Gold / silicon dioxide hydrophobic composite aerogel and preparation method thereof

Abstract

The invention provides gold / silicon dioxide hydrophobic composite aerogel and a preparation method thereof, and belongs to the technical field of novel aerogel preparation, and the composite aerogel comprises gold nanoparticles and silicon dioxide aerogel with hydrophobic property. The specific preparation method comprises the following steps: preparing the gold nanoparticles, and adding the prepared gold nanoparticles in the aerogel preparation process to obtain the gold / silicon dioxide hydrophobic composite aerogel. Compared with the traditional aerogel preparation technology, the preparation method has the advantages that the gaseous carbon dioxide is introduced to catalyze the aerogel, so that the requirement of adding supercritical carbon dioxide in the traditional preparation method on equipment is effectively reduced, and the preparation cost of the aerogel material is greatly reduced. The prepared gold / silicon dioxide hydrophobic composite aerogel has good SERS performance and is suitable for the fields of detection of organic harmful functional groups in water and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparing new aerogels. BACKGROUND

[0002] Polycyclic aromatic hydrocarbons (PAHs) as persistent organic pollutants containing two or more benzene rings, widely distributed in water, soil and atmospheric environment, can be activated in vivo as a strong carcinogenic compounds, and pose a serious threat to the ecosystem and public health. At present, the systematic monitoring of pollutants mainly relies on traditional methods such as high performance liquid chromatography-fluorescence detection method (HPLC-FLD) and gas chromatography-mass spectrometry (GC-MS). Although these methods have a wide range of applications, they rely on complex and lengthy sample pretreatment procedures, including organic solvent extraction, purification and concentration steps, which are not only tedious and time-consuming, but also difficult to achieve rapid on-site detection, and use a large amount of toxic solvents, which are not friendly to operators and the environment. Therefore, there is an urgent need to develop innovative detection technologies that are fast, low-cost and suitable for on-site analysis, and surface-enhanced Raman spectroscopy (SERS) technology is one of the most promising new methods.

[0003] The performance of SERS technology is based on its active substrate. The composition, morphology and structure of metal substrate have a decisive influence on the sensitivity, stability and repeatability of SERS signal. For example, Zhu et al. can realize the effective enrichment and identification of ppb level target molecules by constructing an Ag NPs / graphene composite material. Xing et al. prepared a super-hydrophobic Au NPs substrate through a simple self-assembly process, and effectively gathered nano-plastic on the SERS active surface by liquid drop evaporation. The dense Au NPs provided a significant enhanced Raman signal. Among the numerous metal materials, gold nanoparticles (Au NPs) have become one of the most widely used SERS substrate materials due to their high chemical stability and excellent plasmonic resonance characteristics. The conventional Au NPs synthesis methods mainly include citrate method, two-phase method and thermal decomposition method. Among them, Turkevich et al. proposed the citrate reduction method which is widely used. The preparation of Au NPs follows a specific rule of nucleation and growth, and the average size, distribution and deviation of the final particles are determined by the gold content, nucleation process and growth rule. The Au NPs prepared by this method have uniform size (about 5-20 nm) and have been widely used in SERS detection in aqueous systems. However, most PAHs (such as naphthalene, anthracene and pyrene) are strongly hydrophobic and difficult to dissolve in water, which seriously limits the application of traditional hydrophilic Au NPs in the high-sensitivity detection of trace PAHs. To solve the above problems and expand the detection ability of SERS technology for trace PAHs, it is crucial to construct a composite substrate with high SERS activity and hydrophobic enrichment function. The huge specific surface area and open three-dimensional network structure of SiO2 aerogel provide an ideal framework for high-density and uniform loading of Au NPs, which helps to form stable Sers "hot spots". Further, by modifying the hydrophobicity of SiO2 aerogel, it can be endowed with the ability to efficiently capture and enrich hydrophobic PAH molecules in aqueous phase, so as to effectively concentrate the target molecules to the high enhancement area around the Au NPs. The efficient synergistic mechanism of "hydrophobic enrichment-in situ detection" is expected to break through the sensitivity limitation of traditional hydrophilic SERS substrate in detecting trace hydrophobic PAHs.

