Design and synthesis of self-ordered mesoporous nanocomposite through controlled in-situ crystallization

Two-dimensional single-crystalline mesoporous high-entropy oxide nanoplates for efficient electrochemical biomass upgrading

Mesoporous single crystals have received more attention than ever in catalysis-related applications due to their unique structural functions. Despite great efforts, their progress in engineering crystallinity and composition has been remarkably slower than expected. In this manuscript, a template-free strategy is developed to prepare two-dimensional high-entropy oxide (HEO) nanoplates with single-crystallinity and penetrated mesoporosity, which further ensures precise control over high-entropy compositions and crystalline phases. Single-crystalline mesoporous HEOs (SC-MHEOs) disclose high electrocatalytic performance in 5-hydroxymethylfurfural oxidation reaction (HMFOR) for efficient biomass upgrading, with remarkable HMF conversion of 99.3% and superior 2,5-furandicarboxylic acid (FDCA) selectivity of 97.7%. Moreover, with nitrate reduction as coupling cathode reaction, SC-MHEO realizes concurrent electrosynthesis of value-added FDCA and ammonia in the two-electrode cell. Our study provides a powerful paradigm for producing a library of novel mesoporous single crystals for important catalysis-related applications, especially in the two-electrode cell.

Catalyst development for O2-assisted oxidative dehydrogenation of propane to propylene

O2-Assisted oxidative dehydrogenation of propane (O2-ODHP) could convert abundant shale gas into propylene as an important chemical raw material, meaning O2-ODHP has practical significance. Thermodynamically, high temperature is beneficial for O2-ODHP; however, high reaction temperature always causes the overoxidation of propylene, leading to a decline in its selectivity. In this regard, it is crucial to achieve low temperatures while maintaining high efficiency and selectivity during O2-ODHP. The use of catalytic technology provides more opportunities for achieving high-efficiency O2-ODHP under mild conditions. Up to now, many kinds of catalytic systems have been elaborately designed, including transition metal oxide catalysts (such as vanadium-based catalysts, molybdenum-based catalysts, etc.), transition metal-based catalysts (such as Pt nanoclusters), rare earth metal oxide catalysts (especially CeO2 related catalysts), and non-metallic catalysts (BN, other B-containing catalysts, and C-based catalysts). In this review, we have summarized the development progress of mainstream catalysts in O2-ODHP, aiming at providing a clear picture to the catalysis community and advancing this research field further.

Ordered Mesoporous Crystalline Frameworks Toward Promising Energy Applications

Ordered mesoporous crystalline frameworks (MCFs), which possess both functional frameworks and well-defined porosity, receive considerable attention because of their unique properties including high surface areas, large pore sizes, tailored porous structures, and compositions. Construction of novel crystalline mesoporous architectures that allows for rich accessible active sites and efficient mass transfer is envisaged to offer ample opportunities for potential energy-related applications. In this review, the rational synthesis, unique structures, and energy applications of MCFs are the main focus. After summarizing the synthetic approaches, an emphasis is placed on the delicate control of crystallites, mesophases, and nano-architectures by concluding basic principles and showing representative examples. Afterward, the currently fabricated components of MCFs such as metals, metal oxides, metal sulfides, and metal-organic frameworks are described in sequence. Further, typical applications of MCFs in rechargeable batteries, supercapacitors, electrocatalysis, and photocatalysis are highlighted. This review ends with the possible development and synthetic challenges of MCFs as well as a future prospect for high-efficiency energy applications, which underscores a pathway for developing advanced materials.

