Mesoporous TiO₂ Mesocrystals: Remarkable Defects-Induced Crystallite-Interface Reactivity and Their in Situ Conversion to Single Crystals

Abstract

Oriented self-assembly between inorganic nanocrystals and surfactants is emerging as a route for obtaining new mesocrystalline semiconductors. However, the actual synthesis of mesoporous semiconductor mesocrystals with abundant surface sites is extremely difficult, and the corresponding new physical and chemical properties arising from such an intrinsic porous mesocrystalline nature, which is of fundamental importance for designing high-efficiency nanostructured devices, have been rarely explored and poorly understood. Herein, we report a simple evaporation-driven oriented assembly method to grow unprecedented olive-shaped mesoporous TiO2 mesocrystals (FDU-19) self-organized by ultrathin flake-like anatase nanocrystals (∼8 nm in thickness). The mesoporous mesocrystals FDU-19 exhibit an ultrahigh surface area (∼189 m2/g), large internal pore volume (0.56 cm3/g), and abundant defects (oxygen vacancies or unsaturated Ti3+ sites), inducing remarkable crystallite-interface reactivity. It is found that the mesocrystals FDU-19 can be easily fused in situ into mesoporous anatase single crystals (SC-FDU-19) by annealing in air. More significantly, by annealing in a vacuum (∼4.0 × 10–5 Pa), the mesocrystals experience an abrupt three-dimensional to two-dimensional structural transformation to form ultrathin anatase single-crystal nanosheets (NS-FDU-19, ∼8 nm in thickness) dominated by nearly 90% exposed reactive (001) facets. The balance between attraction and electrostatic repulsion is proposed to determine the resulting geometry and dimensionality. Dye-sensitized solar cells based on FDU-19 and SC-FDU-19 samples show ultrahigh photoconversion efficiencies of up to 11.6% and 11.3%, respectively, which are largely attributed to their intrinsic single-crystal nature as well as high porosity. This work gives new understanding of physical and chemical properties of mesoporous semiconductor mesocrystals and opens up a new pathway for designing various single-crystal semiconductors with desired mesostructures for applications in catalysis, sensors, drug delivery, optical devices, etc.

Mesoporous materials for energy conversion and storage devices

“…Mesoporous materials with diverse morphologies and tunable pore architectures have been prepared by many synthetic routes based on soft templating, including, but not limited to, aqueous, non-aqueous (also known as the evaporation-induced self-assembly (EISA) process) and hydrothermal processes. The integration of aqueous and EISA processes produces a more versatile procedure, termed the solvent evaporation-induced aggregating assembly (EIAA) method 21 , which is more tolerant to water and can create mesoporous materials by controlling solvent evaporation [22][23][24] . The hard-templating route (FIG.…”

Thermal Induced Strain Relaxation of 1D Iron Oxide for Solid Electrolyte Interphase Control and Lithium Storage Improvement

“…Another increase of annealing temperature to 800 °C results in the formation of ladder-like nanostructures, consisted of two long sides crossed by parallel rungs (Figure 2h,l). [48] Additionally, the high-resolution transmission electron microscopy (HRTEM) images of α-Fe 2 O 3 -500, α-Fe 2 O 3 -600, α-Fe 2 O 3 -700, and α-Fe 2 O 3 -800 all show the same lattice fringes of 3.6 Å, corresponding to the (0 1 2) lattice plane ( Figure S7, Supporting Information). For α-Fe 2 O 3 -500 and α-Fe 2 O 3 -600, a hysteresis loop at a higher pressure (P/P 0 = 0.90-0.99) probably reveals the interchannel macroporous caused from structural defects, while for α-Fe 2 O 3 -700 and α-Fe 2 O 3 -800, no obvious hysteresis loop at a higher pressure (P/P 0 = 0.90-0.99) is observed, indicating less structural defects.…”

Template synthesis of metal tungsten nanowire bundles with high field electron emission performance

“…The mesoporous silica SBA-15 hard template was prepared by hydrothermal synthesis according to the established procedures 36,37 . Typically, 25.0 g of triblock copolymer Pluronic P123 was dissolved in 700 mL of water and stirred overnight.…”