Structure-directing Template Research Articles

A simple approach for fabrication of interconnected graphitized macroporous carbon foam with uniform mesopore walls by using hydrothermal method

Three-dimensional (3D) highly interconnected graphitized macroporous carbon foam with uniform mesopore walls has been successfully fabricated by a simple and efficient hydrothermal approach using resorcinol and formaldehyde as carbon precursors. The commercially available cheap polyurethane (PU) foam and Pluronic F127 were used as a sacrificial polymer and mesoporous structure-directing templates, respectively. The graphitic structure of carbon foam was obtained by catalytic graphitization method using iron as catalyst. Three different carbon foams such as graphitized macro-mesoporous carbon (GMMC) foam, amorphous macro-mesoporous carbon (AMMC) foam and graphitized macroporous carbon (GMC) foam were fabricated and their physicochemical and mechanical properties were systematically measured and compared. It was found that GMMC possess well interconnected macroporous structure with uniform mesopores located in the macroporous skeletal walls of continuous framework. Besides, GMMC foam possesses a well-defined graphitic framework with high surface area (445m2/g), high pore volume (0.35cm3/g), uniform mesopores (3.87nm), high open porosity (90%), low density (0.30g/cm3) with good mechanical strength (1.25MPa) and high electrical conductivity (11S/cm) which makes it a promising material for many potential applications.

Soluble salt self-assembly-assisted synthesis of three-dimensional hierarchical porous carbon networks for supercapacitors

Three-dimensional hierarchical porous carbons are synthesized via a simple one-pot method using the self-assembly of various water-soluble salts as structure-directing templates, which exhibit excellent capacitive performance.

Dependency of magnetic microwave absorption on surface architecture of Co20Ni80 hierarchical structures studied by electron holography.

To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as -33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<-10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g(-1) for urchin-like and 96.41 emu g(-1) for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ''(μ')(-2)(f)(-1) is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.

Surfactant-free synthesis of SrTiO3 hierarchical structures in ethanol/water mixed solvent at room temperature

SrTiO3 hierarchical structures can be synthesized in ethanol/water mixed solvent at room temperature without using any structure-directing templates.

Facile synthesis of PbS nanorods induced by concentration difference

This report describes a simple method to synthesize PbS nanorods by aqueous chemical method under ambient conditions without the surface-capping molecules or structure-directing templates. X-ray diffraction studies revealed that the prepared sample is a polycrystalline powder crystallized in face centered cubic (fcc) PbS structure with the crystallites orientated preferentially along the (200) direction. The SEM analysis shows the formation of PbS nanorods of width 80nm and length 410nm. The compositional analysis confirms the presence of Pb and S. The optical absorption study of PbS nanostructures shows the blue-shift with respect to those of the bulk counterpart due to quantum confinement effect. Electrical measurement reveals that the prepared PbS nanorods exhibits the semiconducting nature.

Trigonal pyramidal oxyanions as structure-directing templates for the synthesis of silver dithiolate clusters

Trigonal pyramidal oxyanions, EO 3 2− (E = S, Se, Te), were utilized as a template in the formation of Ag16 clusters, which dimerize via intermolecular Ag-S bonds to form a Ag32 cluster stabilized by 1,1-dithiolate ligands. Structural elucidations on [Ag16(EO3){S2P(OEt)2}12]2+ in comparison with tetrahedral oxyanioncentered Ag16 clusters previously characterized from this group clearly suggest that the lone-pair electrons on chalcogen center has a structure-directing effect.

Effect of Mg doping on growth and photoluminescence of AlN hexagonal nanorods

Pure and Mg-doped AlN hexagonal nanorods (HNRs) were synthesized by a simple thermal chemical vapor deposition process without structure-directing templates or catalysts. Mg incorporation promoted not only axial but also radial growth rate of AlN HNRs compared to undoped sample. The corresponding optical properties of the products were investigated by room-temperature photoluminescence (PL) measurement. Quite broad ultraviolet emission bands centered at 280nm and 330nm for AlN HNRs and AlN:Mg HNRs, respectively, were observed. Multi-peak fitting analysis shows that various defects conduced to the broad emission bands of the two samples, and Mg doping has increased the proportion of VN which changed the relative intensity of peaks, instead of forming Mg impurity energy levels that directly affect luminescence.

