Hydrothermal synthesis of well-dispersed ultrafine N-doped TiO2 nanoparticles with enhanced photocatalytic activity under visible light

Ultrafine nitrogen-doped TiO₂ nanoparticles with narrow particle size distribution, good dispersion, and high surface area were synthesized in the presence of urea and PEG-4000 via a hydrothermal procedure. TEM observation, N₂ adsorption, XRD, UV-vis spectroscopy, the Raman spectroscopy and XPS analysis were conducted to characterize the synthesized TiO₂ particles. The synthesized TiO₂ particles were a mixture of 49.5% anatase and 50.5% rutile with a size of around 5 nm. The photocatalytic activities were tested in the degradation of an aqueous solution of a reactive Brilliant Blue KN-R under both UV and visible light. The synthesized TiO₂ particles showed much higher photocatalytic activity than a commercial P25 TiO₂ powder under both UV and visible light irradiations. The high performance is associated to N doping, the reduced particle size, good dispersion, high surface area, and a quantum size effect.     

Effect of sol–gel pH on XRD peak broadening,lattice strain,ferroelectric domain orientation,and optical bandgap of nanocrystalline Pb1.1(Zr0.52Ti0.48)O3

Nanocrystalline Pb_1.1(Zr_0.52Ti_0.48)O₃ (PZT) samples were prepared using a citrate–nitrate sol–gel process near the morphotropic phase boundary. The effect of pH on the lattice parameters (tetragonality and lattice constants), crystal structure [strain broadening, relative phase content, ferroelectric domain (FD) orientation and nanocrystallite size], microstructure (grain size and particle morphology) and optical bandgap was investigated. The samples were characterized using X-ray diffraction (XRD), the size strain plot (SSP) method, Fourier-transform infrared spectroscopy, and the classical Tauc relation. The particle morphology was investigated using field-emission scanning electron microscopy. The XRD results revealed a perovskite structure and coexisting tetragonal and rhombohedral phases for all PZT samples. Lattice strain and peak broadening were determined from SSP and XRD results. The behavior of these parameters was in agreement for all pH values. The optical bandgap for PZT was estimated from UV-vis absorption spectra. We found that for PZT the maximum relative tetragonal phase content, c/a ratio, and FD orientation along the a-axis occurred at pH 4.     

Electrochemical capacitance from carbon nanotubes decorated with titanium dioxide nanoparticles in acid electrolyte

The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with TiO₂ nanoparticles was investigated. A chemical-wet impregnation was used to deposit different TiO₂ particle densities onto the CNT surface, which was chemically oxidized by nitric acid. Transmission electron microscopy showed that each TiO₂ nanoparticle has an average size of 30-50 nm. Nitrogen physisorption measurement indicated that the porosity of CNTs is partially hindered by some titania aggregations at high surface coverage. Cyclic voltammetry measurements in 1 M H₂SO₄ showed that (i) an obvious redox peak can be found after the introduction of TiO₂ and (ii) the specific peak current is proportional to the TiO₂ loading. This enhancement of electrochemical activity was attributed to the fact that TiO₂ particles act as a redox site for the improvement of energy storage. According to our calculation, the electrochemical capacitance of TiO₂ nanocatalysts in acid electrolyte was estimated to be 180 F/g. Charge-discharge cycling demonstrated that the TiO₂-CNT composite electrode maintains stable cycleability of over 200 cycles.     

X-ray and AFM studies of polydisperse TiO2 (anatase) particles

Titanium dioxide (TiO₂) materials of a high chemical purity, as-prepared by the thermal hydrolysis, as well as subsequently modified by adsorption of different metal cations (Fe³⁺, Co²⁺, Cu²⁺), have been investigated by the X-ray diffraction, X-ray fluorescence and AFM microscopy methods. All TiO₂ powders have a fine-dispersated anatase structure and consist of grown together nanocrystallites of ∼8-17 nm. TiO₂ particles, usually ranging from 100 to 600 nm, show the ability to form large agglomerates, up to 2 μm in size. Contrary to the pure anatase, metal-modified TiO₂ particles possess a positive charge on their surface and can be lifted away by the AFM tip from the substrate surface during the scanning. This effect is mostly pronounced for the Fe-modified TiO₂ sample, where particles up to 250 nm are removed. The possible interaction mechanisms between different TiO₂ particles and the silicon tip are discussed. The electrostatic force has been found to play an essential role in the sample-tip interaction processes, and its value depends on the type of metal cation used.     