[0004] Based on the above analysis, the application proposes a hydrophobic modification strategy based on CO2 pressurized catalytic hydrolysis of hexamethyldisilazane (HMDS), and constructs a hydrophobic SiO2 composite aerogel loaded with Au NPs. The influence of Au NPs content on the microstructure, hydrophobicity and SERS sensitivity of the material under CO2 pressurized modification conditions is investigated. By optimizing the synthesis parameters, the porous structure and surface properties of the material are regulated to enhance its enrichment ability for typical PAHs (naphthalene, anthracene and pyrene). SUMMARY

[0005] The application provides a gold / silicon dioxide hydrophobic composite aerogel and a preparation method thereof, and the following application purposes are achieved: the SiO2 aerogel is hydrophobically modified, and is combined with gold nanoparticles, so that the aerogel has the ability of efficiently capturing and enriching hydrophobic PAHs molecules in an aqueous phase, and the target object is effectively concentrated in a high enhancement area around the Au NPs.

[0006] The technical solution adopted by the application is divided into two steps, and specifically comprises the following steps: Step one, preparation of gold nanoparticles, a 1% gold nanoparticle tetrachloroauric acid solution is added to deionized water, heated to boiling, then sodium citrate is added until the solution turns red, and a gold nanoparticle solution is obtained; Step two, preparation of a gold / silica hydrophobic composite aerogel, water glass is added to deionized water to obtain solution A, and 25% dilute hydrochloric acid is added to deionized water to obtain solution B, solution A is added dropwise to solution B while stirring, so that the pH of the mixed solution reaches 2.5, ammonia is added, a wet gel is obtained, the gold nanoparticle solution obtained in step one is quickly added, after the wet gel is aged, it is placed in a high-pressure reaction kettle, n-hexanol, ethanol and hexamethyldisilazane are added to the reaction kettle, the reaction is carried out at 50 °C for 1 h, inert gas is continuously introduced into the reaction kettle, after the reaction is completed, the temperature is increased to 60 °C and the sample is placed in a 90 °C oven for drying, and finally Au@SiO2 is obtained.

[0007] The ratio of tetrachloroauric acid to deionized water in step one is 1:100, and the amount of sodium citrate added is 4% to 8% of the total mass of the solution.

[0008] The ratio of water glass to deionized water in step two is 1:1.

[0009] After the ammonia is added in step two, the pH of the mixed solution should reach neutral.

[0010] The ratio of n-hexanol, ethanol and hexamethyldisilazane added in step two is 30:1:3.

[0011] The amount of gold nanoparticle solution added in step two is 80 mL to 160 mL.

[0012] The inert gas continuously introduced in step two is carbon dioxide.

[0013] The gold / silicon dioxide hydrophobic composite aerogel has certain application potential in the field of SERS.

[0014] The gold / silicon dioxide hydrophobic composite aerogel and the preparation method thereof optimize the preparation technology of traditional aerogel.Compared with the traditional aerogel, the critical carbon dioxide is used to process the wet aerogel material, and the air tightness and pressure resistance of the equipment are extremely high. The carbon dioxide gas is introduced in the preparation process, so that the cost of the preparation equipment is greatly reduced, and a solid foundation is laid for future large-scale production.

[0015] The gold / silica hydrophobic composite aerogel and the preparation method thereof can realize the regulation of the hydrophobicity, specific surface area and pore volume of the prepared aerogel by regulating the content of gold nanoparticles, and break through the limitation of single structure and strong randomness of traditional process.

