Defect-mediated optical properties of Fe-substituted TiO2 nanoparticles

Here, sol–gel derived Fe–TiO₂ anatase nanoparticles with varying concentrations of Ti_(1–x)Fe_xO₂ (x = 0%, 1%, 5%, 10%) were prepared. The structural, morphological, and optical properties of prepared samples were studied. X-ray diffraction (XRD) patterns show the formation of pure anatase phase. The mean crystallite size of Fe–TiO₂ decreases with increase in the concentration of Fe. Fourier transform infrared spectroscopy (FTIR) spectra confirmed the presence of Ti–O vibrational band for all the samples. In Raman spectrum, peak broadening and red shifting linked with Eg ∼144 cm^–1 divulge the Fe substitution at Ti sites into host lattice structure. Photoluminescence (PL) spectra verified nine peaks related to near band-edge emission and various defect states. The UV–vis diffuse reflectance spectra represent redshift and reduction in the bandgap energy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations show that the size of the grains decreases with increase in Fe doping concentration. The study shows that Fe-doped TiO₂ anatase phase nanoparticles are suitable for photocatalytic activity and solar cell applications.     

Effect of heat treatment on crystal phase and photocatalytic activity of Tm doped TiO2 nanoparticles

Abstract

Abstract

Tm doped TiO₂ nanoparticles have been synthesised by hydrolysis-precipitation method. The effect of heat treatment on the crystal phase and photocatalytic activity of Tm doped TiO₂ nanoparticles has been studied. The prepared samples were characterised by transmission electron microscopy, X-ray diffraction, Fourier transformed infrared and diffuse reflection spectrum analysis. The results show that Tm³⁺ doping can effectively inhibit the phase transformation from antase to rutile and decrease the crystallite size of nano-TiO₂ particles. There is an optimal Tm doping (1·4?mol.-%) after calcination at 550°C for the photocatalytic activity of methylene blue degradation.     

Fabrication of TiO2‒Ag nanocomposite thin films via one-step gas-phase deposition

In this work, TiO₂‒Ag nanocomposite thin films were fabricated for the first time via simultaneous plasma-enhanced chemical vapor deposition and physical vapor deposition of TiO₂ and Ag nanoparticles in the gas-phase, respectively. The presence of Ag nanoparticles in the prepared nanocomposites has been confirmed using transmission electron microscopy and energy dispersive X-ray spectrometry techniques. The obtained electron microscopy images showed that the average size of TiO₂‒Ag nanoparticles was larger than that of pristine TiO₂. Moreover, the temperature of the anatase transformation into the rutile phase was decreased due to the presence of Ag nanoparticles in the TiO₂ matrix, while the photocatalytic activity of the produced nanocomposite (estimated by studying the degradation of methylene blue aqueous solution under UV irradiation) was 35% greater than that of pristine TiO₂. Therefore, the addition of Ag nanoparticles into the TiO₂ matrix significantly affected the morphology, phase transformation temperature, and photocatalytic performance of the fabricated material.     

Doping concentration dependence of microstructure and magnetic behaviours in Co-doped TiO2 nanorods

Co-doped titanium dioxide (TiO₂) nanorods with different doping concentrations were fabricated by a molten salt method. It is found that the morphology of TiO₂ changes from nanorods to nanoparticles with increasing doping concentration. The mechanism for the structure and phase evolution is investigated in detail. Undoped TiO₂ nanorods show strong ferromagnetism at room temperature, whereas incorporating of Co deteriorates the ferromagnetic ordering. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) results demonstrate that the ferromagnetism is associated with Ti vacancy.     

Aluminium-doped TiO2 nanotubes with enhanced light-harvesting properties

Titanium dioxide (TiO₂) application in light-harvesting processes is hindered by its wide band gap. Strategies such as morphology shifts from nanoparticles to nanotubes and doping of fabricated nanostructures are widely used to address this issue. Combining both approaches, this work successfully synthesizes, for the first time, aluminium-doped TiO₂ nanotubes via a single-step anodization method at three distinct potentials (20, 40 and 60 V). SEM images revealed the successful formation of remarkably thin layers of TiO₂ nanotubes produced at 40 and 60 V. X-ray diffractograms and Raman spectra suggest the successful insertion of aluminium into the anatase lattice. Diffuse reflectance confirmed the doping process through a marked effect on the absorbance of visible light for the higher voltages, as well as through a reduction in the optical band gap. For utilization purposes, the photoelectrochemical performance of 40 V Al–TiO₂ was able to deliver a comparable response to that of a compact TiO₂ layer of the same thickness. The current density developed by the 60 V sample was increased by 120% in comparison to the undoped material, despite having an absorbance much lower than that of the latter. Overall, synthesizing an Al-doped TiO₂ nanotubular structure has proven to be a great strategy in the development of materials for application in advanced light-harvesting electrodes.     

