Synthesis and White-Light Emission of ZnO/HfO2: Eu Nanocables

ZnO/HfO₂:Eu nanocables were prepared by radio frequency sputtering with electrospun ZnO nanofibers as cores. The well-crystallized ZnO/HfO₂:Eu nanocables showed a uniform intact core–shell structure, which consisted of a hexagonal ZnO core and a monoclinic HfO₂ shell. The photoluminescence properties of the samples were characterized. A white-light band emission consisted of blue, green, and red emissions was observed in the nanocables. The blue and green emissions can be attributed to the zinc vacancy and oxygen vacancy defects in ZnO/HfO₂:Eu nanocables, and the yellow–red emissions are derived from the inner 4f-shell transitions of corresponding Eu³⁺ ions in HfO₂:Eu shells. Enhanced white-light emission was observed in the nanocables. The enhancement of the emission is ascribed to the structural changes after coaxial synthesis.     

Enhanced light scattering and photovoltaic performance for dye-sensitized solar cells by embedding submicron SiO2/TiO2 core/shell particles in photoanode

The introduction of light scattering in the photoanodes of dye-sensitized solar cells is one of the most effective approaches to enhance their photovoltaic performance. In this work, we prepared submicron SiO₂/TiO₂ core/shell particles and embedded these particles in the nanostructured TiO₂ photoanodes for light to scatter in the dye-sensitized solar cells. Due to the large difference in the refractive index between the SiO₂ core and the TiO₂ shell, the embedded submicron SiO₂/TiO₂ core/shell particles showed strong light scattering effect. Light absorbance of the dyed photoanode with the embedded SiO₂/TiO₂ particles for light scattering was found to be three times stronger than the one without light scattering particles over a wide wavelength range. The power conversion efficiency of dye-sensitized solar cells was increased by about 50% after the introduction of light scattering SiO₂/TiO₂ core/shell particles in the photoanode. This work will provide a base for further enhancement in the photovoltaic performance of dye-sensitized solar cells by optimizing the submicron SiO₂/TiO₂ core/shell particles and the photoanodes.     

Morphology and kinetic mechanism of facile one-step preparing TiO2/polyacrylate/TiO2 multilayer core–shell hybrid emulsion via miniemulsion polymerization

In this paper, we report a facile method for the preparation of TiO₂/polyacrylate/TiO₂ multilayer core–shell hybrid emulsion through polymerization. The chemical compositions of the copolymer were studied with Fourier transform infrared. TEM images reveal that nanocomposites show different core–shell structures with different TiO₂ contents. As the weight percentage of TiO₂ is 2 wt% (based on monomer, same below), there are no TiO₂ cores in some nanocomposites. When TiO₂ increases to 3 wt%, the TiO₂/polymer/TiO₂ multilayer core–shell composite particles are prepared. But the TiO₂ shells disappeared when the TiO₂ content kept increasing. TGA shows that the TiO₂ dispersed in latex films uniformly and the thermal stabilization improved with increasing TiO₂ contents. The effect of operating variables such as polymerization temperature and the concentrations of polymerizable emulsifier, initiator, extremely hydrophilic monomer, modified TiO₂ and HD on the kinetic behaviors was investigated. The formation mechanism of TiO₂/polymer/TiO₂ multilayer core–shell structure was inferred.     

AgBr@Ag/TiO2 core–shell composite with excellent visible light photocatalytic activity and hydrothermal stability

AgBr@Ag/TiO₂ core–shell photocatalysts were fabricated by a facile green route. TiO₂ was uniformly coated on the surface of cubic AgBr, making AgBr@Ag/TiO₂ core–shell photocatalyst show excellent hydrothermal stability. Beneficial from that Ag nanoparticles and AgBr can respond to visible light and core–shell structure can effectively separate the photogenerated electrons and holes, AgBr@Ag/TiO₂ core–shell composites exhibited outstanding visible light photocatalytic activity for the degradation of acid orange 7. The activity of AgBr@Ag/TiO₂ is related to the thickness of TiO₂ shell, and the optimal shell thickness for obtaining the highest activity is 10 nm.     

A novel SiCN@TiO2 core–shell ceramic microspheres derived from a polymeric precursor

A novel core–shell ceramic microspheres, composed of a SiCN inner core and TiO₂ nanoparticles outer shell, were prepared via emulsion technique and polymer-derived ceramics (PDCs) method. The forming process of SiCN@TiO₂ core–shell ceramic microspheres were controlled by adjusting the ratio of raw material, curing temperature and pyrolysis temperature. The morphology, chemical composition and phase transformation were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). PVSZ@TiO₂ microspheres with good spherical structure and uniform-dispersed TiO₂ surface were fabricated at 200 °C with raw material ratio of 25%. After pyrolyzed at 1400 °C, the obtained SiCN@TiO₂ core–shell ceramic microspheres retained spherical structure. The XRD showed that the products were mainly composed of rutile TiO₂, SiC and Si₃N₄ crystalline phase, which were generated by polyvinylsilazane.     

Modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO2 thin films using ultrathin interfacial layers

In this study, tailoring the microstructures and ferroelectric(FE)/antiferroelectric(AFE) properties of nanoscale ZrO₂ thin films is demonstrated with an intentional introduction of sub-nanometre interfacial layers. The ferroelectricity of ZrO₂ thin films is significantly enhanced by the HfO₂ interfacial layers, while the TiO₂ interfacial layers lead to a dramatic transformation of ZrO₂ from ferroelectricity into antiferroelectricity. The HfO₂ and TiO₂ interfacial layers boost the formation of the polar orthorhombic phase with (111)-texture and the non-polar tetragonal phase with (110)-texture in the FE/AFE ZrO₂ thin films, respectively, as evidenced by grazing incidence, out-of-plane, and in-plane X-ray diffraction measurements. Furthermore, the modulation of ferroelectricity and antiferroelectricity of nanoscale ZrO₂ thin films by the HfO₂/TiO₂ interfacial layers can be achieved without high-temperature annealing, which is highly advantageous to process integration. The findings demonstrate the important role of the interfaces in the effective tuning of FE/AFE properties of nanoscale thin films.     

Synthesis and optical limiting effects in ZrO2 and ZrO2@SiO2 core–shell nanostructures

ZrO₂ nanoparticles were synthesized by the chemical precipitation method and coated with silica through seeded polymerization technique to form core–shell type ZrO₂@SiO₂ nanostructures. The structural, morphological and silica coating formation of the bare and silica coated particles were studied using Transmission electron microscopy, X-ray diffraction and Fourier Transform Infrared Spectroscopy. Thermogravimetric analysis and Zeta potential measurements were performed to check the thermal and dispersion stability of the nanostructures. The optical limiting performance of these nanostructures was studied using open-aperture Z-scan technique in which nanosecond laser pulses at 532 nm have been used for optical excitation. Both bare and silica coated ZrO₂ nanoparticles exhibited good optical limiting behavior due to excited state absorption, arising from effective three photon absorption. It is observed that the optical nonlinearity is enhanced in core shell structures as compared with the bare particles.     

Core–shell structured Cu@m-SiO2 and Cu/ZnO@m-SiO2 catalysts for methanol synthesis from CO2 hydrogenation

The core–shell catalysts with Cu and Cu/ZnO nanoparticles coated by mesoporous silica shells are prepared for CO₂ hydrogenation to methanol. With the confined effect of silica shell, the size of Cu nanoparticles is only about 5.0 nm, which results in high activity for CO₂ conversion. The CH₃OH selectivity is enhanced significantly with the introduction of ZnO. The core–shell structured catalysts endow the Cu nanoparticles trapped inside with excellent anti-aggregation and no deactivation is observed with time-on-stream. Therefore, the core–shell Cu/ZnO@m-SiO₂ catalyst exhibits the maximum CH₃OH yield with high stability.     

Preparation of CdS/TiO2 nanotube arrays and the enhanced photocatalytic property

In this paper, a series of CdS/TiO₂ NTs have been synthesized by SILAR method. The as-prepared CdS/TiO₂ NTs have been analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), and ultraviolet–visible (UV–vis). And their photocatalytic activities have been investigated on the degradation of methylene blue under simulated solar light irradiation. XRD results indicate that TiO₂ NTs were anatase phase, CdS nanoparticles were hexagonal phase. FESEM results indicate that low deposition concentration can keep the nanotubular structures. UV–vis results indicate that CdS can be used to improve the absorbing capability of TiO₂ NTs for visible light, and the content of CdS affects the band gap. Photocatalytic results indicate that CdS nanoparticles are conducive to improve the photocatalytic efficiency of TiO₂ NTs, and the highest degradation rate can reach 93.8%. And the photocatalytic mechanism of CdS/TiO₂ NTs to methylene blue is also described.     

