Synthesis and Infrared Stealth Property of Ordered Mesoporous

Oct 4, 2013 - The mesoporous structure was evaluated by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N2 adsorption...
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Synthesis and Infrared Stealth Property of Ordered Mesoporous Carbon−Aluminum-Doped Zinc Oxide Composites Wei Wang, Linping Zhang,* Ying Liu, Hong Xu, Yi Zhong, and Zhiping Mao* Key Laboratory of Science & Technology of Eco-Textile (Ministry of Education), Donghua University, 2999 North Renmin Road, Shanghai 201620, People’s Republic of China ABSTRACT: Ordered mesoporous carbon−aluminum-doped zinc oxide (C-AZO) composites were prepared by the solventevaporation induced self-assembly method (EISA). The mesoporous structure was evaluated by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N2 adsorption−desorption. The results showed that the composites had uniform pore size and high surface area. Textural characteristics of the nanocomposites were affected by the carbonization temperature. The specific area and pore volume increased upon increasing the calcination temperature, while the pore diameter decreased. The infrared emissivity value (8−14 μm) of ordered mesoporous C-AZO was measured by an IR-2 Infrared Emissometer. The results showed that infrared emissivity was as low as 0.39, which exhibited outstanding performance of infrared stealth. respectively.23,24 Carbon−silica nanocomposites with highly dispersed Fe species were also successfully prepared by J. H. Zhou.25 It was found that the infrared emissivity was 0.498. All relevant materials reported had a great application in the thermal infrared stealth field. However, there were few reports about the ordered mesoporous carbon−semiconductor materials with low infrared emissivity. Thus, development of a novel functional material, which combines the conductivity of carbon and the high infrared reflectivity of semiconductor, is crucial to the thermal stealthy paint. Herein, we report a facile route to prepare ordered mesoporous C-AZO composites in which the resol and AZO sol were assembled with block-copolymer Pluronic F127 in an ethanol solution during the evaporation process. The C-AZO nanocomposites exhibited an ordered mesostructure and high thermal stability up to 700 °C under N2 atmosphere. The composites had different surface area and uniform pore size, which resulted from various reaction conditions. The nanocomposites also exhibited low infrared emissivity at wavelengths from 8 to14 μm.

1. INTRODUCTION Infrared stealth materials are important in both civil and military stealthy applications due to the inexpensive infrared imaging systems which leak the personal privacy of and threaten the armed forces. To date, control of infrared emissivity was critical for infrared camouflage besides decreasing the skin temperature of the materials.1−3 Now various new materials with low emissivity have been researched in extensive work, such as conductive polymeric materials, metallic thin films, inorganic/ organic composites coating, and semiconductive materials.4−8 However, the infrared stealth performance of conductive polymeric materials was not obvious.9 Metallic thin film was easily exposed to visible light and a laser band due to the reflection of the metallic gloss. Furthermore, it was easy to be oxidized in air atmosphere, which resulted in higher infrared emissivity.10 Application of the low-emissivity inorganic/organic composite coatings was limited due to the poor thermal resistance and mechanical properties.11,12 Most of the studies focus on semiconductor materials, AZO, ITO, and ATO, due to the possibility of microwave and infrared integration stealthy ability. However, ITO and ATO had many disadvantages such as toxic raw materials and high production cost, which limited their development. Thus, AZO, which had advantages of simple technique process and facilities, low cost, easy operation, environmental friendliness, high conductivity, and intense reflectivity, was regarded as the most important and promising material for infrared camouflage.13−15 Mesoporous carbons with metal and metal oxide nanoparticles loaded or embedded16,17 into their frameworks attracted much attention for various applications involving separation,18 adsorption,19 energy storage20 and electrodes.21 Furthermore, ordered mesoporous nanocomposites also had a great potential application in the military camouflage field according to a recent investigation, as a result of the high conductivity and tunable porosities.22 Two kinds of ordered carbon/oxides nanocomposites C-Al2O3 and C-TiO2 reported by T. Wang were fabricated using the evaporation-induced triconstituent assembly method with infrared emissivity of 0.46 and 0.447, © 2013 American Chemical Society

