Effect of NaHCO3 on synthesis of anatase TiO2 nanopowders by thermal processing of the precursor

Titanium dioxide (TiO₂) nanopowders were successfully prepared by thermal processing of the precursor of titanium hydroxide, urea and sodium acid carbonate (NaHCO₃). The products were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that NaHCO₃ has a certain effect on the average crystallite size and dispersity of TiO₂ nanopowders, at the same time other phases (Na₂SO₄ and Na₂CO₃) will be introduced. However, Na₂SO₄ has distinctive intercalation ability and catalytic activity. TiO₂ (anatase) powders can be prepared at ?600 °C for 2 h with addition of 2–10 wt% NaHCO₃, and the average crystallite size is 20.0–22.3 nm. The surface of the sample mainly consists of Ti, O, C, Na and S five species elements.     

Synthesis and characterization of rice grains like Nitrogen-doped TiO2 nanostructures by electrospinning–photocatalysis

Rice grain-shaped Nitrogen-doped titanium dioxide (N–TiO₂) nano/mesostructures were fabricated through a combination of sol–gel and electrospinning methods. As-spun nanofibers were continuous and upon thermal treatment at 500° C for 1 h in air, the continuous fibers break into rice grain-shaped TiO₂ nanostructures of average diameter 50–80 nm. The nanostructures were characterized by spectroscopy, microscopy and powder X-ray diffraction. The rice grains consist of spherical particles of average diameter of ~ 18 nm and with N doping, their average diameters decrease from ~ 18 to ~ 12 nm. The presence of N in the TiO₂ lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The band-gap of TiO₂ reduced from 3.19 eV to 2.83 eV upon increasing doping level of N from 0% to 5% (w/w), respectively. The N–TiO₂ rice grains showed an enhanced UV light-assisted photocatalysis compared to pure TiO₂ in the photodegradation of Alizarin Red S dye, an industrially important anthraquinone dye.     

Effect of Na2SiO3 on synthesis of TiO2 nanopowders by thermal processing of the precursor

TiO₂ nanopowders could be prepared by thermal processing of the precursor of titanium hydroxide, urea and Na₂SiO₃. The powders were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that Na₂SiO₃ has an important effect on the average crystallite size and dispersity of TiO₂ nanopowders, and other phases (Na₂SO₄ and SiO₂) will be introduced. However, Na₂SO₄ has distinctive intercalation ability and catalytic activity; SiO₂ coating layers can effectively inhibit the agglomeration of TiO₂ nanopowders. TiO₂ (anatase) powders with well dispersity can be prepared at ～600 °C for 2 h with addition of 2–6 wt.% Na₂SiO₃, and the average crystallite size is 15.5–22.1 nm. The surface of the sample mainly consists of Ti, O, C, Si, Na and S six species elements.     

Effect of ZrO2 addition on the mechanical properties of porous TiO2 bone scaffolds

This study aimed at the investigation of the effect of zirconium dioxide (ZrO₂) addition on the mechanical properties of titanium dioxide (TiO₂) bone scaffolds. The highly biocompatible TiO₂ has been identified as a promising material for bone scaffolds, whereas the more bioinert ZrO₂ is known for its excellent mechanical properties. Ultra-porous TiO₂ scaffolds (> 89% porosity) were produced using polymer sponge replication with 0–40 wt.% of the TiO₂ raw material substituted with ZrO₂. Microstructure, chemical composition, and pore architectural features of the prepared ceramic foams were characterised and related to their mechanical strength. Addition of 1 wt.% of ZrO₂ led to 16% increase in the mean compressive strength without significant changes in the pore architectural parameters of TiO₂ scaffolds. Further ZrO₂ additions resulted in reduction of compressive strength in comparison to containing no ZrO₂. The appearance of zirconium titanate (ZrTiO₄) phase was found to hinder the densification of the ceramic material during sintering resulting in poor intergranular connections and thus significantly reducing the compressive strength of the highly porous ceramic foam scaffolds.     

Synthesis of crystal MFe2O4 (M = Mg,Cu, Ni) microspheres

A low-temperature solvothermal synthetic method was developed for the large-scale synthesis of uniform-sized ferrite MFe₂O₄ (M = Mg, Cu, Ni) microspheres. The size of the as-prepared ferrite MFe₂O₄ microspheres could be controlled to be diameters 300–800 nm in diameter by adjusting some growth parameters, such as reaction time and concentration. The structures of the as-prepared ferrite MFe₂O₄ microspheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The magnetic properties of the ferrite MFe₂O₄ microspheres were also investigated.     