First-principles study for quasi-static growth model in FeAl intermetallic based on Wulff cluster model

In order to investigate the structure of FeAl mesoscopic crystals segregating in liquid state alloys, we have determined their equilibrium structures (Wulff shape) based on the Wulff cluster model. For non-stoichiometric surface terminations, the chemical environment is taken into account through the chemical potential of the constituents. In this case, different cluster shapes change as a function of the chemical environment. In order to model the growth process in more detail, we propose a quasi-static growth model based on the sequential addition of (sub-)monolayers in the most favorable surface directions. Thus, a sequence of different Wulff shapes results in the growth process, as illustrated for the FeAl intermetallic compound. This model is proved preliminarily by calculating the concentration trend of Al/Fe atoms on both Al-terminated and Fe-terminated surfaces, and by simulating the most stable layer adsorbed on these two surfaces. This model might be helpful in analyzing the growth processes including nucleation barriers during nucleation processes theoretically.

Mesoporous TiO2 Single-Crystal Particles from Controlled Crystallization-Driven Mono-Micelle Assembly as an Efficient Photocatalyst

Mesoporous materials with crystalline frameworks have been widely explored in many fields due to their unique structure and crystalline feature, but accurate manipulations over crystalline scaffolds, mainly composed of uncontrolled polymorphs, are still lacking. Herein, we explored a controlled crystallization-driven monomicelle assembly approach to construct a type of uniform mesoporous TiO2 particles with atomically aligned single-crystal frameworks. The resultant mesoporous TiO2 single-crystal particles possess an angular shape ∼80 nm in diameter, good mesoporosity (a high surface area of 112 m2 g-1 and a mean pore size at 8.3 nm), and highly oriented anatase frameworks. By adjusting the evaporation rate during assembly, such a facile solution-processed strategy further enables the regulation of the particle size and mesopore size without the destruction of the oriented crystallites. Such a combination of ordered mesoporosity and crystalline orientation provides both effective mass and charge transportation, leading to a significant increase in the hydrogen generation rate. A maximum hydrogen evolution rate of 12.5 mmol g-1 h-1 can be realized, along with great stability under solar light. Our study is envisaged to extend the possibility of mesoporous single crystal growth to a range of functional ceramics and semiconductors toward advanced applications.

Stepwise Monomicelle Assembly for Highly Ordered Mesoporous TiO2 Membranes with Precisely Tailored Mesophase and Porosity

Mesoporous materials with crystalline frameworks have been acknowledged as very attractive materials in various applications. Nevertheless, due to the cracking issue during crystallization and incompatible hydrolysis and assembly, the precise control for crystalline mesoscale membranes is quite infertile. Herein, we presented an ingenious stepwise monomicelle assembly route for the syntheses of highly ordered mesoporous crystalline TiO₂ membranes with delicately controlled mesophase, mesoporosity, and thickness. Such a process involves the preparation of monomicelle hydrogels and follows self-assembly by stepwise solvent evaporation, which enables the sensitive hydrolysis of TiO₂ oligomers and dilatory micelle assembly to be united. In consequence, the fabricated mesoporous TiO₂ membranes exhibit a broad flexibility, including tunable ordered mesophases (worm-like, hexagonal p6mm to body-centered cubic Im3̅m), controlled mesopore sizes (3.0-8.0 nm), and anatase grain sizes (2.3-8.4 nm). Besides, such mesostructured crystalline TiO₂ membranes can be extended to diverse substrates (Ti, Ag, Si, FTO) with tailored thickness. The great mesoporosity of the in situ fabricated mesoscopic membranes also affords excellent pseudocapacitive behavior for sodium ion storage. This study underscores a novel pathway for balancing the interaction of precursors and micelles, which could have implications for synthesizing crystalline mesostructures in higher controllability.