2. EXPERIMENTAL PROCEDURE 2.1. Materials. Zinc acetate dihydrate, aluminum nitrate nonahydrate, monoethanol amine (MEA), phenol, formalin solution (37 wt %), sodium hydroxide, hydrochloric acid, and ethanol were purchased from Shanghai Chemical Agent Co. Pluronic F127 (Mw = 12 600, EO106PO70EO106, EO = ethylene oxide, PO = propylene oxide) was purchased from Sigma Aldrich Corp. All chemicals were used as received without any further purification. Deionized water was used in all experiments. 2.2. Preparation of Resol Precursors and AZO Sol. Resol, with a low molecular weight (Mw < 500), was prepared Received: Revised: Accepted: Published: 15066

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Figure 1. Schematic representation of the process used to prepare mesoporous C-AZO.

Figure 2. SAXS patterns of mesoporous C-AZO (12) nanocomposites thermal polymerized at 110 °C; carbonated at 350, 500, 700, and 900 °C, (inset) corresponding figure of q = 0.6−1.5 nm−1 at 10× magnification .

2.3. Preparation of Mesoporous C-AZO Composites. Mesoporous C-AZO was prepared using the evaporation induced self-assembly (EISA) strategy. In a detailed procedure, 1 mL of HCl was added into 9 mL of ethanol as solution A for further use. One gram of triblock copolymer F127 was dissolved in 16 g of ethanol with stirring to afford a clear solution. Then, 1 g of solution A was added. The mixture was stirred for 2 h at 40 °C. Afterward, 1 g of AZO sol and 5 g of resols’ ethanolic solution (20 wt %) were added in sequence. After stirring for 2 h, the mixture was transferred into dishes and dried at 40 °C. Thermopolymerization of the polymer

with phenol and formaldehyde according to the procedure reported previously.26 AZO sol was prepared by the sol−gel process. For a typical preparation, Zn(CH3COO)2·2H2O (2.1950 g) and MEA (0.6108 g) were added into ethanol (10 mL) with vigorous stirring to obtain a clear solution. Then, Al(NO3)3·9H2O (0.4506 g) was introduced at room temperature. The weight ratio of Al2O3 in the final product was selected as 7 wt % to obtain the material with lowest emissivity.14 Upon further stirring for 2 h at 80 °C under refluxing, the mixture was cooled to room temperature for further use.14 15067

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and put into a controlled atmosphere furnace to carbonize at different temperatures under nitrogen atmosphere for 2 h. The ramping rate was 1 °C/min below 600 and 5 °C/min above 600 °C. Products were obtained and named as C-AZO-x. “C-AZO-x” denoted the mesoporous C-AZO nanocomposites, wherein x represents the calcination temperature of the nanocomposite. Nanocomposites with different contents of AZO were obtained by controlling the mass of the AZO sol. The resulting samples were named as C-AZO(y)-500, wherein y represents the weight percentage of AZO in the nanocomposite. For comparison, the pure order carbon nanocomposite and AZO were prepared. 2.4. Characterization. Small-angle X-ray scattering (SAXS) measurements were taken on a SAXSess MC2 small-angle X-ray scattering system (Anton Paar, Austria) using Cu Kα radiation (40 kV, 20 mA). The d-spacing values were calculated