Preparation of Ag nanoparticles loaded TiO2 nanoplate arrays on activated carbon fibers with enhanced photocatalytic activity

Ag loaded TiO₂ nanoplate array which grew on activated carbon fiber (ACF) was prepared in the present work. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue (MB) was used to investigate the activity of the synthesized samples. Under both UV and visible light irradiation, the Ag loaded samples showed enhanced photocatalytic activity. Besides, the effect of the deposition dosage of Ag nanoparticles on the photocatalytic activity was also investigated. Under UV light irradiation, the Ag nanoparticles acted as electron traps, which enhanced electron–hole separation efficiency of TiO₂. Under visible light irradiation, the Ag nanoparticles showed surface plasmon resonance, which induced the visible light responsive photocatalytic activity for the obtained samples.     

Effect of concentration of Fe-dopant on the photoelectrochemical properties of Titania nanotube arrays

TiO₂ nanotubes have attracted great attention because of their photoelectrochemical activity. Metallic doping using a simple and rapid synthesizing approach can be a way to enhance this application. This paper describes a novel one-step anodization synthesis of Fe-doped TiO₂ nanotubes with various concentrations of iron doping. FESEM, XRD, and EDX were used to analyze the effect of doping concentration on the morphology, structure, and composition of the prepared samples respectively, and the results showed the formation of the anatase phase of TiO₂ nanotube arrays with Fe incorporation in the TiO₂ lattice. Although the Fe insertion in the TiO₂ lattice leads to better crystallinity, the non-uniformity in the morphology of doped samples suggests that adequate doping is required to maintain uniformity in the morphology. The absorption spectra of all the Fe-doped TiO₂ samples showed a red shift in their absorption edges compared to pristine TiO₂. This shift was observed more in the samples with higher doping concentrations. The photocurrent density of Fe-doped samples was observed to be significantly higher than that of the pristine TiO2 sample. This improvement was found to be concentration-dependent, with the best results being obtained from a sample doped at a level of 0.5%. The samples also showed high photostability, which, together with the increased photocurrent density, points to Fe-doped TiO₂ as a promising photoanode material.     

An Amalgam of Mg-Doped TiO2 Nanoparticles Prepared by Sol–Gel Method for Effective Antimicrobial and Photocatalytic Activity

In this study, undoped and Magnesium doped TiO₂ nanoparticles (Mg-TiO₂ NPs) are successfully synthesized via a simple sol–gel method cost-effectively. The prepared Mg- TiO₂ NPs is characterized by UV–Vis, FTIR, PL, XRD, FESEM, TEM, and EDAX. UV–Visible Spectroscopy showed that an increase in the optical bandgap concerning the concentration of dopant Mg increases. The bandgap values were found to be 3.57–3.54 eV. FTIR spectra shows that the presence of the characteristic stretching and bending vibrational band of Ti–O bonding at 468 cm^?1 and shifts in vibrational bands were observed for Mg-TiO₂ NPs. PL spectra of Mg- TiO₂ NPs at different concentrations exhibit a strong UV emission band. X-ray diffraction confirmed the formation of the tetragonal anatase phase. The average crystallite size of synthesized samples was found to be 22–19 nm. The average crystallite size of Mg- TiO₂ NPs decreases with increasing the concentration of dopant Mg. The FESEM and TEM analysis confirmed that the spherical morphology for both TiO₂ and Mg-TiO₂ NPs. SAED pattern confirms the crystalline nature of prepared samples. EDAX spectra confirm the presence of Ti, O, and Mg and confirm that Mg²⁺ ions are present in the TiO₂ lattices. The prepared samples were investigated against gram-positive and gram-negative bacteria. The prepared samples exhibit potent antibacterial activity against gram-negative bacteria than the gram-positive bacteria. The prepared samples exhibit significant photocatalytic degradation for Methylene blue (MB).

