Enhancing Photoactivity of TiO2(B)/Anatase Core–Shell Nanofibers by Selectively Doping Cerium Ions into the TiO2(B) Core

Cerium ions (Ce³⁺⁾ can be selectively doped into the TiO₂(B) core of TiO₂(B)/anatase core–shell nanofibers by means of a simple one‐pot hydrothermal treatment of a starting material of hydrogen trititanate (H₂Ti₃O₇) nanofibers. These Ce³⁺ ions (≈0.202 nm) are located on the (110) lattice planes of the TiO₂(B) core in tunnels (width≈0.297 nm). The introduction of Ce³⁺ ions reduces the defects of the TiO₂(B) core by inhibiting the faster growth of (110) lattice planes. More importantly, the redox potential of the Ce³⁺/Ce⁴⁺ couple (E°(Ce³⁺/Ce⁴⁺)=1.715 V versus the normal hydrogen electrode) is more negative than the valence band of TiO₂(B). Therefore, once the Ce³⁺‐doped nanofibers are irradiated by UV light, the doped Ce³⁺ ions—in close vicinity to the interface between the TiO₂(B) core and anatase nanoshell—can efficiently trap the photogenerated holes. This facilitates the migration of holes from the anatase shell and leaves more photogenerated electrons in the anatase nanoshell, which results in a highly efficient separation of photogenerated charges in the anatase nanoshell. Hence, this enhanced charge‐separation mechanism accelerates dye degradation and alcohol oxidation processes. The one‐pot treatment doping strategy is also used to selectively dope other metal ions with variable oxidation states such as Co^2+/3+ and Cu^+/2+ ions. The doping substantially improves the photocatalytic activity of the mixed‐phase nanofibers. In contrast, the doping of ions with an invariable oxidation state, such as Zn²⁺, Ca²⁺, or Mg²⁺, does not enhance the photoactivity of the mixed‐phase nanofibers as the ions could not trap the photogenerated holes.     

Electrochemical Properties of Fiber‐in‐Tube‐ and Filled‐Structured TiO2 Nanofiber Anode Materials for Lithium‐Ion Batteries

Phase‐pure anatase TiO₂ nanofibers with a fiber‐in‐tube structure were prepared by the electrospinning process. The burning of titanium‐oxide‐carbon composite nanofibers with a filled structure formed as an intermediate product under an oxygen atmosphere produced carbon‐free TiO₂ nanofibers with a fiber‐in‐tube structure. The sizes of the nanofiber core and hollow nanotube were 140 and 500 nm, respectively. The heat treatment of the electrospun nanofibers at 450 and 500 °C under an air atmosphere produced grey and white filled‐structured TiO₂ nanofibers, respectively. The initial discharge capacities of the TiO₂ nanofibers with the fiber‐in‐tube and filled structures and the commercial TiO₂ nanopowders were 231, 134, and 223 mA h g^?1, respectively, and their corresponding charge capacities were 170, 100, and 169 mA h g^?1, respectively. The 1000th discharge capacities of the TiO₂ nanofibers with the fiber‐in‐tube and filled structures and the commercial TiO₂ nanopowders were 177, 64, and 101 mA h g^?1, respectively, and their capacity retentions measured from the second cycle were 89, 82, and 52 %, respectively. The TiO₂ nanofibers with the fiber‐in‐tube structure exhibited low charge transfer resistance and structural stability during cycling and better cycling and rate performances than the TiO₂ nanofibers with filled structures and the commercial TiO₂ nanopowders.     

Mesoporous Carbon Nanofibers Embedded with MoS2 Nanocrystals for Extraordinary Li‐Ion Storage

