacterial performance: The "double charge attack" mechanism of quaternary ammonium salt can destroy the integrity of bacterial cell membranes, achieving an antibacterial rate of ≥98.5% against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, etc. (85~95% for single quaternary ammonium salt modification), and a long antibacterial effect (≥3 months), solving the problem of microbial contamination of catalysts in wastewater treatment, biocatalysis, and other scenarios; 3. Catalyst application innovation breakthroughs: As a carrier: the bipolar groups of the quaternary ammonium salt form synergistic adsorption with the metal active components (Pt, Pd, Cu, etc.), avoiding metal particle agglomeration. The metal particle size can be controlled within ≤5nm, and the dispersion uniformity is ≥90% (compared to ≤70% for traditional silica sol carriers), increasing the number of catalytic active sites by 40%. As a binder: the quaternary ammonium salt enhances the bonding force between silica sol and the catalyst matrix (molecular sieves, activated alumina, etc.). After catalyst molding, the wear loss rate is ≤5% (compared to ≥15% for traditional binders), the compressive strength is ≥15MPa, and the activity retention rate after 50 cycles is ≥90% (compared to ≥75% for traditional products). 4. Simple process and easy to scale up: The "one-step hydrolysis + low-temperature stirring" process is adopted, which does not require high-temperature aging or complex post-treatment. The reaction time is 3~6h, and the production efficiency is increased by 30% compared with the existing process. The raw materials are readily available and the cost is controllable.

[0023] In the above embodiments, the dropping method has a significant impact on ensuring product performance. Specifically, the method is as follows: Forward dropping (A→B): The low-concentration quaternary ammonium salt solution is slowly introduced into the silica sol dispersion, which can ensure the uniformity of the system concentration. The quaternary ammonium salt and the silica sol hydroxyl groups gradually and uniformly combine, and the dual electrostatic repulsion effect is fully utilized.

[0024] Reverse droplet addition (B→A): When silica sol enters a high-concentration quaternary ammonium salt system, local concentration imbalance causes agglomeration, which damages the product structure and stability. This is also the most common problem that is most likely to occur in unoptimized processes.

[0025] The above bottlenecks directly determine the effect of the modification reaction. If the order of addition is ignored, even if parameters such as temperature and stirring are controlled, it is impossible to prepare high-performance bis-quaternary ammonium salt modified silica sol.

[0026] In a preferred embodiment, the bisquaternary ammonium salt is selected from trimethyl-(3-trimethylammoniumpropyl)ammonium dihalide, hexamethylammonium halide, or 1,3-bis(trimethylammoniumpropyl)propane dihalide. Trimethyl-(3-trimethylammoniumpropyl)ammonium dibromide (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) is preferred as the bisquaternary ammonium salt compound, and the molecule contains two permanent positive charges (N...). + Its charge density is twice that of a single quaternary ammonium salt.

[0027] In a preferred embodiment, in step 1): the pH value of the weakly acidic alcohol-water solution is 3-5.5; the hydrolysis of the bisquaternary ammonium salt is carried out under ultrasonic conditions, preferably ultrasonic dispersion for 20-30 min (power 300-500W), followed by static hydrolysis for 1.5-2.5 h. The weakly acidic environment promotes hydrolysis, avoids the decomposition of the bisquaternary ammonium group, and improves hydrolysis efficiency through ultrasonic hydrolysis.

[0028] In a preferred embodiment, the mass ratio of the bisquaternary ammonium salt to the alcohol-water solvent is 1:(6~12); the mass ratio of alcohol to water in the alcohol-water solvent is 1:(2~4); the alcohol is selected from at least one of ethanol and isopropanol. Taking trimethyl-(3-trimethylammoniumpropyl)ammonium dihalide as an example, it is readily soluble in alcohol-water mixed solvents, exhibits high stability of the bisquaternary ammonium group, and its trimethoxysilyl-like structure is easily hydrolyzed and forms chemical bonds with hydroxyl groups on the silica sol surface.

[0029] In a preferred embodiment, the silica sol dispersion is obtained by dispersing silica sol under the condition of a dispersant, wherein the dispersant is selected from anionic dispersants and nonionic dispersants.

[0030] In a preferred embodiment, the mass ratio of the dispersant to the silica sol is (0.1~1):100.

[0031] In a preferred embodiment, the mass ratio of the quaternary ammonium salt hydrolysate to the silica sol dispersion is 1:(8~15); the dropping rate of the quaternary ammonium salt hydrolysate is 10~25 ml / min; the reaction temperature of the silica sol dispersion and the quaternary ammonium salt hydrolysate is 10~25℃, controlled by a water bath, and the reaction time is 3~5 h.

