Study of the growth of CeO2 nanoparticles onto titanate nanotubes

We report the study of the growth of CeO₂ nanoparticles on the external walls and Ce⁴⁺ intercalation within the titanate nanotubes. The materials were fully characterized by multiple techniques, such as: Raman spectroscopy, infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The ion exchange processes in the titanate nanotubes were carried out using different concentrations of Ce⁴⁺ in aqueous solution. Our results indicate that the growth of CeO₂ nanoparticles grown mediated by the hydrolysis in the colloidal species of Ce and the attachment onto the titanate nanotubes happened and get it strongly anchored to the titanate nanotube surface by a simple electrostatic interaction between the nanoparticles and titanate nanotubes, which can explain the small size and even distribution of nanoparticles on titanate supports. It was demonstrated that it is possible to control the amount and size of CeO₂ nanoparticles onto the nanotube surface, the species of the Ce ions intercalated between the layers of titanate nanotubes, and the materials could be tuned for using in specific catalysis in according with the amount of CeO₂ nanoparticles, their oxygen vacancies/defects and the types of Ce species (Ce⁴⁺ or Ce³⁺) present into the nanotubes.     

Spectroscopic studies of interfacial structures of CeO2-TiO2 mixed oxides

We have investigated the geometric and electronic structures of the cerium oxide (CeO₂)-titanium dioxide (TiO₂) mixed oxides with various Ce/TiO₂ weight ratios prepared by the sol-gel method in detail by means of X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (XPS), Raman spectroscopy excited by 325 and 514.5 nm lasers, and scanning electron microscope (SEM). Existence of cerium effectively inhibits the phase transition of TiO₂ from the anatase phase to the rutile phase. XRD peaks of TiO₂ anatase attenuate continuously with the increasing amount of CeO₂ in the mixed oxide, but the XRD peaks of cubic CeO₂ appear only after the weight ratio of Ce/TiO₂ reaches 0.50. The average crystalline sizes of TiO₂ anatase and cubic CeO₂ in CeO₂-TiO₂ mixed oxides are smaller than those in the corresponding individual TiO₂ anatase and cubic CeO₂. Raman spectroscopy excited by the 514.5 nm laser detects CeO₂ after the weight ratio of Ce/TiO₂ reaches 0.70 whereas Raman spectroscopy excited by the 325 nm laser detects CeO₂ after the weight ratio of Ce/TiO₂ reaches 0.90. XPS results demonstrate that Ti exists in the form of Ti⁴⁺ in the CeO₂-TiO₂ mixed oxide. Ce is completely in the form of Ce³⁺ in the mixed oxides with a 0.05 weight ratio of Ce/TiO₂. With the increasing weight ratio of Ce/TiO₂, Ce⁴⁺ dominates. On basis of these results, we proposed that CeO₂ initially nucleates at the defects (oxygen vacancies) within TiO₂ anatase, forming an interface bridged with oxygen between CeO₂ and TiO₂ anatase. At the interface, Ce species cannot substitute Ti⁴⁺ in the lattice of TiO₂ anatase whereas Ti⁴⁺ can substitute Ce⁴⁺ in the lattice of cubic CeO₂. The decreasing concentration of oxygen vacancies, the Ti-O-Ce interface, and the decreasing average crystalline size of TiO₂ anatase act to inhibit the phase transformation of TiO₂ anatase. With the increasing amounts of CeO₂, the CeO₂ clusters continuously grow and form cubic CeO₂ nanocrystals. Spectroscopic results strongly demonstrate that the surface region of CeO₂-TiO₂ mixed oxide is enriched with TiO₂.     

