A simple H2O2-assisted route to hollow TiO2 structures with different crystal structures and morphologies

Hollow TiO₂ structures have been synthesized on a large scale in H₂O₂ aqueous solution by a simple hydrothermal method. The morphologies and crystal structures of hollow TiO₂ structures can be controlled by titanium sources. Hollow anatase TiO₂ microspheres composed of nanoparticles are prepared using titanium powder as titanium source. With the pH value increased, TiO₂ nanoparticles and cuboids with cylindrical hollow interiors are formed, respectively. However, hollow rutile TiO₂ microspheres comprising radially aligned nanorods are fabricated using TiCl₃ as titanium source.     

Fabrication of TiO2 hollow fibers with surface nanostructure

Polyvinyl alcohol-TiO₂ (PVA-TiO₂) core sheath nanofibers were fabricated by electrospinning an aqueous solution of PVA and introducing the thread-like droplets directly into a titanium tetraisopropoxide (TTIP)/hexane solution. Rod-like and sheet-like structures of lepidocrocite-type layered titanate formed on the surface of the TiO₂ sheath of the nanofibers by alkaline treatment in 1 mol L⁻¹ aqueous NaOH solution at 363 K. The nanofibers were converted to hollow TiO₂ nanofibers with surface nanostructure and anatase crystallinity by acid treatment to remove sodium ions and heat treatment at 773 K. The surface nanostructures enhanced the crystallinity and external surface area of the nanofiber and contributed to the improvement of photocatalytic oxidation activity.     

One-pot polyelectrolyte assisted hydrothermal synthesis of TiO2-reduced graphene oxide nanocomposite

We demonstrated a facile and efficient strategy for the fabrication of poly(diallyldimethylammonium chloride) (PDDA)-assisted reduced graphene oxide (RGO) sheets–titanium dioxide (TiO₂) in the absence of any seeds and surfactants. PDDA is used as both a reducing agent and a stabilizer to prepare the colloidal suspension of graphene nanosheets. The incorporation of PDDA successfully turns graphene nanosheets into general platforms for in situ growth of TiO₂. The prepared TiO₂–RGO has been thoroughly characterized by spectroscopic (Fourier-transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy) and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic force microscopy and transmission electron microscopy) have been employed to probe the morphological structures as well as to investigate the exfoliation of RGO sheets. It is interesting to see that the TiO₂–RGO composites exhibited excellent photocatalytic activity to hydrogen evolution.     

Photocatalytic properties of TiO2-P2O5 glass ceramics

Binary TiO₂-P₂O₅ glasses with 69 mol% and 76 mol% TiO₂ were prepared and converted into glass ceramics by heat-treatments. XRD measurements show that the main crystalline phases precipitated in the glass ceramics are anatase-type TiO₂ crystals or (TiO)₂P₂O₇ crystals, depending on the concentration of titanium constituent. Photocatalytic activities of the glass ceramics were evaluated by the decomposition of methylene blue (MB) and measuring the water contact angle. It is found that the glass ceramics containing anatase crystals exhibit both photocatalytic oxidation activity and highly photo-induced hydrophilicity under UV irradiation with intensity of 1.0 mW/cm².     

2D spinodal phase-separated TiO2 films prepared by sol-gel process and photocatalytic activity

For the purpose of obtaining oxide thin films with high photocatalytic activity, we have successfully prepared the TiO₂ anatase polycrystalline films with a two-dimensional spinodal phase-separated structure (2D-SPSS) in micron size by the sol-gel dip-coating method from a titanium tetraisopropoxide solution containing polyoxyethylene(20) nonylphenyl ether. It has been also found that TiO₂ films with a variety of morphologies in addition to the 2D-SPSS can be formed by controlling the molar ratio of water to titanium tetraisopropoxide. The methylene blue photodegradation activity of the 2D-SPSS TiO₂ film was higher than that of dense TiO₂ film prepared from a TiO₂ sol without co-existing polymer. This fact can be interpreted in terms of possessing a high specific surface area available for the photocatalytic reaction.     