[0032] In a preferred embodiment, the silica sol meets at least one of the following conditions: solid content of 15-50%, pH value of 2-10, particle size of 5-100nm, PDI below 0.2, and specific surface area of ​​20-400m² / g, preferably high-purity H-Series silica sol from Guangdong Huierte Company.

[0033] Example 1 (Catalyst Support Type) Composition Ratio (mass percentage): Silica sol (Huierte H-50, solid content 30%, particle size 20nm) 90%, trimethyl-(3-trimethylammonium propyl)ammonium dibromide 2.5%, sodium dodecylbenzenesulfonate 0.3%, ethanol 5%, water 2.2%; Preparation steps: (1) Mix 5g ethanol with 2.2g water, add 2.5g trimethyl-(3-trimethylammonium propyl)ammonium dibromide, adjust pH to 4.5, ultrasonically disperse for 25min and then hydrolyze for 2h to obtain solution A; (2) Add 0.3g sodium dodecylbenzenesulfonate to 90g silica sol, stir at 700rpm for 1h to obtain solution B; (3) Add solution A dropwise to solution B at 15ml / min, stir at 400rpm in a 18℃ water bath for 4h to obtain bisquaternary ammonium salt modified silica sol (support type).

[0034] Example 2 (Catalyst binder type) Composition ratio (mass percentage): 88% silica sol (Huierte H-30, solid content 25%, particle size 15nm), 3.5% trimethyl-(3-trimethylammonium propyl)ammonium dibromide, 0.5% polyethylene glycol 6000, 6% isopropanol, 2% water; Preparation steps: (1) Mix 6g isopropanol with 2g water, add 3.5g trimethyl-(3-trimethylammonium propyl)ammonium dibromide, adjust pH to 4.0, ultrasonically disperse for 30min and then hydrolyze for 1.5h to obtain solution A; (2) Add 0.5g polyethylene glycol 6000 to 88g silica sol, stir at 600rpm for 1.2h to obtain solution B; (3) Add solution A dropwise to solution B at 20ml / min, stir at 350rpm in a 15℃ water bath for 5h to obtain bisquaternary ammonium salt modified silica sol (binder type).

[0035] Example 3 (General type, taking into account both carrier and binder) Composition ratio (mass percentage): 85% silica sol (Huierte H-40, solid content 35%, particle size 30nm), 4% trimethyl-(3-trimethylammonium propyl)ammonium dibromide, 0.8% polyether modified polysiloxane, 4% ethanol, 6.2% water; Preparation steps: (1) Mix 4g ethanol with 6.2g water, add 4g trimethyl-(3-trimethylammonium propyl)ammonium dibromide, adjust pH to 5.0, ultrasonically disperse for 20min and then hydrolyze for 2.5h to obtain solution A; (2) Add 0.8g polyether modified polysiloxane to 85g silica sol, stir at 800rpm for 0.8h to obtain solution B; (3) Add solution A dropwise to solution B at 10ml / min, stir at 500rpm in a 20℃ water bath for 3h to obtain bisquaternary ammonium salt modified silica sol (general type).

[0036] Example 4 (Catalyst Support Type) Composition Ratio (mass percentage): Silica sol (Huiert H-50, solid content 30%, particle size 20nm) 90%, 1,3-bis(trimethylammonium)propane dibromide 2.5%, sodium dodecylbenzenesulfonate 0.3%, ethanol 5%, water 2.2%; Preparation steps: (1) Mix 5g ethanol with 2.2g water, add 2.5g 1,3-bis(trimethylammonium)propane dibromide, adjust pH to 4.5, ultrasonically disperse for 25min, and hydrolyze for 2h to obtain solution A; (2) Add 0.3g sodium dodecylbenzenesulfonate to 90g silica sol, stir at 700rpm for 1h to obtain solution B; (3) Add solution A dropwise to solution B at 15ml / min, stir at 400rpm in a 18℃ water bath for 4h to obtain bisquaternary ammonium salt modified silica sol (carrier type).

[0037] Comparative Example 1 (Monoquaternary ammonium salt modified silica sol) component ratio: silica sol 90%, (3-trimethoxysilylpropyl)trimethylammonium chloride (monoquaternary ammonium salt) 2.5%, sodium dodecylbenzenesulfonate 0.3%, ethanol 5%, water 2.2%; preparation steps: same as Example 1, except that the bisquaternary ammonium salt is replaced with the monoquaternary ammonium salt.

