Photocatalytic La4Ti3O12 nanoparticles fabricated by liquid-feed flame spray pyrolysis

Hexagonal plate-like nanoparticles (NPs) of the layered perovskite La₄Ti₃O₁₂ were fabricated using liquid-feed flame spray pyrolysis (LF-FSP) followed by subsequent heat-treatments. Their photocatalytic activity was evaluated using decolorization of methyl orange solutions under Uv irradiation. LF-FSP combusts metalloorganic precursor aerosols to produce mixtures of cubic simple perovskite (ABO₃) phase and lanthanum oxycarbonate (La₂O_4·846C_0.846) phase with very low agglomeration and average particle sizes (APSs) of 23 nm (as-produced NPs). Rietveld refinement of synchrotron XRD powder patterns verified that the simple perovskite in the as-produced NPs is LaTiO₃ (originally cubic Pm-3m-type space group) and heat-treating gives NPs of the trigonal layered perovskite La₄Ti₃O₁₂ (R-3-type space group). La₄Ti₃O₁₂ NPs heat-treated at 1100 °C/3-6h/air exhibits hexagonal plate-like morphology and high crystallinity offering enhanced photocatalytic degradation of methyl orange solutions compared to the as-produced NPs. The LF-FSP approach to obtaining layered perovskite La₄Ti₃O₁₂ NPs provides a simple route to photocatalytic materials in reasonable quantities.     

Effect of precursors on the morphology and the photocatalytic water-splitting activity of layered perovskite La2Ti2O7

A [110] layered perovskite, La₂Ti₂O₇, was a good photocatalyst under ultraviolet light in water splitting reaction. The material was synthesized with La₂O₃ and TiO₂ as precursors by solid-state transformation. The morphology and photocatalytic activity of La₂Ti₂O₇ depended on the preparation methods, as well as purity and morphology of the precursors. Wet-grinding of precursors in ethanol gave a product with higher crystallinity and phase purity, and thus higher photocatalytic activity, than dry-grinding without solvent. It was important to reduce the particle size of La₂O₃, as it usually had larger initial particle sizes than TiO₂. Thus, the particle size of La₂O₃ had a strong effect on the crystallinity and surface area of the product La₂Ti₂O₇. On the other hand, a severe chemical purity control was required for TiO₂, while the effect of morphology was relatively small. In all cases, a high degree of crystallinity and purity of the prepared La₂Ti₂O₇ was critical to show a high photocatalytic water-splitting activity.     

Photocatalytic Water Splitting over La2Ti2O7 Synthesized by the Polymerizable Complex Method

Highly donor-doped (110) layered perovskite materials, La₂Ti₂O₇, with high surface areas were synthesized by the polymerizable complex (PC) method. Relative to La₂Ti₂O₇ prepared by the solid state reaction (SSR) method, PC catalysts showed higher surface areas, crystallization at lower temperatures, higher phase purity, more uniform morphology and better-distributed nickel on the outer surface of La₂Ti₂O₇. All these factors led to higher photocatalytic activity for overall water splitting under UV irradiation. The quantum yield of the reaction over La₂Ti₂O₇ prepared by the PC method was as high as 27%, which was about twofold greater than that over La₂Ti₂O₇ prepared by the SSR method.     

Photocatalytic Oxidation of Isopropanol in Aqueous Solution Using Perovskite‐Structured La2Ti2O7

This study is focused on the application of a highly‐doped layered perovskite, La₂Ti₂O₇, as the photocatalyst for the photocatalytic decomposition of isopropanol (IPA). The La₂Ti₂O₇ powder prepared by solid state reaction was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), UV‐Vis diffuse reflectance spectrophotometry (UV‐DRS), X‐ray photoelectron spectroscopy (XPS), and zeta potential. The temporal behavior of the photocatalytic decomposition of IPA in aqueous solution by the UV/La₂Ti₂O₇, with a photoreactor operated in a recirculation mode, was studied under various conditions including solution pH, light intensity, and La₂Ti₂O₇ loading. The decomposition of IPA in aqueous solution by La₂Ti₂O₇ photocatalytic processes was found to be technically feasible. A kinetic equation was developed for modeling the photocatalytic decomposition of IPA by the UV/La₂Ti₂O₇ photocatalytic processes.     