Long-term thermal stability of Li4TiO4–Li2TiO3 core–shell breeding pebbles under continuous heating in H2/Ar atmosphere

The long-term thermal stability of tritium breeding materials during service is a key factor to ensure efficient tritium release. In this study, the long-term thermal stability of advanced Li₄TiO₄–Li₂TiO₃ core–shell breeding pebbles under continuous heating in 1%H₂/Ar at 900°C was investigated for the first time. The results show that this core–shell material loses 3.4% Li mass after heating for 30 days, resulting in a reduction in Li density to .415 g/cm³, which is still significantly higher than other breeding materials. The moisture in the sample bed will determine the form of Li volatilization and thus affect the rate of Li mass loss. The core–shell pebbles maintain favorable phase stability during long-term heating, and the grain sizes of the Li₂TO₃ shell and Li₄TiO₄ core after 30 days of heating are 6.5 ± 1.5 and 6.9 ± 2.5 μm, respectively. Moreover, the samples did not crack or collapse during long-term heating and still had a satisfactory crushing strength of 37.61 ± 7.13 N after 30 days of heating. Overall, the high Li density and good thermal stability during long-term heating demonstrate that the Li₄TiO₄–Li₂TiO₃ core–shell breeding pebbles are a very reliable tritium breeding material for long-term service under harsh operating conditions.     

Fabrication of core–shell nanocomposites with enhanced photocatalytic efficacy

The current study establishes the unprecedented involvement in the evolution and production of novel core–shell nanocomposites composed of nanosized titanium dioxide and aniline‐o‐phenylenediamine copolymer. TiO₂@copoly(aniline and o‐phenylenediamine) (TiO₂@PANI‐o‐PDA) core–shell nanocomposites were chemically synthesized in a molar ratio of 5:1 of the particular monomers and several weights of nano‐TiO₂ via oxidative copolymerization. The construction of the TiO₂@PANI‐o‐PDA core–shell nanocomposites was ascertained from Fourier transform IR spectroscopy, UV–visible spectroscopy and XRD. A reasonable thermal behavior for the original copolymer and the TiO₂@PANI‐o‐PDA core–shell nanocomposites was investigated. The bare PANI‐o‐PDA copolymer was thermally less stable than the TiO₂@PANI‐o‐PDA nanocomposites. The core–shell feature of the nanocomposites was found to have core and shell sizes of 17 nm and 19–26 nm, respectively. In addition, it was found that the addition of a high ratio of TiO₂ nanoparticles increases the electrical conductivity and consequently lowers the electrical resistivity of the TiO₂@PANI‐o‐PDA core–shell nanocomposites. The hybrid photocatalysts exhibit a dramatic photocatalytic efficacy of methylene blue degradation under solar light irradiation. A plausible interpretation of the photocatalytic degradation results of methylene blue is also demonstrated. Our setup introduces a facile, inexpensive, unique and efficient technique for developing new core–shell nanomaterials with various required functionalities and colloidal stabilities. © 2018 Society of Chemical Industry     

Fabrication of plasmonic Au/TiO2 nanotube arrays with enhanced photoelectrocatalytic activities

Uniformly dispersed Au nanoparticles (NPs) deposited on the surface of highly ordered TiO₂ nanotube arrays (Au/TiO₂ NTs) were synthesized through a two-step process including anodization method and microwave-assisted chemical reduction route. The investigation indicated that Au NPs grew uniformly on the walls of TiO₂ NTs. Au/TiO₂ NTs exhibited excellent visible light absorption due to the LSPR effect of Au NPs. Au/TiO₂ NTs exhibited much higher photocurrent density and the photoconversion efficiency of Au decorated TiO₂ NTs was about 2.05 times greater than that of bare TiO₂ NTs. Besides, the PL intensity of Au/TiO₂ NTs was much lower than that of TiO₂ NTs, revealing a decrease in charge carrier recombination. The prepared Au/TiO₂ NTs exhibited superior photoelectrocatalytic activity and stability in the degradation of MB under simulated solar light irradiation. The synergy effect between nanotubular structures of TiO₂ and uniformly dispersed Au nanoparticles, as well as the small bias potential and strong interaction between Au and TiO₂, facilitated the Au plasmon-induced charge separation and transfer, which lead to highly efficient and stable photoelectrocatalytic activity.     