MoS₂ nanocrystals embedded in mesoporous carbon nanofibers are synthesized through an electrospinning process followed by calcination. The resultant nanofibers are 100–150 nm in diameter and constructed from MoS₂ nanocrystals with a lateral diameter of around 7 nm with specific surface areas of 135.9 m² g^?1. The MoS₂@C nanofibers are treated at 450 °C in H₂ and comparison samples annealed at 800 °C in N₂. The heat treatments are designed to achieve good crystallinity and desired mesoporous microstructure, resulting in enhanced electrochemical performance. The small amount of oxygen in the nanofibers annealed in H₂ contributes to obtaining a lower internal resistance, and thus, improving the conductivity. The results show that the nanofibers obtained at 450 °C in H₂ deliver an extraordinary capacity of 1022 mA h g^?1 and improved cyclic stability, with only 2.3 % capacity loss after 165 cycles at a current density of 100 mA g^?1, as well as an outstanding rate capability. The greatly improved kinetics and cycling stability of the mesoporous MoS₂@C nanofibers can be attributed to the crosslinked conductive carbon nanofibers, the large specific surface area, the good crystallinity of MoS₂, and the robust mesoporous microstructure. The resulting nanofiber electrodes, with short mass‐ and charge‐transport pathways, improved electrical conductivity, and large contact area exposed to electrolyte, permitting fast diffusional flux of Li ions, explains the improved kinetics of the interfacial charge‐transfer reaction and the diffusivity of the MoS₂@C mesoporous nanofibers. It is believed that the integration of MoS₂ nanocrystals and mesoporous carbon nanofibers may have a synergistic effect, giving a promising anode, and widening the applicability range into high performance and mass production in the Li‐ion battery market.     

Synthesis of Monodisperse Hollow Carbon Nanocapsules by Using Protective Silica Shells

Monodisperse hollow carbon nanocapsules (<200 nm) with mesoporous shells were synthesized by coating their outer shells with silica to prevent aggregation during their high‐temperature annealing. Monodispersed silica nanoparticles were used as starting materials and octadecyltrimethoxysilane (C18TMS) was used as a carbon source to create core–shell nanostructures. These core–shell nanoparticles were coated with silica on their outer shell to form a second shell layer. This outer silica shell prevented aggregation during calcination. The samples were characterized by TEM, SEM, dynamic light scattering (DLS), UV/Vis spectroscopy, and by using the Brunauer–Emmett–Teller (BET) method. The as‐synthesized hollow carbon nanoparticles exhibited a high surface area (1123 m² g^?1) and formed stable dispersions in water after the pegylation process. The drug‐loading and drug‐release properties of these hollow carbon nanocapsules were also investigated.     

Mesoporous Core–Shell Fenton Nanocatalyst: A Mild,Operationally Simple Approach to the Synthesis of Adipic Acid

Mesoporous nanoparticles composed of γ‐Al₂O₃ cores and α‐Fe₂O₃ shells were synthesized in aqueous medium. The surface charge of γ‐Al₂O₃ helps to form the core–shell nanocrystals. The core–shell structure and formation mechanism have been investigated by wide‐angle XRD, energy‐dispersive X‐ray spectroscopy, and elemental mapping by ultrahigh‐resolution (UHR) TEM and X‐ray photoelectron spectroscopy. The N₂ adsorption–desorption isotherm of this core–shell materials, which is of type IV, is characteristic of a mesoporous material having a BET surface area of 385 m² g^?1 and an average pore size of about 3.2 nm. The SEM images revealed that the mesoporosity in this core–shell material is due to self‐aggregation of tiny spherical nanocrystals with sizes of about 15–20 nm. Diffuse‐reflectance UV/Vis spectra, elemental mapping by UHRTEM, and wide‐angle XRD patterns indicate that the materials are composed of aluminum oxide cores and iron oxide shells. These Al₂O₃@Fe₂O₃ core–shell nanoparticles act as a heterogeneous Fenton nanocatalyst in the presence of hydrogen peroxide, and show high catalytic efficiency for the one‐pot conversion of cyclohexanone to adipic acid in water. The heterogeneous nature of the catalyst was confirmed by a hot filtration test and analysis of the reaction mixture by atomic absorption spectroscopy. The kinetics of the reaction was monitored by gas chromatography and ¹H NMR spectroscopy. The new core–shell catalyst remained in a separate solid phase, which could easily be removed from the reaction mixture by simple filtration and the catalyst reused efficiently.     

