{"paper_id":"1089c242-3d87-4342-8fcd-f06ee823d142","body_text":"Fe2O3/SiO2 composite aerogels powders for high-temperature thermal insulation based on EDTA chelated aqueous precursor | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Fe 2 O 3 /SiO 2 composite aerogels powders for high-temperature thermal insulation based on EDTA chelated aqueous precursor Yuan Qi, Jinmin Wang, Xingxing Zhang, Yongqing Wu, Xiangdong Gao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7692578/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 29 Dec, 2025 Read the published version in Journal of Porous Materials → Version 1 posted 7 You are reading this latest preprint version Abstract SiO 2 aerogel is a typical thermal insulation material suitable for varied high temperature industrial applications. However, its radiative transparency seriously hampers its application scenario. Herein, we integrated infrared (IR) opacified Fe 2 O 3 nanoparticles into silica aerogel system and developed a Fe 2 O 3 /SiO 2 composite aerogel (FSA) by using industrial water glass and ambient pressure drying process. Especially, we chelated Fe 3+ with disodium ethylenediaminetetraacetic (EDTA-2Na) to avoid the loss of Fe 3+ in the gelling, solvent-exchanging and hydrophobic modification processes. FSA powders with 3-11% concentration exhibit an amorphous structure, high porosity with small nanopores (11-12 nm). The EDS analysis confirms the presence of Fe in the aerogel framework. The high-temperature thermal insulation properties of the FSA powders were enhanced compared with the pure SiO 2 aerogel powders, yielding a cold surface temperature of 456 ℃ after heating at 600 ℃ for 30 min, 26 ℃ lower than pure SiO 2 aerogel. The EDTA-2Na chelating agent improves the dispersion of Fe 3+ and further reduces the temperature by 6 ℃, demonstrating its positive effect on the insulation performance. SiO2 Fe Doping Aerogel Infrared shielding Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction With the development of industry and science and technology, traditional thermal insulation materials (such as polystyrene foam, mineral wool, etc.) are flammable [ 1 ], easy to age [ 2 ], and have high thermal conductivity [ 3 ], which has made it difficult to satisfy people’s demand for high-performance thermal insulation materials. SiO 2 nanoporous materials, especially SiO 2 aerogel, effectively inhibit solid-phase heat conduction as well as convective heat transfer due to their unique mesoporous structure that makes the pore size below 100 nm, thus improving their thermal insulation performance at high temperatures [ 4 ]. SiO 2 aerogel have a three-dimensional (3D) nano grid structure with backbones and pores at the nanoscale. This material possesses low density, high porosity, large specific surface area, thermal conductivity, and low dielectric constant [ 5 – 7 ]. These excellent properties make it valuable for non-negligible applications in aerospace [ 8 , 9 ], new energy batteries [ 10 ], and thermal insulation [ 11 ]. However, even as a high-performance thermal insulation material, SiO 2 aerogel still have some limitations and face severe problems. The conventional SiO 2 aerogels are almost transparent to radiation in the IR wavelength range of 3 ~ 8 µm [ 12 , 13 ] When the temperature of the hot and cold surfaces reaches 100 ℃, the percentage of thermal radiation in the heat transfer gradually increases and becomes impossible to ignore [ 14 , 15 ]. This leads to a decrease in the high-temperature thermal insulation performance of SiO 2 aerogel, which greatly limits their practical applications at high temperatures. The doping of shading agents has been established as an effective method among the numerous attempts made to improve the high-temperature thermal insulation performance of SiO 2 aerogel. The shading agent can improve the high-temperature thermal insulation performance of SiO 2 aerogel by enhancing the absorption or reflection of infrared and reducing the infrared radiation heat transfer at high temperatures [ 16 ]. Ma et al. prepared TiO 2 -SiO 2 composite aerogels with high resistance to high-energy laser irradiation and improved the light-shielding performance of the aerogels by doping TiO 2, realizing the structural integrity even when the thermal barrier difference reaches 1275 ℃ [ 17 ]. By establishing a theoretical model, He et al. found that an increase in TiO 2 content reduced the radiative heat transfer and increased the thermal conductivity simultaneously [ 18 ]. Wu et al. prepared ZrO 2 /SiO 2 fiber paper-reinforced aerogels with a dual-network structure by combining the sol-gel method with the traditional paper-making process. The resulting ZrO 2 /SiO 2 aerogels exhibited an effective specific extinction coefficient 19.5 times higher than that of SiO 2 aerogels in the wavelength range of 3 ~ 5 µm [ 19 ]. Pang et al. synthesized SiC-SiO 2 aerogels and found that SiC, as a shading agent, could effectively improve the thermal insulation at a content of 1% under large temperature differences without significantly increasing the aerogel’s thermal conductivity [ 20 ]. In addition, carbon [ 21 ], Fe 3 O 4 [ 22 ], and yttrium [ 23 ] are also good shading agents. Despite considerable advances in this field, the current shading agents have limitations, such as the high cost of TiO 2 raw materials. Although carbon has excellent shading properties, higher doping levels can increase the thermal conductivity and lead to the oxidation at high temperatures [ 24 ]. Iron oxide exhibits strong IR radiation absorption in the wavelength bands of 0.5–0.9 µm, above 1.4 µm, and 5–7 µm, making it an effective IR masking agent. Additionally, it offers superior stability and high-temperature resistance, making it suitable for incorporation into SiO 2 aerogels as an efficient IR shielding material [ 25 , 26 ]. Luo et al. prepared iron-doped silica aerogels via the sol-gel method and atmospheric pressure drying using an organosilicon precursor, which exhibited a porosity exceeding 90% and a thermal stability approximately 100 ℃ higher than pure SiO 2 aerogels [ 27 ]. Casas et al. synthesized silica-iron oxide nanocomposites using Fe(NO 3 ) 3 ·9H 2 O and FeNa(EDTA)·2H 2 O as iron sources via supercritical drying (SCD). The resulting nanocomposites demonstrated soft magnetic properties, low density, and low resistivity [ 28 ]. Tu et al. fabricated SiO 2 /Fe 2 O 3 composite aerogels via SCD, demonstrating low-density (0.04 g/cm 3 ), high specific surface area (705 m 2 /g), low thermal conductivity (0.026 W/(m·K)) and good thermal stability at temperatures up to 1100 ℃ [ 29 ]. The drying of the wet gel is a kernel process for the preparation of aerogel, and currently three drying methods are used, i.e., SCD [ 30 , 31 ], freeze drying (FD) [ 32 , 33 ] and atmospheric pressure drying (APD) [ 34 – 36 ]. The SCD has been widely used in industry, but it is long been accused of complicated operation, potential danger and high cost [ 37 ]. The FD is often used in a laboratory scale, with the drawback of poor product quality, long drying period and pore collapse [ 38 ]. In contrast, the APD is the developing trend of the aerogel production because of its low facility cost, simple operation, short cycle time and high product quality [ 39 ]. The silica source of aerogel is also greatly important for the commercialization of aerogel materials. Researchers prepared aerogels mostly using organosilicon sources such as tetraethyl orthosilicate (TEOS) [ 40 ], tetramethoxysilane (TMOS) [ 41 ], methyltriethoxysilane (MTES) [ 42 ], and methyltrimethoxysilane (MTMS) [ 43 – 45 ]. However, the cost of organosilica source is high, so the use of inorganic silica source as the silica precursor can significantly reduce the cost of raw materials, and gradually become the focus of current research [ 46 , 47 ]. However, the use of inorganic silica precursor will inevitably bring a large number of hydroxyl groups in the precursor. The introduction of the dopant ions (e.g., Fe 3+ ) will result in the precipitation in the SiO 2 aqueous sol with high pH values, which will affect the microstructure and properties of the composite aerogel significantly. However, few study focus on this aspect and find an appropriate solution for this up to now. Herein, we developed a novel method to prepare FSA based on inorganic materials (water glass and iron nitrate) and the APD technique, by using EDTA-2Na as the chelating agent of Fe 3+ ions, to avoid precipitation and iron agglomeration. The packing density, crystallinity, microstructure, thermal stability and thermal insulation properties of the composite aerogels were examined, and effects of the Fe/Si molar ratio and EDTA-2Na level were investigated. 2. Experimental 2.1 Materials Industrial water glass (SiO 2 content: 28 wt%) was purchased from Shanghai Qingfeng Chemical Factory (China). Hydrochloric acid (HCl, AR) and hexamethylene tetramine (HMT, AR grade) were obtained from Sinopharm Chemical Reagent Co. Ltd. (China). Ferric nitrate nonahydrate (Fe(NO 3 ) 3 ·9H 2 O, AR) was supplied by Shanghai Aladdin Biochemical Technology Co. Ltd. (China). Anhydrous ethanol (EtOH, AR) was acquired from Shanghai Lingfeng Chemical Reagent Co. Ltd. (China). Hexamethyldisilazane (HMDS, ≥ 99.5%) and cyclohexane (CyH, AR) were purchased from Shanghai Aladdin Biochemical Technology Co. Ltd. (China) and Shandong Keyuan Biochemical Co. Ltd. (China), respectively. 