Synthesis, thermal stability, and photocatalytic activity of nanocrystalline titanium carbide

Titanium carbide (TiC) was prepared via one simple route by the reaction of metallic magnesium powders with titanium dioxide (TiO₂) and potassium acetate (CH₃COOK) in an autoclave at 600 °C and 8 h. Phase structure and morphology were characterized by X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). The results indicated that the product was cubic TiC, which consisted of particles with an average size of about 100 nm in diameter. The product was also studied by the thermogravimetric analysis (TGA) and its photocatalysis. It had good thermal stability and oxidation resistance below 350 °C in air. In addition, we discovered that the cubic TiC powders exhibited photocatalytic activity in degradation of Rhodamine-B (RhB) under 500 W mercury lamp light irradiation.     

Synthesis of hexatitanate and titanium dioxide fibers by ion-exchange approach

Hexatitanate (K₂Ti₆O₁₃) and titanium dioxide (TiO₂) fibers were synthesized by ion-exchange method using fibrous potassium titanate (K₄Ti₃O₈) as initial material. Fibrous K₄Ti₃O₈ was prepared by treating TiO₂ with 80 wt.% concentrated KOH solution at 220 °C for 2 h under atmospheric pressure. Then, high qualities of K₂Ti₆O₁₃ and TiO₂ fibers were formed by a thermal treatment of the hydrolytic intermediates K_4−bH_bTi₃O₈ (1.2 ≤ b ≤ 3.0) and H₄Ti₃O₈, which were quantitatively obtained by controlling the pH value ranging from 10.9 to 12.0 and from 2.0 to 5.0 in the hydrolytic process of K₄Ti₃O₈, respectively. Based on the experimental results, the possible ion-exchange and phase transformation mechanisms in the reaction process were discussed.     

Synthesis of Sn-doped ZnO nanorods and their photocatalytic properties

Sn-doped ZnO nanorods were fabricated by a hydrothermal route, and characterized by X-ray diffraction, field emission scanning electron microscope, UV-vis spectroscopy, Raman spectra, solid-state nuclear magnetic resonance (NMR) spectra, and room temperature photoluminescence spectroscopy. Solid-state NMR result confirms that Sn⁴⁺ was successfully incorporated into the crystal lattice of ZnO. Room temperature photoluminescence showed that all the as-synthesized products exhibited a weak UV emission (380 nm) and a strong visible emission (540 nm), but the intensities of the latter emission increased with increase in Sn concentration. The improvement of visible emission at 540 nm in the Sn-doped ZnO samples was suggested to be a result of the lattice defects increased by doping of Sn in zinc oxide. In addition, the photocatalytic studies indicated that Sn-doped ZnO nanorods are a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes.     

Low-temperature hydrothermal synthesis of phase-pure rutile titania nanocrystals: Time temperature tuning of morphology and photocatalytic activity

In this paper, a simple and efficient methodology for the low-temperature synthesis of phase-pure nanocrystalline rutile TiO₂ with tuned morphology is reported. Control on morphology has been achieved by simple variation of the hydrothermal process, starting with titanium-tetrachloride without using mineralizers, additives or templating agents. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns showed no other phases of TiO₂ establishing the formation of phase-pure rutile titania in the entire temperature range of synthesis (40-150 °C) and most noticeably even at a considerably low temperature (40 °C). Fourier transform infrared (FT-IR) spectra strongly indicated the presence of hydroxyl group or surface adsorbed water and the thermogravimetry and differential thermo-gravimetry (TG-DTG) showed no phase change up to 1000 °C. A combination of reaction parameters (temperature, time) with a thorough transmission electron microscopy (TEM) study demonstrated the formation of phase-pure rutile titania nanocrystals as nano-rods, bunched nano-spindles or spherical nanoparticles depending on the hydrothermal reaction conditions. The photocatalytic activity of the synthesized nanocrystals has been successfully evaluated on the photodegradation of methyl orange (MO), a well-known pollutant azo-dye, as a model reaction.     

Ligand-assisted hydrothermal synthesis of ZnWO4 rods and their photocatalytic activities

ZnWO₄ rods were prepared using a ligand-assisted hydrothermal method with ZnCl₂ and Na₂WO₄ in the presence of various amines as ligands for zinc ions. The choice of ligand was found to play an important role in the formation of ZnWO₄ rods. The aspect ratio of the ZnWO₄ rods increased with increasing ligand strength. XRD and HRTEM confirmed that the ZnWO₄ rods grow along the [1 0 0] direction. The photochemical activities of the ZnWO₄ rods for the decomposition of Rhodamine 6G were examined. The photocatalytic activity was found to depend on the aspect ratio of the ZnWO₄ rods.     

