SrTiO3 Particles Research Articles

Enhanced photocatalytic activity of SrTiO3 particles by surface decoration with Ag nanoparticles for dye degradation

Ag nanoparticles with size of 5–15 nm were deposited onto SrTiO3 particles with size of 55 nm via a photocatalytic reduction method to yield Ag–SrTiO3 composite photocatalysts. The photocatalytic activity of prepared samples was evaluated by the degradation of acid orange 7 under ultraviolet light irradiation. It is demonstrated that the Ag–SrTiO3 composites exhibit an enhanced photocatalytic activity compared to bare SrTiO3 particles. Photoluminescence spectra of the samples were measured, revealing that the decoration of Ag onto SrTiO3 particles results in a reduction in recombination of photogenerated electron/hole pairs. Hydroxyl radicals were detected by fluorimetry using terephthalic acid as a probe molecule, showing an enhanced yield over the irradiated Ag–SrTiO3 composites. Based on the experimental results, the photocatalytic activity enhancement of Ag-decorated SrTiO3 particles can be explained by the fact that photogenerated electrons are effectively transferred from the conduction band of SrTiO3 to Ag nanoparticles, leading to an increased separation and availability of electrons and holes for the photocatalytic reaction. In addition, hydroxyl radicals are suggested to be the dominant active species responsible for the dye degradation.

SrTiO3 single crystals enclosed with high-indexed {0 2 3} facets and {0 0 1} facets for photocatalytic hydrogen and oxygen evolution

SrTiO3 single crystals enclosed with high-indexed {023} facets and {001} facets were facilely synthesized via a one-pot solvothermal method. The ratio of {023} to {001} facets could be simply adjusted by tuning the NaOH and EA concentrations during the solvothermal growth process. It was demonstrated that the photocatalytic activities of the variously shaped SrTiO3 should be closely related to the morphology of SrTiO3, i.e., the ratio of {023} to {001} facet. The highest photocatalytic activities are achieved for SrTiO3 single crystals with the ratio of {023} to {001} facet tuned to 35:65, with hydrogen and oxygen evolution rates reaching 71.1 and 30.0μmol/h, respectively, which are about 9.5 and 3.0 times higher than those of the irregular SrTiO3 particles. Facet selective photo-deposition of metal ions reveals that the high-indexed {023} facets provided active sites for photo-oxidation reaction, while the {001} facets offered active sites for photo-reduction reaction. Such spatially separated photoactive reduction and oxidation sites should benefit charge separation in a SrTiO3 single crystal, leading to higher photocatalytic activity related to the irregular SrTiO3 particles.

Low-temperature route to metal titanate perovskite nanoparticles for photocatalytic applications

MTiO3 (M=Ca, Sr, Ba) nanoparticles were synthesized by a one-step room-temperature ultrasound synthesis in ionic liquid. The obtained samples are characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption, UV–vis diffuse reflectance, Raman and IR spectroscopy and their capability in photocatalytic hydrogen evolution and methylene blue degradation was tested. Powder X-ray diffraction and Raman spectroscopic investigations revealed the products to crystallize in the cubic perovskite structure. SEM observations showed that the obtained CaTiO3 consists of nanospheres, BaTiO3 of raspberry-like shaped particles of 20nm in diameter. SrTiO3 particles have cubic-like morphology with an edge length varying from 100 to 300nm. SrTiO3 exhibited the highest catalytic activity for photocatalytic H2 evolution using only 0.025wt.% Rh as co-catalyst and for the degradation of methylene blue under UV irradiation. The influence of parameters such as synthesis method, calcination temperature, and doping with nitrogen on the morphology, crystallinity, chemical composition, and photocatalytic acivity of SrTiO3 was studied. Heating the as-prepared SrTiO3 to 700°C for extended time leads to a decrease in surface area and catalytic activity. Ionothermal prepared SrTiO3 exhibits a higher activity than sonochemically prepared one without co-catalyst due to a synergistic effect of anatase which is present in small amount as a by-phase. After photodeposition of Rh, however, the activity is lower than that of the sonochemically prepared SrTiO3. Nitrogen-doped SrTiO3 showed photocatalytic acivity under visible light irradiation.

