Anatase Shell Research Articles

Direct deposition of anatase TiO2 on thermally unstable gold nanobipyramid: Morphology-conserved plasmonic nanohybrid for combinational photothermal and photocatalytic cancer therapy

Deposition of crystalline titanium dioxide (TiO2) on gold nanostructures has been considered as a promising strategy for near-infrared (NIR) light-activated photocatalysis. A typical route comprises pre-deposition of amorphous TiO2 on the gold surface and its ensuing crystallization by high-temperature annealing. Such condition, however, is not compatible with highly plasmonic but thermally unstable sharp-tipped gold nanostructures, causing structural disruption and plasmonic decline. Herein, we report a hybridization method excluding high-temperature annealing, i.e., direct deposition of anatase TiO2 onto sharp-tipped gold nanobipyramid (Au NBP/a-TiO2) with conserving their morphology without agglomeration via low-temperature hydrothermal reaction. In addition to keeping the plasmonic photothermal performance, Au NBP/a-TiO2 exhibits enhanced photocatalytic generation of reactive oxygen species in response to the NIR excitation, evidencing the efficient injection of hot electrons from the Au NBP to the anatase shell. In vitro and in vivo studies revealed that the efficient photocatalytic/photothermal responses of Au NBP/a-TiO2, along with dispersion stability in biological media and minimal toxicity, hold potential for synergistic photothermal and photodynamic therapy. We believe that the low-temperature synthetic method introduced here might offer a general way of crystalline deposition of TiO2 on a variety of gold nanostructures, broadening the spectrum of NIR-responsive photocatalytic hybrid nanostructures for biomedical applications.

Gold-core lithium-doped titania shell nanostructures for plasmon-enhanced visible light harvesting with photocatalytic activity

A simple sol-gel synthesis method has been developed to synthesize uniform nanospheres of gold lithium-doped titanium dioxide in anatase phase (Au/Li-TiO2) with a well-defined core-shell structure with the Li-doped titania as shell and Au nanoparticles as core. The resulting core-shell nanoparticles have a high surface area (~494 m2/g) and uniform pore size (~3.5 nm) for the anatase shell. The synthesis of the gold nanoparticles refers to the classical Turkevich synthesis, and the diameter can be regulated by adjusting the amount of HAuCl4. The gold nanoparticles were first covered with citrate group and subsequently removed by thermal treatment. The catalytic performance of Au/Li-TiO2 was investigated using the degradation of rhodamine B in water for a model reaction using UVb and visible light. The high surface area of the anatase shells provides direct access for the reactant molecules to diffuse and subsequently interact with the gold cores.

Insights into the Photothermal Hydrogen Production from Glycerol Aqueous Solutions over Noble Metal‐Free Ti@TiO2 Core–Shell Nanoparticles

AbstractPhotocatalytic production of hydrogen from renewable sources with platinum group metal‐free catalysts is of great importance for environmentally friendly energetics. Herein, Ti@TiO2 core–shell nanoparticles prepared by sonohydrothermal treatment of titanium metal nanoparticles are examined for hydrogen generation from aqueous glycerol solutions under vis/NIR light irradiation. It is shown that photocatalytic reforming of glycerol in the presence of Ti@TiO2 exhibits strong photothermal effect allowing more efficient use of solar energy. Apparent activation energy equal to E act = 27 ± 2 kJ mol−1 indicates that the thermal effect is related to the diffusion of reaction intermediates at catalyst surface rather than to the activation of chemical bonds. The photoexcitation mechanism of Ti@TiO2 particles involves interband transitions in nonplasmonic Ti metal core followed by nonradiative Landau damping. Effective electron–hole separation between Ti core and nanocrystalline TiO2 anatase shell in Ti@TiO2 nanoparticles is confirmed by photoluminescence spectroscopy. In studied system, photothermal hydrogen production is not accompanied by CO2 emission indicating that glycerol is oxidized to glyceric acid without further decarboxylation.

Hierarchically structural TiO2 nanorods composed of rutile core and anatase shell as a durable anode material for lithium-ion intercalation

In the present work, hierarchically structural TiO2 nanorods composed of rutile core and anatase shell were successfully synthesized via a one-step hydrothermal route for the first time, and then were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning and transmission electron microscopy (SEM/TEM) measurements. It was found that the crystal phases of the same can be easily adjusted by changing the amount of the reactant during the reaction process. Furthermore, the sample was used as an anode for lithium-ion intercalation and exhibited high capacity and long-term cycling stability due to the synergistic effects of dual-phase TiO2. For instance, the capacities of 102.7 and 84.7mAhg−1 can be kept at 10 C for 1000cycles and 20 C for 5000cycles, respectively.

