Impact of reaction temperature,stirring and cosolvent on the solvothermal synthesis of anatase TiO2 and TiO2/titanate hybrid nanostructures: Elucidating the growth mechanism

One-dimensional anatase TiO₂ and hybrid TiO₂/titanate nanostructures are synthesized by a simple low temperature solvothermal route followed by the Na⁺/H⁺ ion-exchange and final calcination process. We investigated the impact of reaction temperature, stirring conditions and cosolvent on the morphologies of the as-prepared nanostructures. Nanotubes and nanorods are formed in alkaline solution, while nanorods/nanowires and nanoporous nanoribbons are formed in alkaline water–ethanol and alkaline water–ethylene glycol mixed solvents, respectively. X-ray diffraction, Raman scattering and high-resolution transmission electron microscopy studies are employed to identify the structure and phase composition. The formation of different morphologies of the as-synthesized nanostructures is investigated by field emission scanning electron microscopy and transmission electron microscopy. The growth mechanism and reaction process of the as-prepared nanostructures are explained based on the experimental observations. The photoluminescence, optical absorption and the tuning of band gap of the prepared samples are also studied. This work will be valuable for understanding the growth mechanism of various nanostructured TiO₂ and to explore the commercial applications of nanoporous nanoribbons of TiO₂.     

A simple electrophoretic deposition method to prepare TiO2-B nanoribbon thin films for dye-sensitized solar cells

This paper describes a simple method utilizing electrophoretic deposition (EPD) to quickly synthesize hydrogen titanate nanoribbon films. The subsequent heating of the hydrogen titanate nanoribbon films causes the dehydration of interlayered OH groups, thereby leading to TiO₂-B nanoribbon films. Thick, uniform TiO₂-B nanoribbon films were obtained from prepared alkali suspensions. The crystal structure of the hydrogen titanate and TiO₂-B nanoribbon films obtained from EPD underwent analysis by X-ray diffraction and high-resolution transmission electron microscope. EPD controlled the thickness of TiO₂-B nanoribbons films. TiO₂-B-coated fluorine-doped tin oxide films were dye-sensitized with N3 and used as a photoanode in an electrochemical solar cell. The solar cell yielded conversion efficiencies of 0.87% for an incident solar energy of 100 mW/cm².     

Surface modification of elongated one-dimensional titanium dioxide structures with ferromagnetic nanoparticles

Nanostructured TiO₂ in the form of elongated one-dimensional structures having a highly ordered layered morphology, with cobalt-containing agglomerates on their surface, has been prepared by hydrothermal treatment of CoTiO₃ powder in the presence of chitosan, a bioactive natural polymer. The synthesis products have been characterized by scanning electron microscopy, transmission electron microscopy, IR spectroscopy, X-ray diffraction, elemental analysis, and magnetic measurements. The structures have been shown to be up to several microns in length, and their typical width ranges from 100 to 400 nm. The one-dimensional structures retain high thermal stability at calcination temperatures of up to 800°C. After vacuum heat treatment at 600°C and above, the nanostructured material possesses anomalously high ferromagnetic characteristics.     

Influence of nitric acid-assisted hydrothermal conditions on the characteristics of TiO2 catalysts and their activity in the oxidative steam reforming of methanol

Titania (TiO₂) nanoparticles (NPs) with different morphologies (spherical, rod-shaped, and mixed) were prepared by hydrothermal treatment of different nitric acid (HNO₃)/titanium (IV) isopropoxide (TTIP) molar ratios (0.25, 0.5, 1.0, and 1.7) at different hydrothermal temperatures (90, 150, 200, and 250 °C), hydrothermal times (6, 12, and 24 h), and calcination temperatures (500, 625, and 750 °C). The crystalline structure, morphology, and surface texture of the obtained TiO₂ NPs were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherm, field emission-scanning electron microscopy, and high resolution-transmission electron microscopy analyses. Under a larger HNO₃: TTIP molar ratio, higher hydrothermal temperature, and higher hydrothermal time, the spherical mixed anatase–rutile phase TiO₂ NPs were converted to a nanorod (NR)-shaped rutile phase (TiO₂-R). The TiO₂-R NRs gave the highest methanol conversion level (65%) and hydrogen yield (45%) in the oxidative steam reforming of methanol at 400 °C.     

