Uniform Hierarchical Structure Research Articles

Rapid YFeO3 gas sensor for detecting formaldehyde working at room temperature

The YFeO3 (12 h, 24 h, 48 h and 72 h) microcrystals were prepared by hydrothermal process. Structural characterization using X-ray diffraction confirms the orthorhombic perovskite of the synthesized materials. YFeO3 based gas sensor has good selectivity to formaldehyde. The response value of YFeO3 (72 h) sensor is up to 318 for 100 ppm formaldehyde at room temperature. Furthermore, YFeO3 has an ultra-fast response-recovery time of about 6.3 s/0.9 s and exhibits excellent cycle repeatability and stability. This trait can play significant practical role in kind of sensors with real-time detectability. Further SEM and XPS analysis suggest that enhanced sensing property can be related to the uniform hierarchical structure and high oxygen vacancies. Our research indicates that adjusting the experimental approach can alter the structural and sensing properties of the sample.

Stable Deep‐Blue Electroluminescence from Hierarchical Crystalline Structure Based on Planar Conformational Terfluorenes: Benefits of Preventing Defect Structures Formation

AbstractLiner‐type organic conjugated molecules with 1D π‐electron delocalization present conformation‐dependent intramolecular optoelectronic behavior. Significantly different from non‐planar ones, the coplanar conformational backbone of π‐conjugated molecules can enhance intramolecular π‐electron delocalization and dominate intermolecular π‐electron coupling, which are the fundamental parameters for improving their optoelectronic properties. Herein, the effect of the formation of coplanar conformation on intermolecular packing and optoelectrical properties of liner‐type steric terfluorene (DSFX‐SFSO) toward solution‐processed deep‐blue organic light‐emitting diodes (OLEDs) is systematically demonstrated. Firstly, uniform and continuous crystalline films based on the planar conformational DSFX‐SFSO molecules are achieved via thermal annealing at 160 °C, which can avoid microscale crystallization processing. Contrary to amorphous ones, these hierarchical crystalline films present robust deep‐blue emission with an efficiency of > 60%, due to the suppression of defect structures. More interestingly, this hierarchical crystalline film has a stable and efficient deep‐blue electroluminescence (CIE: 0.15, 0.09) without the obvious defective green‐band emission, even at 500 mA cm−2, also further confirming the excellent and perfect molecular landscape to obtain single‐chromophore excitonic behavior from single planar‐terfluorene segments. Therefore, obtaining a uniform hierarchical structure based on planar conformational molecules is an effective strategy to optimize the optoelectrical properties for optoelectronic applications.

Hydrothermal Process to Prepare Novel Phase Titanium Sub-Oxide Ti6O11 from Nano Rutile Titanium Dioxide Particles with Different Autodave Reactors

Hydrothermal process method using different dimensions reactors with volume 100 ml (homemade) was employed to prepare titanium sub-oxide Ti6O11, where one gram of TiO2 nanoparticles 30-50 nm and 3M (20 ml) of NaOH as suspension was used . The samples are characterized using X-ray diffraction, Raman spectroscopy, and Field Emission Scanning Electron Microscopy (FE-SEM). X-ray diffraction revealed the formation of sub- oxide titanium Ti6O11 of triclinic structure with Magneli phase, when the temperature applied was 363K for 9h.While FE-SEM showed uniform hierarchical structures with planar grass-like shapes. A novel phase has been found from rutile titanium.

Fabrication of a superhydrophobic fabric with a uniform hierarchical structure via a bottom-blown stirring method for highly efficient oil–water separation

Highly efficient and multifunctional superhydrophobic fabrics have attracted widespread attention because of the urgent need for oil–water separation technologies. A superhydrophobic polyester fabric with a uniform surface roughness was fabricated via a novel bottom-blown stirring method. The water contact angle increased from 95.3° ± 1.1° of pure polyester fabric to 152.5° ± 0.7°, and the improved uniform roughness led to superhydrophobic fabric with a high separation efficiency (>99.5%) and oil flux (29443 L m−2 h−1), even after 10 cycles of oil–water separation. As the control group, the fabric prepared via traditional magnetic stirring methods could not separate the oil from the water after two cycles. Furthermore, the superhydrophobic fabric showed high mechanical abrasion resistance, even after 100 abrasion cycles on sandpaper (1000 mesh). In addition, the superhydrophobic fabric showed excellent self-cleaning properties and chemical stability. This work provides a new method for fabricating superhydrophobic fabrics with uniform roughness properties that lead to high separation efficiencies and abrasiveness for practical applications in oil–water separation.

