Improved photo-catalytic activity of single-crystalline TiO2 nanowires surrounded by Pt cube nanoparticles

We report improved photo-catalytic properties of single-crystalline TiO₂ nanowires surrounded by Pt cubes for methanol electrooxidation under UV illumination. The TiO₂–Pt consists of single-crystalline TiO₂ nanowires grown along [0 0 1] direction and Pt cube nanoparticles with dominantly exposed {1 0 0} facets confirmed by transmission electron microscopy images and fast Fourier transform patterns. The nanostructure electrode consisting of TiO₂ nanowires and Pt cubes exhibits a remarkably improved performance for methanol electrooxidation in acid solution as compared to that of TiO₂ nanowires.     

Hydrothermal preparation of Ag-TiO2 nanostructures with exposed {001}/{101} facets for enhancing visible light photocatalytic activity

Nano-composite materials of Ag nanoparticles dispersed TiO₂ nanocubes with exposed {001}/{101} crystal faces were fabricated mainly via a flexible one-step method of hydrothermal treatment with different content of Ag from 1 up to 3 mol%. Prepared photocatalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. These analysis was carried out for understanding the contribution of different content of silver for enhancing the photocatalytic activity of TiO₂ nanocubes. Prepared silver nanoparticles had small particle size and grafted to the {101} crystal face of TiO₂ with the role of template control agent and linking agent. The photocatalytic performance of Ag-TiO₂ nanocubes were researched via Rhodamine B dye removal under visible light irradiation ( ≧420 nm). Ag-TiO₂ composite materials with the content of 2 mol% Ag showed the best photocatalytic activity for degradation of Rhodamine B, which was five times more than bare TiO₂ and associated with the localized surface plasmon resonance (LSPR) propelled effect. The mechanism by which silver enhanced the photocatalytic activity of TiO₂ was also demonstrated.     

In situ synthesis of ultrathin 2-D TiO2 with high energy facets on graphene oxide for enhancing photocatalytic activity

Two kinds of TiO₂ with novel structures, interpenetrating anatase TiO₂ tablets (IP-TiO₂), and overlapping anatase TiO₂ nanosheets (OL-TiO₂) with exposed {0 0 1} facets, are synthesized. The graphene oxide (GO) supported ultrathin TiO₂ nanosheets (OL-TiO₂/GO) is also prepared by one-pot hydrothermal method. The microscopic feature, morphology, phase, and nitrogen adsorption–desorption isotherms are characterized. The performance of photocatalytic degradation of methyl blue is also measured. Compared with IP-TiO₂, the OL-TiO₂ with GO possess higher photocatalytic efficiency. The GO can improve the photocatalytic property by increasing specific surface area, accelerating the separation of electron–hole pairs, as well as extending the electron life. The growth process of TiO₂ nanosheets on graphene oxide layers probably follows a step-growth mechanism with F⁻ as morphology controlling agent. The steps on the surface can improve the photocatalytic activity further due to the increase of dangling bonds of 5-coordinated Ti (Ti_5c) which are considered to be the active sites in the photocatalytic reaction.     

Regulating Photocatalytic Selectivity of Anatase TiO2 with {101}, {001}, and {111} Facets

In this work, we demonstrate a novel approach to control the photocatalytic selectivity of TiO₂ though different dominant crystal facets. {101}, {111}, and {001} facets exposed nanoscale anatase TiO₂ were obtained by a simple hydrothermal route with different ratio of NH₄⁺ and F^?, then a calcined progress to clear surface adsorbent atoms. Results reveal that {101} exposed TiO₂ has some remain binding N with a mode of unsaturated N_3c exhibits selectively photocatalytic degradation of methylene orange (MO) in a methylene blue (MB) and methyl orange (MO) mixed solution, whereas TiO₂ with exposed {111} and {001} facets exhibits photocatalytic selectivity for MB. The {111} facets of anatase TiO₂ exhibit a better photocatalytic selective ability than {001} facets. It confirms that the photocatalytic selectivity can be affected by different dominant crystal facets. In a deeper analysis, there are many unsaturated O_2c on the surface of {001} and {111} facets, which enhances adsorbent selectivity and relevant photocatalytic activity of MB, at the same time, the unsaturated O_2c on the surface of {111} facets is much more than that on the surface of {001} facets results in a better photocatalytic selectivity of {111} facets. This research hopes that developing a new strategy for photocatalytic selectivity and providing a deeper understanding of different crystal facets of TiO₂.     

