Synthesis and characterization of Fe doped titanium dioxide nanopowders

Titanium dioxide nanopowders, doped with different amounts of Fe³⁺ ions (0.3-5 mass%), were synthesized by acid-catalyzed sol-gel method in a non-aqueous medium. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and determination of izoelectric points as well as particle diameters. Careful investigation of porous structure was provided by application of nitrogen adsorption-desorption method. Structure analysis showed that the obtained nanopowders exhibited the anatase crystal structure, independent of the amount of iron dopants. The presence of Fe³⁺ ions in anatase decreases the value of isoelectric point of undoped TiO₂. Unlike crystal structure, porosity parameters are strongly affected by the amount of iron ions incorporated in TiO₂ lattice. The mesoporosity of TiO₂ can be successfully controlled by changing the amount of iron dopants.     

XPS and UV–vis studies of Ga-doped zinc oxide nanoparticles synthesized by gelatin based sol-gel approach

Undoped and gallium-doped ZnO nanoparticles, (ZnO NPs) (Zn_1−xGa_xO, x=0.0, 0.03, 0.06, 0.09, 0.12, 0.15), were synthesized by a gelatin-based, sol–gel method. Structural and morphological studies of the resulting products were carried out via X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The XRD results revealed that the sample products were crystalline with a hexagonal wurtzite phase. Furthermore, the TEM images indicated ZnO NPs having approximately spherical shapes, with their particle size distributed over the nanometer range. The XRD and TEM results also showed a decrease in crystallite and particle sizes of NPs from x=0.0 to 0.15. The size-strain plot (SSP) method was employed to study the individual contributions of crystallite sizes and lattice strain to the peak broadening of the undoped and doped ZnO NPs. The effect of doping on the optical band-gap and crystalline quality was also investigated, using ultraviolet-visible (UV–vis), X-ray photoluminescence (XPS), and spectroscopies of the pure and doped ZnO NPs. It was observed that the band-gap and O-vacancies of the doped ZnO NPs were red-shifted in comparison with those of the undoped ZnO NPs in UV–vis and XPS results.     

Optical and structural modification of boron-doped CoGa2O4 particles

We mainly focused on synthesis of boron doped cobalt gallium oxide (B doped CoGa₂O₄) nanoparticles. In the study, varied amount of B doped CoGa₂O₄ nanopowders were produced employing Sol-Gel technique. The structural characterizations of the particles were performed using x-ray powder diffractometer (XRD) and x-ray photoelectron spectroscopy (XPS) measurements. Rietveld refinements were utilized to investigate B atom replacement and thus, the changes in lattice parameters. Furthermore, the reflectance and absorbance performances were measured by UV–visible spectrophotometer in order to determine electronic energy level configurations through the band gap. The relationship between crystal structural and formation of electronic energy levels was also investigated according to the locations of substituted B atoms.     

Optical and Structure Properties of Nanocrystalline Titania Powders with Cu Dopant

TiO₂ nanopowders doped by Cu were prepared by the sol–gel method. The effects of Cu doping on the structural, optical, and photo-catalytic properties of titania nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis absorption spectroscopy. XRD results suggest that adding impurities has a significant effect on anatase phase stability, crystallinity, and particle size of TiO₂. Titania rutile phase formation in the system (Ti–Cu) was promoted by Cu²⁺ doped TiO₂. The photo-catalytic activity was evaluated by photo-catalytic degradation kinetics of aqueous methylene orange (MO) under visible radiation. The results show that the photo-catalytic activity of the 5 %Cu doped TiO₂ nanopowders has a larger degradation efficiency than pure TiO ₂ under visible light. Also, the minimum band gap was estimated to be ～ 1.9–2 eV from UV–Vis spectra.     