Template‐Free Synthesis of Hollow Porous Strontium Titanate Particles

Strontium titanate (SrTiO3) is a potential photocatalyst of H2 evolution for providing green energy. One of the main strategies for increasing the efficiency of H2 evolution is to increase the surface area of photocatalysts. In this study, spray pyrolysis was used because of its superior flexibility in morphological control. Three typical reactants, nitric acid, acetic acid, and citric acid, were added to Sr and Ti precursors to form various morphological SrTiO3 powders. The SrTiO3 powders were investigated by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, focused ion beam technique, and the Brunauer–Emmett–Teller (BET) method to determine the phase composition, surface morphology, geometry, inner structure, and specific surface area, respectively. Four main morphologies of SrTiO3 particles, namely, porous, concave porous, wrinkled spherical, and hollow porous structures, were obtained. Among these powders, SrTiO3 particles prepared with citric acid had the highest surface area (46.9 m2/g) because of their hollow porous structure. Finally, the formation mechanisms of these four distinct SrTiO3 morphologies are discussed.

Manipulation of morphology of strontium titanate particles by spray pyrolysis

Strontium titanate (SrTiO3) materials are used in industrial applications such as catalyst supports, solid oxide fuel cell anodes, and red-emitting phosphors, and these applications require different particle morphologies, either porous or solid. Spray pyrolysis (SP) is a potential process for preparing SrTiO3 because it is simple and continuous, but to date, no solid spherical shape has been reported. One possible challenge is the instability of the precursor solution, which can cause non-homogenous precipitation of porous structures. In this study, precursors with various concentrations of a new additive, acetic acid, were chosen for the preparation of SrTiO3 particles. The resulting particles were observed to have three main morphologies: bumpy solid, bumpy porous, and wrinkled porous. The experimental results suggest that the morphological formation mechanisms are highly correlated with esterification behaviors, which is controlled by the additive concentration of acetic acid. In summary, the SP formation mechanisms of SrTiO3 particles identified in this study could be used to control particle morphology for industrial applications.

Solvothermal Synthesis of Shape-Controlled Perovskite MTiO<sub>3</sub> (M = Ba, Sr, and Ca) Particles in H<sub>2</sub>O/Polyols Mixed Solutions

Perovskite oxides MTiO3 (M = Ba, Sr and Ca) with various phase, size, and shape were systematically prepared by solvothermal method in H2O/glycols mixed solutions. Shape control of the BaTiO3 and SrTiO3 particles was achieved by choice of glycols, and anisotropic rod-shaped fine BaTiO3 particles with a tetragonal crystal system were selectively synthesized by use of ethylene glycol. On the other hand, cubic- and spherical-shaped BaTiO3 particles were also obtained in H2O and H2O/diethylene glycol systems. These BaTiO3 particles had a cubic crystal system. Meanwhile, concave cubic-shaped CaTiO3 particles with an orthorhombic phase were synthesized. In our method, triethanolamine–titanium complex was used as the titanium source of MTiO3. Both of the specific adsorption of triethanolamine and solvent effect of glycols is the competitive factor for the control of final particle size and shape.

BiVO4–Ru/SrTiO3:Rh composite Z-scheme photocatalyst for solar water splitting

BiVO4–SrTiO3:Rh composites in which the Rh-doped SrTiO3 particles of a H2-evolving photocatalyst attached on the BiVO4 particles of an O2-evolving photocatalyst were prepared by an impregnation method and a liquid–solid state reaction. The composites showed photocatalytic activity for Z-schematic water splitting under visible light or simulated sunlight irradiation without an electron mediator. The optimum pH for the water splitting was neutral. Water splitting over the composite proceeded via an interparticle electron transfer from BiVO4 to Ru/SrTiO3:Rh particles at the large interfacial area obtained by those preparation methods. The photocatalytic water splitting activity of the composite depended on the crystallinity and morphology of BiVO4. The composite prepared by the liquid–solid state reaction showed the highest photocatalytic activity. This was due to the formation of well-crystallized BiVO4 single-crystal-like particles. The BiVO4–Ru/SrTiO3:Rh composite photocatalyst gave a quantum yield of 1.6% at 420 nm and a stable activity. Thus, we have developed the simplest system requiring no additives, except for photocatalyst powder and water, for photocatalytic solar water splitting.

Hydrothermal Synthesis and Characterization of Nb<sup>5+</sup>-Doped SrTiO<sub>3</sub> Powders

Nb5+-doped SrTiO3 (STO) particles were synthesized by a simple hydrothermal reaction at 150 °C for 4h. It was found that the main diffraction peaks of Nb5+-doped STO samples with different dosage of dopants shifted gradually to low angles, indicating the little lattice parameter expansions which result from the partial substitution of Ti4+ (0.061 nm) by Nb5+ (0.064 nm) in perovskite structure. From the lattice parameters, the max Nb5+ dopant concentration is about 2 mol%, and the particles obtained were 200 nm-sized and monodispersed.