Hydrothermal processing of dye-adsorbing one-dimensional hydrogen titanate

One-dimensional hydrogen titanate consisting of mixed nanobelts, nanotubes, and nanorods have been processed via hydrothermal followed by high temperature calcination. The processed products have been characterized via transmission electron microscope, X-ray diffraction, spectrophotometer, spectrofluorometer, and Brunauer-Emmett-Teller surface-area measurement techniques for analyzing their morphology, structure, specific surface-area, band-gap, and photoluminescence. The dye-adsorption (in the dark) and photocatalytic activity (under ultraviolet-radiation exposure) of hydrothermally processed one-dimensional hydrogen titanate have been examined using methylene blue as a model catalytic dye agent. Under the present processing and test conditions, it is demonstrated that one-dimensional hydrogen titanate is a better dye-adsorbent than a photocatalyst due to its higher specific surface-area and relatively lower crystallinity.     

Facile synthesis of nano-TiO2/stellerite composite with efficient photocatalytic degradation of phenol

In this paper, we report a kind of nano-TiO₂/stellerite composite with enhanced photoactivity, which was synthesized by a typical homogeneous precipitation method followed by a calcination crystallization process using natural stellerite as support. The as-prepared composites were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption-desorption, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results showed that TiO₂ loading amounts and calcination temperatures had significant influence on the adsorption and photocatalytic degradation properties of phenol. Moreover, it was indicated that the TiO₂ nanoparticles (NPs) with smaller grain size (around 12.0?nm) and narrower size distributions were uniformly deposited on the surface of stellerite as a layer of film. Compared with commercial P25, the received composite exhibited more superior photocatalytic degradation performance towards phenol. The enhanced photocatalytic degradation performance should result from the better dispersibility of TiO₂ NPs and higher separation efficiency of photogenerated electron-hole pairs. This work may set foundation for the practical application of this new composite photocatalyst in the field of wastewater treatment.     

Anatase–CMK-3 nanocomposite development for hydrogen uptake and storage

The nanometric carbon CMK-3 modified with TiO₂ in anatase phase was synthesized and applied to energy uptake and storage. TiO₂ nanoclusters are important for hydrogen energy harvesting. The creation of porous structures or large surface with TiO₂ nanoclusters inside can potentially face the challenge of improving their efficiency. In the present work, we report the synthesis and characterization of TiO₂–CMK-3 material assembled from anatase nanoparticles dispersed in the nanometric carbon CMK-3. The resulting nanocomposite was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and N₂ adsorption–desorption analysis. The newly synthesized hybrid composites exhibited significantly enhanced H₂ storage, in which CMK-3-ordered porous carbon modified with anatase nanoclusters proved to be a material for hydrogen uptake. The nanoparticles of anatase (～5 nm) incorporated onto CMK-3 showed higher hydrogen uptake at low and high pressures (2.9 wt% of H₂ sorption at 10 bar and 77 K) than CMK-3. The approach includes a discussion of H₂ adsorption process and storage properties.     

Synthesis and characterization of solar photoactive TiO2 nanoparticles with enhanced structural and optical properties

The structural, morphological, and optical properties of the sol–gel derived TiO₂ nanoparticles at different pH and calcination temperature were investigated in the present study. X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), UV–Visible(Vis) spectroscopy, energy dispersive studies (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoluminescence (PL) spectroscopy, BET surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution and pore volume analysis were used to characterize the prepared TiO₂ photocatalyst. The range of crystallite size and band gap of the synthesized TiO₂ samples were in the range of 20–80?nm and 2.5–3.2?eV respectively. The photocatalytic performance of prepared TiO₂ photocatalysts was evaluated by photodegradation of Methylene Blue (MB) solution under simulated solar irradiation. Results illustrate that the synthesized TiO₂ exhibits visible light activity at higher calcination temperature. Crystallinity and surface area plays a vital role in the overall performance of the prepared TiO₂ photocatalyst.     

Free-standing TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>/PANI composite nanofibers for ammonia sensors

Free-standing TiO₂–SiO₂/polyaniline (TS/PANI) composite nanofibers were prepared by electrospinning, in situ polymerization and calcination method. The effect of tetra-n-butyl titanate (TBT) in the electrospinning solution on the morphology and the ammonia sensing properties of TS/PANI composite nanofibers were investigated. The obtained nanofibers were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, thermo-gravimetric analysis and gas sensor test system. It is proved that too much TBT in the solution would make the fibrous morphology and ammonia sensing properties worse. Gas sensing tests showed that the TS/PANI composite nanofibers ammonia sensor can work at room temperature and possess ideal response values, selectivity and repeatability. With the increase in TiO₂ content in the TS nanofibers, the ammonia sensing properties were improved because of the increase in P–N heterojunctions formed between TiO₂ and PANI in the sensors.     