2.2 Preparation of FSA Figure 1a illustrates the preparation process of FSA. Initially, SiO 2 sol was prepared by mixing water glass with deionized water (volume ratio 1:4), stirring for 30 min, and acidifying with acidic cationic resin for 30 min. Ferric nitrate solutions were prepared by dissolving ferric nitrate hydrate in deionized water with Fe/Si molar ratios of 3%, 5%, 7%, 9%, and 11%, followed by 30 min of stirring. The SiO 2 sol was then mixed with the ferric nitrate solution and stirred for 60 min. EDTA-2Na was added and stirred for 60 min to form a composite sol. Subsequently, an aqueous HMT solution was added dropwise to the composite sol, which was gelled at 80 ℃ and aged for 24 h to form a composite gel. The gel was immersed in EtOH (2–3 times its volume) at 60 ℃ for 6 h, modified with HMDS in cyclohexane at 55 ℃ for 6 h, and finally dried in air at 200 ℃ for 2 h to obtain the FSA. Samples were labeled as FSA3, FSA5, FSA7, FSA9, and FSA11 according to the Fe/Si molar ratio. To examine the effect of the chelating agent, additional samples were prepared with a fixed Fe/Si ratio of 7% and varying EDTA-2Na/Fe molar ratios from 0 to 1, labeled as FSAE0, FSAE25, FSAE50, FSAE75, and FSA7 (also denoted as FSAE100). A pure silica aerogel (SA) was synthesized using a similar procedure for comparison. 2.3 Characterization The packing density was obtained by measuring the ratio of mass to volume using a weighing balance with a 10 mL measuring cylinder ( \\(\\:\\rho\\:\\:=\\frac{m}{V}\\) ).The crystallinity of FSA powders was characterized using an X-ray diffraction (XRD, D8 ADVANCE, Bruker, Germany) (copper target, 20 kV, diffraction angles: 10° to 80°). A Hitachi SU9000 low voltage scanning electron microscope (SEM) was used to observe the microscopic morphology of FSAs powders at a low accelerating voltage of 1 kV to minimize the depth of penetration of the electron beam and to improve the resolution of the surface details. Field emission transmission electron microscopy (FE-TEM, JEM-2100F, Nippon Electron Co., Ltd., Japan) was used to analyze the microstructure and microscopic crystallinity of FSA. X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250, USA) was used to analyze the chemical states of Si and O in FSA. Fourier transform infrared spectroscopy (FTIR, Bruker Tensor 27, Germany) was used to measure the infrared transmittance of FSA and SA in the range of 400–4000 cm − 1 . The pore structure was analyzed by a four-station specific surface pore size analyzer (Quadrasorb SI, USA) using the Brunauer-Emmett-Tteller (BET) method. Thermogravimetric and differential scanning calorimetric properties were analyzed by a simultaneous thermal analyzer (TG&DSC, STA449F5, NETZSCH, Germany) in an air environment from room temperature up to 1000 ℃ at a ramp rate of 10 ℃/min. The thermal insulation properties of the aerogel powders were measured by a home-made setup. The samples were packed in a 5 cm × 5 cm × 1 cm tinplate box with vibration, placed in the center of a flat-plate heating furnace (Chemat, KW-4KH-600, USA), and a thermocouple was placed at the cold surface end. While the hot surface temperature was fixed at 300 ℃ and 600 ℃, respectively, the cold surface temperature was recorded every 10 s by using a paperless recorder (MIK-R9600, Hangzhou MIK Sensors Co., Ltd.). A glass fiber mat was placed over the thermocouple and tinplate box to maintain the temperature uniformity during the whole test process. 3. Results and discussion 3.1 Formation mechanism of FSA mediated by EDTA Fig. 1b presents the formation process of FSA with or without EDTA-2Na in the precursor. The kernel function of EDTA-2Na chelating reagent in the precursor is to form [Fe(EDTA)] - chelate-ions, which is stable at a wide pH range, thus avoiding the precipitation of Fe(OH) 3 in the SiO 2 sol when HMT was added. Though a large part of [Fe(EDTA)] - chelate-ions is discharged from the gel during the solvent exchanging and surface modifying process, some are left in the nanopores of the gel, forming the nanosized Fe 2 O 3 embedded in SiO 2 aerogel. Without EDTA-2Na, the free Fe 3+ ions will transform to Fe(OH) 3 aggregates, thus forming the mixture of SiO 2 aerogel and Fe 2 O 3 mi croparticle. Fig. 2 shows photographs of the gel and powder forms of 7% Fe-doped samples with varying EDTA/Fe molar ratios, along with the corresponding density profiles of the FSA. Both the gel and powder gradually lighten in color as the EDTA ratio increases, indicating improved iron chelation and enhanced material homogeneity. The aerogel prepared without EDTA exhibits a relatively high density. Systematic addition of EDTA significantly reduces density, demonstrating its role in modifying the aerogel structure. Furthermore, iron ion concentration also affects the packing density. Simultaneously, all FSA samples exhibit elevated densities, likely due to the thermal decomposition of the Fe(EDTA) - pore solution during drying, which releases Fe 3+ . Subsequent hydrolysis and aggregation of Fe 3+ under high pH conditions further enhance density. The significantly higher density of FSA3 is attributed to its lower Fe 3+ content. While higher Fe 3+ concentrations promote the formation of α-FeOOH through hydrolysis, lower concentrations favor γ-FeO(OH) formation [48]. Upon further drying, γ-FeO(OH) transforms into magnetite, whereas α-FeOOH yields hematite. The stronger hydrophilicity of magnetite compared to hematite contributes to the increased density of FSA3. While increased packing density improves high-temperature insulation, excessive density may adversely affect performance. 3.2 Crystallinity and microstructure of FSA Fig. 3a presents the XRD patterns of pure SiO 2 aerogel (SA), FSA3, FSA7 and FSA11. It can be seen that both SA and FSA samples exhibit amorphous features, and with the increase of Fe content, the broad peak of FSA change little, which indicates that the introduction of Fe 3+ in the precursor does not affect the crystallinity of silica aerogel. Further heat treatment of the FSA7 sample also does not result in the crystalline peak, as shown in Fig. 3b. Fig. 4a-d gives the SEM images of SA, FSA3, FSA7 and FSA11, with the Fig. 4e and f showing the EDS analysis. While the SA sample exhibits a loose, porous nanostructure with a relatively large pore size, three FSA structures exhibit denser pore structure. In addition, the particle size in FSA is obviously larger than that in SA. With the increase of the Fe content, the agglomeration of neighboring particle is more popular, which indicates that the introduction of Fe 3+ may promote the densification of the SiO 2 skeleton. EDS analysis shows that the content of Fe in FSA7 is 0.66, much lower than that in the precursor. The dissolution of Fe 3+ from the gel during the solvent exchanging and the modifying process is the underlying reason. Despite the low content, the distribution of Fe in the FSA7 sample is uniform, guaranteeing the full shading of the IR radiation in the thermal insulation process. Fig. 5 presents TEM images of FSA7 at different resolutions, SAED pattern and EDS analysis. Fe 2 O 3 presents an agglomerated morphology in the 3D mesh structure of SiO 2 , while SiO 2 is tightly wrapped around it. Under high-magnification observation, no distinct lattice fringes corresponding to large-scale Fe 2 O 3 particles were detected at the iron aggregation sites; however, fine granular structures were observed, as evidenced in Fig. 5a-d . This indicates that Fe 2 O 3 presents a more uniform amorphous structure (amorphous iron oxide), in the FSA, and this conclusion is also supported by Fig. 5e with SAED pattern. However, the agglomeration of Fe 2 O 3 nanoparticles also makes the FSA have a relatively dense structure, which explains the higher density of the aerogel. 3.3 Pore structure of FSA Fig. 6a-c demonstrates the N 2 adsorption-desorption isotherms, pore size distribution curves, and specific surface area variation curves with iron content of SiO 2 aerogels with FSA3, FSA7, and FSA11. Fig. 6a displays a Type IV adsorption isotherm with distinct capillary condensation in the relative pressure range of 0.4-1.0, consistent with mesoporous materials possessing a 3D network structure [49]. Although iron doping reduces the maximum adsorption capacity, the presence of an H1-type hysteresis loop indicates cylindrical pore geometry. The steep rise in the N₂ adsorption-desorption curve near P/P₀ ≈ 1.0, without attaining a plateau, suggests the coexistence of mesopores and macropores in the FSA [50]. Figure 6b presents the pore size distributions of SA, FSA3, FSA7, and FSA11, exhibiting peaks predominantly between 10 and 15 nm. With increasing doping levels, the distribution shifts toward smaller pores. These pore dimensions effectively enhance phonon scattering at pore walls, thereby suppressing heat transfer [51]. As shown in Fig. 6c , both specific surface areas of Fe-doped samples (FSA3, FSA7, FSA11) are substantially reduced compared to pure SA. The specific surface area and pore volume of the Fe-doped samples (FSA3, FSA7, FSA11) are significantly reduced compared to pure SA, yetshow no significant variation across different doping levels. This suggests the formation of amorphous iron oxide within the pore channels [52]. At low iron doping levels (FSA3), the pore volume increases, while further doping leads to its reduction. Overall, iron incorporation decreases both the pore size and specific surface area. This phenomenon is likely attributable to the hydrophilicity of Fe 2 O 3 nanoparticles, which promotes the collapse of nanopores due to surface tension during high-temperature drying, thereby attenuating the nanoporous structure. 