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.     

Hydrothermal synthesis of a nanostructured TiO<Subscript>2</Subscript>-based material in the presence of chitosan

Quasi-one-dimensional TiO₂-based nanostructures have been produced through hydrothermal treatment-without additives and in the presence of chitosan—of anatase nanopowder synthesized by an electrochemical sol-gel process. The morphology, phase composition, and structure of the hydrothermal synthesis products were studied by various physicochemical characterization techniques, including high-resolution electron microscopy, X-ray diffraction, and IR spectroscopy. The results demonstrate that the forming one-dimensional structures are isostructural with β-titanic acid, H₂Ti₃O₇. Heat treatment at t ≥ 500°C yields a mixture of sodium polytitanates, Na _y Ti _x O_{2x + 1}, with y = 0.5–2 and x = 2–5. The surface morphology and shape of the nanostructures persist up to 700°C. The key features of the formation of quasi-one-dimensional TiO₂-based structures in the presence of chitosan have been identified.     

Poly(3-hydroxybutyrate)-based hybrid materials with photocatalytic and magnetic properties prepared by electrospinning and electrospraying

Several types of nanostructured hybrid fibrous materials containing poly(3-hydroxybutyrate), nanoparticles from iron oxide (Fe₃O₄) and titanium dioxide (TiO₂), and chitosan or chitosan oligosaccharides (COS) were prepared. The design of the surface of the materials and their magnetic properties were tailored purposefully by conjunction of electrospinning and electrospraying. The surface and bulk morphologies of the obtained nanostructured materials were examined by SEM. Further, the distribution of Fe₃O₄ and TiO₂ nanoparticles was estimated by TEM analyses, as well as their surface chemical composition was determined by XPS. It was found that the simultaneous electrospinning and electrospraying of Fe₃O₄/chitosan or TiO₂/COS dispersions resulted in uniform distribution of the nanoparticles along the length of the fibers, while electrospraying of the mixed Fe₃O₄/TiO₂/chitosan dispersion led to agglomerate formation. Furthermore, the nanostructured hybrid materials preserved the magnetic properties of Fe₃O₄ embedded therein. It was demonstrated that the hybrid materials of different designs displayed excellent photocatalytic activity under UV light irradiation against a model organic contaminant—methylene blue, even after threefold use of the materials.     

Preparation of micro-nano-composites of TiO2/carbon nanostructures,C-CNT macroscopic shaping and their applications

Micro-nano-composites of TiO₂/carbon were synthesised using a collage of carbon nanostructures (carbon nanotubes (CNTs) and carbon nanofibers (CNFs)) on a TiO₂ surface through a TiO₂ sol-gel layer. C-CNT macroscopic shaping (C-CNT composites) were produced using CNTs as a starting material and a phenol-formaldehyde (PF) or polystyrene (PS) polymer as an adhesive. The morphologies of the composites were characterised by scanning electron microscopy (SEM). The collage of carbon nanostructures on the surface of TiO₂ in the composite was observed by transmission electronic microscopy (TEM). The superhydrophobicity of the C-CNT macroscopic shapes was demonstrated by contact angle measurements using AutoCAD software. The photoactivity of the composites was examined by the conversion of methylene blue (MB) in aqueous solution under irradiation from high-pressure mercury lamp. Higher photoactivity was observed using the TiO₂/carbon nanostructure composites than with TiO₂ alone.     

Synthesis of TiO2 nanopellet by TiCl4 as a precursor for degradation of RhodamineB

In the present investigation in order to promote TiO₂ pellet structure and its photocatalytic activity, two new precursors were synthesized in the powder and sol forms, using sol–gel method with precipitation of TiCl₄. Since TiO₂ pellets are normally synthesized by the commercial TiO₂ powder (DegussaP25), in this investigation and in the first step a new synthesized TiO₂ powder was produced and compared with DegussaP25. Subsequently, two types of pellet were made by the new synthesized powder and titania sol. The characterization of the synthesized TiO₂ powder and pellet were performed by XRD, FT-IR, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The result showed that by the new procedure utilized here, without using any additive not only the surface area of the produced TiO₂ powder has been increased, but also the crystalline phase is completely in the anatase form. It was also found that the synthesized pellets by the sol precursor had better morphological structure than the synthesized pellets by theTiO₂ powder (either DegussaP25 or new synthesized powder). Ultimately, in order to evaluate photocatalytic activity of TiO₂ powders and pellet, degradation of RhodamineB was tested.     