Preparation and visible light photocatalytic activity of carbon quantum dots/TiO2 nanosheet composites

Carbon quantum dots (C QDs)/TiO₂ nanosheet (TNS) composites were prepared by a simple low temperature process in which TNS were dispersed in C QDs solution, and dried at 60 °C. The C QDs/TNS composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM) and high-resolution TEM. The results indicated that C QDs were well combined with TNS through surface carbon–oxygen groups. The photocatalytic activity was investigated by degradation of rhodamine B under visible light irradiation. The photocatalytic activity of C QDs/TNS composites was significantly enhanced compared with that of C QDs/P25 composites and pure TNS, which indicated that the unique up-converted photoluminescence behavior of C QDs and highly reactive {0 0 1} facets of TNS both played important roles in the enhancement of photocatalytic activity of C QDs/TNS composites.     

Template-assisted hydrothermal synthesis and photocatalytic activity of novel TiO2 hollow nanostructures

TiO₂ hollow nanostructures were successfully synthesized by a controlled hydrothermal precipitation reaction using Resorcinol–Formaldehyde resin spheres as templates in aqueous solution, and then removal of the RF resins spheres by calcination in air at 450 °C for 4 h. The obtained TiO₂ hollow spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption analysis, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under UV illumination. The results indicated TiO₂ hollow nanostructures exhibit the excellent photocatalytic activity probably due to the unique hollow micro-architectures.     

Novel dual heterojunction between MoS2 and anatase TiO2 with coexposed {101} and {001} facets

This work prepared an anatase TiO₂ by controlling coexposed {101} and {001} facets. The anatase TiO₂ was composited with MoS₂, and the photocatalytic behavior was studied. The relationship between the exposed ratio of {001} facets and the enhancement proportion by the composite was compared. An appropriate exposed ratio of {001} facets, instead of a high ratio, can cause the highest enhancement proportion for photocatalytic activity. This finding confirmed that exposed {001} facets are not the main factors for improving photocatalytic activity. Dual heterojunction was observed to form between MoS₂ and anatase TiO₂ with coexposed {101} and {001} facets, which is a crystal‐face heterojunction between {101} and {001} facets and a semiconductor heterojunction between MoS₂ and {001} facets of TiO₂. In this dual heterojunction, photo‐induced electrons in TiO₂ will flow into {101} facets of TiO₂, instead of MoS₂, whereas the photo‐induced holes in TiO₂ will flow into MoS₂ to reach a high separation efficiency. This finding further revealed the elevating mechanism of constructing heterojunction based on coexposed crystal faces.     

Synthesis of uniform anatase TiO2 microspheres with exposed {001} facets: Without HF utilization and Its photocatalytic selectivity

Uniform anatase TiO₂ microspheres with a high percentage of exposed {001} facets have been successfully synthesized by a one-step hydrothermal strategy in the presence of H₂O₂ and (NH₄)₂CO₃ solution. The as-synthesized anatase TiO₂ microspheres with exposed {001} facets exhibited higher photocatalytic selectivity for degradation of methylene blue and methylene orange mixed solution under UV light irradiation at room temperature than anatase TiO₂ microspheres without {001} facets exposing and P25 TiO₂.     

Simple fabrication of thermally stable apertured N-doped TiO2 microtubes as a highly efficient photocatalyst under visible light irradiation

Apertured N-doped TiO₂ microtubes have been fabricated by simple hydrolysis of titania tetrachloride using ammonia without any external templates. The morphology and microstucture characteristics of apertured N-doped TiO₂ microtubes were characterized by means of the specific surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of microtubes and mesoporous microstructure were maintained after a heat treatment at 723 K for 3 h, exhibiting significantly thermal stability. The catalysts exhibited high ultraviolet and visible light photocatalytic activity in degrading phenol and methyl orange.     