Engineered nanostructures within sol-gel bioactive glass for enhanced bioactivity and modulated drug delivery

The engineering of nanocrystalline phase in amorphous oxide materials such as bioactive glass is emerging as a new area of great technological and scientific interest in the field of biomaterials. This study reports for the first time the infusion of apatite nanocrystals in sol-gel-derived bioactive glass using P123 as the structure-directing agent. The synthesis of a multicomponent 80SiO₂-15CaO-5P₂O₅ bioactive glass material having a hierarchically ordered mesoporous structure with uniformly grown nanocrystals of apatite was achieved through a sono-assisted surfactant-templated sol-gel method. The bulk crystallographic analysis together with microstructural characterizations shows that the nanocrystalline apatite domains are uniformly dispersed as well as embedded along the mesopores. These nanocrystalline domains were found to influence the textural properties. In addition, macroscopic evidence for higher signs of bonelike matrix formation was observed by the biomineralization study in simulated body fluids. Osteostimulatory effects of these glass samples were evident by cultures in a osteogenic and non-osteogenic mediums with human osteosarcoma cells and a higher osteopromotive potential was authenticated by the alkaline phosphatase activity and alizarin red staining. Further, this study shows a new strategy to prolong the drug release period on account of the nanocrystalline phase and hierarchically positioned mesopores, thus making it a better drug delivery matrix as well.

Versatile Synthesis of Mesoporous Crystalline TiO2 Materials by Monomicelle Assembly

Mesoscale TiO₂ structures have realized many technological applications-ranging from catalysis and biomedicine to energy storage and conversion-because of their large mesoporosities offering desirable accessibility and mass transport. Tailoring mesoporous TiO₂ structures with novel mesoscopic and microscopic configurations is envisaged to offer ample opportunities for further applications. In this Review, we explain how to synthesize novel mesoporous TiO₂ materials and present recent examples. An emphasis is placed on a "monomicelle assembly" strategy as an emerging and powerful approach to direct the formation of mesostructured TiO₂ with precise control over its structural orientations and architectures. Furthermore, typical examples of mesoporous TiO₂ for applications in batteries and photocatalysis are highlighted. The Review ends with an outlook towards the synthesis of mesoporous TiO₂ with tailored architectures by self-assembly, which could pave the way for developing advanced energy conversion and storage devices.

Ordered mesoporous metal oxides for electrochemical applications: correlation between structure, electrical properties and device performance

Ordered mesoporous metal oxides with a high specific surface area, tailored porosity and engineered interfaces are promising materials for electrochemical applications. In particular, the method of evaporation-induced self-assembly allows the formation of nanocrystalline films of controlled thickness on polar substrates. In general, mesoporous materials have the advantage of benefiting from a unique combination of structural, chemical and physical properties. This Perspective article addresses the structural characteristics and the electrical (charge-transport) properties of mesoporous metal oxides and how these affect their application in energy storage, catalysis and gas sensing.

Controlled synthesis of mesoporous single-crystalline TiO2 nanoparticles for efficient photocatalytic H2 evolution

Mesoporous single-crystals have emerged as a unique family of functional materials, exhibiting excellent performance in various applications, owing to their well-defined accessible mesoporosity and highly single-crystalline structures. Precise tailoring structures of mesoporous single-crystals at the nanoscale remains an unsolved scientific and technical challenge. Herein, we report a facile and general approach for the synthesis of mesoporous single-crystalline TiO₂ nanoparticles (designated as MSC-TNs) with distinctive traits including tunable morphologies, controllable particle sizes, well dispersity, high hydrophilicity, well-defined mesoporosity and single-crystal nature. Specifically, the amount of water employed in the precursor solution was seen to give fine control over the particle sizes and morphologies of MSC-TNs. MSC-TNs with different sizes show excellent photocatalytic activity in production of hydrogen from water. Under the illumination of 300 W Xe lamp, MSC-TNs were shown to provide good photodegradation performance with Rhodamine 6 G, as well as H₂ production when loaded 1 wt % Pt. In a CH₃OH solution H₂ was evolved with a rate of 8.98 mmol h^-1 g^-1, which is significantly higher than with commercial P25 nanoparticles (4.02 mmol h^-1 g^-1).

