•Zirconia/silica aerogel is prepared via a novel supercritical deposition method.•Crystal growth and phase transition upon heat treatment are effectively inhibited.•The composite aerogel exhibits high thermal stability.•It shows a high specific surface area of 172 m2/g after heat treatment at 1000 °C.Highly thermally stable zirconia/silica composite aerogels are prepared via a supercritical deposition method, which involves the deposition by zirconium alkoxide and partially hydrolyzed alkoxysilane during high-temperature ethanol supercritical fluid drying. The zirconia crystal growth and phase transition of the composite aerogels upon heat treatment are effectively inhibited by supercritical deposition, which significantly enhances the thermal stability of the aerogels. The resultant zirconia/silica composite aerogels exhibit a high specific surface area of 172 m2/g and a large pore volume of 0.97 cm3/g after heat treatment at 1000 °C. The resultant materials are promising candidates as high-temperature catalysts, catalyst supports, thermal insulators, etc.

Nano-architectured carbon aerogel/Ni(OH)2 composites have been prepared via a wet chemical approach that combines the sol–gel preparation of a highly porous carbon aerogel using microcrystalline cellulose, a low-cost and renewable polymer, as the carbon source and subsequent homogeneous deposition of Ni(OH)2 nanoparticles onto the backbone of the carbon aerogel via a two-step chemical precipitation process. The deposited Ni(OH)2 has small particle size (3–10 nm) and uniform dispersion and is well exposed to the electrolyte. The resulting composite possesses an interconnected, three-dimensional, high-surface-area (327 m2 g−1) nanostructure, which provides efficient transport of electrolyte ions and electrons and enables a fuller utilization of Ni(OH)2, thus leading to excellent electrochemical performance. The composite electrode exhibits high specific capacitance of 1906 and 1206 F g−1 at current density of 1 and 20 A g−1, respectively, which are much higher than those of Ni(OH)2. Moreover 89% capacitance is retained after 4000 cycles, implying a good cycling stability.

Nano-architectured carbon aerogel/Ni(OH)2 composites have been prepared via a wet chemical approach that combines the sol–gel preparation of a highly porous carbon aerogel using microcrystalline cellulose, a low-cost and renewable polymer, as the carbon source and subsequent homogeneous deposition of Ni(OH)2 nanoparticles onto the backbone of the carbon aerogel via a two-step chemical precipitation process. The deposited Ni(OH)2 has small particle size (3–10 nm) and uniform dispersion and is well exposed to the electrolyte. The resulting composite possesses an interconnected, three-dimensional, high-surface-area (327 m2 g−1) nanostructure, which provides efficient transport of electrolyte ions and electrons and enables a fuller utilization of Ni(OH)2, thus leading to excellent electrochemical performance. The composite electrode exhibits high specific capacitance of 1906 and 1206 F g−1 at current density of 1 and 20 A g−1, respectively, which are much higher than those of Ni(OH)2. Moreover 89% capacitance is retained after 4000 cycles, implying a good cycling stability.

Highly thermally stable alumina-based aerogels are synthesized by the acetone–aniline in situ water formation method and modified by partially hydrolyzed aluminum tri-sec-butoxide at different temperatures (25, 45, and 60 °C). The effects of modification, especially modification temperature, on microstructure and thermal stability of alumina-based aerogels are investigated. After the modification, the morphologies of alumina-based aerogels change from the network structures with interconnected needle-like particles to those with stacked sheet-like particles, resulting in a better heat resistance. The thermal stability of alumina-based aerogels enhances with the increasing modification temperature, whereas the high temperature (more than 60 °C) would lead to the dissolution of wet gels during the modification process due to the high solubility. After annealing at 1200 °C for 2 h, the 45 °C-modified alumina-based aerogel exhibits the best thermal stability with the lowest linear shrinkage of ~7% and the highest specific surface area of 154 m2/g. In addition, the modified aerogels remain in the θ-Al2O3 phase while the unmodified one transforms into α-Al2O3 phase after 1300 °C annealing. The alumina-based aerogels are further reinforced by incorporating with mullite fiber felt and TiO2. The obtained composites show ultralow thermal conductivities of 0.065, 0.086, and 0.118 W/mK at 800, 1000, and 1200 °C, respectively.Open image in new window