Nitrogen-doped anatase titania nanorods with reactive {101} + {010} facets exposure produced from ultrathin titania nanosheets for high photocatalytic performance

To obtain high performance catalysts for the photooxidation of organic pollutants in water, nitrogen-doped TiO₂ nanorods with {101} + {010} facets exposure were successfully synthesized by using ultrathin two-dimensional titania nanosheets as precursor. The nitrogen-doped one-dimensional nanorods had a uniform size within 100 nm. The crystal structure of nitrogen-doped TiO₂ nanorods (anatase) didn't alter even though subjected from morphology transformation, however, their crystallinity improved tremendously, and the exposure and proportion of active facets changed, which synergistically boosted the catalytic efficiency. This integrated technology including modification, morphology and phase control might be indicative for fabrication of advanced photocatalysts to remedy environmental pollutant and produce clean energy in the future.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Synthesis of parallel squared nanosheet-assembled Bi2WO6 microstructures under alkalescent hydrothermal treatment

The hierarchical Bi₂WO₆ microstructures, which were two-dimensionally assembled by parallel squared nanosheets, were synthesized under alkalescent hydrothermal treatment. The crystalline phase, morphology, size, lattice plane and crystalline structure of the products were characterized by X-ray diffraction, scanning/transmission electron microscopy and selected area electron diffraction. The formation of parallel squared nanosheet-assembled hierarchical Bi₂WO₆ microstructures was elucidated by the oriented attachment growth mechanism based on our experimental results. The aqueous ammonia, which was employed as the alkalescent environment, had a critical effect on the formation of such hierarchical Bi₂WO₆ microstructures with a large proportion of {001} facets. The parallel squared nanosheet-assembled hierarchical Bi₂WO₆ microstructures obtained at the hydrothermal temperature of 120 °C showed high photocatalytic activity under visible-light irradiation.     

Synthesis,characterization, and photocatalytic properties of ZnO nano-flower containing TiO2 NPs

In this study, TiO₂-impregnated ZnO nano-flowers were synthesized by one-pot hydrothermal process. Aqueous suspension containing ZnO precursor and commercial TiO₂ NPs (P25) is heated at 140 °C for 2 h. The morphology and structure of as-synthesized particles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), which revealed that TiO₂ NPs were attached on the surface of ZnO flower. It was observed that the presence of TiO₂ NPs in the hydrothermal solution could sufficiently decrease the size of ZnO flower. The hybrid nanostructure, with unique morphology, obtained from this convenient method (low temperature, less time, and less number of reagents) was found to be effective photocatalyst under UV-irradiation.     

Supercritical hydrothermal synthesis of titanium dioxide nanostructures with controlled phase and morphology

A novel template- and organic-free synthesis of TiO₂ nanostructures with controlled phase and morphology was realized through batch supercritical hydrothermal treatment (400 °C) of titanate nanotubes (TNTs) with H₂O₂ in NaOH aqueous solution. Well-defined 3D titanate hierarchical spheres (THSs), 2D multilayered titanate nanosheets (TNSs), and 1D monodisperse anatase nanorods (ANRs) exposing (0 1 0) facets were prepared in 15 min by slightly varying the NaOH solution pH. Specifically, the obtained Na/H-THSs (without/with HCl neutralization) exhibited highly porous structures with large specific surface area (109 m² g⁻¹ and 196 m² g⁻¹, respectively). Temperature-dependent phase and morphology evolutions of products under subcritical condition (200 and 300 °C) were investigated. The formation of the TiO₂ nanostructures from TNTs was proposed mainly following a dissolution–nucleation-growth mechanism, suggesting that both supercritical temperature and NaOH solution pH were determinant factors governing the nucleation and growth process and thus the phase and morphology.     

Fast removal of surface damage layer from single crystal diamond by using chemical etching in molten KCl + KOH solution

To fast remove the surface damage layer from single-crystal-diamond, we have developed a chemical etching process using molten KCl and KOH solution at high temperature around 1100 °C. High removal rate about R_{001} = 2.0 μm/h, R_{101} = 20 μm/h and R_{111} = 26 μm/h was achieved for the {001} sample surfaces, {101} and {111} sample edges, respectively. Laser microscope observation has confirmed that the {001} surface flatness has been greatly improved after etching and surface roughness formed during previous lift-off process has been effectively removed.     

Preferential {1 0 0} etching of boron-doped diamond electrodes and diamond particles by CO2 activation

The etching behavior of polycrystalline boron-doped diamond (BDD) electrodes and diamond particles with gaseous CO₂ at 800 and 900 °C was investigated by field-emission scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Polycrystalline BDD (800 ppm), composed of a mixture of cubic {1 0 0} and triangular {1 1 1} orientated planes, was used so as to pursue the possibility of preferential etching by high temperature CO₂ treatment. Nanometer sized pits were observed on the {1 0 0} planes while no change was observable for the {1 1 1} planes when the activation temperature was 800 °C. The difference in the etching behavior by CO₂ with regard to the different planes was clarified using diamond particles and comparing with steam activation. The results demonstrate that CO₂ activation leads to preferential {1 0 0} etching, whereas steam-activation results in preferential {1 1 1} etching.     

