Anatase TiO2 Spheres Research Articles

Synthesis and characterizations of molybdenum-doped titanium dioxide nanoparticles for photocatalytic removal of chromium (VI) from aqueous solutions

The photocatalytic removal of toxic heavy metals using titanium dioxide nanoparticles is an emerging technology for environmental remediation. Pure and Mo-doped TiO2 nanoparticles were synthesized using a modified sol-gel process, and then characterized by field emission scanning electron microscopy (FE-SEM) and particle size analysis (PSA) to determine their morphology and size, while X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) were used to determine their crystalline phase and composition. Brunauer–Emmett–Teller (BET) analysis was used to measure the surface area and porosity of the synthesized catalysts applying Langmuir and BET models. The catalyst was mainly composed of spherical anatase TiO2 particles, with a diameter in the range of 15–75 nm, and the maximum doping percentage of Mo was 3.3%. The Langmuir surface area of pure and Mo-doped TiO2was 91.63 and 128.73 m2/g, and the average pore volume was 0.029 and 0.032 cm3/g, respectively. The nanomaterials were used in the photocatalytic removal of Cr(VI) from aqueous solutions, and the adsorption isotherms indicated that the catalyst uptake (qe,max) amounts for Mo-doped TiO2 and pure TiO2 were 12.5 and 6.5 mg/L, respectively. Moreover, the equilibrium removal percentage was improved from 41% for pure TiO2 to 90% for Mo-doped TiO2, which confirms that photocatalytic activity is enhanced by doping TiO2 with molybdenum.

Microwave-assisted self-template synthesis of mesoporous anatase TiO2 spheres for non-aqueous Al-ion batteries: Textural property optimization and enhanced reversible Al3+ storage

Mesoporous anatase TiO2 spheres (MATS) are elaborated via microwave-assisted rapid crystallization of hydrous TiO2 colloidal spheres (HTCS) self-template. Tuning the hydrothermal and calcination temperatures allow for textural property-controllable synthesis. The optimal MATS are demonstrated as a promising cathode material of aluminium-ion batteries (AIBs) and show superior rate and capacity performances. Their large surface area and porous structure offer a robust and interconnected scaffold for Al3+ insertion/exertion with higher reversibility. The constructed non-aqueous AIBs with RTILs electrolyte deliver the highest initial capacity of 145.3 mA h g−1 at 0.2C with high Coulombic efficiency of ≈ 96.5%, and a reversible capacity of 78.0 mA h g−1 at 1C can be retained after 200 cycles with high Coulombic efficiency of ≈ 98.6%. Our study on the Al storage mechanism further shows the charge/discharge process involves the extraction/insertion of Al species (Al3+, AlCl4−, Al2Cl7−, etc.) into the TiO2 crystal lattices with the formation of intermediate aluminium titanium oxides (Al2Ti7O15 and Al2TiO5) and non-oxides (Ti(AlCl4)2 and Ti(ClO4)4). The continuous enrichment of the latter during cycling greatly deteriorates the reversibility of AIBs.

Hydrothermal Separation of Titanium Vanadium and Chromium from a Pregnant Oxalic Acid Leachate.

The separation of titanium, vanadium and chromium in vanadium slag (VS) is a difficult problem restricting the comprehensive utilization of VS. This paper presents the first study on the separation of titanium, vanadium and chromium from oxalic acid leachate of VS. Firstly, the separation of titanium from the leachate by hydrothermal method was studied. The results show that more than 99% of titanium in the leachate was precipitated in the form of spherical anatase TiO2 with the purity of 95.7%. Then, the extraction separation of vanadium and chromium from the titanium-free filtrate by three-stage extraction of acidified N235 extractant and four-stage stripping of HCl solution was investigated. The extraction mechanism was identified as the anion exchange reaction between acidified N235 extractant and vanadium and chromium complex anions, which were further stripped by HCl solution in the stripping process. After obtaining the concentrated and purified stripping solution containing vanadium and chromium, the separation of vanadium and chromium from the stripping solution by hydrothermal method was studied, and the product was mainly composed of VO2 and Cr2O3. This process provides an idea for the comprehensive utilization of titanium, vanadium and chromium in oxalic acid system.