Enhanced photocurrent of nitrogen-doped TiO2 film for dye-sensitized solar cells

Nitrogen (n)-doped titanium dioxide (TiO₂) was prepared with varying doping extent by a general sol–gel process with a pure TiO₂ film as the control sample. The n-doped-2 electrode showed the maximum conversion efficiency with an open-circuit voltage (V_oc) of 0.726 V, a photocurrent (J_sc) of 10.52 mA cm^?2, a fill factor of 63.6%, and an efficiency of 4.86%, compared to 0.751 V, 7.4 mA cm^?2, 67.1%, and 3.73%, respectively, for the undoped (u-doped) TiO₂ electrode. The approximate 23% enhancement in the conversion efficiency of the n-doped-2 TiO₂ electrode-based dye-sensitized solar cells (DSSCs) was mostly ascribed to the increase of light absorption in the near-vis absorbance and partially to the morphological characteristics of the n-doped TiO₂ film. Additionally, the doping type of nitrogen in the TiO₂ lattice was closely studied using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The relation between the doping type and the electron behavior in the DSSCs was also examined.     

Sodium gluconate-assisted hydrothermal synthesis,characterization and electrochemical performance of LiFePO4 powders

Nano- and micro-sized LiFePO₄ powders were synthesized by a sodium gluconate (C₆H₁₁NaO₇)-assisted hydrothermal synthesis method at 220 °C for 10 h with pH = 2–7. The resulting powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS). The obtained data showed that the pH of synthesis solution played a key role in the formation of the LiFePO₄ powders with different morphologies, such as ball-like microspheres, irregular microspheres with the agglomerated rods and particles, sphere-like nanoparticles and nano-ellipsoids. The results from electrochemical performance measurements revealed that the charge–discharge cycling characteristics of the samples were strongly dependent on their morphologies. In particular, the ellipsoidal LiFePO₄ nanoparticles with the average size of 70–90 nm showed the highest initial discharge capacity of 150 mA h g⁻¹ at 0.1 C rate, and cycling stability of the ellipsoidal LiFePO₄ nanoparticles was optimum among all the samples prepared due to their dual advantages of high tap density and good diffusion property. The present study offers a simple morphology-controllable route, without carbon coating or doping with supervalent cations, to synthesize and to design high performance cathode materials for lithium-ion batteries.     

Hydrothermal synthesis and characterization of TiO2 nanostructures using LiOH as a solvent

In the present study, we performed hydrothermal method as a simple and efficient route for the synthesis of rutile TiO₂ nanostructures in various concentrations of lithium hydroxide solutions. TiO₂ nanopowders with average sizes of 15 and 23 nm were prepared using 4 M and 7 M LiOH solutions. X-ray diffraction analysis (XRD), transmission electron microscope (FEG-STEM), scanning electron microscopy (SEM), and Brunauer–Emmet–Teller (BET) analyses were used in order to characterize the obtained products and comparison of the morphology of the powders obtained in different concentrations of LiOH solvent. It was shown that alkali solution concentration has affected the crystallinity, agglomeration ratio, particle size and specific surface area of the obtained rutile phases.     

Preparation of high strength macroporous hydroxyapatite scaffold

Hydroxyapatite (HAp) powder was prepared from CaNO₃·4H₂O and (NH₄)₂HPO₄ by wet-chemical method and has phase stable up to 1250 °C. High strength macroporous HAp–naphthalene (HN) and HAp–naphthalene–benzene (HNB) scaffolds were fabricated by adapting sintering method. The resulting HAp scaffolds have porosity about 60 vol.% with compressive strength of ~ 11 MPa and average pore diameter in the range of ~ 125 μm. The incorporation of benzene in HN scaffold reduces the strength whereas enhanced both the porosity and pore size distribution. XRD, FTIR, SEM and mercury porosimeter techniques were used to study the phase purity, morphology, pore size and pore size distribution of scaffold. The study compared the effect of concentration of naphthalene on strength, porosity and pore size distribution on both HN and HNB scaffold. In-vitro bioactivity studies on HN and HNB scaffolds show the nucleation of spherical carbonated apatite particles on the surface in SBF solution.     

Adsorption and photocatalysis of nanocrystalline TiO2 particles prepared by sol–gel method for methylene blue degradation

Titanium dioxide (TiO₂) powders were synthesized by using TiO₂ colloidal sol prepared from titanium-tetraisopropoxide (TTIP) and used as a starting material by applying the sol–gel method. The effect of aging times and temperatures on physical and chemical properties of TiO₂ sol particles was systematically investigated. The results showed that the crystallinity and average particle size of TiO₂ can be successfully controlled by adjusting the aging time and temperature. The samples after calcination of TiO₂ powders were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and nitrogen adsorption measurements. In addition, the photocatalytic activity of synthesized TiO₂ powders was evaluated by studying the degradation of 10 ppm aqueous methylene blue dye under 32 W high pressure mercury vapor lamp with 100 mg of TiO₂ powders. The highest photocatalytic activity was observed in TiO₂ powder synthesized at 90 °C for 0 h attributed to the presence of anatase and rutile phases in an 80:20 ratio.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Synthesis of titanium carbide and TiC–SiO2 nanocomposite powder using rutile and Si by mechanically activated sintering