Synthesis and characterization of sulfonated poly(styrene-b-(ethylene-ran-butylene)-b-styrene)/(strontium titanate) nanocomposites

Nanocomposite films were prepared via syntheses of SrTiO3 nanoparticles in films of sulfonated poly(styrene-b-ethylene-co-butylene-b-styrene) (sSEBS) block copolymer templates. SrTiO3 ionic and alkoxide precursors permeated selectively into styrene domains in which formation and growth of crystalline nanoparticles occurred through hydrolysis-precipitation reactions. FTIR spectra verified SrTiO3 composition and WAXD patterns identified crystalline SrTiO3 within the templates. AFM images for both unfilled sSEBS and sSEBS/SrTiO3 microtomed films showed mesophase separation characterized by lamellar morphologies suggesting that SrTiO3 particle insertion did not alter template morphology. Uniform distribution of Ti and Sr along the nanocomposite internal film cross sections and external surfaces was seen using ESEM/EDX. TEM images showed clusters of parallel SrTiO3 rods in sulfonated styrene domains. Agreement of SrTiO3 rod width in TEM images with domain size in AFM images supports the template hypothesis. Selected area electron diffraction studies of SrTiO3 clusters inside sSEBS/SrTiO3 provided direct identification of in situ formation of crystalline SrTiO3 particles. WAXD studies demonstrated that in situ – grown particles have the same crystal structure as those produced outside the template. The frequency dependent broadband dielectric responses of these materials, both filled and unfilled, reflect strong polarizability that is more sensitive to degree of sulfonation than from insertion of SrTiO3 nanoparticles.

The enhancement of photovoltaic parameters in dye-sensitized solar cells of nano-crystalline SnO2 by incorporating with large SrTiO3 particles

In this paper, the performance of nano-porous electrodes made of a composite material of SrTiO3 and SnO2 are compared with those made of bare SnO2. When these particular devices are analyzed in a comparative mode the results confirmed the enhancement of photovoltaic parameters in the former device. The performance of respective cells were examined by several methods including I−V characteristic measurements, photocurrent action spectra, dark I−V measurements, Mott−Schottky measurements and X-ray diffraction measurements. Even though such improvements in this particular cell could be explicated by the formation of a potential energy barrier of SrTiO3 particles of comparably large width at the SrTiO3/SnO2 interface, the passivation of voids in the SnO2 film by SrTiO3 particles to a certain extent could not be totally ruled out. Besides, high energetic electrons injected by dye molecules move more credibly through mini-bands formed in the chain of nano-crystalline SnO2 particles to the back contact. The blocking of the recombination path and the shifting up of the uppermost electron occupied level of SnO2 accompanying the conduction band edge in the SrTiO3/SnO2 composite film, may have lead to the observed enhancement of the fill factor and photovoltage, respectively.

Influence of synthesis route on the morphology of SrTiO3 particles

ABSTRACTThe cubic perovskite SrTiO3 is an important semiconductor oxide with a band gap of 3.2 eV. It has a wide variety of applications such as: dielectric materials, photoluminescent devices, and in photocatalysis. It is conventionally obtained by the classic solid state synthesis (SS), in which TiO2 and SrCO3 react for several hours at temperatures as high as 1200 °C. Besides the high energy demand, SS is not useful for the control of physical characteristics, such as particle size and morphology, which has become essential for some of its applications. It is known that many soft and green routes can produce SrTiO3. Among them, the hydrothermal (HT) and sol-precipitation (SP) methods, as well as the molten salt synthesis (MS) are interesting not only due to their low cost and energy use, but also because of the possibility of particle size and shape control. This study compares the size and morphology of the SrTiO3 particles obtained by these three synthetic pathways. Scanning electron microscopy (SEM) was used to compare particle size and morphology, and X-ray diffraction (XRD) was used to confirm the perovskite formation as well as to determine the Scherrer’s particle size.

Solution synthesis and growth mechanism of SrTiO3mesocrystals

Single-crystalline SrTiO3 mesocrystals were synthesized via sol–precipitation coupled with a hydrothermal process using oleic acid as a capping agent. To clarify the growth mechanism, the time-dependence morphology, size, and growth process of SrTiO3 mesocrystal were investigated. SrTiO3 mesocrystals formed from oriented aggregates of Sr–Ti–O nanorods, which were subsequently transformed into irregular morphologies via the formation of the SrTiO3 phase. Then oriented fusion of the irregular particles gave a mesocrystal structure. The addition of oleic acid accelerated the formation of Sr–Ti–O nanorods, oriented the fusion of irregular SrTiO3 particles, and formed the cubic morphology of SrTiO3 mesocrystals.