A benign hydrothermal synthesis of nanopencils-like zinc oxide nanoflowers

Synthesis of zinc oxide (ZnO) nanoflowers and nanopencils is normally carried out with the help of structure-directing chemicals and templates. Besides releasing environmentally toxic substances, the use of these chemicals restricts the practical applications of nanostructures. In this paper, we report a typical template-free and environmentally benign synthesis of ZnO nanoflowers with nanopencils-like petals through a facile hydrothermal method. The as-synthesized ZnO nanoflowers were characterized using X-ray diffraction, field emission scanning electron microscopy, tunneling electron microscopy (TEM), high resolution TEM, and energy-dispersive X-ray spectroscopy techniques. The results reveal high quality and impurity-free hexagonal wurtzite phase ZnO nanoflowers of nanopencils-like petals having a length of 100–150 nm and a diameter of 45–60 nm.

Alkaline earth guests in polyoxopalladate chemistry: from nanocube to nanostar via an open-shell structure.

The three novel, discrete palladium(II)-oxo clusters [CaPd12O8(PhAsO3)8](6-) (CaPd12), [SrPd12O6(OH)3(PhAsO3)6(OAc)3](4-) (SrPd12), and [BaPd15O10(PhAsO3)10](8-) (BaPd15) encapsulating alkaline earth metal ions were prepared and fully characterized by a multitude of solution and solid-state physicochemical techniques. We have discovered a structure-directing template effect induced by the respective size of the alkaline earth guest ion, which determines the detailed condensation arrangement of the peripheral Pd(II)-oxo shell. The unprecedented SrPd12 with an open-shell type structure is of particular importance and reflects a successful strategy for deliberate design of new structural classes of polyoxo-noble-metalates. Furthermore, the unusual acetate-water ligand exchange phenomenon renders SrPd12 as a promising candidate for noble-metal-based catalysis.

Thermochromic luminescent nest-like silver thiolate cluster.

A novel discrete open high-nuclearity nest-like silver thiolate cluster complex, [Ag33 S3 (StBu)16 (CF3 COO)9 (NO3 )(CH3 CN)2 ](NO3 ) (1), has been isolated with nitrate and S(2-) anions acting as structure-directing templates. Its similar nest-like structure has been assembled into an extended layer [Ag31 S3 (StBu)16 (NO3 )9 ]n (2) by adjustment of auxiliary ligand. More interestingly, both complexes exhibit temperature-dependent luminescence of high sensitivity with a large fluorescence enhancement (12-fold for 1, 21-fold for 2), which can be easily recognized by the naked-eye (dramatic red-shift Δ=104 nm for 1, larger Δ=113 nm for 2 at 77 K compared to those at 298 K). The correlation between luminescent thermochromism and temperature-dependent variation of the coordination modes of template NO3 (-) anion, Ag⋅⋅⋅S and Ag⋅⋅⋅Ag distances are also elucidated through variable-temperature single-crystal X-ray crystal structure (VT-SCXRD) analyses.

Open Framework Fluorides As Insertion/Conversion Cathodes for Li and Na Batteries

