Maintaining the structure of templated porous materials for reactive and high-temperature applications

Highly porous α-alumina powders prepared with the self-assembly of an asymmetric PS-b-PEO diblock copolymer

Crystallization to γ-Al₂O₃ followed by transformation to α-Al₂O₃ was achieved around PS-b-PEO templated extra-large pores having low surface curvature.

Porous TiO2with large surface area is an efficient catalyst carrier for the recovery of wastewater containing an ultrahigh concentration of dye

Preparation of porous TiO₂as an excellent catalyst carrier to load iron and degrade ultrahigh concentration of dye in wastewater over 95% in 30 min.

A smart thermo- and pH-responsive microfiltration membrane based on three-dimensional inverse colloidal crystals

In this paper, a thermo- and pH-responsive microfiltration membrane was prepared based on three-dimensional (3D) inverse colloidal crystals (ICC). To manufacture the smart ICC membrane, the typical thermo-responsive N-isopropylacrylamide (NIPAM) and pH-responsive methacrylic acid (MAA) were polymerized inside silica colloidal crystals. The smart ICC membranes were characterized by SEM, IR and contact angle measurements. Moreover, the permeability of smart microfiltration membrane was carried out by the KCl diffusion tests. The result showed that effective diameter of the polymer ICC membrane can be reversible tuned by temperature and pH. Besides, the functional ICC membrane showed outstanding temperature- and pH-responsive gating property, which was applied to separate particles of different sizes. The savvy environment-responsive gating membranes have potential uses in filtration, separation, purification, sensor and other applications.

Fabrication and Electrochemical Performance of Structured Mesoscale Open Shell V2O5 Networks

Crystalline vanadium pentoxide (V₂O₅) has attracted significant interest as a potential cathode material for energy storage applications due to its high theoretical capacity. Unfortunately, the material suffers from low conductivity as well as slow lithium ion diffusion, both of which affect how fast the electrode can be charged/discharged and how many times it can be cycled. Colloidal crystal templating (CCT) provides a simple approach to create well-organized 3-D nanostructures of materials, resulting in a significant increase in surface area that can lead to marked improvements in electrochemical performance. Here, a single layer of open shell V₂O₅ architectures ca. 1 μm in height with ca. 100 nm wall thickness was fabricated using CCT, and the electrochemical properties of these assemblies were evaluated. A decrease in polarization effects, resulting from the higher surface area mesostructured features, was found to produce significantly enhanced electrochemical performance. The discharge capacity of an unpatterned thin film of V₂O₅ (∼8.1 μAh/cm²) was found to increase to ∼10.2 μAh/cm² when the material was patterned by CCT, affording enhanced charge storage capabilities as well as a decrease in the irreversible degradation during charge-discharge cycling. This work demonstrates the importance of creating mesoscale electrode surfaces for improving the performance of energy storage devices and provides fundamental understanding of the means to improve device performance.

Effects of surface diffusion on high temperature selective emitters

Using morphological and optical simulations of 1D tantalum photonic crystals at 1200K, surface diffusion was determined to gradually reduce the efficiency of selective emitters. This was attributed to shifting resonance peaks and declining emissivity caused by changes to the cavity dimensions and the aperture width. Decreasing the structure's curvature through larger periods and smaller cavity widths, as well as generating smoother transitions in curvature through the introduction of rounded cavities, was found to alleviate this degradation. An optimized structure, that shows both high efficiency selective emissivity and resistance to surface diffusion, was presented.

Improved photocatalytic activity in a surfactant-assisted synthesized Ti-containing MOF photocatalyst under blue LED irradiation

Amine-functionalized MIL-125 was synthesized in the presence of a structure directing agent. Enhancement of its photocatalytic activity under LED irradiation is described.

Organic Molecular Crystals: From Non-Porous Structure to Potential Porous Structure Controlled by Reaction Temperature

Reported here are two novel organic crystals, L 1 and L·(DMF)1.5 2 (DMF = (CH3)2NCHO), showing non-porous and microporous structure, where the formations can be precisely controlled by varying the reaction temperature. The reason for this exciting discovery could be directly related to the various degrees of distortion in the organic molecules as observed in 1 and 2, where detailed structural studies were carried out.