Low temperature hydrothermal synthesis of monodispersed flower-like titanate nanosheets

Monodispersed flower-like titanate superstructure was successfully prepared by simple hydrothermal process without any surfactant or template. N₂-sorption analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD) observation of as-synthesized product revealed the formation of flower-like titanate with diameter of about 250–450 nm and BET surface area (S_BET) of 350.7 m² g^?1. Upon thermal treatment at 500 °C, the titanate nanosheets were converted into anatase TiO₂ with moderate deformation of their structures. The as-prepared flower-like titanate showed high photocatalytic activity for H₂ evolution from water splitting reaction. Moreover, the sample heat treated at 500 °C exhibited higher photocatalytic activity than that of commercial TiO₂ anatase powder (ST-01).     

Water vapor adsorption and photocatalytic pollutant degradation with TiO2–sepiolite nanocomposites

A new nanocomposite containing a titanium dioxide photocatalyst and low-cost sepiolite was prepared and tested for its potential multifunctional application in water vapor adsorption and pollutant photodegradation. The nanocomposite was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric and differential thermogravimetric analyses (TGA/DTG), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and surface area (BET) measurements. The XRD patterns of the nanocomposites exhibited the characteristic sepiolite and anatase reflections, while the SEM images revealed the surface morphology of the raw sepiolite after the modification with the sol gel prepared with TiO₂. In the TGA/DTG, up to 100 °C, three stages of water removal were analyzed and attributed to surface and zeolitic water loss. Upon TiO₂ loading, the overall mass loss of sepiolite was reduced to half, but the three stages of water loss were rearranged with low loading (10 wt.%) or were reduced to two stages with higher loading (20 wt.%). The hydrophilic nature of the raw sepiolite was retained after the TiO₂ loading, while the water vapor uptake was reduced to 20–30% with relative humidities from 30 to 80% and loadings up to 20 wt.%. In addition, the efficiencies of the supported photocatalysts were investigated using β-naphthol as a model pollutant compound. All prepared catalysts exhibited higher activities than when using the bare TiO₂ sample. Therefore, the TiO₂–sepiolite nanocomposite can be potentially applied for combined photocatalytic degradation processes and water vapor adsorption to allow for evaporative cooling.     

Preparation of oriented SiO32− doped TiO2 film and degradation of methylene blue under visible light irradiation

SiO₃^2? doped TiO₂ films with oriented nanoneedle and nanorectangle block structure has been firstly synthesized by hydrothermal synthesis method. The prepared samples are characterized, X-ray diffraction (XRD) results demonstrate that the SiO₃^2? doped TiO₂ films are rutile and brookite phases. The scanning electron microscope (SEM) analysis reveals that the quantity of O₂ affects the morphology of the SiO₃^2? doped TiO₂ films (SiTiA films prepared with unmodified substrate). The SiO₃^2? doped TiO₂ films (SiTiB films prepared with modified substrate) display two layers, one is porous structure, the other is nanoneedle structure. UV–vis, IR, transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) microscopy all prove that SiO₃^2? have been doped in the TiO₂ crystal structure. They have remarkable red shift and higher photocatalytic activity of degradation of methylene blue than P-25 under visible light (λ > 420 nm) irradiation. Besides, photocatalytic activity of the film is stable during 4 times recycling.     

Improved activity of a graphene–TiO2 hybrid electrode in an electrochemical supercapacitor

We present a simple and fast approach for the synthesis of a graphene–TiO₂ hybrid nanostructure using a microwave-assisted technique. The microstructure, composition, and morphology were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. The electrochemical properties were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. Structural analysis revealed a homogeneous distribution of nanosized TiO₂ particles on graphene nanosheets. The material exhibited a high specific capacitance of 165 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M Na₂SO₄ electrolyte solution. Theenhanced supercapacitance property of these materials could be ascribed to the increased conductivity of TiO₂ and better utilization of graphene. Moreover, the material exhibited long-term cycle stability, retaining ∼90% specific capacitance after 5000 cycles, which suggests that it has potential as an electrode material for high-performance electrochemical supercapacitors.