Effect of calcination temperature on structural,magnetic and optical properties of multiferroic YFeO3 nanopowders synthesized by a low temperature solid-state reaction

Nanosize multiferroic YFeO₃ powders have been synthesized via the low temperature solid-state reaction. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy all indicated that the phase-pure orthorhombic YFeO₃ powders were obtained at 800 °C with a size below 150 nm. X-ray photoelectron spectroscopy (XPS) showed the Fe³⁺ ions to be predominant. Magnetic hysteresis loops exhibited some ferromagnetic behaviour of the YFeO₃ nanopowders at ambient temperature. The maximum and remnant magnetizations of the powders were about 2.49 and 0.88 emu/g, respectively. Moreover, optical measurements demonstrated that the optical band gap of the nanopowders was around 2.4 eV, proving that they can strongly absorb visible light. So an easy and efficient way to synthesize YFeO₃ nanopowders with promising application in the magnetic and optical fields has been successfully developed.     

Defect induced magnetic transition in Co doped CeO2 sputtered thin films

Cobalt-doped cerium dioxide thin films exhibit room temperature ferromagnetism due to high oxygen mobility in doped CeO₂ lattice. CeO₂ is an excellent doping matrix as there is a possibility of it losing oxygen while retaining its structure. This leads to increased oxygen mobility within the fluorite CeO₂ lattice, leading to formation of Ce³⁺ and Ce⁴⁺ species. Magnetic ceria materials are important in several applications from magnetic data storage devices to magnetically recoverable catalysts. In this paper, the room temperature ferromagnetism of rf sputtered Co doped CeO₂ thin films is reported whereas undoped CeO₂ thin films exhibit paramagnetic behavior. The ferromagnetic properties of the Co doped films were explained based on oxygen vacancies created by Co ions in Ce sites. This is further supported by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman. Change in surface morphology due to Co doping of the samples were analyzed using atomic force microscopy (AFM).     

Optimization of particle size,dispersity, and conductivity of 8 mol% Y2O3 doped tetragonal zirconia polycrystalline nanopowder prepared by modified sol-gel method via activated carbon absorption

8 mol% Y₂O₃ doped tetragonal zirconia polycrystalline (8Y-TZP) ceramic nanopowders were synthesized via a novel modified sol-gel method employing zirconium carbonate basic as zirconium resources. The activated carbon as a dispersant was added to the precursor solution during the formation of the sol. The phase behavior, thermal decomposition, microstructure morphology, and electrochemical performance of nanopowders with the addition of activated carbons were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), particles size distribution, and electrochemical impedance spectroscopy analysis (EIS). After adding the activated carbon, the average crystallite size of 8Y-TZP nanopowders decreased from about 53.16–33.51 nm when calcined at 900 ℃, and the 8Y-TZP nanopowders were produced loosely agglomerated. Meanwhile, compacts prepared by pressing the as-obtained 8Y-TZP nanopowders sintered to 98.8% relative density at 1600 ℃ and exhibited an average grain size of 0.89 µm, which brought a positive effect on ionic conductivity (0.079 S·cm^?1).     

Photoluminescence properties of praseodymium doped cerium oxide nanocrystals

The structure and photoluminescence (PL) properties of CeO₂ nanocrystals synthesized by the microwave-assisted hydrothermal (MAH) method with different praseodymium (Pr³⁺) ions contents were performed. X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance ultraviolet-visible (UV-vis), Fourier transform Raman (FT-Raman) spectroscopies and PL measurements at room temperature were employed. XRD patterns indicated that the nanocrystals are free of secondary phases and crystallize in the cubic structure while FT-Raman revealed a typical scattering mode of fluorite type. The UV-vis spectra suggested the presence of intermediate energy levels in the band gap of these nanocrystals. The most intense PL emission was obtained for CeO₂ nanocrystals doped with 1.6% of Pr³⁺ ions and smaller particle size.     

Temperature Stability and Photocatalytic Activity of Nanocrystalline Cristobalite Powders with Cu Dopant

The SiO₂ nanoparticles doped by 10 % mol Cu were prepared via a sol-gel method under process control. The effects of doping and calcination temperature on the structural and photo-catalytic properties of SiO₂ nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. Cristobalite and tridymite crystalline phases were found at a calcinations temperature range of 900～1200 °C and amorphous phase was formed at a temperature of 800 °C for doped SiO₂. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methyl orange (MO) under visible radiation. The results show that the photocatalytic activity of the 10 % mol Cu doped SiO₂ nanopowders have a larger degradation efficiency than pure SiO₂ under visible light at 900 °C temperature.     