Fe doping induced enhancement in room temperature ferromagnetism and selective cytotoxicity of CeO2 nanoparticles

In the present study, structural, optical, magnetic properties as well as cytotoxicity of undoped and Fe doped Ceria (CeO₂) nanoparticles synthesized by simple soft chemical method have been reported. SEM and XRD results have shown that the synthesized samples are comprised of ultrafine spherical nanoparticles having single phase cubic fluorite structure of CeO₂. Raman spectroscopy results have depicted a red shift in F_2g mode with Fe doping which reveals enhancement in the oxygen vacancies. The optical band gap calculated from UV–visible absorption spectra has been found to vary unsystematically with Fe doping which is associated with the creation of impurity level and abundance in oxygen vacancies with Fe doping. The oxygen vacancies have introduced the room temperature ferromagnetism (RTFM) in undoped and Fe doped CeO₂ nanoparticles. The saturation magnetization (M_s) value of pristine CeO₂ nanoparticles has been found to be 0.00083 emu/g which is increased up to 0.0126 emu/g for 7% Fe doped nanoparticles. For cytotoxicity tests, the synthesized nanoparticles induced effects on Neuroblastoma cancer cells & HEK-293 healthy cells have been analyzed via CCK-8 analysis. It has been observed that the prepared undoped and Fe doped CeO₂ nanoparticles have nontoxic nature towards healthy cells while they are extremely toxic towards cancerous cells. Furthermore, the anticancer activity is found to enhance with Fe doping. The selective toxicity and enhancement in anticancer activity with Fe doping has observed to be strongly correlated with reactive oxygen species (ROS) generation.     

Estimation of contact area of nanoparticles in chains using continuum elastic contact mechanics

In this research, we have studied the doping behaviors of eight transition metal ion dopants on the crystal phase, particle sizes, XRD patterns, adsorption spectra, anatase fraction, and photoreactivity of TiO₂ nanoparticles. The pristine and ion-doped TiO₂ nanoparticles of 15.91-25.47 nm were prepared using sol–gel method. Test metal ion concentrations ranged from 0.00002 to 0.2 at.%. The absorption spectra of the TiO₂ nanoparticles were characterized using UV-Visible spectrometer. The wavelength of the absorption edge of TiO₂ was estimated using the spectra derivative-tangent method. The photoreactivities of pristine and ion-doped TiO₂ nanoparticles under UV irradiation were quantified by the decoloring rate of methyl orange. XRD patterns were recorded using a Rigaku D/MAX-2500 V diffractometer with Cu Kα radiation (50 kV and 250 mA), and particle size and anatase fraction were calculated. Results reveal that different ion doping exhibited complex effects on the studied characteristics of TiO₂ nanoparticles. In general, red shift occurred to ion-doped TiO₂ nanoparticles, but still with higher TiO₂ photoreactivities when doped with Fe³⁺ and Ni²⁺ ions. Among the ions investigated, Ni-doped TiO₂ nanoparticles have shown highest photoreactivity at the concentration of 0.002 at.%, about 1.9 times that of the pristine TiO₂. Ion doping was shown to reduce the diameter and influence the fraction of anatase. Data also indicated that the combination of anatase diameter and ion radius might play an important role in the photoreactivity of TiO₂ nanoparticles. This investigation contributes to the understanding of complex ion doping effects on TiO₂ nanoparticles, and provides references for enhancing their environmental application.     

纳米Ce1-x(Fe0.5La0.5)xO2-δ固溶体的水热合成及光谱分析

采用水热方法合成Ce1-x(Fe0.5 La0.5)xO2-δ固溶体.利用X射线衍射技术(X-ray diffraction technique,XRD)表征样品的相结构,并对固溶体的晶胞参数进行拟合,通过紫外可见漫反射光谱(UV-Vis diffraction spectrum)及拉曼光谱(Raman spectru...     

