Hard-Sphere Packing and Icosahedral Assembly in the Formation of Mesoporous Materials

Chemically Assisted Formation of Monolayer Colloidosomes on Functional Particles

A chemically assisted method is developed to form a monolayer polymer colloidosome shell on various functional materials. Functional carbon nanobubble colloidosomes or their derived hybrid structures can be fabricated by a subsequent thermal treatment.

Preparation and unique dielectric properties of nanoporous materials with well-controlled closed-nanopores

Although general porous materials have a low dielectric constant, their uncontrollable opened porous structure results in high dielectric loss and poor barrier properties, thus limiting their application as interconnect dielectrics.

Transcription of G-quartet supramolecular aggregates into hierarchical mesoporous silica nanotubes

Hierarchical porous silica nanotubes or porous silica hollow spheres were prepared employing a low concentration of G-quartet supramolecular aggregates as a template.

Synthesis of mesoporous carbon nanoparticles with large and tunable pore sizes

Mesoporous carbon nanoparticles (MCNs) with large and adjustable pores have been synthesized by using poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a template and resorcinol-formaldehyde (RF) as a carbon precursor. The resulting MCNs possess small diameters (100-126 nm) and high BET surface areas (up to 646 m(2) g(-1)). By using home-designed block copolymers, the pore size of MCNs can be tuned in the range of 13-32 nm. Importantly, the pore size of 32 nm is the largest among the MCNs prepared by the soft-templating route. The formation mechanism and structure evolution of MCNs were studied by TEM and DLS measurements, based on which a soft-templating/sphere packing mechanism was proposed. Because of the large pores and small particle sizes, the resulting MCNs were excellent nano-carriers to deliver biomolecules into cancer cells. MCNs were further demonstrated with negligible toxicity. It is anticipated that this carbon material with large pores and small particle sizes may have excellent potential in drug/gene delivery.

Tuning of the temperature window for unit-cell and pore-size enlargement in face-centered-cubic large-mesopore silicas templated by swollen block copolymer micelles

The unit-cell size and pore diameter as functions of temperature are investigated in the syntheses of FDU-12 silicas with face-centered cubic structure templated by Pluronic (PEO-PPO-PEO) block copolymer micelles swollen by toluene. The temperature range in which the unit-cell size and pore size strongly increase as temperature decreases is correlated with the critical micelle temperature (CMT) of the surfactant. While Pluronic F127 affords a wide range of unit-cell parameters (28-51 nm) and pore diameters (16-32 nm), it renders moderately enlarged pore sizes at 25 °C. The use of Pluronic F108 with higher CMT affords FDU-12 with very large unit-cell size (∼49 nm) and large pore diameter (27 nm) at 23 °C. Large unit-cell size (40-41 nm) and pore size (22 nm) were obtained even at 25 °C. The application of Pluronics F87 and F88 with much smaller molecular weights and higher CMTs also allows one to synthesize FDU-12 with quite large unit-cell parameters and pore sizes at room temperature. The present work demonstrates that one can judiciously select Pluronic surfactants with appropriate CMT to shift the temperature range in which the pore diameter is readily tunable.

Asymmetric block copolymers for supramolecular templating of inorganic nanospace materials

This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self-assemblies with more diverse morphological and functional features than those constructed by EOn POm EOn type symmetric triblock copolymers, thereby affording well-designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.

Single-micelle-templated synthesis of hollow silica nanospheres with tunable pore structures

Single-micelle-templated hollow silica nanospheres with inner diameter tunable from 16 to 44 nm were synthesized using Pluronic F108 surfactant and suitable micelle swelling agent through control of initial synthesis temperature.

Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement

Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential. Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure. Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.

Functionalized hollow siliceous spheres for VOCs removal with high efficiency and stability

Functionalized hollow siliceous spheres (HSSs) have been prepared by surface modification with trimethylchlorosilane (TMCS) for the removal of volatile organic compounds (VOCs). The resultant HSSs-TMCS possesses a uniform and well-dispersed hollow spherical structure, high surface area, large total pore volume, high VOCs adsorption capacity, and small water vapor adsorption capacity. The adsorption and desorption performance of HSSs-TMCS under static (n-hexane and 93# gasoline) and dynamic (n-hexane) conditions was investigated. Compared with commercial silica gel (SG) and activated carbon (AC), HSSs-TMCS show higher capacity of adsorbing n-hexane and 93# gasoline with good stability and low water vapor adsorption capacity under static adsorption conditions, higher dynamic adsorption capacity and stable breakthrough time under dynamic adsorption conditions. The high efficiency and stability of functionalized HSSs are associated with their unique hollow morphology and structure parameters. The designed HSSs-TMCS with high VOCs removal capacity and recyclability are promising candidates for the treatment of air pollution.