Effect of Zr Substitution for Ti in KLaTiO4 for Photocatalytic Water Splitting

The effect of substitution of Zr for Ti in KLaTiO₄ with a layered perovskite structure has been studied on the photocatalytic decomposition of water under the UV light irradiation. Both the optical property and the crystallinity of KLaTiO₄ were varied by the substitution of Zr for Ti. As Zr content was increased, the crystallinity of KLaZr_xTi_1-xO₄ was increased, which had a positive effect on the photocatalytic activity in the water splitting reaction. However, the direct band gap property was lost gradually with increase of Zr content, which resulted in lowering the photocatalytic activity. As a result, the highest activity was obtained for KLaZr_0.3Ti_0.7O₄. Although the absorption coefficients of photons for KLaZr_0.1Ti_0.9O₄ and KLaTiO₄ were higher than those for KLaZr_0.3Ti_0.7O₄, the crystal structure was disordered, which resulted in lowering the activity. The nickel-loaded catalysts showed a higher activity than unloaded perovskites by a factor of greater than 2.     

Influence of orientation and ferroelectric domains on the photochemical reactivity of La2Ti2O7

The effects of crystal orientation and ferroelectric domain structure on the photochemical reactivity of La₂Ti₂O₇ have been measured. Electron backscattered diffraction was used to determine the orientations of the surfaces of crystals in a ceramic specimen, piezo-force microscopy was used to determine the domain structure, and the photocathodic reduction of silver from an aqueous silver nitrate solution was used to evaluate the photochemical reactivity. The reactivity is greatest on (001) surfaces (this is the orientation of the layers in this (110)_p layered perovskite structure) while surfaces perpendicular to this orientation have the least reactivity. Complex domain structures were observed within the grains, but they appeared to have no effect on the photocathodic reduction of silver, in contrast to previous observations on other ferroelectrics. La₂Ti₂O₇ is an example of a ferroelectric oxide in which the crystal orientation has a greater influence on the photochemical reactivity than polarization from the internal domain structure.     

Phase stability and equilibria in the La2O3–TiO2 system

XRD, electron probe wavelength and energy dispersive X-ray analyses were used to reexamine the phase relations in the La₂O₃–TiO₂ system. The diagram was redrawn to include the compound La₄Ti₃O₁₂ in addition to La₄Ti₉O₂₄, La₂Ti₂O₇ and La₂TiO₅. Above 1455°C a cation deficient perovskite La_2/3TiO₃ is stabilized by a small number of Ti³⁺ ions and remains stable on cooling in air. The proposed diagram represents a section through the system at the normal oxygen pressure in air at 1 atm, compositions being expressed in terms of the oxide components stable at room temperature.     

Formation of La<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> crystals from amorphous La<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> powders synthesized by the polymerized complex method

Amorphous La₂O-TiO₂ powders were synthesized by the polymerized complex (PC) method. The activation energies for crystallization and grain growth of La₂Ti₂O₇ from these precursors were determined from results of XRD and DTA and compared with those for La₂Ti₂O₇ precursors by the conventional solid-state reaction (SSR). Activation energy of grain growth of La₂Ti₂O₇ in PC-sample was determined to be 7.1 kJ/mol while that of SSR sample was 14.8 kJ/mol. The energy required for the phase transformation from amorphous PC sample to layered perovskite was 432 kJ/mol, while the SSR sample did not show this transition below 900‡C. It was clearly demonstrated that the La₂Ti₂O₇ crystals were formed at a lower temperature and they grew in size faster in the sample prepared by the PC method relative to the sample prepared by the SSR method. Mixing of elements in molecular level in PC preparation appeared responsible for these differences.     

