Synthesis and optical properties of TiO2 nanoparticles

Ultrafine TiO₂ particles have been synthesized successfully by a facile gas flame combustion method. The synthesized sample is characterized by X-ray diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared (FTIR), and photoluminescence (PL) spectroscopy. The as-prepared TiO₂ nanoparticles appear to be a single anatase crystalline phase and the diameter is about 9 nm. Besides a sharp emission at 398 nm originating from the radiative annihilation of excitions, a weak broad band at about 434 nm from the defect-related emission is also discussed.     

Synthesis of highly-active single-crystalline TiO2 nanorods and its application in environmental photocatalysis

Highly-active anatase TiO₂ nanorods have been successfully synthesized via a simple two-step method, hydrothermal treatment of anatase/rutile titanium dioxide nanoparticle powder in a composite-hydroxide eutectic system of 1:1 M KOH/NaOH, followed by acid post-treatment. The morphology and crystalline structure of the obtained nanorods were characterized using XRD, TEM, SEM/EDX and BET surface area analyzer. The obtained TiO₂ nanorods have a good crystallinity and a size distribution (about 4-16 nm); with the dimensions of 200-300 nm length and of 30-50 nm diameter. Compared with its precursor anatase/rutile TiO₂ nanoparticles and the titanate nanotubes, the pure anatase TiO₂ nanorods have a large specific surface area with a mesoporous structure. The photocatalytic performance of the prepared nanorods was tested in the degradation of the commercial Cibacrown Red (FN-R) textile dye, under UV irradiation. Single-crystalline anatase TiO₂ nanorods are more efficient for the dye removal.     

An easier method of preparation of mesoporous anatase TiO2 nanoparticles via ultrasonic irradiation

Mesoporous anatase TiO₂ nanopowder was synthesised by the sol–gel method using ultrasonic irradiation. This method is simple and faster for the synthesis of phase pure mesoporous anatase TiO₂ nanopowder. The product is characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron spectroscopy (TEM), thermo gravimetric analysis, Brunauer–Emmett–Teller (BET) surface area, UV–visible diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy. Analysis of XRD patterns, SEM and TEM image shows that the average particles size is of 19.9 nm and has an anatase structure. The mesoporous nature was determined by the BET method using the Barrett–Joyner–Halenda (BJH) model.     

Synthesis of nano-particles of anatase-TiO2 and preparation of its optically transparent film in PVA

Anatase-TiO₂ nano-particles have been synthesized by using long-carbon chain carboxylic acid and titanium tetrachloride (TiCl₄). As-prepared powder has been calcined at 500 °C to obtain highly crystalline TiO₂. Broad X-ray diffraction (XRD) pattern of as-prepared as well as calcined powder showed all prominent peaks for tetragonal crystal structure representing anatase-TiO₂. The particle diameter by applying Scherrer formula was found to be about 20 nm. It was possible to load as-prepared particles in poly vinyl alcohol (PVA) for optical studies. Optically transparent film showed sharp absorption band for TiO₂ nano-particles at ∼ 300 nm. Photoluminescence (PL) studies of the solution showed emission wavelength at about 330 nm. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) revealed that the particles in the film have uniform distribution and even for the powder no agglomeration was observed. Thermal analysis (TGA) showed that the stability of host polymer is enhanced. FTIR spectra showed presence of carboxylate functional group in the powder.     

Structural phase analysis,band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles

This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO₂ (titania) nanoparticles (NPs) synthesized by employing acid modified sol–gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV–visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer’s formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO₂ in anatase structure in both pure and Co doped TiO₂ NPs. The most intense Raman active E_g peak of TiO₂ NPs shifted to higher energy on doping. Both UV–visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect.     

Solar photocatalytic degradation of methyl orange dye using TiO2 nanoparticles synthesised by sol–gel method in neutral medium

Anatase TiO₂ nanoparticles were synthesised by the sol–gel method in neutral medium, and its photocatalytic activity in the degradation of methyl orange dye under sunlight has been studied. The nanoparticles were characterised using high-resolution X-ray diffraction, high-resolution transmission electron microscopy, micro Raman analysis and diffuse reflectance spectroscopy. The blueshift and asymmetrical broadening associated with phonon confinement effect has been observed in the Raman spectra of pristine nanoparticles. The high temperature annealing of as prepared anatase samples resulted in the phase transformation in to rutile. The mixture of anatase and rutile TiO₂ nanoparticles exhibited faster photocatalytic activity in the degradation of methyl orange than the pristine anatase and rutile phases. The significant enhancement in the photocatalytic activity of mixed TiO₂ nanoparticles is due to the synergistic effects that consist of the antenna effect by the rutile phase and the activation effect by the anatase phase. Since method of preparation of the catalyst is comparatively simple and cost effective, and the energy source used is sunlight, the method can be easily implemented in waste water treatments.     