3.5 Composition analysis of FSA Fig. 7 shows the XPS spectra of FSA7 and SA. XPS survey spectra ( Fig. S1a and c) of FSA7 and SA exhibit three characteristic peaks corresponding to O 1s, C 1s and Si 2p. High-resolution analysis (Fig. S1b and d) confirms the Si 2p peak position at 103.7 eV. Although the Fe 2p peak in Fig.7b is poorly characterized (no signature satellite peaks) due to the low concentration, the low binding energy shift of 0.15 eV for the O 1s peak in Fig. 7a confirms the doping of Fe 3+ . This shift results from the formation of Fe 3+ -modified silicon oxides that weaken Si-O covalent bonds, increasing oxygen electron density and consequently reducing O 1s binding energy. The Fe 2p 3/2 binding energy at 711.9 eV in Fig. 7b confirms the presence of Fe 3+ oxide species. Fig. S2 shows the FTIR spectra of FSA7 and SA. FTIR spectra reveal characteristic Si-O-Si vibrations in both FSA7 and SA samples: asymmetric stretching at 1106 cm -1 , symmetric stretching at 798 cm -1 , and bending at 465 cm -1 [53]. The characteristic peaks at 2970 cm -1 (antisymmetric -CH₃ stretching) and 1260 cm -1 (symmetric Si-CH₃ deformation) confirm the formation of hydrophobic SiO 2 aerogels [54]. No distinct Fe-O vibrational peaks are observed in Fig. S2 , likely due to the low iron content in FSA7. 3.4 Thermal properties of FSA We performed the heat treatment and TG&DSC measurement to examine the microstructure and thermal properties of FSA at high temperature. The sintering temperature was 300 and 600 ℃. Fig. 8 presents SEM images of FSA7 after heat treatment at 300 and 600 ℃, respectively. The FSA7 sample still maintains a loose porous structure after the heat treatment at 300 ℃, but there has been a partial shrinkage of the skeleton. At 600 ℃, it can be clearly seen that part of the SiO 2 skeleton is seriously contracted, but still maintains the 3D mesh structure, which indicates that the FSA can still have good thermal insulation performance at a high temperature of 600 ℃. Fig. 9 shows the N 2 adsorption-desorption isotherms and pore structure of FSA7 after the heat treatment at 300 and 600 ℃. As shown in Fig. 9a , the maximum adsorption capacity of the sample decreases with the increase of the sintering temperature. Moreover, in the high-pressure region (relative pressure approaching 1.0), the adsorption isotherms of the samples treated at 300 ℃ and 600 ℃ exhibit a more plateau-like shape compared to that of the untreated sample, suggesting a notable reduction in the volume of large pores after thermal processing. Fig. 9b further reveals considerable alterations in the pore size distribution after heat treatment. The untreated sample shows a predominant pore size of approximately 11 nm, whereas the heat-treated samples display modal pore sizes around 9.6 and 7.8 nm, respectively. After the treatment at 300 ℃, the sample largely retains its original pore framework, although partial collapse and contraction of macropores and some mesopores are observed. In contrast, after the treatment at 600 ℃, the intensity of the pore size distribution curve decreases markedly, with a pronounced shift toward smaller pore sizes, indicating further reduction of large pores and mesopores, as well as the degradation of the 3D structure. These findings are consistent with the SEM results. As illustrated in Fig. 9c and d , both the average pore size and total pore volume show a declining trend, while the specific surface area initially increases and then decreases. This behavior may be attributed to the relatively mild structural collapse at 300 ℃, which allows the formation of new small pores, resulting in a temporary increase in specific surface area. Fig. 10 shows the TG and DSC curves of SA and FSA7 samples measured in the range of room temperature to 1000 ℃. FSA7 shows an obvious mass loss at room temperature to ~250 ℃, indicating the relatively higher content of water than SA. SA exhibits two distinct exothermic events at 419.3 ℃(methyl group decomposition) and 623.1 ℃ (amorphous-to-crystalline transition) in Fig. 10a , accompanied by 11.66% mass loss up to 998 ℃. The high-temperature transition at 623.1 ℃ involves a structural reorganization from a disordered [SiO 4 ] tetrahedral network to a periodic lattice, leading to internal shrinkage and fracture [55]. FSA7 shows delayed exothermic peaks at 510.4 ℃ and 645.1 ℃, exhibiting 91.1 ℃ and 22.0 ℃ shifts relative to SA. These shifts confirm Fe’s effectiveness in suppressing both methyl decomposition and SiO 2 crystallization, thereby enhancing high-temperature stability. 3.5 Thermal insulation properties of FSA The high-temperature thermal insulation properties of FSA aerogel powders were examined using a home-made setup (as shown in Fig. S3 ) in the single side heating mode. The hot surface temperature was fixed at 300 ℃ and 600 ℃, respectively. Fig. 11 shows the variation of the cold surface temperature of SA and FSA powders with different Fe/Si and EDTA-2Na/Fe molar ratios. At both 300 ℃ and 600 ℃, SA sample exhibits the highest cold-surface temperature among all samples. At the hot surface temperature of 300 ℃, FSA11 and FSA7 show the lowest cold surface temperature of 206 ℃ and 207 ℃, respectively, obviously lower than that of SA (215 ℃). At the hot surface temperature of 600 ℃, FSA11 and FSA7 also show better thermal insulation than other samples, and the cold surface temperature is 456 ℃, 26 ℃ lower than that of SA. These results demonstrate that the introduction of Fe 2 O 3 nanoparticles in SA is of greatly effectiveness in improving the high-temperature thermal insulation properties of SiO 2 aerogel powders. The FSA7 sample fully complexed with EDTA-2Na, possesses the best high-temperature thermal insulation properties at 300 ℃ and 600 ℃, which indicates that the samples modulated by the chelating agent have more homogeneous dispersion of Fe, effectively improving the high temperature insulation properties. Fe is more uniformly dispersed, which effectively inhibits the shrinkage of the 3D skeleton of SiO 2 and is more advantageous at high temperatures. 4. Conclusion This study developed FSA via sol-gel and ambient-pressure drying using inorganic aqueous silica sources, with innovative Fe³⁺ incorporation through EDTA chelation to achieve homogeneous dispersion. Systematic investigation of Fe and EDTA dosages revealed optimized thermal insulation properties. The material features a hierarchical porous structure (11.3 nm average pore size with coexisting meso/macropores), where increasing EDTA enhances the distribution of Fe 2 O 3 nanoparticles uniformity. Compared to pure SiO 2 , the composite demonstrates: (1) localized agglomeration of amorphous iron oxide; (2) reductions in specific surface area, pore volume, and pore size with increasing iron content, likely due to the hydrophilicity of amorphous iron oxide; (3) preservation of nanoporous structure at 600 ℃; and (4) effective inhibition of SiO 2 crystallization at elevated temperatures. Single-side heating tests confirm a 26 ℃ lower cold-side temperature (456 ℃ vs 482 ℃ at 600 ℃). Optimal performance occurs at 7% iron doping, balancing structural stability and thermal insulation. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement: This work was financially supported by Shandong Taishan Industrial Leading Talent Funding Project(2019TSCYCX-32) and the National Natural Science Foundation of China (NSFC) (62275154, 61775131). Author Contribution Y.Q. ,X.G. ,J.W. and X.Z. conceived the study, designed the methodology, performed the formal analysis, and wrote the original draft. All authors reviewed the manuscript. References B. Schartel and T. R. Hull, Fire and Materials 31 , 327 (2007). U. Berardi, Energy 182 , 777 (2019). A. M. Papadopoulos, Energy and Buildings 37 , 77 (2005). M. Koebel, A. Rigacci, and P. Achard, J Sol-Gel Sci Technol 63 , 315 (2012). S.S. 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Yuan, and X. Chen, Journal of Hazardous Materials 362 , 294 (2019). K. M. S. Khalil and S. A. Makhlouf, Applied Surface Science 254 , 3767 (2008). Additional Declarations No competing interests reported. Supplementary Files Supportinginformation.docx Cite Share Download PDF Status: Published Journal Publication published 29 Dec, 2025 Read the published version in Journal of Porous Materials → Version 1 posted Reviewers agreed at journal 05 Oct, 2025 Reviewers agreed at journal 01 Oct, 2025 Reviewers agreed at journal 01 Oct, 2025 Reviewers invited by journal 30 Sep, 2025 Editor assigned by journal 24 Sep, 2025 Submission checks completed at journal 24 Sep, 2025 First submitted to journal 23 Sep, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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agent.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/b47b120f48e5eb1d4770973e.png\"},{\"id\":93426583,\"identity\":\"2851553b-9b09-4640-9f55-b6f9a8f52932\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":472132,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003ePhotos of\\u003cstrong\\u003e (a)-(e)\\u003c/strong\\u003e SA and FSA wet gels and \\u003cstrong\\u003e(f)-(j)\\u003c/strong\\u003e aerogel powders with the Fe/Si molar ratio of 7%. Variation of the packing density of FSA with \\u003cstrong\\u003e(k)\\u003c/strong\\u003e Fe/Si molar ratio and \\u003cstrong\\u003e(l)\\u003c/strong\\u003eEDTA-2Na/Fe molar ratio.