Electrokinetic and antibacterial properties of needle like‐TiO2/polyrhodanine core/shell hybrid nanostructures

The aim of this study was to fabricate needle like‐TiO₂/polyrhodanine nanostructures by polymerizing rhodanine monomer on the TiO₂ nanoparticles' surfaces and investigate their antibacterial activities. The structural, thermal, morphological, surface and electrical properties of non‐covalently functionalized nanoparticles were characterized by using FTIR, XPS, elemental analysis, TGA, XRD, SEM‐EDX, TEM, contact angle, and conductivity measurements. Characterization results confirmed the formation of needle like‐TiO₂/polyrhodanine (PRh) core/shell hybrid nanostructures. Alterations on the surface and electrokinetic properties of the materials were characterized by zeta (ζ)‐potential measurements with the presence of various salts and surfactants. The ζ‐potential of needle like‐TiO₂ was observed to increase from ?7.6 mV to +28.4 mV after forming a core/shell needle like‐TiO₂/PRh nanocomposite structure and with the presence of cetyltrimethyl ammonium bromide (CTAB) surfactant. Thereby colloidally more stable dispersions were formed. Antibacterial properties of needle like‐TiO₂/PRh were also tested against Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli by various methods and they showed good antibacterial activity. The highest killing efficiency was determined for needle like‐TiO₂/PRh against E. coli by colony‐counting method as 0.95. TEM experiments also showed the immobilizations of the nanoparticles on E. coli and revealed the interactions between E. coli and the nanoparticles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41554.     

Optical,thermal and electrical characterization of PEO/CMC incorporated with ZnO/TiO2 NPs for advanced flexible optoelectronic technologies

The optical, thermal, and electrical properties of a blend of polyethylene oxide (PEO) and carboxymethyl cellulose (CMC) are examined in the current work in relation to the effects of zinc oxide (ZnO) and titanium dioxide (TiO₂) nanoparticles. To create hybrid ZnO/TiO₂ NPs nanocomposites with a PEO/CMC matrix, the solution casting method was utilized. The XRD study results demonstrate that the nanocomposite films' crystallinity decreases with increasing ZnO/TiO₂ NP concentrations. FT-IR spectra reveal the interaction between metal oxide NPs and the PEO/CMC composite. UV/Vis analytical spectroscopy was used to calculate the optical properties, such as the energy gap (Eg), refractive index (n), and the number of carbon atoms (M). The inclusion of 7 wt%ZnO/TiO₂ NPs decreased the polymer matrix's allowed direct energy gap from 3.68 to 2.81 eV. The AC conductivity results show that the ${\sigma }_{dc}$ of the nanocomposite samples decreases with increasing ZnO/TiO₂ NPs concentrations. The ${\sigma }_{dc}$ of the final sample (PEO/CMC@7 wt% ZnO/TiO₂) was 5.18 × 10⁻⁷Scm⁻¹. According to exponential factor (S) results, the dominates conduction mechanism is correlated barrier hopping (CBH) with non-Debye relaxation processes. Space charge polarization was demonstrated by large ε′ values in the low-frequency dielectric properties, whereas an increase in energy loss may be related with a larger εʹ' value in the composite samples. These results prove that these nanocomposites can be used in a variety of energy-related devices, such as flexible capacitors, and energy storage systems.     

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO₂/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO₂ sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO₂ and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO₂ and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO₂/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO₂/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO₂/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.     

Preparation,structural and photocatalytic activity of Sn/Fe co-doped TiO2 nanoparticles by sol-gel method

Pure and Sn/Fe co-doped (0.2 at.% Sn and 0.6 at.% Fe, 0.6 at.% Sn and 0.2 at.% Fe, 1.0 at.% Sn and 1.0 at.% Fe) TiO₂ nanoparticles were synthesized via a sol-gel method and subsequently calcined at different temperatures. Furthermore, the particles were analyzed by TG-DSC, XRD, TEM, HRTEM, EDS, SAED and UV–Vis for investigating the influences of dopant and calcination temperature on the thermal effect, composition, morphology, energy band gap (E_g) and the degradation efficiency of methyl orange (MO) under various light irradiations respectively. Results indicated that Sn/Fe co-doping inhibited the crystallization transformation from anatase to rutile phase of TiO₂ and decreased the E_g. The increased calcination temperature and Sn/Fe co-doped effect brought about the abnormal grain growth of TiO₂ nanoparticles. 0.6 at.% Sn/0.2 at.% Fe and 1.0 at.% Sn/1.0 at.% Fe co-doped TiO₂ nanoparticles presented better photocatalytic performance than pure and 0.2 at.% Sn/0.6 at.% Fe co-doped TiO₂ nanoparticles under visible light irradiation mainly due to the decreased E_g. On the contrary, 0.2 at.% Sn and 0.6 at.% Fe co-doped TiO₂ nanoparticles calcined at 650 °C showed the most excellent photocatalytic performance under UV light irradiation, which was about twice as large as that of pure TiO₂ possibly due to the formed hybrid structure of anatase and rutile phase as well as the h⁺-mediated decomposition pathway.     