One-Step Microheterogeneous Formation of Rutile@Anatase Core–Shell Nanostructured Microspheres Discovered by Precise Phase Mapping

Nanostructured core–shell microspheres with a rough rutile core and a thin anatase shell are synthesized via a one-step heterogeneous templated hydrolysis process of TiCl4 vapor on the aerosol water–air interface. The rutile-in-anatase core–shell structure has been evidenced by different electron microscopy techniques, including electron energy-loss spectroscopy and 3D electron tomography. A new mechanism for the formation of a crystalline rutile core inside the anatase shell is proposed based on a statistical evaluation of a large number of electron microscopy data. We found that the control over the TiCl4 vapor pressure, the ratio between TiCl4 and H2O aerosol, and the reaction conditions plays a crucial role in the formation of the core–shell morphology and increases the yield of nanostructured microspheres.

A Plasmonic Colloidal Photocatalyst Composed of a Metal–Organic Framework Core and a Gold/Anatase Shell for Visible‐Light‐Driven Wastewater Purification from Antibiotics and Hydrogen Evolution

Porous coordination polymers (PCP) or metal- organic frameworks (MOF) are promising materials for the generation of photocatalytically active composite materials. Here, a novel synthesis concept is reported, which permits the formation of PCP/MOF-core-Au/anatase-shell materials. These materials are photocatalysts for wastewater purification and hydrogen generation from water under visible-light illumination. MIL-101 (Cr) is utilized as the core material, which directs the size of the core-shell compound and ensures the overall stability. In addition, its excellent reversible large molecule sorption behavior allows the materials synthesis. The crystalline anatase shell is generated stepwise under mild conditions using titanium(IV) isopropoxide as a precursor. The high degree of control of the vapor phase deposition process permits the precise anatase shell formation. The generation of plasmonic active gold particles on the TiO2 shell leads to an efficient material for visible-light-driven photocatalysis with a higher activity than gold-decorated P25 (Degussa).

High Conformity and Large Domain Monocrystalline Anatase on Multiwall Carbon Nanotube Core–Shell Nanostructure: Synthesis, Structure, and Interface

We report a new facile approach to achieve highly conformal thin layers (∼10 nm) of anatase TiO2 on nonfunctionalized carbon nanotubes (CNTs) using atomic layer deposition (ALD). The method adopts an initial deposition of amorphous TiO2 at a low temperature of 60 °C to ensure a good conformity followed by postdeposition annealing at 450 °C under vacuum to induce a complete phase transformation to crystalline anatase TiO2 while retaining the structural integrity of the CNTs. This approach yields unprecedented sizes of monocrystalline anatase shell domains of up to 500 nm along the CNTs. The high quality of the anatase layer is evidenced directly by high-resolution transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Atomic-scale study of the nanostructure cross-section using electron energy loss spectroscopy provides direct evidence that bonding is formed at the interface after annealing. The low grain boundary anatase shell layer with a well-bonded interface to the C...

Surfactant-templating strategy for ultrathin mesoporous TiO2 coating on flexible graphitized carbon supports for high-performance lithium-ion battery

The electrochemical performance of nanocomposites could greatly be improved by rationally designing flexible core-shell heterostructures. Typically, the uniform coating of a thin mesoporous crystalline transition metal oxide shell on flexible graphitized carbon supports can provide both fast ion and electron transport pathways, which is an ideal material for high-performance lithium-ion batteries. Herein, we report a surfactant-templating assembly coating method to deposit an ultrathin mesoporous crystalline TiO2 shell on flexible graphitized carbon supports by using amphiphilic triblock copolymer Pluronic F127 as a template. Taking multi-wall carbon nanotubes (CNTs) as an example support, the obtained flexible CNTs@mTiO2 hybrid mesoporous nanocables exhibit an ultra-high surface area (∼137m2/g), large internal pore volume (∼0.26cm3/g), uniform accessible mesopores (∼6.2nm) and ultrathin highly-crystalline mesoporous anatase shells (∼20nm in thickness). As an anode material for lithium battery, the flexible CNTs@mTiO2 hybrid mesoporous nanocables show high-rate capacity (∼210mAhg−1 at 20C, 1C=170mAg−1), high Coulombic efficiency (nearly 100% during 1000 cycles at 20C) and ultralong-cycling life (keeping ∼210mAhg−1 after 1000 cycles at 20C). The strong synergistic coupling effect between CNT cores and thin mesoporous TiO2 shells, high surface area, accessible large pores and highly crystalline thin mesoporous shells result in excellent performance in lithium batteries. This versatile surfactant-templating assembly coating method can be easily extended to deposit an ultrathin mesoporous TiO2 layer on flat graphene (GR) to form a uniform sandwich-like flexible GR@mTiO2 nanoflakes, which opens up a new opportunity for depositing thin mesoporous transition-metal oxides on graphitized carbon supports for advanced applications in energy conversion and storage, photocatalysis, sensors and drug delivery, etc.