A new approach for the preparation of SrTiO3 nanocubes

This paper describes the preparation of SrTiO3 nanocubes with an average length of ∼20nm. SrTiO3 nanoparticles were prepared using a solvothermal reaction at 240°C for 18h with [(CH3)2CHO]4Ti as a raw material and a little distilled water addition. X-ray diffraction measurements confirmed the presence of perovskite SrTiO3 particles. The water served as an oxygen source for producing the perovskite structure. Furthermore, a new approach to nanocube formation using a mixture of raw materials as titanium sources was investigated. Dispersed SrTiO3 nanocubes were successfully prepared using this approach and a solvothermal reaction performed at 260°C for 18h. SrTiO3 was synthesized from a mixture that included [(CH3)2CHO]4Ti and TiO2 as titanium sources. The [(CH3)2CHO]4Ti and TiO2 contributed to rapid nucleation and crystal growth, respectively. Scanning electron microscopy observations revealed that the particles were nanocubes approximately 20nm in size.

Synthesis of Nano-Sized SrTiO<sub>3</sub> Photocatalyst by Sol-Gel Method

A sol-gel processing technology was employed to synthesize fine SrTiO3 powder by using strontium nitrate (Sr(NO3)2) , butyl titanate (Ti(OC4H9)4) as precursors, citric acid (C6H8O6) as complexing agent and (ethylene) glycol (C2H6O2) as stabilizer. Prepared the precursors in liquid phase and then calcined the precursors to achieve nano-sized SrTiO3 powders. The microstructure and composition of the as-synthesized samples were characterized by X-ray diffraction (XRD), Scan Electron Microscopy (SEM), and the photocatalytic activity was studied. The results showed that all the SrTiO3 particles were identified as perovskite phase. The pH values, the content of the acetic acid, the heat treat temperature play important roles on the synthesis of the SrTiO3 photocatalyst. When the pH=1, n(Sr(NO3)2 ) : n(Ti(OC4H9)4) = 1 : 1, n(Sr(NO3)2 ) : n(C6H8O6)=1:1.7, the product has better rate of photodegradation for the Methylene Blue under the ultraviolet condition.

Hydrothermal Synthesis of SrTiO3 Nanoplates Through Epitaxial Self-Assembly of Nanocubes

SrTiO3 nanoplates are obtained by the precipitation of an aqueous gel suspension. The gel suspension is prepared by hydrolysis of a Titanium isopropoxide [Ti(OCH(CH3)2)4] solution with NaOH and the addition of Sr(NO3)2. The amount of additive oleic acid plays a significant role in the formation of pure SrTiO3 phase with specific morphologies. The results of transmission electron microscopy (TEM) and electron diffraction (ED) investigations provide evidences that the oriented aggregation of small nanocubes is the dominant growth mechanism for the formation of the observed SrTiO3 nanoplates. The primary nanocrystals are self-assembled in a highly oriented fashion, producing defective single-crystal particles. The above results show that the directional aggregation process can be controlled by changing the temperature of the suspension as well as by adding organic molecules, by which the SrTiO3 particles can be obtained with a controlled size and shape.

Photocatalytic Degradation of Various Dyes by Strontium Titanate Nanoparticles

A simple polyacrylamide gel method was used to prepare strontium titanate (SrTiO3) nanoparticles. X-ray diffraction (XRD) analysis reveals that single-phase SrTiO3 can be synthesized at a calcination temperature of 550 °C. Scanning electron microscope (SEM) observation shows that the as-prepared SrTiO3 particles are regularly shaped like spheres and highly uniform in size with an average diameter of ~55 nm. Ultraviolet (UV)-visible diffuse reflectance spectrum analysis indicates that the bandgap of the sample is 3.23 eV. The Brunauer-Emmett-Teller (BET) specific surface area of the sample is measured, by the N2 adsorption-desorption technique, to be 26.4 m2•g−1. The photocatalytic experiments reveal that the SrTiO3 nanoparticles can effectively degrade various dyes including congo red (CR), rhodamine B (RhB), methyl orange (MO), and methylene blue (MB) under UV irradiation.