In situ construction of elemental phosphorus nanorod-modified TiO2 photocatalysts for efficient visible-light-driven H2 generation

In this work, we constructed a red phosphorus (RP)/TiO2 composite system via a chemical vapor deposition strategy. The evolution of the fibrous phased RP nanorods on the surface of anatase TiO2 spheres was rationally adjusted by controlling the composition of precursors. The optimal RP/TiO2 composite exhibited a significantly enhanced visible-light-driven photocatalytic H2 generation rate of 681 μmol h−1 g−1. The tightly interior surface bonding between RP and TiO2 greatly promoted the efficient charge transfer and redistribution by suppressing the charge recombination and self-trapping processes within TiO2, resulting in prolonged lifetimes of the active charges during the photocatalytic process as investigated in detailed using femtosecond time-resolved transient absorption (fs-TA) spectroscopy.

Tunable optical properties of Au nanoparticles encapsulated TiO2 spheres and their improved sunlight mediated photocatalytic activity

Plasmonic nanoparticles mediated improved light absorption and enhancement in the charge carrier lifetime of the semiconductor provides a tremendous contribution in the field of advanced photocatalysis. We report the synthesis of Au nanoparticles encapsulated TiO2 nanospheres with tunable optical properties using the variation in the size of Au nanoparticles. Microscopy studies manifest the morphological changes and average size modulation from 42 to 297 nm with the variation in the size of Au nanoparticles. HRTEM, Elemental mapping, Raman and XRD studies assure the formation of anatase TiO2 spheres contained Au nanoparticles. UV-DRS studies indicate the modulation in the bandgap and optical absorption with the particle size variation of Au nanoparticles. Photoluminescence results indicate the reduction in the recombination rate with the increment in the size of Au nanoparticles. Au nanoparticles contained TiO2 spheres were employed for the sunlight-induced breakdown of MB, MG and MO molecules in water. Most efficient Au-TiO2 nanohybrids decompose the 20 μM MB, 10 μM MG and 10 μM MO molecule solution in 30, 20 and 10 min, respectively. The outstanding photodegradation ability of Au-TiO2 nanohybrids spheres can be attributed to the creation of the Schottky interface between Au and TiO2 nanoparticles and their improved visible light-harvesting ability.

Absorption mechanism of dopamine/DOPAC-modified TiO2 nanoparticles by time-dependent density functional theory calculations

Donor-modified TiO2 nanoparticles are interesting hybrid systems shifting the absorption edge of this semiconductor from the ultra-violet to the visible or infrared light spectrum, which is a benefit for several applications ranging from photochemistry, photocatalysis, photovoltaics, or photodynamic therapy. Here, we investigate the absorption properties of two catechol-like molecules, that is, dopamine and DOPAC ligands, when anchored to a spherical anatase TiO2 nanoparticle of realistic size (2.2 nm), by means of time-dependent density functional theory calculations. By the differential absorbance spectra with the bare nanoparticle, we show how it is possible to determine the injection mechanism. Since new low-energy absorption peaks are observed, we infer a direct charge transfer injection, which, unexpectedly, does not involve the lowest energy conduction band states. We also find that the more perpendicular the molecular benzene ring is to the surface, the more intense is the absorption, which suggests aiming at high molecular packing in the synthesis. Through a comparative investigation with a flat TiO2 surface model, we unravel both the curvature and coverage effects.

Synthesis of Methyl-Capped TiO2-SiO2 Janus Pickering Emulsifiers for Selective Photodegradation of Water-Soluble Dyes.

Recently, Pickering emulsion stabilized by Janus particles has received considerable attention for interfacial reactions and droplet manipulation. However, its potential interests have been rarely explored because of the difficulties in designing and fabricating Janus particles for Pickering emulsion with suitable applications. Also, photocatalytic materials are scarcely applied as emulsifiers in Pickering emulsions because of their photogenerated hydrophilicity. This work reports the synthesis of methyl-capped Janus TiO2-SiO2 particles (MJTSs), which can be used as a novel emulsifier and photocatalyst simultaneously. The MJTSs, composed of an anatase TiO2 sphere and silica rod, are prepared by inverse emulsion-based step-by-step growth. We demonstrate that the Pickering emulsion stabilized by MJTSs represents extraordinary ability of emulsification, excellent stability, and tunable emulsion type (water in oil or oil in water). In addition, the MJTSs exhibit photocatalytic activity in decomposition of pollutants in the water phase while maintaining the stability of the Pickering emulsion.