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/dcb8e9c795ce8d07c1fbad1c.png\"},{\"id\":93426580,\"identity\":\"84e03ca8-6848-4f87-b6e4-54bb1dbd7a23\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:12\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":101969,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eXRD patterns of \\u003cstrong\\u003e(a)\\u003c/strong\\u003e SA and FSA powders with different Fe/Si molar ratios, and \\u003cstrong\\u003e(b)\\u003c/strong\\u003e as-prepared FSA7 and heat-treated sample at 300 and 600 ℃.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/bd9185687f572e09887eaa7d.png\"},{\"id\":93426603,\"identity\":\"01680c07-1884-4f3f-a537-5110be8b3eb1\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":490739,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSEM images of \\u003cstrong\\u003e(a)\\u003c/strong\\u003e SA; \\u003cstrong\\u003e(b)\\u003c/strong\\u003e FSA3; \\u003cstrong\\u003e(c)\\u003c/strong\\u003e FSA7 and \\u003cstrong\\u003e(d)\\u003c/strong\\u003e FSA11. \\u003cstrong\\u003e(e)\\u003c/strong\\u003e EDS element mappings and \\u003cstrong\\u003e(f)\\u003c/strong\\u003e spectrum of FSA7.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/651c4332b31ebf11d646e489.png\"},{\"id\":93426585,\"identity\":\"01f5b545-1ced-44c0-9834-9e9e95e2b0d1\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":831746,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003e(a)-(d)\\u003c/strong\\u003e TEM images of FSN7 at different resolution; \\u003cstrong\\u003e(e)\\u003c/strong\\u003e SAED pattern and \\u003cstrong\\u003e(f)\\u003c/strong\\u003eEDS element mapping of FSN7.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/082770ae71fb63f249444ea5.png\"},{\"id\":93427283,\"identity\":\"3dc458d2-a345-45b2-8a90-6747f0b69c5d\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 17:01:13\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":141553,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003e(a)\\u003c/strong\\u003e N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherms and \\u003cstrong\\u003e(b)\\u003c/strong\\u003e pore size distribution of SA, FSA3, FSA7 and FSA11. Variation of \\u003cstrong\\u003e(c)\\u003c/strong\\u003e specific surface area and \\u003cstrong\\u003e(d)\\u003c/strong\\u003e average pore diameter with Fe content in FSA.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/db8dfde999b6320e9f98a3b1.png\"},{\"id\":93426592,\"identity\":\"9cbfdc25-7c99-41ba-8f0c-a29d325d4eec\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":7,\"title\":\"Figure 7\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":120305,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eXPS spectra of FSA7 and SA: \\u003cstrong\\u003e(a)\\u003c/strong\\u003e O 1s of SA and FSA7; \\u003cstrong\\u003e(b)\\u003c/strong\\u003e Fe 2p of SA and FSA7.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"7.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/a3eda03c930cf959eee7a129.png\"},{\"id\":93426595,\"identity\":\"01699a4a-164d-42e8-aefe-fc2fb65f3f21\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":8,\"title\":\"Figure 8\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":429430,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSEM images of FSA7 sintered at \\u003cstrong\\u003e(a)\\u003c/strong\\u003e 300 ℃ and \\u003cstrong\\u003e(b)\\u003c/strong\\u003e 600 ℃.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"8.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/e7573ad9181313ec4dda520d.png\"},{\"id\":93426586,\"identity\":\"104943c1-0b8c-4ea9-bc9f-9033a307a60d\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":9,\"title\":\"Figure 9\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":145313,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eN\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherms and pore structure information of FSA7 after different heat treatment temperatures. \\u003cstrong\\u003e(a)\\u003c/strong\\u003e N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherm and \\u003cstrong\\u003e(b)\\u003c/strong\\u003e pore size distribution of FAS7, variation of \\u003cstrong\\u003e(c)\\u003c/strong\\u003e specific surface area and \\u003cstrong\\u003e(d)\\u003c/strong\\u003e average pore diameter of FAS7.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"9.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/95b2817186bd763ba18bec37.png\"},{\"id\":93426584,\"identity\":\"1b224627-da3d-42e4-b5f4-e263e991d3d3\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"png\",\"order_by\":10,\"title\":\"Figure 10\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":79089,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eTG and DSC curves of \\u003cstrong\\u003e(a)\\u003c/strong\\u003e SA and \\u003cstrong\\u003e(b)\\u003c/strong\\u003e FSA7.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"10.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/638302e0a44a7028d9253faf.png\"},{\"id\":93427285,\"identity\":\"124f3777-dc06-4943-a461-f2149919300c\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 17:01:13\",\"extension\":\"png\",\"order_by\":11,\"title\":\"Figure 11\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":157249,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eVariation of the cold surface temperature of \\u003cstrong\\u003e(a-b)\\u003c/strong\\u003e SA and FSA with different Fe/Si molar ratio and \\u003cstrong\\u003e(c-d)\\u003c/strong\\u003e with different EDTA content, with the hot surface temperature of 300 ℃ and 600 ℃. \\u003cstrong\\u003e(e)\\u003c/strong\\u003e Schematic illustration of the high-temperature heating apparatus.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"11.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/46ee6c5a49eeecd148c1b509.png\"},{\"id\":99545460,\"identity\":\"56ddee55-17af-4766-a097-b1ee8e7af0e0\",\"added_by\":\"auto\",\"created_at\":\"2026-01-05 16:07:52\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":3956793,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/f8ce7ad7-fb06-4219-b02f-c8cbc950a7e1.pdf\"},{\"id\":93426590,\"identity\":\"1b2d7539-b54a-4091-8485-4c942da21437\",\"added_by\":\"auto\",\"created_at\":\"2025-10-13 16:53:13\",\"extension\":\"docx\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":1356077,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Supportinginformation.docx\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7692578/v1/e532dbc2457aaaaf9380b01b.docx\"}],\"financialInterests\":\"No competing interests reported.\",\"formattedTitle\":\"\\u003cp\\u003e\\u003cstrong\\u003eFe\\u003c/strong\\u003e\\u003csub\\u003e\\u003cstrong\\u003e2\\u003c/strong\\u003e\\u003c/sub\\u003e\\u003cstrong\\u003eO\\u003c/strong\\u003e\\u003csub\\u003e\\u003cstrong\\u003e3\\u003c/strong\\u003e\\u003c/sub\\u003e\\u003cstrong\\u003e/SiO\\u003c/strong\\u003e\\u003csub\\u003e\\u003cstrong\\u003e2\\u003c/strong\\u003e\\u003c/sub\\u003e\\u003cstrong\\u003e composite aerogels powders for high-temperature thermal insulation based on EDTA chelated aqueous precursor\\u003c/strong\\u003e\\u003c/p\\u003e\",\"fulltext\":[{\"header\":\"1. Introduction\",\"content\":\"\\u003cp\\u003eWith the development of industry and science and technology, traditional thermal insulation materials (such as polystyrene foam, mineral wool, etc.) are flammable [\\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e], easy to age [\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e], and have high thermal conductivity [\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e], which has made it difficult to satisfy people\\u0026rsquo;s demand for high-performance thermal insulation materials.\\u003c/p\\u003e\\u003cp\\u003eSiO\\u003csub\\u003e2\\u003c/sub\\u003e nanoporous materials, especially SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel, effectively inhibit solid-phase heat conduction as well as convective heat transfer due to their unique mesoporous structure that makes the pore size below 100 nm, thus improving their thermal insulation performance at high temperatures [\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e]. SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel have a three-dimensional (3D) nano grid structure with backbones and pores at the nanoscale. This material possesses low density, high porosity, large specific surface area, thermal conductivity, and low dielectric constant [\\u003cspan additionalcitationids=\\\"CR6\\\" citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e7\\u003c/span\\u003e]. These excellent properties make it valuable for non-negligible applications in aerospace [\\u003cspan citationid=\\\"CR8\\\" class=\\\"CitationRef\\\"\\u003e8\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e9\\u003c/span\\u003e], new energy batteries [\\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e10\\u003c/span\\u003e], and thermal insulation [\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e]. However, even as a high-performance thermal insulation material, SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel still have some limitations and face severe problems. The conventional SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels are almost transparent to radiation in the IR wavelength range of 3\\u0026thinsp;~\\u0026thinsp;8 \\u0026micro;m [\\u003cspan citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e] When the temperature of the hot and cold surfaces reaches 100 ℃, the percentage of thermal radiation in the heat transfer gradually increases and becomes impossible to ignore [\\u003cspan citationid=\\\"CR14\\\" class=\\\"CitationRef\\\"\\u003e14\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e15\\u003c/span\\u003e]. This leads to a decrease in the high-temperature thermal insulation performance of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel, which greatly limits their practical applications at high temperatures.