[0016] The gold / silica hydrophobic composite aerogel and the preparation method thereof, wherein the SiO2 aerogel modified by methyl has good hydrophobicity, and gold nanoparticles are loaded in the interior, the synergistic effect between the characteristics of mutual aggregation of hydrophobic particles in water and the SERS performance of gold nanoparticles can realize the detection of trace polycyclic aromatic hydrocarbons in water, and the application field of aerogel is expanded. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 (a) is an SEM photo of SiO2 aerogel; (b) is an SEM photo of Au@SiO2 aerogel; (c) is an EDS photo of Si in Au@SiO2 aerogel; (d) is an EDS photo of O in Au@SiO2 aerogel; (e) is an EDS photo of C in Au@SiO2 aerogel; (f) is an EDS photo of Au in Au@SiO2 aerogel.

[0018] Figure 2 It is the Fourier transform infrared transmission spectrum diagram of Au NPS, SiO2 aerogel and Au@SiO2.

[0019] Figure 3 (a) is a TEM photo of Au@SiO2; (b) is a high-resolution TEM photo of Au@SiO2; (c) is a TEM photo of gold nanoparticles in Au@SiO2.

[0020] Figure 4 It is a contact angle comparison diagram of Au@SiO2 with different gold nanoparticle contents.

[0021] Figure 5 It is a thermogravimetric curve spectrum diagram of different samples.

[0022] Figure 6 It is a specific surface area and pore volume comparison diagram of Au@SiO2 with different gold nanoparticle contents.

[0023] Figure 7 SERS spectra of pyrene probe molecule for different samples.

[0024] Figure 8 (a) Surface-enhanced SERS spectra of pyrene under different concentrations (10 -3 -10 -9 M) gradient; (b) Linear relationship of pyrene. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. EMBODIMENT

[0026] Step one: 1 mL of 1% HAuCl4 solution (1 g of HAuCl4 dissolved in 100 mL of deionized water) was added to 99 mL of deionized water, heated to boiling, 0.04 g of sodium citrate was added to the aqueous solution of HAuCl4, the solution turned red, and the reaction was carried out for 15 min to obtain an Au NPs solution containing 0.01% (w / v) HAuCl4, as shown in FIG. a. Figure 1

[0027] Step two: 1 mL of water glass was diluted in 1 mL of deionized water to obtain solution A, and 0.6 mL of 25% mass fraction dilute hydrochloric acid was added to 2.8 mL of deionized water to obtain solution B, while stirring, solution A was added dropwise to solution B until the pH of the mixed solution reached 2.5, 5% ammonia water was added to adjust the pH to neutral to obtain a wet gel, 80 mL of Au NPs solution was quickly added, and after the wet gel aged for a certain period of time, it was placed in a high-pressure reaction kettle, and C6H 14 30 mL, C2H5OH 1 mL, HMDS 3 mL, the reaction temperature was set to 50°C, the reaction time was 1 h, and CO2 was continuously introduced into the reaction kettle, after the reaction was completed, the temperature was raised to 60°C and the sample was placed in a 90°C oven to dry, and finally a hydrophobic Au@SiO2 composite aerogel was obtained. EMBODIMENT

[0028] ​Step one: 1 mL of 1% HAuCl4 solution (1 g of HAuCl4 dissolved in 100 ml of deionized water) was added to 99 ml of deionized water, heated to boiling, 0.04 g of sodium citrate was added to the aqueous solution of HAuCl4, the solution turned red, and the reaction was allowed to proceed for 15 min to obtain a Au NPs solution containing 0.01% (w / v) HAuCl4, as shown in Fig. a. Figure 1