Magnetic characteristics and optical band alignments of rare earth (Sm+3, Nd+3) doped garnet ferrite nanoparticles (NPs)

Yttrium iron garnet (YIG) nanoparticles (NPs) doped with rare earth (RE) metal ions (Y_2.5Sm_0.5Fe₅O₁₂, Y_2.5Nd_0.5Fe₅O₁₂) were successfully synthesized by sol-gel auto combustion approach. The cubic crystalline structure and morphology of the prepared garnet ferrite NPs were analyzed by X-ray diffractometer (XRD) and field emission scanning electron microscopy (FESEM). The cubic crystalline garnet phase of the synthesized YIG, Sm-YIG and Nd-YIG samples was successfully achieved at 950 °C sintering temperature. The force constant and absorption bands were estimated by using Fourier transform infrared spectroscopy (FTIR). The doping effect of RE metal ions on the chemical states of YIG were examined by x-ray photoelectron microscopy (XPS). The valence band (from 12.63 eV to 13.22 eV), conduction band (from 10.89 eV to 11.34 eV) edges and optical bandgap values of RE doped YIG samples were calculated using UV–Vis spectroscopy and ultraviolet photo electron spectroscopy (UPS). The magnetic analysis of the prepared NPs was studied using vibrating sample magnetometer (VSM). The XPS analysis of RE doped YIG samples exhibit the existence of RE (Sm⁺³, Nd⁺³) contents on the surface of YIG ferrite by decreasing the oxygen lattice in garnet structure. The optical bandgap (from 1.74 eV to 1.88 eV) explains the semiconducting nature of the synthesized NPs. The UPS results confirm the valence band position of YIG doped samples. The saturation magnetization and remanence of RE doped garnet ferrite samples increased from 13.45 to 18.83 emu/g and 4.06–6.53 emu/g, respectively.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Growth and characterization of the Al-doped and Al–Sn co-doped ZnO nanostructures

In the present work, well-dispersed structures of spherical-like pure ZnO, Al doped ZnO (AZO) and Al, Sn co-doped ZnO (ATZO) nanocrystals were successfully synthesized by using zinc acetate dihydrate as the starting material and also the low temperature hydrothermal process without any additional surfactant or catalytic agent. The ZnO structures were characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The XRD results revealed that ZnO powders have a hexagonal crystal structure and the TEM indicated that the nanoparticles self-aggregate. An X-ray photoelectron spectroscopy (XPS) study confirmed the substitution of Zn²⁺ by Sn and Al ions. Optical properties of the ZnO structures were investigated by Raman spectroscopy and room-temperature photoluminescence (PL) spectroscopy. The Raman spectroscopy results demonstrated that the doped ZnO nanoparticles had a higher crystalline quality than that of pure ZnO. Room-temperature PL spectra of these structures showed a strong UV emission peak and a relative weak green emission peak, and the UV peak of the doped ZnO nanoparticles was blue-shifted with respect to that of the undoped ZnO nanoparticles.     

Wet chemistry approach to the preparation of tantalum-doped hydroxyapatite: Dopant content effects

Tantalum-doped hydroxyapatite (Ta-doped HA) nanopowders with different Ta contents were synthesized by a wet-chemical precipitation route. The structure modification and charge compensation mechanism were investigated by various characterization techniques. Due to the smaller size of tantalum ions compared to the Ca²⁺ size, it was assumed that the tantalum ions occupy either the Ca²⁺ and/or the interstitial positions in the HA lattice, where the charge imbalance from to this substitution was compensated by the Ca²⁺ vacancies. From the XRD patterns, the as-synthesized nanopowders were poorly crystalline apatite in the absence and presence of different dopant contents. The hexagonal HA and tricalcium phosphate (β-TCP) phases as biphasic calcium phosphate mixtures were formed after heating at 900 °C. In addition to the β-TCP phase, minor extra phases such as calcium oxide (CaO) and calcium pyrophosphate (Ca₂P₂O₇) were identified from the HA decomposition. The FTIR results indicated that the decrease of structural hydroxyl groups depended on both tantalum oxyanions and carbonate contents. In the XPS profile, the Ta 4 f peak of the doped sample could be decomposed into four main components, which showed different oxidation states for tantalum (TaO₂ oxide). According to the TEM observations, the doped calcined powder at 900 °C was composed of uniform nanoneedles with an average length and width of 120 ± 50 and 10 ± 5 nm, respectively.     

