Co-doped TiO2 Nanopowders Research Articles

Crystallization kinetics study of In-doped and (In-Cr) co-doped TiO2 nanopowders using in-situ high-temperature synchrotron radiation diffraction

The influence of TiO2 nanopowder doping with 4 wt% indium and 2 wt% each of indium and chromium on phase transformation was studied. Samples were heated from ambient temperature to 950 °C in sealed quartz capillaries, and in-situ synchrotron radiation diffraction measurements were obtained. Capillary sealing yielded an increase in capillary gas pressure to 0.42 MPa at 950 °C in proportion to absolute temperature by Gay-Lussac’s Law. The initial synthesized samples were amorphous, and crystalline anatase appeared at 200 °C. Crystalline rutile appeared at 850 °C for the nanomaterials that were doped with In and In and Cr. A change in sealed-capillary oxygen partial pressure yielded a decrease and an increase in crystallization temperature, respectively, for the amorphous-to-anatase and anatase-to-rutile transformations. Crystalline titania (anatase and rutile) formed from the amorphous titania by 800 °C and 900 °C, for materials doped with In and In-Cr, respectively. The anatase concentration that was dominant in the In-doped materials up to 950 °C and the higher rutile concentration for the In-Cr doped materials from 900 to 950 °C results from the defect structure that was induced by doping. Cr-ions in the Ti sub-lattice retarded the transformation of anatase to rutile when compared with the retarding effect of mixed In/Cr ions. The transformation results because of the relatively smaller radius of Cr-ions when compared with the In-ions. The differences in phase-transformation kinetics for In, In-Cr and for undoped nanopowders in the literature agree with the calculated transformation activation energies.

Appearance of itinerant electrons detected by IR spectroscopy and its correlation with surface magnetism in Co-doped TiO2 nanopowders

IR absorption and magnetic data for the titanium dioxide nanopowders are studied. Additional absorption in IR range is revealed in nanocrystalline TiO2 and Co-doped TiO2 after reducing annealing and explained by appearance of the oxygen vacancies and delocalised charge carriers. Increasing of the absorption in IR range after annealing of Co-doped TiO2 in vacuum (or decreasing of this contribution after annealing in air) correlates with arising (or vanishing) of ferromagnetic contribution.

Enhanced optical and photo catalytic properties of V and La co doped TiO2 nanoparticles

To enhance the visible photo-catalytic activity of TiO2, La/V co-doped TiO2 materials were synthesized through a nonaqueous method of which the purpose was to reduce the aggregation between TiO2 particles. Different samples of La and V co-doped TiO2 nanoparticles were prepared through simple sol–gel synthesis method by using Vanadium(III) chloride as V precursor, Lanthanum(III) chloride heptahydrate as La precursor, and titanium (IV) butoxide (TBT) as titanium precursor. The effects of co-doping content on the structural, optical, and photo-catalytic properties of nanoparticles have been studied by X-ray diffraction (XRD), TEM, SEM and UV–Vis absorption spectroscopy. XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO2. Titania rutile phase formation in ternary system (Ti–La–V) was inhibited by La3+ and promoted by V4+ co-doped TiO2 in high concentration of vanadium and 22.6 mol% anatase composition is retained at 15% vanadium. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methylen orange under visible radiation. The results show that the photocatalytic activity of the 10 mol% V and 5 mol% La co-doped TiO2 nanopowders has a larger degradation efficiency than pure TiO2 under visible light.

Optical and structural properties of TiO2 nanopowders with Ce/Sn doping at various calcination temperature and time

In this paper, the influence of calcination temperature and time has been investigated on the structural, morphological, optical, and photo-catalytic properties of Sn/Ce co-doped TiO2 nano-powders prepared via sol–gel process. They were calcined at the temperatures in the range of 475–975 °C for 1 and 2 h. The photocatalytic ability of TiO2 powders was evaluated by means of methylene blue degradation experiments conducted under the irradiation of simulated solar light. The X-ray diffraction results showed that the tensile strain in the host lattice was present. The comparison with undoped and Sn or Ce-doped TiO2, co-doped TiO2 shows an obviously higher catalytic activity under visible light irradiation. The absorbance spectrum of Ce and Sn co-doped TiO2 exhibited significant red-shift to visible region. The red-shift is caused by the appearance of a new electronic state in the middle of the TiO2 band-gap. FESEM images show the formation of doped TiO2 nanoparticles with small size in structure and spherical in shape. The FTIR spectra exhibited peaks corresponding to the anatase and rutile structure phases of TiO2.

