Single-crystalline Anatase TiO2 Research Articles

Pt Single Atoms as Co‐Catalysts on CdS‐Sensitized Single‐Crystalline TiO2 Nanoflakes for Enhanced Visible Light Photocatalytic H2 Generation

AbstractStudies on single‐atom catalysts (SACs) with individually isolated metal atoms anchored on specific supports have gained great interest in photocatalysis due to their enhanced catalytic activity and optimal atom utilization. By providing an optimized number of active sites and enhancing their intrinsic activity, SACs afford a distinctive platform for photocatalysis at the atomic level. In this study, we investigate the photocatalytic H2 generation of Pt single atoms (SAs) anchored on CdS‐sensitized single crystalline anatase TiO2 nanoflakes (ATNF) in the visible spectral range. Vertically‐aligned ATNF were synthesized on fluorine‐doped tin oxide substrates by a hydrothermal process, which were further sensitized by CdS nanoislands (NIs) using the successive ionic layer adsorption and reaction (SILAR) technique. Finally, a reactive‐deposition approach was used to successfully anchor Pt SAs on CdS‐sensitized ATNF. Under optimized conditions, the highest photocatalytic H2 evolution on Pt‐anchored single atom CdS sensitized ATNF was 17.8 μL h−1 under visible light illumination, which is 15.8, 7.5, and 6.7‐fold higher than bare CdS/FTO, PtSA/CdS/FTO, and ATNF, respectively. Overall, the density of Pt SAs plays a vital role via strong trapping of the photogenerated electrons and significantly improves the efficiency of electron‐hole separation, making PtSA/ATNF efficient solar‐driven photocatalysts.

Fabrication and Photocatalytic Activity of Single Crystalline TiO2 Hierarchically Structured Microspheres

Single crystalline anatase TiO2 microspheres with co-exposed {001}/{101} facets were prepared by a facile one-pot hydrothermal method using NaF as a morphology controlling agent. The influences of the NaF amount on the morphology and also on the photocatalytic activity were investigated systematically. The obtained microspheres possessed better morphology when the concentration of NaF was chosen at 0.1 mol/L, and the experimental results indicated that the crystal structure and morphology played important roles on the photocatalytic activity, based on the experimental results it was found that the photocatalytic degradation efficiency of TiO2 microspheres on Tetracycline hydrochloride could reach 76.4% in 2 h. Finally, a growth mechanism was proposed by investigating the growth process, i.e., a synergistic effect of F ions modified Ostwald ripening and oriented attachment.

A facile synthesis of porous amorphous/crystalline TiO2 hybrids for enhanced electrochromic performances

Porous crystalline/amorphous TiO2 (c/a-TiO2) hybrid films have been successfully grown on FTO substrates via a solvothermal reaction followed by a simple air annealing treatment. By adjusting reaction temperature, the porous structure and the proportion of amorphous TiO2 phase can be feasibly modulated. The in-situ transformation of crystalline TiO2 from amorphous phase could ensure the optimal crystalline/amorphous interface contact. The obtained c/a-TiO2 hybrid films shows excellent electrochromic properties which can switch between green color and transparent state with large optical contrast (59.3%) at 700 nm, high coloration efficiency (24.3 cm2 C−1) and short switching time (bleaching time of 2.0 s and coloration time of 12.1 s). Due to the desired porous structure for short Li+ ions diffusion paths and crystalline/amorphous interface enables low energy barrier and fast ion migration during the insertion/extraction of Li+ ions, the c/a-TiO2 hybrid film not only exhibits lower threshold voltage (+0.2 ∼ −1.5 V vs Ag/AgCl) and faster response than single crystalline anatase TiO2 (c-TiO2) counterpart, but also owns higher coloration efficiency and better durability than single amorphous TiO2 (a-TiO2). Compared to the commonly blue color of c-TiO2, the success to gain green color by using the prepared c/a-TiO2 hybrid film makes it very attractive for constructing electrochromic devices. Our study here also offers an alternative way of designing TiO2-based nanostructures for high-efficiency electrochromic applications.