Ball-in-ball hierarchical design of P2-type layered oxide as high performance Na-ion battery cathodes

Hierarchical microstructures assembled with nanostructures can effectively enhance the electrochemical performances of electrode materials for rechargeable Li/Na-ion batteries. Due to the large ionic radius of sodium, this kind of design and synthesis is more important for Na-battery cathodes, which represent a cost-effective alternative for energy storage applications. Here ball-in-ball hierarchical microspheres assembled with micron shaped flakes of the P2-type Na0.7Ni0.18Mn0.64Co0.18O2 have been designed and synthesized via hydrothermal reaction followed by stepwise calcination process. As a cathode material of the Na-ion battery, this novel and uniform hierarchical structure exhibits very high specific capacity and superior rate performance with discharge capacities of 208 mAh g−1 at 0.05 C and 46 mAh g−1 at 10 C, and an excellent cycling stability with about 78% capacity retention at 1 C after 50 cycles. These performances are better than any layered oxide cathode material for reversible Na-ion batteries reported in the literature, prepared via the conventional solid-state method. Combining ex-situ x-ray absorption spectroscopy characterization, x-ray diffraction, field emission scanning electron microscopy, scanning transmission electron microscopy and electrochemical characterization, we demonstrate that the superior performances can be attributed to the unique ball-in-ball hierarchical structure assembled with micron shaped flakes. This configuration could effectively reduce the path of Na ion diffusion, increases the contact area between electrodes and electrolyte and buffers the volume changes during the Na ion insertion/extraction processes.

A Highly Efficient Electrocatalyst Derived from Polyaniline@CNTs−SPS for the Oxygen Reduction Reaction

AbstractIt is of vital importance to develop novel, low‐cost, and high‐efficiency electrocatalysts for the oxygen reduction reaction (ORR), which have a considerable impact on electrochemical energy conversion and storage devices, such as fuel cells and metal−air batteries. In this work, we demonstrate highly active nitrogen‐doped carbons with uniform hierarchical structures through sulfonated polystyrene (SPS), regulating the distribution of the PANI covering on carbon nanotubes (CNTs), prepared by using a reliable and controllable route. The as‐prepared electrocatalyst shows outstanding activity towards the ORR in alkaline media, manifesting comparable or even better performance compared to commercial Pt/C. The optimized nitrogen‐doped CNTs exhibit an onset potential (Eonset) of 0.94 V (vs. reversible hydrogen electrode (RHE)) and half‐wave potential (E1/2) of 0.83 V (vs. RHE) in 0.1 M KOH with superior stability, durability, and methanol tolerance, suggesting their promising applications in fuel cells and metal−air batteries. The significantly improved electrochemical properties demonstrate that the unique SPS layer anchoring on the surface of CNTs in the as‐designed PANI@CNTs‐SPS contributes to a uniform distribution of nitrogen sites throughout the catalyst.

Mosquito eyes inspired surfaces with robust antireflectivity and superhydrophobicity

Inspired by the compound eyes of the mosquito, the uniform hierarchical structures with antireflectivity and superhydrophobicity has been designed and prepared by spinning technology. Microscale silica spheres and nanoscale colloidal particles were assembled on glass substrate to produce binary structures. To enhance the hydrophobicity, particles were modified by N-(β-aminoethyl)-γ-aminopropylmethylbimethoxy silane (KH-602) before deposition. And annealing process was used to strengthen the mechanical robustness. The resultant structures exhibited low reflections of less than 0.5%, and high static water contact angle (WCA) of larger than 160°. Furthermore, tape adhesion test and washing test showed that the artificial nano-/micro- structures had excellent mechanical robustness. Meanwhile the superhydrophobic surface owned the capacities of self-cleaning ability and chemical stability. We anticipate that these advantages could potentially enhance the performance of optoelectronic devices and help them to survive in terrible environment. Moreover, this self-assembly method is facile, cost effective, and suitable for high-throughput fabrication of binary colloidal arrays.

Hierarchical porous nano-MFI zeolite-pillared montmorillonite clay synthesized by recrystallization for hydrocracking of residual oil

An MFI zeolite nanosheet-pillared montmorillonite clay (MPC) with a uniform hierarchical structure was synthesized by a recrystallization method.

Architecture engineering toward highly active palladium integrated titanium dioxide yolk-double-shell nanoreactor for catalytic applications.