Crystallographic Structure and Ferroelectricity of (AxLa1−x)2Ti2O7 (A = Sm and Eu) Solid Solutions with High Tc

The solubility and ferroelectric properties of (A_xLa_1?x)₂Ti₂O₇ (A = Sm and Eu) solid solutions were investigated. The crystallographic structure of the solid solutions was studied using X‐ray diffraction and Raman spectroscopy. The solubility limits of Eu and Sm in (A_xLa_1?x) ₂Ti₂O₇ were found to be greater than x = 0.5 and 0.8, respectively. The solid solutions had a monoclinic perovskite‐like layered structure (PLS), similar to that of the pure La₂Ti₂O₇, when x was less than the solubility limit. When x was above the solubility limit the materials were biphase. The biphases of (Sm_xLa_1?x)Ti₂O₇ (x = 0.9) consisted of (Sm_xLa_1?x)₂Ti₂O₇ with PLS and pure Sm₂Ti₂O₇ with pyrochlore structure, and the biphases of (Eu_xLa_1?x)Ti₂O₇ (x = 0.6, 0.7, and 0.8) consisted of (Eu_xLa_1?x)₂Ti₂O₇ with PLS structure and La³⁺ doped Eu₂Ti₂O₇ with pyrochlore structure. The effect of A‐site substitution on the properties of La₂Ti₂O₇ was investigated by measuring the dielectric permittivity and loss at different frequencies and temperatures. The highest piezoelectric constant d₃₃ was 2.8 pC/N for (Sm_0.1La_0.9)Ti₂O₇.     

BiOCl nanosheet/Bi4Ti3O12 nanofiber heterostructures with enhanced photocatalytic activity

Aurivillius oxide semiconductors are important photocatalyst because of their unique electronic structure and layered crystal. In this paper, two kinds of Aurivillius oxide semiconductors heterostructures based on Bi₄Ti₃O₁₂ nanofibers frameworks and BiOCl nanosheets are successfully synthesized by combining the electrospinning technique and solvothermal method. The high-resolution transmission electron microscopy results reveal that an intimate interface between Bi₄Ti₃O₁₂ nanofibers and BiOCl nanosheets forms in the heterojunctions. Photocatalytic tests show that the BiOCl/Bi₄Ti₃O₁₂ heterostructures exhibit enhanced photocatalytic activity than bare Bi₄Ti₃O₁₂ and BiOCl, mainly owing to the photoinduced interfacial charge transfer based on the photosynergistic effect of the BiOCl/Bi₄Ti₃O₁₂ heterojunction. At the end, the photocatalytic mechanism with O₂⁻ production was studied.     

Facile one-pot synthesis of porous Ln2Ti2O7 (Ln = Nd,Gd, Er) with photocatalytic degradation performance for methyl orange

Porous nanocrystalline Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was prepared by a facile self-propagating combustion method using metal nitrates (Ln(NO₃)₃ (Ln = Nd, Gd, Er), TiO(NO₃)₂) and glycine. The photocatalytic activity of Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) was evaluated by the photocatalytic degradation of methyl orange (MO). The results showed that the photocatalytic activity of Ln₂Ti₂O₇ (Ln = Gd, Er) with cubic pyrochlore structure was higher than that of Nd₂Ti₂O₇ with monoclinic perovskite structure and Gd₂Ti₂O₇ showed the best photocatalytic activity. The different photocatalytic activities observed for Ln₂Ti₂O₇ (Ln = Nd, Gd, Er) could be related to its different crystal structures and Ln 4f shells.     

Preparation of ZnIn2S4/K2La2Ti3O10 composites and their photocatalytic H2 evolution from aqueous Na2S/Na2SO3 under visible light irradiation

ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were synthesized via a hydrothermal route. The photocatalysts were characterized by the X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis) diffuse reflection spectra and photoluminescence measurements. The UV–vis results indicated that ZnIn₂S₄/K₂La₂Ti₃O₁₀ has a strong absorption in the visible light region. The compositions of ZnIn₂S₄/K₂La₂Ti₃O₁₀ composite photocatalysts were optimized according to the photocatalytic activity for hydrogen production from aqueous Na₂S/Na₂SO₃. The composite photocatalyst loading 25 wt.% ZnIn₂S₄ exhibited the highest photocatalytic activity, the amount of H₂ production was 6.29 mmol/g after 3 h irradiation under visible light irradiation.     