Enhancement of fluorescence and magnetic properties of CeF3:RE3+ (Tb,Gd) nanoparticles via multi-band UV excitation and Li doping regulation

In this study, hydrothermal synthesis of CeF₃: Tb, Gd nanoparticles doped with Li⁺ alkali metal ions were demonstrated using introduction of Li⁺ ions through LiNO₃ nitrate. These nanoparticles have dual properties of magnetic fluorescence. X-ray diffraction, Fourier transform infrared spectrometer, XPS and photoluminescence spectra, and vibrating sample magnetometry were used to characterize structural properties, surface functional groups, fluorescence, and magnetic properties of these particles. Results show that CeF₃: Tb, Gd nanoparticles exhibit bright green light emission under excitation at 258 nm and 378 nm ultraviolet band. Through the modification of Li⁺ ions, luminous intensity of green light is further improved. Energy transfer between rare earth ions was investigated via photoluminescence spectroscopy. This work demonstrates potential applications of Li doped CeF₃: Tb, Gd nanoparticles as photomagnetic dual-functional materials in fields of biological imaging, solid state lighting, and magnetic biological separation.     

Characteristics of nano-sized ZnGa2O4 phosphor prepared by solution combustion method and solid state reaction method

ZnGa₂O₄ phosphors were prepared by both SCM (solution combustion method) and SSRM (solid state reaction method). The properties of the both ZnGa₂O₄ phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5-fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn²⁺ ions. The highest PL peak was observed with Mn²⁺ ions of 0.003 mol fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels.     

Photocatalytic activities of electrospun tin oxide doped titanium dioxide nanofibers

SnO₂ doped TiO₂ electropsun nanofiber photocatalysts were successfully prepared by means of electrospinning process. The surface morphology, structure and optical properties of the resultant products were characterized by field-emission electron microscopy (FE-SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) techniques. The utilized physiochemical analyses indicated that the introduced SnO₂ doped TiO₂ nanofibers have a smooth surface and uniform diameters along their lengths. The photocatalytic performance of the composite nanofibers was tested for degradation of methylene blue (MB) and methyl orange (MO) dye solution under ultraviolet (UV) irradiation. Under the UV irradiation, the photocatalytic reaction rate in case of utilizing SnO₂-doped TiO₂ nanofibers was rapidly increased than that of the pristine TiO₂ nanofibers. Overall, this study demonstrates cheap, stable and effective material for photocatalytic degradation at room temperature.     

Preparation and characterization of TiO2 photocatalysts by Fe doping together with Au deposition for the degradation of organic pollutants

Fe³⁺ doped TiO₂ deposited with Au (Au/Fe–TiO₂) was successfully prepared with an attempt to extend light absorption of TiO₂ into the visible region and reduce the rapid recombination of electrons and holes. The samples were characterized by X-ray diffraction (XRD), N₂ physical adsorption, Raman spectroscopy, atomic absorption flame emission spectroscopy (AAS), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The photocatalytic activities of the samples were evaluated for the degradation of 2,4-chlorophenol in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. The results of XRD, XPS and high-resolution transmission electron microscopy (HRTEM) analysis indicated that Fe³⁺ substituted for Ti⁴⁺ in the lattice of TiO₂, Au existed as Au⁰ on the surface of the photocatalyst and the mean particle size of Au was 8 nm. Diffuse reflectance measurements showed an extension of light absorption into the visible region for Au/Fe–TiO₂, and PL analysis indicated that the electron–hole recombination rate has been effectively inhibited when Au deposited on the surface of Fe-doped TiO₂. Compared with Fe doped TiO₂ sample and Au deposited TiO₂ sample, the Au/Fe–TiO₂ photocatalyst exhibited excellent visible light and UV light activity and the synergistic effects of Fe³⁺ and Au was responsible for improving the photocatalytic activity.     