Table 1. Texture of the Ordered Mesostructured C-AZO Composites Prepared by the EISA Method sample name

a/nm

d10/ nm

SBET/ m2g−1

Vt/cm3 g−1

C-AZO(12)-350 C-AZO(12)-500 C-AZO(12)-700 C-AZO(12)-900 C-AZO(5)-500 C-AZO(16)-500

13.8 13.3 12.6

12.0 11.5 11.0

14.5 12.7

12.5 11.0

160 254 559 830 117 285

0.152 0.167 0.260 0.390 0.085 0.185

D/nm

RTG

4.4 3.8 3.2

10.1 11.9 11.7 11.7 5.5 16.1

4.2 3.8

Note: unit-cell parameter (a), interplanar spacing (d10), surface area (BET), average pore size (D), total pore volume (Vt), and measured residues by TG measurement (RTG).

precursors was carried out at 110 °C for 24 h in an oven. The as-made products were collected by scraping from the dishes

Figure 3. (a) N2 adsorption−desorption isotherms at 350, 500, 700, and 900 °C (for clarity, isotherms for C-AZO-350,C-AZO-500, and C-AZO-700 are offset vertically by 110, 110, and 60 cm3 g−1, respectively); (b) pore size distribution of mesoporous C-AZO(12) nanocomposites pyrolyzed at 350, 500, 700, and 900 °C in N2. 15068

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Figure 4. TEM images of mesoporous C-AZO(12) nanocomposite pyrolyzed at (a) 350, (b, c) 500, and (d) 700 °C in N2; (inset) corresponding FFT diffractogram.

Wide angle powder X-ray diffraction measurements (WXRD) were carried out using a Rigaku diffractometer (Rigaku Ltd.). Measurements were conducted with Cu Kα (40KV, 200 mA) wavelength. Relevant elements were recorded on an IE 300 X Energy Dispersive Spectrometer. Thermogravimetric analysis (TG) was performed on the NETZSCH Instruments (Germany) to determine the inorganic residue. Each sample was tested in an air atmosphere, from room temperature to 850 °C, with a heating rate of 10 °C/min. Infrared Emissivity Measurement. Prepared samples calcinated at 500 °C were used as the filling with a weight ratio of 45%. The water-borne polyurethane (PU) was used as adhesive. Aluminum sheet, properly degreased in diluted NaOH and chemically polished in diluted HNO3, was used as the substrate for the coating. The thickness of the coating was controlled at 75 or 150 μm by the automatic coater (Shanghai Environmental Engineering Technology Co., China), which was equipped with a thickness controller. The infrared emissivity value at a wavelength of 8−14 μm was measured by an IR-2 Infrared Emissometer (Shanghai Institute of Technological Physics of the Chinese Academy of Sciences). All values were obtained by averaging all data measured from 10 different regions of each coating.

according to the formula d = 2π/q, and unit-cell parameters were calculated by the formula a = 2d10/√3. Nitrogen sorption isotherms were measured at 77 K with a Micromerics Tristar II 3020 system. Before measurements, samples were degassed at 250 °C in vacuum for 6 h. Specific surface areas were calculated using the Brunauer−Emmett− Teller (BET) method. Pore volumes and pore size distributions were derived from the adsorption branches of the isotherms based on the Barrett−Joyner−Halanda (BJH) model. Transmission electron microscopy (TEM) images were recorded on a JEOL 2100 microscope operated at 200 kV. Samples for TEM observations were dispersed in ethanol after being ground, drop cast onto a carbon-coated microgrid, and dried before analysis.

3. RESULTS AND DISCUSSION 3.1. Structure of Mesoporous C-AZO Nanocomposites. The synthesis strategy for ordered mesoporous carbon− aluminum-doped zinc oxide (C-AZO) composites was presented in Figure 1. The mesostructured C-AZO composites were prepared by the solvent-evaporation induced selfassembly method (EISA) using a low molecular weight resol as an organic precursor, metal oxide sol as an inorganic precursor, and amphiphilic triblock copolymer F127 as a template. The results of the powder SAXS measurements for these nanocomposites are shown in Figure 2. For the as-made films there were three intense diffraction peaks at 0.436, 0.736, and 1.16 nm−1, which suggested typical ordered mesostructure.27

