阅读说明：本技术 苯基增强柔性二氧化硅气凝胶及制备方法和应用 (Phenyl-reinforced flexible silica aerogel, and preparation method and application thereof ) 是由 聂朝胤 张瑜 于 2021-01-27 设计创作，主要内容包括：本发明公开了一种苯基增强柔性二氧化硅气凝胶及制备方法和应用,所述的苯基增强柔性二氧化硅气凝胶以至少一种包括苯基基团的第一硅源和至少一种包括甲基基团的第二硅源作为前驱体,通过溶胶-凝胶法制得。其具有超疏水性、优异的机械性能、良好的油水分离能力、优异的热稳定性和阻燃性。所述制备方法包括如下步骤：步骤一,按照上述的苯基增强柔性二氧化硅气凝胶备料；步骤二,酸化水解,将CTAB溶解于酸溶液中,得到混合溶液,再将第一硅源和第二硅源加入到混合溶液中,持续搅拌使得第一硅源和第二硅源酸化水解；步骤三,碱化缩聚,向酸化水解后的溶液中加入碱,碱化缩聚形成凝胶；步骤四,老化、干燥得到苯基增强柔性二氧化硅气凝胶。(The invention discloses phenyl-reinforced flexible silica aerogel, a preparation method and application thereof. The composite material has super-hydrophobicity, excellent mechanical property, good oil-water separation capability, excellent thermal stability and flame retardance. The preparation method comprises the following steps: preparing materials according to the phenyl reinforced flexible silica aerogel; step two, acidifying and hydrolyzing, namely dissolving CTAB in an acid solution to obtain a mixed solution, adding a first silicon source and a second silicon source into the mixed solution, and continuously stirring to acidify and hydrolyze the first silicon source and the second silicon source; step three, alkalization polycondensation, namely adding alkali into the acidified and hydrolyzed solution, and alkalization polycondensation to form gel; and step four, aging and drying to obtain the phenyl reinforced flexible silica aerogel.)

1. A phenyl-reinforced flexible silica aerogel, characterized in that: the silicon-based organic silicon-.

2. Phenyl-reinforced flexible silica aerogel according to claim 1, characterized in that: the first silicon source is at least one of phenyl triethoxysilane, diphenyl diethoxy silane and triphenyl ethoxysilane, and the second silicon source is at least one of methyl triethoxysilane, dimethyl diethoxy silane, trimethyl ethoxysilane and dodecyl trimethoxy silane.

3. Phenyl-reinforced flexible silica aerogel according to claim 1 or 2, characterized in that: the first silicon source is phenyltriethoxysilane, the second silicon source is methyltriethoxysilane and dimethyldiethoxysilane, and the molar ratio of the methyltriethoxysilane to the dimethyldiethoxysilane to the phenyltriethoxysilane is 1: 0.35-0.45: 0.02 to 0.20.

4. The preparation method of the phenyl-reinforced flexible silica aerogel is characterized by comprising the following steps:

preparing a phenyl-reinforced flexible silica aerogel material according to any one of claims 1 to 3;

step two, acidifying and hydrolyzing, namely dissolving CTAB in acid to obtain a mixed solution, adding a first silicon source and a second silicon source into the mixed solution, and continuously stirring to acidify and hydrolyze the first silicon source and the second silicon source;

step three, alkalization polycondensation, namely adding alkali into the acidified and hydrolyzed solution, and alkalization polycondensation to form gel;

and step four, aging and drying to obtain the phenyl reinforced flexible silica aerogel.

5. The method for preparing phenyl-reinforced flexible silica aerogel according to claim 4, characterized in that: and in the third step, the alkalization polycondensation temperature is 65-80 ℃, and the alkalization polycondensation time is 2-5 h.

6. The method for preparing phenyl-reinforced flexible silica aerogel according to claim 4, characterized in that: and the aging temperature in the fourth step is the same as the alkalization polycondensation temperature, and the aging time is 18-23 h.

7. The method for preparing phenyl-reinforced flexible silica aerogel according to claim 4, characterized in that: and the drying temperature in the fourth step is 55-75 ℃, and the drying time is 7-10 h.

8. The method for preparing phenyl-reinforced flexible silica aerogel according to claim 4, characterized in that: the acid in the second step is hydrochloric acid, oxalic acid or acetic acid, and the alkali in the third step is urea or ammonia water.