Controllable Synthesis and Crystallization of Nanoporous TiO2 Deep-Submicrospheres and Nanospheres via an Organic Acid-Mediated Sol-Gel Process.

Although considerable progress has been achieved in the preparation of uniform hydrous TiO2 spheres (HTS) through the sol-gel process, there is plenty of room left in tailoring the size and morphology of HTS on the deep-submicron scale or even nanoscale since the diameters of the so far reported HTS are mostly on the (sub)micron scale (0.3-1.2 μm). Here, we develop a novel titanium tetraisopropoxide (TTIP)-organic acid (OA)-acetonitrile (ACN)-methanol (MeOH)-H2O system, which facilitates the control of nanoporous HTS to the range of 50-300 nm. The synthetic parameters including OA, (co-)solvent, concentration of precursor, and reaction temperature are comprehensively optimized, aiming at reproducible preparation and precise size control. Among the various OAs, n-valeric acid presents the best capability in controlling the spherical morphology and size uniformity. The synthesized amorphous HTS containing numerous micropores and mesopores show excellent hydrothermal stability and offer suitable self-template for the subsequent synthesis of mesoporous anatase TiO2 spheres (MAT) with a large surface area of 99.1 m2/g. The obtained TiO2 deep-submicrospheres and nanospheres with tunable sizes show great potential in various research fields.

A photoelectrochemical aptasensor constructed with core-shell CuS-TiO2 heterostructure for detection of microcystin-LR

In this work, a CuS-TiO2 heterojunction composite was prepared by dispersedly depositing CuS nanoparticles on TiO2 nanospheres surface with a hydrothermal method, and was then used to construct a photoelectrochemical (PEC) aptasensor for sensitive detection of microcystin-LR (MC-LR) in aquatic environment. The energy bands of CuS nanoparticles and spherical anatase TiO2 were well matched, which enhanced the photo-to-current conversion efficiency. The composite exhibited the enhanced visible light absorption, the improved separation of photo-generated charges, and the reduced self-aggregation of CuS nanoparticles, leading to the enhanced photocurrent response. The PEC aptasensor was constructed by immobilizing CuS-TiO2 composite on ITO electrode with chitosan film that further covalently bound aminated aptamer. After the target, microcystin-LR (MC-LR) as an analyte model, was captured by the aptamer on the aptasensor, it could be oxidized by the photo-generated hole to impede the electron-hole recombination and further amplify the photocurrent. The PEC aptasensor showed superior analytical performance for MC-LR with a linear range of 5.0 × 10−5 nM to 250 nM and a detection limit of 2.0 × 10−5 nM. The detection results with the aptasensor for practical water samples indicated its promising application in environmental monitoring.

N-doped hollow urchin-like anatase TiO2@C composite as a novel anode for Li-ion batteries

N-doped hollow urchin-like anatase TiO2 spheres (HUTSs) with carbon coating (HUTS@C) are prepared through a facile and scalable hydrothermal reaction followed by coating of polypyrrole and carbonization. The HUTS is composed of radially grown anatase nanorods and possesses an enhanced percentage of exposed {001} facets compared with P25 TiO2 nanoparticles. After the carbon coating, the HUTS@C retains the hollow nanostructure although covered with an N-doped carbon layer. As an anode for Li-ion batteries, the HUTS@C delivers a higher capacity of 165.1 mAh g−1 at 1C after 200 cycles and better rate capability (111.7 mAh g−1 at 10C) than the HUTS. Further electrochemical studies reveal that the HUTS@C has a better electrochemical reversibility, lower charge-transfer resistance, and higher Li-ion diffusion coefficient due to its unique nanosctructure including the hollow core, anatase phase of TiO2 microspheres with high exposed {001} facets and the N-doped carbon layer, which facilitates mass transport and enhances electrical conductivity.

Ultraviolet photodetector using pn junction formed by transferrable hollow n-TiO2 nano-spheres monolayer.

