Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol–gel derived titania powders
TL;DR: In this article, the role of any magnetic impurity or any Ni metal in the origin of the RTFM has been ruled out by energy dispersive X-ray spectroscopy (EDS), XPS, transmission electron microscopy (TEM) and high resolution TEM (HRTEM) analysis.
About: This article is published in Materials Chemistry and Physics.The article was published on 2012-03-15. It has received 42 citations till now. The article focuses on the topics: Magnetic semiconductor & Curie temperature.
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TL;DR: In this paper, the authors present the latest developments in the fabrication of different higher dimensional TiO2 nanostructured materials that aim to address these inherent limitations to an otherwise very promising material.
305 citations
TL;DR: In this article, structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling were investigated.
Abstract: We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μB/f.u. at 12 kOe applied field and coe...
80 citations
TL;DR: In this paper, the photodegradation of Rhodamine B dye in aqueous medium has been investigated under UV-vis light irradiation and the Ni-doped TiO 2 showed ferromagnetic behavior at room temperature, which makes its recovery and subsequent fast reutilization possible.
Abstract: Ni (1 wt%)-, Pt (1 wt%)- and [Ni (0.5 wt%)/Pt (0.5 wt%)]-doped TiO 2 nanoporous catalysts have been successfully obtained through a facile two-step hydrothermal route. TiO 2 crystallizes mostly in the anatase phase and acts as a mesoporous matrix. Meanwhile, Ni, Pt and Ni/Pt dopants form small nanoparticles (NPs) (3–95 nm in diameter) which are hosted by the TiO 2 framework. The resulting composites exhibit a rather large surface area, in the range of 186–200 m 2 /g. The band gap energy reduces from 3.03 eV for the undoped TiO 2 to 2.15 eV for the Pt-loaded TiO 2 . As a consequence, absorption expands toward the visible light range. The photodegradation of Rhodamine B dye in aqueous medium has been investigated under UV–vis light irradiation. The presence of Ni, Pt and Ni/Pt NPs significantly enhances the photocatalytic activity of the material. Furthermore, the Ni-doped TiO 2 shows ferromagnetic behavior at room temperature, which makes its recovery and subsequent fast reutilization possible. Interestingly, this sample also exhibits the best stability upon recycling. Considering all the current challenges in sustainable water remediation, these new photocatalysts could find applications in real environmental contexts in the near future.
80 citations
TL;DR: In this article, the effects of transition metal doping to metal-oxide nanoparticles (TiO2) were studied using a variety of characterization techniques, including X-ray diffraction, Fourier transform-infrared (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, field-emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM).
Abstract: In this research, the effects of transition metal (Ni) doping to metal-oxide nanoparticles (TiO2) were studied. Various weight ratios (5, 10, 15, and 20%) of Ni-to-TiO2 nanoparticles were synthesized using the sol–gel technique. These doped nanoparticles were prepared using titanium butoxide and nickel nitrate as precursors and methanol as a solvent. The effects of Ni doping to TiO2 were examined using a variety of characterization techniques, X-ray diffraction (XRD), Fourier-transform-infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, field-emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM). The XRD reveals that the Ni-doped TiO2 crystallizes in a tetragonal structure with anatase phase. The particle size and lattice strain were calculated by Williamson–Hall equation. The presence of strong chemical bonding and functional groups at the interface of TiO2 nanoparticles was confirmed by FTIR. The optical properties of undoped and doped samples were recorded by UV–Vis spectroscopy. The saturation magnetization (Ms) was found higher for undoped as compared to doped samples. The surface morphology and the element structure of the Ni-doped TiO2 nanoparticles were examined by FESEM.
70 citations
TL;DR: In this paper, undoped and Ni-doped TiO 2 ( x Ni ǫ = 0.00, 0.50, 1.00 and 2.50 ) thin films fabricated on glass substrates by using a combination of solid-state reaction and dip coating techniques.
67 citations
Cites background or result from "Effect of Ni doping on the microstr..."
...reported that the magnetic moment of TiNiO2 rises at lower Ni concentrations but with increasing Ni concentration it decreases (Bahadur et al., 2012)....
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...…as illustrated by VSM results in Table 2, which is in agreement with the earlier reports that content of added magnetic ions, substituting the host lattice cations, may induce proportional ferromagnetic behavior, in the host lattice (Bahadur et al., 2012; Sabry, Al-Haidarie, & Kudhier, 2016)....
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...Recently, Bahadur et al. reported that the magnetic moment of TiNiO2 rises at lower Ni concentrations but with increasing Ni concentration it decreases (Bahadur et al., 2012)....
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...In RKKY interactions, Ni ions are ferromagnetically coupled through the free carriers (Bahadur et al., 2012)....
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...In RKKY interactions, Ni+2 ions are ferromagnetically coupled through the free carriers (Bahadur et al., 2012)....