Figure 5. WXRD pattern of mesoporous C-AZO nanocomposite carbonated at 350, 500, 700, and 900 °C. 15069

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Figure 6. EDS pattern of mesoporous C-AZO(12) nanocomposite carboniated at 500 °C.

classification.29,30 A hysteresis loop at a relative pressure of p/p0 > 0.4 with a distinct capillary condensation step suggested a narrow mesopore size distribution. Structural parameters including the surface area (BET), average pore size (D), and total pore volume (Vt) were presented in Table 1. Pore diameters of materials carbonized at 350, 500, and 700 °C were calculated to be 4.4, 3.8, and 3.2 nm, respectively. The pore size showed a downward trend, which could be attributed to shrinkage of the structure. However, the surface area and pore volume were found to increase gradually with a rise in the calcination temperature, owing to the increase of microporous structure.31,32 In agreement with the previous SAXS results, the mesoporous structure was destroyed when the carbonization temperature reached 900 °C. It was noteworthy that the N2 isotherms were not closed at low relative pressures, indicating that some organic polymer was incorporated into the framework.28 To further obtain the structural information of the samples, typical TEM images were recorded in Figure 4. It was found that the degree of ordered mesoporous channel decreased upon increasing calcination temperature. Figure 4a, 4b, and 4c indicated that mesoporous channels were highly arranged and paralleled each other after the nanocomposites calcined at 350 and 500 °C in N2 atmosphere. These results showed that the nanocomposites had a large region well-ordered mesopores with 1-D channels.33 The interplanar spacing estimated from Figure 4b was 11.6 nm, almost equal to the result obtained from SAXS. However, the mesostructure collapsed slightly after heating at 700 °C. Compared with the pore size obtained from N2 adsorption−desorption isotherms, the mesoporous channel seemed much larger. It was because that the mesoporous channel included the pore walls. Exact analysis of pore sizes and thickness of the pore walls is very difficult and not possible without additional simulations because of the focus problem.34 In addition, from Figure 4b, it was clearly seen that AZO particles were loaded on the framework of the carbon. The crystalline structure of AZO inside the nanocomposite was investigated by wide-angle XRD (Figure 5). Apparently, a broad peak at 21.57° was observed, which was attributed to the typical of amorphous carbon materials. Other diffraction peaks at 31.640°, 34.300°, 36.140°, 47.440°, 56.460°, 62.739°, 67.820°, and 68.961° were well indexed to pure wurtzite structure of ZnO (JCPDS Card 36-1451). No peak of Al2O3 was observed in this sample. However, the EDS pattern in Figure 6 clearly showed the characteristic peak of aluminum, which identified that aluminum was doped. According to the EDS

Figure 7. TG curves of pure mesoporous carbon and mesoporous CAZO(12)-500 nanocomposite under air atmosphere.

The unit-cell parameter (a) was calculated to be 16.6 nm. After removing the template at 350 °C, two scattering peaks at 0.524 and 0.867 nm−1 were observed. It suggested that an ordered structure remained. However, the scattering peaks shifted rightward and the intensities of the peaks were less than those of the as-made films due to shrinkage of pore channels.28 The unit-cell parameter (a) was reduced to 13.8 nm. From the calculations, the structural contraction ratio in the cell parameters (a) was 17.5%. Carbonization of the film at 500 °C resulted in a relatively poorly resolved structure which was evidenced by only one weakening scattering peak being found. The unit-cell parameter (a) was further reduced from 13.8 to 13.3 nm upon calcination (Table 1), reflecting a 3.6% framework shrinkage. The result indicated that the mesoporous structure was rigid. Furthermore, the intensity of the scattering peak weakened for the sample calcinated at 700 °C, while the peak disappeared for the sample heated at 900 °C. The disappearance of the mesostruction was related to elimination of template during the thermal treatment process.23,26 The interplanar spacings (d10) of the various mesoporous materials calculated according to the formula d = 2π/q are listed in Table 1. Figure 3a illustrates the N2 adsorption−desorption isotherms of the C-AZO materials, and Figure 3b describes the corresponding pore size distribution curves obtained from the adsorption branches. All samples except the material calcinated at 900 °C showed a type IV isotherm according to the IUPAC 15070