Large-scale synthesis and characterization of fan-shaped rutile TiO2 nanostructures

Large-scale fan-shaped rutile TiO₂ nanostructures have been synthesized by means of a simple hydrothermal method using only TiCl₄ as titanium source and chloroform/water as solvents. The physicochemical features of the fan-shaped TiO₂ nanostructures are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), nitrogen absorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FTIR). Structural characterization indicates that the fan-shaped TiO₂ nanostructures are composed of several TiO₂ nanorods with diameters of about 5 nm and lengths of 300-350 nm. The average pore size and BET surface area of the fan-shaped TiO₂ nanostructures are 6.2 nm and 59 m²/g, respectively. Optical adsorption investigation shows that the fan-shaped TiO₂ nanostructures possess optical band gap energy of 3.11 eV.     

Structural and magnetic properties of nanocomposites based on nanostructured polyaniline and titania nanotubes

Nanocomposites consisting of self-assembled polyaniline (PANI) nanostructures and titania nanotubes (TiO₂-NT) were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous dispersion of TiO₂-NT (outer diameter ~10 nm), without added acid. The influence of initial mole ratio of aniline to TiO₂ (80, 20, and 5) on the morphology, electrical conductivity, molecular structure, crystallinity, and magnetic properties of synthesized PANI/TiO₂ nanocomposites was studied. Transmission electron microscopy, Raman spectroscopy, and X-ray powder diffraction proved that the shape and structure of TiO₂-NT in the final nanocomposites were preserved. The shape of PANI nanostructures formed in the nanocomposites was influenced by the initial aniline/TiO₂-NT mole ratio. Nanotubes and nanorods are predominant PANI nanostructures in the nanocomposite prepared with the highest aniline/TiO₂ mol ratio of 80. The decrease of aniline/TiO₂ molar ratio induced more pronounced formation of nanorod network. The electrical conductivity of PANI/TiO₂ nanocomposites was in the range (1.3–2.4) × 10^?3 S cm^?1. The nanocomposites exhibit weak ferromagnetic behavior. Approximately order of magnitude lower values of coercive field and remanent magnetization were obtained for nanocomposite samples in comparison to pure PANI.     

The use of ZrO2 mixed TiO2 nanostructures as efficient dye-sensitized solar cells' electrodes

The mixed oxide of zirconium (ZrO₂) and titanium (TiO₂) nanostructures have been synthesized and used as electrodes for dye-sensitized solar cells (DSC). The TiO₂–ZrO₂ mixed oxide powder has a larger surface area than the pure component of TiO₂. For the UV action spectra of unsensitized photochemical cell, the TiO₂–ZrO₂ mixed oxide electrode band gap (E_g) around 3.27 eV, which is higher than that of pure component of titania (E_g = 3.2 eV). The increases in both of BET surface area and band gap contributed to the improvement on short-circuit photocurrent and open-circuit voltage, respectively. The DSC fabricated by TiO₂–ZrO₂ mixed oxide electrode significantly improved solar energy conversion efficiency when compared to a cell that was fabricated only by pure component of TiO₂.     

Atomic layer deposition of ferromagnetic cobalt doped titanium oxide thin films

TiO₂ thin films doped or mixed with cobalt oxide were grown by atomic layer deposition using titanium tetramethoxide and cobalt(III)acetylacetonate as metal precursors. The films could be deposited using both O₃ and H₂O as oxygen precursors. The films grown using water exhibited considerably smoother surface than those grown with ozone. The TiO₂:Co films with Co/(Co + Ti) cation ratio ranging from 0.01 to 0.30 were crystallized by annealing at 650 °C, possessing mixed phase composition comprising rutile and anatase and, additionally, CoTiO₃ or CoTi₂O₅. The annealed films demonstrated magnetic response expressed by magnetization curves with certain hysteresis and coercive fields.     

