Two-dimensional (2D) nanomaterials have been the focus of substantial research interest recently owing to their fascinating and excellent properties. However, 2D porous materials have remained quite rare due to the difficulty of creating pores in 2D nanostructures. Here, we have synthesized a novel type of single-layered 2D mesoporous TiO nanosheets with very uniform size and thickness as well as ordered mesostructure from an unprecedented hydrothermal-induced solvent-confined assembly approach. The F127/TiO spherical monomicelles are first formed and redispersed in ethanol and glycerol, followed by a hydrothermal treatment to assemble these subunits into single-layered 2D mesostructure owing to the confinement effect of highly adhered glycerol solvent. The obtained 2D mesoporous TiO nanosheets have a relative mean size at around 500 × 500 nm and can be randomly stacked into a bulk. The TiO nanosheets possess only one layer of ordered mesopores with a pore size of 4.0 nm, a very high surface area of 210 m g and a uniform thickness of 5.5 nm. The thickness can be further manipulated from 5.5 to 27.6 nm via simply tuning precursor concentration or solvent ratio. Due to the well-defined 2D morphology and large mesoporosity as well as crystalline anatase mesopore walls, these uniform TiO nanosheets are capable of providing large accessible voids for sodium ion adsorption and intercalation as well as preventing volume expansion. As expected, these mesoporous TiO nanosheets have exhibited an excellent reversible capacity of 220 mAh g at 100 mA g as sodium-ion battery anodes, and they can retain at 199 mAh g after numerous cycles at different current densities. The capacity is retained at 44 mAh g even at a large current density of 10 A g after 10 000 cycles, demonstrating a remarkable performance for energy storage.

We have demonstrated a facile hydrothermal approach to synthesize a novel type of mesoporous TiO 2 material with highly controllable structure. By regulating the synthetic conditions, the mesoporous TiO 2 can be well controlled with desired crystallites and architectures. The resulting mesoporous TiO 2 exhibits excellent penetration properties and photocatalytic performance. These unique mesoporous TiO 2 microspheres produced at moderate conditions could afford great opportunities in achieving high performance in various practical applications.

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 TiO2 microspheres with controllable phase junctions have been synthesized by a facile coordination-mediated self-assembly method.

Constructing three-dimensional (3-D) hierarchical mesostructures with unique morphology, pore orientation, single-crystal nature, and functionality remains a great challenge in materials science. Here, we report a confined microemulsion self-assembly approach to synthesize an unprecedented type of 3-D highly ordered mesoporous TiO superstructure (Level-1), which consists of 1 spherical core and 12 symmetric satellite hemispheres epitaxially growing out of the core vertices. A more complex and asymmetric TiO superstructure (Level-2) with 13 spherical cores and up to 44 symmetric satellite hemispheres can also be well manipulated by increasing the size or content of impregnated TiO precursor emulsion droplets. The obtained 3-D mesoporous TiO superstructures have well-defined bouquet-posy-like topologies, oriented hexagonal mesochannels, high accessible surface area (134-148 m/g), large pore volume (0.48-0.51 cm/g), and well single-crystalline anatase walls with dominant (001) active facets. More interestingly, all cylindrical mesopore channels are highly interconnected and radially distributed within the whole superstructures, and all TiO nanocrystal building blocks are oriented grown into a single-crystal anatase wall, making them ideal candidates for various applications ranging from catalysis to optoelectronics. As expected, the bouquet-posy-like mesoporous TiO superstructure supported catalysts show excellent catalytic activity (≥99.7%) and selectivity (≥96%) in cis-semihydrogenation of various alkynes, exceeding that of commercial TiO (P25) supported catalyst by a factor of 10. No decay in the activity was observed for 25 cycles, revealing a high stability of the mesoporous TiO superstructure supported catalyst.

Two-dimensional (2D) heterostructures endowed with mesoporosities offer exciting opportunities in electrocatalysis, photocatalysis, energy storage, and conversion technologies due to their integrated functionalities, abundant active sites and shortened diffusion distance. However, layered mesostructures have not been combined due to the immense difficulties by conventional chemical, mechanical exfoliation or self-assembly approaches. Herein, we explore a bottom-up strategy, carried out under mild conditions, for the facile synthesis of monolayered mesoporous-titania–mesoporous-carbon vertical heterostructure with uniform mesopore size, which enables ultrahigh rate capability and cycling longevity for pseudocapacitive sodium-ion storage in nonaqueous electrolyte. Such a brand-new type of heterostructure consists of well-ordered monolayered mesoporous titania nanosheets and surrounding two mesoporous carbon monolayers assembled at both sides. Remarkably, the combination of interconnected large mesoporosity and heterointerface leads to highly promoted reversible pseudocapacitance (96.4% of total charge storage at a sweep rate of 1 mV s–1), and it enables the material to retain strong mechanical stability during the rapid sodiation and desodiation processes. This study reveals the importance of incorporating mesopores into heterointerface as a strategy for enhancing charge storage kinetics of electroactive materials.

We have demonstrated a confined interfacial monomicelle assembly approach for accurately coating ordered monolayered TiO 2 mesopores on diverse surfaces. By regulating the synthetic conditions, the coated mesoporous TiO 2 layers can be well controlled with desired thickness, mesopore size, and switchable coated surfaces. The resulting monolayered mesoporous TiO 2 exhibit excellent sodiumstorage properties. This unique mesoporous TiO 2 coating strategy affords great potential in constructing multicomponent nanostructures with mesoporosities for advanced technologies.

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