Low temperature facile synthesis of anatase TiO2 coated multiwalled carbon nanotube nanocomposites

Anatase TiO₂ coated multiwalled carbon nanotube (MWNT) nanocomposites were prepared by combining the sol-gel method with a self assembly technique at a low temperature. XRD, TEM, FTIR and XPS spectra were applied to characterize the crystal phase, microstructure, and other physicochemical properties of the sample. The results showed that MWNTs were covered with a 12-20 nm thickness layer of anatase TiO₂ or surrounded by a 30 -290 nm thickness coating of anatase TiO₂. The layer or coating is constructed of TiO₂ nanoparticles about 5.8 nm. Furthermore, as-prepared composite was rich in surface hydroxyl groups.     

Surface characteristics and photoactivity of silver-modified palygorskite clays coated with nanosized titanium dioxide particles

This paper presents the results of a study in which nanosized titanium dioxide (TiO₂) crystal particles were coated onto the surface of palygorskite fibrous clay which had been modified by silver ions using titanium tetrachloride as a precursor. Coated TiO₂ particles with the anatase structure were formed after calcining at 400 °C for 2 h in air. Various analytical techniques were used to characterize the surface properties of titanium dioxide particles on the palygorskite. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that TiO₂ particles were supported on the surface of the palygorskite clays and their size was in the range of 3–6 nm. The titanium oxide coatings were found to be very active for the photocatalytic decomposition of methylene blue.     

TiO2/Si nanowires hybrid system for efficient photocatalytic degradation of organic dye

Herein, titanium dioxide (TiO₂)-coated vertically aligned silicon nanowires (SiNWs/TiO₂) were fabricated and evaluated for photocatalytic degradation of organic dyes. Aligned SiNWs arrays were prepared by facile metal-assisted chemical-etching process with varying the etching time that was followed by TiO₂ nanoparticles coating using sputtering technique. The TiO₂ film crystallized in pure anatase phase with an average crystalline size of 50 nm, as was elucidated with X-ray diffraction studies. SEM analysis showed nanowires with varying lengths from 2.5 to 13.5 µm and confirmed the homogenous surface decoration with TiO₂. The homogeneous distribution of TiO₂ nanoparticles on nanowires was co-evidenced with Energy-Dispersive X-ray spectroscopy (EDX) and Raman spectra analysis. The developed SiNWs/TiO₂ was exploited for photocatalytic degradation of methylene blue; the role of hydrogen peroxide was also elucidated. The highest photocatalytic efficiency of 96% was achieved for SiNWs/TiO₂ with optimum nanowire length of 3.5 μm. The developed photocatalyst was found to be almost stable even after 190 days (~?5 months) and could be used as reusable and easily removable photocatalysts. The current study highlighted the SiNWs/TiO₂/H₂O₂ system as excellent candidate for water remediation applications.

     

A novel single-step synthesis of N-doped TiO2 via a sonochemical method

A novel single-step synthetic method for the preparation of anatase N-doped TiO₂ nanocrystalline at low temperature has been devoleped. The N-doped anatase TiO₂ nanoparticles were synthesized by sonication of the solution of tetraisopropyl titanium and urea in water and isopropyl alcohol at 80 °C for 150 min. The as-prepared sample was characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–vis absorption spectrum. The product structure depends on the reaction temperature and reaction time. The photocatalytic activity of the as-prepared photocatalyst was evaluated via the photodegradation of an azo dye direct sky blue 5B. The results show that the N-doped TiO₂ nanocrystalline prepared via sonication exhibit an excellent photocatalytic activity under UV light and simulated sunlight.     

Synthesis of nanostructured TiO2 particles in room temperature ionic liquid and its photocatalytic performance

Nanostructured TiO₂ particles were synthesized by sol-gel method with room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) as a reaction medium. The structure and morphology of TiO₂ nanoparticles were characterized with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared TiO₂ nanoparticles present anatase crystal phase even without being calcined at high temperature, and show better photocatalytic performance in the degradation of methyl orange. The photocatalytic efficiency increases evidently along with increasing the concentration of nanostructure TiO₂, and the degradation percent can reach 100% at the optimal catalyst concentration (2.0 g/L).     