[0038] Comparative Example 2 (unmodified silica sol) compared to Example 1 used Huerte H-50 silica sol (30% solid content, 20nm particle size) directly without any modification treatment.

[0039] Comparative Example 3 (Catalyst using conventional modified silica sol, commercially available product) Commercially available amino-modified silica sol (30% solid content, 20nm particle size).

[0040] The difference between Comparative Example 4 and Example 1 is that solution B was added dropwise to solution A.

[0041] 1. Storage stability test 1) The particle size change was tested at different pH values ​​(2, 7, 10) (test instrument: Malvern Zetasizer Nano ZS), and the coefficient of variation ((standard deviation / average particle size) × 100%) at pH value 2. The results are shown in Table 1.

[0042] Table 1: Particle size of samples with different pH values

[0043] Analysis: The bis-quaternary ammonium salt modified silica sol (Examples 1-3) exhibited stable particle size and strong anti-agglomeration ability across all pH environments (Example 2 showed the best performance); the comparative samples (mono-quaternary ammonium salt, unmodified, and commercially available amino-modified) were prone to agglomeration under acidic conditions (unmodified silica sol was the worst). Overall, the bis-quaternary ammonium salt modified silica sol demonstrated significantly better pH adaptability and storage stability than the comparative samples.

[0044] 2) Place the sample in a 60℃ oven and observe the gelation time; the results are shown in Table 2.

[0045] Table 2:

[0046] Analysis: The quaternary ammonium salt modified silica sol (Examples 1-3) exhibited excellent stability with gel times exceeding 20 months at 60°C under various pH conditions. In contrast, the gel times of the comparative samples (monoquaternary ammonium salt, unmodified, and commercially available amino-modified) were significantly shorter (unmodified silica sol only 2-4 months), and their stability was worse under acidic conditions.

[0047] 2. Antibacterial performance test: The antibacterial rate against Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 29213) was tested using the inhibition zone method (test standard: GB / T 21510-2008). The results are shown in Table 3.

[0048] Table 3: Comparison of antibacterial properties of the examples and comparative examples

[0049] Analysis: Examples 1-4 showed antibacterial rates of ≥98.5% against both types of bacteria, and the diameter of the inhibition zone was significantly larger than that of the single quaternary ammonium salt modified product and the commercially available product—double quaternary ammonium salt. The dual charge attack mechanism can more thoroughly destroy the bacterial cell membrane, achieving broad-spectrum and highly efficient antibacterial activity and solving the problem of catalyst inactivation in microbial contamination scenarios.

[0050] 3. X-ray photoelectron spectroscopy test: X-ray photoelectron spectroscopy was tested on the products of Example 1 and Comparative Examples 1 to 3. The results are shown in Figure 1.

[0051] Analysis of Si 2p binding energy (100-110 eV) from Figure 1 shows that the Si 2p binding energy of all samples is concentrated around 102-104 eV, indicating that silicon mainly exists in the form of Si-O bonds. The theoretical binding energy of Si-O is 103.36 eV, and the figures show conventional 1430 and sodium hydroxide type.

[0052] The lower binding energy around Si in Example 1 and Comparative Example 1 indicates that the strength or environment of their silicon-oxygen bonds may differ. This suggests the presence of ammonium ions around Si, which lowers the binding energy. However, no Si-N bonds were observed during the detection, indicating that the presence of ammonium ions on the silica sol surface affects its surface energy and charge, but does not affect the internal nanoparticles. Specifically, Example 1 exhibits more ammonium activity on its surface than Comparative Example 1, thus influencing the silica sol surface changes.

[0053] 4. Crystallinity test of catalyst (XRD) The crystallinity of the products of Example 1 and Comparative Examples 1 to 3 was tested by X-ray diffraction (XRD, Cu Kα rays) (crystallization = diffraction peak area of ​​crystalline phase / total diffraction peak area × 100%), and the results are shown in Table 4.

[0054] Table 4: Crystallinity test results of the examples and comparative examples

[0055] Analysis: The catalyst in Example 1 has a crystallinity of 87.3%, which is significantly higher than that of the comparative example, indicating that the symmetrical structure of the bis-quaternary ammonium salt has a clear advantage as a crystal growth template.