9. Use of the phenyl-reinforced flexible silica aerogel according to any one of claims 1 to 3 or the phenyl-reinforced flexible silica aerogel prepared by the preparation method according to any one of claims 4 to 8 in a high-temperature or humid environment.

10. Application of the phenyl-reinforced flexible silica aerogel according to any one of claims 1 to 3 or the phenyl-reinforced flexible silica aerogel prepared by the preparation method according to any one of claims 4 to 8 in the fields of heat insulation materials, waste gas and wastewater treatment, catalysts, medicines and electronic products.

Technical Field

The invention relates to the technical field of aerogel, in particular to phenyl-reinforced flexible silicon dioxide aerogel and a preparation method and application thereof.

Background

The silica aerogel has a plurality of excellent properties such as low density, high porosity, large specific surface area, excellent hydrophobicity, low thermal conductivity and the like, is widely applied to the fields of aerospace, construction, catalysis, heat insulation, microelectronics, medicine and the like, and the framework of the silica aerogel is mainly formed by interconnecting Si-O-Si bonds. Due to the existence of a large number of Si-O-Si bonds, the pure silicon dioxide aerogel network is a rigid structure, so that the mechanical property of the pure silicon dioxide aerogel network is poor, and the pure silicon dioxide aerogel network is easy to crack under the action of external force, so that the aerogel network structure is damaged, and the application range of the pure silicon dioxide aerogel network is severely limited.

In order to improve the mechanical properties of silica aerogel to broaden its application range, researchers have conducted extensive studies. There are two main methods used so far.

Firstly, the flexibility of the silica aerogel is improved by introducing a polymer with good flexibility. Kim et al at the furniture preparation of cellulose-SiO₂ composite aerogels with high SiO₂contents using a LiBr aqueous solution discloses the addition of silica particles to an aqueous solution of lithium bromide containing cellulose to prepare a cellulose-silica composite aerogel. The obtained aerogel has excellent mechanical properties, thermal stability and lower heat conductivity coefficient. Zhang et al, in Multiscale mullite fiber/while re-expressed silica aerogel nanocomposites with enhanced compressive strength and thermal insulation performance, disclose the embedding of mullite fibers/whiskers into a silica aerogel to produce a reinforced composite aerogel having a high specific surface area and superior pressure resistance. Although the composite aerogels thus obtained exhibit excellent mechanical properties, such methods of enhancing the mechanical properties of silica aerogels assisted by external factors are generally complex and expensive, and are not conducive to large-scale production and application of aerogels. In addition, as the skeleton structure of the composite aerogel is not changed essentially, the introduction of a large amount of polymer inevitably increases the density and the thermal conductivity of the aerogel.

And secondly, introducing siloxane containing hydrophobic groups as a precursor, and converting the skeleton structure of the silicon dioxide aerogel from a rigid structure to a flexible structure by utilizing the characteristic that the hydrophobic groups do not participate in hydrolysis and polycondensation reactions. This method is widely used because of its simplicity and low cost. Some hydrophobic siloxanes containing methyl groups, for example: methyltriethoxysilane, MTES, methyltrimethoxysilane, MTMS, dimethyldiethoxysilane, dedims, trimethyltrimethoxysilane, TMMS, and dodecyltrimethoxysilane, DTMS, are the most commonly used siloxanes to enhance the mechanical properties of silica aerogels. Wang et al disclose that flexible silica aerogels are prepared by a simple sol-gel process using DTMS and tetramethoxysilane TMOS as co-precursors, in the synthesis of flexible mesoporous aerogels with super-reactivity for effective removal of layred and emulsified oil from water, and are used for the separation of oil-in-water emulsions. Gao et al, in the Ambient compressed flexible silica aerogel for construction of monolithic shape-stabilized phase materials, disclose that TMMS, MTMS and TEOS are used to successfully synthesize flexible silica aerogel, and combine it with phase change energy storage materials, which improves the application range of phase change energy storage materials. However, the presence of a large number of methyl groups makes the thermal stability and flame retardancy of the flexible silica aerogel relatively poor, severely limiting the application range of the flexible silica aerogel. Therefore, finding a simple and convenient method to improve the mechanical properties and the thermal stability and the flame retardancy of the silica aerogel is a problem to be solved urgently at present.

Disclosure of Invention

The invention aims to provide a phenyl-reinforced flexible silica aerogel, a preparation method and application thereof, wherein the phenyl-reinforced flexible silica aerogel has super-hydrophobicity, excellent mechanical properties, good oil-water separation capability, excellent thermal stability and flame retardance.