Surfactant-free synthesis of Bi2WO6 multilayered disks with visible-light-induced photocatalytic activity

The synthesis of bismuth tungstate (Bi₂WO₆) multilayered disk which was constructed by oriented square nanoplates was easily realized via a simple surfactant-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were used to investigate the as-obtained product. The results indicated that the three-dimensional (3D) Bi₂WO₆ multilayered disk was constructed by self-assembly of square nanoplates via a perfect oriented manner. The formation mechanism of the product was carefully investigated on the basis of the results of time-dependent experiments. In addition, studies of the photocatalytic property demonstrated that the as-obtained Bi₂WO₆ could exhibit excellent visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB).     

Fabrication and efficient photocatalytic degradation of methylene blue over CuO/BiVO4 composite under visible-light irradiation

CuO/BiVO₄ composite photocatalysts were prepared by solution combustion synthesis method and impregnation technique. X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scan electron microscopy and UV-vis diffusion reflectance spectra were used to identify the physical properties and photophysical properties of CuO/BiVO₄ composite photocatalysts. The photocatalysts exhibit the enhanced photocatalytic properties for degradation of methylene blue under visible-light (λ > 420 nm). The mechanism of improved photocatalytic activity is also discussed.     

Characterisation and photocatalytic activity of structure-controlled spherical granules of an anatase/hydroxyapatite composite

Materials that can purify the environments are desirable. Anatase (TiO₂) has received attention because it is stable and can decompose organic substances because of its photocatalytic activity. To make use of anatase effectively, we deposited nano-sized anatase particles on porous hydroxyapatite (HA) ceramics composed of rod-shaped particles. Spherical porous HA granules composed of rod-shaped HA particles were prepared using a hydrothermal process. The granules were soaked in a solution containing a water-soluble titanium complex and then hydrothermally treated. Nano-sized anatase particles were deposited on each rod-shaped HA particle. The anatase/HA granules composed of rod-shaped HA particles showed higher photocatalytic activity than those composed of globular HA particles. The granules are expected to be useful as an environment-purifying material with high manageability and photocatalytic activity.     

TiO2 supported on rod-like mesoporous silica SBA-15: Preparation, characterization and photocatalytic behaviour

TiO₂ nanoparticles have been successfully incorporated in the pores of mesoporous silica SBA-15 with different morphologies by a wet impregnation method. The composites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma (ICP) emission spectroscopy, transmission electron microscopy (TEM), N₂-sorption and UV-Vis diffuse reflectance spectroscopy. The photodegradation of methyl orange (MO) was used to study their photocatalytic property. It is indicated that the morphology of SBA-15 had a great influence on the photocatalytic activity of the composites. When TiO₂/SBA-15 composite was prepared by loading TiO₂ nanoparticles on uniform rod-like SBA-15 of 1 μm length, it showed higher photocatalytic degradation rate than that on less regular but much larger SBA-15 support. This difference was rationalized in terms of the homogeneously distributed and shorter channels of rod-like SBA-15, which favored mass transport and improved the efficient utilization of the pore surface.     

Characterization and photocatalytic activity of Bi3TiNbO9 nanocrystallines synthesized by sol-gel process

Nanocrystalline Bi₃TiNbO₉ powders were synthesized by a sol-gel process, based on a colloid solution of bismuth acetate, titanium butoxide and niobium ethoxide. X-ray diffraction analysis revealed that pure Aurivillius phase of Bi₃TiNbO₉ could be prepared at a calcination temperature of 500 °C. By using scanning electron microscopy and gas adsorption method, the morphology and the specific surface area of the powders were examined. The photophysical properties of Bi₃TiNbO₉ were investigated by means of the UV-visible diffuse reflectance spectrum, from which a band gap ∼3.2 eV was empirically calculated. The as-prepared Bi₃TiNbO₉ powders were applied in the photodegradation of organic contaminant for the first time, and they showed effective photocatalytic activity for the complete decomposition of methyl orange under UV light irradiation.     