Exploring meso-/microporous composite molecular sieves with core-shell structures

A series of core–shell‐structured composite molecular sieves comprising zeolite single crystals (i.e., ZSM‐5) as a core and ordered mesoporous silica as a shell were synthesized by means of a surfactant‐directed sol–gel process in basic medium by using cetyltrimethylammonium bromide (CTAB) as a template and tetraethylorthosilicate (TEOS) as silica precursor. Through this coating method, uniform mesoporous silica shells closely grow around the anisotropic zeolite single crystals, the shell thickness of which can easily be tuned in the range of 15–100 nm by changing the ratio of TEOS/zeolite. The obtained composite molecular sieves have compact meso‐/micropore junctions that form a hierarchical pore structure from ordered mesopore channels (2.4–3.0 nm in diameter) to zeolite micropores (≈0.51 nm). The short‐time kinetic diffusion efficiency of benzene molecules within pristine ZSM‐5 (≈7.88×10^?19 m² s^?1) is almost retainable after covering with 75 nm‐thick mesoporous silica shells (≈7.25×10^?19 m² s^?1), which reflects the greatly opened junctions between closely connected mesopores (shell) and micropores (core). The core–shell composite shows greatly enhanced adsorption capacity (≈1.35 mmol g^?1) for large molecules such as 1,3,5‐triisopropylbenzene relative to that of pristine ZSM‐5 (≈0.4 mmol g^?1) owing to the mesoporous silica shells. When Al species are introduced during the coating process, the core–shell composite molecular sieves demonstrate a graded acidity distribution from weak acidity of mesopores (predominant Lewis acid sites) to accessible strong acidity of zeolite cores (Lewis and Brønsted acid sites). The probe catalytic cracking reaction of n‐dodecane shows the superiority of the unique core–shell structure over pristine ZSM‐5. Insight into the core–shell composite structure with hierarchical pore and graded acidity distribution show great potential for petroleum catalytic processes.     

Template‐Free Synthesis of Core–Shell TiO2 Microspheres Covered with High‐Energy {116}‐Facet‐Exposed N‐Doped Nanosheets and Enhanced Photocatalytic Activity under Visible Light

Core–shell TiO₂ microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high‐energy facets of TiO₂ also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core–shell structure is difficult to achieve and requires multiple‐steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high‐energy facet production. Therefore, it is still a significant challenge to develop low‐temperature, template‐free, shape‐controlled, and relative green self‐assembly routes for the formation of core–shell‐structured TiO₂ microspheres with high‐energy facets. Here, we report a template‐ and hydrofluoric acid free solvothermal self‐assembly approach to synthesize core–shell TiO₂ microspheres covered with high‐energy {116}‐facet‐exposed nanosheets, an approach in which 1,4‐butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high‐energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6‐tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core–shell structure, {116}‐plane‐oriented nanosheets, in situ N doping, and large surface areas has been found.     

Solution‐blown nylon 6–chitosan core–shell nanofiber for highly efficient affinity adsorption

A facile spinning‐based strategy was developed to fabricate chitosan (CS) surface nanofiber‐based affinity membranes for protein adsorption. The core–shell nanofiber mat of nylon 6–CS was prepared via coaxial solution blowing process. The nanofibers have a diameter range of 60–300 nm. The core–shell structure was confirmed by transmission electron microscopy, and CS was observed as a thin layer that uniformly adhered to the core. The dye ligand of cibacron blue F3GA (CB F3GA) was further covalently immobilized on the nanofibers with a content of 425 µmol/g. The pristine and CB F3GA‐attached mats were studied in protein adsorption. High bovine serum albumin adsorption capacities of 91.9 and 219.6 mg/g were obtained for pristine and CB F3GA‐attached mats, respectively. Given its properties of high flux rate and low pressure drop, CB F3GA‐attached nylon 6–CS nanofiber mat meets the requirements of highly effective affinity membrane chromatography. Copyright © 2016 John Wiley & Sons, Ltd.     