The phenyl-reinforced flexible silica aerogel provided by the invention is prepared by taking at least one first silicon source containing phenyl groups and at least one second silicon source containing methyl groups as precursors through a sol-gel method.

Further, the first silicon source is at least one of phenyl triethoxysilane, diphenyl diethoxy silane and triphenyl ethoxysilane, and the second silicon source is at least one of methyl triethoxysilane, dimethyl diethoxy silane, trimethyl ethoxysilane and dodecyl trimethoxysilane.

Further, the first silicon source is phenyltriethoxysilane, the second silicon source is methyltriethoxysilane and dimethyldiethoxysilane, and the molar ratio of the methyltriethoxysilane to the dimethyldiethoxysilane to the phenyltriethoxysilane is 1: 0.35-0.45: 0.02 to 0.20.

A preparation method of phenyl-reinforced flexible silica aerogel comprises the following steps:

preparing materials according to the phenyl reinforced flexible silica aerogel;

step two, acidifying and hydrolyzing, namely dissolving CTAB in acid to obtain a mixed solution, adding a first silicon source and a second silicon source into the mixed solution, and continuously stirring to acidify and hydrolyze the first silicon source and the second silicon source;

step three, alkalization polycondensation, namely adding alkali into the acidified and hydrolyzed solution, and alkalization polycondensation to form gel;

and step four, aging and drying to obtain the phenyl reinforced flexible silica aerogel.

Further, the alkalization polycondensation temperature in the third step is 65-80 ℃, and the alkalization polycondensation time is 2-5 h.

Further, the aging temperature in the fourth step is the same as the alkalization polycondensation temperature, and the aging time is 18-23 h.

Further, the drying temperature in the fourth step is 55-75 ℃, and the drying time is 7-10 hours.

Further, the acid in the second step is acetic acid, hydrochloric acid or oxalic acid, and the alkali in the third step is urea or ammonia water.

The phenyl-reinforced flexible silica aerogel or the phenyl-reinforced flexible silica aerogel prepared by the preparation method is applied to a high-temperature or humid environment.

The phenyl-reinforced flexible silica aerogel or the phenyl-reinforced flexible silica aerogel prepared by the preparation method is applied to the fields of heat insulation materials, waste gas and wastewater treatment, catalysts, medicines and electronic products.

Compared with the prior art, the invention has the following beneficial effects.

1. According to the invention, a multi-silicon-source system is formed by introducing a first silicon source comprising a phenyl group, and the phenyl-enhanced flexible silica aerogel is prepared by combining a simple sol-gel method with normal-pressure drying, compared with a methyl group, the phenyl group with a larger volume can form a larger steric hindrance, and meanwhile, a p pi-d pi conjugation effect exists between the phenyl group and a Si atom, so that the hydrolytic polycondensation rate of the first silicon source comprising the phenyl group under the condition of alkali catalysis is very low due to the two factors, and finally, only the surface layer of secondary particles can be subjected to polycondensation reaction to form a film-like structure to cover the surface of an aerogel framework, so that the connection between the secondary particles is enhanced. With the increase of the first silicon source, the function of the phenyl group for reinforcing the aerogel skeleton is more and more obvious, which is reflected in that the aerogel skeleton gradually changes from a fragile particle structure to a reinforced non-particle structure. It should be noted that, compared with the aerogel without the first silicon source, even if only a small amount of the first silicon source is added, a layer of film-like structure appears on the aerogel skeleton, and the film-like structure is more widely distributed along with the increase of the first silicon source, and meanwhile, the connection between the secondary particles forming the aerogel is tighter.

2. According to the invention, the introduced phenyl group in the first silicon source is a rigid group, the rigidity of the aerogel can be improved by introducing the phenyl group into the flexible aerogel skeleton, the compressive strength of the aerogel is increased, and meanwhile, the connection of the aerogel skeleton is enhanced by the film-like structure covering the surface of the secondary particles, so that the aerogel skeleton can be restored to the original state after being compressed. Phenyl-reinforced silica aerogels not only have excellent compressive resilience, but can also be bent to a considerable angle, and upon release of an external force, the aerogels can return substantially to their original state, which has been very rare in previous reports on aerogel flexibility.