\\u003c/p\\u003e\\u003cp\\u003eThe doping of shading agents has been established as an effective method among the numerous attempts made to improve the high-temperature thermal insulation performance of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel. The shading agent can improve the high-temperature thermal insulation performance of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel by enhancing the absorption or reflection of infrared and reducing the infrared radiation heat transfer at high temperatures [\\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e]. Ma et al. prepared TiO\\u003csub\\u003e2\\u003c/sub\\u003e-SiO\\u003csub\\u003e2\\u003c/sub\\u003e composite aerogels with high resistance to high-energy laser irradiation and improved the light-shielding performance of the aerogels by doping TiO\\u003csub\\u003e2,\\u003c/sub\\u003e realizing the structural integrity even when the thermal barrier difference reaches 1275 ℃ [\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e]. By establishing a theoretical model, He et al. found that an increase in TiO\\u003csub\\u003e2\\u003c/sub\\u003e content reduced the radiative heat transfer and increased the thermal conductivity simultaneously [\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e]. Wu et al. prepared ZrO\\u003csub\\u003e2\\u003c/sub\\u003e/SiO\\u003csub\\u003e2\\u003c/sub\\u003e fiber paper-reinforced aerogels with a dual-network structure by combining the sol-gel method with the traditional paper-making process. The resulting ZrO\\u003csub\\u003e2\\u003c/sub\\u003e/SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels exhibited an effective specific extinction coefficient 19.5 times higher than that of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels in the wavelength range of 3\\u0026thinsp;~\\u0026thinsp;5 \\u0026micro;m [\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e]. Pang et al. synthesized SiC-SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels and found that SiC, as a shading agent, could effectively improve the thermal insulation at a content of 1% under large temperature differences without significantly increasing the aerogel\\u0026rsquo;s thermal conductivity [\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e]. In addition, carbon [\\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e21\\u003c/span\\u003e], Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e [\\u003cspan citationid=\\\"CR22\\\" class=\\\"CitationRef\\\"\\u003e22\\u003c/span\\u003e], and yttrium [\\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e23\\u003c/span\\u003e] are also good shading agents. Despite considerable advances in this field, the current shading agents have limitations, such as the high cost of TiO\\u003csub\\u003e2\\u003c/sub\\u003e raw materials. Although carbon has excellent shading properties, higher doping levels can increase the thermal conductivity and lead to the oxidation at high temperatures [\\u003cspan citationid=\\\"CR24\\\" class=\\\"CitationRef\\\"\\u003e24\\u003c/span\\u003e].\\u003c/p\\u003e\\u003cp\\u003eIron oxide exhibits strong IR radiation absorption in the wavelength bands of 0.5\\u0026ndash;0.9 \\u0026micro;m, above 1.4 \\u0026micro;m, and 5\\u0026ndash;7 \\u0026micro;m, making it an effective IR masking agent. Additionally, it offers superior stability and high-temperature resistance, making it suitable for incorporation into SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels as an efficient IR shielding material [\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e26\\u003c/span\\u003e]. Luo et al. prepared iron-doped silica aerogels via the sol-gel method and atmospheric pressure drying using an organosilicon precursor, which exhibited a porosity exceeding 90% and a thermal stability approximately 100 ℃ higher than pure SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels [\\u003cspan citationid=\\\"CR27\\\" class=\\\"CitationRef\\\"\\u003e27\\u003c/span\\u003e]. Casas et al. synthesized silica-iron oxide nanocomposites using Fe(NO\\u003csub\\u003e3\\u003c/sub\\u003e)\\u003csub\\u003e3\\u003c/sub\\u003e\\u0026middot;9H\\u003csub\\u003e2\\u003c/sub\\u003eO and FeNa(EDTA)\\u0026middot;2H\\u003csub\\u003e2\\u003c/sub\\u003eO as iron sources via supercritical drying (SCD). The resulting nanocomposites demonstrated soft magnetic properties, low density, and low resistivity [\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e]. Tu et al. fabricated SiO\\u003csub\\u003e2\\u003c/sub\\u003e/Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e composite aerogels via SCD, demonstrating low-density (0.04 g/cm\\u003csup\\u003e3\\u003c/sup\\u003e), high specific surface area (705 m\\u003csup\\u003e2\\u003c/sup\\u003e/g), low thermal conductivity (0.026 W/(m\\u0026middot;K)) and good thermal stability at temperatures up to 1100 ℃ [\\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e29\\u003c/span\\u003e].\\u003c/p\\u003e\\u003cp\\u003eThe drying of the wet gel is a kernel process for the preparation of aerogel, and currently three drying methods are used, i.e., SCD [\\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e30\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e], freeze drying (FD) [\\u003cspan citationid=\\\"CR32\\\" class=\\\"CitationRef\\\"\\u003e32\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e33\\u003c/span\\u003e] and atmospheric pressure drying (APD) [\\u003cspan additionalcitationids=\\\"CR35\\\" citationid=\\\"CR34\\\" class=\\\"CitationRef\\\"\\u003e34\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR36\\\" class=\\\"CitationRef\\\"\\u003e36\\u003c/span\\u003e]. The SCD has been widely used in industry, but it is long been accused of complicated operation, potential danger and high cost [\\u003cspan citationid=\\\"CR37\\\" class=\\\"CitationRef\\\"\\u003e37\\u003c/span\\u003e]. The FD is often used in a laboratory scale, with the drawback of poor product quality, long drying period and pore collapse [\\u003cspan citationid=\\\"CR38\\\" class=\\\"CitationRef\\\"\\u003e38\\u003c/span\\u003e]. In contrast, the APD is the developing trend of the aerogel production because of its low facility cost, simple operation, short cycle time and high product quality [\\u003cspan citationid=\\\"CR39\\\" class=\\\"CitationRef\\\"\\u003e39\\u003c/span\\u003e].\\u003c/p\\u003e\\u003cp\\u003eThe silica source of aerogel is also greatly important for the commercialization of aerogel materials. Researchers prepared aerogels mostly using organosilicon sources such as tetraethyl orthosilicate (TEOS) [\\u003cspan citationid=\\\"CR40\\\" class=\\\"CitationRef\\\"\\u003e40\\u003c/span\\u003e], tetramethoxysilane (TMOS) [\\u003cspan citationid=\\\"CR41\\\" class=\\\"CitationRef\\\"\\u003e41\\u003c/span\\u003e], methyltriethoxysilane (MTES) [\\u003cspan citationid=\\\"CR42\\\" class=\\\"CitationRef\\\"\\u003e42\\u003c/span\\u003e], and methyltrimethoxysilane (MTMS) [\\u003cspan additionalcitationids=\\\"CR44\\\" citationid=\\\"CR43\\\" class=\\\"CitationRef\\\"\\u003e43\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR45\\\" class=\\\"CitationRef\\\"\\u003e45\\u003c/span\\u003e]. However, the cost of organosilica source is high, so the use of inorganic silica source as the silica precursor can significantly reduce the cost of raw materials, and gradually become the focus of current research [\\u003cspan citationid=\\\"CR46\\\" class=\\\"CitationRef\\\"\\u003e46\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR47\\\" class=\\\"CitationRef\\\"\\u003e47\\u003c/span\\u003e]. However, the use of inorganic silica precursor will inevitably bring a large number of hydroxyl groups in the precursor. The introduction of the dopant ions (e.g., Fe\\u003csup\\u003e3+\\u003c/sup\\u003e) will result in the precipitation in the SiO\\u003csub\\u003e2\\u003c/sub\\u003e aqueous sol with high pH values, which will affect the microstructure and properties of the composite aerogel significantly. However, few study focus on this aspect and find an appropriate solution for this up to now.\\u003c/p\\u003e\\u003cp\\u003eHerein, we developed a novel method to prepare FSA based on inorganic materials (water glass and iron nitrate) and the APD technique, by using EDTA-2Na as the chelating agent of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e ions, to avoid precipitation and iron agglomeration. The packing density, crystallinity, microstructure, thermal stability and thermal insulation properties of the composite aerogels were examined, and effects of the Fe/Si molar ratio and EDTA-2Na level were investigated.