A facile “dark”-deposition approach for Pt single‐atom trapping on facetted anatase TiO2 nanoflakes and use in photocatalytic H2 generation

In recent years, single-atom (SA) catalysts have become strongly investigated in electrocatalysis and increasingly also in photocatalysis. Here we demonstrate that single-crystalline anatase TiO2 nanoflake (NF) layers after a facile thermal air annealing process provide suitable anchoring sites for Pt SAs. Remarkably, such air annealed (001) faceted single-crystalline TiO2 nanoflakes can trap and stabilize Pt SAs and assemblies when immersed into a Pt precursor solution for sufficient time in absence of any illumination, i.e., under "dark deposition” conditions. These decorated species act as more efficient co-catalysts for the H2 evolution reaction, compared to the classical Pt nanoparticles (NPs). Here we show that such single-crystal-based TiO2 photocatalyst, decorated with Pt SAs, can display a 4-fold increase in photocatalytic H2 production at a lower Pt loading than observed for a classical Pt nanoparticle Pt/TiO2 arrangement.

Array of single crystalline anatase TiO2 nanotubes with significant enhancement of photoresponse

Anatase TiO2 nanotubes array (ATONA) has attracted tremendous attention owing to its promising applications in solar cells, water splitting and organic pollutants photocatalytic degradation. However, the activity of ATONAs was greatly suppressed by the grain boundaries existed in the tube walls, which acted as carrier scattering and recombination centers. Herein, we report a novel strategy to prepare array of single crystalline anatase TiO2 nanotubes (SC-ATONAs) with significant enhancement of the photocatalytic activity and UV photo response performance compared to the polycrystalline counterparts. The growth of SC-ATONAs was achieved by establishing a crystallization temperature gradient along the tube wall, which ensured the crystallization started from the nucleation of a single nucleus at the bottom of amorphous TiO2 nanotubes prepared by Ti anodization. These findings pave the way to prepare single-crystalline nanotubes with superior performance for other materials.

Correlation between Photocatalytic Activity and Carrier Lifetime: Acetic Acid on Single-Crystal Surfaces of Anatase and Rutile TiO2

Photocatalytic activity and lifetime of photoexcited carriers on well-defined single-crystalline anatase and rutile TiO2 surfaces with different surface orientation have been systematically studied by photoelectron spectroscopy. Photocatalytic activity, evaluated with reference to the photocatalytic degradation of acetic acid, has a positive and linear correlation with carrier lifetime at the crystal surface, which was determined by following the time evolution of the ultraviolet-induced surface photovoltage. This indicates that the carrier lifetime is a prime factor for the photocatalytic activity so that it can be viewed as the origin of the crystal-surface-orientation dependence of the photocatalytic activity.

Effects of {001} Facet of Anatase TiO2 Single-crystalline Nanosheets on Photoexcited Electron Transfer from Near-infrared Dye-sensitizer

Single-crystalline anatase TiO2 nanosheets predominantly exposing the {001} facet at a surface fraction of more than 75% were constructed on transparent conductive oxide glass substrates. Application of these nanoarchitectures of TiO2 demonstrated photoelectric conversion while using near-infrared absorbing dye-sensitizer. In contrast, regular mesoporous TiO2 films with a much larger effective surface area did not exhibit a photoelectric response with the same dye-sensitizer. The results obtained here emphasize the importance of the contacted crystalline facet of TiO2 in photoinduced charge separation for minimizing the potential drop for interfacial charge-carrier transfer in dye-sensitized solar cell systems. Especially, the observed improvement of electron injection by contacted facet could contribute to the efficient photoexcited electron injection from near-infrared dye-sensitizers possessing relatively small HOMO–LUMO gap.

Effective excitons separation on graphene supported ZrO2[sbnd]TiO2 heterojunction for enhanced H2 production under solar light