Structural, magnetic and electronic structure studies of Mn doped TiO2 thin films

We report structural, magnetic and electronic structure study of Mn doped TiO₂ thin films grown using pulsed laser deposition method. The films were characterized using X-ray diffraction (XRD), dc magnetization, X-ray magnetic circular dichroism (XMCD) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. XRD results indicate that films exhibit single phase nature with rutile structure and exclude the secondary phase related to Mn metal cluster or any oxide phase of Mn. Magnetization studies reveal that both the films (3% and 5% Mn doped TiO₂) exhibit room temperature ferromagnetism and saturation magnetization increases with increase in concentration of Mn doping. The spectral features of XMCD at Mn L_3,2 edge show that Mn²⁺ ions contribute to the ferromagnetism. NEXAFS spectra measured at O K edge show a strong hybridization between Mn, Ti 3d and O 2p orbitals. NEXAFS spectra measured at Mn and Ti L_3,2 edge show that Mn exist in +2 valence state, whereas, Ti is in +4 state in Mn doped TiO₂ films.     

Controlled synthesis of CeO<Subscript>2</Subscript> nanoparticles using novel amphiphilic cerium complex precursors

Maleic anhydride was grafted by long-chain alcohols (1-hexadecanol, 1-octadecanol) to amphiphilic mono-L cis-butene dicarboxylates (L = hexadecyl, octadecyl), i.e., MAH, MAO, respectively. Subsequently, corresponding amphiphilic cerium complexes with these two mono-L cis-butene dicarboxylate ligands (Ce(L')₃, L'= MAH, MAO) were synthesized and behaved as the precursors to prepare CeO₂ nanoparticles for both of which can form nanosized micelle-like aggregates by special self-assembly in the wet chemical process. The nanoparticles were further characterized by Fourier transform-infrared spectroscopy (FTIR), Diffuse reflectance ultraviolet-visible spectra (DRUVS), scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). Both the CeO₂ nanoparticles are in a cubic fluorite structure and present regular and well-dispersion club-like morphology with average particle size in the range of 40–70 nm. Besides, the strong ultraviolet–visible absorption for these CeO₂ nanoparticles can be found at the long-wavelength ultraviolet to visible region of 200–500 nm.     

Structural, magnetic and transport properties of Ni-doped ZnO films

In this work, Ni-doped ZnO (Zn_1−xNi_xO, x=0, 0.03, 0.06, 0.11) films were prepared using magnetron sputtering. X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), temperature dependence electrical resistance, Hall and magnetic measurements were utilized in order to study the properties of the Ni-doped ZnO films. XRD and XAS results indicate that all the samples have a ZnO wurtzite structure and Ni atoms incorporated into ZnO host matrix without forming any secondary phase. The Hall and electrical resistance measurements revealed that the resistivity increased by Ni doping, and all the Ni-doped ZnO films exhibited n-type semiconducting behavior. The magnetic measurements showed that for the samples with x=0.06 and 0.11 are room-temperature ferromagnetic having a saturation magnetization of 0.33 and 0.39 μ_B/Ni, respectively. The bound-magnetic-polaron mediated exchange is proposed to be the possible mechanism for the room-temperature ferromagnetism in this work.     

Synthesis and microstructure of Co/Ni: MgGa<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

This report discusses the preparation and microstructure of Co/Ni co-doped MgGa₂O₄ nanoparticles. The nanoparticles with the size of 20–55 nm were synthesized by sol-gel method. The phase and crystallinity were confirmed by X-ray powder diffraction (XRD) pattern. The particle size was estimated according to XRD data and transmission electron microscopy. The electronic structure was studied using X-ray photoelectron spectroscopy (XPS). The XPS studies showed that Ga³⁺ ions possess tetrahedral and octahedral sites of spinel structure and the inverse degree (two times of the fraction of tetrahedral Ga³⁺ ions) has increased with the increase of the doping concentration of Co²⁺ and Ni²⁺ ions. For Co/Ni co-doped MgGa₂O₄, two broad absorption bands of 350~500 and 550~700 nm were observed in the absorption spectra. The broad band at 350~500 nm was assigned to the combination of the absorption of octahedral Co²⁺ and Ni²⁺ ions, whereas the absorption band at 550~700 nm is mainly due to tetrahedrally coordinated Co²⁺ ions and octahedrally coordinated Ni²⁺ ions.     