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Figure 8. (a) N2 adsorption−desorption isotherm of mesoporous C-AZO nanocomposites with different AZO contents; (b) corresponding pore size distribution.

pound in Figure 7b. In other words, the inorganic residue was 12 wt % in the ordered mesoporous C-AZO(12)-500 nanocomposite. The C-AZO nanocomposites with different AZO contents in the range of 5−21 wt % were prepared using different amounts of AZO sol. It was noted that the mesoporous structure was destroyed when the AZO content in the C-AZO nanocomposite reached 21 wt %. N2 adsorption−desorption isotherms and pore size distributions of the nanocomposites with different amounts of AZO are described in Figure 8. All samples were found to own IV type isotherms, reflecting the characteristics of mesoporous materials. The well-defined and intense step at p/p0 = 0.4−0.6 was associated with capillary condensation, indicating that the nanocomposites had uniform pore size. As Figure 8b shows, the pore diameters of materials with different AZO contents (5% and 16%) were calculated to

results, the doped Al2O3 content in the AZO was calculated to be 8 wt %, almost equal to the expected composition from the stoichiometry of the theoretical mass. On the basis of the above results, C-AZO nanocomposite had been prepared successfully. The TG measurement was performed to determine the amount of AZO and carbon included in the composite. The measured residues designated RTG and expressed in percent were shown in Table 1. The curves of mesoporous carbon and C-AZO(12)-500 were depicted in Figure 7. From Figure 7a it was found that there was an intense weight loss of 99.2 wt % for pure mesoporous carbon in air between 380 and 580 °C. It suggested that mesoporous carbon nearly burned out after 580 °C in air atmosphere. Similarly, 88 wt % loss of ordered mesoporous C-AZO(12)-500 nanocomposite occurred at the same temperature range due to combustion of carbon com15071

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Figure 11. Average infrared emissivity at 8−14 μm of the coatings (the Al-doped content of AZO in the C-AZO(12)-500 composites were 5%, 6%, 7%, 8%, and 9% with a thickness of 75 μm).

Figure 9. Average infrared emissivity at 8−14 μm of the coatings with different various coating thickness.

where ε0 is the dielectric constant of a vacuum.36 It was noteworthy that the high electrical conductivity contributed to the low infrared emissivity. Therefore, the ordered mesoporous C-AZO nanocomposite had advantages of the high reflectance of AZO,13−15 high conductivity of carbon,22 and high porosity in mesoporous nanocomposites,26 which contributed to the decrease of the infrared emissivity. Ordered mesoporous C-AZO materials calcinated at 500 °C were used as the filling with a weight ratio 45% to prepare the coatings. As shown in Figure 9, the average infrared emissivity of different composite coatings increased with coating thickness. Infrared emissivity was strongly affected by the binder due to its high absorbance in the infrared wave band.37 The emissivity value of a composite coating of PU, pure mesoporous carbon, AZO, and C-AZO (12)-500 was 0.59, 0.52, 0.43, and 0.40 in the range of 8−14 μm. Accoding to eq 2, the low infrared emissivity of the pure mesoporous carbon was due to the high electrical conductivity of carbon. AZO had lower infrared emissivity than pure mesoporous carbon, as can be ascribed to the high conductivity and intense reflectivity according to the above two equations. In addition, both the surface effect and the microdimension effect of the mesoporous material lead to the decrease of infrared emissivity.23 In conclusion, the infrared emissivity of C-AZO was lower than pure carbon or pure AZO. Furthermore, C-AZO composites with different AZO contents were selected as coatings to confirm the effect of the C-AZO composites on the infrared emissivity. It was noted that the infrared emissivity of the nanocomposites decreased with increasing AZO contents in Figure 10. In addition, the infrared emissivity reached the lowest value of 0.39 when the AZO content was 16 wt % in the nanocomposites. It was possible that the ordered mesoporous C-AZO played a significant role in lowering the infrared emissivity value of composite coating, which was attributed to the synergistic effect of the intrinsic reflectance of AZO and the microdimension for the mesoporous nanocomposites.25 However, the emissivity of the coating rose up to 0.52 when the AZO content was 21 wt % in the nanocomposites due to the collapsed mesoporous structure. In addition, the effect of the Al-doped content in AZO of the C-AZO composites on the emissivity of coating was presented in Figure 11. It was found that the normal integrated emissivity