A Universal Lab-on-Salt-Particle Approach to 2D Single-Layer Ordered Mesoporous Materials

The advantages of existing ordered mesoporous materials have not yet been fully realized, due to their limited accessibility of in-pore surface and long mass-diffusion length. A general, controllable, and scalable synthesis of a family of two-dimensional (2D) single-layer ordered mesoporous materials (SOMMs) with completely exposed mesopore channels, significantly improved mass diffusion, and diverse framework composition is reported here. The SOMMs are synthesized via a surface-limited cooperative assembly (SLCA) on water-removable substrates of inorganic salts (e.g., NaCl), combined with vacuum filtration. As a proof of concept, the obtained CeO₂ -based SOMMs show superior catalytic performance in CO oxidation with high conversion efficiency, ≈33 times higher than that of conventional bulk mesoporous CeO₂ . This SLCA is a promising approach for developing next-generation porous materials for various applications.

A General and Straightforward Route to Noble Metal-Decorated Mesoporous Transition-Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition-metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane-assisted one-pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated-free noble metal nanoparticles, including Au/WO₃ , Au/TiO₂ , Au/NbO_x , and Pt/WO₃ . 3-mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂ PtCl₄ ) by mercapto (SH) groups, resulting in coassembly with poly(ethylene oxide)-b-polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14-20 nm), high specific surface area (61-138 m² g^-1 ), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃ , in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε-phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air /R_gas = 36-50 ppm of ethanol), high selectivity, and excellent low-concentration detection capability (down to 50 ppb) at low working temperature (200 °C).

Continuous Mesoporous Aluminum Oxide Film with Perpendicularly Oriented Mesopore Channels

Mesoporous aluminum oxide (MAO) films with perpendicularly oriented cylindrical mesopores (pore diameter: ca. 10 nm) were successfully deposited on a glass substrate by a surfactant-templating approach using aluminum nitrate as an aluminum source. The perpendicular orientation of mesopores was confirmed by grazing-incidence small-angle X-ray scattering and neutron reflection experiments. The thickness of the MAO film was around 100 nm, with a surface roughness of less than 6 nm. Since the inner surface of MAO pores was positively charged, negatively charged glucose oxidase molecules could be densely loaded into the cylindrical mesopores without significant loss of enzymatic activity. The present MAO film is potentially useful as an inorganic host material for an enzyme toward the development of a biocatalytic system.

Barium titanate at the nanoscale: controlled synthesis and dielectric and ferroelectric properties

The current trend in the miniaturization of electronic devices has driven the investigation into many nanostructured materials. The ferroelectric material barium titanate (BaTiO3) has garnered considerable attention over the past decade owing to its excellent dielectric and ferroelectric properties. This has led to significant progress in synthetic techniques that yield high quality BaTiO3 nanocrystals (NCs) with well-defined morphologies (e.g., nanoparticles, nanorods, nanocubes and nanowires) and controlled crystal phases (e.g., cubic, tetragonal and multi-phase). The ability to produce nanoscale BaTiO3 with controlled properties enables theoretical and experimental studies on the intriguing yet complex dielectric properties of individual BaTiO3 NCs as well as BaTiO3/polymer nanocomposites. Compared with polymer-free individual BaTiO3 NCs, BaTiO3/polymer nanocomposites possess several advantages. The polymeric component enables simple solution processibility, high breakdown strength and light weight for device scalability. The BaTiO3 component enables a high dielectric constant. In this review, we highlight recent advances in the synthesis of high-quality BaTiO3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol-gel methods. We also summarize the dielectric and ferroelectric properties of individual BaTiO3 NCs and devices based on BaTiO3 NCs via theoretical modeling and experimental piezoresponse force microscopy (PFM) studies. In addition, viable synthetic strategies for novel BaTiO3/polymer nanocomposites and their structure-composition-performance relationship are discussed. Lastly, a perspective on the future direction of nanostructured BaTiO3-based materials is presented.