Recently, low-density porous framework solids, such as materials based on metal-organic frameworks (MOFs), zeolitic frameworks, or Prussian blue (PB) analogues, have been attracting significant attention because of their diverse applications as energy storage materials, proton conductors, wide-band-gap semiconductors, catalysts, selective gas absorbers, and nanoporous carbon precursors. These phases are generally assembled at low temperature by precipitation, solvothermal, or ionothermal synthesis. Ionic liquids (ILs) are well-suited candidates as reaction media, with the cations potentially serving as structure-directing templates to order and polymerize surrounding inorganic/organic units, likely leading to structural expansion with lowered crystal density. This strategy was recently discovered to be especially useful for developing novel open-structure Li storage cathodes (e.g., tavorite polyanion frameworks or iron fluoride polymorphs [1-4]) that are characterized by enhanced ion transport in multidimensional channels and extended solid-solution reaction zones.Electroactive MOFs and PB analogues exhibit quite open channels, the sizes of which may even reach the mesoporous range and hence exceed the optimal width for ion insertion. Furthermore, these frameworks are usually of high molecular weight because of their heavy skeletons and/or the existence of channel fillers. As far as electrochemical storage is concerned, these factors limit the reversible capacity in the context of Li batteries. In terms of electrochemical storage, not only are Li-based batteries of interest, but also in view of globally limited Li resources, Na-based batteries are seen as a potential alternative for both electric vehicles and large-scale grid-based electrical energy storage. As the ionic radius of Na+ (1.02 Å) is 34% larger than that of Li+(0.76 Å), suitable Li storage materials are not automatically feasible for Na batteries, and in turn, channels that are oversized for Li may be well-suited for Na. To further improve the energy/power density of Li- or Na-based batteries, structure modification of oxide/polyanion materials with moderate expansion of ion channels has been demonstrated to be a successful strategy. However, one should pay attention to the fact that the synthesis of more expanded structures usually comes at the cost of a decrease in ion channel dimensionality, mostly leading to the formation of 1D or 2D channel structures that have a greater potential to become blocked or degraded. Also, in the case of interconnected open 3D channels, structure expansion upon storage is still a great challenge. Fluorides are expected to exhibit larger capacities than most of the oxides without tradeoffs in terms of working voltage as long as their poor conductivity can be compensated. In the past decades, such studies mainly focused on commercially available ReO3-type FeF3 electroactivated by high-energy ball milling of FeF3/C composites to generate C-FeF3 nanodomains as insertion or conversion cathodes for Li batteries. Recently, our group prepared an open-structure fluoride for Li battery applications.[2,5] As reported for the hexagonal tungsten−bronze (HTB)-type compound FeF3·0.33H2O characterized by open 1D channels, the Li insertion mechanism was intrinsically modified, and the miscibility gap present in ReO3-type FeF3 was completely removed in the HTB phase, favoring complete solid-solution behavior in the 3 V region. An improved intrinsic conductivity enabled the fluoride to act as a highly electroactive Li battery cathode without in situ addition of conductive species. However, the presence of single ion channels, which are prone to partial blockage by H2O molecule fillers, still limits the extension of fluoride materials into Na batteries.Most recently, we report a novel open-framework fluoride pyrochlore phase, FeF3·0.5H2O, that is structurally similar to the known AlF3·0.5H2O and characterized by a much larger cell volume (∼1130 Å3) than in HTB-type FeF3·0.33H2O (∼710 Å3) or ReO3-type FeF3 (∼310 Å3). [6] Notably, it exhibits a higher pore density due to interconnected 3D ion channels without a serious tradeoff concerning channel size compared with HTB-type fluoride, suggesting a more favorable cation insertion capacity. The storage performance should also benefit from the more tightly confined H2O molecules in the zigzag channels of the pyrochlore phase as opposed to the straight channels of the HTB phase.

H2V3O8 nanobelts as a novel stable electrode material with good reversible redox performance

Belt-like nanocrystalline H2V3O8 has been successfully synthesized via a hydrothermal process using vanadium pentoxide as inorganic precursor and 1,4-butanediol as structure-directing template. It is found that the reaction time has a significant effect on the morphology of the product. The as-synthesized H2V3O8 nanobelts are up to several of micrometers in length and about 35nm in average width. The nanobelts show a large BET surface area which favors the electrochemical properties. The optical properties of the as-synthesized H2V3O8 nanobelts were investigated by UV–visible absorption and photoluminescence. The band gap was found to be 2.75eV. Electrochemical measurements have revealed reversible redox behavior with doping/dedoping process corresponding to reversible cation intercalation/deintercalation. This process is easier in propylene carbonate than in aqueous solvent and is easier for the small Li+ to the larger Na+ one and to the largest K+ cation. This has been assigned to a probable presence of different tunnel cavities in the orthorhombic H2V3O8 lattice.