3. The phenyl-enhanced silica aerogel disclosed by the invention has stronger hydrophobicity and excellent oil-water separation capability, the hydrophobicity of the aerogel is mainly influenced by surface energy and a microstructure, on one hand, the surface energy is closely related to the length of a hydrophobic chain, and the longer the hydrophobic chain is, the lower the surface energy is, the better the hydrophobicity of the aerogel is. On the other hand, the micro-nanostructured surface has a certain micro roughness, which helps to increase the hydrophobicity of the aerogel. The phenyl groups derived from the first silicon source possess longer hydrophobic chains than the methyl groups, and thus, the hydrophobicity of the aerogel gradually increases as the first silicon source increases. However, the increase of a large amount of hydrophobic groups can significantly improve the phase separation degree of the system, so that the skeleton structure of the aerogel is coarsened, and the micro roughness of the surface is damaged, so that the use ratio of the first silicon source and the second silicon source needs to be limited according to actual conditions. The stronger hydrophobicity of the phenyl enhanced flexible silica not only enables the phenyl enhanced flexible silica to separate organic pollutants floating on the water surface, such as engine oil and normal hexane, but also has excellent separation capability on organic pollutants with density higher than that of water.

4. The phenyl-reinforced silicon dioxide aerogel disclosed by the invention has excellent thermal stability, phenyl groups have larger steric hindrance, the breakage of polymer molecular chains is prevented, and meanwhile, Si-C₆H₅The bond can generate self-crosslinking in the pyrolysis process to form an aromatic ring, so that the crosslinking degree of the aerogel is further improved, and the silicon dioxide aerogel has excellent thermal stability.

5. The phenyl-reinforced silica aerogel disclosed by the invention has good flame retardance, and in the combustion process, phenyl groups can be gradually changed into carbon with a protection effect, so that flame can be prevented from further invading into a three-dimensional network structure of the aerogel.

6. The phenyl reinforced silica aerogel disclosed by the invention has good flexibility and strong shape recovery capability, can be repeatedly used, is particularly used for oil-water separation, can discharge pollutants in the aerogel through extrusion, and is convenient and rapid. Simultaneously because the flexibility is better, and then can follow the shape design according to corresponding spare part shape to the aerogel for the aerogel can be better laminate with spare part.

7. The preparation method provided by the invention is simple in process flow, the precursor formed by the first silicon source and the second silicon source generates a corresponding hydrolysate under the action of acidification and hydrolysis, a gel network is formed under the action of alkalization and polycondensation, and finally the product is obtained in a normal-pressure drying mode, and complex solvent exchange and surface modification steps are not needed in the whole preparation process.

Drawings

FIG. 1 is a schematic view of the hydrolysis and polycondensation mechanism of the phenyl-reinforced silica aerogel according to the present invention;

FIG. 2 is a photograph of aerogels obtained at different PTES/MTES molar ratios;

FIG. 3 is a Fourier transform infrared spectrum of an aerogel obtained under different PTES/MTES molar ratios;

FIG. 4 is a micrograph of aerogels obtained at different PTES/MTES molar ratios;

FIG. 5 is a graph showing the stress-strain curves of aerogels obtained under different PTES/MTES molar ratios;

FIG. 6 is a graph of Young's modulus and stress at 80% strain for aerogels obtained at different PTES/MTES molar ratios;

FIG. 7 is a schematic diagram of the adsorption capacity of a phenyl-reinforced silica aerogel according to a first embodiment of the present invention;

FIG. 8 is a graph showing the comparison of the adsorption capacities of phenyl-reinforced silica aerogel according to the first embodiment of the present invention and conventional aerogel;

FIG. 9 is one of the schematic diagrams showing the comparison of thermal stabilities of P-0 and P-0.12 under a nitrogen atmosphere;

FIG. 10 is a second graphical representation of the comparison of the thermal stability of P-0 and P-0.12 under nitrogen;

FIG. 11 is a comparative graphical representation of the flame retardancy of P-0 and P-0.12.

Detailed Description

The present invention will be described in detail with reference to the following embodiments in conjunction with the accompanying drawings.

The raw material sources of the following examples are respectively: methyltriethoxysilane (MTES, 98%), dimethyldiethoxysilane (DEDMS, 97%), phenyltriethoxysilane (PTES, 98%) and cetyltrimethylammonium bromide (CTAB, 99%) were all purchased from McClin biochemicals, Inc., acetic acid (CH)₃COOH，AR) Purchased to a chemical reagent manufacturing plant of Corlon, Urea (H)₂NCONH₂AR) from national pharmaceutical group chemical Co., Ltd, absolute ethanol (C)₂H₅OH, AR) was purchased from chongqing chemical group limited. All materials were purchased for use without further purification.