Controlling the conditions for synthesis of strontium titanate nanopowders from celestite ore

Strontium titanate SrTiO3 nanopowders have been successfully prepared through oxalate precursor route using Egyptian celestite ore. Celestite ore was reduced with the carbon at the annealed temperature of 1100°C for 3 h to obtain water soluble strontium sulphide that treated with a dilute hydrochloric acid to produce strontium chloride. The formed strontium chloride and titanium dioxide were mixed with a certain amount of oxalic acid to form strontium titanium oxalate complexing precursors. The effect of oxalic acid molar ratio, annealing temperature, time and hydrogen peroxide additive on the crystal structure, crystallite size and microstructure was systematically studied. The results revealed that a well crystallite single phase of SrTiO3 nanopowders was achieved in the presence of hydrogen peroxide using 1·5 molar ratio of oxalic acid at the annealing temperature of 1000°C for 1 h. The crystallite size of the formed powders increased with increasing annealing temperature and time. The crystallite size was in the range between 50 and 80 nm. The SEM images of the formed SrTiO3 particles appeared as cube-like structure. The band gap energy and the direct current resistivity of the produced powders were ∼3·6 eV and 4·403×104 Ω m respectively for the sample in the presence of 10% hydrogen peroxide annealed at 1000°C for 2 h.

Low Temperature Synthesis of Titanium Complex Oxides by a New Synthetic Route of Water-soluble Titanium Complex from Titanium Chloride and Titanium Sulfate as Starting Materials

Water-soluble titanium complexes are attractive titanium sources for solution synthesis of titanium-based materials using water as a solvent due to their high stability in aqueous solution in wide range of pH, and have been made from expensive metal titanium ultrafine powder. In this study, TiCl4 and Ti(SO4)2 that are inexpensive reagents than metal titanium fine powder were chosen as starting materials. TiCl4 and Ti(SO4)2 were dropped into distilled water and large amount of NaOH solution was added here, then precipitates of Ti(OH)4 were obtained. Then precipitates were washed with distilled water and dissolved into mixed solution of H2O2 and NH3. And lactic acid as complexing agent was added to the solutions to obtain water-soluble titanium lactate complex solutions. These complex solutions generated no precipitate at pH 0 to 12 for 6 months. Yields of Ti in the both processes were 85 % and removal ratios of Cl- and SO42- ions were 99 and 93 %, respectively. MCO3 (M=Ca2+, Sr2+, Ba2+) were dissolved in the complex solution prepared from TiCl4, and the solution was dried and heated at 873 K for 5 h. Very fine and crystalline particles of CaTiO3, SrTiO3 and BaTiO3 were obtained by heating at 873 K in this solution method, while large particles of CaTiO3, SrTiO3 and BaTiO3 were obtained at 1273 K in solid-state reaction. Low temperature synthesis of titanium complex oxides by a new synthetic route of water-soluble titanium complex from titanium chloride and titanium sulfate as starting materials was successfully achieved.

Synthesis of titanium-based ceramics by a new synthetic route of water-soluble titanium complexes

We developed a new synthetic route of water-soluble complexes using TiCl4 and Ti(SO4)2 as starting materials. The yield of Ti and the removal rate of the Cl− ion were over 85 and 98%, respectively. The lactato titanium complex solution obtained by this new synthetic route remained stable for more than 3 months without any precipitation. Single-phase CaTiO3, SrTiO3, and BaTiO3 were synthesized from the lactato titanium complex by heating at 873 K for 5 h. The nano-structured CaTiO3, SrTiO3, and BaTiO3 particle sizes were 50, 30, and 30 nm in diameter, respectively, and smaller than those obtained by the solid-state method. We have succeeded in the synthesis of very fine particles of CaTiO3, SrTiO3, and BaTiO3 at a temperature 400 K lower than that required for the solid-state method.

Synthesis of Plate-Like SrTiO<sub>3</sub> Particles

Micro-scale plake-like SrTO3 particles were synthesized by two routes of topochemical conversion. One is by growing on Sr3Ti2O7 (S3T2) core particles in molten salt condition, and the other is from the layer-structured SrBi4Ti4O15 (SBT) precursor in a KCl medium. The effects of the morphology and size of the precursor to platelet SrTiO3 crystals were studied. X-ray diffraction analysis revealed that the crystallographic {010} plane of SBT was converted into the pseudo-cubic {001} plane of SrTiO3. The polycrystalline SrTiO3 particles from BST precursor exhibited a plate-like shape with 10-15μm in length and a high aspect ratio, and were more suitable for preparing textured ceramics by templated grain growth process than the platelets from the S3T2 precursors.