Bin Zhou

As highly porous nanomaterials, aerogels are fascinating due to their remarkable structural properties and performance

Silica aerogels exhibit a unique nanostructure with low thermal conductivity and low density, making them attractive materials for thermal isolation under extreme conditions. The TiO₂ particle is one of the common industrial additives used to reduce the thermal radiation of aerogel composites under high-temperature environments, but its influence on thermal resistance is almost unknown. Herein, we report the effect of TiO₂ nanoparticles with different crystal phases and different sizes on the thermal stability of silica aerogel composites. By adding TiO₂ nanoparticles, the aerogel can significantly resist collapse at high temperatures (up to 1000 °C). And compared with the rutile phase TiO₂, the anatase phase TiO₂ shows much higher temperature resistance performance, with shrinkage of only one-sixth of the rutile phase after 800 °C treatment. Interestingly, energy-dispersive spectrometer mapping results show that after 800 °C treatment, silica nanoparticles (NPs) are squeezed out in between anatase TiO₂ particles, which resists the coarsening of silica NPs and ultimately enhances the stability of aerogel composites. The optimal anatase phase TiO₂-doped silica aerogel demonstrates the integrated properties of crack-free morphology (2.84% shrinkage), low thermal conductivity (29.30 mW/(m·K)) and low density (149.4 mg/cm³) after 800 °C treatment. This study may provide new insights for developing oxide-doped silica aerogels with both high-temperature resistance and low thermal radiation.

Normally, stirring is regarded as a technology to disperse the substances in liquid evenly. However, Einstein’s tea leaf paradox (ETLP) describes the phenomenon that tea leaves concentrate in a “doughnut” shape via a secondary flow effect while stirring. Herein, to demonstrate ETLP-induced concentration in nanofluid, we simulated the nanoparticle trajectory under stirring and made a grayscale analysis of SiO ₂ nanofluids during stirring and standing processes. Unexpectedly, a localized concentration effect in the layer flow was found beside the macroscopic ETLP effect. Subsequently, the localized concentration was applied to achieve the ultrafast aggregation of Au nanoparticles to form gold aerogels (GAs). The skeleton size of GAs was adjusted from about 10 to 200 nm by only adjusting the temperature of HAuCl ₄ solution. The fabricated GAs had extremely high purity and crystallinity, revealing potential applications in photocatalysis and surface-enhanced Raman scattering.

To improve the accessibility of polyimide aerogels (PAs) in diverse application scenarios, the major objective is to create PAs in dimension/geometry on demand. However, their ability to deliver excellent performance and expanded applications remains challenging. Herein, the three-dimensional (3D) printing of Pas, which simultaneously addresses the above concerns, is proposed using a combination of a one-step chemical-imidization sol–gel strategy and direct ink writing. The resultant 3D-printed PAs exhibit many desirable properties, such as high specific surface area (561.7 m² g⁻¹), low density (66.1 ± 1.4 kg m⁻³), low thermal conductivity (39.89 ± 0.16 mW m⁻¹ K⁻¹), low shrinkage (<7%), exceptional thermal stability (up to 450 °C) and good mechanical properties. They also possess excellent heat/cold preservation, heat/cold/moisture insulation, air/light permeability, and ammonia/moisture adsorption. All of these are highly desirable for addressing severe environmental concerns. Moreover, the application scalability of 3D-printed PAs is confirmed by the successful incorporation of carbon nanotubes, and the subsequent expanded functionality and application potential. The flexibility of inks/materials and the manipulability of the structures and functions, demonstrates great prospect for synergy management of thermal insulation, gas permeability and light absorption, thus expanding the application of PAs.

A well‐designed pore structure and optimized interface will improve specific capacitances of carbon‐based supercapacitor electrodes significantly. Herein, a simple strategy is used to prepare the hierarchically porous 3D‐printed carbon aerogel (CA) electrodes via combining direct ink writing, freezing drying, carbonization, and polypyrrole (PPy) posttreatment. The 3D‐printed CA electrodes without PPy present a quasi‐proportional increase in areal capacitance as thickness, achieving an extremely high areal capacitance of 6875 mF cm^–2 under a thickness of 2.2 mm. Additionally, PPy posttreated 3D‐printed CA (PPy@CA) electrode has improved wettability and contact conductivity, which shows a further significant increase of areal capacitance to 8126 mF cm^–2. After 10 000 continuous cycles, the PPy@CA electrode exhibits an excellent cyclic stability similar to that of 3D‐printed CA electrode by maintaining 91% of its original capacitance. This simple strategy may provide a novel insight to dramatically boost the energy storage properties of supercapacitor electrodes and their functionalization.