\\u003c/p\\u003e\"},{\"header\":\"2. Experimental\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e\\n \\u003ch2\\u003e2.1 Materials\\u003c/h2\\u003e\\n \\u003cp\\u003eIndustrial water glass (SiO\\u003csub\\u003e2\\u003c/sub\\u003e content: 28 wt%) was purchased from Shanghai Qingfeng Chemical Factory (China). Hydrochloric acid (HCl, AR) and hexamethylene tetramine (HMT, AR grade) were obtained from Sinopharm Chemical Reagent Co. Ltd. (China). Ferric nitrate nonahydrate (Fe(NO\\u003csub\\u003e3\\u003c/sub\\u003e)\\u003csub\\u003e3\\u003c/sub\\u003e\\u0026middot;9H\\u003csub\\u003e2\\u003c/sub\\u003eO, AR) was supplied by Shanghai Aladdin Biochemical Technology Co. Ltd. (China). Anhydrous ethanol (EtOH, AR) was acquired from Shanghai Lingfeng Chemical Reagent Co. Ltd. (China). Hexamethyldisilazane (HMDS, \\u0026ge;\\u0026thinsp;99.5%) and cyclohexane (CyH, AR) were purchased from Shanghai Aladdin Biochemical Technology Co. Ltd. (China) and Shandong Keyuan Biochemical Co. Ltd. (China), respectively.\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e\\n \\u003ch2\\u003e2.2 Preparation of FSA\\u003c/h2\\u003e\\n \\u003cp\\u003e\\u003cstrong\\u003eFigure\\u0026nbsp;1a\\u003c/strong\\u003e illustrates the preparation process of FSA. Initially, SiO\\u003csub\\u003e2\\u003c/sub\\u003e sol was prepared by mixing water glass with deionized water (volume ratio 1:4), stirring for 30 min, and acidifying with acidic cationic resin for 30 min. Ferric nitrate solutions were prepared by dissolving ferric nitrate hydrate in deionized water with Fe/Si molar ratios of 3%, 5%, 7%, 9%, and 11%, followed by 30 min of stirring. The SiO\\u003csub\\u003e2\\u003c/sub\\u003e sol was then mixed with the ferric nitrate solution and stirred for 60 min. EDTA-2Na was added and stirred for 60 min to form a composite sol. Subsequently, an aqueous HMT solution was added dropwise to the composite sol, which was gelled at 80 ℃ and aged for 24 h to form a composite gel. The gel was immersed in EtOH (2\\u0026ndash;3 times its volume) at 60 ℃ for 6 h, modified with HMDS in cyclohexane at 55 ℃ for 6 h, and finally dried in air at 200 ℃ for 2 h to obtain the FSA. Samples were labeled as FSA3, FSA5, FSA7, FSA9, and FSA11 according to the Fe/Si molar ratio. To examine the effect of the chelating agent, additional samples were prepared with a fixed Fe/Si ratio of 7% and varying EDTA-2Na/Fe molar ratios from 0 to 1, labeled as FSAE0, FSAE25, FSAE50, FSAE75, and FSA7 (also denoted as FSAE100). A pure silica aerogel (SA) was synthesized using a similar procedure for comparison.\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec5\\\" class=\\\"Section2\\\"\\u003e\\n \\u003ch2\\u003e2.3 Characterization\\u003c/h2\\u003e\\n \\u003cp\\u003eThe packing density was obtained by measuring the ratio of mass to volume using a weighing balance with a 10 mL measuring cylinder (\\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\:\\\\rho\\\\:\\\\:=\\\\frac{m}{V}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e).The crystallinity of FSA powders was characterized using an X-ray diffraction (XRD, D8 ADVANCE, Bruker, Germany) (copper target, 20 kV, diffraction angles: 10\\u0026deg; to 80\\u0026deg;). A Hitachi SU9000 low voltage scanning electron microscope (SEM) was used to observe the microscopic morphology of FSAs powders at a low accelerating voltage of 1 kV to minimize the depth of penetration of the electron beam and to improve the resolution of the surface details. Field emission transmission electron microscopy (FE-TEM, JEM-2100F, Nippon Electron Co., Ltd., Japan) was used to analyze the microstructure and microscopic crystallinity of FSA. X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250, USA) was used to analyze the chemical states of Si and O in FSA. Fourier transform infrared spectroscopy (FTIR, Bruker Tensor 27, Germany) was used to measure the infrared transmittance of FSA and SA in the range of 400\\u0026ndash;4000 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e. The pore structure was analyzed by a four-station specific surface pore size analyzer (Quadrasorb SI, USA) using the Brunauer-Emmett-Tteller (BET) method. Thermogravimetric and differential scanning calorimetric properties were analyzed by a simultaneous thermal analyzer (TG\\u0026amp;DSC, STA449F5, NETZSCH, Germany) in an air environment from room temperature up to 1000 ℃ at a ramp rate of 10 ℃/min. The thermal insulation properties of the aerogel powders were measured by a home-made setup. The samples were packed in a 5 cm \\u0026times; 5 cm \\u0026times; 1 cm tinplate box with vibration, placed in the center of a flat-plate heating furnace (Chemat, KW-4KH-600, USA), and a thermocouple was placed at the cold surface end. While the hot surface temperature was fixed at 300 ℃ and 600 ℃, respectively, the cold surface temperature was recorded every 10 s by using a paperless recorder (MIK-R9600, Hangzhou MIK Sensors Co., Ltd.). A glass fiber mat was placed over the thermocouple and tinplate box to maintain the temperature uniformity during the whole test process.\\u003c/p\\u003e\\n\\u003c/div\\u003e\"},{\"header\":\"3. Results and discussion\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003e3.1 Formation mechanism of FSA mediated by EDTA\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 1b\\u003c/strong\\u003e presents the formation process of FSA with or without EDTA-2Na in the precursor. The kernel function of EDTA-2Na chelating reagent in the precursor is to form [Fe(EDTA)]\\u003csup\\u003e-\\u003c/sup\\u003e chelate-ions, which is stable at a wide pH range, thus avoiding the precipitation of Fe(OH)\\u003csub\\u003e3\\u003c/sub\\u003e in the SiO\\u003csub\\u003e2\\u003c/sub\\u003e sol when HMT was added. Though a large part of [Fe(EDTA)]\\u003csup\\u003e-\\u003c/sup\\u003e chelate-ions is discharged from the gel during the solvent exchanging and surface modifying process, some are left in the nanopores of the gel, forming the nanosized Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e embedded in SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel. Without EDTA-2Na, the free Fe\\u003csup\\u003e3+\\u003c/sup\\u003e ions will transform to Fe(OH)\\u003csub\\u003e3\\u003c/sub\\u003e aggregates, thus forming the mixture of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel and Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e mi\\u003cstrong\\u003ecroparticle.\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 2\\u003c/strong\\u003e shows photographs of the gel and powder forms of 7% Fe-doped samples with varying EDTA/Fe molar ratios, along with the corresponding density profiles of the FSA. Both the gel and powder gradually lighten in color as the EDTA ratio increases, indicating improved iron chelation and enhanced material homogeneity. The aerogel prepared without EDTA exhibits a relatively high density. Systematic addition of EDTA significantly reduces density, demonstrating its role in modifying the aerogel structure. Furthermore, iron ion concentration also affects the packing density. Simultaneously, all FSA samples exhibit elevated densities, likely due to the thermal decomposition of the Fe(EDTA)\\u003csup\\u003e-\\u003c/sup\\u003e pore solution during drying, which releases Fe\\u003csup\\u003e3+\\u003c/sup\\u003e. Subsequent hydrolysis and aggregation of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e under high pH conditions further enhance density. The significantly higher density of FSA3 is attributed to its lower Fe\\u003csup\\u003e3+\\u003c/sup\\u003e content. While higher Fe\\u003csup\\u003e3+\\u003c/sup\\u003e concentrations promote the formation of α-FeOOH through hydrolysis, lower concentrations favor γ-FeO(OH) formation [48]. Upon further drying, γ-FeO(OH) transforms into magnetite, whereas α-FeOOH yields hematite. The stronger hydrophilicity of magnetite compared to hematite contributes to the increased density of FSA3. While increased packing density improves high-temperature insulation, excessive density may adversely affect performance.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e3.2 Crystallinity and microstructure of FSA\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 3a\\u003c/strong\\u003e presents the XRD patterns of pure SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel (SA), FSA3, FSA7 and FSA11. It can be seen that both SA and FSA samples exhibit amorphous features, and with the increase of Fe content, the broad peak of FSA change little, which indicates that the introduction of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e in the precursor does not affect the crystallinity of silica aerogel. Further heat treatment of the FSA7 sample also does not result in the crystalline peak, as shown in \\u003cstrong\\u003eFig. 3b.\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eFig. 4a-d gives the SEM images of SA, FSA3, FSA7 and FSA11, with the Fig. 4e and f showing the EDS analysis. While the SA sample exhibits a loose, porous nanostructure with a relatively large pore size, three FSA structures exhibit denser pore structure. In addition, the particle size in FSA is obviously larger than that in SA. With the increase of the Fe content, the agglomeration of neighboring particle is more popular, which indicates that the introduction of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e may promote the densification of the SiO\\u003csub\\u003e2\\u003c/sub\\u003e skeleton. EDS analysis shows that the content of Fe in FSA7 is 0.66, much lower than that in the precursor. The dissolution of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e from the gel during the solvent exchanging and the modifying process is the underlying reason. Despite the low content, the distribution of Fe in the FSA7 sample is uniform, guaranteeing the full shading of the IR radiation in the thermal insulation process.