Phase transition of Eu2Ti2O7 under high pressure and a new ferroelectric phase with perovskite‐like layered structure

Ferroelectrics with perovskite‐like layered (PL) structure are well‐known for their high T_c and the application prospect of high‐temperature‐piezoelectric sensing. In this study, the PL‐structure Eu₂Ti₂O₇ was prepared by 1‐step high‐pressure sintering, which show the pyrochlore structure of Eu₂Ti₂O₇ would change into PL structure at 11 GPa, 1300°C. The PL‐structure Eu₂Ti₂O₇ is metastable, which will change back to pyrochlore structure at about 900°C in the air. The PL‐structure Eu₂Ti₂O₇ was confirmed as a high‐temperature ferroelectric material for the first time. The ferroelectric domain switching was directly observed using piezoelectric force microscope. The piezoelectric constant of the PL Eu₂Ti₂O₇ ceramic was measured as 0.7‐0.9 pC/N and its thermal depoling temperature (T_d) was determined as 800°C, which is associated with the PL‐pyrochlore transition.     

Effects of Nickel-Loading Method on the Water-Splitting Activity of a Layered NiO x /Sr4Ti3O10 Photocatalyst

Sr₄Ti₃O₁₀, which is known to have a Ruddlesden-Popper phase as a layered perovskite-type oxide, showed activity leading to the decomposition of pure water into H₂ and O₂ without any co-catalyst, when irradiated with light under 395 nm. When NiO _x was loaded onto Sr₄Ti₃O₁₀ both by the impregnation (I) method and the vapor deposition (VD) method, this photocatalytic activity drastically increased. Nickel acetylacetonate, when used with the VD method, was found to give rise to more efficient photocatalytic activity than that obtained using nickel nitrate with the impregnation method.     

Synthesis and photocatalytic properties of H2La2Ti3O10/TiO2 intercalated nanomaterial

H₂La₂Ti₃O₁₀/ TiO₂ intercalated nanomaterial was fabricated by successive intercalation reactions of H₂La₂Ti₃O₁₀ with n-C₆H₁₃NH₂/C₂H₅OH mixed solution and acid TiO₂ sol, followed by irradiating with a high-pressure mercury lamp. The intercalated materials possess a gallery height of 0.46 nm and a specific surface area of 31.58 m²·g⁻¹, which indicate the formation of a porous material. H₂La₂Ti₃O₁₀/TiO₂ shows photocatalytic activity for the decomposition of organic dye under irradiation with visible light and the activity of TiO₂ intercalated material was superior to the unsupported one.     

Synthesis,structure and electrochemical properties of Al doped high entropy perovskite Lix(LiLaCaSrBa)Ti1-xAlxO3

In this work, the Al doped high entropy perovskite Li_0.2La_0.2Ca_0.2Sr_0.2Ba_0.2TiO₃ ceramic is synthesized by using a solid state reaction method, and the effect of different doping amount on the crystal structures and conductivity are also studied. The result proves that doping leads to a positive influence on the conductivity of ceramic. The material of Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ (LLCSBTA-0.1) exhibits a high total conductivity with approximately 3.92 × 10^-7 S cm^-1 at 30 °C and an activation energy of 0.39 eV. The beneficial result can be ascribed to the increase of Li ⁺ concentration. The Li_0.2La_0.2Ca_0.2Sr_0.2Ba_0.2TiO₃ presents a pure cubic perovskite structure, but with partial tetragonal structure due to the addition of Al₂O₃. However, these high entropy perovskite ceramics showed porous structures which are unfavourable for lithium ion conduction. The electrochemical property of the Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ as electrode is investigated as well. The results show that the Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ electrode exhibits good cyclability and stability for the insert-extraction of lithium ions with the specific capacity of 58.6 mA h g^?1.     