We report an ultraviolet (UV) photodetector with a universally transferable monolayer film with ordered hollow TiO2 spheres on p-GaN. After forming a TiO2 monolayer film by unidirectional rubbing of hollow TiO2 spheres on a polydimethylsiloxane (PDMS) supporting plate, we used a 5% polyvinyl alcohol (PVA) aqueous solution to transfer the film onto the target substrate. The PVA/TiO2 monolayer film was detached from the PDMS film and transferred to the p-GaN/Al2O3 substrate. To investigate the effects of crystallized phases of the TiO2 hollow spheres, anatase and rutile TiO2 sphere monolayers prepared by combining template synthesis and thermal treatment. The responsiveness of the UV photodetectors using anatase and rutile hollow n-TiO2 monolayer/p-GaN was 0.203 A/W at 312 nm and 0.093 A/W at 327 nm, respectively.

Solvent effects on microstructures and properties of three-dimensional hierarchical TiO2 microsphere structures synthesized via solvothermal approach

One-step solvothermal method has been proved to be a simple and efficient route to synthesize three-dimensional (3D) hierarchical TiO2 microsphere structures, but discrepant properties of the solvent media had been claimed as the major factors determining microstructures and properties of the final products. In this study, several typical solvents, including alkane, aromatic hydrocarbons, halohydrocarbon, ketone, organic acid, mono- and dihydric alcohols, were selected to comprehensively investigate the effect of solvents on the morphology, crystal structure, specific surface area, porous property and light harvesting capability of the final products. According to the experimental results, a good interface separating titanium precursor with aqueous phase in the reaction solution, created by non-polar solvents, or polar solvents which are immiscible with titanium precursor, was the decisive factor for the formation of quasi-3D urchin-like TiO2 microspheres self-assembled from one-dimensional (1D) nanostructures, and concentrated H+ induced by organic acid medium was also helpful. Meanwhile, without the liquid-liquid interface or extremely low solution pH, anatase TiO2 sphere structures with big specific surface area comprising of nanoparticles or nanosheets would be formed, and performed well in photodegradation of pollutants in water.

Controlled Assembly of Nanorod TiO2 Crystals via a Sintering Process: Photoanode Properties in Dye-Sensitized Solar Cells

We present for the first time a synthetic method of obtaining 1D TiO2 nanorods with sintering methods using bundle-shaped 3D rutile TiO2 particles (3D BR-TiO2) with the dimensions of around 100 nm. The purpose of this research is (i) to control crystallization of the mixture of two kinds of TiO2 semiconductor nanocrystals, that is, 3D BR-TiO2 and spherical anatase TiO2 (SA-TiO2) on FTO substrate via sintering process and (ii) to establish a new method to create photoanodes in dye-sensitized solar cells (DSSCs). In addition, we focus on the preparation of low-cost and environmentally friendly titania electrode by adopting the “water-based” nanofluids. Our results provide useful guidance on how to improve the photovoltaic performance by reshaping the numerous 3D TiO2 particles to 1D TiO2-based electrodes with sintering technique.

Effect of incorporation of multiwalled carbon nanotubes on photodegradation efficiency of mesoporous anatase TiO2 spheres

Composites consisting of mesoporous anatase TiO2 spheres and multiwalled carbon nanotubes (MWCNTs) were synthesized via sol–gel and solvothermal processes. The nanocomposites showed enhanced photocatalytic activity because of their large specific surface areas (104–190 m2/g), the presence of TiO2 in the anatase phase, and the reduced band gap energy (from 3.30 to 2.08 eV). In particular, of the materials prepared, the nanocomposite containing 20 wt% MWCNTs exhibited the best photocatalytic efficiency and degradation rate. The nanocomposites also showed improved pollutant adsorption capacity, electron–hole pair lifetime, light absorption capability, and absorbance of visible light. Further, the nanocomposites exhibited excellent stability and durability even after four cycles.

Monodispersibility and size control in the preparation of spherical titania particles by thermal hydrolysis of TiCl4 in various solvents

Spherical anatase TiO2 particles were successfully synthesized by the thermal hydrolysis of TiCl4 in various solvents. In the case of n-propanol, isopropanol, and acetone with an RH ratio of 3, spherical titania particles were produced. In contrast, spherical TiO2 particles did not form in methanol and ethanol because of their high dielectric constants. In this study, different oscillators (an oven, and isothermal and ultrasonic oscillators) were used to prepare titania prior to studying the morphology and particle size. The spherical TiO2 particles prepared using the ultrasonic oscillator were much smaller than those obtained using the other heating methods, because of the lower temperature gradient in the solution; however, a narrower size distribution of particles was observed in the TiO2 prepared in an oven. The presence of acetylacetone as a dispersing agent in the starting solutions significantly reduced the particle size. The optimum concentration of acetylacetone of 0.8mg/cm3 resulted in more uniform TiO2 spheres with an average particle size of 1.4µm.