Silica–titania composite aerogels were synthesized by chemical liquid deposition of titania onto nanoporous silica scaffolds. This novel deposition process was based on chemisorption of partially hydrolyzed titanium alkoxides from solution onto silica nanoparticle surfaces and subsequent hydrolysis and condensation to afford titania nanoparticles on the silica surface. The titania is homogeneously distributed in the silica–titania composite aerogels, and the titania content can be effectively controlled by regulating the deposition cycles. The resultant composite aerogel with 15 deposition cycles possessed a high specific surface area (SSA) of 425 m2/g, a small particle size of 5–14 nm, and a large pore volume and pore size of 2.41 cm3/g and 18.1 nm, respectively, after heat treatment at 600 °C and showed high photocatalytic activity in the photodegradation of methylene blue under UV-light irradiation. Its photocatalytic activity highly depends on the deposition cycles and heat treatment. The combination of small particle size, high SSA, and enhanced crystallinity after heat treatment at 600 °C contributes to the excellent photocatalytic property of the silica–titania composite aerogel. The higher SSAs compared to those of the reported titania aerogels (<200 m2/g at 600 °C) at high temperatures combined with the simple method makes the silica–titania aerogels promising candidates as photocatalysts.Keywords: chemical liquid deposition; photocatalyst; silica−titania composite aerogel; sol−gel; specific surface area

•Titania aerogels are prepared via a novel supercritical deposition method.•The nanoparticles are reinforced and mechanical strength is effectively enhanced.•Crystal growth upon heat treatment is effectively restricted.•The resulting aerogel shows enhanced heat resistance.Heat-resistant, strong titania aerogels are prepared via a novel supercritical deposition method. This deposition process is based on deposition by partially hydrolyzed titanium alkoxide and alkoxysilane during high-temperature supercritical fluid drying. The nanoparticles are significantly reinforced, and the crystal growth of titania upon heat treatment is effectively restricted by supercritical deposition, which leads to the enhanced mechanical strength and heat resistance of titania aerogels. The Young’s modulus of the resulting titania aerogel is enhanced up to 4.2 MPa. The specific surface area of the optimized titania aerogel increases up to 147 m2/g and the corresponding linear shrinkage decreases to as low as 11% after heat treatment at 1000 °C. This may significantly contributed to the high-temperature applications of titania aerogels in thermal insulations, catalysts, catalyst supports, etc.

Robust, highly thermally stable, MOx/(MOx–SiO2)/SiO2 core–shell nanostructured metal oxide aerogels with a MOx core and (MOx–SiO2)/SiO2 shell are produced via novel alkoxide chemical liquid deposition techniques. The core–shell nanostructure not only significantly reinforces the nanoparticles but also effectively inhibits the crystal growth and phase transition of metal oxide upon heat treatment, which enhances the heat resistance from approximate 400–800 °C up to 1000–1300 °C. The resultant core–shell nanostructured Al2O3, ZrO2, and TiO2 aerogels can support at least 5800 times their weight and exhibit high surface areas of 139, 186, and 154 m2/g after fired at 1300, 1000, and 1000 °C, respectively, which are the highest surface areas for metal oxide aerogels ever reported. We demonstrate that the core–shell ZrO2 and TiO2 aerogels show enhanced adsorption and photocatalytic performances, respectively, for dye after fired at 1000 °C. The core–shell Al2O3 aerogel/mullite fiber/TiO2 composite possesses ultralow thermal conductivities of 0.058, 0.080, and 0.11 W/mK at 800, 1000, and 1200 °C, respectively, which are the lowest values for inorganic aerogels ever reported. The resulting materials are promising candidates as high-temperature (400–1300 °C) thermal superinsulators, adsorbents, and catalysts.

