Pure La2Ti2O7 Research Articles

Microstructure and electrochemical hydrogen storage properties of nanosized doped La2Ti2O7 solid solutions

Hydrothermal-sintering method was employed to obtain pure and Li, Co, Mn, Cu and Zn doped La2Ti2O7 solid solutions. The substitution sites of doping ions are discussed. X-ray diffraction (XRD) results indicate that the doped ions were incorporated into the lattice of La2Ti2O7 successfully. Transmission electron microscopy (TEM) measurements prove that the doped ions with smaller radius induce the contraction of lattice. The results of UV and photoluminescence (PL) tests show that the doped ions cause the red-shift of band gap energies and enhance the concentrations of oxygen vacancies and defects. The electrochemical hydrogen storage properties of the samples were measured at 303 and 333 K, respectively. The discharge capacities of the doped samples keep growing by increasing the cycle number at 333 K. Meanwhile, the doped samples possess better kinetic performances than the pure La2Ti2O7. Among the samples, the Mn, Co and Li ions doped samples exhibit better electrochemical hydrogen storage properties. The hydrogen storage properties are closely related with the characteristics of doped ions, crystallite sizes, the content of the oxygen vacancies and defects in the lattice of La2Ti2O7.

A photochemical route in the synthesis and characterization of La2Ti2O7 and La2Ti2O7/AgO films and its evaluation in Congo red degradation and as antibacterial control to Staphylococcus aureus.

In this article, we propose a simple photochemical method to synthesize pure La2Ti2O7 films and La2Ti2O7 films doped with silver at 1.0, 3.0, and 5.0 mol%. After annealing the photo-deposited films at 900 °C, XRD, SEM, and XPS analyses showed the formation of a monoclinic La2Ti2O7 phase and the presence of Ag and AgO in doped samples. Photocatalytic tests for Congo red degradation demonstrated that pure La2Ti2O7 achieved 25.4% degradation, while doped samples reached a maximum of 92.7% degradation. Moreover, increasing silver doping on La2Ti2O7 films significantly reduced the growth of Staphylococcus aureus, indicating potential antibacterial properties. The enhanced photoactivity was attributed to the formation of a type I heterojunction between La2Ti2O7 and AgO, and a degradation mechanism was proposed based on Congo red degradation.

Preparation of La2Ti2O7 by Sol-Gel Method and Its Photocatalytic Activity

Using lanthanum nitrate, butyl titanate and citric acid as the main raw materials, lanthanum titanate (La2Ti2O7) was successfully prepared by sol-gel method. The samples were characterized by thermogravimetric differential thermal analysis (TG-DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Fourier infrared spectroscopy (FT-IR). Using 10 mg/L azo dye methyl orange solution as simulated sewage, the photocatalytic activity of La2Ti2O7 was studied by changing the synthesis temperature and light time under ultraviolet light. The results show that pure La2Ti2O7 samples can be obtained at 600 °C∼900 °C. SEM showed that La2Ti2O7 was dominated by irregular particles, and the average grain size was 4 ∼ 6μm. The La2Ti2O7 samples are consistent with approximation zero order kinetic for the degradation of methyl orange. The photocatalytic results showed that the photocatalytic activity of La2Ti2O7 prepared by calcination at 800 °C and 900 °C for methyl orange solution was significantly better than that of other temperature sections. The photocatalytic activity of La2Ti2O7 calcined at 900 °C was the best, and the degradation rate of methyl orange reached about 95% for degradation 60 min. This indicates that La2Ti2O7 is a novel photocatalyst with wide application prospects in the field of UV photocatalysis.