Influence of mesopore distribution on photocatalytic behaviors of anatase TiO2 spherical nanostructures

Mesoporous anatase TiO2 spheres were synthesized via sol–gel and solvothermal processes using ammonia. The crystallite size was shown to increase with the increasing amount of aqueous ammonia used, leading to a larger pore size. The mesopore volume of the materials reaches up to 0.308cm3g−1. The TiO2 spheres showed improved catalytic activity in organic dye photodegradation owing to their high specific surface area, pore volume, and optimal pore size, which enable an increase of light absorption capability, as well as fast mass transfer by the optimal mesopore structure.

Study on photo-induced charge transfer properties in CdS quantum-dot-sensitized mesoporous TiO2 photoelectrode

In this study, well-crystallized mesoporous anatase TiO2 spheres (TiO2-MS) were prepared via a simple sol–gel process followed by subsequent hydrothermal treatment and then used as photoelectrode for quantum-dot-sensitized solar cell (QDSC) application. The mesoporous structure exhibits efficient QD loading and good light-scattering properties for light harvesting. In the meantime, both surface photovoltage technique based on lock-in amplifier and transient photovoltage measurement reveal that the QDs-sensitized mesoporous TiO2 sphere photoelectrode is conducive to promote the separation of photo-induced charges and reduce the charge recombination owing to the efficient charge transfer. As a result, the QDSCs based on mesoporous TiO2 spheres photoelectrode shows a power conversion efficiency of 1.34 %, which is significantly higher than that derived from P25 nanoparticle electrode. The relation between the performance of QDSCs and their photovoltage characterization was also discussed.

Narrow-linewidth red-emission Eu3+-doped TiO2 spheres for light-emitting diodes

In this work, the amorphous Eu3+-doped TiO2 spheres were synthesized by low cost mixed-solvent method, while the anatase and rutile spheres can be obtained by annealing the as-synthesized amorphous TiO2 spheres at elevated temperatures. The optical properties of Eu3+-doped TiO2 spheres were also investigated, and strong red emission (centered at 610 nm) with narrow line-width of 30 nm was observed under 465 nm or 394 nm excitations for the Eu3+-doped anatase TiO2 spheres. Our findings indicate the potential of using Eu3+-doped TiO2 spheres to achieve red emission with InGaN blue light emitting diodes (LEDs). Owing to the high light extraction efficiency in the GaN-based LEDs using anatase TiO2 spheres as demonstrated in our previous works, this work shows the strong potential of Eu3+-doped TiO2 spheres as the red phosphor material for high efficiency GaN-based white light-emitting diode.

Synthesis of Mesoporous Anatase TiO2 Sphere with High Surface Area and Enhanced Photocatalytic Activity

Mesoporous anatase TiO 2 spheres with high surface area (119 m 2 g −1 ) were successfully synthesized via a facile and green template-free method. The prepared TiO 2 was characterized by X-ray diffraction (XRD), N 2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis absorbance spectra. It was found that the prepared TiO 2 is characterized by pure anatase phase, which shows uniform spheres and has a typical mesostructure with a high specific surface area and a large pore volume. The effects of complexant (acetylacetone) amount, crystallization temperature and calcination temperature were also investigated. Based on the results, a sketch for the preparation of mesoporous TiO 2 was proposed. First, complex formed between tetrabutyl titanate and acetylacetone in ethanol. After introduction of aqueous of ammonia sulfate and urea, hydrolysis of tetrabutyl titanate would occur slowly, and sol of TiO 2 was formed. Then, crystallization proceeded under hydrothermal conditions. Calcination process favored the formation of bigger TiO 2 crystal through combining of the small crystals in TiO 2 . This led to the formation of bigger mesopores between TiO 2 crystals. Photocatalytic activity of the prepared TiO 2 was evaluated by decomposition of methyl orange.

Highly efficient dye-sensitized solar cell performance from template derived high surface area mesoporous TiO2 nanospheres

High surface area mesoporous anatase TiO2 spheres are synthesized using ethylene glycol as a template by a solvothermal method.