Dynamic diffraction studies on the crystallization, phase transformation, and activation energies in anodized titania nanotubes

The influence of calcination time on the phase transformation and crystallization kinetics of anodized titania nanotube arrays was studied using in-situ isothermal and non-isothermal synchrotron radiation diffraction from room temperature to 900 â—¦ C. Anatase first crystallized at 400 â—¦ C, while rutile crystallized at 550 â—¦ C. Isothermal heating of the anodized titania nanotubes by an increase in the calcination time at 400, 450, 500, 550, 600, and 650 â—¦ C resulted in a slight reduction in anatase abundance, but an increase in the abundance of rutile because of an anatase-to-rutile transformation. The Avrami equation was used to model the titania crystallization mechanism and the Arrhenius equation was used to estimate the activation energies of the titania phase transformation. Activation energies of 22 (10) kJ/mol for the titanium-to-anatase transformation, and 207 (17) kJ/mol for the anatase-to-rutile transformation were estimated

Effect of pressure on TiO2 crystallization kinetics using in-situ high-temperature synchrotron radiation diffraction

The phase transformation behavior of TiO 2 sol-gel synthesized nanopowder heated in a sealed quartz capillary from room temperature to 800°C was studied using in-situ synchrotron radiation diffraction (SRD). Sealing of the capillary resulted in an increase in capillary gas pressure with temperature. The pressures inside the sealed capillary were calculated using Gay-Lussac's Law, and they reached 0.36 MPa at 800°C. The as-synthesized material was entirely amorphous at room temperature, with crystalline anatase first appearing by 200°C (24 wt% absolute), then increasing rapidly in concentration to 89 wt% by 300°C and then increasing more slowly to 97 wt% by 800°C, with there being no indication of the anatase-to-rutile transformation up to 800°C. The best estimate of activation energy for the amorphous-to-anatase transformation from the SRD data was 10(2) kJ/mol, which is much lower than that observed when heating the material under atmospheric pressure in a laboratory XRD experiment, 38(5) kJ/mol. For the experiment under atmospheric pressure, the anatase crystallization temperature was delayed by ~200°C, first appearing after heating the sample to 400°C, after which crystalline rutile was first observed after heating to 600°C. The estimated activation energy for the anatase-to-rutile transformation was 120(18) kJ/mol, which agrees with estimates for titania nanofibers heated under atmospheric pressure. Thus, heating the nanopowders material under pressure promoted the amorphous-to-anatase transformation, but retarded the anatase-to-rutile transformation. This behavior is believed to occur in an oxygen-rich environment and interstitial titanium is also expected to form when the material is heated under high gas pressure. This suggests that atmospheric oxygen appears to accelerate the amorphous-to-anatase transformation, whereas interstitial titanium inhibits TiO 2 structure relaxation, which is required for the anatase-to-rutile transformation

Activation energies for phase transformations in electrospun titania nanofibers: comparing the influence of argon and air atmospheres

This paper reports on titania absolute phase level (amorphous, anatase, and rutile forms) changes in electrospun amorphous titania nanofibers from 25 to 900 °C in air and argon atmospheres. A novel method was developed to extract absolute levels of amorphous titania and crystalline anatase and rutile from the synchrotron radiation diffraction (SRD) data. This is a sequel to a relative phase concentrations study that has been reported previously by Albetran et al. (Appl Phys A 116:161 [2014]). Determination of absolute phase levels facilitated estimation of the activation energies for the amorphous-to-anatase transformation of 45(9) kJ/mol in argon and 69(17) in air, and for the anatase-to-rutile transformation energies of 97(7) kJ/mol for argon and 129(5) for air. An activation energy estimate for amorphous-to-crystalline titania in argon of 142(21) kJ/mol, achieved using differential scanning calorimetry (DSC), is consistent with the SRD results. The differences in phase transition and activation energies when the titania nanofibers are heated in argon is attributed to the presence of substantial oxygen vacancies in anatase. Estimates of anatase and rutile oxygen site occupancies from the SRD data show that anatase has discernible oxygen vacancies in argon, which correspond to stoichiometric TiO2−x with x < 0.4 that the anatase stoichiometry in air is TiO2. Rutile does not have significant oxygen vacancies in either argon or air

Crystallization kinetics and phase transformations in aluminium ion-implanted electrospun TiO2 nanofibers

Electrospun TiO2 nanofibers were implanted with aluminum ions, and their crystallization kinetics, phase transformations, and activation energies were investigated from 25 to 900 °C by in situ high-temperature synchrotron radiation diffraction. The amorphous non-implanted and Al ion-implanted TiO2 nanofibers transformed to crystalline anatase at 600 °C and to rutile at 700 °C. The TiO2 phase transformation of the Al ion-implanted material was accelerated relative to non-implanted sample. Compared with non-implanted nanofibers, the Al-implanted materials yielded a decreased activation energies from 69(17) to 29(2) kJ/mol for amorphous-to-anatase transformation and from 112(15) to 129(5) kJ/mol for anatase-to-rutile transformation. A substitution of smaller Al ions for Ti in the TiO2 crystal structure results in accelerated titania phase transformation and a concomitant reduction in the activation energies

Effect of vanadium ion implantation on the crystallization kinetics and phase transformation of electrospun TiO2 nanofibers