Structural,magnetic and optical properties of diluted magnetic semiconductor (DMS) phase of Ni modified CuO nanoparticles

Control on the size of copper oxide (CuO) in the nano range is a highly motivating approach to study its multifunctional nature. The present investigation reports a sol-gel derived Ni doped CuO nanoparticles (Cu_1-xNi_xO). Rietveld refinement of the XRD spectra confirms the formation of single monoclinic phase of Cu_1-xNi_xO nanoparticles having crystallite size within the range of 19–21 nm. Raman spectra show the presence of characteristics Raman active modes and vibrational bands in the Cu_1-xNi_xO samples that corroborate the monoclinic phase of the samples as revealed by refinement of XRD data. The estimated band gap of pure CuO is found to be ∼1.43 eV, which decreases with the increase of dopant concentration into CuO matrix. This result is in line with estimated crystallite size. Magnetization curves confirm the weak ferromagnetic nature of Cu_1-xNi_xO nanoparticles which reveal the DMS phase. This weak magnetic nature may be induced in the samples due to the exchange interaction between the localized magnetic d-spins of Ni ions and carriers (holes or electrons) from the valence band of pristine CuO lattice. Replacement of Cu⁺² by Ni⁺² ions into the host CuO lattice induces the magnetization. The quantified value of squareness ratio (S < 0.5) confirms the inter-grain magnetic interactions in the Cu_1-xNi_xO nanoparticles which is also the reason of weak induced magnetization.     

Investigation of Physical and electrochemical properties of Ni doped CeO2 Thin films: DFT calculation

Undoped and Ni-doped thin films of cerium dioxide have been deposited by spray pyrolysis technique on the glass substrate at the optimized temperature (450 ± 5) °C. Thin films Ce_1-xNi_xO₂ doped by different concentrations of Ni was characterized by X-ray diffraction. Raman analysis showed a peak at 461 ± 1 cm⁻¹ position for the undoped film, which corresponds to the active mode (F_2g mode) of the cubic fluorite structure. SEM images showed that the particles have a uniform spherical shape. EDS data have confirmed all elements (Ce, Ni and O) existence. Optical properties of samples show a decrease in band gap energy with increasing the nickel rate. Cyclic voltammetry indicates that the storage capacity of samples increases as the Ni rate increases. The EIS of CeO₂/ITO electrodes displays a small semicircular at high frequency. The theoretical results obtained using WIEN2k match well with the experimental ones.     

Evidences of the evolution from solid solution to surface segregation in Ni‐doped SnO2 nanoparticles using Raman spectroscopy

Ni‐doped SnO₂ nanoparticles, promising for gas‐sensing applications, have been synthesized by a polymer precursor method. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) data analyses indicate the exclusive formation of nanosized particles with rutile‐type phase (tetragonal SnO₂) for Ni contents below 10 mol%. The mean crystallite size shows a progressive reduction with the Ni content. Room‐temperature Raman spectra of Ni‐doped SnO₂ nanoparticles show the presence of Raman active modes and modes activated by size effects. From the evolution of the A_1g mode with the Ni content, a solubility limit at ∼2 mol% was estimated. Below that content, Raman results are consistent with the occurrence of solid solution (ss) and surface segregation (seg.) of Ni ions. Above ∼2 mol% Ni, the redshift of A_1g mode suggests that the surface segregation of Ni ions takes place. Disorder‐activated bands were determined and their integrated intensity evolution with the Ni content suggest that the solid‐solution regime favors the increase of disorder; meanwhile, that disorder becomes weaker as the Ni content is increased. Copyright © 2010 John Wiley & Sons, Ltd.     