Recyclable silver-decorated magnetic titania nanocomposite with enhanced visible-light photocatalytic activity

We report a fabrication of rationally-designed multicomponent nanocomposites comprising a magnetite core and an outer silver-decorated anatase shell and their application for visible-light photodegradation of organic compounds. The nanocomposites exhibit a well-defined core-shell structure, superparamagnetic behavior, wide-spectrum photoresponse and markedly enhanced visible-light photocatalytic activity. The enhancement of the photocatalytic activity increases with the density of decorated Ag nanoparticles in the ternary system. More importantly, the obtained nanostructured photocatalysts could be easily collected and separated by applying an external magnetic field and reused at least eight times without any appreciable reduction in photocatalytic efficiency. The enhanced photocatalytic activity and good chemical stability, in combination with the excellent magnetic recyclability, make this multifunctional nanostructure as a promising integrated system for applications in environmental remediation.

Dielectric performance of polymer-based composites containing core-shell Ag@TiO2 nanoparticle fillers

This paper reports composites prepared by embedding core-shell Ag@TiO2 fillers into polytetrafluoroethylene. Ag nanoparticles were homogeneously coated with TiO2, to give a shell thickness of approximately ∼8–10 nm. The composite containing Ag@TiO2 nanoparticles with rutile shells exhibited better dielectric properties than the composite containing Ag@TiO2 nanoparticles with anatase shells. The relative permittivity (εr) of the composite containing 70 vol. % filler was approximately 240 at 100 Hz, which was more than 100 times higher than that of pure polytetrafluoroethylene (εr = 2.1). An effective medium percolation theory model is used to account for the dielectric constant of the composite.

General strategy to synthesize uniform mesoporous TiO2/graphene/mesoporous TiO2 sandwich-like nanosheets for highly reversible lithium storage.

Uniform oxide deposition on graphene to form a sandwich-like configuration is a well-known challenge mainly due to their large lattice mismatches and poor affinities. Herein, we report a general strategy to synthesize uniform mesoporous TiO2/graphene/mesoporous TiO2 sandwich-like nanosheets (denoted as G@mTiO2), which cannot be achieved by conventional one-pot synthetic methods. We show that by rational control of hydrolysis and condensation of Ti precursors in a slow way, GO sheets can be conformably coated by amorphous TiO2 shells, which then can be facilely transformed into the well-defined G@mTiO2 nanosheets by annealing. This amorphous-to-crystalline strategy conveniently allows bypassing strain fields that would inevitably arise if direct growth of mesoporous anatase shells on graphene. As distinct from the most common structures of graphene-based composites (mixed, wrapped, or anchored models), the resultant materials display a uniform sandwich-like configuration: few-layer graphene conformably encapsulated by mesoporous TiO2 shells. This new G@mTiO2 nanosheet exhibits ultrathin nature (∼34 nm), small size and high crystalline nanocrystals (∼6 nm), high surface areas (∼252 m(2)/g) and uniform mesopores (∼3.4 nm). We further show that the thickness of mesoporous TiO2 shells can be facilely adjusted as desired by controlling the ammonia content, and this facile strategy can be easily extended to design other oxide/graphene/oxide sandwich-like materials. More importantly, we showcase the benefits of the resultant G@mTiO2 nanosheets as anodes in lithium ion batteries: they deliver an extra high capacity, an excellent high-rate capability, and long cycle life.

Encapsulation of Au nanoparticles with well-crystallized anatase TiO2 mesoporous hollow spheres for increased thermal stability

Uniform Auencap/TiO2 hollow microspheres, in which sub-10 nm Au nanoparticles are coated with a mesoporous anatase TiO2 shell, are prepared by a protected-calcinating process. The method involves the preparation of SiO2@Au@TiO2 colloidal composites, sequential deposition of carbon and then SiO2 layers through solvothermal and sol–gel processes, crystallization of TiO2 by calcination and finally etching of the inner and outer silica layers to produce the hollow structure. The protected crystallization process suppresses the excessive growth of TiO2 and eventually produces mesoporous anatase shells with high surface area. Additionally, by simply controlling the crystallization temperature, it can be convenient to tune the porosity and crystallinity of the TiO2 shell, meanwhile maintaining the small size of Au nanoparticles. When used as the catalyst for the reduction of 4-nitrophenol, the synthesized Auencap/TiO2 catalysts exhibit significantly enhanced catalytic performance. Moreover, the obtained Auencap/TiO2 hollow spheres show a superior thermal stability, as it resists sintering during the additional calcination at 500 °C, whereas the sample prepared by deposited Au nanoparticles on commercial P25(Au/P25) was found to sinter severely.