Shock synthesis of nanocrystalline La2Ti2O7 powder

Perovskite La2Ti2O7 nanocrystalline powder was obtained through the shock synthesis method. In the study, La2O3 and TiO2 powders were mixed through ball milling and, subsequently, shocked by a flyer at a velocity of 3.2 km/s. After shock treatment, the sample was recovered and characterized via various techniques, such as x-ray diffraction, Raman, scanning electron microscope, transmission electron microscope, and ultraviolet-visible diffuse reflection spectrum analysis, to find the presence of La2Ti2O7 nanocrystalline powder with an average grain size of approximately 30 nm in the recovered samples with different yields. Moreover, the results further confirm that the high shock temperature and long ball milling treatment induce higher activation of precursors to improve the La2Ti2O7 content in the recovered samples. By adjusting the relative density of precursor and the ball milling period, pure La2Ti2O7 nanocrystalline powder was obtained. The formation mechanism of La2Ti2O7 was carefully illustrated. This study presents a new method to synthesize La2Ti2O7 nanocrystalline powder by detonation-driven flyer impact.

Thermoelectric Study of La2Ti2-xNbxO7 (0≤x≤0.25) Ceramic Materials

La2Ti2-xNbxO7 (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25) powders were synthesised via solid state reaction method, followed by sintering at 1673 K in a reducing atmosphere of 5% H2/N2 gas. The crystal structure, microstructure and thermoelectric (TE) properties of the pure and Nb-doped La2Ti2O7 ceramics were investigated. All compositions were single phase with porous microstructures consistent with their low experimental densities. Thermoelectric results of Nb-doped compositions showed improved properties in comparison to pure La2Ti2O7, suggesting that cation doping has the potential to improve the thermoelectric properties. Generally, the TE results obtained are not suitable for thermoelectric applications. However, the high Seebeck coefficient (≥190 μV/K) and glass-like thermal conductivity ( ≤2.26 w / m.k ) values achieved have opened a new window for exploring the thermoelectric potentials of La2Ti2O7 and other related oxides.

Hierarchically 1D CdS decorated on 2D perovskite-type La2Ti2O7 nanosheet hybrids with enhanced photocatalytic performance

In this paper, a heterojunction of hierarchically one-dimensional (1D) cadmium sulfide (CdS) nanowires decorated on the two-dimensional (2D) La2Ti2O7 (LTO) has been fabricated by a simple two-step hydrothermal process. The structure, morphology and surface chemical composition of CdS/LTO were studied by a variety of characterizations, in which the X-ray photoelectron spectroscopy (XPS) results showed a strong interaction between CdS and LTO through S–O bonds. The type II band alignment of CdS/LTO for favorable electron transfer from CdS to LTO and hole transfer from LTO to CdS was clarified by ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy and Mott–Schottky (M–S) plot measurements. In the absence of any co-catalyst, H2 production from water splitting and Rhodamine B (RhB) decomposition in aqueous solution were carried out to evaluate the photocatalytic activities, showing that the photocatalytic performance of CdS/LTO was superior to that of pure LTO and CdS under visible light and simulated sunlight. The optimal CdS content in the CdS/LTO system was determined to be 7.5 wt%. The present results show an effective pathway to design a 1D/2D heterojunction photocatalyst in the face of overwhelming problems of energy crisis and environmental pollution.

Improved Electrical Properties of Layer Structured La2Ti1.96V0.04O7 Ceramics

La2Ti1.96V0.04O7 (LTVO) ceramics with Ti4+ ions partially substituted by V5+ ions at B sites show excellent electrical properties. The dopant V5+ ions do not result in collapse of the cell layered structure, but they lead to the enhanced distortions of BO6 oxygen octahedrons. Impedance spectroscopy reveals that a certain number of defects are formed due to the substitution of Ti4+ ions by V5+ ions. Meanwhile, the concentration of oxygen vacancies is decreased compared to pure La2Ti2O7 (LTO) ceramics. The direct current resistivity of LTVO ceramics obtained from alternating current (AC) impedance fitting at 600°C is 1.3 × 106 Ω cm, which is more than five times of that of the pure LTO at the same temperature (2.2 × 105 Ω cm). The substitution of Ti4+ ions by V5+ ions greatly enhances the piezoelectric coefficient, d33 = 4.8 pC/N. Therefore, the doping of V5+ ions in the B sites of LTO ceramics should be a good choice for enhancing their piezoelectric properties and resistivity at high temperature regimes.