Rational design of the hierarchical architecture of a material with well controlled functionality is crucially important for improving its properties. In this paper, we present the general strategies for rationally designing and constructing three types of hierarchical Pd integrated TiO2 double-shell architectures, i.e. yolk-double-shell TiO2 architecture (Pd@TiO2/Pd@TiO2) with yolk-type Pd nanoparticles residing inside the central cavity of the hollow TiO2 structure; ultrafine Pd nanoparticles homogenously dispersed on both the external and internal surfaces of the inner TiO2 shell; and double-shell TiO2 architecture (@TiO2/Pd@TiO2) with Pd nanoparticles solely loaded on the external surface of the inner TiO2 shell, and double-shell TiO2 architecture (@TiO2@Pd@TiO2) with Pd nanoparticles dispersed in the interlayer space of double TiO2 shells, via newly developed Pd(2+) ion-diffusion and Pd sol impregnation methodologies. These architectures are well controlled in structure, size, morphology, and configuration with Pd nanoparticles existing in various locations. Owing to the variable synergistic effects arising from the location discrepancies of Pd nanoparticle in the architectures, they exhibit remarkable variations in catalytic activity. In particular, different from previously reported yolk-shell structures, the obtained yolk-double-shell Pd@TiO2/Pd@TiO2 architecture, which is revealed for the first time, possesses a uniform hierarchical structure, narrow size distribution, and good monodispersibility, and it creates two Pd-TiO2 interfaces on the external and internal surfaces of the inner TiO2 shell, leading to the strongest synergistic effect of Pd nanoparticles with TiO2 shell. Furthermore, the interlayer chamber between the double TiO2 shells connecting with the central cavity of the hollow TiO2 structure through the mesoporous TiO2 wall forms a nanoreactor for enriching the reactants and preventing the deletion of Pd nanoparticles during the reaction, thus greatly accelerating the reaction speed. Owing to its structural features, yolk-double-shell Pd@TiO2/Pd@TiO2 architecture exhibits extremely high catalytic performance on the Suzuki-Miyaura coupling reaction. The synthetic methodologies are robust for fabricating double-shell architectures with various configurations for applications such as in catalysis, drug delivery, and medicine release. The obtained double-shell architectures may be used as novel catalyst systems with highly efficient catalytic performance for other catalytic reactions.

A high activity photocatalyst of hierarchical 3D flowerlike ZnO microspheres: Synthesis, characterization and catalytic activity

In this study, three-dimensional (3D) hierarchical flowerlike ZnO microspheres have been hydrothermally synthesized by means of two surfactants at 100°C and characterized by XRD, SEM, TEM, TG, FT-IR and UV–Vis spectroscopies. The results show that the 3D flowerlike ZnO microspheres are composed of 2D nanosheets. A possible formation mechanism is proposed: 0D Zn5(CO3)2(OH)6 colloids tend to form 2D nanosheets with the aid of sodium dodecyl sulfonic, and then, these nanosheets can assemble to 3D flowerlike microspheres by means of two surfactants of sodium dodecyl sulfonic and PEG 600. The flowerlike ZnO has low bandgap energy and exhibits high catalytic activity for photocatalytic degradation of Rhodamin B, which is attributed to its unique morphology and uniform hierarchical structure that significantly facilitates the diffusion and mass transportation of organic molecules and oxygen species in the degradation reaction.

Luminescence properties of hierarchical CaMoO 4 microspheres derived by ionic liquid-assisted process

Hierarchical calcium molybdate (CaMoO 4) nanostructured microspheres were synthesized via a facile room-temperature route assisted by an ionic liquid, 1- n-butyl-3-methylimidazolium chloride. The product was characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that micro-scaled CaMoO 4 powders were assembled by nanoparticles with diameters ranging from 10 to 20 nm. The optical absorbance, photoluminescence emission (PL), and luminescence excitation (PLE) were investigated. The PL spectra excited at 273 nm have a strong green emission band maximum at 511 nm, which is attributed to the charge-transfer transitions within the MoO 4 2− complex, and the luminescence intensity indicated a good luminescence quality of the CaMoO 4 materials. By varying the amount of this assisted agent, we found that the ionic liquid played a crucial role as a surfactant in the formation of CaMoO 4 materials with uniform hierarchical structure, which may be beneficial to the luminescence performance. This study presented a promising preparation strategy towards other luminescent materials.