Sol-gel preparation and properties of TiO2-P2O5 bulk glasses

Monolithic transparent and colorless, or Ti³⁺-free TiO₂-P₂O₅ glasses containing very large amounts of TiO₂ (up to 93 mol%) were successfully prepared by heat-treating the xerogels, which were made from titanium tetraisopropoxide and triethyl phosphate, through the sol-gel reaction. The density and refractive index n_632.8 nm of the sol-gel-derived glasses were higher than the melt-derived glasses of the corresponding compositions. The glasses of TiO₂ content of larger than 80 mol% seemed somewhat porous, but n_632.8 nm of these glasses was very high as 2.2-2.3. Higher density and higher n_632.8 nm than the melt-derived glasses were considered to be due to more abundance of six-fold coordinated Ti⁴⁺ ions.     

Self-propagating high-temperature synthesis products in Fe2O3/TiO2/Al and Fe2O3/TiO2/Al/C thermite systems

This work examines the microstructure and elemental composition of the air combustion products of Fe₂O₃/TiO₂/Al and Fe₂O₃/TiO₂/Al/C thermite mixtures. These systems are shown to differ markedly in the composition and morphology of inclusions and the mechanism of their formation. The metallic phase of the combustion products is shown to contain nanometer-sized titanium nitride inclusions. A mechanism is proposed for the crystallization and oxidation of the combustion products.     

Photoelectrochemical property of ZnFe2O4/TiO2 double-layered films

ZnFe₂O₄/TiO₂ double-layered films on indium-tin oxide (ITO) substrate were prepared by a dip-coating method, and the optical absorption and photocurrent of the as-prepared films were measured. In the double-layered films, the onset of fundamental absorption edge shifts to a longer wavelength, and even shifts to a longer wavelength than that of ZnFe₂O₄-only film as the ZnFe₂O₄ layer thickness increases. Application of the coupled photoanodes double-layered films composed of ZnFe₂O₄ and TiO₂ can obviously increase the photocurrent. It was found that the photocurrent density of ZnFe₂O₄/TiO₂ double-layered films first increased and then decreased with increasing the ZnFe₂O₄ layer thickness. A five-fold increase in the photocurrent density was obtained compared with TiO₂-only films under optimum condition.     

Electrochromic investigation of sol-gel-derived thin films of TiO2-V2O5

Thin films of TiO₂ and TiO₂-V₂O₅ were obtained by dip-coating sol-gel technique. Sols were prepared from titanium ethoxide and inorganic V₂O₅ sol received by dissolution of vanadium pentoxide in hydrogen peroxide. Sol-gel TiO₂ and TiO₂-V₂O₅ films are deposited on conductive glass substrates. TiO₂ and TiO₂-V₂O₅ systems were characterized by FTIR and Raman spectroscopy. Optical transmittance measurements were carried out. Electrochromic characterization was recorded by cyclic voltammetry using three-electrode arrangement. All samples demonstrated electrochromic effect.     

A low-temperature process to synthesize rutile phase TiO2 and mixed phase TiO2 composites

This works employed K₂Ti₄O₉, a novel Ti source, to prepare TiO₂ powders. By a “low-temperature dissolution-reprecipitation process” (LTDRP), rutile phase TiO₂ was successfully synthesized after reacting at 50 °C for 48 h. The obtained sample showed a specific surface area about 45 m²/g, and excellent activity in photo-destruction of NO_x gas. The coupling of rutile phase TiO₂ with commercial anatase TiO₂ showed significant effect in further enhancing the photocatalytic activity.     

Novel ceramic–polymer composites synthesized by compaction of polymer-encapsulated TiO2-nanoparticles

A novel processing route for producing composites from ceramic particles and a thermoplastic polymer with high ceramic content was developed. Via a radical emulsion polymerization reaction in an aqueous suspension, titanium dioxide is encapsulated by a thin layer of poly(methyl methacrylate). Subsequently, the coated particles are compacted by applying high pressure (∼1 GPa) at a temperature above the glass transition temperature of the polymer (∼160 °C). This technique enables producing dense, hard and stiff composites at low processing temperatures. Microstructural investigations of composites by scanning electron microscopy confirm successful coating of titanium dioxide particles by polymer. Compositions were estimated from thermogravimetric measurements. A maximum TiO₂ volume content of almost 70% was achieved. For characterizing mechanical properties, Vickers microhardness as well as flexural strength and elastic modulus were determined. With respect to pure PMMA, composites exhibit a 10-fold increase in microhardness. Furthermore, a strong increase in elastic modulus with TiO₂ contents, up to 40 GPa at 66 vol.% TiO₂ was observed. These moduli are among the highest found in literature for ceramic polymer composites. However, bending strength of the material is still low.     