Recyclable, Biocompatible, Magnetic Titanium Dioxide Nanoparticles with Immobilized Enzymes for Biocatalysis.

Clean break: Magnetic nanoparticles are fabricated with mesoporous anatase shells, which are biocompatible for enzyme immobilization (see picture; HRP=horseradish peroxidase). The nanobiocatalyst can be easily collected with an external magnet and recycled. Immobilized enzymes with low activity after several cycles can be decomposed with UV radiation and thus the nanoparticles are recyclable for new enzyme immobilization.

Core-shell VO2@TiO2 nanorods that combine thermochromic and photocatalytic properties for application as energy-saving smart coatings

Vanadium dioxide (VO2) is a Mott phase transition compound that can be applied as a thermochromic smart material for energy saving and comfort, and titanium dioxide (TiO2) is a well-known photocatalyst for self-cleaning coatings. In this paper, we report a VO2@TiO2 core-shell structure, in which the VO2 nanorod core exhibits a remarkable modulation ability for solar infrared light, and the TiO2 anatase shell exhibits significant photocatalytic degradation of organic dye. In addition, the TiO2 overcoating not only increased the luminous transmittance of VO2 based on an antireflection effect, but also modified the intrinsic colour of VO2 films from yellow to light blue. The TiO2 also enhanced the chemical stability of VO2 against oxidation. This is the first report of such a single nanoparticle structure with both thermochromic and photocatalytic properties that offer significant potential for creating a multifunctional smart coating.

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

Cerium ions (Ce(3+)) 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 Ce(3+) 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 Ce(3+) 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 Ce(3+)/Ce(4+) couple (E°(Ce(3+)/Ce(4+))=1.715 V versus the normal hydrogen electrode) is more negative than the valence band of TiO2(B). Therefore, once the Ce(3+)-doped nanofibers are irradiated by UV light, the doped Ce(3+) 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 Zn(2+), Ca(2+), or Mg(2+), does not enhance the photoactivity of the mixed-phase nanofibers as the ions could not trap the photogenerated holes.

Synthesis of the double-shell anatase–rutile TiO2 hollow spheres with enhanced photocatalytic activity

A novel double-shell TiO2 hollow sphere with an inner anatase shell and an outer rutile shell was synthesized by a simple sol-gel method and silica protected calcination process. The structure and formation mechanism was proposed based on characterization using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The double-shell spheres have a uniform diameter of 360 nm and a typical yolk-shell structure. Moreover, the double-shell TiO2 hollow spheres possess a large specific surface area (169 m(2) g(-1)). Due to the high surface area, multiple light reflection and beneficial electron conduction between the inner anatase and outer rutile shell of this special structure, the as-prepared double-shell TiO2 catalysts show remarkably enhanced photoactivity compared to the commercial P25 catalyst. In particular, rhodamine B molecules can be completely decomposed in the presence of the double-shell spheres after 60 minutes of irradiation with UV light. In addition, the high activity is retained after five cycles, indicating the stability and reusability of the double-shell catalyst.

TiO2 rutile–anatase core–shell nanorod and nanotube arrays for photocatalytic applications

Rutile and anatase mixed TiO2 is a promising material for photocatalytic applications. In this work, rutile–anatase core–shell nanotube (NT) and nanorod (NR) structures were fabricated directly on a fluorine doped SnO2 (FTO) glass substrate using a hydrothermal growing/etching and TiCl4 post-treatment method. A pure rutile phase NT/NR core was coated with a roughened anatase shell. The nanostructures were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-vis reflectance and transmittance spectra. The photocatalytic capability was measured by investigating the speed of methyl blue degradation UV. The core–shell NT structure showed superior photocatalytic properties due to larger light absorbing areas, higher light trapping capability and enhanced charge separation efficiency.