Facile and large-scale synthesis of hollow TiO2 nanostructures from TiCl3 solution

Hollow TiO₂ nanostructures were successfully synthesized by a hydrothermal process using TiCl₃ solution as Ti sources. The as-obtained product consists of quasi-spherical hollow nanostructures in the diameter of about 500 nm with anatase phase. The control experiments indicated that the synergism of H₂O₂ and KBF₄ plays an important role in the formation of hollow TiO₂ nanostructures. Compared with solid TiO₂ nanostructures, the photocatalytic property of hollow TiO₂ nanostructures has been markedly improved in degradation of methyl orange under UV light. This synthesis procedure is facile and thus promotes large-scale production of hollow TiO₂ nanostructures.     

Effect of TiO2 morphology on in vitro bioactivity of polycaprolactone/TiO2 nanocomposites

TiO₂ nanostructures with different morphologies (spherical, tube, leaf-like and flower-like particles) were synthesized via a facile hydrothermal process. Polycaprolactone (PCL)/10 vol.% TiO₂ nanocomposites were prepared by solvent casting methods. In vitro bioactivity of the nanocomposite films was examined by immersion in the simulated body fluid (SBF) for up to 28 days. It was found that the morphology of titania nanostructures significantly influence the in vitro bioactivity of PCL/TiO₂ nanocomposites. This observation was attributed to the amount of anatase phase and the specific surface area of the TiO₂ nanostructures, which provide high surface exposure to SBF.     

Covalent functionalization of metal oxide and carbon nanostructures with polyoctasilsesquioxane (POSS) and their incorporation in polymer composites

Polyoctasilsesquioxane (POSS) has been employed to covalently functionalize nanostructures of TiO₂, ZnO and Fe₂O₃ as well as carbon nanotubes, nanodiamond and graphene to enable their dispersion in polar solvents. Covalent functionalization of these nanostructures with POSS has been established by electron microscopy, EDAX analysis and infrared spectroscopy. On heating the POSS-functionalized nanostructures, silica-coated nanostructures are obtained. POSS-functionalized nanoparticles of TiO₂, Fe₂O₃ and graphite were utilized to prepare polymer-nanostructure composites based on PVA and nylon-6,6.     

Urchin-like core-shell TiO2/α-MnO2 nanostructures as an active catalyst for rechargeable lithium-oxygen battery

A selection of appropriate electrocatalysts with a unique design is a promising solution to promote oxidation and reduction reactions in lithium-oxygen (Li-O₂) batteries. Here, an effective integrated design of urchin-like core-shell TiO₂/α-MnO₂ nanostructure is constructed to develop an efficient catalyst electrode for Li-O₂ batteries. For this purpose, TiO₂ nanoparticles are biosynthesized by an eco-friendly process using flower extract of Matricaria chamomilla as both reducing and stabilizing agents. Then, MnO₂ nanocrystals are grown on the surface of TiO₂ nanoparticles under different reaction times to observe their evolution in terms of morphology and crystalline structure of MnO₂. The electrochemical behavior of the as-prepared core-shell TiO₂/α-MnO₂ nanostructures is evaluated in Li-O₂ cells. The TiO₂/α-MnO₂ electrode is exhibited a lower overpotential and higher specific capacity than the bare TiO₂ electrode. This could have resulted from the bifunctional catalytic activity of TiO₂ and α-MnO₂ coupled with urchin-like MnO₂ nanostructures. Furthermore, the internal resistance of the cell is recorded using electrochemical impedance spectroscopy technique, and reactions of the Li⁺ and O₂ on the cathode surface are investigated by cyclic voltammetry.     