Enhanced electrochemical performance of carbon-coated TiO2 nanobarbed fibers as anode material for lithium-ion batteries

We report the electrochemical performance of carbon-coated TiO₂ nanobarbed fibers (TiO₂@C NBFs) as anode material for lithium-ion batteries. The TiO₂@C NBFs are composed of TiO₂ nanorods grown on TiO₂ nanofibers as a core, coated with a carbon shell. These nanostructures form a conductive network showing high capacity and C-rate performance due to fast lithium-ion diffusion and effective electron transfer. The TiO₂@C NBFs show a specific reversible capacity of approximately 170 mAh g^− 1 after 200 cycles at a 0.5 A g^− 1 current density, and exhibit a discharge rate capability of 4 A g^− 1 while retaining a capacity of about 70 mAh g^− 1. The uniformly coated amorphous carbon layer plays an important role to improve the electrical conductivity during the lithiation–delithiation process.     

Hierarchical Fe3O4@TiO2 Yolk–Shell Microspheres with Enhanced Microwave‐Absorption Properties

A facile and efficient strategy for the synthesis of hierarchical yolk–shell microspheres with magnetic Fe₃O₄ cores and dielectric TiO₂ shells has been developed. Various Fe₃O₄@TiO₂ yolk–shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk–shell microspheres, such as the complex permittivity and permeability, were investigated. The electromagnetic data demonstrate that the as‐synthesized Fe₃O₄@TiO₂ yolk–shell microspheres exhibit significantly enhanced microwave absorption properties compared with pure Fe₃O₄ and our previously reported Fe₃O₄@TiO₂ core–shell microspheres, which may result from the unique yolk–shell structure with a large surface area and high porosity, as well as synergistic effects between the functional Fe₃O₄ cores and TiO₂ shells.     

TiO2@CdS core–shell nanorods films: Fabrication and dramatically enhanced photoelectrochemical properties

In this paper, we prepared TiO₂@CdS core–shell nanorods films electrodes using a simple and low-cost chemical bath deposition method. The core–shell nanorods films electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrometry techniques. After applying these TiO₂@CdS core–shell nanorods electrodes in photovoltaic cells, we found that the photocurrent was dramatically enhanced, comparing with those of bare TiO₂ nanorods and CdS films electrodes. Moreover, TiO₂@CdS core–shell nanorods film electrode showed better cell performance than CdS nanoparticles deposited TiO₂ nanoparticles (P25) film electrode. A photocurrent of 1.31 mA/cm², a fill factor of 0.43, an open circuit photovoltage of 0.44 V, and a conversion efficiency of 0.8% were obtained under an illumination of 32 mW/cm², when the CdS nanoparticles deposited on TiO₂ nanorods film for about 20 min. The maximum quantum efficiency of 5.0% was obtained at an incident wavelength of 500 nm. We believe that TiO₂@CdS core–shell heterostructured nanorods are excellent candidates for studying some fundamental aspects on charge separation and transfer in the fields of photovoltaic cells and photocatalysis.     

Sulfur Encapsulated in a TiO2‐Anchored Hollow Carbon Nanofiber Hybrid Nanostructure for Lithium–Sulfur Batteries

A hollow carbon nanofiber hybrid nanostructure anchored with titanium dioxide (HCNF@TiO₂) was prepared as a matrix for effective trapping of sulfur and polysulfides as a cathode material for Li–S batteries. The synthesized composites were characterized and examined by X‐ray diffraction, nitrogen adsorption–desorption measurements, field‐emission scanning electron microscopy, scanning transmission electron microscopy, and electrochemical methods such as galvanostatic charge/discharge, rate performance, and electrochemical impedance spectroscopy tests. The obtained HCNF@TiO₂–S composite showed a clear core–shell structure with TiO₂ nanoparticles coating the surface of the HCNF and sulfur homogeneously distributed in the coating layer. The HCNF@TiO₂–S composite exhibited much better electrochemical performance than the HCNF–S composite, which delivered an initial discharge capacity of 1040 mA h g^?1 and maintained 650 mAh g^?1 after 200 cycles at a 0.5 C rate. The improvements of electrochemical performances might be attributed to the unique hybrid nanostructure of HCNF@TiO₂ and good dispersion of sulfur in the HCNF@TiO₂–S composite.     

