Spherical Architecture Research Articles

Three-dimensional graphene-based spheres and crumpled balls: micro- and nano-structures, synthesis strategies, properties and applications

3D spherical and crumpled-ball graphene-based architectures with diverse, fascinating properties and applications are reviewed for the first time.

Biochemistry-directed hollow porous microspheres: bottom-up self-assembled polyanion-based cathodes for sodium ion batteries.

Biochemistry-directed synthesis of functional nanomaterials has attracted great interest in energy storage, catalysis and other applications. The unique ability of biological systems to guide molecule self-assembling facilitates the construction of distinctive architectures with desirable physicochemical characteristics. Herein, we report a biochemistry-directed "bottom-up" approach to construct hollow porous microspheres of polyanion materials for sodium ion batteries. Two kinds of polyanions, i.e. Na3V2(PO4)3 and Na3.12Fe2.44(P2O7)2, are employed as cases in this study. The microalgae cell realizes the formation of a spherical "bottom" bio-precursor. Its tiny core is subjected to destruction and its tough shell tends to carbonize upon calcination, resulting in the hollow porous microspheres for the "top" product. The nanoscale crystals of the polyanion materials are tightly enwrapped by the highly-conductive framework in the hollow microsphere, resulting in the hierarchical nano-microstructure. The whole formation process is disclosed as a "bottom-up" mechanism. Moreover, the biochemistry-directed self-assembly process is confirmed to play a crucial role in the construction of the final architecture. Taking advantage of the well-defined hollow-microsphere architecture, the abundant interior voids and the highly-conductive framework, polyanion materials show favourable sodium-intercalation kinetics. Both materials are capable of high-rate long-term cycling. After five hundred cycles at 20 C and 10 C, Na3V2(PO4)3 and Na(3.12)Fe2.44(P2O7)2 retain 96.2% and 93.1% of the initial capacity, respectively. Therefore, the biochemistry-directed technique provides a low-cost, highly-efficient and widely applicable strategy to produce high-performance polyanion-based cathodes for sodium ion batteries.

Functionalized C@TiO2 hollow spherical architecture for multifunctional applications.

Hierarchical anatase titania (TiO2) with a hollow spherical architecture decorated with functionalized carbon dots (C(F)@THS) was synthesized by a solvothermal decomposition of titanium(IV) isopropoxide (TTIP) in the presence of a solution mixture containing thiourea and citric acid. Interestingly, the concomitant presence of thiourea and citric acid has been found to be essential to obtain such hierarchical hollow architecture because individual constituents produced non-hollow spheres when hydrothermally treated with TTIP. The co-existence of these two constituents also accelerates the growth of hollow spheres. BET surface area study of C(F)@THS revealed the existence of a slit like mesoporosity with a surface area value of 81 m(2) g(-1). Time dependent FESEM and TEM studies confirmed the formation of nanoflake like structures in the intermediate stages followed by the growth of a hollow spherical architecture. We proposed that these nanoflakes get accumulated on the bubble surface to form such hollow spherical morphology. The PL spectral study and Raman shift of the as prepared C(F)@THS confirmed the presence of functionalized graphitic C dots on the surface. A thorough XPS analysis was conducted to explore the nature and relative atomic concentration of the functional groups (-COOH, -CONH2, -NH2). This C(F)@THS sample showed very fast and selective dye (methylene blue and methyl violet) adsorption ability (even from a mixture of two different dye solutions) due to these δ-site containing functional groups on the surface. As C(F)@THS showed only two times reusability for adsorption, the dye adsorbed C(F)@THS was calcined at 450 °C in air to yield organic free anatase TiO2 hollow spheres (THS) with a retention of the original structure. THS was recycled as an efficient and a reusable photocatalyst (k = 9.36 × 10(-2) min(-1)) as well as a photoanode in dye sensitized solar cells (DSSCs) having Jsc value of 19.58 mA cm(-2) with overall efficiency of 6.48%.