     

Photocatalytic performance of Al and Nb-doped TiO2 nanoparticles prepared by microwave-assisted hydrothermal method

Microwave-assisted hydrothermal synthesis of aluminum (Al)-doped TiO₂ (ALT) and niobium (Nb)-doped TiO₂ (NBT) nanoparticles were carried out. Investigations were performed to examine the crystallinity, vibrational modes, surface morphology, and composition using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS), respectively. The XRD study indicated the higher crystallinity of the ALT particles compared to the Al and Nb-doped TiO₂ (ALNBT) particles, and only the presence of the anatase phase was observed in all samples. As a result of doping, the Raman mode at ∼147 cm⁻¹ is found to be shifted toward a higher wavenumber for both samples. SEM analysis showed the spherical morphology of ALT and NBT nanoparticles. The elemental composition peaks of Al, titanium, Nb, and oxygen were noticed by EDS measurements. Furthermore, both prepared nanoparticles were used as photocatalytic materials. The Nb and Al-doped samples showed an improvement in the photocatalysis response in relation to the pure TiO₂ sample, in which Al-doped sample was able to decolorize 100% of rhodamine B in 75 min of analysis.     

Morphological,spectroscopic and photocatalytic properties of Eu3+:TiO2 synthesized by solid-state and hydrothermal-assisted sol-gel processes

Eu³⁺ doped TiO₂ powders were synthesized by solid-state reaction and hydrothermal-assisted sol-gel process. They were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence techniques. Both synthetic procedures yield the pure anatase phase of titania. The excitation and emission spectra and the decay profiles were measured for different thermal treatments of the samples, in order to investigate the effects of the synthesis conditions on the doping mechanism. The photocatalytic activity was investigated by measuring the degradation of methylene blue under UV light irradiation and a correlation between its efficiency and the luminescence performance has been proposed.     

Magnetic and optical properties of Nd/TiO2- rGO nanocomposites

Graphene, the thinnest 2-dimensional atomic material, is successively used as a composite material has it significantly improves optical, thermal, mechanical and electrical properties. Neodymium being a strong paramagnetic substance is capable of storing large amount of magnetic energy because of their greater number of unpaired electrons in their electron orbital structure. This paper focuses on the influence of graphene on the structural, optical and magnetic properties of rare earth neodymium (Nd) doped TiO₂ nanoparticles. Nd doped TiO₂ nanoparticles are deposited on reduced graphene oxide (rGO) sheets forming the nanocomposites by hydrothermal treatment. The nano size, structure and phase of the composites are analysed by X-ray diffraction and Raman spectra. Dispersion of pure TiO₂ and Nd/TiO₂ nanoparticles on the rGO sheets is studied with FESEM and HRTEM micrographs alongside the elemental composition confirmed by EDAX. Increased surface area and pore size analysis is revealed by BET isotherms and BJH data. Absorption edges are blue shifted owing to particle size and experimental conditions. PL and EPR spectra confirm the presence of paramagnetic defect centres in the nanocomposites. The M − H hysteresis curves of the composites reveal the ferromagnetic behaviour at room temperature.     

The synthesis and morphology characteristic study of BAO-ODPA polyimide/TiO2 nano hybrid films

Hybrid nanocomposite films of titanium dioxide (TiO₂) in polyimide (PI) from 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) and 4,4′-oxydiphthalic anhydride (ODPA) have been successfully fabricated by an in situ sol-gel process. These nanocomposite films exhibit fair good optical transparency up to 40 wt% of TiO₂ content. X-ray diffraction spectroscopy shows three sharp peaks in pure BAO-ODPA PI. It results from the intermolecular regularity. However, the intermolecular regularity in the hybrid film is disrupted by the introduction of TiO₂ nanoparticles with no sharp peak in XRD spectra. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results confirm the formation of TiO₂ particles in PI matrix. The surface Ti content is much lower than the theoretical bulk content in all hybrid films. The ratio of the former to the latter increases with the TiO₂ content and levels off at TiO₂ wt%≥20. Transmission electron microscope (TEM) images show that the TiO₂ phase is well dispersed in the polymer matrix. The size of the TiO₂ phase increases from 10 to 40 nm when the TiO₂ content is 5-30 wt%, respectively.     

