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Photocatalysis is a new type of renewable energy technology used in environmental treatment and hydrogen energy production. In this regard, a new class of photocatalysts, TiO2 aerogels, are attractive for having the chemical characteristics of TiO2 nanomaterials such as high catalytic activity, good stability, non-toxic, and non-polluting, and the structural characteristics of aerogels such as large specific surface area, high porosity, the 3-dimensional interconnected network structure composed of relatively uniform nanoparticles, and high light transmittance. Here we review the recent progress in TiO2 aerogels for photocatalysis, focusing on preparation techniques, the crystalline phases’ influence on photocatalytic properties, the modification of photocatalytic properties, and the analysis and discussion of future development. In particular, we first summarize various preparation techniques, including sol–gel method, nanoparticles self-assembly synthesis, and high-temperature aerosol technique, then detail the structure and composition of TiO2 crystalline phases that affect the photocatalytic properties. Subsequently, we discuss strategies to further enhance the photocatalytic properties of TiO2 aerogels by the composite of SiO2 aerogel semiconductors, the doping of metal dopants, and the doping or composite of non-metallic substances, and elaborate the modification mechanism and the modification effect achieved. Finally, combined with the research status of TiO2 aerogels and the development experience of other aerogels, we conduct a reasonable analysis and discussion on their further research directions and industrialization roads.

Conventional SiO2 aerogels composed of 0-dimensional nanoparticles do not have large-scale compression, tensile, and shear deformation capabilities, and the poor mechanical properties hinder their further development and application. We report a scalable strategy to construct the nanoporous network of a SiO2 aerogel by alternately linking octa-(aminophenyl)-T8-POSS and hexaphthalic acid. The resulting SiO2 aerogel exhibits high strengths (compression, tensile and shear strengths are 26.4, 9.16, and 8.31 MPa, respectively), excellent deformabilities (fracture compression, tensile, and shear strains are 82.63%, 57.81% and 108.02%, respectively), flexbile processability and good structural stability (only 1.7% plastic deformation occurs after 100 load–unload cycles at a large compression strain of 70%). Also, the mesoporous interconnected nanoskeleton with high porosity and the composition of fully hydrophobic groups also give the aerogel low thermal conductivities (0.02854 W/(m K) at 25 °C and 0.04638 W/(m K) at 300 °C) and superhydrophobic properties (hydrophobic angle 160° and saturated mass moisture absorption rate about 0.375%). The combination of these excellent properties ensures that the aerogel can be used as an efficient thermal insulation material for extreme environments, such as those where comprehensive mechanical and hydrophobic properties are strictly required. [ABSTRACT FROM AUTHOR]

Lithium ion capacitors with liquid electrolyte are prone to leakage, combustion, explosion and other dangerous accidents. To solve these problems, the solid gel separator prepared by polyvinylidene fluoride - six fluoropropene (PVDF-HFP) is used in this work to improve the safety and stability of lithium ion supercapacitors. The PVDF-HFP based gel separator was used to replace the commercial separator and electrolyte in the lithium ion capacitor. The solid-state lithium ion supercapacitor was matched with porous carbon (PC) and hard carbon (HC). The maximum energy density of the device is 148.76 wh/kg, even at the power density of 33.6 kW/kg, which still retains 20.6 wh/kg. In addition, 83.3% capacity of solid-state lithium-ion supercapacitor is retained after 8000 times of charge and discharge. The requirements of high power energy density, high cycle stability and high safety are realized.

The NiCo2S4/C hybrid material was successfully prepared by a simple one-step hydrothermal method. Carbon composite increases the specific surface area of the material and provides more ion attachment points during the electrochemical process. Conducive to the ion transportation and transfer, the composition of carbon material greatly improves the conductivity of the hybrid material. Electric double-layer capacitor materials can accept transferred ions faster than pseudocapacitor materials, enable the hybrid materials better adapt to intensity current changes. Compared with a single carbon material or a pseudocapacitance material, it has a higher specific capacity. This discovery is of great significance to the research of pseudocapacitive materials and supercapacitors.