Efficient green and red up-conversion emissions in Er/Yb co-doped TiO2 nanopowders prepared by hydrothermal-assisted sol–gel process

In this work, erbium and ytterbium co-doped titanium dioxide (Er–Yb:TiO2) nanopowders have been successfully prepared by hydrothermal-assisted sol–gel method using supercritical drying of ethyl alcohol and annealing at 500°C for 1h. Nanopowders were prepared with fixed 5mol% Erbium concentration and various Ytterbium concentrations of 5 and 10mol%. The powders were characterized by studying their structural, morphology and photo-luminescent properties. The annealing treatment at 500°C was found to enhance the crystallinity of the TiO2 anatase structure and the upconversion (UC) emission of the nanopowders. UC emissions were investigated under 980nm excitation, and the Er–Yb:TiO2 nanopowders exhibited the intense green (520–570nm) and red (640–690nm) upconverted emissions of Er ions originating from an efficient Yb–Er energy transfer process. The absolute upconversion quantum yield (UC-QY) of each nanopowders was measured for the UC emissions centered at 525, 550 and 655nm at varying excitation power densities. UC-QY analysis has revealed that 5mol% Er–5mol% Yb:TiO2 nanopowders possess the highest total quantum yield of 2.8±0.1% with a power density of 16.7W/cm2. These results make these nanopowders promising materials for efficient upconversion in photonic applications.

Effect of Cobalt Dopant on Structural and Optical Properties of Co-Precipitated TiO<sub>2</sub> Nanopowders

The effects of cobalt (Co) addition on structural and optical properties of TiO2 nanopowders have been investigated. A co-precipitation method was employed to synthesize TiO2 nanoparticles with various Co additives from 0-10 mol% using tetrabutyl titanate and Cobalt (II) nitrate hexahydrate as starting precursors for Ti and Co source, respectively. The crystallinity of Co-doped TiO2 nanopowders is heightened by calcination process. The crystal structure, phase formation and the corresponding functional groups of Co-doped TiO2 were analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The scanning electron microscope (SEM) was taken to observe their morphologies. The chemical compositions of Co additive into TiO2 matrix are confirmed by EDAX. Their optical properties were investigated by diffuse reflectance spectroscopy. Diffuse reflectance spectra of samples exhibit the increasing absorption in visible region with an increasing Co content. The overall characterization results indicated that the crystallinity and optical properties of TiO2 nanoparticles are significantly affected by Co dopant.

Comparison of optical and structural properties of Cu doped and Cu/Zr co-doped TiO2 nanopowders calcined at various temperatures

TiO2 nanopowders doped with Cu and Zr were prepared via process-controlled sol–gel method. The effects of Zr and Cu doping on the structural and photocatalytic properties of synthesized nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope, FTIR, and UV–Vis absorption spectroscopy. XRD results suggested that adding dopants has a great effect on crystallinity and particle size of TiO2. Titania rutile phase formation was inhibited by Zr4+ and promoted by Cu2+ doping. The photocatalytic activity was evaluated by degradation kinetics of aqueous methyl orange under visible spectra radiation. The results showed that the photocatalytic activity of the 15 % Zr-doped TiO2 nanopowder has a larger degradation efficiency than 5 % Cu-doped and pure TiO2 under visible light.

Photocatalytic activities of europium (III) and niobium (V) co-doped TiO2 nanopowders synthesized in Ar/O2 radio-frequency thermal plasmas