High-energy ball milling was applied with subsequent heat treatment for synthesizing nanoparticles of TiC powders by the carbothermic and carbosilisisothermic reduction of titanium oxide (rutile type). The milling procedure involved milling of TiO₂/C and TiO₂/Si/C powders at room temperature in an argon atmosphere. The progress of the mechanically induced solid state reaction was monitored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that TiC nanoparticles were duly synthesized in the TiO₂/C system at 1700 °C in 60-h milled samples. In the non-milled samples, although heated at the same temperature, only a minor amount of a lower degree of titanium oxide (Ti₃O₅) was observed to form. Further, in other non-milled samples, but with Si initially present, despite heating to 1550 °C no TiC phase was detected. However, using Si as a reducing agent accompanied by graphite, after 60 h ball milling, only Si remained as a distinguishable crystalline phase. Further, heat treatment of activated powders by forming the interphase compounds (such as Ti₃Si₅ and Ti₅Si₃) remarkably decreased the synthesis temperature to 900 °C for the 60 h milled samples.     

Solvothermal synthesis of monodispersed CoZr4(PO4)6 microspheres and their application as microwave absorber

Monodispersed CoZr₄(PO₄)₆ microspheres with a diameter of 40 μm were achieved via a combining solvothermal and calcination route. The crystallinity of the calcined microspheres with shell structure was improved, while the monodisperse property and morphologies remained. The possible formation mechanism of the porous CoZr₄(PO₄)₆ microspheres with nanoshell was proposed. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) technologies, thermal analysis (TG and DSC), nitrogen adsorption–desorption isotherms and network analyzer. The sample calcined at 900 °C shows a strongest absorbability in the radar-wave absorbability test.     

Effect of SiO2 nanoparticles on the phase transformation of TiO2 in micron-sized porous TiO2–SiO2 mixed particles

Spherical and nanoporous TiO₂ and TiO₂–SiO₂ mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO₂/SiO₂) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO₂ and TiO₂–SiO₂ particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO₂–SiO₂ (50 wt.% SiO₂) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO₂ particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO₂ content in the TiO₂–SiO₂ mixed particles increased.     

A general approach to monodisperse perovskite microspheres

BaTiO₃, PbTiO₃, SrTiO₃, and Pb(Zr,Ti)O₃ microspheres with uniform size and narrow size distribution have been successfully synthesized by a novel hydrothermal and annealing approach. In this approach, the chemical reaction and crystallization process of the ABO₃ perovskite oxides were separated in two steps. Spherical particles containing the B-site ions were obtained first via a controlled hydrolysis and aging process. Then, during hydrothermal treatment, the A-site ions were incorporated in situ into the microspheres to form amorphous perovskite microspheres. The particles were further crystallized with preserved spherical morphology under subsequent annealing treatment. The BET surface areas of the TiO₂ gel particles, the amorphous PbTiO₃ and the as-annealed PbTiO₃ microspheres were 245.7 m²/g, 41.67 m²/g and 4.53 m²/g, respectively, showing a significant change of the surface feature in the preparation process. This approach also allowed the microspheres diameters to be manipulated from 100 nm to 1500 nm in a controlled manner. Most of the microspheres were composed by closely packed nano-sized particles. Furthermore, the Pb(Zr,Ti)O₃ microspheres with an average diameter of 200 nm exhibited single crystal features, indicating highly oriented growth in the crystallization process. The microspheres were very stable, and still maintained spherical shape after higher temperature calcination.     

Recovery of high surface area mesoporous silica from waste hexafluorosilicic acid (H2SiF6) of fertilizer industry

In this article we report recovery of mesoporous silica from the waste material (hexafluorosilicic acid) of phosphate fertilizer industry. The process involves the reaction of hexafluorosilicic acid (50 ml, 24 wt% H₂SiF₆) and 100 ml, 0.297 M Na₂CO₃ to generate the alkaline aqueous slurry. Silica was separated from the slurry by filtration and the sodium fluoride was extracted from the aqueous solution by evaporation method. The obtained mesoporous silica was characterized by N₂ absorption/desorption (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and EDS. The results confirm that the separation of silica and NaF was successful and the final products have high purity. The silica product was found to have an average pore diameter of 4.14 nm and a high surface area (up to 800 m²/g). The process reported in this study may significantly reduce the release of hazardous materials into the environment and it might confer economic benefits to the responsible industries.     