[0029] Step two: 1 mL of water glass was diluted in 1 mL of deionized water to obtain solution A, 0.6 mL of 25% mass fraction dilute hydrochloric acid was added to 2.8 mL of deionized water to obtain solution B, solution A was added dropwise to solution B while stirring constantly, the pH of the mixed solution was adjusted to 2.5, 5% ammonia water was added to neutralize the solution to obtain a wet gel, 90 mL of Au NPs solution was quickly added, and after the wet gel was aged for a certain period of time, it was placed in a high-pressure reaction kettle, and C6H 14 30 mL, C2H5OH 1 mL, HMDS 3 mL, the reaction temperature was set to 50°C, the reaction time was 1 h, and CO2 was continuously introduced into the reaction kettle, after the reaction was completed, the temperature was raised to 60°C and the sample was placed in a 90°C oven for drying, and finally a hydrophobic Au@SiO2 composite aerogel was obtained. Example

[0030] Step one: 1 mL of 1% HAuCl4 solution (1 g of HAuCl4 dissolved in 100 ml of deionized water) was added to 99 ml of deionized water, heated to boiling, 0.04 g of sodium citrate was added to the aqueous solution of HAuCl4, the solution turned red, and the reaction was allowed to proceed for 15 min to obtain a Au NPs solution containing 0.01% (w / v) HAuCl4, as shown in Fig. a. Figure 1

[0031] Step two: 1 mL of water glass was diluted in 1 mL of deionized water to obtain solution A, 0.6 mL of 25% mass fraction dilute hydrochloric acid was added to 2.8 mL of deionized water to obtain solution B, solution A was added dropwise to solution B while stirring constantly, the pH of the mixed solution was adjusted to 2.5, 5% ammonia water was added to neutralize the solution to obtain a wet gel, 90 mL of Au NPs solution was quickly added, and after the wet gel was aged for a certain period of time, it was placed in a high-pressure reaction kettle, and C6H 14 ​​30 mL, C2H5OH 1 mL, HMDS 3 mL, set the reaction temperature to 50 °C, the reaction time is 1 h, and continuously introduce CO2 into the reaction kettle, after the reaction is completed, the temperature is raised to 60 °C and placed for 1 h, finally the sample is taken out and placed in a 90 °C oven to dry, finally the hydrophobic Au@SiO2 composite aerogel is obtained. Example

[0032] Step one: 1 mL of 1% HAuCl4 solution (1 g of HAuCl4 is dissolved in 100 ml of deionized water) is added to 99 ml of deionized water, heated to boiling, 0.04 g of sodium citrate is added to the aqueous solution of HAuCl4, the solution turns red, and the reaction is carried out for 15 min to obtain an Au NPs solution containing 0.01% (w / v) HAuCl4, as shown in Figure 1 a.

[0033] Step two: 1 mL of water glass is diluted in 1 mL of deionized water to obtain solution A, and 0.6 mL of 25% mass fraction dilute hydrochloric acid is added to 2.8 mL of deionized water to obtain solution B, while stirring, solution A is added dropwise to solution B until the pH of the mixed solution reaches 2.5, 5% ammonia is added to adjust to neutral to obtain a wet gel, 130 mL of Au NPs solution is quickly added, and after the wet gel is aged for a certain period of time, it is placed in a high-pressure reaction kettle, and C6H 14 30 mL, C2H5OH 1 mL, HMDS 3 mL, set the reaction temperature to 50 °C, the reaction time is 1 h, and continuously introduce CO2 into the reaction kettle, after the reaction is completed, the temperature is raised to 60 °C and placed for 1 h, finally the sample is taken out and placed in a 90 °C oven to dry, finally the hydrophobic Au@SiO2 composite aerogel is obtained. Example

[0034] [0036hot to boiling, 0.04 g of sodium citrate is added to the aqueous solution of HAuCl4, the solution turns red, and the reaction is carried out for 15 min to obtain an Au NPs solution containing 0.01% (w / v) HAuCl4, as shown in Figure 1 a.