Monolithic TiO₂ aerogels without severe shrink were obtained by the sol-gel method with the addition of the surfactant cetyltrimethylammonium bromide (CTAB) to control the hydrolysis and polycondensation process and acetonitrile solvent as the solvent to improve the crystallinity. After CO₂ supercritical drying, the shrinkage ratio of monolithic TiO₂ aerogels modified by CTAB decreased by up to ∼26.9%, compared with the pure TiO₂ aerogel. Their apparent densities were all lower than 300 g/cm³. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR) and BET Specific Surface Area Analysis were used to analyze the as-synthesized samples. The results revealed that all the samples were anatase-TiO₂ phase with nanoporous network structures. The specific surface areas reached 250.2 m²/g confirmed by the BET (Brunaur–Emmett–Teller method) analysis. However, TiO₂ aerogels without the addition of CTAB showed evident agglomeration and collapse of the network in comparison with CTAB-added samples. To further study the structure-property relationship, the photocatalysis performance of as-synthesized and 300°C-calcined aerogels was carried out contrastively. Interestingly, the influences of the CTAB adding amount of as-synthesized and calcined TiO₂ aerogels are negative and positive, respectively, which is probably due to the synergistic effect of CTAB hindrance and grain refinement. Potentially, This kind of TiO₂ aerogels assisted by CATB with low density, small shrinkage, improved formability, high specific surface area and fine crystalline grain may be applied in various applications, such as electrochemistry, photocatalysis, etc.

Resorcinol-formaldehyde/titanium dioxide composite (RF/TiO₂) gel was prepared simultaneously by acid catalysis and then dried to aerogel with supercritical fluid CO₂. The carbon/titanium dioxide aerogel was obtained by carbonization and then converted to nanoporous titanium carbide/carbon composite aerogel via 800 °C magnesiothermic catalysis. Meanwhile, the evolution of the samples in different stages was characterized by X-ray diffraction (XRD), an energy-dispersive X-ray (EDX) spectrometer, a scanning electron microscope (SEM), a transmission electron microscope (TEM) and specific surface area analysis (BET). The results showed that the final product was nanoporous TiC/C composite aerogel with a low apparent density of 339.5 mg/cm³ and a high specific surface area of 459.5 m²/g. Comparing to C aerogel, it could also be considered as one type of highly potential material with efficient photothermal conversion. The idea of converting oxide–carbon composite into titanium carbide via the confining template and low-temperature magnesiothermic catalysis may provide new sight to the synthesis of novel nanoscale carbide materials.

The trans-resveratrol (RSV)-loaded silica aerogel (RLSA) was prepared by the sol-gel method, adding the drug during the aging process, solvent replacement and freeze drying. A series of characterizations showed that RSV stays in the silica aerogel in two ways. First, RSV precipitates due to minimal solubility in water during the solvent replacement process. After freeze drying, the solvent evaporates and the RSV recrystallizes. It can be seen from scanning electron microscope (SEM) and transmission electron microscope (TEM) images that the recrystallized RSV with micron-sized long rod-shaped is integrated with the dense silica network skeleton. Second, from small-angle X-ray scattering (SAXS) results, a portion of the RSV molecules is not crystallized and the size is extremely small. This can be attached to the primary and secondary particles of silica to enhance its network structure and inhibit shrinkage, which is why the volume and pore size of RLSA is larger. In addition, the diffusion of RSV in silica alcogel was studied by a one-dimensional model. The apparent diffusion coefficients of inward diffusion, outward diffusion and internal diffusion were calculated by fitting the time- and position-dependent concentration data. It was found that the outward diffusion coefficient (5.25 × 10⁻¹⁰ m²/s) is larger than the inward (2.93 × 10⁻¹⁰ m²/s), which is probably due to the interface effect. The diffusion coefficients obtained for different concentrations in the same process (inward diffusion) are found to be different. This suggests that the apparent diffusion coefficient obtained is affected by molecular adsorption.