Controllable and Repeatable Synthesis of Thermally Stable Anatase Nanocrystal−Silica Composites with Highly Ordered Hexagonal Mesostructures

Hierarchically macro-/mesoporous Ti-Si oxides photonic crystal with highly efficient photocatalytic capability

Hierarchically macro-/mesoporous Ti-Si oxides photonic crystal (i-Ti-Si PC) with highly efficient photocatalytic activity has been synthesized by combining colloidal crystal template and amphiphilic triblock copolymer. It was found that the thermal stability of mesoporous structures in the composite matrix were improved due to the introduction of silica acting as glue and linking anatase nanoparticles together, and the photocatalytic activity of the i-Ti-Si PCs was affected by the calcination conditions. The influences of photonic and structural effect of the i-Ti-Si PCs on photocatalytic activity were investigated. Photodegradation efficiency of the i-Ti-Si PCs was 2.1 times higher than that of TiO(2) photonic crystals (i-TiO(2) PCs) in the photodegradation of Rhodamine B (RB) dye as a result of higher surface area. When the energy of slow photon (SP) was optimized to the abosorption region of TiO(2), a maximum enhanced factor of 15.6 was achieved in comparison to nanocrystalline TiO(2) films (nc-TiO(2)), which originated from the synergetic effect of SP enhancement and high surface area.

Simulating mechanical deformation in nanomaterials with application for energy storage in nanoporous architectures

Central to porous nanomaterials, with applications spanning catalysts to fuel cells is their (perceived) "fragile" structure, which must remain structurally intact during application lifespan. Here, we use atomistic simulation to explore the mechanical strength of a porous nanomaterial as a first step to characterizing the structural durability of nanoporous materials. In particular, we simulate the mechanical deformation of mesoporous Li-MnO(2) under stress using molecular dynamics simulation. Specifically, such rechargeable Li-ion battery materials suffer volume changes during charge/discharge cycles as Li ions are repeatedly inserted and extracted from the host beta-MnO(2) causing failure as a result of localized stress. However, mesoporous beta-MnO(2) does not suffer structural collapse during cycling. To explain this behavior, we generate a full atomistic model of mesoporous beta-MnO(2) and simulate localized stress associated with charge/discharge cycles. We calculate that mesoporous beta-MnO(2) undergoes a volume expansion of about 16% when Li is fully intercalated, which can only be sustained without structural collapse, if the nanoarchitecture is symmetrically porous, enabling elastic deformation during intercalation. Conversely, we predict that unsymmetric materials, such as nanoparticulate beta-MnO(2), deform plastically, resulting in structural collapse of (Li) storage sites and blocked transport pathways; animations revealing elastic and plastic deformation mechanisms under mechanical load and crystallization of mesoporous Li-MnO(2) are presented at the atomistic level.

Fabrication of supported mesoporous TiO2 membranes: matching the assembled and interparticle pores for an improved ultrafiltration performance

We report the fabrication and ultrafiltration performances of an asymmetric composite membrane with a mesoporous TiO2 skin layer coated on a macroporous alumina support. Mesoporous TiO2 was first prepared and deposited on the substrate through a sol-gel process where a ethylene oxide and propylene oxide triblock polymer (PEO-PPO-PEO, P123) was used to modify the properties of the sols and also to introduce assembled pores in the skin layer. The obtained mesoporous TiO2 membrane was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. We found that there were two types of wormlike mesopores present in the TiO2 membrane: interparticle and assembled pores. By carefully controlling the sol properties, we made the two types of pores match each other, which means the size of the interparticle pores is close or smaller than that of the assembled pores. This pore-size matching ensures a narrow pore-size distribution and, consequently, a good retention performance of the obtained TiO2 membrane. The pore size of the TiO2 membrane is ca. 6 nm, as revealed by both nitrogen adsorption and dextran separation experiments, and it has a pure water flux of 7.12 L/(m(2) x h x bar) and a cutoff molecular weight of 19 000 Da, which is very attractive for applications in the enrichment and separation of proteins and polypeptides.

Mapping nanostructure: a systematic enumeration of nanomaterials by assembling nanobuilding blocks at crystallographic positions

Nanomaterials synthesized from nanobuilding blocks promise size-dependent properties, associated with individual nanoparticles, together with collective properties of ordered arrays. However, one cannot position nanoparticles at specific locations; rather innovative ways of coaxing these particles to self-assemble must be devised. Conversely, model nanoparticles can be placed in any desired position, which enables a systematic enumeration of nanostructure from model nanobuilding blocks. This is desirable because a list of chemically feasible hypothetical structures will help guide the design of strategies leading to their synthesis. Moreover, the models can help characterize nanostructure, calculate (predict) properties, or simulate processes. Here, we start to formulate and use a simulation strategy to generate atomistic models of nanomaterials, which can, potentially, be synthesized from nanobuilding block precursors. Clearly, this represents a formidable task because the number of ways nanoparticles can be arranged into a superlattice is infinite. Nevertheless, numerical tools are available to help build nanoparticle arrays in a systematic way. Here, we exploit the "rules of crystallography" and position nanoparticles, rather than atoms, at crystallographic sites. Specifically, we explore nanoparticle arrays with cubic, tetragonal, and hexagonal symmetries together with primitive, face centered cubic and body centered cubic nanoparticle "packing". We also explore binary nanoparticle superlattices. The resulting nanomaterials, spanning CeO(2), Ti-doped CeO(2), ZnO, ZnS, MgO, CaO, SrO, and BaO, comprise framework architectures, with cavities interconnected by channels traversing (zero), one, two and three dimensions. The final, fully atomistic models comprise three hierarchical levels of structural complexity: crystal structure, microstructure (i.e., grain boundaries, dislocations), and superlattice structure.