[0035] Step two; 1 mL of water glass was diluted into 1 mL of deionized water to obtain solution A, and 0.6 mL of 25% mass fraction dilute hydrochloric acid was added into 2.8 mL of deionized water to obtain solution B, while continuously stirring, solution A was added dropwise into solution B, so that the pH of the mixed solution reached 2.5, 5% ammonia water was added to neutralize to obtain a wet gel, 150 mL of AuNPs solution was quickly added, after the wet gel was aged for a certain period of time, it was placed in a high-pressure reaction kettle, and C6H 14 30 mL, C2H5OH 1 mL, HMDS 3 mL, the reaction temperature was set to 50°C, the reaction time was 1 h, and CO2 was continuously introduced into the reaction kettle, after the reaction was completed, the temperature was raised to 60°C and stood for 1 h, finally the sample was taken out and placed in a 90°C oven for drying, finally the hydrophobic Au@SiO2 composite aerogel was obtained. Example

[0036] Step one: 1 mL of 1% HAuCl4 solution (1 g of HAuCl4 was dissolved in 100 ml of deionized water) was added to 99 ml of deionized water, heated to boiling, 0.04 g of sodium citrate was added to the aqueous solution of HAuCl4, the solution turned red, and the reaction was carried out for 15 min to obtain an AuNPs solution containing 0.01% (w / v) HAuCl4, as shown in Figure 1 a.

[0037] Step two; 1 mL of water glass was diluted into 1 mL of deionized water to obtain solution A, and 0.6 mL of 25% mass fraction dilute hydrochloric acid was added into 2.8 mL of deionized water to obtain solution B, while continuously stirring, solution A was added dropwise into solution B, so that the pH of the mixed solution reached 2.5, 5% ammonia water was added to neutralize to obtain a wet gel, 160 mL of AuNPs solution was quickly added, after the wet gel was aged for a certain period of time, it was placed in a high-pressure reaction kettle, and C6H 14 30 mL, C2H5OH 1 mL, HMDS 3 mL, the reaction temperature was set to 50°C, the reaction time was 1 h, and CO2 was continuously introduced into the reaction kettle, after the reaction was completed, the temperature was raised to 60°C and stood for 1 h, finally the sample was taken out and placed in a 90°C oven for drying, finally the hydrophobic Au@SiO2 composite aerogel was obtained.

[0038] The structure and morphological characteristics of the SiO2 aerogel before and after the addition of AuNPs were characterized by SEM. Figure 1 (a) shows that the CO2 pressurized hydrophobic modified SiO2 aerogel without the addition of AuNPs has obvious particle agglomeration phenomenon. Figure 1(b) As shown, after introducing Au NPs in the system of preparing SiO2 aerogel by hydrolysis of HMDS catalyzed by CO2 pressurization, the Au@SiO2 composite aerogel with hydrophobic performance constructed can be seen that the microstructure is significantly optimized after adding Au NPs, the sample surface particle agglomeration phenomenon is obviously reduced, which is composed of a large number of small particles, forming a loose porous microstructure, and the pore distribution is uniform, which is mainly due to the space stability of metal Au effectively inhibiting the agglomeration of SiO2 aerogel surface particles. Figure 1 (c)- Figure 1 (f) As shown, the surface element distribution of the sample surface is observed by EDS, and the sample surface contains a large amount of Si, O, C and Au elements, and the existence of Au elements on the surface indirectly shows that Au NPs are loaded on the hydrophobic SiO2 aerogel skeleton.