A new strategy for co-assembling π-conjugated polymer/cadmium sulfide hybrids into an efficient charge-transporting nanochannel array by using an all-conjugated diblock copolymer motif

In this study, a novel organic/inorganic hybrid material containing cadmium sulfide (CdS) nanoparticles was synthesized in situ by using an all π-conjugated block copolymer as both a synergistic long-range ordered structure-directing template and an efficient exciton quencher for the nanohybrid. The conducting–conducting block copolymer of poly(2,5-dihexyloxy-para-phenylene)-b-poly(3-hexyl thiophene) (PPP-P3HT) was used as a linear nanoreactor for the quantum dot synthesis to yield nanohybrids with highly ordered donor/acceptor (D/A) nanowire morphology that exhibit enhanced optoelectronic properties. The synthesized PPP-P3HT/CdS-OH nanohybrid possessed a one-dimensional D/A coaxial nanowire structure of uniform width (∼10 nm), wherein the synthesized CdS quantum dots were embedded, resulting in a display of superior long-term stability in a solution medium. By a simple drop casting process, the hybrid materials with highly ordered organic/inorganic nanochannel arrays could also be preserved in a thin film state, as evidenced by TEM and X-ray measurements, for device applications. The PPP-P3HT block copolymer exhibited significantly better hole mobility than its P3HT homopolymer counterpart. In addition, the resulting PPP-P3HT/CdS-OH hybrid systems displayed a considerably enhanced PL quench effect and shorter exciton lifetime due to efficient charge transfer between the P3HT block and the confining CdS nanoparticles in the P3HT/CdS coaxial domain of the hybrid nanowire structure. Therefore, the PPP-P3HT/CdS-OH nanohybrids can be used as bicontinuous nanochannels for efficient charge separation and charge transport, which show potential for use in future optoelectronic applications.

Preparation of three-dimensionally ordered macroporous polycysteine film and application in sensitive detection of 4-chlorophenol

Polystyrene microspheres with diameter of 350nm were prepared, and then used to arrange on the surface of glassy carbon electrode (GCE) as structure-directing template. By successive cyclic sweeps between −1.0V and 2.0V in pH 7 phosphate buffer containing 10mM cysteine, polycysteine film was electrodeposited on polystyrene microspheres-arranged GCE. After removing polystyrene template, a three-dimensionally ordered macroporous (3-DOM) polycysteine film was achieved, as confirmed by scanning electron microscopy measurements. Electrochemical responses of K3[Fe(CN)6] probe indicated that 3-DOM polycysteine film-modified GCE exhibited larger active area, compared with GCE, polycysteine film-modified GCE and electrochemically oxidized GCE. The application of 3-DOM polycysteine film in electrochemical detection of 4-chlorophenol was studied. Due to ordered porous structures, the 3-DOM polycysteine film-modified GCE displayed signal enhancement effects, and enhanced the oxidation peak currents of 4-chlorophenol. As a result, a sensitive electrochemical method was developed for the detection of 4-chlorophenol, and the detection limit was 1.67×10−8M. This new method was used to detect 4-chlorophenol in water samples, and the value of recovery was over the range from 99.6% to 107%.

TiO2 Nanospheres: A Facile Size‐Tunable Synthesis and Effective Light‐Harvesting Layer for Dye‐Sensitized Solar Cells

A facile route to synthesize amorphous TiO2 nanospheres by a controlled oxidation and hydrolysis process without any structure-directing agents or templates is presented. The size of the amorphous TiO2 nanospheres can be easily turned from 20 to 1500 nm by adjusting either the Ti species or ethanol content in the reaction solution. The phase structure of nanospheres can be controlled by hydrothermal treatment. The TiO2 nanospheres show excellent size-dependent light-scattering effects and can be structured into a light-harvesting layer for dye-sensitized solar cells with a quite high power conversion efficiency of 9.25 %.

Graphene Coupled Schiff‐base Porous Polymers: Towards Nitrogen‐enriched Porous Carbon Nanosheets with Ultrahigh Electrochemical Capacity

Schiff-base type porous polymer sheets with ultrahigh nitrogen content have been successfully synthesized by utilizing aminated graphene oxide as a 2D structure-directing template via dynamic covalent chemistry. Nitrogen-enriched porous carbon nanosheets were thus prepared by thermal pyrolysis of the 2D porous polymers, showing exceptionally high capacitance up to 424 F g(-1) at 0.1 A g(-1) in 6 m KOH, superior to that of porous carbons without graphene involved.