One‐Dimensional Densely Aligned Perovskite‐Decorated Semiconductor Heterojunctions with Enhanced Photocatalytic Activity

By using one‐dimensional rutile TiO₂ nanorod arrays as the structure‐directing scaffold as well as the TiO₂ source to two consecutive hydrothermal reactions, densely aligned SrTiO₃‐modified rutile TiO₂ heterojunction photocatalysts are crafted for the first time. The first hydrothermal processing yielded nanostructured rutile TiO₂ with the hollow openings on the top of nanorods (i.e., partially etched rutile TiO₂ nanorod arrays; denoted PE‐TNRAs). The subsequent second hydrothermal treatment in the presence of Sr²⁺ transforms the surface of partially etched rutile TiO₂ nanorods into SrTiO₃ nanoparticles via the concurrent dissolution of TiO₂ and precipitation of SrTiO₃ while retaining the cylindrical shape (i.e., forming SrTiO₃‐decorated rutile TiO₂ composite nanorods; denoted STO‐TNRAs). The structural and composition characterizations substantiate the success in achieving STO‐TNRA nanostructures. In comparison to PE‐TNRAs, STO‐TNRA photocatalysts exhibit higher photocurrents and larger photocatalytic degradation rates of methylene blue (3.21 times over PE‐TNRAs) under UV light illumination as a direct consequence of improved charge carrier mobility and enhanced electron/hole separation. Such 1D perovskite‐decorated semiconductor nanoarrays are very attractive for optoelectronic applications in photovoltaics, photocatalytic hydrogen production, among other areas.     

Mechanically activated combustion synthesis of Ti3AlC2/Al2O3 nanocomposite from TiO2/Al/C powder mixtures

Ti₃AlC₂/Al₂O₃ nanocomposite powder was synthesized by mechanical-activation-assisted combustion synthesis of TiO₂, Al and C powder mixtures. The effect of mechanical activation time of 3TiO₂-5Al-2C powder mixtures, via high energy planetary milling (up to 20?h), on the phase transformation after combustion synthesis was experimentally investigated. X-ray diffraction (XRD) was used to characterize as-milled and thermally treated powder mixtures. The morphology and microstructure of as-fabricated products were also studied by scanning electron microscopy (SEM) and field-emission gun electron microscopy (FESEM). The experimental results showed that mechanical activation via ball-milling increased the initial extra energy of TiO₂-Al-C powder mixtures, which is needed to enhance the reactivity of powder mixture and make it possible to ignite and sustain the combustion reaction to form Ti₃AlC₂/Al₂O₃ nanocomposite. TiC, AlTi and Al₂O₃ intermediate phases were formed when the initial 10?h milled powder mixtures were thermally treated. The desired Ti₃AlC₂/Al₂O₃ nanocomposite was synthesized after thermal treatment of 20?h milled powder and consequent combustion synthesis and FESEM result confirmed that produced powder had nanocrystalline structure.     

In-situ synthesis of TiO2 nanostructures on Ti foil for enhanced and stable photocatalytic performance

TiO_2 nanostructures with strong interfacial adhesion and diverse morphologies have been in-situ grown on Ti foil substrate through a multiple-step method based on conventional plasma electrolytic oxidation(PEO) technology, hydrothermal reaction and ion exchange process. The PEO process is critical to the formation of TiO_2 seeding layer for the nucleation of Na_2Ti_3O_7 and H_2Ti_3O_7 mediates that are strongly attached to the Ti foil. An ion exchange reaction can finally lead to the formation of H_2Ti_3O_7 nanostructures with diverse morphologies and the calcination process can turn the H_2Ti_3O_7 nanostructures into TiO_2 nanostructures with enhanced crystallinity. The morphology of the TiO_2 nanostructures including nanoparticles(NP), nanowhiskers(NWK), nanowires(NW) and nanosheets(NS) can be easily tailored by controlling the NaOH concentration and reaction time during hydrothermal process. The morphology, composition and optical properties of TiO_2 photocatalysts were analyzed using scanning electron microscope(SEM), X-ray diffraction(XRD), photoluminescence(PL) spectroscopy and UV–vis absorption spectrum. Photocatalytic tests indicate that the TiO_2 nanosheets calcined at 500?C show good crystallization and the best capability of decomposing organic pollutants. The decoration of Ag cocatalyst can further improve the photocatalytic performance of the TiO_2 nanosheets as a result of the enhanced charger separation efficiency. Cyclic photocatalytic test using TiO_2 nanostructures grown on Ti foil substrate demonstrates the superior stability in the photodegradation of organic pollutant, suggesting the promising potential of in-situ growth technology for industrial application.     