A double-layer broadband antireflective (AR) coating was prepared on glass substrate via sol–gel process using two kinds of acid-catalyzed TEOS-derived silica sols. The relative dense layer with a porosity of ∼10% was obtained from an as-prepared sol, while the porous layer with a porosity of ∼55% was from a modified one with block copolymer (BCP) Pluronic F127 as template which results in abundant ordered mesopores. The two layers give rise to a reasonable refractive index gradient from air to the substrate and thus high transmittance in a wide wavelength range, and both of them have the same tough skeleton despite different porosity, for which each single-layer and the double-layer coatings all behaved well in the mechanical property tests. The high transmittance and the strong ability of resisting abrasion make this coating promising for applications in some harsh conditions. In addition, the preparation is simple, low-cost, time-saving, and flexible for realizing the optical property.

Because of ultralow thermal conductivity, excellent catalytic activity, and better heat resistance than silica aerogel, alumina-based aerogel has drawn great interest as thermal insulators and catalysts. However, it is too fragile and sinters above 1000 °C (it shrinks drastically, >50%, and leaves the surface area as low as 10–70 m2/g at 1300 °C), which badly limits its high-temperature applications. Herein, super heat-resistant, strong alumina aerogels are prepared via a novel acetone-aniline in situ water formation (ISWF) method combined with novel modification techniques: supercritical fluid modification (SCFM) and hexamethyldisilazane gas phase modification. The heat resistance of alumina aerogel is enhanced up to 1300 °C via this method. The shrinkage of the optimized alumina aerogel is reduced to as low as 1 and 5% and the corresponding surface area reaches up to 152–261 and 125–136 m2/g after being heated to 1200 and 1300 °C for 2 h, respectively. The strength is significantly increased by more than 120% through SCFM. It also exhibits excellent thermal insulation properties at temperatures up to 1300 °C. This may significantly contribute to their practical ultrahigh-temperature applications in thermal insulations, catalysts, catalyst supports, etc.Keywords: alumina aerogel; heat resistance; sol−gel; specific surface area; supercritical fluid modification;

The surface liquidity of a water droplet is eliminated by rubbing hydrophobic particles onto the droplet surface using a sol–gel silica coating with extremely weak binding force, which results in solid-like deformability of a liquid drop.

A Fe2O3 nanoparticle/carbon aerogel composite (Fe2O3/CA) is prepared from a carbon aerogel prepared by a sol–gel process by a simple soaking in a Fe(NO3)3 solution and subsequent heat treatment at 600 °C. Thermal gravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy are used to characterize the products. The electrochemical performance of samples with different Fe2O3 content is evaluated. The optimal sample Fe2O3/CA-60 exhibits a good capacity retention of 916 and 617 mAh g−1 for the 1st and 100th cycle, respectively, which is much better than that of pure Fe2O3 and CA. The improved cycling performance, specific capacity and rate capability of Fe2O3/CA is mainly attributed to the synergistic effects of the nanoporous network skeleton of CA and the uniformly dispersed Fe2O3 nanoparticles.Graphical abstractHighlights► Fe2O3 nanoparticle/carbon aerogel composite is prepared by a simple soaking method. ► First discharge and charge capacities are 1521 and 916 mAh g−1, respectively. ► A good capacity retention of 617 mAh g−1 after 100 cycles. ► More than 500 times charge–discharge cyclability. ► Improved cyclability owing to high conductivity and large surface area of skeleton.

Activated carbon aerogels (ACAs) with hierarchically porous structures and high specific surface area have been prepared via CO2 and KOH activation processes. The pore structures of ACAs are characterized by N2 adsorption/desorption and scanning electron microscopy. The experimental results show that the ACAs contain three types of pores: micropores with diameters below 2 nm, small mesopores with diameters from 2 to 4 nm and large pores or channels with diameters over 30 nm. The typical sample ACAs-4, which possess pore volume of 2.73 cm3 g−1 and specific surface area of 2119 m2 g−1, exhibits high specific capacitances of 250 F g−1 and 198 F g−1 at the current densities of 0.5 A g−1 and 20 A g−1 respectively in 6 M KOH aqueous solution. Furthermore, the resultant ACAs electrode materials also exhibit high power density, good cycling stability and long lifetime. With these features, ACAs are expected to be promising electrode materials for electrical double layer capacitors.

