One of the challenges in material science has been to prepare macro-or mesoporous zeolite. Although examples of their synthesis exist, there is a need for a facile yet versatile approach to such hierarchical structures. Here we report a concept for designing a single quaternary ammonium head amphiphilic template with strong ordered self-assembling ability through p-p stacking in hydrophobic side, which stabilizes the mesostructure to form singlecrystalline mesostructured zeolite nanosheets. The concept is demonstrated for the formation of a new type of MFI (zeolite framework code by International Zeolite Association) nanosheets joined with a 90°rotational boundary, which results in a mesoporous zeolite with highly specific surface area even after calcination. Low binding energies for this selfassembling system are supported by a theoretical analysis. A geometrical matching between the arrangement of aromatic groups and the zeolitic framework is speculated for the formation of single-crystalline MFI nanosheets.

As an emerging star of 2D nanomaterials, 2D transition metal carbides and nitrides, named MXenes, present a large potential in various research areas owing to their intrinsic multilayer structure and intriguing physico‐chemical properties. However, the fabrication and application of functional MXene‐based devices still remain challenging as they are prone to oxidative degradation under ambient environment. Within this review, the preparation methods of MXenes focusing on the recent investigations on their thermal structure–stability relationships in inert, oxidizing, and aqueous environments are systematically introduced. Moreover, the key factors that affect the oxidation of MXenes, such as, atmosphere, temperature, composition, microstructure, and aqueous environment, are reviewed. Based on different scenarios, strategies for avoiding or delaying the oxidation of MXenes are proposed to encourage the utilization of MXenes in complicated environments, especially at high temperature. Furthermore, the chemistry of MXene‐derived oxides is analyzed, which can offer perspectives on the further design and fabrication of novel 2D composites with the unique structures of MXenes being preserved.

Powder metallurgy (PM) of titanium is a potentially cost-effective alternative to conventional wrought titanium. This article examines both traditional and emerging technologies, including the production of powder, and the sintering, microstructure, and mechanical properties of PM Ti. The production methods of powder are classified into two categories: (1) powder that is produced as the product of extractive metallurgy processes, and (2) powder that is made from Ti sponge, ingot, mill products, or scrap. A new hydrogen-assisted magnesium reduction (HAMR) process is also discussed. The mechanical properties of Ti-6Al-4V produced using various PM processes are analyzed based on their dependence on unique microstructural features, oxygen content, porosity, and grain size. In particular, the fatigue properties of PM Ti-6Al-4V are examined as functions of microstructure. A hydrogen-enabled approach for microstructural engineering that can be used to produce PM Ti with wroughtlike microstructure and properties is also presented.

No abstract

Titania represents the most widely used oxide semiconductor for photocatalysts and photovoltaics, [1][2][3][4][5][6][7][8][9][10][11][12] and its performance is heavily governed by its surface area and the exposed crystal planes. [13][14][15][16][17][18] To date, however, as-made TiO 2 samples have been limited to the single crystals with low surface area or porous polycrystals exposing their less-active planes. We report herein the synthesis of high-surface-area, singlecrystal-like anatase with controlled mesoporous network and preferential exposure of the highly active (001) planes. This simple solution-growth method is readily extendable to the synthesis of other mesoporous single crystals beyond TiO 2 , providing a new class of materials for catalysis, energy storage and conversion, and other applications.The photocatalytic activity of TiO 2 is generally dependent on its crystallography. [13][14][15][16][17][18][19] For example, the (001) planes of anatase are much more active than the (101) planes, which are the most commonly observed and thermodynamically more stable crystalline planes in the anatase form.[19] Significant effort has therefore been devoted to synthesize TiO 2 crystals with preferential (001) plane exposure. [5,[13][14][15][16][17][18] As well as crystallographic control, equally important is building networks of pores within the crystals to increase the surface area and provide pore-dependent activity and selectivity. [20][21][22] To date, although a large number of porous TiO 2 have been made using sol-gel and softor hard-templating approaches, [1,6,8,21,[23][24][25] the current materials are limited to porous TiO 2 with amorphous or polycrystalline frameworks that exhibit low photocatalytic activity and charge-transport capability. Herein, using a method of crystal oriented growth, we report the synthesis of highly active mesoporous, singlecrystal-like TiO 2 (mesocages) with both preferential (001) plane exposure and controllable mesoporous networks.As illustrated in Figure 1, we started with precursor solutions containing SO 4 2À ; solvothermal reactions generate TiO 2 building crystals of which the (001) planes are preferably adsorbed by the SO 4 2À anions. Attached growth of the building crystals created crystal clusters with the protected (001) planes (step 1). Further growth led to TiO 2 crystals with preferential (001) plane exposure and disordered mesoporous networks that originate from the voids among the building crystals (step 2). To construct an ordered mesoporous channels, the growth was confined within a scaffold with ordered pore channels, such as the silica containing 2D (SBA-15, P6mm space group) and 3D (KIT-6, Ia3d space group) ordered mesopores. Subsequent scaffold removal resulted in TiO 2 crystals with replicated 2D hexagonal structure (step 3) or 3D (step 4) ordered network structure, respectively.The TiO 2 crystals with disordered mesoporous structure show an average diameter of 600 nm (Figure 2 a), and are composed of component crystals with an average diameter of 8....

An active and durable Au/TiO(2) photocatalyst was prepared by in situ encapsulation of Au particles into core-shell TiO(2) spheres based on consecutive solvothermal and hydrothermal treatments.

Whether or not a coarse grained force field (CGFF) can be made to be transferrable is an important question to be addressed. By comparing potential energy with potential of mean force (PMF) of a molecular dimer, we proposed to use a free energy function (FE-12-6) with the parameters in entropic and energetic terms explicitly to represent the nonbond interactions in CGFF. Although the FE-12-6 function cannot accurately describe the PMF curves, a cancelation of short radii and strong repulsion makes the function a good approximation. For nonpolar molecules represented by linear alkanes, FE-12-6 is demonstrated to be highly effective in representing the nonbond interactions in CGFF. The force field parameters are well transferrable among different alkane molecules, in different thermodynamic states and for predicting various thermodynamic properties including heats of vaporization, vapor-liquid-equilibrium coexistence curves, surface tensions, and liquid densities.

The extensibility of force field is a key to solve the missing parameter problem commonly found in force field applications. The extensibility of conventional force fields is traditionally managed in the parameterization procedure, which becomes impractical as the coverage of the force field increases above a threshold. A hierarchical atom-type definition (HAD) scheme is proposed to make extensible atom type definitions, which ensures that the force field developed based on the definitions are extensible. To demonstrate how HAD works and to prepare a foundation for future developments, two general force fields based on AMBER and DFF functional forms are parameterized for common organic molecules. The force field parameters are derived from the same set of quantum mechanical data and experimental liquid data using an automated parameterization tool, and validated by calculating molecular and liquid properties. The hydration free energies are calculated successfully by introducing a polarization scaling factor to the dispersion term between the solvent and solute molecules. © 2015 Wiley Periodicals, Inc.