Ti3 C2 : An Ideal Co-catalyst?

How 2D Ti3 C2 enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti3 C2 , rather than 2D Ti3 C2 itself, that play the role of co-catalyst for La2 Ti2 O7 /Ti3 C2 (LTC) composites during the photocatalytic reaction. After modification of Ti3 C2 derivatives, the photocatalytic efficiency of La2 Ti2 O7 is enhanced 16 times over pure La2 Ti2 O7 . Solid-state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti3 C2 and LTC composites. The GQDs are formed during the chemical change from Ti3 AlC2 to Ti3 C2 via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp2 π-conjugation GQDs. 2D Ti3 C2 is completely oxidized to COx modified TiOx species, causing Ti3 C2 to lose its electrical conductivity and the role as co-catalyst. GQDs largely suppress the photogenerated charge recombination of La2 Ti2 O7 , as revealed by the photoluminescence (PL) and transient photocurrent.

Ti3C2: An Ideal Co‐catalyst?

AbstractHow 2D Ti3C2 enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti3C2, rather than 2D Ti3C2 itself, that play the role of co‐catalyst for La2Ti2O7/Ti3C2 (LTC) composites during the photocatalytic reaction. After modification of Ti3C2 derivatives, the photocatalytic efficiency of La2Ti2O7 is enhanced 16 times over pure La2Ti2O7. Solid‐state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti3C2 and LTC composites. The GQDs are formed during the chemical change from Ti3AlC2 to Ti3C2 via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp2 π‐conjugation GQDs. 2D Ti3C2 is completely oxidized to COx modified TiOx species, causing Ti3C2 to lose its electrical conductivity and the role as co‐catalyst. GQDs largely suppress the photogenerated charge recombination of La2Ti2O7, as revealed by the photoluminescence (PL) and transient photocurrent.

Synthesis of visible-light-driven g-C3N4/La2Ti2O7 heterojunction photocatalysts for improved photocatalytic performance

The investigation of photocatalysts used in degrading organic pollutant is highly valuable for ameliorating the environmental pollution. Herein, the g-C3N4/La2Ti2O7 heterojunction was successfully fabricated by an impregnation route. The as-obtained composite g-C3N4/La2Ti2O7 presents photocatalytic properties for degradation of the model organic pollutant rhodamine B (RhB) under visible light irradiation. A sequence of characterizations confirmed that the g-C3N4/La2Ti2O7 has an enhanced capability of light absorption than pristine g-C3N4 and La2Ti2O7. In the photocatalytic experiment, the degradation rate of RhB by 10% g-C3N4/La2Ti2O7 (g-C3N4 accounts for 10% in the total mass) composite is about 90%, which is 5 times pure La2Ti2O7 and 3 times pure g-C3N4. This impressive improvement could be ascribed to the formation of a heterostructure between La2Ti2O7 and g-C3N4, and improved migration efficiency of photogenerated electrons and holes.

Synthesis of novel visible-light-driven p-n type heterojunction Cr2O3/La2Ti2O7 photocatalysts with improved photocatalytic performance

In this work, a series of Cr2O3/La2Ti2O7 composite photocatalysts were fabricated via a simple two-step method; their morphology, crystalline structure and optical property were characterized respectively. Compared with the pure La2Ti2O7, all the as-prepared nanocomposites exhibited much higher photocatalytic activity in degradation of different pollutants under visible light irradiation, and the optimal mass ratio of Cr2O3 was 14%. The pseudo-first-order model was applied to further evaluate the photocatalytic activity of composites for Rhodamine B (RhB) and reactive brilliant red X-3B (X-3B) degradation reaction. In addition, the photocurrent and photoluminescence (PL) were measured, respectively. And the active species participated in photocatalytic process were demonstrated by trapping test.