Low-cost and large-scale synthesis of functional porous materials for phosphate removal with high performance

A facile spray drying technique has been developed for large-scale and template-free production of nanoporous silica with controlled morphology, large pore size, and high pore volume, using commercially available fumed silica, Aerosil 200, as a sole precursor. This approach can be applied to the preparation of functional nanoporous materials, in this study, lanthanum oxide functionalised silica microspheres by introducing lanthanum nitrate in situ during the spray drying process and followed by a post-calcination process. The resultant lanthanum functionalised Aerosil microspheres manifest high phosphate adsorption capacity (up to 2.317 mmol g(-1)), fast kinetics, and excellent adsorption performance at a low phosphate concentration (1 mg L(-1)). In virtue of the easy and scalable synthesis method, low cost and high performances of the product, the materials we reported here are promising for water treatment. Our approach may be general and extended to the synthesis of other functional nanoporous materials with versatile applications.

Two-dimensional mesoporous carbon nanosheets and their derived graphene nanosheets: synthesis and efficient lithium ion storage

We report a new solution deposition method to synthesize an unprecedented type of two-dimensional ordered mesoporous carbon nanosheets via a controlled low-concentration monomicelle close-packing assembly approach. These obtained carbon nanosheets possess only one layer of ordered mesopores on the surface of a substrate, typically the inner walls of anodic aluminum oxide pore channels, and can be further converted into mesoporous graphene nanosheets by carbonization. The atomically flat graphene layers with mesopores provide high surface area for lithium ion adsorption and intercalation, while the ordered mesopores perpendicular to the graphene layer enable efficient ion transport as well as volume expansion flexibility, thus representing a unique orthogonal architecture for excellent lithium ion storage capacity and cycling performance. Lithium ion battery anodes made of the mesoporous graphene nanosheets have exhibited an excellent reversible capacity of 1040 mAh/g at 100 mA/g, and they can retain at 833 mAh/g even after numerous cycles at varied current densities. Even at a large current density of 5 A/g, the reversible capacity is retained around 255 mAh/g, larger than for most other porous carbon-based anodes previously reported, suggesting a remarkably promising candidate for energy storage.

Highly ordered cubic mesoporous materials with the same symmetry but tunable pore structures

In this article, two highly ordered mesoporous silica materials with the same face-centered cubic (fcc) symmetry but distinctly different pore structures have been synthesized by simply changing the amount of silica source. Their structures have been extensively studied by Synchrotron small-angle X-ray scattering, N(2) sorption analysis, scanning and transmission electron microscopy observations, and electron tomography. One mesoporous material formed by a hard sphere packing (HSP) pathway exhibits a bimodal pore distribution, while the other has a conventional FDU-12-type mesostructure with a single-sized pore. By increasing the amount of the silica source, the cavities formed by the packing of composite spherical micelles in the HSP mesostructure are gradually filled by the excess of siliceous species, leading to the conventional FDU-12-type mesostructure with the disappearance of bimodal pores. The pore connectivity of the HSP mesoporous material hydrothermally treated at 150 °C has been further investigated. Taking advantage of the ultrathin tomographic slices, the sizes of cage, cavity, and connectivity are measured to be 14.5, 10.5, and 6.4 nm, respectively. More importantly, the pore connection between the cage and cavity is directly observed to occur along the ⟨100⟩ direction, different from the FDU-12-type mesostructure in which the connection appears between two adjacent cages along the ⟨110⟩ direction. This work represents an unusual example where two ordered cage-type mesoporous materials with the same symmetry can be synthesized by slightly changing the synthesis condition, but their pore structures and pore connections are significantly different. Our finding is important for understanding the formation mechanism and for the rational design and controllable synthesis of novel mesoporous materials.

Access to ultralarge-pore ordered mesoporous materials through selection of surfactant/swelling-agent micellar templates

The surfactant-micelle-templating method has revolutionized the synthesis of high-surface-area materials with mesopores (diameter 2-50 nm) that have well-defined shapes and sizes. One of the major benefits of this method is the ability to tailor the pore size by manipulating the size of the templating micelles. The uniform pores typically form ordered arrays. Although the choice of surfactant can tune the size of the micelles, it is more convenient to use a single surfactant and tailor the micelle size by adding a swelling agent. Unfortunately, the swelling agent tends to induce disorder or heterogeneity in the resulting structures, which can make this approach difficult to implement. We hypothesized that the swelling agents that are moderately solubilized within the micelles of a particular surfactant could generate well-defined micelle-templated structures with significantly enlarged pores. Using this idea, we could judiciously select candidate swelling agents from families of compounds whose extent of solubilization in the surfactant micelles systematically changes with variations in the compound structure. Alkyl-substituted benzenes proved very useful as swelling agents, because their extent of solubilization in micelles of common Pluronic surfactants (EO(m)PO(n)EO(m); EO = ethylene oxide, PO = propylene oxide) significantly increases as the number or size of alkyl substituents decreases. On the basis of these principles, we identified 1,3,5-triisopropylbenzene and cyclohexane as swelling agents for the synthesis of ultralarge-pore SBA-15 silica (pore diameter up to 26 nm) and organosilicas with 2-D hexagonal structures of cylindrical mesopores. Moreover, we used xylene, ethylbenzene, and toluene as swelling agents for the synthesis of large-pore (pore diameter up to 37 nm) face-centered cubic silicas and organosilicas with spherical mesopores. During the early stages of the synthesis, the entrances to large cylindrical and spherical mesopores of these materials were much smaller than the inner pore diameter. Therefore we can often use calcination at sufficiently high temperatures (400-950 °C) to produce closed-pore silicas. Using hydrothermal treatments, we can obtain materials with large pore entrance sizes. In Pluronic-templated synthesis, we observed the propensity for formation of single-micelle-templated nanoparticles as the ratio of the framework precursor to surfactant decreased, and this process afforded organosilica nanotubes and uniform hollow spheres with inner diameters up to ∼21 nm. Consequently, the adjustment of variables in the micelle-templated synthesis allows researchers to tailor the pore size and connectivity and to form either periodic pore arrays or individual nanoparticles.