Example one, a phenyl-reinforced flexible silica aerogel is prepared by a sol-gel method using a mixture of a first silicon source and a second silicon source as a precursor, wherein the first silicon source is phenyltriethoxysilane PTES, the second silicon source is methyltriethoxysilane MTES and dimethyldiethoxysilane DEDMS, and the molar ratio of the methyltriethoxysilane MTES, the dimethyldiethoxysilane DEDMS, and the phenyltriethoxysilane PTES is 1: 0.38: 0.12. the preparation method comprises the following steps:

step one, preparing materials according to the phenyl reinforced flexible silica aerogel. Acetic acid is adopted for acidification and hydrolysis, urea is adopted for alkalization and polycondensation, and the molar ratio of the components is MTES: DEDMS: PTES 1: 0.38: 0.12.

and step two, acidifying and hydrolyzing, namely dissolving 1g of Cetyl Trimethyl Ammonium Bromide (CTAB) in 15ml of acetic acid solution with the concentration of 1mol/L under the stirring condition to obtain a mixed solution, mixing MTES, DEDMS and PTES according to the molar ratio, adding the mixed solution into the mixed solution, and continuously stirring for 1h to acidify and hydrolyze the first silicon source and the second silicon source.

And step three, alkalization polycondensation, namely adding 5g of urea into the acidified and hydrolyzed solution, pouring the urea into a mold after the urea is fully dissolved, putting the mold into a drying oven at the temperature of 80 ℃, and alkalization polycondensation to form gel, wherein the gel time is 3 hours.

And step four, aging the obtained gel for 21 hours at the temperature of 80 ℃ to obtain an aged wet gel, cleaning the aged wet gel for 3 times by using alcohol, and then putting the cleaned wet gel into a drying box at the temperature of 60 ℃ to dry the wet gel at normal pressure for 8 hours to obtain the phenyl-reinforced silicon dioxide aerogel, which is recorded as P-0.12.

In the second embodiment, the difference from the first embodiment is: the molar ratio of PTES to MTES was 0.04, and the remainder was the same as in example one, and the phenyl-reinforced silica aerogel obtained was designated P-0.04.

In the third embodiment, the difference from the first embodiment is that: the molar ratio of PTES to MTES was 0.08, and the remainder was the same as in example one, and the phenyl-reinforced silica aerogel obtained was designated P-0.08.

Example four, in order to investigate the effect of the addition of PTES on the performance of silica aerogel, analysis was performed without adding PTES and with an excessively large amount of PTES as comparative examples.

Comparative example one: the mole ratio of PTES to MTES is 0 without adding PTES, the other preparation process parameters are the same as the first embodiment, and the prepared silica aerogel is marked as P-0.

Comparative example two: the difference from the first embodiment is that: the molar ratio of PTES to MTES was 0.16, and the rest was the same as in example one, and the silica aerogel obtained was designated as P-0.16.

Comparative example three: the difference from the first embodiment is that: the molar ratio of PTES to MTES was 0.20, the same as in example one except that the product obtained was designated P-0.20.

Characterization means, density of aerogel ρ_bObtained by the ratio of mass m to volume V; the porosity is calculated by the following equation:where ρ is_sIs the skeleton density of the aerogel, and is usually 2.2g/cm³。

The microscopic morphology of the obtained aerogel was observed by means of a field emission scanning electron microscope (FESEM, JEM-7800F, Japan) using an acceleration voltage of 10 kV. The chemical composition of the aerogel was characterized by Fourier transform Infrared Spectroscopy (FTIR, Nicolet6700, USA) at a measured wave number of 400cm^-1～2000cm^-1. The mechanical properties of the aerogel are tested by using a uniaxial compression testing machine (CMT4503, China), and the loading speed is 2 mm/min; the Young's modulus of the aerogel is obtained by the linear region of the first 10% strain of the stress-strain curve. The thermal stability of the aerogel was characterized by a thermal analyzer (TGA, STA409PC, Germany) with a heating rate of 10 ℃/min at an air flow rate of 30ml/minHeating the mixture from 25 ℃ to 800 ℃; the aerogel contact angles were measured using a contact angle tester (dataphysics oca25, Germany) using a drop volume of 5 μ l and all contact angles were tested 3 times and the average was taken as the final experimental data. The results of the characterization of the density, porosity and contact angle for examples one to three and comparative examples one to three are shown in table 1.