Synthesis of colloidal silicalite-1 at high temperatures

Stable colloidal suspensions of silicalite-1 were prepared by hydrothermal treatment of clear precursor suspensions at high temperatures, 150 and 170°C. The precursor suspensions were pretreated prior to hydrothermal treatment. Different pretreatment procedures were applied, namely ultrasonic treatment or heating at 45–60°C, for different periods of time. In all cases, the size of the crystals decreased with increasing the time of pretreatment. The pretreatment procedure was found to influence the behavior of the tetrapropylammonium hydroxide solution used as structure-directing template during hydrothermal treatment. Colloidal stability of pretreated samples was improved compared to samples prepared by direct hydrothermal treatment.

Custom‐Made Morphologies of ZnO Nanostructured Films Templated by a Poly(styrene‐block‐ethylene oxide) Diblock Copolymer Obtained by a Sol–Gel Technique

Zinc oxide (ZnO) nanostructured films are synthesized on silicon substrates to form different morphologies that consist of foamlike structures, wormlike aggregates, circular vesicles, and spherical granules. The synthesis involves a sol-gel mechanism coupled with an amphiphilic diblock copolymer poly(styrene-block-ethylene oxide), P(S-b-EO), which acts as a structure-directing template. The ZnO precursor zinc acetate dihydrate (ZAD) is incorporated into the poly(ethylene oxide) block. Different morphologies are obtained by adjusting the weight fractions of the solvents and ZAD. The sizes of the structure in solution for different sol-gels are probed by means of dynamic light scattering. Thin-film samples with ZnO nanostructures are prepared by spin coating and solution casting followed by a calcination step. On the basis of various selected combinations of weight fractions of the ingredients used, a ternary phase diagram is constructed to show the compositional boundaries of the investigated morphologies. The evolution and formation mechanisms of the morphologies are addressed in brief. The surface morphologies of the ZnO nanostructures are studied with SEM. The inner structures of the samples are probed by means of grazing incidence small-angle X-ray scattering to complement the SEM investigations. XRD measurements confirm the crystallization of the ZnO in the wurtzite phase upon calcination of the nanocomposite film in air. The optical properties of ZnO are analyzed by FTIR and UV/Vis spectroscopy.

Hexagonal hydrated tungsten oxide nanomaterials: Hydrothermal synthesis and electrochemical properties

Nanocrystalline hexagonal hydrated tungsten oxide h-WO3·1/3H2O has been synthesized by hydrothermal process using sodium tungstate as inorganic precursor and three n-alkyl chain sodium sulfate surfactants (n=10, 12 and 14) as structure-directing templates. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the structure, the morphology and the composition of the material. The length of the alkyl chain of the surfactant molecules has a marked effect on the morphology and, particularly, on the particle size of the material. Nanofibers (about 50nm in diameter) are obtained when sodium decyl sulfate is used as surfactant. Whereas, nanoneedles are obtained with sodium dodecyl (about 60nm in diameter) or sodium tetradecyl sulfate (about 80nm in diameter) as surfactant.Thin films of h-WO3·1/3H2O deposited on ITO substrates were electrochemically characterized by cyclic voltammetry; they show the same behavior whatever the surfactant. The voltammograms show reversible redox behavior with doping/dedoping process corresponding to reversible cation intercalation/de-intercalation into the crystal lattice of the nanofibers. This process is easier in propylene carbonate than in aqueous solvent and is easier for the small Li+ cation than larger ones, Na+ and K+. This is attributed to probable presence of two different tunnel cavities in the h-WO3·1/3H2O lattice.

Rapid hydrothermal synthesis of MIL-101(Cr) metal–organic framework nanocrystals using expanded graphite as a structure-directing template

Abstract Nanoscale MIL-101(Cr) metal–organic frameworks with giant pores, very large Brunauer–Emmett–Teller surface areas, and small dimensions in the nanoscale regime, were synthesized in high yields by an expanded graphite (EG)-templated hydrothermal strategy. Compared with a conventional hydrothermal method, the size of the MIL-101(Cr) crystals can be well controlled at nanoscale and the reaction time can be largely shortened from 8 to 2 h using such an EG-templated hydrothermal method. The size of the MIL-101(Cr) crystals can be well controlled and the synthesis cycle can be largely shortened for many practical applications.