Surface‐Enhanced Fluorescence from Fluorophore‐Assembled Monolayers by Using Ag@SiO2 Nanoparticles

A new and simple procedure to enhance the fluorescence of analytes on the surfaces of a solid substrate is demonstrated based on Ag@SiO₂ nanoparticles. Two kinds of silver–silica core–shell nanoparticles with shell thicknesses of around 3 and 15 nm have been prepared and used as enhancing agents, respectively. By simply pipetting drops of the enhancing agents onto substrate surfaces with Rose Bengal monolayers, an enhancement of about 27 times, compared with the control sample, is achieved by using the Ag@SiO₂ nanoparticles with shells of about 3 nm, whereas an enhancement of around 11.7 times is obtained when using those with thicker shells. The effects of shell thickness and surface density of the enhancing agents on the enhancement have been investigated experimentally. The results show that this method can be potentially helpful in fluorescence‐based surface analysis.     

Electrospun nanofibers of ZnO‐TiO2 hybrid: characterization and potential as an extracellular scaffold for supporting myoblasts

One‐dimensional nanofibers have attracted tremendous attention because of their potential applications. Electrospinning technology enables industrial production of these nanofibers. This study aims to fabricate one‐dimensional ZnO doped TiO₂ by electrospinning and to characterize these hybrid nanofibers. The nanocomposite was prepared using colloidal gel composed of zinc nitrate, titanium isopropoxide and polyvinyl acetate. X‐ray diffraction, energy dispersive x‐ray analysis and transmission electron microscopy analysis confirmed the purity and crystalline nature of this material, whereas the diameter of these nanofibres estimated from scanning electron microscope (SEM), field emission SEM and transmission electron microscopy are between 200 and 300 nm. Cell counting with Kit‐8 assay at regular time intervals and phase‐contrast microscopy data revealed that C2C12 cells proliferated well on ZnO/TiO₂ nanofibers between 1 and 10 µg/ml, and cellular attachments are visible by SEM. The nanostructured ZnO/TiO₂ hybrid nanofibers show higher cell adhesion, proliferation and spreading behavior compared with the titanium substrate and control. Our study suggests that ZnO/TiO₂ nanofibers could potentially be used in tissue engineering applications. The scalability, low cost, reproducibility and high‐throughput capability of this technology is potentially beneficial to examine and optimizing a wide array of cell‐nanofiber systems prior to in vivo experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Metallodielectric Hollow Shells: Optical and Catalytic Properties

Metallodielectric composites with tunable optical properties were prepared by layer‐by‐layer assembly of gold nanorods on polystyrene (PS) spheres and subsequent deposition of SiO₂ or TiO₂ encapsulating shells through a sol–gel process. The optical properties of the core‐shells were tailored in the visible and the near‐infrared region through the gold nanorod aspect ratio and the gold nanoparticle density. Removal of the PS core by dissolution in an appropriate solvent, such as THF, yielded metallodielectric hollow shells with optical properties identical to those of the original composites. The presence of gold and the porosity of the SiO₂ or TiO₂ shells, suitable to allow diffusion of reactants and products, make these materials of interest as catalysts, as demonstrated by the reduction of potassium hexacyanoferrate(III) with NaBH₄.     

Quantitative evaluation of antibacterial activities of nanoparticles (ZnO,TiO2, ZnO/TiO2, SnO2, CuO,ZrO2, and AgNO3) incorporated into polyvinyl butyral nanofibers

Novel hybrid polyvinyl butyral nanofibers have been developed for antimicrobial applications. The nanofiber mats were obtained from a needleless rod electrospinning system. The novel inorganic antibacterial agents were incorporated into the nanofibers, and their antibacterial activity was compared. The obtained nanoparticle/nanofiber hybrid mats have a good surface morphology. The results indicated that the CuO, ZnO, ZnO/TiO₂, and AgNO₃ nanoparticle‐incorporated nanofiber layers have excellent antibacterial activity against to Escherichia coli compared with TiO₂, SnO₂, and ZrO₂ ones. Copyright © 2016 John Wiley & Sons, Ltd.     