Effect of B‐site cation on the catalytic activity of La1−xCaxBO3 (B = Fe,Ni) perovskite‐type oxides for toluene combustion

Background The effect of the B cation on the surface properties and catalytic activity in the total combustion of toluene over La_1?xCa_xBO₃ (B = Fe,Ni) perovskite‐type oxides was studied. Result For the La_1?xCa_xFeO₃ series, the perovskite structure was maintained in the range of substitution studied. A completely different behaviour was observed for the La_1?xCa_xNiO₃ series. A Brownmillerite‐type structure (La₂Ni₂O₅) with a large degree of phase segregation as well dispersed mixed oxides was observed upon the substitution of La for Ca. In the Fe series, the catalytic activity in the total combustion of toluene showed that the insertion of calcium ions into the perovskite lattice resulted in higher activity relative to the unsubstituted LaFeO₃ perovskite. In contrast, for the Ni series, substitution results in solids with lower activity than the pure LaNiO₃ perovskite. Conclusion For the Fe series, higher activity and stability are attributed to a synergy between Fe⁴⁺/Fe³⁺ and the oxygen vacancies generated by the calcium substitution. For the Ni counterpart, the structural modification leads to a lower activity of substituted solids compared with the pure LaNiO₃ perovskite, indicating that Ni³⁺ ions are the active sites for toluene oxidation. Copyright © 2011 Society of Chemical Industry     

Study on La2(Hf1-xTix)2O7 (x ≤ 0.20) pyrochlores for potential thermal/environmental barrier coating applications

Lanthanum hafnate (La₂Hf₂O₇) with a pyrochlore structure has excellent high temperature stability and low thermal conductivity, which is promising for thermal/environmental barrier coatings (T/EBCs) applications. To reduce its thermal expansion coefficient (TEC) so as to better match SiC_f/SiC composites, a smaller tetravalent dopant Ti⁴⁺ has been introduced in the Hf-sites to form La₂(Hf_1-xTi_x)₂O₇ (x ≤ 0.20). The phase composition and microstructure confirms that La₂(Hf_1-xTi_x)₂O₇ solid solutions possess a pure pyrochlore structure. With an increase of x, their TECs are decreasing consistently, whilst their thermal conductivities of La₂(Hf_1-xTi_x)₂O₇ are slightly increasing at high temperature but still much lower than those of meta-stable yttria partially stabilized zirconia, both of which are attributing to an increase of elastic modulus after Ti⁴⁺ doping on Hf-sites. The extremely excellent high temperature stability, relatively low thermal conductivities and low TECs suggest that La₂(Hf_1-xTi_x)₂O₇ is a prospective candidate material for T/EBC applications.     

A novel series of photocatalysts with an ion-exchangeable layered structure of niobate

Ion-exchangeable niobates, A(M _n–1Nb _n O_3n+1) (A = Na, K, Rb, Cs; M = La, Ca etc.), with a layered perovskite structure are found to show a unique photocatalytic activity, especially in those H⁺-exchanged forms, for H₂ evolution from aqueous alcohol solutions as well as O₂ evolution from an aqueous silver nitrate solution.     

Structural,morphological, and electrochemical behavior of titanium-doped SrFe1-xTixO3-δ (x = 0.1–0.5) perovskite as a cobalt-free solid oxide fuel cell cathode

Titanium, Ti-doped SrFe_1-xTi_xO_3-δ (x = 0.1–0.5) perovskite-structured ceramics were synthesized via solution combustion. The structural, morphological, and electrochemical behaviors of the as-synthesized materials were investigated to determine the applicability of SrFe_1-xTi_xO_3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction analysis confirmed the formation of a single-phase cubic perovskite structure. The unit volume of this perovskite structure increased as the amount of Ti dopant increased. Morphological analysis revealed that the porosity of the SrFe_1-xTi_xO_3-δ perovskite cathode film was inversely proportional to the amount of Ti dopant. The cathode SrFe_0·9Ti_0·1O_3-δ film exhibited a high porosity of 24.74 ± 0.52%, a low but acceptable hardness value of 0.70 ± 0.01 GPa and an area specific resistance of 0.57 Ω cm². These results suggested that cobalt-free SrFe_1-xTi_xO_3-δ cathode was still not good enough to be compared with the existing cobalt-containing cathode such as lanthanum strontium cobalt ferrite. But, the results obtained from this work can be considered as a major turning point as the literature works on SrFe_1-xTi_xO_3-δ cathode showed excellence electrochemical performance. The contradict result between the present and past studies proved that the use of SrFe_1-xTi_xO_3-δ cathode is worthy of being studied into details to confirm its capability.