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TL;DR: It is shown that the underlying mechanism that controls doping is the initial adsorption of impurities on the nanocrystal surface during growth, and that a variety of doped nanocrystals—for applications from solar cells to spintronics—can be anticipated.
Abstract: Doping--the intentional introduction of impurities into a material--is fundamental to controlling the properties of bulk semiconductors. This has stimulated similar efforts to dope semiconductor nanocrystals. Despite some successes, many of these efforts have failed, for reasons that remain unclear. For example, Mn can be incorporated into nanocrystals of CdS and ZnSe (refs 7-9), but not into CdSe (ref. 12)--despite comparable bulk solubilities of near 50 per cent. These difficulties, which have hindered development of new nanocrystalline materials, are often attributed to 'self-purification', an allegedly intrinsic mechanism whereby impurities are expelled. Here we show instead that the underlying mechanism that controls doping is the initial adsorption of impurities on the nanocrystal surface during growth. We find that adsorption--and therefore doping efficiency--is determined by three main factors: surface morphology, nanocrystal shape, and surfactants in the growth solution. Calculated Mn adsorption energies and equilibrium shapes for several nanocrystals lead to specific doping predictions. These are confirmed by measuring how the Mn concentration in ZnSe varies with nanocrystal size and shape. Finally, we use our predictions to incorporate Mn into previously undopable CdSe nanocrystals. This success establishes that earlier difficulties with doping are not intrinsic, and suggests that a variety of doped nanocrystals--for applications from solar cells to spintronics--can be anticipated.
1,449 citations
TL;DR: In this article, the phase stability of anatase and rutile was analyzed thermodynamically, and it was shown that anatase becomes more stable than rutsile when the particle size decreases below 14 nm.
Abstract: The phase stability of nanocrystalline anatase and rutile was analyzed thermodynamically. According to the present analysis, anatase becomes more stable than rutile when the particle size decreases belowca. 14 nm. The calculated phase boundary between nanocrystalline anatase and rutile coincides with the experimental data for appearance of rutile during coarsening of nanocrystalline anatase. Both surface free energy and surface stress play important roles in the thermodynamic phase stability, which is a function of particle size.
1,212 citations
TL;DR: In this article, it was shown that the surface energy of rutile is significantly larger than that of anatase, and the reversal of stabilities of anatases and rutiles at small crystallite sizes.
Abstract: Kinetic studies conducted primarily between 465 and 525 degrees C demonstrate that the rate of the polymorphic anatase to rutile transformation increases dramatically when the reacting anatase is very finely crystalline. Coarsening of the reactant anatase and product rutile crystallites occurs simultaneously with the transformation. Kinetic behavior and quantification of transformation rate as a function of average crystallite size indicate that the increase in favorable nucleation sites is a likely cause of increase in transformation rate at small crystallite sizes. Additionally, experimental evidence supports the reversal of stabilities of anatase and rutile at small crystallite sizes. It is proposed that the reversal of stabilities is the result of rutile having a higher surface energy than the anatase phase. Data for coarsening kinetics of anatase and rutile supports the prediction that the surface energy of rutile is significantly larger than that of anatase. Thermodynamic data and theoretical estimates are used to show that a 15% greater surface energy for rutile causes the total free energy of rutile to be greater (less negative) than anatase at crystallite diameters in the few nanometer range. Given the fact that anatase and rutile structures have no polymerized octahedral fragments in common, this may be significant in determining the nature of the nucleated phase.
691 citations
TL;DR: In this article, the electronic structures of titanium dioxide (TiO 2 ) doped with 3d transition metals (V, Cr, Mn, Fe, Co and Ni) have been analyzed by ab initio band calculations based on the density functional theory with the full-potential linearized-augmented-plane-wave method.
638 citations
TL;DR: It could be found that the impurity bands and abundant surface states were introduced into the interfacial layer of TiO2 because of Ag simultaneously doping and depositing, which could improve the absorption capability for visible light of the photocatalysts.
Abstract: Ag−TiO2 catalysts with different Ag contents were prepared via a sol−gel method in the absence of light. Based on the characterizations of XRD, photoluminescence (PL), surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and XPS as well as the evaluation of the photocatalytic activity for degrading rhodamine B(RhB) solutions, it was found that the Ag dopant promoted the phase transformation as well as had an inhibition effect on the growth of anatase crystallite. The PL and SPS intensities were decreased with increasing Ag content, indicating that the Ag dopant could effectively inhibit the recombination of the photoinduced electrons and holes. However, the active sites capturing the photoinduced electrons reduced, while the Ag content exceeded 5 mol %. At rather low Ag dopant concentrations, the migration and diffusion of Ag+ ions were predominant, while at rather high Ag dopant concentrations, the migration, diffusion, and reduction of Ag ions simultaneously ...
540 citations