This paper shows that the performance of resorcinol–formaldehyde-based carbon aerogels in electrical double-layer capacitors (EDLCs) can be significantly enhanced by a simple treatment with CO2 activation. The changes in the specific surface area lead to high capacitance values, which provide a noticeable energy density. The CO2 activated carbon aerogels have a high specific surface area up to 3431 m2/g and specific capacitances three times higher than that of the raw carbon aerogels. The activated carbon aerogels obtained the specific capacitance at 152 F/g and energy density of 27.5 Wh/kg at the current density of 0.3 A/g in 1 M Et4NBF4–AN electrolyte. Furthermore, an excellent rate capability, low equivalent series resistance (ESR), and a good cycling stability over 8000 cycles of the resulting carbon aerogels were also confirmed by electrochemical measurements as galvanostatic charge–discharge, cyclic voltammetry and electrochemical impedance spectroscopy.Graphical abstractHighlights► The CO2 activated carbon aerogels have a high specific surface area up to 3431 m2/g. ► Specific capacitances are three times higher than that of the raw carbon aerogels. ► Obtained the specific capacitance at 152 F/g and energy density of 27.5 Wh/kg. ► A good cycling stability over 8000 cycles.

Sol–gel silica coatings prepared for high-power laser applications were optimized by a two-step structure modification through treatment of the sol with poly(ethylene glycol) (PEG), followed by treatment of the coating with ammonia. The effect of each treatment on the laser-induced damage threshold (LIDT) at 1064 nm wavelength was studied, mainly in terms of the change in the coating’s structure. Both of these treatments increased the LIDT, and the greatest LIDT was achieved by combining the two treatments. The LIDT increase can be attributed to the decrease in structural defects such as nodular defect and the variety of pore-distribution, resulting from PEG and ammonia treatments, respectively. The procedure of producing coated glass with high LIDT for 1064 nm laser irradiation was suggested, involving substrate etching, sol modification, and coating treatment.

A silica microsphere suspension and a silica sol are employed in a two-step dipping process for the preparation of a superhydrophobic surface. It's not only a facile way to achieve the lotus effect, but can also create a multi-functional surface with different wetabilities, adhesive forces and transparencies.

Alumina aerogels were prepared by a sol–gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m2/g. It was transformed to γ-Al2O3 after heat treatment at 800 °C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4 MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30 °C and 400 °C were 0.028 W/mK and 0.065 W/mK respectively.Research highlights► A new method for the synthesis of monolithic alumina aerogels was presented. ► Nitric acid is introduced to control the hydrolysis and condensation rates of aluminum alkoxide. ► Gelation time increases rapidly with increasing concentration of nitric acid. ► Aerogels obtained via this method were robust and with high surface areas.

A double-layer broadband antireflective (AR) and scratch-resistant coating with hydrophobic surface is fabricated via sol–gel process using acid and base catalyzed silica as precursor solutions. The coating is composed of a dense and a porous silica films of which the refractive indices are high and low respectively, realizing a step-index gradient structure with glass as the substrate. The AR property of the coating is optimized to maximize the amplification yield of the laser disk amplifiers used in high power laser system. The average transmittance of BK7 glass coated in this way increased to more than 99.5% over the range of 500 to 850 nm. After NH3-heat treatment at 200 °C, the scratch-resistance of the coating is improved in a large degree. Trimethylchlorosilane is employed to modify the coating surface to improve the optical stability by resisting moisture. These treatments can ensure that this broadband AR coating is durable for its real application.

The surface liquidity of a water droplet is eliminated by rubbing hydrophobic particles onto the droplet surface using a sol–gel silica coating with extremely weak binding force, which results in solid-like deformability of a liquid drop.

A silica microsphere suspension and a silica sol are employed in a two-step dipping process for the preparation of a superhydrophobic surface. It's not only a facile way to achieve the lotus effect, but can also create a multi-functional surface with different wetabilities, adhesive forces and transparencies.