Visible light active Cu-doped iron oxide for photocatalytic treatment of methylene blue

In recent work, pure α-Fe₂O₃ (F-1) and series of 5% Cu doped Fe₂O₃ (CF-5) , 10% Cu doped Fe₂O₃ (CF-10) and 15% Cu doped Fe₂O₃ (CF-15) nanoparticles by facile chemical coprecipitation method were synthesized to study the effect of concentration of doping for photocatalytic activity. As prepared F-1, CF-5, CF-10, CF-15 nanoparticles were subjected to X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) techniques to analyse the structural and functional groups features. These characterization techniques confirmed the successful doping of Cu ²⁺ ions in α-Fe₂O₃. The crystallite size of synthesized samples was calculated by Scherrer formula. Gradually decline in crystallite size from 18 to 15 nm was observed for undoped to doped samples. Scanning electron microscopic (SEM) analysis expressed that doping of Cu reduced the aggregation of particles and enhanced the surface area of nanoparticles. UV–Visible spectroscopic analysis of synthesized samples was used to calculate the bandgap energy of F-1, CF-5, CF-10, CF-15 nanoparticles i.e., 2.0, 1.7, 1.5, 1.4eV respectively. Narrowing bandgap energy of doped hematite supported to perform excellent photocatalytic activity. Maximum degradation of methylene blue was recorded via CF-10 within 140 min. Higher degradation rate of methylene blue by optimal concentration of CF-10 is due to effective electron trapping ability of photocatalyst.     

Preparation of CdS/TiO2 nanotube arrays and the enhanced photocatalytic property

In this paper, a series of CdS/TiO₂ NTs have been synthesized by SILAR method. The as-prepared CdS/TiO₂ NTs have been analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), and ultraviolet–visible (UV–vis). And their photocatalytic activities have been investigated on the degradation of methylene blue under simulated solar light irradiation. XRD results indicate that TiO₂ NTs were anatase phase, CdS nanoparticles were hexagonal phase. FESEM results indicate that low deposition concentration can keep the nanotubular structures. UV–vis results indicate that CdS can be used to improve the absorbing capability of TiO₂ NTs for visible light, and the content of CdS affects the band gap. Photocatalytic results indicate that CdS nanoparticles are conducive to improve the photocatalytic efficiency of TiO₂ NTs, and the highest degradation rate can reach 93.8%. And the photocatalytic mechanism of CdS/TiO₂ NTs to methylene blue is also described.     

Synthesis of TiO<Subscript>2</Subscript> Nanoparticles by Microemulsion/Heat Treated Method and Photodegradation of Methylene Blue

In this work, TiO₂ nanoparticles were prepared by microemulsion (ME)/heat treated method and its photodecomposition property of methylene blue. Microemulsion (ME) consisted of water, cyclohexane and an anionic surfactant such as bis (2-ethylhexyl) sodium sulfosuccinate (AOT). Titanium tetraisopropoxide (TTIP) was dropped into the ME solution and then then TiO₂ nanoparticles were formed by the hydrolysis reaction between TTIP in the organic solvent and the water in the core of ME. The smallest diameter of the particles was 20 nm in the system of cyclohexane with surfactant when the molar ratio of water to surfactant was 2. The effect of the process parameters (water/surfactant ratio, different temperatures) on the final characteristics has been investigated, in terms of structural phase and particle size. The TiO₂ nanoparticles were characterized by means of X-ray diffraction, Transmission and scanning electron microscopy, Fourier-Transformed infrared and differential thermal analysis. TiO₂ nanoparticles prepared in this condition were collected as amorphous powder, and converted to anatase phase at less than 350 °C, which is lower than the ordinal phase transition temperature. The crystallite size and crystallinity increase with an increase of heat treated s temperature. The particles are shown to have a spherical shape and have a uniform size distribution. The size of nanoparticles raises with an increase of water/surfactant ratio. In the photocatalytic decomposition of methylene blue, the photocatalytic activity is mainly determined by the crystallinity of TiO₂. In addition, the TiO₂ heat treated at 350 °C shows the highest activity on the photocatalytic decomposition of methylene blue (k = 1.7 × 10⁻² min⁻¹).     