Ag/TiO2 sol prepared by a sol–gel method and its photocatalytic activity

Ag/TiO₂ sol with narrow particle size distribution was synthesized using TiCl₄ as the starting material. TiCl₄ was converted to Ti(OH)₄ gel. The Ag/TiO₂ sol was prepared by a process where H₂O₂ was added and then heated at 90–97 °C. After condensation reaction and crystallization, a transparent sol with suspended Ag/TiO₂ was formed. Ag/TiO₂ was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, contact angle analysis, and X-ray photoelectron spectroscopy. The photocatalytic properties of Ag/TiO₂ film were evaluated by degradation of methylene blue in aqueous solution under UV light irradiation. The suspended Ag/TiO₂ particles were rhombus primary particles with the major axis ca. 40 nm and the minor axis ca. 10 nm. Ag nanoparticles were well dispersed on TiO₂ and the particle size was only 1–2 nm. Ag could restrain the recombination of photo-generated electrons and holes effectively. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The thin film had strong hydrophilicity after being illuminated by UV light. Ag/TiO₂ film showed a significant increase in photocatalytic activity compared to the TiO₂ film. The high amount of surface hydroxyls on Ag/TiO₂ film also played an important role in its photocatalytic activity.     

Preparation and characterization of poly(lactic acid)-grafted TiO2 nanoparticles with improved dispersions

Poly(lactic acid) (PLA)-grafted TiO₂ particles were prepared by in situ melt polycondensation of lactic acid onto the surface of TiO₂ nanoparticles. The resulting products were characterized by FTIR, XPS, TG-FTIR, XRD analysis and electron microscopy observation so as to have a better understanding of bonding between the graft polymer and nanoparticles. New characteristic peaks of Ti-carboxylic coordination bond, the changes in the relative intensities of the infrared absorption bands of graft polymer and the two decomposition stage of PLA-grafted TiO₂ confirmed that PLA was grafted on the surface of TiO₂ nanoparticles. By attachment of PLA, the PLA-grafted TiO₂ samples exhibited much better dispersion and a slightly larger particle size than bare TiO₂ particles. PLA-grafted TiO₂ nanoparticles will find wide applications in biomedical and eco-friendly materials, especially as fillers in PLA matrix.     

Synthesis of nano-sized antimony-doped tin oxide (ATO) particles using a DC arc plasma jet

Nano-sized antimony-doped tin oxide (ATO) particles were synthesized using DC arc plasma jet. The precursors SnCl₄ and SbCl₅ were injected into the plasma flame in the vapor phase. ATO powder could conveniently be synthesized without any other post-treatment in this study. To control the doping amount of antimony in the ATO particles, the Sb/Sn molar ratio was used as an operating variable. To study the effect of carrier gas on the particle size, argon and oxygen gases were used. The results of XRD and TGA show that all Sb ions penetrated the SnO₂ lattice to substitute Sn ions. With the increased SbCl₅ concentration in source material, the Sb doping level was also increased. The size of the particles synthesized using the argon carrier gas was much smaller than that of the particles prepared using the oxygen carrier gas. For the argon gas, PSA results and SEM images reveal that the average particle size was 19 nm. However, for the oxygen gas, the average particle size was 31 nm.     

Effect of aluminium doping and annealing on structural and optical properties of cerium oxide nanocrystals

Nanocrystalline fluorite-like structures of Ce_1−xAl_xO_2−δ compounds were prepared by the chemical precipitation method using cerium chloride and aluminium chloride as precursors. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). The effects of aluminium doping concentration and annealing on particle size, lattice parameter and band gap energies were investigated. The particle size of Al-doped CeO₂ samples were found to decrease with Al concentration and it increases from 6 to 20 nm as annealing temperature increases to 900 °C.     

