The organization of different nano objects with tunable sizes, morphologies, and functions into integrated nanostructures is critical to the development of novel nanosystems that display high performances in sensing, catalysis, and so on. Herein, using acetylacetone as a chelating agent, phenolic resol as a carbon source, metal nitrates as metal sources, and amphiphilic copolymers as a template, we demonstrate a chelate-assisted multicomponent coassembly method to synthesize ordered mesoporous carbon with uniform metal-containing nanoparticles. The obtained nanocomposites have a 2-D hexagonally arranged pore structure, uniform pore size (~4.0 nm), high surface area (~500 m(2)/g), moderate pore volume (~0.30 cm(3)/g), uniform and highly dispersed Fe(2)O(3) nanoparticles, and constant Fe(2)O(3) contents around 10 wt %. By adjusting acetylacetone amount, the size of Fe(2)O(3) nanoparticles is readily tunable from 8.3 to 22.1 nm. More importantly, it is found that the metal-containing nanoparticles are partially embedded in the carbon framework with the remaining part exposed in the mesopore channels. This unique semiexposure structure not only provides an excellent confinement effect and exposed surface for catalysis but also helps to tightly trap the nanoparticles and prevent aggregating during catalysis. Fischer-Tropsch synthesis results show that as the size of iron nanoparticles decreases, the mesoporous Fe-carbon nanocomposites exhibit significantly improved catalytic performances with C(5+) selectivity up to 68%, much better than any reported promoter-free Fe-based catalysts due to the unique semiexposure morphology of metal-containing nanoparticles confined in the mesoporous carbon matrix.

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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.

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