Microstructures and photo-catalytic properties of B3+ and F− co-doped TiO2 films

The nano-crystalline B³⁺ and F^? co-doped titanium dioxide films were successfully prepared by the improved sol–gel process. The as-prepared specimens were characterised using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), the Brunauer–Emmett–Teller (BET) surface area, X-ray photo-electron spectroscopy, photoluminescence spectra and UV–Vis diffuse reflectance spectroscopy. The photo-catalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. The results of XRD, FE-SEM and BET analysis indicated that the TiO₂ films were composed of nano-particles. B³⁺ and F^? co-doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Diffuse reflectance measurements showed that co-doping could clearly extend the absorbance spectra of TiO₂ into visible region. Compared with pure TiO₂, B³⁺ doped or F^? doped TiO₂ film, the B³⁺ and F^? co-doped TiO₂ film exhibited excellent photo-catalytic activity. It is believed that the surface microstructure of the films and the doping methods of the two ions are responsible for improving the photo-catalytic activity.     

Preparation and characterization of N–I co-doped nanocrystal anatase TiO2 with enhanced photocatalytic activity under visible-light irradiation

N–I co-doped TiO₂ nanoparticles were prepared by hydrolysis method, using ammonia and iodic acid as the doping sources and Ti(OBu)₄ as the titanium source. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible diffuse reflection spectroscopy (UV–vis DRS). XRD spectra show that N–I–TiO₂ samples calcined at 673 K for 3 h are of anatase structure. XPS analysis of N–I–TiO₂samples indicates that some N atoms replace O atoms in TiO₂ lattice, and I exist in I⁷⁺, I⁻ and I⁵⁺ chemical states in the samples. UV–vis DRS results reveal that N–I–TiO₂ had significant optical absorption in the region of 400–600 nm. The photocatalytic activity of catalysts was evaluated by monitoring the photocatalytic degradation of methyl orange (MO). Compared with P25 and mono-doped TiO₂, N–I–TiO₂ powder shows higher photocatalytic activity under both visible-light (λ > 420 nm) and UV–vis light irradiation. Furthermore, N–I–TiO₂ also displays higher COD removal rate under UV–vis light irradiation.     

Characterization and photocatalysis of Eu3+–TiO2 sol in the hydrosol reaction system

In this paper, 3.0 mol% lanthanide europium ion modified TiO₂ sol (Eu³⁺–TiO₂) was fabricated by chemical coprecipitation–peptization method with TiCl₄ as precursor. Eu³⁺–TiO₂ sol particles were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), transmission electron microscope (TEM) and particle size distribution (PSD). Eu³⁺–TiO₂ sol particles prepared at low temperature (70 °C) had anatase semicrystalline structure. Eu³⁺–TiO₂ sol sample homogeneously dispersed in the aqueous medium and presented narrow distribution characterization with 7 nm in mean size. Interfacial adsorption experiment shows that small particle size and positive charge of sol particles contributed to the good adsorption of X-3B dye on the TiO₂ surface. The photoelectrochemical property was investigated about electrons transfer efficiency between dye molecule and TiO₂ particles. A novel hydrosol reaction system was designed to conduct X-3B photodegradation reaction. The excellent photocatalytic activity for X-3B degradation under visible light irradiation was ascribed to effective scavenging electrons by Eu³⁺ ion. Moreover, X-3B photocatalytic degradation mechanism under visible light excitation was proposed as photosensitization–photocatalysis.     

TiO2 thin films for dyes photodegradation

The aim of the present study is to investigate the influence of the TiO₂ specific surface (powder, film) on the photocatalytic degradation of methyl orange. Porous TiO₂ films were deposited on transparent conducting oxide substrates by spray pyrolysis deposition. The films were characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy, and the UV-Vis spectroscopy. The XRD spectra of nanoporous TiO₂ films revealed an anatase, crystalline structure that is known as the most suitable structure in photocatalysis. The average thickness of the films was 260 nm and the measured band gap is 3.44 eV. The influence of the operational parameters (dye concentration, contact time) on the degradation rate of the dye on TiO₂ was examined. There were calculated the kinetic parameters and the process efficiency. Using thin films of TiO₂ is technologically recommended but raises problems due to lowering the amount of catalyst available for the dye degradation.     