[0056] 5. Mechanical Properties as a Binder: The products of Examples 2 and Comparative Examples 1-3 were used as binders and mixed with molecular sieve (ZSM-5) to form a catalyst (binder addition amount 10%). The catalyst wear loss rate and compressive strength were tested (test standard: HG / T 3556-2018). The results are shown in Table 5: Table 5: Test Results of Catalyst Mechanical Properties

[0057] Analysis: The catalyst in Example 2 had a wear loss rate of only 4.2%, a compressive strength of 16.8 MPa, and an activity retention rate of 92.5% after 50 cycles. The bis-quaternary ammonium salt enhanced the bonding force between silica sol and molecular sieve, improved the structural stability of the catalyst, and met the requirements for recycling.

[0058] This invention achieves a breakthrough in catalyst crystallinity through the directional modification of quaternary ammonium salts, utilizing a "crystal growth template" mechanism, while simultaneously optimizing stability, antibacterial properties, and mechanical properties. The prepared quaternary ammonium salt-modified silica sol possesses four core advantages: 1) XRD crystallinity ≥85%, selectivity ≥95%; 2) no gelation after 24 months of storage at 60℃, stable under acidic conditions; 3) antibacterial rate against pathogenic bacteria ≥98.5%; 4) uniform metal dispersion and high mechanical strength. This invention provides a novel functional material for the catalyst field that combines high selectivity and long-term stability, and can be widely applied in catalytic hydrogenation, VOCs oxidation, and other scenarios, yielding significant economic and social benefits.

[0059] 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, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A bisquaternary ammonium salt modified silica sol, characterized in that, It is obtained by fully reacting silica sol dispersion and bisquaternary ammonium salt hydrolysate under stirring, wherein the bisquaternary ammonium salt hydrolysate is added dropwise; the bisquaternary ammonium salt hydrolysate is obtained by hydrolyzing bisquaternary ammonium salt in a weakly acidic alcohol aqueous solution.

2. The bisquaternary ammonium salt modified silica sol as described in claim 1, characterized in that, The quaternary ammonium salt is selected from trimethyl-(3-trimethylammoniumpropyl)ammonium dihalide, hexamethylammonium halide, or 1,3-bis(trimethylammoniumpropyl)propane dihalide.

3. The bisquaternary ammonium salt modified silica sol as described in claim 1, characterized in that, The pH value of the weakly acidic alcohol-water solution is 3 to 5.5; and / or, the hydrolysis of the bisquaternary ammonium salt is carried out under ultrasonic conditions; and / or, the hydrolysis time of the bisquaternary ammonium salt is 1.5 to 2.5 h.

4. The bisquaternary ammonium salt modified silica sol as described in claim 1, characterized in that, The mass ratio of the quaternary ammonium salt to the alcohol-water solvent is 1:(6~12); and / or, the mass ratio of alcohol to water in the alcohol-water solvent is 1:(2~4); and / or, the alcohol is selected from at least one of ethanol and isopropanol.

5. The bisquaternary ammonium salt modified silica sol as described in claim 1, characterized in that, The silica sol dispersion is obtained by dispersing silica sol under the condition of a dispersant, wherein the dispersant is selected from anionic dispersants and nonionic dispersants.

6. The bisquaternary ammonium salt modified silica sol as described in claim 5, characterized in that, The mass ratio of the dispersant to the silica sol is (0.1~1):

100.

7. The bisquaternary ammonium salt modified silica sol as described in claim 1, characterized in that, The mass ratio of the quaternary ammonium salt hydrolysate to the silica sol dispersion is 1:(8~15); and / or, the dropping rate of the quaternary ammonium salt hydrolysate is 10~25 ml / min; and / or, the reaction temperature of the silica sol dispersion and the quaternary ammonium salt hydrolysate is 10~25℃, and the reaction time is 3~5 h.

8. The bisquaternary ammonium salt modified silica sol as described in claim 1, characterized in that, The silica sol meets at least one of the following conditions: solid content of 15-50%, pH value of 2-10, particle size of 5-100nm, PDI of less than 0.2, and specific surface area of ​​20-400m² / g.

9. The application of the bisquaternary ammonium salt modified silica sol according to any one of claims 1 to 8, characterized in that, The applications include at least one of the following: heavy metal ion adsorption in water treatment, substrate modification of antibacterial coatings, functional modification of adsorption materials, catalyst carriers, catalyst molding binders for catalytic hydrogenation, catalytic oxidation of VOCs, and catalytic degradation of wastewater.

10. The application as described in claim 9, characterized in that, When the quaternary ammonium salt modified silica sol is used as a catalyst support or catalyst forming binder, the prepared catalyst satisfies the following condition: XRD crystallinity ≥ 85%.

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