A novel photocatalyst comprises of ZrO2TiO2 immobilized on reduced graphene oxide (rGO) – a ternary heterojunction (ZrO2TiO2/rGO) was synthesized by using facile chemical method. The nanocomposite was prepared with a strategy to achieve better utilization of excitons for catalytic reactions by channelizing from metal oxide surfaces to rGO support. TEM and XRD analysis results revealed the heterojunction formed between ZrO2 and single crystalline anatase TiO2. The mesoporous structure of ZrO2TiO2 was confirmed using BET analysis. The red shift in absorption edge position of ZrO2TiO2/rGO photocatalyst was characterized by using diffuse reflectance UV–Visible spectra. ZrO2TiO2/rGO showed greater interfacial charge transfer efficiency than ZrO2TiO2, which was evidenced by well suppressed PL intensity and high photocurrent of ZrO2TiO2/rGO. The suitable band gap of 1.0 wt% ZrO2TiO2/rGO facilitated the utilization of solar light in a wide range by responding to the light of energy equal to as well as greater than 2.95 eV by the additional formation of excited high-energy electrons (HEEs). ZrO2TiO2/rGO showed the enhanced H2 production than TiO2/rGO, which revealed the role of ZrO2 for the effective charge separation at the heterojunction and the solar light response. The optimum loading of 1.0 wt% of ZrO2 and rGO on TiO2 showed the highest photocatalytic performance (7773 μmolh−1gcat−1) for hydrogen (H2) production under direct solar light irradiation.

Epitaxial growth and properties of Nb-doped anatase TiO2 films on LSAT by MOCVD

High quality single crystalline Nb-doped anatase phase TiO2 films with different Nb concentrations were deposited on LSAT (100) substrates by metal organic chemical vapor deposition (MOCVD) at 600 °C. The influences of Nb concentration on the structural, electrical and optical properties of the films have been investigated. The obtained films were single crystalline anatase TiO2 and the epitaxial relationship between the films and the substrates was confirmed as TiO2 (001) || LSAT (100) with TiO2 [010] || LSAT [010]. The resistivity of the films was reduced by almost 8 orders of magnitude after Nb doping and a minimum resistivity of 4.0 × 10−2Ω⋅cm was obtained in 0.6% Nb-doped samples. The films achieved a maximum mobility as high as 13.5 cm2⋅V−1⋅s−1. The carrier concentration was in a range of 9.4 × 1017–1.7 × 1019 cm−3. The optical transmittance of the films in the visible range exceeded 93% and the optical band gap was varied from 3.48 to 3.53 eV.

Ordered Single-Crystalline Anatase TiO2 Nanorod Clusters Planted on Graphene for Fast Charge Transfer in Photoelectrochemical Solar Cells.

Achieving efficient charge transport is a great challenge in nanostructured TiO2 -electrode-based photoelectrochemical cells. Inspired by excellent directional charge transport and the well-known electroconductibility of 1D anatase TiO2 nanostructured materials and graphene, respectively, planting ordered, single-crystalline anatase TiO2 nanorod clusters on graphene sheets (rGO/ATRCs) via a facial one-pot solvothermal method is reported. The hierarchical rGO/ATRCs nanostructure can serve as an efficient light-harvesting electrode for dye-sensitized solar cells. In addition, the obtained high-crystallinity anatase TiO2 nanorods in rGO/ATRCs possess a lower density of trap states, thus facilitating diffusion-driven charge transport and suppressing electron recombination. Moreover, the novel architecture significantly enhances the trap-free charge diffusion coefficient, which contributes to superior electron mobility properties. By virtue of more efficient charge transport and higher energy conversion efficiency, the rGO/ATRCs developed in this work show significant advantages over conventional rGO-TiO2 nanoparticle counterparts in photoelectrochemical cells.

Single-crystalline anatase TiO2 nanoleaf: Simple topochemical synthesis and light-scattering effect for dye-sensitized solar cells

A topochemical process was used to synthesize {010}-faceted leaflike anatase TiO2 nanocrystals from exfoliated layered titanate nanosheets. A light scattering effect of the leaflike anatase nanocrystals with a crystal size of 300nm in length and 30nm in width was studied as a light scattering layer on a P25 nanocrystalline-TiO2 film for dye-sensitized solar cells (DSSCs). The light scattering layer fabricated using the leaflike nanocrystals exhibits a synergistic effect of light scattering and dye-loading for enhancement of light harvesting, which enhanced 28% of energy conversion efficiency of DSSCs by enhancing 33% of Jsc. The leaflike nanocrystals oriented to the direction vertical to the direction of incident light in the scattering layer improve the scattering effect of the scattering layer, and the dye molecules adsorbed on the {010}-faceted anatase exhibit high performance for photoelectron generation.

Shape-controlled synthesis of single-crystalline anatase TiO2 micro/nanoarchitectures for efficient dye-sensitized solar cells

Single crystal TiO2 nanocrystals were assembled into different TiO2 micro/nanoarchitectures. Various characterizations are conducted to understand the correlation between particle morphology, crystallinity, surface energy and anisotropic crystal growth of the nanocrystals.