Effect of TiO2 and nanoclay on the properties of wood polymer nanocomposite

High density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and poly(vinyl chloride) (PVC) with Phragmiteskarka wood flour (WF) and polyethylene-co-glycidyl methacrylate (PE-co-GMA) was used to develop wood polymer composite (WPC) by solution blending method. The effect of addition of nanoclay and TiO₂ on the properties of the composite was examined. The exfoliation of silicate layers and dispersion of TiO₂ nanopowder was studied by X-ray diffractometry and transmission electron microscopy. The improvement in miscibility among polymers due to addition of compatibilizer was studied by scanning electron microscopy (SEM). WPC treated with 3 phr each of clay and TiO₂ showed an improvement in thermal stability. Mechanical, UV resistance and flame retarding properties were also enhanced after the incorporation of clay/TiO₂ nanopowder to the composites. Both water and water vapor absorption were found to decrease due to inclusion of nanoclay and TiO₂ in WPC.     

Preparation of nanostructured TiO2 ceramics by spark plasma sintering

The effect of spark plasma sintering (SPS) on the densification of TiO₂ ceramics was investigated using a nanocrystalline TiO₂ powder. A fully-dense TiO₂ specimen with an average grain size of ∼200 nm was obtained by SPS at 700 °C for 1 h. In contrast, a theoretical density specimen could only be obtained using conventional sintering above 900 °C for 1 h with an average grain size of 1-2 μm.     

Macroporous TiO2/carbon composites prepared via a simple soaking process

A new-type composite photocatalyst of three-dimensional ordered macroporous (3DOM) TiO₂/C was prepared and tested in this paper. 3DOM carbon materials were first prepared by colloidal crystal templating process, and then the sols of TiO₂ from tetrabutyl titanate were infiltrated in the macroporous structures via capillary force. After calcinations at nitrogen flow, TiO₂/C composite materials were prepared. The obtained samples were analyzed by SEM, TEM, XRD and BET. The results indicated that macroporous TiO₂/C can remain the three-dimensional ordered structure and TiO₂ nanoparticles distributed in the interior of macropores uniformly. Eventually, 3DOM TiO₂/C materials were used as a new-type photocatalysts to decompose the methyl orange solution under ultraviolet light, which displayed excellent catalytic activity and regenerative ability.     

Nonstoichiometric orthorhombic titanium oxide, TiO2−δ and its thermochromic properties

Redox relationship among anatase, rutile, and a new nonstoichiometric orthorhombic titanium oxide was elucidated. Single crystal of nonstoichiometric orthorhombic titanium oxide TiO_1.94 was prepared by reducing a single crystal of rutile TiO₂ at 950 °C in H₂ for 1 h based on this relationship. The single crystallinity was demonstrated by both the Laue and the Debye-Scherrer methods. Temperature dependence of the conductivity and the reflectance spectrum was measured for the single crystal of TiO_1.94, and it was found that the reflectivity in near-infrared region over 1700 nm gradually increased with increasing temperature. “Smart windows” using this titanium oxide was proposed.     

Fabrication, structure, and enhanced photocatalytic properties of hierarchical CeO2 nanostructures/TiO2 nanofibers heterostructures

Combining the versatility of electrospinning technique and hydrothermal growth of nanostructures enabled the fabrication of hierarchical CeO₂/TiO₂ nanofibrous mat. The as-prepared hierarchical heterostructure consisted of CeO₂ nanostructures growing on the primary TiO₂ nanofibers. Interestingly, not only were secondary CeO₂ nanostructures successfully grown on TiO₂ nanofibers substrates, but also the CeO₂ nanostructures were uniformly distributed without aggregation on TiO₂ nanofibers. By selecting different alkaline source, CeO₂/TiO₂ heterostructures with CeO₂ nanowalls or nanoparticles were facilely fabricated. The photocatalytic studies suggested that the CeO₂/TiO₂ heterostructures showed enhanced photocatalytic efficiency of photodegradation of dye pollutants compared with bare TiO₂ nanofibers under UV light irradiation.     