Synthesis of single-crystalline, porous TaON microspheres toward visible-light photocatalytic conversion of CO2 into liquid hydrocarbon fuels

The porous spherical architecture of TaON plays a significant role in photoreduction of CO2, including the more reaction sites, easier trapping of photon, and shorter charge transfer distance from interior to surface to expedite charge separation.

Quantification of fluid shear stress in bone tissue engineering scaffolds with spherical and cubical pore architectures.

Recent studies have shown that mechanical stimulation, in the form of fluid perfusion and mechanical compression, can enhance osteogenic differentiation of mesenchymal stem cells and bone cells within tissue engineering scaffolds in vitro. The precise nature of mechanical stimulation within tissue engineering scaffolds is not only dictated by the exogenously applied loading regime, but also depends on the geometric features of the scaffold, in particular architecture, pore size and porosity. However, the precise contribution of each geometric feature towards the resulting mechanical stimulation within a scaffold is difficult to characterise due to the wide range of interacting parameters. In this study, we have applied a fluid-structure interaction model to investigate the role of scaffold geometry (architecture, pore size and porosity) on pore wall shear stress (WSS) under a range of different loading scenarios: fluid perfusion, mechanical compression and a combination of perfusion and compression. It is found that scaffold geometry (spherical and cubical pores), in particular the pore size, has a significant influence on the stimulation within scaffolds. Furthermore, we observed an amplified WSS within scaffolds under a combination of fluid perfusion and mechanical compression, which exceeded that caused by individual fluid perfusion or mechanical compression approximately threefold. By conducting this comprehensive parametric variation study, an expression was generated to allow the design and optimisation of 3D TE scaffolds and inform experimental loading regimes so that a desired level of mechanical stimulation, in terms of WSS is generated within the scaffold.

Dendrimer nanotechnology for enhanced formulation and controlled delivery of resveratrol.

In spite of its wide and beneficial pharmacological potential, resveratrol lags behind other compounds because of its comparatively less impressive pharmacokinetic profile. Resveratrol has very low oral bioavailability and, from a formulation perspective, it has low solubility in water, which leads to its poor absorption upon oral administration. Apart from low aqueous solubility, resveratrol has poor metabolic stability and instability at high pH, and is photosensitive. The pharmacokinetic and formulation-related limitations of resveratrol can be controlled by entrapping the small resveratrol molecule inside highly water-soluble poly(amidoamine) dendrimer nanostructures, which provide spherical architecture and polyvalency at the nanoscale level, thus leading to novel features. Dendrimer architecture is used to entrap resveratrol for enhancement of its solubility and stability in aqueous solution; they can be engineered to control pharmacokinetics and targeting for oral, mucosal, transdermal, or parenteral administration. Dendrimers have the potential to work as excipients with multifunctional capability by enhancing solubility, dissolution, stability, permeability, multiple drug/cosmetic entrapment, controlled delivery, bioavailability, and efficacy of drugs.

Fabrication of conductive carbonaceous spherical architecture from pitch by spray drying

Continuous spray drying used to synthesize amphiphilic sulfonated pitch-based spherical nanoparticles was reported in this study. The spherical particles were further carbonized and activated by KOH to obtain porous spheres. N2 adsorption–desorption, mercury porosimetry and Raman spectroscopy were used to investigate the pore structure and electron conductivity of the resulting spherical activated carbon particles. The results show that the porous spheres had a high specific surface area (e.g., up to 2550m2g−1) and a continuous pore size distribution that varied from micropores to macropores. This interconnected 3-D carbonaceous architecture efficiently improved the electrical conductivity and facilitated a better utilization of the inner-pores for energy storage. These two aspects combine together to guarantee a low internal resistance and a good rate performance to an EDLC using these spherical nanoporous carbons as the electrodes. In 1M TEA-BF4/PC solution, such EDLC showed a specific capacitance of 173Fg−1 at 0.05Ag−1 and 115Fg−1 at 10Ag−1. Its energy density gets to 43.8Whkg−1 and maintains at 24.16Whkg−1 even the power density rises up to 25kWkg−1.