Europium (III) and niobium (V) co-doped TiO2 nanopowders were synthesized in Ar/O2 radio-frequency thermal plasmas by pyrolyzing aqueous precursors that contained various concentrations of Eu3+/(Eu3++Nb5++Ti4+)=0–0.5at.% and Nb5+/(Eu3++Nb5++Ti4+)=0–1.0at.%. Phase identification was performed by X-ray diffraction (XRD), particle morphology was observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and UV–vis absorption spectra were determined by UV–vis spectroscopy. The photocatalytic activities under UV and visible light irradiations were both evaluated by bleaching 20μM of a methyl orange aqueous solution. All the resulting powders had a phase composition of anatase (30–66nm crystalline size) (major phase: ∼80% mass proportion) and rutile (56–94nm crystalline size) polymorphs, with a relatively wide particle size distribution from several nanometers (faceted crystallites) to ∼100nm (spherical particles). The photocatalytic activities dominated by oxygen defects in the TiO2 host lattice for the powders prepared with identical doping concentrations of Eu3+ and Nb5+ were both superior under UV and visible light irradiations over those obtained with different doping amounts. More interestingly, the co-doped powder exhibited an improved photocatalytic performance under 600–700nm visible light illumination than the Eu3+-doped TiO2 and P25 commercial powders.

High temperature stability and photocatalytic activity of nanocrystalline anatase powders with Zr and Si co-dopants

TiO2 nanopowders doped by Si and Zr were prepared by sol–gel method. The effects of Si and Zr doping on the structural, optical, and photo-catalytic properties of titania nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy, transmission 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. Titania rutile phase formation in ternary system (Ti–Si–Zr) was inhibited by Zr4+ and Si4+ co-doped TiO2 in high temperatures (500–900 °C) and 36 mol% anatase composition is retained even after calcination at 1,000 °C. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methylen orange under visible radiation. The results show that the photocatalytic activity of the 20 %Si and 15 %Zr co-doped TiO2 nanopowders have a larger degradation efficiency than pure TiO2 under visible light.

Sol–gel synthesis, characterisation and photocatalytic activity of pure, W-, Ag- and W/Ag co-doped TiO2 nanopowders

Tungsten, silver and tungsten/silver co-doped titania nanopowders were synthesised via an aqueous sol–gel method. The size distribution and zeta potential of the starting sols were determined via photon correlation spectroscopy (PCS). The dried gels were thermally treated at two different temperatures, and the occurrence of amorphous phase was assessed using the combined Rietveld–RIR X-ray powder diffraction method. A systematic study of the optical properties of the powders was made with diffuse reflectance spectroscopy (DRS), and the energy band gaps were calculated using the differential reflectance method; while their morphology was investigated using electron microscopy analysis (TEM). The photocatalytic activity of the samples was assessed in liquid–solid phase, under UVA-light and visible-light irradiation, monitoring the degradation of an organic dye. The influence of the phase composition, optical properties, dimensions, and specific surface area of the powders on the photocatalytic activity was thoroughly discussed.

Tungsten and nitrogen co-doped TiO2 nano-powders with strong visible light response

A two-step method, combining with sol–gel and mechanical alloying (MA) method, was used to fabricate the tungsten and nitrogen co-doped TiO2 nano-powders ((W, N) co-doped TiO2 NPs). The (W, N) co-doped TiO2 NPs showed strong absorbance in visible range, as long as 650nm. Enhanced photocatalytic activities under visible light irradiation were also observed from the results of photodegradation experiments and chemical oxygen demand (COD) analysis. Physical, chemical, and optical properties of the samples were investigated. Possible reasons for the enhanced photocatalytic activities were analyzed based on the experimental results. Oxygen vacancies detected by electron spin response (ESR) spectra, acting as trapping agencies for electrons (e−) to produce active oxygen species (O2−), were proved to be the main cause for the improved photocatalytic performances.

Preparation, characterization and photocatalytic performance of Co/Ni Co-doped TiO2 nanopowders

Co/Ni co-doped TiO2 nanopowders (dopant amount varying from 0 to 0.75 mol.% Co/0.75 mol.% Ni) were prepared by sol-gel method. The nanopowders were characterized by means of X-ray diffraction and transmission electron microscopy, respectively. The results showed that the structure of all the powders was anatase and that the particle size of the powders was in the range of 40–50 nm. The photocatalytic performances of the nanopowders were studied by examining the degradation of methyl orange. The results showed that the dopant amount was a key factor affecting photocatalytic performance. 0.05 mol.% Co/0.05 mol.% Ni co-doped TiO2 nanopowders had the best photocatalytic performance, and the photocatalytic performance of which was also better than that of 0.1 mol.% Co- or 0.1 mol.% Ni-doped TiO2 nanopowders.