Preparation of MgO nano-rods with strong catalytic activity via hydrated basic magnesium carbonates

MgO nano-rods of several microns in length and 50–100 nm in width were prepared by calcining nesquehonite phase, obtained by simple precipitation using (NH₄)₂CO₃ under ambient condition. The MgO nano-rod with reasonably high surface area (75–120 m² g⁻¹) exhibits strong activity in solvent-free base catalyzed Claisen-Schmidt condensation giving 99% conversion in 2 h and is easily recyclable with no significant change in catalytic activity. Presence of numerous basic sites of different strengths (surface hydroxyl groups, low coordinate O²⁻ sites) is attributed to the observed effect.     

Adsorption of nitrogen and oxygen in cobalt (II)-exchanged zeolite A

The cobalt (II)-exchanged zeolite A (NaCoA) was prepared by cation exchange process with zeolite A (NaA) and Co(NO₃)₂ in aqueous solution. A static volumetric system was employed to evaluate the N₂ and O₂ adsorption properties of NaCoA at 298 K. It was found that the N₂ adsorption capacity of NaCoA increased rapidly with the rising pressure, and the adsorption isotherm of N₂ became nonlinear in low pressure region. The O₂ adsorption capacity of NaCoA increased slightly with pressure. The introduction of Co²⁺ into the NaA enhanced the N₂ adsorption capacity and N₂/O₂ selectivity, which could be contributed to the π-complexation between N₂ and Co²⁺. This strong interaction brought about a series of high value for Henry's constant, Langmuir constant, adsorption selectivity and adsorption capacity of N₂ in NaCoA. Infrared spectra were also carried out to illustrate that the N₂ were bonding with Co²⁺.     

Effects of pH on morphosynthesis and photocatalytic activity of calcium titanium oxides via a facile aqueous strategy

By controlling pH values, calcium titanium oxides with various morphologies had been synthesized via a simple hydrothermal route. No surfactants or templates were involved in the shaping process. The results found that pH values had a crucial effect on the crystal phase and shape evolution of the samples. With increasing pH values, the obtained sample changed from one-dimension (1D) CaTi₂O₅ rod or shuttle-like shape to two-dimension (2D) CaTi₂O₄(OH)₂ nanosheets, and then to three-dimension (3D) CaTiO₃ aggregated prisms, butterfly-like dendrites and cross cubic shapes. The formation mechanism was proposed for the evolution of phase and morphology. 3D CaTiO₃ butterfly-like sample showed good photocatalytic activity due to unique morphology, enhanced light harvesting and large surface area.     

Phase content and particle morphology of Bi-Mo-V-O powders produced by aerosol pyrolysis

Aerosol pyrolysis was utilized to synthesize spherical submicron Bi-Mo-V-O powders over a wide range of reactor temperatures (500-1000 °C) and elemental compositions. Evaporative loss of Mo from particles was significant at temperatures of 800 °C or higher; however, this could be compensated by adjustment of the solution composition. The crystalline phase content for powders produced at 800 °C over a wide range of compositions was largely consistent with previously reported binary oxide and ternary solid solution phases. Powder colors ranged from bright yellow to reddish or greenish yellow, and were characterized by the Munsell color parameters. Particle morphology ranged from spherical to faceted and partially hollow particles, and could be largely explained by proximity to the composition-dependent solidus or liquidus temperature. Particle morphology and phase content can also be influenced by the addition of ethanol to the precursor solution.     

Synthesis and characterization of sub-micron size Co-Ni alloys using malonate as precursor

Sub-micron size (0.2-0.6 μm) particles of Co_1−xNi_x (0≤x≤1) alloys have been synthesized by the polyol method using Co-Ni malonates as precursors but without using any protective agents such as PVP or any other surfactants. The synthesized alloys are found to be homogeneous. EDX analysis of the alloys showed particle-to-particle uniformity in composition. SEM showed largely non-agglomerated, almost spherical particles, with a fairly narrow size distribution. In the first reported effort of its kind, WAXS analysis was carried out to estimate the amounts of HCP and FCC phases present in pure Co and Co_0.8Ni_0.2. Coercivity, saturation magnetization and remanent magnetization at room temperature for all the compositions are reported. These results agree well with the composition of the alloys.     