Fabrication and Functionalization of Inorganic Materials Using Amphiphilic Molecules

In this review, the synthesis of inorganic materials with various properties using amphiphilic molecules is examined. Amphiphilic molecules are used for the formation of highly ordered mesostructures and the surface modification. Two examples of the mesostructures are crystalline mesoporous titania (TiO₂) and the novel visible light responsive mesostuructured titania modified with dye in the pores, which can be fabricated using the molecular self-assemblies of amphiphiles as templates. Surface modification using amphiphilic molecules enables the construction of self-assembled arrays of silica particles and the preparation of a film that can control adsorption/desorption behavior of bovine serum albumin (BSA) by light irradiation.

New insights into high temperature hydrothermal synthesis in the preparation of visible-light active, ordered mesoporous SiO2–TiO2 composited photocatalysts

Carbon doped, visible light active and ordered mesoporous TiO₂–SiO₂ nanocomposites have been successfully synthesized via one step high temperature (180 °C) hydrothermal technology.

Accelerated room-temperature crystallization of ultrahigh-surface-area porous anatase titania by storing photogenerated electrons

A technology for storing photogenerated electrons is for the first time applied for significantly accelerating the crystallization of amorphous TiO₂ at room temperature (reducing the reaction time from 80 to 2 days). The resulting porous anatase titania exhibits ultrahigh surface areas up to 736 m² g⁻¹.

Dendritic mesoporous silica–titania nanospheres with enhanced photocatalytic activities

Dendritic mesoporous silica–titania nanospheres (DMSTN) show remarkable performance as a photocatalyst and an adsorbent for photochromic methylene green (MG) dye.

Soft-template construction of three-dimensionally ordered inverse opal structure from Li2FeSiO4/C composite nanofibers for high-rate lithium-ion batteries

Exploring a new method to fabricate small-sized nanofibers is essential to achieve superior performances for energy conversion and storage devices. Here, a novel soft-template strategy is developed to synthesize a three-dimensionally ordered macroporous (3DOM) architecture constructed from small-sized nanofibers. The effectiveness of a nanofiber-assembled three-dimensional inverse opal material as an electrode for high-rate lithium-ion batteries is demonstrated. The small-sized Li2FeSiO4/C composite nanofibers with a diameter of 20-30 nm are grown by employing a tri-block copolymer P123 as a structure directing agent. Accordingly, the macro-mesoporous hierarchical 3DOM architecture constructed from Li2FeSiO4/C nanofibers is further templated from P123 for the nanofibers and a polystyrene colloidal crystal array for the 3DOM architecture. We find that the thermal stability of the nanofiber morphology depends on the self-limited growth of Li2FeSiO4 nanocrystals in a crystalline-amorphous hybrid. As a cathode for a lithium-ion battery, the 3D hierarchical macro-mesoporous cathodes exhibit outstanding high-rate and ultralong-life performances with a capacity retention of 84% after 1500 cycles at 5 C in the voltage window of 1.5-4.5 V, which is greatly improved compared with a simple 3DOM Li2FeSiO4/C nanocomposite.

Mesoporous CuO–ZnO p–n heterojunction based nanocomposites with high specific surface area for enhanced photocatalysis and electrochemical sensing

Mesoporous and core–shell like (p)CuO–(n)ZnO nanocomposites were prepared using microstructural refinement and solid state reactions, which showed enhanced photochemical and electrochemical performances.

SiO2-stabilized Ni/t-ZrO2 catalysts with ordered mesopores: one-pot synthesis and their superior catalytic performance in CO methanation

Ternary SiO₂-stabilized Ni/t-ZrO₂ catalysts with an ordered mesoporous structure were synthesized, which show excellent low temperature activity and thermal stability.

Template-free preparation of mesoporous single crystal In2O3 achieving superior ethanol gas sensing performance

Mesoporous single crystal In₂O₃ with high specific surface area and oxygen vacancy concentration are prepared for enhanced ethanol gas sensing performance.