Application of the statistical Taguchi method to optimize TiO2 nanoparticles synthesis by the hydrothermal assisted sol–gel technique

TiO₂ nanoparticles were synthesized by hydrothermal assisted sol–gel technique. The preparation parameters including pH value, the amount of water, titanium tetra isopropoxide content, temperature and time of hydrothermal process were investigated by Taguchi statistical experiments to determine the influence of synthesizing variables on the optimal conditions and to realize the highest degree of crystallinity or smallest crystallite size. X-ray diffraction (XRD) analysis and direct band gap energy (E_g) values, measured via diffuse reflectance spectra (DRS), proved that all the samples consist of anatase as a unique phase. Transmission electron microscopy (TEM) and specific surface area values showed that the sample with the smallest crystallite size could exert more effective photoactivity confirmed by measuring the decomposition rate of methylene blue. The apparent photodegradation rate constant of the sample with the smallest crystallite size was about five times greater than that of commercial TiO₂.     

Preparation and characterization of high-surface-area titanium dioxide by sol-gel process

One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this work, titanium dioxide (TiO₂) nanoparticles having enhanced surface area were synthesized under the interference of SiO₂. The mixed oxide, SiO₂-TiO₂ (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO₂ nanoparticles were added into the TiO₂ sols after hydrolysis. After condensation and calcination heat treatment, the SiO₂-TiO₂ nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO₂, the SiO₂ was removed subsequently by aqueous NaOH solution. The TiO₂ products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and by N₂ adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO₂ after calcination at 400^°C and the average pore diameter was about 7 nm. The porous TiO₂ products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ～43 nm remained constant upon calcinations from 500 to 700^°C. The specific surface area was increased up to 66% compared to regular TiO₂ samples that were prepared by the similar sol-gel procedure. The porous TiO₂ nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation.     

Effect of Co,Ga, and Nd Additions on the Photocatalytic Properties of TiO<Subscript>2</Subscript> Nanopowders

In the present study, metal-ion-doped TiO₂ powders were prepared by a sol-gel process using titanium isopropoxide as a Ti precursor and cobalt, gallium, or neodymium as a dopant. For the prepared doped TiO₂ nanopowders, the photocatalytic behaviors in the decomposition of aqueous 1,4-dichlorobenzene (DCB) were investigated as a function of doping level and preparation conditions. We found that all of the metal ion doping improved the photocatalytic activity of TiO₂, though Nd doping was the most effective and Co doping was least effective. XRD analyses showed that doping with Ga and Nd ions suppresses the anatase-to-rutile phase transition for TiO₂, whereas doping with Co did not influence the phase transition. The UV-visible absorption spectra for these metal-ion-doped samples were red-shifted by ∼ 20–40 nm depending upon the doping level.Original English Text Copyright © 2005 by Fizika i Khimiya Stekla, Whang, J. Kim, E. Kim, Y. Kim, Lee.This article was submitted by the authors in English.     

Shock-induced high-concentration nitrogen doping of titania

High-concentration nitrogen-doped titania is obtained by detonation-driven flyer impacting on mixtures of TiO₂ and different nitrogen precursors. XRD, IR, and XPS spectra are employed to characterize the phase composition, surface absorption, and N-doping concentration of recovered samples. The N-doping concentration is affected by doping nitrogen resources, initial content of doping nitrogen resources, and flyer velocity. A high nitrogen concentration of 13.6 at.% is achieved by shock loading of the mixture of P25 TiO₂ and 10 wt.% dicyandiamide (C₂N₄H₄) at 3.37 km/s. A possible shock doping mechanism is discussed.     

Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Titanium dioxide nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method in hydrochloric acid solutions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectrum (XPS) and UV–vis spectra were carried out to characterize the composites with different PANI contents. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the modified catalysts. Results show that TiO₂ nanoparticles are deposited by PANI to mitigate TiO₂ particles agglomeration. The modification does not alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction patterns. UV–vis spectra reveal that PANI-modified TiO₂ composites show stronger absorption than neat TiO₂ under the whole range of visible light. The resulting PANI-modified TiO₂ composites exhibit significantly higher photocatalytic activity than that of neat TiO₂ on degradation of phenol aqueous solution under visible light irradiation (λ ≥ 400 nm). An optimum of the synergetic effect is found for an initial molar ratio of aniline to TiO₂ equal to 1/100.