[0039] As Figure 2 shown, Au NPs were prepared with sodium citrate as stabilizer, and its FT-IR spectrum had relatively strong absorption peaks near 1590 cm −1 and 1400 cm −1 , which corresponded to the asymmetric stretching and symmetric stretching of the -COO- group in the sodium citrate molecule, respectively; at the same time, the stretching vibration peak of -OH of crystal water near 3400 cm −1 could prove that Au NPs were effectively wrapped by sodium citrate. After modification of SiO2 aerogel by HMDS, obvious absorption peaks appeared near 850 cm −1 and 1093 cm −1 , which corresponded to the anti-symmetric stretching vibration and symmetric stretching peak of Si-O-Si, respectively, which were the characteristic peaks of the three-dimensional silicon-oxygen network skeleton (Si-O-Si) of SiO2 aerogel, confirming the integrity of its main structure. And there were weak Si-OH absorption peaks near 3400 cm −1 and 950 cm −1 ; at the same time, sharp Si-CH3 absorption peaks appeared near 2964 cm −1 and 1257 cm −1 , indicating that the hydrophobic modification by CO2 pressurization catalyzed by HMDS was completed. In the FT-IR spectrum of the modified Au@SiO2 composite aerogel after introducing Au NPs, obvious -COO- asymmetric stretching and symmetric stretching characteristic peaks appeared near 1590 cm −1 and 1400 cm −1 , respectively. Since Au is a metal element, there is no infrared characteristic absorption peak, and the result shows that the Au NPs coated with sodium citrate have been successfully loaded in the SiO2 aerogel.

[0040] Figure 3As shown in (a), the Au@SiO2 composite aerogel exhibits a typical porous network structure, and a large number of Au NPs can be observed in the SiO2 aerogel, which is consistent with the SEM analysis. Figure 3 As shown in (b), high-resolution electron microscopy (HRTEM) images clearly demonstrate the lattice diffraction fringes of Au NPs in Au@SiO2. HRTEM analysis indicates that the Au NPs in Au@SiO2 possess a well-defined crystal structure with a lattice fringe spacing of approximately 0.242 nm, consistent with the lattice fringes corresponding to Au in the {200} crystal plane family. Furthermore, as... Figure 3 As shown in (c) and 3(d), the elemental relationships of the Au@SiO2 composite aerogel are presented. The measured C content is 10.78%, O content is 59.91%, Si content is 25.72%, and Au content is 4.6%.

[0041] Contact angle test results ( Figure 4 The results showed that when the amount of Au NPs solution added was 80, 90, 100, 130, and 150 mL, the contact angles of the CO2-modified Au@SiO2 composite aerogel were 121.81°, 131.7°, 137.46°, 142.84°, and 136.58°, respectively, all exhibiting significant hydrophobicity. However, when the amount of Au NPs solution added increased to 160 mL, the contact angle dropped sharply to 84°, changing from hydrophobic to hydrophilic. This change is attributed to the fact that excessive Au NPs not only alters the pH environment of the sol, catalyzes the hydrolysis of siloxane bonds (Si-O-Si), and interferes with the normal hydrolysis-condensation process of SiO2, leading to the formation of a fragile and incomplete gel network, but also that the Au NPs aggregates physically cover and occupy a large number of Si-OH reaction sites, hindering the effective grafting of -CH3 groups generated after HMDS hydrolysis, thus causing the hydrophobic modification to fail.

[0042] Thermogravimetric analysis (TGA) Figure 5The results show that the weight loss of the modified Au@SiO2 composite aerogel increases with increasing temperature. The mass loss curves indicate that the thermal decomposition in nitrogen can be divided into three stages: the first stage, from room temperature to 100 °C, is mainly attributed to the evaporation of surface-adsorbed water and residual organic solvents; the second stage mainly occurs between 100 °C and approximately 500 °C, attributed to thermal weight loss due to the decomposition of residual moisture and unreacted silicon precursors in the internal pores; finally, the third stage, from 600 °C to 800 °C, represents thermal weight loss due to the decomposition of organic groups within the Au@SiO2 composite aerogel. When the Au NPs solution addition amounts were 80 mL, 90 mL, 100 mL, 130 mL, and 150 mL, the residual mass rates of the SiO2@Au aerogel were 88.96%, 89.2%, 90.46%, 91.11%, and 90.13%, respectively. The results showed that with an appropriate increase in the amount of AuNPs solution, the thermal stability improved and then tended to be relatively stable; the less weight loss, the more stable the thermal stability curve. Further increasing the amount of AuNPs solution, when the addition volume reached 160 mL, caused a significant increase in sample weight loss due to incomplete absorption of large amounts of water vapor from the air and decomposition of surface citrate. Therefore, excessive AuNPs led to a deterioration in the thermal stability of the SiO2 aerogel.