Ultrathin single-crystalline TiO2 nanosheets anchored on graphene to be hybrid network for high-rate and long cycle-life sodium battery electrode application

Abstract In view of the growing concern about energy management issues, sodium ion batteries (SIBs) as cheap and environmentally friendly devices have increasingly received wide research attentions. The high current rate and long cycle-life of SIBs are considered as two key parameters determining its potential for practical applications. In this work, the rigid single-crystalline anatase TiO2 nanosheets (NSs) with a thickness of ∼4 nm has been firstly prepared, based on which a stable nanostructured network consisting of ultrathin anatase TiO2 NSs homogeneously anchored on graphene through chemical bonding (TiO2 NSs-G) has fabricated by hydrothermal process and subsequent calcination treatment. The morphology, crystallization, chemical compositions and the intimate maximum contact between TiO2 NSs and graphene are confirmed by TEM, SEM, XRD, XPS and Raman characterizations. The results of electrochemical performance tests indicated that the TiO2 NSs-G hybrid network could be consider as a promising anode material for SIBs, in assessment of its remarkably high current rate and long cycle-life aside from the improved specific capacity, rate capability and cycle stability.

Ag-encapsulated Single-Crystalline Anatase TiO2 Nanoparticle photoanodes for enhanced dye-sensitized solar cell performance

In this article, Ag-encapsulated Single-Crystalline Anatase TiO2 Nanoparticles (SC-TiO2@Ag) are prepared and introduced into dye-sensitized solar cells (DSSCs). The Single-Crystalline Anatase TiO2 Nanoparticles (SCANPs) were prepared by the hydrothermal transformation of titanate nanotubes at pH of 2, and the SC-TiO2@Ag plasmonic nanocomposite materials were successfully prepared through a facile stepwise impregnation-chemical reduction method without using any stabilizer or surfactant. An optimized SC-TiO2@Ag modified DSSC is achieved with a power conversion efficiency (PCE) of 8.33%, which is significantly superior to that of the unmodified TiO2 DSSC with a PCE of 6.32%. This enhanced efficiency is mainly attributed to the plasmonic effect, improved interfacial charge transfer, and retarded charge recombination, reduction in the band gap energy, and enhanced the optical absorption of dye, as well as the increase of the amount of the dye absorption. The influence of silver ammonia solution [Ag(NH3)]2OH concentration on the overall efficiency was also investigated, and the optimum concentration was found to be 3 mM.

Mesoporous Assembly of Cuboid Anatase Nanocrystals into Hollow Spheres: Realizing Enhanced Photoactivity of High Energy {001} Facets

Herein, we showcase a unique one-step synthetic strategy to obtain a mesoporous assembly of cuboid anatase nanocrystals into hollow spheres that not only offers high surface area but also predominantly tenders the reactive high energy {001} facets. The detailed experimental studies, parameter optimization, and characterizations reveal the crucial role played by the shape and structure directing agents during nucleation and growth. Concentration of F–-ions plays a determining role in stabilizing the size and shape at the initial stage of formation while an optimal balance of SO42– anions is critical in generating the hollow porous assemblies while retaining the morphology of the primary nanocuboid subunits. The single crystalline anatase TiO2 nanocuboids and their hollow spherical assemblies; both show substantial enhancement in photocatalytic and photoelectrochemical activity when compared with commercial P25. Photoelectrodes fabricated using cuboid nanocrystals demonstrate a superior DSSC efficiency when...

Hydrothermal synthesis and memristive switching behaviors of single-crystalline anatase TiO2 nanowire arrays

A facile one-step hydrothermal method has been reported to prepare the single-crystalline anatase TiO2 nanowire arrays with (101) preferentially oriented on the FTO substrate. The as-prepared Au/TiO2 NWAs/FTO based device exhibits the nonvolatile bipolar memristive switching behaviors with a high HRS/LRS resistance ratio of about three orders of magnitude. The memristive switching behaviors of the device have been elucidated by the Ohmic conduction mechanism and the trap-controlled space charge limited current conduction mechanism. Furthermore, the Schottky barriers modulated by the oxygen vacancies at the Au/TiO2 interface have been suggested to dominate the bipolar memristive switching behaviors of the device. This work demonstrates that the Au/TiO2 NWAs/FTO based device may be a promising candidate for memristor applications.