The influence of V ion implantation on the thermal response of electrospun amorphous TiO2 nanofibers was studied with reference to structural phase transformation behavior, using in situ synchrotron radiation diffraction (SRD) measurements from room temperature to 1000 °C. Analysis of the SRD data provided activation energies for amorphous-to-crystalline TiO2 (anatase and rutile) and anatase-to-rutile transformations, and also assessments of the influence of V ion implantation on microstructure development during calcination using estimates of crystallite size and microstrain. Non-implanted nanofibers were initially amorphous, with crystalline anatase first appearing at 600 °C, followed by rutile at 700 °C. The corresponding activation energies were 69(17) kJ/mol for the amorphous-to-crystalline TiO2 transformation and 129(5) kJ/mol for the anatase-to-rutile transformation. V ion implantation resulted in a lowering of the temperature at which each crystalline phase first appeared, with both phases being initially observed at 500 °C and with the anatase-to-rutile transformation being accelerated relative to the non-implanted sample. The effect of V ion implantation is seen through the substantial reduction in activation energies, which are 25(3) kJ/mol for amorphous-to-crystalline TiO2 and 16(3) kJ/mol for anatase-to-rutile transformations

Effect of chromium-doping on the crystallization and phase stability in anodized TiO2 nanotubes

Production of limitless hydrogen fuel by visible light splitting of water using the photoelectrochemical technology is cost-effective and sustainable. To make this an attractive viable technology will require the design of TiO 2 photocatalyst capable of harnessing the energy of visible light. One possible solution is the doping of TiO2 to reduce its band gap. In this paper, the effect of Cr-doping by ion-implantation on the crystallisation and phase stability of TiO2 nanotubes at elevated temperature is described. The effect of Cr-doping on the resultant microstructures, phase changes and composition depth profiles are discussed in terms of synchrotron radiation diffraction, scanning electron microscopy, and ion-beam analysis by Rutherford backscattering spectrometry

Wettability of Nanostructured Transition-Metal Oxide (Al2O3, CeO2, and AlCeO3) Powder Surfaces

Wettability has been the focal point of many studies in metal oxide materials due to their applications in water&ndash;gas shift reactions, organic reactions, thermochemical water splitting, and photocatalysis. This paper presents the results of systematic experimental studies on the wettability of surfaces of nanostructured transition-metal oxides (TMOs) (Al2O3, CeO2, and AlCeO3). The wettability of nanoparticles was investigated by measuring contact angles of different concentrations of water-based nanofluids (0.05&ndash;0.1 wt%) on the glass slide. The morphology, the heterostructure, and the nature of incorporated nanoparticles were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Characteristic diffraction patterns of the nanomaterials were evaluated using energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The contact angles of water&ndash;Al2O3, water&ndash;CeO2, and water&ndash;AlCeO3 were measured as 77.5 &plusmn; 5&deg;, 89.8 &plusmn; 4&deg;, and 69.2 &plusmn; 1&deg;, respectively. This study suggests that AlCeO3 is strongly water-wet (hydrophilic), while CeO2 is weakly water-wet (hydrophobic). It further demonstrated that the sizes and compositions of the nanoparticles are key parameters that influence their wetting behaviors

Structural, optical and magnetic properties of Tb3+ substituted Co nanoferrites prepared via sonochemical approach

This paper emphasizes the structure, morphology, optical, and magnetic properties of sonochemically prepared terbium-substituted cobalt ferrite nanoparticles, CoTbxFe2-xO4 (0.00 ? x ? 0.10). The formation of cubic spinel nanosized ferrite structure was confirmed by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared (FT-IR) spectroscopy. The crystallites sizes were found in the range of 11–14 nm. Ultraviolet–visible percentage diffuse reflectance investigations were performed on pristine and Tb3+-doped cobalt spinel ferrite CoFe2O4 nanoparticles. The direct energy band gap (Eg) values were determined by applying the Kubelka–Munk theory and Tauc plots were found to be in a narrow band range of 1.37–1.44 eV. Analyses of magnetization versus the magnetic field (M(H)) were performed. The magnetic parameters, including the saturation magnetization (Ms), squareness ratio (SQR = Mr/Ms), magnetic moment (nB), remanence (Mr), and coercivity (Hc) were evaluated. The M(H) curves exhibited a soft ferrimagnetic nature. It was demonstrated that the Tb3+ substitutions strongly influenced the magnetization data. Indeed, the Ms, Mr, Hc, and nB values decreased with increasing Tb3+ substitution. © 2019 Elsevier Ltd and Techna Group S.r.l.Deanship of Scientific Research, King Saud University: 2018-209-IRMC, 2017-576-IRMCThis study was supported by the Deanship of Scientific Research (project applications 2017-576-IRMC and 2018-209-IRMC ) of Imam Abdulrahman Bin Faisal University (Saudi Arabia)

Characterization and optimization of electrospun TiO2/PVP nanofibers using Taguchi design of experiment method

TiO2 nanofibers were prepared within polyvinylpyrrolidone (PVP) polymer using a combination of sol–gel and electrospinning techniques. Based on a Taguchi design of experiment (DoE) method, the effects of sol–gel and electrospinning on the TiO2/PVP nanofibers’ diameter, including titanium isopropoxide (TiP) concentration, flow rate, needle tip-to-collector distance, and applied voltage were evaluated. The analysis of DoE experiments for nanofiber diameters demonstrated that TiP concentration was the most significant factor. An optimum combination to obtain smallest diameters was also determined with a minimum variation for electrospun TiO2/PVP nanofibers. The optimum combination was determined to be a 60% TiP concentration, at a flow rate of 1 ml/h, with the needle tip-to-collector distance at 11 cm (position a), and the applied voltage of 18 kV. This combination was further validated by conducting a confirmation experiment that used two different needles to study the effect of needle size. The average nanofiber diameter was approximately the same for both needle sizes in good accordance with the optimum condition estimated by the Taguchi DoE method