Effect of iron doping and annealing on structural and optical properties of cerium oxide nanocrystals

Nanocrystalline fluorite-like structures of Ce_1−xFe_xO_2−δ compounds were prepared by chemical precipitation method using cerium chloride and iron chloride as precursors. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). The effects of iron doping concentration and annealing on particle size, lattice parameter and band gap energies were investigated. The particle size of Fe-doped CeO₂ samples were found to decrease with iron concentration and it increases from 9 to 26 nm as annealing temperature increases to 900 °C.     

Preparation of nitrogen-doped titanium dioxide with visible-light photocatalytic activity using a facile hydrothermal method

Nitrogen-doped TiO₂ (N-TiO₂) nanoparticles have been successfully prepared via a direct and simple hydrothermal reaction of a commercial Degussa P25 with triethanol amine as solvent and nitrogen source. As-prepared N-TiO₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible light (UV-vis) absorption spectra, electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) techniques. The results confirm that hydrothermal reaction is an effective way to incorporate nitrogen into the TiO₂ lattice, especially nitrogen substitute for titanium. The nitrogen concentration in TiO₂ can be as high as 21% (molar ratio), which is described as Ti_1−yO_2−xN_x+y (in this paper, x=0.36, y=0.27, i.e., Ti_0.73O_1.64N_0.63). The chemical statuses of N have been assigned to N-Ti-O and O-N-O in the TiO₂ lattice as identified by XPS. Photocatalytic degradation of methyl orange has been carried out in both UV-vis (simulated solar light) and the visible region (λ>400 nm). N-TiO₂ exhibits higher activity than the Degussa P25 TiO₂ photocatalyst, particularly under visible-light irradiation. This study has developed a promising and practical pathway to new nitrogen-doped photocatalysts.     

Biological impacts of TiO<Subscript>2</Subscript> on human lung cell lines A549 and H1299: particle size distribution effects

Increasing use of titanium dioxide (TiO₂) nanoparticles in many commercial applications has led to emerging concerns regarding the safety and environmental impact of these materials. In this study, we have investigated the biological impact of nano-TiO₂ (with particle primary size of 20 nm Aeroxide P25) on human lung cell lines in vitro and also the effect of particle size distribution on the particle uptake and apparent toxicity. The biological impact of nano-TiO₂ is shown to be influenced by the concentration and particle size distribution of the TiO₂ and the impact was shown to differ between the two cell lines (A549 and H1299) investigated herein. A549 cell line was shown to be relatively resistant to the total amount of TiO₂ particles uptaken, as measured by cell viability and metabolic assays, while H1299 had a much higher capacity to ingest TiO₂ particles and aggregates, with consequent evidence of impact at concentrations as low as 30–150 μg/mL TiO₂. Evidence gathered from this study suggests that both viability and metabolic assays (measuring metabolic and mitochondrial activities and also cellular ATP level) should be carried out collectively to gain a true assessment of the impact of exposure to TiO₂ particles.     

Mesoporous TiO2-B nanowires synthesized from tetrabutyl titanate

Ultralong mesoporous TiO₂-B nanowires were synthesized via a hybrid hydrothermal-ion exchanging-thermal treatment using tetrabutyl titanate (TBOT) as a raw material. The phase transformations and porous structures of TiO₂-B nanowires were characterized and studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption-desorption measurement. Mesoporous TiO₂-B nanowires showed a length of several micrometers and diameter of about 25 nm. The porous structures of obtained TiO₂-B nanowires were demonstrated by BJH pore distribution measurement. The wirelike morphologies and porous structures of monodisperse nanowires calcined at 600 °C showed little change, which indicated that such nanowires possessed high thermal stability. The formation mechanism of TiO₂-B nanowires with mesoporous structures were also discussed based on our experimental results.     