Preparation of core–shell poly(acrylic acid)/polystyrene/SiO2 hybrid microspheres

Core–shell poly(acrylic acid)/polystyrene/SiO₂ (PAA/PS/SiO₂) hybrid microspheres were prepared by dispersion polymerization with three stages in ethanol and ethyl acetate mixture medium. Using vinyltriethoxysilane (VTEOS) as silane agent, functional silica particles structured vinyl groups on surfaces were prepared by hydrolysis and polycondensation of tetraethoxysilane and VTEOS in core stage. Then, the silica particles were used as seeds to copolymerize with styrene and acrylic acid sequentially in shell stage I and stage II to form PAA/PS/SiO₂ hybrid microspheres. Transmission electron microscope results show that most PAA/PS/SiO₂ hybrid microspheres are about 40 nm in diameter, and the silica cores are about 15 nm in diameter, which covered with a layer of PS about 7.5‐nm thick and a layer of PAA about 5‐nm thick. This core–shell structure is also conformed by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and differential scanning calorimetry. FTIR results show that silica core, PS shell, and PAA outermost shell are bonded by covalents. In the core–shell PAA/PS/SiO₂ hybrid microsphere, the silica core is rigidity, and the PAA outermost shell is polarity, while the PS layer may work as lubricant owning to its superior processing rheological property in polymer blending. These core–shell PAA/PS/SiO₂ hybrid microspheres have potential as new materials for polar polymer modification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1729–1733, 2006     

A novel approach for the synthesis of highly active ZnO/TiO2/Ag2O nanocomposite and its photocatalytic applications

The present work is focused on the preparation of hybrid ZnO/TiO₂/Ag₂O nanocomposite for enhanced photocatalytic activity. The resultant samples are characterized by using XRD, SEM, EDX, HR-TEM, UV-DRS, BET and XPS techniques. X-ray diffraction analysis indicates the co-existence of wurtzite, anatase and cubic phases in ZnO/TiO₂/Ag₂O nanocomposite. The band gap energy value of the photocatalyst is 3.39 eV, which has been evidenced from UV–visible diffuse reflectance spectroscopy measurements. Photocatalytic degradation of methylene blue dye has been investigated by using UV–visible spectrophotometer. From the result, it has been concluded that ZnO/TiO₂/Ag₂O nanocomposite has proven to be an efficient photocatalyst under UV irradiation when compared to that of mono and binary oxide systems. Further, the possible photodegradation mechanism is proposed to support the enhancement of photocatalytic activity towards degradation of dyes.     

Conductive and transparent multilayer films for low-temperature TiO2/Ag/SiO2 electrodes by E-beam evaporation with IAD

Conductive and transparent multilayer thin films consisting of three alternating layers (TiO₂/Ag/SiO₂, TAS) have been fabricated for applications as transparent conducting oxides. Metal oxide and metal layers were prepared by electron-beam evaporation with ion-assisted deposition, and the optical and electrical properties of the resulting films as well as their energy bounding characteristics and microstructures were carefully investigated. The optical properties of the obtained TAS material were compared with those of well-known transparent metal oxide glasses such as ZnO/Ag/ZnO, TiO₂/Ag/TiO₂, ZnO/Cu/ZnO, and ZnO/Al/ZnO. The weathering resistance of the TAS film was improved by using a protective SiO₂ film as the uppermost layer. The transmittance spectra and sheet resistance of the material were carefully measured and analyzed as a function of the layer thickness. By properly adjusting the thickness of the metal and dielectric films, a low sheet resistance of 6.5 ohm/sq and a high average transmittance of over 89% in the 400 to 700 nm wavelength regions were achieved. We found that the Ag layer played a significant role in determining the optical and electrical properties of this film.     

Fabrication of graphene films on TiO2 nanotube arrays for photocatalytic application

Graphene film was formed on the surface of titanium dioxide nanotube (TiO₂ NT) arrays through in situ electrochemical reduction of a graphene oxide dispersion by cyclic voltammetry. The residual oxygen-containing groups and other structural defects such as sp³-hybridized carbons in the electrodeposited graphene were further removed by photo-assisted reduction of the underlying TiO₂ NTs, thus achieving the maximum restoration of π-conjugation in the graphene planes. Spectroscopic, electrochemical, and photoelectrochemical techniques were used to characterize the graphene films, and the use of the resulting graphene–TiO₂ NT material in photocatalysis was investigated. The results showed that the graphene–TiO₂ NT material exhibited a greatly improved photocatalytic activity compared with unmodified TiO₂ NTs.