Lattice distortion and corresponding changes in optical properties of CeO2 nanoparticles on Nd doping

Doping of Nd distorts the lattice structure of CeO₂, increases the lattice strain and expands the lattice. Oxygen vacancies and other ceria related defects contribute to the lattice strain. Shifting and broadening of the F_2g Raman peak of doped sample, compared to pure CeO₂, is indicative of local structure distortion on doping. Dopant induced enhancement of oxygen vacancies, in the CeO₂ lattice, is further confirmed by the generation of a new Raman peak at 543 cm^?1 that is otherwise absent in the pure one. UV–vis spectroscopy gives an understanding of the different types of f–f electronic transition of Nd in the crystalline environment of CeO₂. Effective band gap of CeO₂ reduces upto Nd concentration of 2.5%. The band gap, however, increases at 4% of Nd due to Burstein–Moss shift. Photoluminescence intensity of pure CeO₂ decreases with Nd concentration owing to the increase in the number of non radiative oxygen vacancies. These vacancies act as luminescence quencher and reduce the emission intensity. Photoluminescence excitation spectra confirm the presence of these oxygen vacancies in the CeO₂ nanocrystallites.     

Microstructural characterisation of nanoparticles using, XRD line profiles analysis, FE-SEM and FT-IR

In this investigation, the structural characteristics of α- Fe₂O₃ nanoparticles synthesised by a mechanical milling have been explored. The structure and morphology of samples were characterized by X-ray powder diffraction, field-emission scanning electron microscope (FE-SEM) and FT-IR measurements. The crystallite size and internal strain were evaluated by XRD patterns using Williamson-Hall and Scherrer methods. The results did not reveal any phase change during the milling. The average particle size decreases with a prolongation of milling times, while the lattice parameters and internal strain increase. It was found that using this method allowed the formation of hematite nanoparticles.     

Investigation of electronic structure of Nd-doped TiO2 nanoparticles using synchrotron radiation photoelectron spectroscopy

Doping with transition metal ions in TiO₂ has been found effective to modify the electronic structure of TiO₂ nanoparticles. Application of synchrotron radiation photoelectron spectroscopy (SRPES) to Nd-doped TiO₂ nanoparticles revealed that there existed different peak positions and structure with different doping concentration in the valence band spectra. From the onset of valence band spectrum, it was observed that doping Nd ions alters the electronic structure and makes the band gap of TiO₂ narrow.     

Effect of cobalt doping on structural,optical and redox properties cerium oxide nanoparticles

Cobalt-doped ceria nanoparticles were synthesized using the polyol method under co-precipitation hydrolysis. The structural, morphological, optical and redox properties were observed to investigate the influence of different concentration of cobalt ion doping on the prepared CeO₂ nanomaterials in terms of X-ray diffraction, field-emission transmission electron microscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, UV/vis absorption spectroscopy and temperature program reduction techniques. The optical band gap energy was calculated from the optical absorption spectra for doped ceria nanoparticles, which have been found to be 2.68, 2.77, and 2.82 eV for the 2, 4, and 7 mol% Co ion-doped CeO₂ nanoparticles, respectively. As observed, the band gap energies increases as the doping Co ion concentrations increased, which could be due to significant increased oxygen vacancies with Co doping. The synergistic interaction between Co and CeO₂ was the main factor responsible for high catalytic activity of cobalt-doped CeO₂ model catalysts.     

Influence of phonon confinement,surface stress,and zirconium doping on the Raman vibrational properties of anatase TiO2 nanoparticles