Figure 10. Average infrared emissivity at 8−14 μm of the coatings (mesoporous carbon, C-AZO(5)-500, C-AZO(12)-500, C-AZO(16)500, C-AZO(21)-500) with a thickness of 75 μm.

be 3.4 and 3.8 nm, respectively. BET surface areas increased as the AZO contents increased. 3.2. Infrared Emissivity of Mesoporous C-AZO Composites. If the material was opaque in a frequency region, the relationship between the spectral emittance and the bulk reflectance of the material was in agreement with eq 1 E(ω) = 1 − R(ω)

(1)

where E(ω) is the emissivity value, R(ω) is the reflectance related to properties of the substance, and ω is the frequency valid.35 It was clear that E(ω) and R(ω) had an inverse relationship. In addition, the Hagen−Rubens relation (for normal incidence of radiation) provided a direct relationship between E(ω) and electrical resistivity (ρ) as E(ω) ≈ 2 2ε0ωρ

(2) 15072

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(11) Chou, K. S.; Lu, Y. C. The application of nanosized silver colloids in far infrared low-emissive coating. Thin Solid Films 2007, 515, 7217−7221. (12) Yu, H. J.; Xu, G. Y.; Shen, X. M.; Yan, X. X.; Huang, R.; Li, F. L. Preparation of leafing Cu and its application in low infrared emissivity coatings. J. Alloys Compd. 2009, 484, 395−399. (13) Bel Hadj Tahar, R. Structural and electrical properties of aluminum-doped zinc oxide films prepared by sol-gel process. J. Eur. Ceram. Soc. 2005, 25, 3301−3306. (14) Zhu, D. M.; Li, K.; Luo, F.; Zhou, W. C. Preparation and infrared emissivity of ZnO: Al (AZO) thin films. Appl. Surf. Sci. 2009, 255, 6145−6148. (15) Wang, T.; Diao, X. G.; Wang, X. Inhomogeneous optoelectronic and microstructure property distribution across the substrate of ZnO: Al films deposited by room temperature magnetron sputtering. Appl. Surf. Sci. 2011, 257, 9773−9779. (16) Xia, W. S.; Wan, H. L.; Chen, Y. Cluster model study on the surface interactions of γ-alumina-supported metal oxides. J. Mol. Catal. A 1999, 138, 185−195. (17) Abasov, S. I.; Borovkov, V. Y.; Kazansky, V. B. Infrared and adsorption study of strong metal-support interaction in diluted platinum-alumina catalysts. Catal. Lett. 1992, 15, 269−274. (18) Yao, J. Y.; Li, L. X.; Song, H. H.; Liu, C. Y.; Chen, X. H. Synthesis of magnetically separable ordered mesoporous carbons from F 127/[Ni (H2O)6](NO3) 2/resorcinol-formaldehyde composites. Carbon 2009, 47, 436−444. (19) Liu, R. L.; Ren, Y. J.; Shi, Y. F.; Zhang, F.; Zhang, L. J.; Tu, B.; Zhao, D. Y. Controlled Synthesis of Ordered Mesoporous C-TiO2 Nanocomposites with Crystalline Titania Frameworks from OrganicInorganic-Amphiphilic Coassembly. Chem. Mater. 2007, 20, 1140− 1146. (20) Li, L. X.; Song, H. H.; Chen, X. H. Pore characteristics and electrochemical performance of ordered mesoporous carbons for electric double-layer capacitors. Electrochim. Acta 2006, 51, 5715− 5720. (21) Dai, M. Z.; Song, L. Y.; LaBelle, J. T.; Vogt, B. D. Ordered mesoporous carbon composite films containing cobalt oxide and vanadia for electrochemical applications. Chem. Mater. 