[0043] BET specific surface area and BJH pore volume test results ( Figure 6 The results showed that, under the same conditions, the addition of an appropriate amount of Au NPs solution helped optimize the pore structure of the material, while excessive Au NPs solution caused particle agglomeration and pore blockage, leading to a significant decrease in specific surface area and total pore volume. The BET specific surface area measured under these conditions was 678.30 m². 2 The large specific surface area ( / g) provides abundant adsorption sites for PAHs molecules, effectively eliminating interference from macromolecules while significantly enhancing the enrichment capacity for target pollutants. In summary, when the Au NPs solution is added in 100 mL, the prepared Au@SiO2 composite aerogel possesses a uniform porous structure, good hydrophobicity, and thermal stability. These characteristics collectively lay the foundation for its optimal SERS activity.

[0044] This study systematically investigated the effect of Au NPs solution addition amounts (80, 90, 100, 130, 150 mL) on the SERS enhancement effect of the constructed composite aerogel. Figure 7 As shown, with a concentration of 10 -3Raman spectroscopy analysis of pyrene probe molecules using M as the probe molecule showed that the Raman signal of the pyrene probe molecule gradually increased with the increasing content of Au NPs in the substrate material, reaching its strongest value at an Au NPs solution volume of 100 mL. However, when the Au NPs solution volume exceeded 100 mL, the SERS signal of the pyrene probe molecule gradually weakened with increasing Au NPs content, which is consistent with... Figure 4 The characterization analysis results were consistent. Appropriately increasing the content of Au NPs during preparation helps improve the three-dimensional network structure of SiO2 aerogel and promotes its hydrophobic modification. Simultaneously, increasing the content of Au NPs in the substrate material can excite a stronger local electromagnetic field during detection, increasing surface "hot spots," while the improved hydrophobicity of the substrate enhances the adsorption capacity for pyrene molecules, ensuring that the target molecules are located in the electromagnetic field enhancement region, thus enhancing the SERS detection signal. Therefore, appropriately increasing the content of Au NPs during preparation can significantly enhance the SERS detection effect. However, when the amount of Au NPs added during the preparation process exceeds a certain range, excessive Au NPs will have a negative effect. This is mainly due to the following two aspects: First, although an appropriate amount of Au NPs can play a certain synergistic catalytic role and promote the hydrophobic modification of SiO2 aerogel, excessive Au NPs will interfere with or even destroy the formation of the three-dimensional network structure of SiO2 aerogel. Furthermore, Au NPs aggregates will form and cover and occupy a large number of Si-OH reaction sites, hindering the effective grafting of -CH3 groups generated after HMDS hydrolysis during the hydrophobic modification process, resulting in a poorer hydrophobic modification effect. Second, the prepared Au NPs are hydrophilic themselves, which means that the hydrophobicity of the Au@SiO2 composite aerogel prepared by excessive addition of Au NPs is not improved, or even worsened. The adsorption capacity for target analysis is reduced, and it is impossible to enrich enough target molecules to enhance its SERS detection signal. Based on the above analysis, the Au@SiO2 composite aerogel prepared with 100 mL of Au NPs solution was determined to be the optimal base material for SERS detection and was used in subsequent experiments. The results indicate that pyrene target molecules are mainly enriched on the surface of the Au@SiO2 composite aerogel through physical adsorption without significant chemical changes, providing a reliable basis for the rapid qualitative identification of trace pyrene in complex aquatic environments. Furthermore, the analytical performance of this SERS sensor for pyrene was further evaluated. Figure 8 As shown in (a), at 10 -3 M to 10 -9 Within the M concentration range, the characteristic peak intensity of pyrene ethanol solution at 408, 1240, and 1400 cm⁻¹ gradually decreases with decreasing concentration, but remains relatively constant at 1000 cm⁻¹. -9Even at extremely low concentrations of M, it remained clearly identifiable. Further analysis showed a good linear relationship between Raman intensity and the logarithm of pyrene concentration at characteristic peaks at 408, 1240, and 1400 cm⁻¹. Figure 8 As shown in (b), the correlation coefficient (R²) reaches 0.99, indicating that the Au@SiO2 composite aerogel as the substrate material has the ability to quantitatively detect pyrene within a linear range using SERS. Furthermore, the Au@SiO2 composite aerogel does not introduce interfering peaks within the detection range, which is beneficial for the accurate identification of target substances in complex aquatic environments in real life. In summary, by systematically optimizing the Au NPs content in the Au@SiO2 composite aerogel, this study successfully prepared an Au@SiO2 composite aerogel SERS substrate with high sensitivity, good linear response, and excellent reproducibility, providing an effective platform for the reliable detection of trace PAHs pollutants in industrial wastewater environments.