Enhanced photocatalytic property of nanoporous TiO2/SiO2 micro-particles prepared by aerosol assisted co-assembly of nanoparticles

Nanoporous TiO₂/SiO₂ composite micro-particles were prepared by an aerosol assisted co-assembly (AACA) and their characteristics were investigated for photocatalytic application. The average diameter of resulting co-assembled TiO₂/SiO₂ particles was ranged 4–10 μm, and increased as the precursor concentration increased. The TiO₂/SiO₂ particles were spherical in shape and pores ranged 1–100 nm in diameter. Photocatalytic activity of the as-prepared nanoporous TiO₂/SiO₂ particles was evaluated by measuring the photodegradation of methylene blue (MB) and NO_x. Furthermore, the photocatalytic activity of nanoporous TiO₂/SiO₂ particles was compared with those of commercial TiO₂ nanoparticles and nanoporous TiO₂ particles. The nanoporous TiO₂/SiO₂ particles exhibited the highest photodegradation of MB and NO_x among three samples, which was 80% after 3 h and 55% at 10 min, respectively.     

A novel magnetically separable TiO2/CoFe2O4 nanofiber with high photocatalytic activity under UV–vis light

A novel magnetically separable heterogeneous photocatalyst TiO₂/CoFe₂O₄ nanofiber was prepared by sol–gel method and electrospinning technology, followed by heat treatment at 550 °C for 2 h. The phase structure, morphology and magnetic property of the composite nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope and vibrating sample magnetometer analysis. The photocatalytic studies of TiO₂/CoFe₂O₄ fibers suggested that the presence of CoFe₂O₄ not only enhanced the absorbance of UV light, but also broadened the response region to visible light. The decolorizing efficiency of methylene blue (MB) solution reaches 95.87% over TiO₂/CoFe₂O₄ nanofibers under 300 W Hg lamp after 5 h, which is close to that of Degussa P25. Furthermore, these fibers can be collected with a magnet for reuse and effectively avoid the secondary pollution of the treated water.     

The effects of CeO2 addition on crystallization behavior and pore size in microporous calcium titanium phosphate glass ceramics

In this research the effect of the addition of CeO₂ to microporous Calcium Titanium Phosphate glass ceramics was studied. Different molar percentages of CeO₂ were added to three samples of a base glass whose composition was P₂O₅ 30, CaO 45, TiO₂ 25 (mol%). The first sample had 2 mol% CeO₂, the second sample had 4 mol% CeO₂, and the third sample had 6 mol% CeO₂. The fourth sample did not contain any CeO₂. The glass samples were melted and crystallized to bulk glass ceramics by a conventional method. Differential Thermal Analysis (DTA) was utilized to determine the appropriate nucleation and crystallization temperatures. Among the samples, the DTA curve of the sample which had 2 mol% CeO₂ had the sharpest crystallization peak. Therefore, this sample was chosen to prepare the glass ceramics. Using X-ray Diffraction (XRD) it was found that in all samples β-Ca₃(PO₄)₂ and CaTi₄(PO₄)₆ were the major phases. The β-Ca₃(PO₄)₂ phase was dissolved away by soaking the glass ceramics in HCl, leaving a porous skeleton of CaTi₄(PO₄)₆. CeO₂ addition increased the glass transition temperature and decreased the crystallization time and temperature. It was shown that CeO₂ addition resulted in an increase in the mean pore diameter while the specific surface area decreased. The median pore diameter and specific surface area were determined as 27 nm and 14 m²/g, respectively, for the sample containing 2 mol% CeO₂.     

Microstructural evolution and optical properties of TiO2 synthesized by eggshell membrane templating for DSSCs application

This article presents the bio-inspired synthesis of TiO₂ using eggshell membranes (ESM) as a biotemplate on which the crystals of TiO₂ are nucleated and grown. The microstructure, phase transformations and optical behavior were studied with the objective of understanding the effects of the thermal treatment on the properties of the TiO₂ powder for application in dye sensitized solar cells (DSSC). The technique used for the mimetization of the ESM consists of submerging the biotemplate in an alcoholic solution of TiCl₄ and thermal treating the samples at 600, 700 and 800 °C. Thermal analysis (DTA and TGA) was used to investigate the thermal decomposition of the membranes. X-ray diffraction (XRD) studies revealed the phase evolution and the average crystal sizes. Scanning and transition electron microscopy (SEM and TEM, respectively) were used to investigate the morphology of the obtained powders. UV–vis diffuse reflectance was used to investigate the optical properties. The porosity was also evaluated using a BET instrument. The results indicated that the best features for DSSC application were presented by the sample that was thermally treated at 600 °C. This is reflected in the good replication of the morphology of the used biotemplate, with a nanocrystalline anatase phase (average crystal size 15.82 nm), high surface area (64.8 m²/g), mesoporous structure (average pore size of 26.31 Å) and large band gap (3.31 eV).