We present a comprehensive analysis of the Raman spectra of pure and zirconium‐doped anatase TiO₂ nanoparticles. To account for the wavenumber shifts of the E_g(ν₆) mode as a function of particle size (L) and dopant concentration (x), a modification of the standard phonon confinement model (PCM) is introduced, which takes into account the contribution of surface stress by means of the Laplace–Young equation. Together with X‐ray diffraction (XRD) and transmission electron microscopy data, our analysis shows that the surface stress contribution to the observed blue shift of the Raman wavenumber is of the same magnitude as the spatial phonon confinement effect. Annealing experiments show that Zr‐doped nanoparticles exhibit retarded grain growth and delayed anatase‐to‐rutile phase transition by up to 200 K compared to pure anatase TiO₂. XRD shows that Zr doping leads to a unit cell expansion of the anatase structure. Applying the modified PCM to the x‐dependent variations of the E_g(ν₆) Raman mode, the mode‐Grüneisen parameter is found to increase abruptly at x > 0.07 with a concomitant mode softening. This coincides with the x range over which the Zr cations are reported to be displaced from their position in the tetrahedral lattice, and where Zr precipitation occurs upon annealing. The results have implications for the interpretation of Raman spectra of ionic metal oxide nanoparticles and how these are modified upon cation doping. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of dopant level on structural, optical and magnetic properties of Co-doped anatase TiO2 nanoparticles

Cobalt-doped TiO₂ nanoparticles were synthesized by sol-gel method. The associated structural, optical, compositional and magnetic properties of the nanoparticles as a function of cobalt concentration have been systematically studied. The X-ray powder diffraction reveals that all samples have pure anatase phase tetragonal system and the lattice parameter analysis indicated that Co ions may substitute into the lattice of TiO₂. The average particle size is 15 nm, when found through transmission electron microscope. Optical spectroscopy measurement showed that the bandgap value decreases upon increasing Co concentration. The magnetic measurements revealed that the enhanced room temperature ferromagnetism (RTFM) strongly depends on the doping content.     

Effect of barium doping on the physical properties of zinc oxide nanoparticles elaborated via sonochemical synthesis method

The aim of this work is to study the effect of barium (Ba) doping on the optical, morphological and structural properties of ZnO nanoparticles. Undoped and Ba-doped ZnO have been successfully synthesized via sonochemical method using zinc nitrate, hexamethylenetetramine (HMT) and barium chloride as starting materials. The structural characterization by XRD and FTIR shows that ZnO nanoparticles are polycrystalline with a standard hexagonal ZnO wurtzite crystal structure. Decrease in lattice parameters from diffraction data shows the presence of Ba²⁺ in the ZnO crystal lattice. The morphology of the ZnO nanoparticles has been determined by scanning electron microscopy (SEM). Incorporation of Ba was confirmed from the elemental analysis using EDX. Optical analysis depicted that all samples exhibit an average optical transparency over 80%, in the visible range. Room-temperature photoluminescence (PL) spectra detected a strong ultraviolet emission at 330 nm and two weak emission bands were observed near 417 and 560 nm. Raman spectroscopy analysis of Ba-doped samples reveals the successful doping of Ba ions in the host ZnO.     

Effect of grain size on the magnetic properties of superparamagnetic Ni0.5Zn0.5Fe2O4 nanoparticles by co-precipitation process

Ni_0.5Zn_0.5Fe₂O₄ (NZFO) spinel-type nanoparticles were directly fabricated by the chemical co-precipitation process using metal nitrate and acetate as precursors since nitrogen and carbon would be taken away in the forms of oxynitride and oxycarbide, respectively, after the precursors were annealed and then investigated in detail by employing X-ray diffraction (XRD), magnetic measurement and Raman spectroscopy. XRD analysis indicates that the as-prepared nanocrystals are all of a pure cubic spinel structure with their sizes ranging from 20.8 to 53.3 nm, as well as peaks of some samples shifting to lower angles due to lattice expansion. Calculations from the derived XRD data indicate that the activation energy is 30.83 kJ/mol. The magnetic measurements show that these samples are superparamagnetic. The saturation magnetization increases with annealing temperature, which may be explained by super-exchange interactions of Fe ions occurring at A- and B-sites. The variation of coercivity with particle size is interpreted on the basis of domain structure and crystal anisotropy. Furthermore, these nanoparticles exhibit a redshift phenomenon at lower temperatures seen in the Raman spectra, which could be related to ionic substitution.