TiO2 nanofibre-assisted photodecomposition of Rhodamine B from aqueous solution

Using liquid phase deposition method on cellulose substrate, TiO₂ nanofibres were prepared with TiCl₄ as a precursor. TiO₂ nanofibres were obtained after heat treatment of the cellulose template. The remaining product was composed of micron-size TiO₂ fibres with a nanofiber microstructure. It is shown that nanofibres are formed through the aggregation of TiO₂ nanoparticles. X-ray diffraction analysis of the as-prepared solution indicates the formation of crystalline TiO₂ anatase phase. EDX analysis was employed to measure the adsorbed mass of TiO₂ on cellulose substrate. The effect of deposition time on the growth and morphology was investigated by scanning electron microscopy. Transmission electron microscopy studies demonstrate fine microstructures composed of 10–15?nm?nanoparticles. Surface area of the TiO₂ fibres, measured by Brunauer, Emmett and Teller analysis, was about 104?m²?g^?1. Photodegradation of Rhodamine B as a standard dye shows that the prepared samples have a high photocatalytic activity due to large surface area.     

Effect of SiO2 nanoparticles on the phase transformation of TiO2 in micron-sized porous TiO2–SiO2 mixed particles

Spherical and nanoporous TiO₂ and TiO₂–SiO₂ mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO₂/SiO₂) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO₂ and TiO₂–SiO₂ particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO₂–SiO₂ (50 wt.% SiO₂) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO₂ particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO₂ content in the TiO₂–SiO₂ mixed particles increased.     

Superhydrophilic anatase TiO2 film with the micro- and nanometer-scale hierarchical surface structure

Nanosized anatase TiO₂ film on the ITO glass has been fabricated via spin coat process, with sodium dodecylbenzenesulfonate modified TiO₂ nanoparticles, which is synthesized by a sol-hydrothermal method, and also characterized mainly by means of field emission scanning electron microscopy (FESEM). The results show that the as-prepared anatase TiO₂ film exhibits superhydrophilic characteristic although it is not exposed to ultraviolet irradiation. The high roughness resulting from hierarchical surface structure is responsible for its superhydrophilicity. This work would provide a new route to fabricate newly nanostructured semiconductor films.     

Facile synthesis and characterization of TiO<Subscript>2</Subscript>–graphene–ZnFe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Tb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> ternary nano-hybrids

Rare earth ion (Tb³⁺)-doped zinc ferrite (ZnFe₂O₄) nanoparticles grown on reduced graphene oxide (RGO) prepared through sol–gel method have been reported. During the sol–gel process, graphene oxide was reduced to RGO, and, subsequently, anatase TiO₂ and cubic spinel ZnFe_2?x Tb _x O₄ were grown in situ on the surfaces of the RGO nano-sheets. The structure, surface morphology and chemical composition of ternary nano-composites were studied using scanning electron microscopy, energy-dispersive X-ray, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, photoluminescence spectra and vibrating sample magnetometer (VSM). XRD results showed that the produced TiO₂ was composed of anatase and some rutile phases and ZnFe₂O₄ with a cubic spinel structure. The particle sizes of ZnFe₂O₄ and TiO₂ nanoparticles were in the ranges of ~65–80 and ~17–20 nm, respectively. The saturation magnetization (M _S) determined from VSM was found to linearly increase with Tb³⁺ concentration.     

Photocatalytic degradation of dyes and organic contaminants in water using nanocrystalline anatase and rutile TiO2

Nanocrystalline TiO₂ was synthesized by controlled hydrolysis of titanium tetraisopropoxide. The anatase phase was converted to rutile phase by thermal treatment at 1023 K for 11 h. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared absorption spectrophotometry (FT-IR) and N₂ adsorption (BET) at 77 K. This study compare the photocatalytic activity of the anatase and rutile phases of nanocrystalline TiO₂ for the degradation of acetophenone, nitrobenzene, methylene blue and malachite green present in aqueous solutions. The initial rate of degradation was calculated to compare the photocatalytic activity of anatase and rutile nanocrystalline TiO₂ for the degradation of different substances under ultraviolet light irradiation. The higher photocatalytic activity was obtained in anatase phase TiO₂ for the degradation of all substances as compared with rutile phase. It is concluded that the higher photocatalytic activity in anatase TiO₂ is due to parameters like band-gap, number of hydroxyl groups, surface area and porosity of the catalyst.