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 5\\u003c/strong\\u003e presents TEM images of FSA7 at different resolutions, SAED pattern and EDS analysis. Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e presents an agglomerated morphology in the 3D mesh structure of SiO\\u003csub\\u003e2\\u003c/sub\\u003e, while SiO\\u003csub\\u003e2\\u003c/sub\\u003e is tightly wrapped around it. Under high-magnification observation, no distinct lattice fringes corresponding to large-scale Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e particles were detected at the iron aggregation sites; however, fine granular structures were observed, as evidenced in \\u003cstrong\\u003eFig. 5a-d\\u003c/strong\\u003e. This indicates that Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e presents a more uniform amorphous structure (amorphous iron oxide), in the FSA, and this conclusion is also supported by \\u003cstrong\\u003eFig. 5e\\u003c/strong\\u003e with SAED pattern. However, the agglomeration of Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e nanoparticles also makes the FSA have a relatively dense structure, which explains the higher density of the aerogel.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e3.3 Pore structure of\\u0026nbsp;\\u003c/strong\\u003e\\u003cstrong\\u003eFSA\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 6a-c\\u003c/strong\\u003e demonstrates the N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherms, pore size distribution curves, and specific surface area variation curves with iron content of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels with FSA3, FSA7, and FSA11. \\u003cstrong\\u003eFig. 6a\\u003c/strong\\u003e displays a Type IV adsorption isotherm with distinct capillary condensation in the relative pressure range of 0.4-1.0, consistent with mesoporous materials possessing a 3D network structure [49]. Although iron doping reduces the maximum adsorption capacity, the presence of an H1-type hysteresis loop indicates cylindrical pore geometry. The steep rise in the N₂ adsorption-desorption curve near P/P₀ ≈ 1.0, without attaining a plateau, suggests the coexistence of mesopores and macropores in the FSA [50]. Figure 6b presents the pore size distributions of SA, FSA3, FSA7, and FSA11, exhibiting peaks predominantly between 10 and 15 nm. With increasing doping levels, the distribution shifts toward smaller pores. These pore dimensions effectively enhance phonon scattering at pore walls, thereby suppressing heat transfer [51]. As shown in\\u003cstrong\\u003e\\u0026nbsp;Fig. 6c\\u003c/strong\\u003e, both specific surface areas of Fe-doped samples (FSA3, FSA7, FSA11) are substantially reduced compared to pure SA. The specific surface area and pore volume of the Fe-doped samples (FSA3, FSA7, FSA11) are significantly reduced compared to pure SA, yetshow no significant variation across different doping levels. This suggests the formation of amorphous iron oxide within the pore channels\\u0026nbsp;[52]. At low iron doping levels (FSA3), the pore volume increases, while further doping leads to its reduction. Overall, iron incorporation decreases both the pore size and specific surface area. This phenomenon is likely attributable to the hydrophilicity of Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e nanoparticles, which promotes the collapse of nanopores due to surface tension during high-temperature drying, thereby attenuating the nanoporous structure.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e3.5 Composition analysis of\\u0026nbsp;\\u003c/strong\\u003e\\u003cstrong\\u003eFSA\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 7\\u003c/strong\\u003e shows the XPS spectra of FSA7 and SA. XPS survey spectra (\\u003cstrong\\u003eFig. S1a and c)\\u003c/strong\\u003e of FSA7 and SA exhibit three characteristic peaks corresponding to O 1s, C 1s and Si 2p. High-resolution analysis\\u003cstrong\\u003e\\u0026nbsp;(Fig. S1b and d)\\u003c/strong\\u003e confirms the Si 2p peak position at 103.7 eV. Although the Fe 2p peak \\u003cstrong\\u003ein Fig.7b\\u003c/strong\\u003e is poorly characterized (no signature satellite peaks) due to the low concentration, the low binding energy shift of 0.15 eV for the O 1s peak in \\u003cstrong\\u003eFig. 7a\\u0026nbsp;\\u003c/strong\\u003econfirms the doping of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e. This shift results from the formation of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e-modified silicon oxides that weaken Si-O covalent bonds, increasing oxygen electron density and consequently reducing O 1s binding energy. The Fe 2p\\u003csub\\u003e3/2\\u003c/sub\\u003e binding energy at 711.9 eV in \\u003cstrong\\u003eFig. 7b\\u003c/strong\\u003e confirms the presence of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e oxide species.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. S2\\u003c/strong\\u003e shows the FTIR spectra of FSA7 and SA. FTIR spectra reveal characteristic Si-O-Si vibrations in both FSA7 and SA samples: asymmetric stretching at 1106 cm\\u003csup\\u003e-1\\u003c/sup\\u003e, symmetric stretching at 798 cm\\u003csup\\u003e-1\\u003c/sup\\u003e, and bending at 465 cm\\u003csup\\u003e-1\\u0026nbsp;\\u003c/sup\\u003e[53]. The characteristic peaks at 2970 cm\\u003csup\\u003e-1\\u003c/sup\\u003e (antisymmetric -CH₃ stretching) and 1260 cm\\u003csup\\u003e-1\\u003c/sup\\u003e (symmetric Si-CH₃ deformation) confirm the formation of hydrophobic SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogels [54]. No distinct Fe-O vibrational peaks are observed in \\u003cstrong\\u003eFig. S2\\u003c/strong\\u003e, likely due to the low iron content in FSA7.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e3.4 Thermal properties of\\u0026nbsp;\\u003c/strong\\u003e\\u003cstrong\\u003eFSA\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eWe performed the heat treatment and TG\\u0026amp;DSC measurement to examine the microstructure and thermal properties of FSA at high temperature. The sintering temperature was 300 and 600 ℃.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 8\\u003c/strong\\u003e presents SEM images of FSA7 after heat treatment at 300 and 600 ℃, respectively. The FSA7 sample still maintains a loose porous structure after the heat treatment at 300 ℃, but there has been a partial shrinkage of the skeleton. At 600 ℃, it can be clearly seen that part of the SiO\\u003csub\\u003e2\\u003c/sub\\u003e skeleton is seriously contracted, but still maintains the 3D mesh structure, which indicates that the FSA can still have good thermal insulation performance at a high temperature of 600 ℃.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 9\\u003c/strong\\u003e shows the N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherms and pore structure of FSA7 after the heat treatment at 300 and 600 ℃. As shown in \\u003cstrong\\u003eFig. 9a\\u003c/strong\\u003e, the maximum adsorption capacity of the sample decreases with the increase of the sintering temperature. Moreover, in the high-pressure region (relative pressure approaching 1.0), the adsorption isotherms of the samples treated at 300 ℃ and 600 ℃ exhibit a more plateau-like shape compared to that of the untreated sample, suggesting a notable reduction in the volume of large pores after thermal processing. \\u003cstrong\\u003eFig. 9b\\u003c/strong\\u003e further reveals considerable alterations in the pore size distribution after heat treatment. The untreated sample shows a predominant pore size of approximately 11 nm, whereas the heat-treated samples display modal pore sizes around 9.6 and 7.8 nm, respectively. After the treatment at 300 ℃, the sample largely retains its original pore framework, although partial collapse and contraction of macropores and some mesopores are observed. In contrast, after the treatment at 600 ℃, the intensity of the pore size distribution curve decreases markedly, with a pronounced shift toward smaller pore sizes, indicating further reduction of large pores and mesopores, as well as the degradation of the 3D structure. These findings are consistent with the SEM results. As illustrated in\\u003cstrong\\u003e\\u0026nbsp;Fig. 9c and d\\u003c/strong\\u003e, both the average pore size and total pore volume show a declining trend, while the specific surface area initially increases and then decreases. This behavior may be attributed to the relatively mild structural collapse at 300 ℃, which allows the formation of new small pores, resulting in a temporary increase in specific surface area.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFig. 10\\u003c/strong\\u003e shows the TG and DSC curves of SA and FSA7 samples measured in the range of room temperature to 1000 ℃. FSA7 shows an obvious mass loss at room temperature to ~250 ℃, indicating the relatively higher content of water than SA. SA exhibits two distinct exothermic events at 419.3 ℃(methyl group decomposition) and 623.1 ℃ (amorphous-to-crystalline transition) in \\u003cstrong\\u003eFig. 10a\\u003c/strong\\u003e, accompanied by 11.66% mass loss up to 998 ℃. The high-temperature transition at 623.1 ℃ involves a structural reorganization from a disordered [SiO\\u003csub\\u003e4\\u003c/sub\\u003e] tetrahedral network to a periodic lattice, leading to internal shrinkage and fracture [55]. FSA7\\u0026nbsp;shows delayed exothermic peaks at 510.4 ℃ and 645.1 ℃, exhibiting 91.1 ℃ and 22.0 ℃ shifts relative to SA. These shifts confirm Fe’s effectiveness in suppressing both methyl decomposition and SiO\\u003csub\\u003e2\\u003c/sub\\u003e crystallization, thereby enhancing high-temperature stability.