Preparation and characterization of single crystalline anatase TiO2 epitaxial films on LaAlO3(001) substrates by metal organic chemical vapor deposition

Anatase phase TiO2 (a-TiO2) films have been fabricated on LaAlO3(001) substrates at the substrate temperatures of 500 to 650°C by the metal organic chemical vapor deposition (MOCVD) method using tetrakis-dimethylamino titanium (TDMAT) as the organometallic (OM) source. The structural studies revealed that the TiO2 film prepared at 600°C had the best single crystalline quality with no twins. The out-of-plane and in-plane epitaxial relationships of the films were a-TiO2(004)||LaAlO3(001) and TiO2[100]||LaAlO3[100], respectively. The optical band gap of the films ranged from 3.30 to 3.37eV. The morphology and composition of the TiO2 films have also been studied in detail.

Graphene Oxide-Assisted Synthesis of Microsized Ultrathin Single-Crystalline Anatase TiO2 Nanosheets and Their Application in Dye-Sensitized Solar Cells.

High-quality microsized ultrathin single-crystalline anatase TiO2 nanosheets (MS-TiO2) with exposed {001} facets were synthesized by a facile and low-cost two-step process that combines a graphene oxide (GO)-assisted hydrothermal method with calcination. Both GO and HF play an important role in the formation of well dispersed MS-TiO2. As a novel microsized (1-4 μm) ultrathin two-dimensional (2D) material, MS-TiO2 possesses much higher lateral size and aspect ratio compared to common 2D nanosized (30-60 nm) ultrathin TiO2 nanosheets (NS-TiO2), resulting in excellent electronic conductivity and superior electron transfer and diffusion properties. Here, we fabricated MS-TiO2 and NS-TiO2, both of which were incorporated with the TiO2 nanoparticles (P25) to constitute the hybrid photoanode of dye-sensitized solar cells (DSSCs), and explored the effect of the lateral size (nano- and micro-) of ultrathin TiO2 nanosheets on their electron transfer and diffusion properties. Benefiting from the faster electron transfer rate and short diffusion path of the MS-TiO2, the MS-TiO2/P25 gains the more superior performance compared to pure P25 and NS-TiO2/P25 in the application of DSSCs. Moreover, it is expected that the novel high aspect ratio MS-TiO2 may be applied in diverse fields including photocatalysis, photodetectors, lithium-ion batteries and others concerning the environment and energy.

Highly Efficient Hydrogen Production using Bi2O3/TiO2 Nanostructured Photocatalysts Under Led Light Irradiation

Photocatalytic water splitting (PWS) is one of the cleaner processes for molecular hydrogen (H2) and oxygen (O2) production using semiconductor nanocomposites as efficient photocatalysts. Herein, we report hydrothermal synthesis and modification of Bi2O3 deposited TiO2 nanostructures (Bi-TNS), its water splitting performance under UV-A LED (λ = 365 nm, 20 W) light irradiation. Characterization data reveals that calcined photocatalyst (TNS) have single crystalline anatase TiO2 with mixed morphologies viz., nanotubes, nanorods and nanoparticles. The TEM and DR UV-Vis spectra of Bi2O3 deposited TiO2 composite photocatalysts confirmed anatase phase TiO2 besides mixed morphologies. A dedicated off-line gas chromatograph equipped with molecular sieve column and TCD detector utilized for analysis of H2 and O2 gases. Under optimized conditions, Bi0.5TNS composite showed enhanced rate of H2 production 3,601 μmol.h-1 g-1cat which is much higher than standard TiO2 P-25 nanoparticles. These results illustrated the advantage of nano-size effect of TiO2 and Bi2O3 for enhanced H2 production. Stability of catalyst under light irradiation (100 h) shows that Bi-TNS is a promising photocatalyst for enhanced H2 production using industrial by-product glycerol as scavenger.

Preparation and characterization of single crystalline anatase TiO2 films on LSAT (001) by MOCVD

TiO2 thin films with anatase structure have been prepared on [LaAlO3]0.3[SrAl0.5Ta0.5O3]0.7 (LSAT) (001) substrates by metalorganic chemical vapor deposition (MOCVD) in the substrate temperature range of 500–650 °C.