A thermodynamic study of the systems Tiox (X=Cl2, SeCl4 OR HCl) I. Investigation of the systems TiO2cl2, TiO2seC14 and TiO2tihCl (TiO2 : Ti = 1 : 1)

The equilibrium composition of the gaseous phase and the yield of titanium oxides in the systems TiO₂cl₂, TiO₂seCl₄, TiO₂hCl and TiO₂tihcl (TiO₂ : Ti = 1 : 1) have been calculated with different preset values of temperature, total pressure and oxygen/halogen derivative ratio. In the systems with Cl₂ and SeCl₄ the presence of only one oxide phase of titanium, TiO₂, was established, its amount being higher in the case of chlorine. In the TiO₂-HCl system, Ti₃O₅ was found in the condensed phase along with the prevailing amount of TiO₂. The percentage of Ti₃O₅ increased with the increase in temperature and initial concentration of HCl. It is shown that in the TiO₂-Ti-HCl system the solid phase obtained should be TiO with a Ti₂O₃ admixture in an amount depending on the total pressure.     

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.     

Effect of the SiO2/TiO2 ratio on the solid acidity of SiO2-TiO2/montmorillonite composites

SiO₂-TiO₂/montmorillonite composites with varying SiO₂/TiO₂ molar ratios were synthesized and the effect of the SiO₂/TiO₂ ratio on the solid acidity of the resulting composites was investigated. Four composites with SiO₂/TiO₂ molar ratios of 0, 0.1, 1 and 10 were synthesized by the reaction of colloidal SiO₂-TiO₂ particles prepared from alkoxides with sodium-montmorillonite at room temperature. The composites showed slight expansion and broadening of the XRD basal reflection, corresponding to the intercalation of fine colloidal SiO₂-TiO₂ particles into the montmorillonite sheets and incomplete intercalation to form disordered stacking of exfoliated montmorillonite and colloidal SiO₂-TiO₂ particles. The colloidal particles crystallized to anatase in the low SiO₂/TiO₂ composites but remained amorphous in the high SiO₂/TiO₂ composites. The specific surface areas (S_BET) of the composites measured by N₂ adsorption ranged from 250 to 370 m²/g, considerably greater than in montmorillonite (6 m²/g). The pore size increased with decreasing SiO₂/TiO₂ molar ratio of the composites. The NH₃-TPD spectra of the composites consisted of overlapping peaks, corresponded to temperatures of about 190 and 290 °C. The amounts of solid acid obtained from NH₃-TPD were 186-338 μmol/g in the composites; these values are higher than in the commercial catalyst K10 (85 μmol/g), which is synthesized by acid-treatment of montmorillonite. The present sample with SiO₂/TiO₂ = 0.1 showed the highest amount of acid, about four times higher than K10.     

Effect of KCl, NaCl and CaCl2 mixture on volume combustion synthesis of TiB2 nanoparticles

Preparation of titanium diboride (TiB₂) nanoparticles was carried out by volume combustion synthesis. TiO₂, B₂O₃ and elemental Mg were mixed with 0-60% salt mixture of KCl, NaCl and CaCl₂ with increment of 15% as a low melting temperature diluent. Compressed samples were synthesized in a tubular furnace at a constant heating rate under argon atmosphere. Thermal analysis of the process showed that the addition of the low melting temperature salts mixture led to a significant decrease in ignition and combustion temperatures. Synthesized samples were then leached by nitric and hydrochloric acids to remove impurities. The samples were examined by XRD, SEM and DLS analysis. The results showed the formation of fine deagglomerated particles with the addition of the salts mixture. The results revealed that 45% salts mixture had the smallest average particle size of about 90 nm.