The fabrication of flower-like graphene/octadecylamine composites

Abstract Three-dimensional flower-like nanomaterials have wide application due to the large specific surface area. In this letter, the morphology of octadecylamine (ODA) from several common solvents is studied and it is found that from the chloroform and acetone solution, ODA assembles into petal-like structure, which further forms the spherical or flower-like architecture. Furthermore, the composite materials incorporated reduced graphene oxide (rGO) and ODA could well keep the flower-shaped structure of ODA. XRD results show that the introduction of graphene has little influence on the structure of ODA and contact angle test indicates good hydrophobic performance of the rGO/ODA material.

Ultrafast all-optical technologies for bidirectional optical wireless communications.

In this Letter, a spherical retro-modulator architecture is introduced for operation as a bidirectional transceiver in passive optical wireless communication links. The architecture uses spherical retroreflection to enable retroreflection with broad directionality (2π steradians), and it uses all-optical beam interaction to enable modulation on ultrafast timescales (120fs duration). The spherical retro-modulator is investigated from a theoretical standpoint and is fabricated for testing with three glasses, N-BK7, N-LASF9, and S-LAH79. It is found that the S-LAH79 structure provides the optimal refraction and nonlinearity for the desired retroreflection and modulation capabilities.

Water oxidation catalysis by birnessite@iron oxide core-shell nanocomposites.

In this work, magnetic nanocomposite particles were prepared for water oxidation reactions. The studied catalysts consist of maghemite (γ-Fe2O3), magnetite (Fe3O4), and manganese ferrite (MnFe2O4) nanoparticles as cores coated in situ with birnessite-type manganese oxide shells and were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermal, chemical, and surface analyses, and magnetic measurements. The particles were found to be of nearly spherical core-shell architectures with average diameter of 150 nm. Water oxidation catalysis was examined using Ce(4+) as the sacrificial oxidant. All core-shell particles were found to be active water oxidation catalysts. However, the activity was found to depend on a variety of factors like the type of iron oxide core, the structure and composition of the shell, the coating characteristics, and the surface properties. Catalysts containing magnetite and manganese ferrite as core materials displayed higher catalytic activities per manganese ion (2650 or 3150 mmolO2 molMn(-1) h(-1)) or per mass than nanoiron oxides (no activity) or birnessite alone (1850 mmolO2 molMn(-1) h(-1)). This indicates synergistic effects between the MnOx shell and the FeOx core of the composites and proves the potential of the presented core-shell approach for further catalyst optimization. Additionally, the FeOx cores of the particles allow magnetic recovery of the catalyst and might also be beneficial for applications in water-oxidizing anodes because the incorporation of iron might enhance the overall conductivity of the material.

Liquid flow deposited spinel (Ni,Mn)3O4 thin films for microbolometer applications

A liquid flow deposition (LFD) technique was initially used for the fabrication of single-component Mn3O4 thin films onto Si wafer substrates at a range of substrate temperatures of 30–80°C, with the introduction of an oxidizing reagent (H2O2). As a result, solid thin films were well formed from an aqueous solution. An X-ray diffraction (XRD) analysis showed typical characteristics of hausmannite Mn3O4 with a spinel tetragonal phase. Field-emission scanning electron microscopy (FE-SEM) observations revealed nano-sized grains arranged uniformly on a dense and smooth surface for all of the as-deposited films. On the other hand, the LFD method was then extended to prepare two-component nickel–manganite films according to the binary chemical composition of NixMn3−xO4 with x=0.02–0.2. The as-grown nickel–manganite films showed a surface with a good quality with a spherical bead-like architecture when x≤0.10, while a conversion from spherical grains into highly porous nanowalls in the microstructure was noted in films when x≥0.12. These results signify that it is possible to fabricate various multi-component manganite-oxide thin films at a low temperature. In addition, the dependences of the room-temperature electrical resistivity (ρ) and the temperature coefficient of resistance (TCR) on the Ni substitution level (x) were investigated on films annealed at 400°C.

Conditional pulmonary over-expression of Claudin 6 during embryogenesis delays lung morphogenesis.