Synthesis and enhanced photocatalytic activity of tin oxide nanoparticles coated on multi-walled carbon nanotube

A nanocomposite of SnO₂ nanoparticles coated on multi-walled carbon nanotube (MWNT@SnO₂) was synthesized and characterized by thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, nitrogen physisorption measurements, photoluminescence. The results show that the SnO₂ nanoparticles with a narrow size of 4 nm are uniformly deposited on MWNT. The photocatalytic activity of the nanocomposite was studied using methyl orange as a model organic pollutant. MWNT@SnO₂ exhibits much higher photocatalytic activity than that of commercial TiO₂ (P-25). The promotion is mainly contributed from electron transfer between SnO₂ and MWNT.     

Synthesis and photocatalytic activity of titania microspheres with hierarchical structures

A combined sol-gel and solvothermal process was introduced to fabricate the titania microspheres with hierarchical structures by using lauryl alcohol as the structure-directing agent. Scanning electron microscope, high-resolution transmission electron microscope, Fourier transform infrared spectrograph and powder X-ray powder diffraction indicated that the molar ratio of lauryl alcohol, water and tetra-n-butyl titanate was the key factor for the formation of the mono-dispersed titania with anatase phase and the optimal ratio was 1.2:4:1. The diameter of the end-product was 523 ± 74 nm and it was composed of smaller nanoparticles with about 6.8 nm size in diameter. Photocatalytic activity of the end-product was investigated by employing Rhodamine B and Methylene blue as the model compounds. The target microspheres exhibited the higher photocatalytic efficiency compared with commercial Degussa P25 titania and this result might be due to the hierarchical structures of microspheres according to the analysis of Brunauer-Emmett-Teller specific surface areas.     

Microwave radiation as heating method in the synthesis of titanium dioxide nanoparticles from hexafluorotitanate-organic salts

Nanocrystalline anatase was obtained from ionic liquid-like precursors containing hexafluorotitanate-organic salts and less than 25 wt.% of water, and using boric acid as fluoride scavenger. Two alternative heating methods were explored using either a conventional oven or a domestic microwave apparatus. A significant reduction in the reaction time from 24 h to only few minutes was obtained using the microwave route. The as-prepared materials were characterized by X-ray diffraction, transmission electron microscopy, nitrogen sorption analysis, and attenuated total reflectance Fourier transformed infrared, X-ray photoelectronic and Raman spectroscopes. The convenience of using the microwave heating option was a function of the organic cation present in the precursor. Thus, organic ammonium cations containing only hydrocarbon substituents, such as diethylammonium, phenylammonium and benzyltrimethylammonium led to the precipitation of nanocrystalline anatase powder with high specific surface area (up to 120 m² g⁻¹) in a short processing time (1-3 min). Otherwise, alcohol and carboxylate functionalized cations decomposed under microwave treatment. Moreover, the choice of the organic cation allowed tuning several properties of the end material, such as particle size and pore morphology.     

Vanadium dioxide nanobelts: Hydrothermal synthesis and magnetic properties

VO₂ (B) nanobelts were prepared by a hydrothermal method at 180 °C using V₂O₅·nH₂O sol and H₂C₂O₄·2H₂O as starting agents. The obtained nanobelts have diameters ranging from 50 to 100 nm in width, 20-30 nm in thickness with lengths up to 1.5 μm. Measurements of the static magnetic susceptibility provide evidence for two phase transitions at T₁ = 225 K and T₂ = 290 K, respectively. Below T₁, the data suggest the presence quasi-free as well as of strongly antiferromagnetic correlated spins associated to V⁴⁺-ions.     

Synthesis and characterization of FeVO4 nanoparticles

Iron vanadate (FeVO₄) nanoparticles were synthesized by simple co-precipitation method using various surfactants such as ethylene glycol, polyethylene glycol 200 and polyethylene glycol 400 as the structure directing agents. Systematic investigations on the structural, morphological and magnetic properties of the materials have been studied. The lattice constants of the triclinic structure of FeVO₄ were calculated from the X-ray diffraction (XRD) analyses. The average grain size was estimated to be around 35 nm, which increased with increasing the calcination temperature. The stretching and bending vibrations of Fe-O were evaluated from the FT-IR spectra. Using VSM magnetometer, magnetic property was investigated through magnetic susceptibility and magnetization measurements. FeVO₄ exhibits two magnetic ordering temperatures at T ≈ 20 K and 14 K, which is due to two different chemical environments of Fe ligands such as octahedral FeO₆ and trigonal bipyramidal FeO₅ in a six-column doubly bent chain, respectively.