A Simple Method for the Preparation of TiO2/Ag‐AgCl@Polypyrrole Composite and Its Enhanced Visible‐Light Photocatalytic Activity

A novel and facile method was developed to prepare a visible‐light driven TiO₂/Ag‐AgCl@polypyrrole (PPy) photocatalyst with Ag‐AgCl nanoparticles supported on TiO₂ nanofibers and covered by a thin PPy shell. During the synthesis, the PPy shell and Ag‐AgCl nanoparticles were prepared simultaneously onto TiO₂ nanofibers, which simplified the preparation procedure. In addition, because Ag‐AgCl aggregates were fabricated via partly etching the Ag nanoparticles, their size was well controlled at the nanoscale, which was beneficial for improvement of the contact surface area. Compared with reference photocatalysts, the TiO₂/Ag‐AgCl@PPy composite exhibited an enhanced photodegradation activity towards rhodamine B under visible‐light irradiation. The superior photocatalytic property originated from synergistic effects between TiO₂ nanofibers, Ag‐AgCl nanoparticles and the PPy shell. Furthermore, the TiO₂/Ag‐AgCl@PPy composite could be easily separated and recycled without obvious reduction in activity.     

Fabrication of Electrically Conducting Polypyrrole‐Poly(ethylene oxide) Composite Nanofibers

Summary: Electrically conducting polypyrrole‐poly(ethylene oxide) (PPy‐PEO) composite nanofibers are fabricated via a two‐step process. First, FeCl₃‐containing PEO nanofibers are produced by electrospinning. Second, the PEO‐FeCl₃ electrospun fibers are exposed to pyrrole vapor for the synthesis of polypyrrole. The vapor phase polymerization occurs through the diffusion of pyrrole monomer into the nanofibers. The collected non‐woven fiber mat is composed of 96 ± 30 nm diameter PPy‐PEO nanofibers. FT‐IR, XPS, and conductivity measurements confirm polypyrrole synthesis in the nanofiber.

An SEM image of the PPy‐PEO composite nanofibers. The scale bar in the image is 500 nm.     

Confined Ultrathin Pd‐Ce Nanowires with Outstanding Moisture and SO2 Tolerance in Methane Combustion

An efficient strategy (enhanced metal oxide interaction and core–shell confinement to inhibit the sintering of noble metal) is presented confined ultrathin Pd‐CeO_x nanowire (2.4 nm) catalysts for methane combustion, which enable CH₄ total oxidation at a low temperature of 350 °C, much lower than that of a commercial Pd/Al₂O₃ catalyst (425 °C). Importantly, unexpected stability was observed even under harsh conditions (800 °C, water vapor, and SO₂), owing to the confinement and shielding effect of the porous silica shell together with the promotion of CeO₂. Pd‐CeO_x solid solution nanowires (Pd‐Ce NW) as cores and porous silica as shells (Pd‐CeNW@SiO₂) were rationally prepared by a facile and direct self‐assembly strategy for the first time. This strategy is expected to inspire more active and stable catalysts for use under severe conditions (vehicle emissions control, reforming, and water–gas shift reaction).     

Synthesis of Multifunctional Metal‐ and Metal Oxide Core@Mesoporous Silica Shell Structures by Using a Wet Chemical Approach

We demonstrate a facile wet chemical approach for fabricating spherical metal/metal‐oxide core@mesoporous silica shell hybrid nanoparticles with different core and shell thicknesses. Vertically aligned mesoporous silica (mSiO₂) shells were fabricated over the pre‐synthesized spherical SiO₂ nanoparticles through a three‐step strategy: 1) synthesis of core materials, 2) covering the core with an organic–inorganic composite layer, and 3) removing the organic template through calcinations in air. The mechanisms of hybrid structure formation are proposed. The multifunctional nature of the hybrid structures could be induced by incorporating guest ions/molecules, such as Ag, Mn, and TiO₂, into the pores of an mSiO₂ shell. Mn and TiO₂ cluster‐ incorporated composite structures have been tested to be antioxidizing agents and effective photocatalysts through electron spin resonance, radical scavenging tests, and the photocatalytic degradation of rhodamine B. The possibility of incorporating several hetero‐element guest clusters in these mesoporous composite particles makes them highly attractive for multifunctional applications.