Table 1 characterization results of density, porosity and contact angle of the aerogels prepared

Serial number	Density (g/cm)-3)	Porosity (%)	Contact angle (°)
				P-0	0.068	96.9	145.6
P-0.04	0.073	96.7	152.7
				P-0.08	0.079	96.4	156.9
P-0.12	0.082	96.3	159.8
				P-0.16	0.094	95.7	155.4

Microscopic morphology and chemical composition analysis, the phenyl enhanced flexible silica aerogel is prepared by an acid and alkali two-step sol-gel method, and the method comprises hydrolysis and polycondensation processes of a co-precursor. Referring to fig. 1, MTES, dedims and PTES are hydrolyzed under the action of acetic acid to generate corresponding hydrolysis products, and are polycondensed under the action of urea to form a gel network, and finally, the aerogel is obtained by normal pressure drying. The whole preparation process does not need complicated solvent exchange and surface modification steps. Referring to fig. 2, when the mole ratio of PTES/MTES is less than or equal to 0.12, the appearance of the aerogel has almost no obvious change, whereas when the mole ratio of PTES/MTES is greater than 0.16, the volume shrinkage of the aerogel is obviously increased, and the aerogel has the characteristics of coarse bottom and fine top, and cannot form aerogel blocks with uniform top and bottom. When the molar ratio of PTES/MTES was 0.20 or more, no wet gel was even obtained.

The chemical composition of the resulting aerogel was characterized using a fourier transform infrared spectrometer and the results are shown in figure 3. Absorption peak 1142cm^-1、1027cm^-1And 783cm^-1Due to the symmetric and asymmetric vibrations of the Si-O-Si bond. Strong peak 1274cm^-1It is due to the asymmetric deformation of C-H, which is mainly derived from MTES and DEDMS. Absorption peak 1433cm^-1、 719cm^-1And 699cm^-1Is derived from Si-C₆H₅With increasing PTES, Si-C₆H₅The absorption peak of (a) was gradually increased, indicating that more phenyl groups having rigidity were introduced into the aerogel skeleton. Absorption peak 1597cm^-1Due to the stretching vibration of C ═ C, which is derived from phenyl groups, this also further illustrates the presence of phenyl-containing groups in the aerogel framework.

The microscopic morphology of the obtained aerogel is observed by using a field emission scanning electron microscope, the used accelerating voltage is 10kV, and the result is shown in figure 4, wherein a is the microscopic morphology of P-0, b is the microscopic morphology of P-0.04, c is the microscopic morphology of P-0.08, d is the microscopic morphology of P-0.12, e is the microscopic morphology of P-0.16, and f is the microscopic morphology of P-0.20. With increasing mole ratio of PTES/MTES, the secondary particles making up the aerogel gradually increased. This is due to the strong hydrophobicity of the phenyl group derived from PTES, which increases the degree of phase separation of the system. With the increase of PTES, the phase separation degree of the system is gradually increased, so that the particles forming the aerogel skeleton are gradually increased. It is noted that even with a small amount of PTES (P ═ 0.04), a layer of membranous structure appears on the aerogel skeleton, as indicated by the arrows, compared to the aerogel without PTES.

And along with the increase of PTES, the membrane-like structure also distributes more extensively, and wraps up on flexible silica aerogel surface gradually, and simultaneously, the connection between the secondary particle of constituteing the aerogel is also inseparabler, especially when P is greater than or equal to 0.12, the skeleton of aerogel presents non-granular structure, explains that the introduction of PTES helps the aerogel skeleton to have spherical granular structure to change to non-granular structure, and this kind of non-granular structure makes the connection of aerogel skeleton more firm. Mainly because: compared with a methyl group, a phenyl group with a larger volume can form larger steric hindrance, and a p pi-d pi conjugated effect exists between the phenyl group and a Si atom, so that the hydrolysis and polycondensation rate of PTES under the condition of alkali catalysis is very low, and finally, the polycondensation reaction can only occur on the surface layer of secondary particles, and the formed film-like structure covers the surface of the aerogel skeleton to enhance the connection between the secondary particles. With the increase of PTES, the role of phenyl reinforced aerogel skeleton is more and more obvious, which is reflected in that the aerogel skeleton is gradually changed from a fragile particle structure to a reinforced non-particle structure.