Structure and luminescence properties of Eu3+ doped TiO2 nanocrystals and prolate nanospheroids synthesized by the hydrothermal processing

We report on a new approach to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids. They were synthesized by shape transformation of hydrothermally treated titania nanotubes at different pH and in the presence of Eu³⁺ ions. The use of nanotubes as a precursor to the synthesis of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids opens the possibility of overcoming the problems related to molecular precursors. The shapes and sizes of the nanotubes, Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids were characterized by transmission electron microscopy (TEM) technique. Crystal structures of the resultant powders were investigated by X-ray diffraction (XRD) analysis. The percentage ratio of Eu³⁺ to Ti⁴⁺ ions in doped nanocrystals was determined using inductively coupled plasma atomic emission spectroscopy. The optical characterization was done by using fluorescence and ultraviolet-visible reflection spectroscopies. An average size of faceted Eu³⁺ doped TiO₂ nanocrystals was 13 nm. The lateral dimensions of Eu³⁺ doped TiO₂ prolate nanospheroids varied from 14 to 20 nm, while the length varied from 40 to 80 nm, depending on precursor concentrations. The XRD patterns revealed the homogeneous anatase crystal phase of Eu³⁺ doped TiO₂ nanocrystals and prolate nanospheroids independently of the amount of dopant. A postsynthetic treatment (filtration or dialysis) was applied on the dispersions of the doped nanoparticles in order to study the influence of the dopant position on photoluminescence (PL) spectra. In the red spectral region, room temperature PL signals associated with ⁵D₀ → ⁷F_J (J = 1–4) transitions of Eu³⁺ were observed in all samples. The increased contribution of dopants from the interior region of dialyzed nanocrystals to photoluminescence was confirmed by the increase of R value.     

Effect of Ni Doping on the Structural and Optical Properties of TiO<Subscript>2</Subscript> Nanoparticles at Various Concentration and Temperature

TiO₂ nanopowders doped by Ni were prepared by sol–gel method. The effects of Ni ion (transition metal ion) doping on the physical structural and optical properties of TiO₂ have been investigated by X-ray diffraction (XRD), scanning electron microscopy and UV–Vis absorption spectroscopy. XRD results suggest that adding impurities has a significant effect on anatase phase stability, crystallinity, and particle size of TiO₂. The phase transformation from anatase to rutile was inhibited by Ni ion doped TiO₂ at temperatures 675 °C. The lowest band gap value (2.83 eV) was obtained for TiO₂-4%Ni sample calcined at 675 °C.     

Enhanced visible light-induced photoelectrocatalytic degradation of phenol by carbon nanotube-doped TiO2 electrodes

We used a modified sol-gel method to prepare titanium dioxide and multi-walled carbon nanotube (CNT) composites that we subsequently deposited onto indium tin oxide (ITO) conductive glass plates. We characterized these CNT-doped TiO₂ (CNT-TiO₂) films using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance UV-vis spectroscopy. The photoelectrocatalytic (PEC) activity of the composites was evaluated through their ability to mediate the degradation of phenol. XRD measurements indicated that the TiO₂ component existed solely in the anatase phase and that the crystallinity of the CNTs was low. XPS indicated that carbon atoms could substitute for both oxygen and titanium atoms in the TiO₂ lattice to form Ti-C and Ti-O-C structures, which were responsible for the extra photoabsorption and PEC activity under illumination with visible light, in addition to those provided by the CNTs and carbonaceous and Ti³⁺ species. An interphase interaction between TiO₂ and the CNTs elevated the photoabsorbance of the composites in the visible light region. A sample of TiO₂ doped with 10% CNTs and calcined at 400 °C exhibited the highest photocurrent and PEC efficiency. We systematically investigated the effects of several parameters of the PEC process, including the applied potential and pH, on the phenol conversion.