Radially oriented mesoporous TiO2 microspheres with single-crystal-like anatase walls for high-efficiency optoelectronic devices

Highly crystalline mesoporous materials with oriented configurations are in demand for high-performance energy conversion devices. We report a simple evaporation-driven oriented assembly method to synthesize three-dimensional open mesoporous TiO2 microspheres with a diameter of ~800 nm, well-controlled radially oriented hexagonal mesochannels, and crystalline anatase walls. The mesoporous TiO2 spheres have a large accessible surface area (112 m(2)/g), a large pore volume (0.164 cm(3)/g), and highly single-crystal-like anatase walls with dominant (101) exposed facets, making them ideal for conducting mesoscopic photoanode films. Dye-sensitized solar cells (DSSCs) based on the mesoporous TiO2 microspheres and commercial dye N719 have a photoelectric conversion efficiency of up to 12.1%. This evaporation-driven approach can create opportunities for tailoring the orientation of inorganic building blocks in the assembly of various mesoporous materials.

Aerosol-spray diverse mesoporous metal oxides from metal nitrates

Transition metal oxides are widely used in solar cells, batteries, transistors, memories, transparent conductive electrodes, photocatalysts, gas sensors, supercapacitors, and smart windows. In many of these applications, large surface areas and pore volumes can enhance molecular adsorption, facilitate ion transfer, and increase interfacial areas; the formation of complex oxides (mixed, doped, multimetallic oxides and oxide-based hybrids) can alter electronic band structures, modify/enhance charge carrier concentrations/separation, and introduce desired functionalities. A general synthetic approach to diverse mesoporous metal oxides is therefore very attractive. Here we describe a powerful aerosol-spray method for synthesizing various mesoporous metal oxides from low-cost nitrate salts. During spray, thermal heating of precursor droplets drives solvent evaporation and induces surfactant-directed formation of mesostructures, nitrate decomposition and oxide cross-linking. Thirteen types of monometallic oxides and four groups of complex ones are successfully produced, with mesoporous iron oxide microspheres demonstrated for photocatalytic oxygen evolution and gas sensing with superior performances.

Morphology engineering of nanostructured TiO2 particles

Nanostructured TiO₂ particles with different morphologies obtained by a universal method.

Scaffold-assisted synthesis of crystalline mesoporous titania materials

Scaffold-assisted synthesis of crystalline mesoporous titania materials with controllable structural and crystalline properties.

Organophosphonate bridged anatase mesocrystals: low temperature crystallization, thermal growth and hydrogen photo-evolution

Tuning P-doping: phosphorus dendrimers enabled access, at 60 °C, to ultra-stable organophosphonate-bridged-anatase mesocrystals with a promising water-splitting photo-activity.

Mesoscopically structured nanocrystalline metal oxide thin films

This review describes the main successful strategies that are used to grow mesostructured nanocrystalline metal oxide and SiO₂ films via deposition of sol-gel derived solutions. In addition to the typical physicochemical forces to be considered during crystallization, mesoporous thin films are also affected by the substrate-film relationship and the mesostructure. The substrate can influence the crystallization temperature and the obtained crystallographic orientation due to the interfacial energies and the lattice mismatch. The mesostructure can influence the crystallite orientation, and affects nucleation and growth behavior due to the wall thickness and pore curvature. Three main methods are presented and discussed: templated mesoporosity followed by thermally induced crystallization, mesostructuration of already crystallized metal oxide nanobuilding units and substrate-directed crystallization with an emphasis on very recent results concerning epitaxially grown piezoelectric structured α-quartz films via crystallization of amorphous structured SiO₂ thin films.

Application of Sulfonic Acid Functionalized SBA‐15 as a New Nanoporous Acid Catalyst in the Green One‐Pot Synthesis of Spirooxindole‐4H‐pyrans

Sulfonic acid functionalized SBA‐15 (SBA‐Pr‐SO3H) as a new nanoporous solid acid catalyst was applied in the green one‐pot synthesis of spirooxindole‐4H‐pyrans via condensation of isatins, malononitrile or methyl cyanoacetate or ethyl cyanoacetate, and 4‐hydroxycoumarin in water solvent. SBA‐Pr‐SO3H was proved to be an efficient heterogeneous nanoporous solid acid catalyst with a pore size of 6 nm that could be easily handled and removed from the reaction mixture by simple filtration and can be recovered and reused for several times without any loss of activity. The significant merits of present methodology are its simplicity, short reaction time, good yields, and environmentally benign mild reaction condition as water was used as a green solvent.