Adsorption and photocatalytic decomposition of organic molecules on carbon-coated TiO2

Carbon-coated anatase TiO₂ samples were prepared from the mixture of poly vinyl alcohol (PVA) and commercial TiO₂ (P-25) with different mass ratios and heating temperatures. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive spectrometer (EDX), transmission electron microscope (TEM), and nitrogen adsorption analyses. The adsorption properties and photocatalytic activity of commercial and carbon-coated TiO₂ catalysts were compared for the oxidation of methylene blue (MB) and bisphenol-A (BPA). It was interesting to find that the transition from anatase to rutile was suppressed by carbon coating of TiO₂ at high temperature up to 800 °C. The carbon-coated TiO₂ samples have a higher surface area and a greater adsorption amount than commercial P-25 because of the thin layer of carbon that covered TiO₂. It was also observed that the photodecomposition efficiency was dependent on the crystallinity of the carbon-coated sample.     

Photoluminescence properties of the rare-earth ions in the TiO2 host nanofibers prepared via electrospinning

Luminescent rare-earth (RE) ions doped TiO₂ nanofibers have been prepared by electrospinning of a mixture solution of rare-earth acetylacetone (RE(C₅H₇O₂)₃)/titanium tetraisopropoxide (Ti (OiPr)₄)/poly(vinyl pyrrolidone) (PVP) (RE = Eu, Er, Ce, Pr), followed by calcination at high temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses demonstrated the morphology and the structure of the rare-earth doped TiO₂ nanofibers. Exciting the nanofibers results in an energy transfer from surface states of TiO₂ to that of the rare-earth ions and the photoluminescence is observed from the crystal field states of the rare-earth ions.     

Fabrication of photocatalytic composite of multi-walled carbon nanotubes/TiO2 and its application for desulfurization of diesel

Composite of multi-walled carbon nanotubes (MWNTs) and titanium (IV) oxide (TiO₂) were prepared by a heterogeneous gelation method. The activities of the MWNTs/TiO₂ composites were evaluated by photocatalytic oxidative desulfurization using dibenzothiophene (DBT), 4,6-dimethyl dibenzothiophene (4,6-DMDBT), n-tetradecane, and commercial diesel under irradiation using a high-pressure Hg lamp. The microstructures of MWNTs/TiO₂ composites were characterized by N₂ adsorption, scanning electron microscopy, transmission electron microscope, and X-ray diffraction. It was found that more than 98% of sulfur compounds in commercial diesel were oxidized and removed by the use of the MWNTs/TiO₂ composite as a photocatalyst.     

Hydrothermal synthesis and characterization of TiO2 nanorod arrays on glass substrates

Large-scale, well-aligned single crystalline TiO₂ nanorod arrays were prepared on the pre-treated glass substrate by a hydrothermal approach. The as-prepared TiO₂ nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. X-ray diffraction results show that the main phase of TiO₂ is rutile. Scanning electron microscopy and transmission electron microscopy results demonstrate that the large-scale TiO₂ nanorod arrays grown on the pre-treated glass substrate are well-aligned single crystal and grow along [0 0 1] direction. The average diameter and length of the nanorods are approximately 21 and 400 nm, respectively. The photocatalytic activity of TiO₂ nanorod arrays was investigated by measuring the photodegradation rate of methyl blue aqueous solution under UV irradiation (254 nm). And the results indicate that TiO₂ nanorod arrays exhibit relatively higher photocatalytic activity.     

Hydrothermal synthesis and gas sensing properties of different titanate nanostructures

Anatase TiO₂ nanoparticles and other three different morphologies of titanate nanostructures such as nanotubes, nanosheets and nanowires were successfully prepared by hydrothermal method. The structures and morphologies of the final products were characterized with field-emission scanning electron microscopy (FE-SEM). Phase analysis was carried out using X-ray diffraction (XRD). A novel formation mechanism from anatase TiO₂ nanoparticles to titanate nanowires is proposed based on FE-SEM. The gas sensing properties to ethanol were also investigated. The results indicate that nanotubes, nanosheets, nanowires show much less resistance and larger response than nanoparticles.     