The pressure-strain curve of the aerogel was tested using a uniaxial compression tester, and as a result, referring to fig. 5, P-0.12 was able to be compressed up to 80% strain without cracking, and after unloading the load, the compressed P-0.12 was able to almost completely return to the original state, exhibiting excellent mechanical properties. All samples were able to be easily compressed 80% without cracking, except for P-0.16, where fracture occurred at only about 66% compressive strain. Compared with the aerogel without added PTES, the mechanical properties of the phenyl-reinforced silica aerogel are obviously improved, which is reflected in Young modulus and compressive strength under 80% strain condition, see FIG. 6. Because the phenyl group is a rigid group, the rigidity of the aerogel can be improved by introducing the phenyl group into the flexible aerogel skeleton, and the compressive strength of the aerogel is increased. Thus, with increasing PTES, the Young's modulus of the resulting aerogel increased from 0.45KPa to 1.35KPa, and the compressive strength at 80% strain increased from 51.99KPa to 177.69 KPa. However, too much PTES would convert the silica framework from a flexible to a rigid structure, resulting in cracking of the aerogel with only 66% compressive strain. In addition, the connection of the aerogel skeleton is enhanced by the film-like structure covering the surface of the secondary particles, so that the aerogel skeleton can return to the original state after being compressed. This is evidenced by the increasing amount of aerogel recovery after compression as the PTES/MTES molar ratio increases. Phenyl-reinforced aerogels not only have excellent compression resilience, but can also be bent to a considerable angle, and upon release of an external force, the aerogels can be substantially restored to the original state, which has been very rare in previous reports.

The hydrophobicity of the resulting aerogels was characterized using a contact angle tester and the results are shown in table 1. It can be seen that the hydrophobicity of the aerogel is significantly increased from 145 ° of P-0 to 152.7 ° of P-0.04 when a little PTES is added, and the aerogel shows a trend of increasing hydrophobicity and decreasing hydrophobicity as the molar ratio of PTES/MTES increases, and that the contact angle is maximum at a value of 159.8 ° when the value of P is 0.12. The hydrophobicity of aerogels is mainly influenced by the surface energy and microstructure, on the one hand, the surface energy is closely related to the length of the hydrophobic chains, the longer the hydrophobic chains, the lower the surface energy, the better the hydrophobicity of the aerogel. On the other hand, the micro-nanostructured surface has a certain micro roughness, which helps to increase the hydrophobicity of the aerogel. Phenyl groups derived from PTES possess longer hydrophobic chains than methyl groups, and thus the hydrophobicity of aerogels increases with increasing PTES. However, the increase of a large number of hydrophobic groups can significantly increase the degree of phase separation of the system, so that the pores of the aerogel are increased and are not enough to form a surface with a certain mesoscopic roughness. Therefore, at higher P values (> 0.12), the hydrophobicity of the resulting aerogel is rather reduced.

Referring to FIG. 7, the adsorption capacity of P-0.12 for several organic solvents is shown, including methanol, Chloroform, N-hexane, dimethylacetamide, DMF, Gasoline and diesel, which are common organic pollutants in our daily life, and the adsorption capacity of P-0.12 for organic pollutants is between 9.7 and 17.6g/g, which is much higher than that of 7.8 to 13.2g/g of elastic mesoporous aerogel, 6.8 to 13.7g/g of polypropylene-based reinforced silica aerogel, 5 to 12.8g/g of polymethylsilsesquioxane silica aerogel, 4 to 12g/g of cellulose and 5.8 to 11.6g/g of silica sponge. P-0.12 possesses such excellent adsorption capacity because it possesses a porosity of 96.3%.

In addition, P-0.12 has super-hydrophobicity and excellent mechanical property, and can be used for oil-water separation. After P-0.12 was placed in the oil-water mixture, P-0.12 merely floated in the oil layer due to its excellent oleophilic and hydrophobic ability and extremely low density, rather than sinking to the bottom of the beaker where the water layer was present. And (2) putting 0.3g of P-0.12 into a beaker filled with 20ml of n-hexane dyed with oil red O and 30lm of deionized water, taking out after 10 seconds, transferring the organic solvent in an external force extrusion mode, and putting the aerogel into the organic solvent again for next adsorption after the extrusion is finished. The excellent mechanical properties allow P-0.12 to be directly removed by extrusion after adsorption is complete. After 8 times of cyclic adsorption, n-hexane in water was completely removed, and the dried P-0.12 still maintained the original appearance, exhibiting excellent cyclic adsorption capacity due to the excellent compressive strength and flexibility of the phenyl-reinforced aerogel. Moreover, the excellent hydrophobicity of P-0.12 not only can separate organic pollutants floating on the water surface, such as engine oil and normal hexane, but also has excellent separation capability on organic pollutants with density higher than that of water, such as trichloromethane.