Claudin 6 (Cldn6) is a tetraspanin protein expressed by barrier epithelial cells. In order to assess the effects of persistent tight junctions involving Cldn6 during lung development, a doxycycline (dox)-inducible conditional transgenic mouse was generated that up-regulates Cldn6 in the distal lung. Pups had unlimited access to dox from conception until sacrifice date at embryonic day (E) 18.5. Quantitative PCR, immunoblotting, and immunohistochemistry revealed significantly elevated Cldn6 expression in transgenic mice compared to non-transgenic controls. There were no differences in terms of lung size, lung weight, or whole body weight at the time of necropsy. Histological evaluations led to the discovery that E18.5 Cldn6 transgenic pups appeared to be in the early canalicular stage of development coincident with fewer, thickened respiratory airspaces. In contrast, controls appeared to have entered the saccular stage characterized by thin airspace walls and spherical architecture. Immunostaining for transcriptional regulators including TTF-1 and FoxA2 was conducted to assess cell differentiation and specific cell types were identified via staining for pro-surfactant protein C (alveolar type II epithelial cells) or Clara Cell Secretory Protein (cub or Clara cells). Lastly, cell turnover was qualitatively measured via staining for cell proliferation or apoptosis. These data suggest that Cldn6 is an important junctional protein potentially involved in the programming of epithelial cells during lung development. Furthermore, genetic down-regulation of Cldn6 as development proceeds may influence differentiation observed in the transition from the canalicular to the saccular lung.

Therapeutic applications of spherical nucleic acids.

Spherical nucleic acids (SNAs) represent an emerging class of nanoparticle-based therapeutics. SNAs consist of densely functionalized and highly oriented oligonucleotides on the surface of a nanoparticle which can either be inorganic (such as gold or platinum) or hollow (such as liposomal or silica-based). The spherical architecture of the oligonucleotide shell confers unique advantages over traditional nucleic acid delivery methods, including entry into nearly all cells independent of transfection agents and resistance to nuclease degradation. Furthermore, SNAs can penetrate biological barriers, including the blood-brain and blood-tumor barriers as well as the epidermis, and have demonstrated efficacy in several murine disease models in the absence of significant adverse side effects. In this chapter, we will focus on the applications of SNAs in cancer therapy as well as discuss multimodal SNAs for drug delivery and imaging.

Facile interfacial synthesis of large sized 3D gold spherical architectures with strong individual particle SERS response and high reproducibility

Large sized gold spherical architectures with strong individual particle SERS response and high reproducibility have been prepared at the toluene–water interface.

Biomimetic synthesis of nanostructured SnO particles from Sn6O4(OH)4in aqueous solution of gelatin

Nanostructured SnO particles were produced by aging Sn6O4(OH)4 in aqueous solutions containing HCl and gelatin at 60 °C, where the morphologies of the SnO products depended on the pH value and the gelatin concentration of the solutions. Flower-like and spherical architectures consisting of radially-branched platy units were obtained by the addition of gelatin, where the branching of SnO crystals was promoted with decreasing pH value and with increasing gelatin contents. The branched structures thus obtained could be formed via diffusion-controlled growth of SnO crystals in viscous solutions.

Facile fabrication of spherical architecture of Ni/Al layered double hydroxide based on in situ transformation mechanism

Spherical architectures of nickel–aluminum layered double hydroxide (NiAl‐LDH) with hydrotalcite‐like nanoflakes as building blocks were facilely fabricated by precipitation reaction in aqueous solution without any surfactants and organic solvents. Growth of such unique structure undergoes preorganization of primary nanospheres of colloidal amorphous aluminum hydroxide (AAH) in solution, followed by nucleation and crystallizaion of LDH from exterior to interior of AAH spheres by an in situ transformation mechanism. The structure and morphology of LDH spheres depend on both starting raw materials and synthetic parameters including reaction time, reaction temperature, and aqueous ammonia dosage. NiAl‐LDH sphere as positive electrode material delivers improved rechargeable and discharge capacity, with the highest discharge capacity of 173 mAh g−1 at a current density of 30 mA g−1 within a potential range from −0.1 to 0.45 V in 10 mol L−1 KOH solution, due to the faster diffusion processes in the spherical architecture than the powder sample. © 2014 American Institute of Chemical Engineers AIChE J 60: 4027–4036, 2014

Liposomal spherical nucleic acids.