Visible-light-driven heterojunction photocatalysts based on g-C3N4 decorated La2Ti2O7: Effective transportation of photogenerated carriers in this heterostructure

Lanthanide titanate (La2Ti2O7) with strong reduction-oxidation ability has been regarded as a new promising photocatalyst. To boost its photocatalytic activity, g-C3N4/La2Ti2O7 composites were designed and constructed. The results reveal that La2Ti2O7 nanosheets were well attached to the surface of g-C3N4 and the composites had good visible-light absorption properties. Significantly, compared to pure La2Ti2O7 and g-C3N4, the composites exhibited outstanding photocatalytic performance under visible-light irradiation. The enhanced photocatalytic activity could be derived from the effective transportation of photogenerated electrons from g-C3N4 to La2Ti2O7. The electrons with high reduction ability can generate more active species to participate in the photodegradation reaction.

Fractional precipitation synthesis and photoluminescence of La2Ti2O7:xEu3+ phosphors

Eu3+ ions activated La2Ti2O7 (La2Ti2O7:xEu3+) phosphors have been successfully synthesized by a fractional precipitation method from commercially available La2O3, Eu2O3, HNO3, Ti(SO4)2·9H2O and NH3·H2O as the starting materials. Detailed characterizations of the synthetic products were obtained by fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), differential thermal analysis, thermogravimetry and derivative thermogravimetry (DTA-TG-DTG), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. The results show that the precursor is composed of amorphous particles with quasi-spherical in shape and about 50 nm in size. Moreover, the precursor could be converted into pure La2Ti2O7 phase by calcining at 1000 °C for 2 h in air. The as-synthesized La2Ti2O7 particles are approximate polyhedron in shape and about 100–200 nm in size. PL spectroscopy of La2Ti2O7:xEu3+ phosphors reveals that the strongest emission peak is located at 616 nm under 275 nm ultraviolet (UV) light excitation, which corresponds to the 5D0→7F2 transition of Eu3+ ions. The quenching concentration of Eu3+ ions is 10.0 mol%, and its corresponding fluorescence lifetime was 1.82 ms according to the linear fitting result. Decay study reveals that the 5D0→7F2 transition of Eu3+ ions has a single exponential decay behavior.

Enhanced Solar Hydrogen Generation by a Heterojunction of Perovskite-type La2 Ti2 O7 Nanosheets Doped with CdS Quantum Dots.

A heterojunction of a perovskite-type La2 Ti2 O7 (LTO)/CdS quantum dot (QD) nanocomposite was prepared by the chemical bath deposition method. The solar-light-driven H2 generation results show that this CdS QDs/LTO heterojunction exhibits great improvement in the photocatalytic H2 production and its photoelectrochemical properties in comparison with pure CdS QDs and LTO nanosheets. A possible enhanced mechanism of photoinduced interfacial charge transfer between CdS and LTO is proposed for the heterojunction. The shift of the CdS conduction band (CB) edge can enlarge the CB potential difference between CdS QDs and LTO, enhancing transferred driven force of the interfacial electrons and finally improving the two components' separation activity of photogenerated carriers. This study provides a promising method for constructing an efficient photoinduced interfacial charge transfer over LTO and CdS QD heterojunctions for photocatalytic hydrogen production.

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

The solubility and ferroelectric properties of (AxLa1−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 (AxLa1−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 (SmxLa1−x)Ti2O7 (x = 0.9) consisted of (SmxLa1−x)2Ti2O7 with PLS and pure Sm2Ti2O7 with pyrochlore structure, and the biphases of (EuxLa1−x)Ti2O7 (x = 0.6, 0.7, and 0.8) consisted of (EuxLa1−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 (Sm0.1La0.9)Ti2O7.