Thermal stability is one of the most important properties of aerogels. The thermal stability of P-0 and P-0.12 under nitrogen atmosphere was tested, respectively, and the results are shown in FIGS. 9 and 10. The maximum degradation rate temperature of the phenyl-reinforced flexible aerogel P-0.12 in a nitrogen atmosphere is up to 742.9 ℃, compared with the maximum degradation rate temperature of the flexible aerogel P-0 without PTES, the maximum degradation rate temperature is improved by over 150 ℃, and the improvement is very rare in previous reports on the thermal stability of the flexible silica aerogel. The reason why the phenyl-reinforced aerogel has such excellent thermal stability is that: the phenyl group has larger steric hindrance, which hinders the breaking of polymer molecular chains, and simultaneously Si-C₆H₅The bond can generate self-crosslinking to form an aromatic ring in the pyrolysis process, and the crosslinking degree of the aerogel is further improved. In addition, as is apparent from FIG. 9, the remaining weight of P-0.12 after the completion of the thermal stability test is much higher than that of P-0, which also indicates that the phenyl-reinforced flexible silica aerogel has excellent thermal stability.

Referring to FIG. 11, the flame retardant properties of P-0 and P-0.12, respectively, were tested, and aerogel P-0 without added PTES burned immediately upon flame exposure, and continued to burn even after the aerogel was removed from the flame. This is due to the presence of the methyl group-CH in the aerogel₃Is easily ignited. In contrast, aerogel P-0.12 with PTES added did not ignite after coming into contact with the flame, but rather served as a flame barrier. After the phenyl reinforced aerogel is removed from the flame, the phenyl reinforced aerogel does not continuously burn like P-0, which shows that the phenyl reinforced silica aerogel has excellent flame retardant performance. During the contact of P-0.12 with the flame, red light appears at the bottom, and after leaving the flame, the red light is very shortThe time has elapsed, due to the accumulation of stable silica at the bottom of the aerogel, which, when the aerogel is removed from the flame, rapidly decreases in temperature, with the consequent disappearance of the red light. By comparing the appearances of P-0 and P-0.12 after combustion, it can be easily found that P-0 is seriously burnt, even the inside of the aerogel is burnt, which indicates that the flame retardant property of P-0 is poor. In contrast, there was little trace of scorch in the interior of P-0.12 after combustion, which further indicates that the phenyl-reinforced aerogel possessed excellent flame retardancy. This is attributed to the fact that during the combustion process, the phenyl groups gradually become a protective char, blocking further penetration of the flame into the aerogel three-dimensional network.

Example five, using at least one first silicon source comprising phenyl groups and at least one second silicon source comprising methyl groups as precursors, the first silicon source being triphenylethoxysilane and the second silicon source being trimethylethoxysilane, prepared by a sol-gel method, it has good flexibility, mechanical properties, hydrophobicity, thermal stability and flame retardancy as tested by properties.

Example six, using as precursors at least one first silicon source comprising phenyl groups, which is a mixture of triphenylethoxysilane and diphenyldiethoxysilane, and at least one second silicon source comprising methyl groups, which is a mixture of trimethylethoxysilane and dodecyltrimethoxysilane, prepared by a sol-gel method, has good flexibility, mechanical properties, hydrophobicity, thermal stability and flame retardancy as tested for properties.

Example seven, using as precursors at least one first silicon source comprising phenyl groups and at least one second silicon source comprising methyl groups, the first silicon source being diphenyldiethoxysilane and the second silicon source being a mixture of trimethylethoxysilane and dimethyldiethoxysilane, prepared by a sol-gel method, has good flexibility, mechanical properties, hydrophobicity, thermal stability and flame retardancy as measured by performance tests.

From the performance analysis, the introduction of the first silicon source containing the phenyl group improves the mechanical property, hydrophobicity, good oil-water separation capability, thermal stability and flame retardance of the flexible silica aerogel, so that the flexible silica aerogel can be applied in extreme environments such as high temperature and humidity, and the application range is expanded. And can also be applied to the fields of heat insulation materials, waste gas and waste water treatment, catalysts, medicines and electronic products like the conventional flexible silica aerogel.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.