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e3.5 Thermal insulation properties of FSA\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe high-temperature thermal insulation properties of FSA aerogel powders were examined using a home-made setup (as shown in \\u003cstrong\\u003eFig. S3\\u003c/strong\\u003e) in the single side heating mode. The hot surface temperature was fixed at 300 ℃ and 600 ℃, respectively.\\u003cstrong\\u003e\\u0026nbsp;Fig. 11\\u003c/strong\\u003e shows the variation of the cold surface temperature of SA and FSA powders with different Fe/Si and EDTA-2Na/Fe molar ratios. At both 300 ℃ and 600 ℃, SA sample exhibits the highest cold-surface temperature among all samples. At the hot surface temperature of 300 ℃, FSA11 and FSA7 show the lowest cold surface temperature of 206 ℃ and 207 ℃, respectively, obviously lower than that of SA (215 ℃). At the hot surface temperature of 600 ℃, FSA11 and FSA7 also show better thermal insulation than other samples, and the cold surface temperature is 456 ℃, 26 ℃ lower than that of SA. These results demonstrate that the introduction of Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e nanoparticles in SA is of greatly effectiveness in improving the high-temperature thermal insulation properties of SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel powders. The FSA7 sample fully complexed with EDTA-2Na, possesses the best high-temperature thermal insulation properties at 300 ℃ and 600 ℃, which indicates that the samples modulated by the chelating agent have more homogeneous dispersion of Fe, effectively improving the high temperature insulation properties. Fe is more uniformly dispersed, which effectively inhibits the shrinkage of \\u0026nbsp;the 3D skeleton of SiO\\u003csub\\u003e2\\u003c/sub\\u003e and is more advantageous at high temperatures.\\u003c/p\\u003e\"},{\"header\":\"4. Conclusion\",\"content\":\"\\u003cp\\u003eThis study developed FSA via sol-gel and ambient-pressure drying using inorganic aqueous silica sources, with innovative Fe\\u0026sup3;⁺ incorporation through EDTA chelation to achieve homogeneous dispersion. Systematic investigation of Fe and EDTA dosages revealed optimized thermal insulation properties. The material features a hierarchical porous structure (11.3 nm average pore size with coexisting meso/macropores), where increasing EDTA enhances the distribution of Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e nanoparticles uniformity. Compared to pure SiO\\u003csub\\u003e2\\u003c/sub\\u003e, the composite demonstrates: (1) localized agglomeration of amorphous iron oxide; (2) reductions in specific surface area, pore volume, and pore size with increasing iron content, likely due to the hydrophilicity of amorphous iron oxide; (3) preservation of nanoporous structure at 600 ℃; and (4) effective inhibition of SiO\\u003csub\\u003e2\\u003c/sub\\u003e crystallization at elevated temperatures. Single-side heating tests confirm a 26 ℃ lower cold-side temperature (456 ℃ vs 482 ℃ at 600 ℃). Optimal performance occurs at 7% iron doping, balancing structural stability and thermal insulation.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eDeclaration of competing interest\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eAcknowledgement:\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThis work was financially supported by Shandong Taishan Industrial Leading Talent Funding Project(2019TSCYCX-32) and the National Natural Science Foundation of China (NSFC) (62275154, 61775131).\\u003c/p\\u003e\\u003ch2\\u003eAuthor Contribution\\u003c/h2\\u003e\\u003cp\\u003eY.Q. ,X.G. ,J.W. and X.Z. conceived the study, designed the methodology, performed the formal analysis, and wrote the original draft. 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Makhlouf, Applied Surface Science \\u003cstrong\\u003e254\\u003c/strong\\u003e, 3767 (2008).\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":true,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"journal-of-porous-materials\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"jopo\",\"sideBox\":\"Learn more about [Journal of Porous Materials](http://link.springer.com/journal/10934)\",\"snPcode\":\"10934\",\"submissionUrl\":\"https://submission.nature.com/new-submission/10934/3\",\"title\":\"Journal of Porous Materials\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"em\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false},\"keywords\":\"SiO2, Fe Doping, Aerogel, Infrared shielding\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-7692578/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-7692578/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eSiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel is a typical thermal insulation material suitable for varied high temperature industrial applications. However, its radiative transparency seriously hampers its application scenario. Herein, we integrated infrared (IR) opacified Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e nanoparticles into silica aerogel system and developed a Fe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e/SiO\\u003csub\\u003e2\\u003c/sub\\u003e composite aerogel (FSA) by using industrial water glass and ambient pressure drying process. Especially, we chelated Fe\\u003csup\\u003e3+\\u003c/sup\\u003e with disodium ethylenediaminetetraacetic (EDTA-2Na) to avoid the loss of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e in the gelling, solvent-exchanging and hydrophobic modification processes. FSA powders with 3-11% concentration exhibit an amorphous structure, high porosity with small nanopores (11-12 nm). The EDS analysis confirms the presence of Fe in the aerogel framework. The high-temperature thermal insulation properties of the FSA powders were enhanced compared with the pure SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel powders, yielding a cold surface temperature of 456 ℃ after heating at 600 ℃ for 30 min, 26 ℃ lower than pure SiO\\u003csub\\u003e2\\u003c/sub\\u003e aerogel. The EDTA-2Na chelating agent improves the dispersion of Fe\\u003csup\\u003e3+\\u003c/sup\\u003e and further reduces the temperature by 6 ℃, demonstrating its positive effect on the insulation performance.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Fe2O3/SiO2 composite aerogels powders for high-temperature thermal insulation based on EDTA chelated aqueous precursor\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2025-10-13 16:53:08\",\"doi\":\"10.21203/rs.3.rs-7692578/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0},{\"type\":\"reviewerAgreed\",\"content\":\"313683447625133081125351498723852208078\",\"date\":\"2025-10-06T00:07:39+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"190636800762729037114935060344640004805\",\"date\":\"2025-10-01T19:18:02+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"244060883018895399879907158358074125460\",\"date\":\"2025-10-01T11:53:45+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"\",\"date\":\"2025-09-30T20:05:37+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorAssigned\",\"content\":\"\",\"date\":\"2025-09-24T10:37:31+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"checksComplete\",\"content\":\"\",\"date\":\"2025-09-24T10:36:25+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"submitted\",\"content\":\"Journal of Porous Materials\",\"date\":\"2025-09-23T09:26:41+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"journal-of-porous-materials\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"jopo\",\"sideBox\":\"Learn more about [Journal of Porous Materials](http://link.springer.com/journal/10934)\",\"snPcode\":\"10934\",\"submissionUrl\":\"https://submission.nature.com/new-submission/10934/3\",\"title\":\"Journal of Porous Materials\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"em\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false}}],\"origin\":\"\",\"ownerIdentity\":\"6db5373a-e24f-40c2-b8dd-fcfa998e8b8c\",\"owner\":[],\"postedDate\":\"October 13th, 2025\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"published-in-journal\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2026-01-05T16:04:11+00:00\",\"versionOfRecord\":{\"articleIdentity\":\"rs-7692578\",\"link\":\"https://doi.org/10.1007/s10934-025-01900-z\",\"journal\":{\"identity\":\"journal-of-porous-materials\",\"isVorOnly\":false,\"title\":\"Journal of Porous Materials\"},\"publishedOn\":\"2025-12-29 15:58:24\",\"publishedOnDateReadable\":\"December 29th, 2025\"},\"versionCreatedAt\":\"2025-10-13 16:53:08\",\"video\":\"\",\"vorDoi\":\"10.1007/s10934-025-01900-z\",\"vorDoiUrl\":\"https://doi.org/10.1007/s10934-025-01900-z\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-7692578\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-7692578\",\"identity\":\"rs-7692578\",\"version\":[\"v1\"]},\"buildId\":\"XKTyCvWXoU3ODBz1xrDgd\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}