Nitrogen-doped perovskite-type La2Ti2O7 decorated on graphene composites exhibiting efficient photocatalytic activity toward bisphenol A in water

Nitrogen-doped lanthanum titanate decorated on graphene sheets (GR/N-doped La2Ti2O7) used as photocatalyst was prepared by a two-step process. To synthesize GR/N-doped La2Ti2O7, La2Ti2O7 was initially developed under heat treatment in NH3 and subsequently decorated on GR by hydrothermal processing. The resulting GR/N-doped La2Ti2O7 was characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Characterization results indicated that N-doped La2Ti2O7 was approximately 6–8nm thick with single-crystalline perovskite structure and chemically attached onto GR nanosheets by the formation of TiN bond, TiC bond, and oxynitrides. The application of GR/N-doped La2Ti2O7 composites to bisphenol A decomposition exhibits high photocatalytic efficiency under irradiation compared with pure La2Ti2O7 materials. This finding was due to the synergistic effect of great adsorption, enhanced light absorption, efficient charge separation and transfer processes in the presence of GR, and reduced band gap energy because of N doping. This study provides new insights into the fabrication and practical application of high-performance photocatalysts in wastewater treatment.

Reduced thermal conductivity by nanoscale intergrowths in perovskite like layered structure La2Ti2O7

The effect of substitution and oxidation-reduction on the thermal conductivity of perovskite-like layered structure (PLS) ceramics was investigated in relation to mass contrast and non-stoichiometry. Sr (acceptor) was substituted on the A site, while Ta (donor) was substituted on the B site of La2Ti2O7. Substitution in PLS materials creates atomic scale disorders to accommodate the non-stoichiometry. High resolution transmission electron microscopy and X ray diffraction revealed that acceptor substitution in La2Ti2O7 produced nanoscale intergrowths of n = 5 layered phase, while donor substitution produced nanoscale intergrowths of n = 3 layered phase. As a result of these nanoscale intergrowths, the thermal conductivity value reduced by as much as ∼20%. Pure La2Ti2O7 has a thermal conductivity value of ∼1.3 W/m K which dropped to a value of ∼1.12 W/m K for Sr doped La2Ti2O7 and ∼0.93 W/m K for Ta doped La2Ti2O7 at 573 K.

Room temperature multiferroic properties of Mn doped La2Ti2O7

Polycrystalline La2Ti2-xMnxO7 (LTMO) (x = 0−0.16) ceramics fabricated by the conventional solid-state reaction are utilized to investigate the effect of Mn doping on the ferroelectric (FE) and ferromagnetism (FM) systematically. Both the FE and FM properties strongly depend on the doping level of Mn atoms, which directly induces a structural phase transition from monoclinic to orthorhombic. Compared with pure La2Ti2O7 (LTO), remnant polarization decreases sharply with the doping level at first, and slightly increases when x ≥ 0.08, which is proposed to result from the evolution oxygen vacancies. All the doped samples exhibit weak FM property at room temperature, until the maximum can be observed for x = 0.08. Mn3+-Mn4+ double-exchange and anti-FM Mn3+-Mn3+ and Mn4+-Mn4+ super-exchange interactions are responsible for the different ferromagnetic behavior of LTMO.

Mixed Hydroxide Precursors for La2Ti2O7 and Nd2Ti2O7 by Homogeneous Precipitation

Feasibility of formation of stoichiometric precursors of either M2 (TiO)2(C2O4)5 4H2O (M = La and Nd) or coprecipitated hydroxides of M(OH)3+TiO(OH)2 was investigated by two solution routes at different pH values. Composition of precipitates obtained at pH = 7.0 by coprecipitation method starting from La or Nd nitrates and potassium titanyl oxalate corresponded to a physical mixture of La or Nd(C2O4)3 9.5H2O and TiO(OH)27·H2O which on thermal decomposition did not yield phase pure M2Ti2O7. However, precipitation from La or Nd nitrates and titanium tertrachloride by urea hydrolysis yielded homogeneous mixture of hydroxides of La or Nd and Ti, which on pyrolysis at 950°C yielded phase pure La2Ti2O7 and Nd2Ti2O7. Use of potassium titanyl oxalate as precursor for Ti, led to selective precipitation of La or Nd oxalate even at pH as low as 0.1 leading to sequential precipitation of La or Nd oxalate followed by Ti hydroxide at pH = 3.0. The resultant precipitate on pyrolysis underwent typical solid-state reaction.