Core-regenerated vapor–solid growth of hierarchical stem-like VOx nanocrystals on VO2@TiO2 core–shell nanorods: microstructure and mechanism

This paper presents a novel vapor–solid growth approach of stem-like 1D vanadium oxide nanostructures in a core-regenerated fashion on VO2@TiO2 core–shell rods under a very low temperature (400 °C). The composition and microstructure of the as-grown nanostructures were analyzed by HRTEM, EDS and XPS, confirming the vapor–solid mechanism. The confinement effect of the shell was analyzed by varying experimental parameters (coating thickness and heating rate), and the shell was found to play a critical role in generating and accumulating vapor with supersaturated concentration for the nanocrystal nucleation. Additionally, PVP was added as a surface modifier to favor the growth, probably by forming carbonaceous/nitrogen gaseous species as carrier media, as deduced by FTIR analysis. By exploring the impact of different heating rates, we found that the mass transfer process was facilitated only using a relatively high heating rate (>1.33 °C s−1). However, such a growth was still limited only within the early stages (~15 min), because the confined vacuum interface will disappear with the progress of the crystallization of the nanoporous anatase shell. A unique 1D rods to 2D nano-flakes evolution can be achieved by increasing the heating rate from 1.3 °C s−1 to over 8 °C s−1. These findings provide a valuable understanding on the thermodynamics and kinetics during an unique VS based nanocrystal growing process, and also showed a new method to obtain hierarchical heterogeneous nanostructures.

Core–Shell Nanostructured Catalysts

Novel nanotechnologies have allowed great improvements in the syn-thesis of catalysts with well-controlled size, shape, and surface properties. Transition metal nanostructures with specific sizes and shapes, for instance, have shown great promise as catalysts with high selectivities and relative ease of recycling. Researchers have already demonstrated new selective catalysis with solution-dispersed or supported-metal nanocatalysts, in some cases applied to new types of reactions. Several challenges remain, however, particularly in improving the structural stability of the catalytic active phase. Core-shell nanostructures are nanoparticles encapsulated and protected by an outer shell that isolates the nanoparticles and prevents their migration and coalescence during the catalytic reactions. The synthesis and characterization of effective core-shell catalysts has been at the center of our research efforts and is the focus of this Account. Efficient core-shell catalysts require porous shells that allow free access of chemical species from the outside to the surface of nanocatalysts. For this purpose, we have developed a surface-protected etching process to prepare mesoporous silica and titania shells with controllable porosity. In certain cases, we can tune catalytic reaction rates by adjusting the porosity of the outer shell. We also designed and successfully applied a silica-protected calcination method to prepare crystalline shells with high surface area, using anatase titania as a model system. We achieved a high degree of control over the crystallinity and porosity of the anatase shells, allowing for the systematic optimization of their photocatalytic activity. Core-shell nanostructures also provide a great opportunity for controlling the interaction among the different components in ways that might boost structural stability or catalytic activity. For example, we fabricated a SiO₂/Au/N-doped TiO₂ core-shell photocatalyst with a sandwich structure that showed excellent catalytic activity for the oxidation of organic compounds under UV, visible, and direct sunlight. The enhanced photocatalytic efficiency of this nanostructure resulted from an added interfacial nonmetal doping, which improved visible light absorption, and from plasmonic metal decoration that enhanced light harvesting and charge separation. In addition to our synthetic efforts, we have developed ways to evaluate the accessibility of reactants to the metal cores and to characterize the catalytic properties of the core-shell samples we have synthesized. We have adapted infrared absorption spectroscopy and titration experiments using carbon monoxide and other molecules as probes to study adsorption on the surface of metal cores in metal oxide-shell structures in situ in both gas and liquid phases. In particular, the experiments in solution have provided insights into the ease of diffusion of molecules of different sizes in and out of the shells in these catalysts.

Preparation of magnetically recoverable Fe3O4@SiO2@meso-TiO2 nanocomposites with enhanced photocatalytic ability

A simple and efficient method has been developed to fabricate core–shell structured Fe3O4@SiO2@meso-TiO2 nanocomposites with enhanced photocatalytic activity in this paper. The as-made core–shell structure is composed of a central magnetite core with a strong response to external fields, an interlayer of SiO2, and an outer layer of TiO2 nanocrystals with mesoporous structure. Fe3O4@SiO2 was obtained through a sol–gel process. To avoid magnetic loss caused by magnetite core phase transition and particle reunion, we adopt a mild synthetic method to get anatase shell instead of traditional high-temperature calcination. The structure of resulting composites was characterized and their photocatalytic activities were also tested. Fe3O4@SiO2@meso-TiO2 composite exhibits higher photocatalytic activities than Fe3O4@SiO2@solid-TiO2 for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the high surface area and pore volume created by mesoporous anatase shell.