Synthesis of high tap density Li3V2(PO4)3 cathode materials using mixed lithium precursors

High tap density Li₃V₂(PO₄)₃ cathode materials were synthesized using mixed LiF and LiNO₃ as lithium precursors, LiNO₃ was used as the sintering agent. Rietveld refinement results show that no impurities phases are detected in products. Particle size distribution and tap density measurement results show that particle size and tap density of products can be increased by the addition of LiNO₃. Electrochemical characterization results show that electrochemical performance of products is declined with the increase in contents of LiNO₃ in the lithium precursors. Only a small amount of LiNO₃ added in the lithium precursors (mole ratio of LiNO₃ to LiF is 1:9) can increase the tap density and also retain the good performance of products. Scanning electron microscopy (SEM) images indicate that the samples prepared by mixed lithium precursors present particles agglomerate, and the particle size increased with increase in contents of LiNO₃. Large amount of LiNO₃ added in the lithium precursors induces the particles to become spheric and smooth, which worsens the performance. The particles obtained with the mole ratio of LiNO₃ to LiF in 1:9 show a flake-like shape with a high specific surface area, which leads to good electrochemical performance.     

Preparation of alkaline solid polymer electrolyte based on PVA-TiO2-KOH-H2O and its performance in Zn-Ni battery

A novel composite alkaline polymer electrolyte based on poly(vinyl alcohol) (PVA) polymer matrix, titanium dioxide (TiO₂) ceramic fillers, KOH, and H₂O was prepared by a solution casting method. The properties of PVA-TiO₂-KOH alkaline polymer electrolyte films were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and AC impedance techniques. DSC and XRD results showed that the domain of amorphous region in the PVA polymer matrix augmented when TiO₂ filler was added. The SEM result showed that TiO₂ particles dispersed into the PVA matrix although some TiO₂ aggregates of several micrometers were formed. The alkaline polymer electrolyte showed excellent electrochemical properties. The room temperature (20 °C) ionic conductivity values of typical samples were between 0.102 and 0.171 S cm⁻¹. The Zn-Ni secondary battery with the alkaline polymer electrolyte PVA-TiO₂-KOH had excellent electrochemical property at the low charge-discharge rate.     

Near-edge X-ray absorption fine structure spectroscopy and structural properties of Ni-doped CeO2 nanoparticles

Ni-doped CeO₂ nanoparticles were prepared by using the co-precipitation method. The prepared nanoparticles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The XRD results infer that Ni-doped CeO₂ nanoparticles have single phase nature similar to that of pure CeO₂ nanoparticles. We have calculated lattice parameters using Powder-X software, particle size using Scherer’s formula and strain using the Williamson-Hall method for all the synthesized samples. We have observed a systematic decrease in the lattice parameters, particle size and strain with an increase in Ni doping in CeO₂. The FE-SEM micrographs also confirm that Ni-doped CeO₂ have nanocrystalline behavior and particles are spherical shaped. From the Raman spectra, it is observed that the intensity of classical CeO₂ vibration modes first increases then decreases with Ni doping. The NEXAFS spectra measured at Ce M_4,5 and Ni L_3,2 edges clearly indicate that Ce ions are in the +4 valence state and Ni ions are in the +2 valence state.     

An investigation on the behavior of fine-grained magnetite particles as a function of size and surface modification

By using a KNO₃-aging ferrous hydroxide gel method, Fe₃O₄ particles with sizes ranging from 35 to 1500 nm were synthesized. The particles were covered with a silica coating to form Fe₃O₄-SiO₂ core-shell structures by using the improved conventional Stöber polycondensation method. The thickness of the SiO₂ covering on magnetite particles surface varies from 10 to 20 nm. The morphology, size and composition of the particles were determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The particles with and without coating with SiO₂ were pressed into slices with an oil press at 10 MPa. Subsequently, the coercive forces H_C of the particles were measured by VSM at room temperature, and the critical size for a single domain was estimated. The shape of the particles is basically spherical when the size is smaller than 800 nm, while it is hexagonal for larger particles. The H_C of Fe₃O₄-SiO₂ core-shell structure was larger than that of the uncoated Fe₃O₄ particles by 20%, which was explained to be due to the reduction of inter-particle magnetostatic interaction, supported by an agreement with the packing factor. The dependence of H_C on magnetic particle size could be explained and fitted by the Heewell-Knozam stacking density equation and object-oriented micromagnetic computing framework (OOMMF) micromagnetic software. the results agree well with the experimental data.     