Compositional effects on densification and microstructural evolution of bismuth titanate

The effects of small compositional variations on the densification and microstructural evolution of bismuth titanate (Bi₄Ti₃O₁₂) powder compacts were investigated during sintering and during hot forging. For a nominally stoichiometric Bi₄Ti₃O₁₂ composition, sintering commenced at 870°C, leading to a relatively dense microstructure (relative density >97% of the theoretical value) with randomly aligned elongated grains after 1 h at 1100°C. Small additions (1 weight percent) of Bi₂O₃ or TiO₂ to the nominally stoichiometric Bi₄Ti₃O₁₂ composition shifted the onset of sintering to lower or higher temperatures, respectively, but did not significantly alter the final density. Hot forging produced a microstructure of aligned, elongated grains. The small compositional variations did not seriously influence the ability to develop the elongated grain alignment. However, subsequent annealing of the hot forged materials produced significant changes in the aligned grain microstructure. The elongated grain alignment in the nominally stoichiometric Bi₄Ti₃O₁₂ composition was destroyed during subsequent annealing for less than 2 h at 1100°C.     

Fabrication and magnetic property of α-Fe2O3 nanoparticles/TiO2 nanowires hybrid structure

α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is fabricated by two-step hydrothermal treatment. TiO₂ nanowires are prepared by heating of titanate nanowires, which are obtained by hydrothermal treatment of TiO₂ powder and further repeated HCl treatment. α-Fe₂O₃ nanoparticles are deposited on the surface of TiO₂ nanowires by hydrothermal treatment in Fe(NO₃)₃ solution. The HRTEM images confirm the junctions between α-Fe₂O₃ nanoparticles and TiO₂ nanowires. The formation of hybrid structures has significant influence on the magnetic properties of α-Fe₂O₃. The Morin transition temperature of α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is 190 K, which is determined by the sharp peak in the differential ZFC curve. Whereas there is no observable Morin transition for the corresponding isolated α-Fe₂O₃ nanoparticles with similar average particles size of ca. 20 nm.     

Decomposition of the molecular precursor Bu4Sn6S6 on the surface of TiO2 to prepare semiconductor composite photocatalysts

In this work, the single source organometallic precursor Bu₄Sn₆S₆ was impregnated and decomposed on the surface of TiO₂ to produce semiconductor composites. ¹¹⁹Sn Mössbauer, Raman and ultra violet/visible spectroscopies, powder X-ray diffraction, temperature programmed reduction and surface area suggest for Sn contents of 1, 5 and 10 wt%, the formation of a highly dispersed unstable SnS phase which is readily oxidized by air at room temperature to form SnO₂ on the TiO₂ surface. The composite with Sn 30 wt% produced a mixture with the phases SnS/γ-Sn₂S₃ and SnO₂. Photocatalytic experiments with the composites SnX_n/TiO₂ using the textile dye Drimaren red as a probe molecule showed a first-order reaction with rate constants k_absorbance for the composites with Sn 1 and 5% higher than pure TiO₂ which was explained by the formation of the more active photocatalyst composite SnO₂/TiO₂.     

Dimensionality-dependent photocatalytic activity of TiO2-based nanostructures: nanosheets with a superior catalytic property

TiO₂-based nanostructures usually possess excellent photochemical properties. However, the relationship between their dimensionality and photocatalytic activity was rarely investigated. In this study, a series of TiO₂-based nanostructures in various dimensionalities (such as nanosheets, nanotubes) were obtained by hydrothermal treatment of P25, and the process of structural evolution was also systematically investigated by TEM, BET, Raman, and XRD analysis. Much higher rate constant (3.7 × 10^?2 min^?1) for the degradation of rhodamine B was found for nanosheets, comparing with those of three-dimensional P25 nanoparticles (0.59 × 10^?2 min^?1) and one-dimensional nanotubes (0.85 × 10^?2 min^?1). It is found that the hydrothermally prepared TiO₂-based nanosheets possess small thickness (ca. 5 nm) and plentiful surface hydroxyl groups, and the reason why TiO₂-based nanosheets possess superior photocatalytic activity is also discussed in detail from the microstructure and surface chemical states. In addition, TiO₂-based nanosheets exhibit good reusability in the cyclic experiments, implying a potential application for photocatalytic degradation of organic pollutants.