A novel class of metal-free spherical nucleic acid nanostructures was synthesized from readily available starting components. These particles consist of 30 nm liposomal cores, composed of an FDA-approved 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid monomer. The surface of the liposomes was functionalized with DNA strands modified with a tocopherol tail that intercalates into the phospholipid layer of the liposomal core via hydrophobic interactions. The spherical nucleic acid architecture not only stabilizes these constructs but also facilitates cellular internalization and gene regulation in SKOV-3 cells.

Micrometer-size vesicle formation triggered by UV light.

Vesicle formation is a fundamental kinetic process related to the vesicle budding and endocytosis in a cell. In the vesicle formation by artificial means, transformation of lamellar lipid aggregates into spherical architectures is a key process and known to be prompted by e.g. heat, infrared irradiation, and alternating electric field induction. Here we report UV-light-driven formation of vesicles from particles consisting of crumpled phospholipid multilayer membranes involving a photoactive amphiphilic compound composed of 1,4-bis(4-phenylethynyl)benzene (BPEB) units. The particles can readily be prepared from a mixture of these components, which is casted on the glass surface followed by addition of water under ultrasonic radiation. Interestingly, upon irradiation with UV light, micrometer-size vesicles were generated from the particles. Neither infrared light irradiation nor heating prompted the vesicle formation. Taking advantage of the benefits of light, we successfully demonstrated micrometer-scale spatiotemporal control of single vesicle formation. It is also revealed that the BPEB units in the amphiphile are essential for this phenomenon.

Smart Stimuli-Responsive Spherical Nanostructures Constructed from Supramolecular Metallodendrimers via Hierarchical Self-Assembly

In this article, we present the design and construction of a series of supramolecular poly(benzyl ether) metallodendrimers featuring a well-defined hexagonal metallacycle at their cores via coordination-driven self-assembly. It was found that the second generation metallodendrimer 3c was able to hierarchically self-assemble into the regular vesicle-like structures. These nanoscale vesicles were monodisperse in shape and relatively monodisperse in size as detected in SEM, TEM, AFM, and DLS experiments. Notably, this kind of hierarchically formed vesicle-like nanostructure adopted a discrete metallacycle as the main skeleton, which is obviously different from many previous reports of nanoscale spherical architectures. Moreover, such supramolecular vesicle-like structures could encapsulate some fluorescent molecules, like BODIPY and SRB, etc. By taking advantage of the dynamic nature of metal-ligand bonds, the disassembly and reassembly of the hexagonal cavity core could be reversibly controlled by the addition and removal of bromide ions, resulting in the transition from the vesicles to micelles. Thus, the controlled release of fluorescence dye was successfully realized by the halide-induced vesicles-micelles transition. These findings not only enrich the library of supramolecular metallodenrimers but also provide a new avenue to the construction of novel "smart" nanomaterials, which have potential application in functional molecules delivery and release.

Photocatalytic and Antifungal Activity of Flower-Like Copper Oxide Nanostructures

CuO/Cu(OH)2 nanostructures composed of hierarchical two-dimensional (2D) nanosheets and spherical architectures constructed by ultrathin nanowalls in thickness were generated by simply immersing copper foil substrate into air, DI water, and 20 mM NH4OH solution at 25°C. The presence of hydroxyl groups in ammonia bath extremely affected the self-assembling of tiny 2D nanosheets and nanowalls into intricate hierarchical nanostructures. Raman spectroscopy as well as XRD patterns confirmed the presence of thick layer of the CuO monoclinic single-phase nanocrystals at the surface of sample grown in DI water where in alkaline bath, oxide and hydroxide phases were stabilized. Fungicidal activity in addition to photocatalytic methylene blue degradation of the CuO/Cu(OH)2 nanostructures were studied. The vertical nanoflakes of CuO/Cu(OH)2 grown at ammonia bath showed the strongest antifungal and photocatalytic activity among the samples.