Understanding the role of cyclodextrins in the self-assembly, crystallinity, and porosity of titania nanostructures

A series of mesoporous titania photocatalysts with tailorable structural and textural characteristics was prepared in aqueous phase via a colloidal self-assembly approach using various cyclodextrins (CDs) as structure-directing agents. The photocatalysts and the structure-directing agents were characterized at different stages of the synthesis by combining X-ray diffraction, N2-adsorption, field emission scanning electron microscopy, transmission electron microscopy, UV-visible spectroscopy, dynamic light scattering, and surface tension measurements. The results demonstrate that the cyclic macromolecules efficiently direct the self-assembly of titania colloids, resulting in a fine-tuning of the crystal phase composition, crystallite size, surface area, particle morphology, pore volume, and pore size. Depending on the chemical nature of the substituents in the cyclodextrin ring, synergistic or competitive effects arising from the adsorption capacity of these cyclic oligosaccharides onto titania surface, surface-active properties, and ability to aggregate in water by intermolecular interactions were found to substantially impact the characteristics of the final material. We propose that, in contrast to the native cyclodextrins, which tend to favor the local agglomeration of titania nanoparticles due to the strong intermolecular interactions, the substitution of hydroxyl groups by a relatively large number of methoxyl or 2-hydropropoxyl ones in the β-CD derivatives allows for creating smoother interfaces, thus facilitating the self-assembly of the colloids in a more homogeneous network. The photocatalytic activity of those titania materials was evaluated in the photodegradation of a toxic herbicide, phenoxyacetic acid, and was correlated to the structural and textural characteristics of the photocatalysts.

The preparation of tubular heterostructures based on titanium dioxide and silica nanotubes and their photocatalytic activity

Tubular heterostructures based on titanium dioxide (TiO2) and silica nanotubes (SNTs) with high photocatalytic activity have been successfully obtained by a simple combination of an electrospinning technique and a solvothermal process. The as-prepared products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and N2 absorption-desorption experiments. The results confirmed that SNTs with high specific surface area were obtained by efficiently controlling the phase separation and solvent evaporation during the process of electrospinning and calcination, and TiO2 was successfully grown on the SNT substrates. The obtained titanium dioxide/silica nanotubes (TiO2/SNTs) heterostructures showed high photocatalytic activities to degrade Rhodamine 6G because of the formation of heterostructures, which might improve the separation of photogenerated electrons and holes. Furthermore, the TiO2/SNTs heterostructures could be easily recycled without an evident decrease in photocatalytic activity.

The oriented growth of tungsten oxide in ordered mesoporous carbon and their electrochemical performance

Electrocatalysts for hydrogen oxidation and methanol oxidation are the heart of the proton exchange membrane fuel cell. In spite of tremendous efforts, developing low-cost anodic electrocatalysts with high catalytic activity and corrosion resistance is still a great challenge. Here, we report a nanocomposite consisting of oriented WO3 nanorods grown in ordered mesoporous carbon as a high-performance functional catalyst carrier for proton exchange membrane fuel cells. As a result of the catalytic graphitization effect of tungsten compounds, the degree of graphitization and conductivity of mesoporous carbon film were improved even at a low temperature. Furthermore, compared with ordered mesoporous carbon, ordered mesoporous C-WO3 nanocomposites possess favorable hydrophilicity, excellent corrosion resistance and notable electrocatalytic activities. The unusual electrocatalytic activities arise from the ideal physical properties of the carrier and synergetic catalysis between Pt and WO3.