Periodic organosilica hollow nanospheres as anode materials for lithium ion rechargeable batteries

Polymeric micelles with core-shell-corona architecture have been found to be the efficient colloidal templates for synthesis of periodic organosilica hollow nanospheres over a broad pH range from acidic to alkaline media. In alkaline medium, poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) (PS-PMAPTAC-PEO) micelles yield benzene-silica hollow nanospheres with molecular scale periodicity of benzene groups in the shell domain of hollow particles. Whereas, an acidic medium (pH 4) produces diverse hollow particles with benzene, ethylene, and a mixture of ethylene and dipropyldisulfide bridging functionalities using poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) micelles. These hollow particles were thoroughly characterized by powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TG/DTA), Fourier transformation infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), magic angle spinning-nuclear magnetic resonance ((29)Si MAS NMR and (13)CP-MAS NMR), Raman spectroscopy, and nitrogen adsorption/desorption analyses. The benzene-silica hollow nanospheres with molecular scale periodicity in the shell domain exhibit higher cycling performance of up to 300 cycles in lithium ion rechargeable batteries compared with micron-sized dense benzene-silica particles.

Self-assembly of 6-O- and 6'-O-hexadecylsucroses mixture under aqueous conditions

In this paper, we report the self-assembly of 6-O- and 6'-O-hexadecylsucroses mixture under aqueous conditions. The mixture was synthesized by a five-step sequence from sucrose. The SEM image of a sample prepared by drying a dispersion of the mixture in water showed nanoparticles with the diameter of ∼50nm and aggregates that were formed by further assembly of them. The XRD measurement of the sample exhibited the diffraction pattern assignable to face-centered cubic (FCC) structure and the diameter of a sphere, which took part in the FCC structure, was calculated to be 5.1nm. This value was relatively close to that observed in the DLS measurement of a dispersion of the mixture in water and estimated for a spherical micelle based on the molecular sizes of the two sucrose ethers. On the basis of the above findings, the following self-assembly process of the mixture under aqueous conditions was proposed. The mixture formed the spherical micelles with the diameter of ∼5-7nm in water. The micelles regularly organized according to the FCC structure during the drying process from the aqueous dispersion to construct the nanoparticles with the diameter of ∼50nm. Several numbers of the nanoparticles further assembled to form the aggregates.

Extension of size of monodisperse silica nanospheres and their well-ordered assembly

A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)(4) (TEOS), water and arginine under weakly basic conditions (pH 9-10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported.

Recent progress on silica coating of nanoparticles and related nanomaterials

In recent years, new strategies for silica coating of inorganic nanoparticles and organic nanomaterials, which differ from the classical methodologies, have emerged at the forefront of materials science. Silica as a coating material promises an unparalleled opportunity for enhancement of colloidal properties and functions by using core-shell rational designs and profiting from its synthetic versatility. This contribution provides a brief overview of recent progress in the synthesis of silica-coated nanomaterials and their significant impact in different areas such as spectroscopy, magnetism, catalysis, and biology.

Ultrasmall, well-dispersed, hollow siliceous spheres with enhanced endocytosis properties

The synthesis of ultrasmall, well-dispersed, hollow siliceous spheres (HSSs) by using a block copolymer as the template and tetraethoxysilane as a silica source under acidic conditions is reported. After removing the surfactant core of as-synthesized, spherical, silica-coated block-copolymer micelles, HSSs with a uniform particle size of 24.7 nm, a cavity diameter of 11.7 nm, and a wall thickness of 6.5 nm are obtained. It is shown that by surface functionalization of HSSs with methyl groups during synthesis, HSSs can be further dispersed in solvents such as water or ethanol to form a stable sol. Moreover, the hollow cavities are accessible for further loading of functional components. In addition, it is demonstrated that HSSs possess superior endocytosis properties for HeLa cells compared to those of conventional mesoporous silica nanoparticles. A feasible and designable strategy for synthesizing novel well-dispersed hollow structures with ultrasmall diameters instead of conventional ordered mesostructures is provided. It is expected that HSSs may find broad applications in bionanotechnology, such as drug carriers, cell imaging, and targeted therapy.