2011, 23, 2869−2878. (22) She, L.; Li, J.; Wan, Y.; Yao, X. D.; Tu, B.; Zhao, D. Y. Synthesis of ordered mesoporous MgO/carbon composites by a one-pot assembly of amphiphilic triblock copolymers. J. Mater. Chem. 2011, 21, 795−800. (23) Wang, T.; He, J. P.; Zhou, J. H.; Ding, X. C.; Zhao, J. Q.; Wu, S. C.; Guo, Y. X. Electromagnetic wave absorption and infrared camouflage of ordered mesoporous carbon-alumina nanocomposites. Microporous Mesoporous Mater. 2010, 134, 58−64. (24) Wang, T.; He, J. P.; Zhou, J. H.; Tang, J.; Guo, Y. X.; Ding, X. C.; Wu, S. C.; Zhao, J. Q. Microwave absorption properties and infrared emissivities of ordered mesoporous C−TiO2 nanocomposites with crystalline framework. J. Solid State Chem. 2010, 183, 2797−2804. (25) Zhou, J. H.; He, J. P.; L, G. X.; Wang, T.; Sun, D.; Ding, X. C.; Zhao, J. Q.; Wu, S. C. Direct Incorporation of Magnetic Constituents within Ordered Mesoporous Carbon-Silica Nanocomposites for Highly Efficient Electromagnetic Wave Absorbers. J. Phys. Chem. C . 2010, 114, 7611−7617. (26) Meng, Y.; Gu, D.; Zhang, F. Q.; Shi, Y. S.; Yang, H. F.; Li, Z.; Yu, C. Z.; Tu, B.; Zhao, D. Y. Ordered Mesoporous Polymers and Homologous Carbon Frameworks: Amphiphilic Surfactant Templating and Direct Transformation. Angew. Chem., Int. Ed. 2005, 44, 7053− 7059. (27) Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279, 548−552. (28) Zhai, Y. P.; Tu, B.; Zhao, D. Y. Organosilane-assisted synthesis of ordered mesoporous poly (furfuryl alcohol) composites. J. Mater. Chem. 2009, 19, 131−140.

of the coatings was almost stable by various Al-doped contents, keeping at 0.39 approximately. It was possibly because that the content of Al in the C-AZO nanocomposites was relatively less. In spite of that, the infrared emissivity of the ordered mesoporous C-AZO was as low as 0.39, showing potential application of these novel nanocomposites in infrared camouflaging.

4. CONCLUSIONS The ordered mesoporous C-AZO composites were prepared through combination of the sol−gel process and evaporation induced triconstituent coassembly approach. In this method, resol was as the carbon source, F127 as the template, and AZO sol as the inorganic precursor. The porous material exhibited thermal stability, big surface area, and uniform pore size. The N2 adsorption−desorption and TEM results showed that the calcination temperature was a pivotal factor to obtain good thermally stable ordered mesoporous materials. The infrared emissivity value of C-AZO reduced less than 0.4, displaying a super performance in infrared camouflaging.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is dedicated to Professor James Trotter in celebration of his 80th birthday. The authors gratefully acknowledge funding by the National Key Technology R & D Program (No. 2011BAE07B08) and the Fundamental Research Funds for the Central Universities (No. 13D110530).

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dx.doi.org/10.1021/ie401827s | Ind. Eng. Chem. Res. 2013, 52, 15066−15074