Fabrication and characterization of TiO2/short MWNTs with enhanced photocatalytic activity

TiO₂/short MWNTs nanocomposites were prepared by the sol–gel method using butyl titanate and short MWNTs as starting materials in the solvent of isopropyl alcohol. Their photocatalytic activity in the degradation of X-3B was studied. The effects of mass ratio of short MWNTs to butyl titanate, and heat-treatment temperature on the photoactivity of TiO₂/short MWNTs nanocomposites were discussed. For comparison purpose, other photocatalysts were also employed in the photodegradation experiment. Thermogravimetric–differential thermal analysis (TG–DTA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–Vis absorption spectra were utilized to characterize the prepared photocatalysts. The results showed that the TiO₂/short MWNTs nanocomposites synthesized with 1% mass ratio of short MWNTs to butyl titanate had the best photoactivity.     

Preparation and characterization of ATO nanoparticles by various coprecipitation

A series of Sb doped SnO₂ (ATO) nanoparticles, with Sb doping levels 0–20 at.% has been prepared by two different coprecipitation routes. Effect of preparation process, Sb doping concentration and calcination temperature on the crystallinity and morphology of ATO nanoparticles were investigated and analyzed. The prepared nanoparticles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, selective area electron diffraction, X-ray diffraction and energy dispersive X-ray spectroscopy. Results indicated that the prepared ATO nanoparticles were tetragonal, and isostructural with rutile lattice structure as known from bulk SnO₂. The ATO nanoparticles prepared via process I (homogeneous coprecipitation) presented obviously weaker crystallinity, smaller average crystallite size and harder agglomeration than that prepared via process II (heterogeneous coprecipitation). The crystallinity and average crystallite size of ATO nanoparticles prepared via process II increased with increasing calcination temperatures and reducing Sb doping concentrations, respectively. The increased crystallinity, dispersibility and average crystallite size for ATO nanoparticles prepared via process II may be due to the formation of ATO crystal nuclei, leading to an improved formation dynamics of ATO nanoparticles.     

Preparation and characterization of titanate nanotubes/carbon composites

Titanate nanotubes/carbon composites(TNT/CCs) were synthesized by allowing carbon-coated TiO₂ (CCT) powder to react with a dense aqueous solution of NaOH at 120 °C for a proper period of time. As-prepared CCT and TNT/CCs were characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectrometry. The processes for formation of titanate nanotubes/carbon composites were discussed. It was found that the TiO₂ particles in TiO₂-carbon composite were enwrapped by a fine layer of carbon with a thickness of about 4 nm. This carbon layer functioned to inhibit the transformation from anatase TiO₂ to orthorhombic titanate. As a result, the anatase TiO₂ in CCT was incompletely transformed into orthorhombic titanate nanotubes upon 24 h of reaction in the dense and hot NaOH solution. When the carbon layers were gradually peeled off along with the formation of more orthorhombic titanate nanotubes at extended reaction durations (e.g., 72 h), anatase TiO₂ particles in CCT were completely transformed into orthorhombic titanate nanotubes, yielding TNT/CCs whose morphology was highly dependent on the reaction time and temperature.     

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Synthesis and characterisation of nano-sized nickel titanate photocatalyst

Visible light activated nickel titanate (NiTiO₃) nanopowders were synthesised by a simple and organic-free co-precipitation method. X-ray diffraction and transmission electron microscopy were used to characterise the crystal structure. The average crystalline size of the synthesised nickel titanate is found to be 100?nm. The visible light photocatalytic activity was evaluated on the basis of photobleaching of methyl orange in aqueous solution. The results show that NiTiO₃ exhibits good photocatalytic activity under visible light irradiation. The enhanced photocatalytic activity of nickel titanate under visible light is due to the lower band-gap value of nickel titanate (3.10?eV) compared to that of TiO₂ (3.23?eV).     

Synthesis of titanium dioxide nanotubes via one-step dynamic hydrothermal process

Titanium dioxide (TiO₂) nanotubes were synthesized via one-step dynamic hydrothermal process from commercial TiO₂ powder. The effects of NaOH concentration, reaction time, reaction temperature, stirring process and washing on the morphology, and the exchange ions of the nanotubes were investigated. The morphology of the nanotubes was characterized in detail with transmission electron microscopy and scanning electron microscope. In the dynamic hydrothermal process, stirring can reduce the reaction time of transformation from particles to nanotubes. The nanotubes were formed when the expected reaction temperature reached to 130 °C. Energy dispersive X-ray analysis was used to determine the exchange of sodium ions and protons in washing process. The Na⁺ ions attached in the nanotubes were removed completely by HCl aqueous solution and deionized water treatments. X-ray diffraction patterns showed the titanate phase of the as-synthesized sample and anatase phase of TiO₂ nanotubes after calcination process at 400 °C for 2 h.