Claims

1. A gold / silica hydrophobic composite aerogel, characterized in that... The material is formed by combining hydrophobic silica aerogel and gold nanoparticles. The hydrophobic silica aerogel has a porous structure and contains a large number of methyl groups on its surface. The porous structure contains gold nanoparticles. The chemical formula of a gold / silica hydrophobic composite aerogel is Au@SiO2.

2. The gold / silica hydrophobic composite aerogel according to claim 1, characterized in that... The preparation method of the material consists of two steps, specifically: Step 1, Preparation of gold nanoparticles: Add a 1% tetrachloroauric acid solution of gold nanoparticles to deionized water, heat to boiling, and then add sodium citrate until the solution turns red to obtain a gold nanoparticle solution. Step 2: Preparation of a gold / silica hydrophobic composite aerogel. Water glass is added to deionized water to obtain solution A. Then, 25% (w / w) dilute hydrochloric acid is added to the deionized water to obtain solution B. Solution A is added dropwise to solution B while continuously stirring until the pH of the mixed solution reaches 2.

5. Ammonia is added to obtain a wet gel. The gold nanoparticle solution obtained in Step 1 is quickly added. After the wet gel ages, it is placed in a high-pressure reactor. Simultaneously, hexanol, ethanol, and hexamethyldisilazane are added to the reactor. The reaction is carried out at 50°C for 1 hour, with inert gas continuously introduced into the reactor. After the reaction is complete, the temperature is raised to 60°C and allowed to stand for 1 hour. Finally, the sample is removed and dried in a 90°C oven to obtain Au@SiO2.

3. The method for preparing a gold / silica hydrophobic composite aerogel according to claim 2, characterized in that, In step one, the ratio of tetrachloroauric acid to deionized water is 1:100, and the amount of sodium citrate added is 4% to 8% of the total mass of the solution.

4. The method for preparing a gold / silica hydrophobic composite aerogel according to claim 2, characterized in that, In step two, the ratio of water glass to deionized water is 1:

1.

5. The method for preparing a gold / silica hydrophobic composite aerogel according to claim 2, characterized in that, After adding ammonia in step two, the pH of the mixed solution should reach neutral.

6. The method for preparing a gold / silica hydrophobic composite aerogel according to claim 2, characterized in that, In step two, the ratio of hexanol, ethanol, and hexamethyldisilazane is 30:1:

3.

7. The method for preparing a gold / silica hydrophobic composite aerogel according to claim 2, characterized in that, In step two, the amount of gold nanoparticle solution added is 80 mL to 160 mL.

8. The method for preparing a gold / silica hydrophobic composite aerogel according to claim 2, characterized in that, The inert gas continuously introduced in step two is carbon dioxide.

9. The gold / silica hydrophobic composite aerogel according to claim 1 has certain application potential in the field of SERS.

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