Contact potential barriers and characterization of Ag-doped composite TiO2 nanotubes

Ag-doping TiO₂ composite nanotubes (Ag-TNTs) were synthesized by alkaline fusion followed by hydrothermal treatment. The microstructure and morphology of the materials were characterized by XRD, TEM, XPS, SPS (surface photovoltage spectroscopy), FISPS (electric field-induced surface photovoltage spectroscopy) and Raman spectroscopy. First-principles calculations based on density-functional theory (DFT) showed the formation of several impurity levels near the top of the valence band in the band gap (E_g) of rutile TiO₂ due to Ag doping. A “double junction” is proposed, involving a Schottky junction and p–n junction (denoted as “Ag-p–n junction”) occurring between the Ag particles and the nanotube surface, as well as forming inside TiO₂ nanotubes, respectively. The strongly built-in electric field of the junctions promotes the separation of photo-holes and photoelectrons, enhancing the photocatalytic efficiency. XRD results indicated that the composite Ag-TNTs exist as a mixture of anatase and rutile phases. XPS results showed that Ti⁴⁺ is the primary state of Ti. Raman spectral analysis of Ag-TNTs revealed the presence of a new peak at 271 cm⁻¹. The red-shift of the absorption light wavelength of Ag-TNTs was 0.16 eV (20 nm) due to a considerable narrowing of E_g by the existing impurity levels.     

Crystallization study of sol-gel un-doped and Pd-doped TiO2 materials

Sol-gel nanostructured titania materials have been reported to have applications in areas ranging from optics via solar energy to gas sensors. In order to enhance the photocatalytic activity, there are many studies regarding the doping of titanium dioxide (TiO₂) material with either non-metals (S, C, N, P) or metals (Ag, Pt, Nd, Fe). The present work has studied some un-doped and Pd-doped sol-gel TiO₂ materials (films and gels), with various surface morphologies and structures, obtained by simultaneous gelation of both precursors Ti(OEt)₄ and Pd(acac)₂. Their structural evaluation and crystallization behavior with thermal treatment were followed by DTA/TG analysis, infrared (IR) spectroscopy, Fourier transform infrared (FTIR), spectroellipsometry (SE), X-ray diffraction (XRD) and atomic force microscope (AFM). The influence of Pd on TiO₂ crystallization for both supported and un-supported materials was studied (lattice parameters, crystallite sizes, internal microstrains). The changes in the optical properties of the TiO₂-based vitreous materials were correlated with the changes of the structure. The hydrophilic properties of the films were also connected with their structure, composition and surface morphology.     

TiO2/MgAl layered double hydroxides mechanical mixtures as efficient photocatalysts in phenol degradation

MgAl layered double hydroxides (MgAl LDH) were synthesized by the sol-gel method using ultrasound irradiation in the crystallization step. The interlayer anions were nitrate and acetylacetonate-ethoxide. The solids were characterized by XRD, N₂-physisorption and TEM. TiO₂/MgAl LDH mixtures were prepared by mixing the MgAl LDH (as prepared) or the calcined sample with TiO₂ (Aldrich, 99.9% anatase) in different weight ratios. Photocatalytic activities of the TiO₂/MgAl LDH mixtures were evaluated through the degradation of phenol as model pollutant. TiO₂/MgAl LDH mixture (1:1) was more photocatalytically active for the degradation of phenol than pure TiO₂. The synergy effect was attributed to a higher production of ^•OH radicals, which were formed from the structural hydroxides. Also, the hydrotalcite phase enhanced the phenol adsorption and transfer to the TiO₂ sites where the phenol was photocatalytically degradated.     

Size-induced effect on nano-crystalline CoFe2O4

Cobalt ferrite (CoFe₂O₄) nano-particles have been synthesized successfully and we studied the effect of temperature on them. The particles have been annealed at different temperatures ranging from 373 to 1173 K. Significant effect on the physical parameters like crystalline phase, crystallite size, particle size, lattice strain and magnetic properties of the nano-particles has been investigated. The studies have been carried out using a powder X-ray diffractometer (XRD), a transmission electron microscope (TEM) and a vibrating sample magnetometer (VSM). A thorough study of the variation of specific surface area and particle size with annealing is presented here, with their effects on saturation magnetization.