One-pot facile synthesis of ant-cave-structured metal oxide-carbon microballs by continuous process for use as anode materials in Li-ion batteries

This paper introduces a facile one-pot method for synthesizing a new structured material, named "ant-cave microball", by continuous ultrasonic spray pyrolysis. The ant-cave-structured microballs are prepared from a colloidal spray solution with polystyrene nanobeads and sucrose. Networking between the nanovoids formed by decomposition of the polystyrene nanobeads results in the formation of nanochannels. The electrochemical properties of these ant-cave-structured MoO3-C microballs, prepared as the first target material for lithium ion batteries, are investigated. The nanochannels are uniformly distributed inside the microballs with MoO3 and carbon components uniformly distributed within the microballs. Further, the microballs have initial discharge and charge capacities of 1212 and 841 mA h g(-1), respectively, at a current density of 2 A g(-1), and the initial discharge and charge capacities based on the weight of MoO3 (disregarding carbon component) are as high as 1814 and 1259 mA h g(-1). The microballs deliver a high discharge capacity of 733 mA h g(-1) even after 300 cycles. This is although microsized MoO3 powders with a filled structure have discharge capacities of 1256 and 345 mA h g(-1) for the first and 300th cycles, respectively.

Microporous brookite-phase titania made by replication of a metal-organic framework

Metal-organic frameworks (MOFs) provide access to structures with nanoscale pores, the size and connectivity of which can be controlled by combining the appropriate metals and linkers. To date, there have been no reports of using MOFs as templates to make porous, crystalline metal oxides. Microporous titania replicas were made from the MOF template HKUST-1 by dehydration, infiltration with titanium isopropoxide, and subsequent hydrothermal treatment at 200 °C. Etching of the MOF with 1 M aqueous HCl followed by 5% H2O2 yielded a titania replica that retained the morphology of the parent HKUST-1 crystals and contained partially ordered micropores as well as disordered mesopores. Interestingly, the synthesis of porous titania from the HKUST-1 template stabilized the formation of brookite, a rare titania polymorph.

Novel nanostructures of rutile fabricated by templating against yarns of polystyrene nanofibrils and their catalytic applications

This Article describes a facile approach to the synthesis of rutile nanostructures in the form of porous fibers or bundles of nanotubes by maneuvering the surface wettability of yarns made of polystyrene nanofibrils. Specifically, hierarchically porous fibers were obtained by hydrolyzing titanium tetraisopropoxide to form TiO2 nanoparticles in the void spaces among hydrophobic nanofibrils in each yarn. After calcination in air at 800 °C, the resultant fibers were comprised of many interconnected rutile nanoparticles whose diameters were in the range 20-80 nm. After converting the nanofibrils and yarns into hydrophilic surfaces through plasma treatment, however, the TiO2 formed conformal coatings on the surfaces of nanofibrils in each yarn during hydrolysis instead of just filling the void spaces among the nanofibrils. As a result, bundles of rutile nanotubes were obtained after the sample had been calcined in air at 800 °C. The thermodynamically stable rutile nanostructures were then explored as supports for Pt nanoparticles whose catalytic activity was evaluated using the reduction of p-nitrophenol by NaBH4. The Pt supported on porous rutile fibers exhibited a better performance than the Pt on rutile nanotubes in terms of both induction time (t(ind)) and apparent rate constant (k(app)).

Maneuvering the internal porosity and surface morphology of electrospun polystyrene yarns by controlling the solvent and relative humidity

This article presents a simple and reliable method for generating polystyrene (PS) yarns composed of bundles of nanofibrils by using a proper combination of solvent and relative humidity. We elucidated the mechanism responsible for the formation of this new morphology by systematically investigating the molecular interactions among the polymer, solvent(s), and water vapor. We demonstrated that vapor-induced phase separation played a pivotal role in generating the yarns with a unique structure. Furthermore, we discovered that the low vapor pressure of N,N-dimethylformamide (DMF) was critical to the evolution of pores in the interiors. On the contrary, the relatively high vapor pressure of tetrahydrofuran (THF) hindered the formation of interior pores but excelled in creating a rough surface. In all cases, our results clearly indicate that the formation of either internal porosity or surface roughness required the presence of water vapor, a nonsolvent of the polymer, at a proper level of relative humidity. The exact morphology or pore structure was dependent on the speed of evaporation of the solvent(s) (DMF, THF, and their mixtures) as well as the interdiffusion and penetration of the nonsolvent (water) and solvent(s). Our findings can serve as guidelines for the preparation of fibers with desired porosity both internally and externally through electrospinning.