Perovskite CaTiO3 Research Articles

High pressure dissociation of CaTiO3 perovskite into CaO and CaTi2O5

In this study, we investigated phase transformations of CaTiO3 perovskite using x-ray diffraction at high pressure and high temperature up to 170 GPa and 4500 K in a laser-heated diamond-anvil cell. We report a high-pressure dissociation of CaTiO3 into CaO-B2 and CaTi2O5 with a monoclinic P2/m structure, instead of the expected transformation of the orthorhombic distorted perovskite structure into a post-perovskite phase. We propose that this transition may be favored by the B1 to B2 phase change of CaO at around 60 GPa. In order to provide additional information on the high pressure properties of CaTiO3 perovskite, we measured its melting temperature using CO2 laser heated diamond anvil cell up to 55 GPa yielding a fit of the melting curve to a Kraut-Kennedy empirical law according to: Tm (K) = 2188 ∗ [1 + 4.23 ∗ (ΔV/V0)]. To provide some further insight into the thermodynamic properties of CaTiO3, we determined the P-V-T equation of state of the orthorhombic mineral perovskite, fitted by using a third order Birch-Murnaghan equation of state and a Berman thermal expansion model. The fit of the data yields to K0 = 180.6(4) GPa, K′0 = 4 (fixed), ∂K/∂T = −0.022(1) GPa K−1, α1 = 3.25(5) x 10−5 K−1, α2 = 1.3(1) x 10−8 K−2

Ab initio computations of BaZrO3, CaTiO3, SrTiO3 perovskite as well as WO3 and ReO3 (001) surfaces

We computed, at the ab initio level, BaZrO3, CaTiO3, SrTiO3 as well as WO3 and ReO3 (001) surfaces and analyzed systematic tendencies therein. As obtained by our ab initio hybrid DFT-HF computations, at BO2-terminated (001) surfaces of investigated ABO3 perovskites as well as WO3 and ReO3 oxides, all top-layer ions shift in the direction of the crystal bulk. The single-deviation from this tendency is upward shift of the WO2-terminated WO3 (001) surface top layer O ion by the magnitude of +0.42% of the bulk lattice constant a0. In contrary, all second layer ions, with the single exception of ReO2-terminated ReO3 (001) surface O ion, shifts upwards. Our computed BO2-terminated SrTiO3, CaTiO3, BaZrO3, WO3 and ReO3 (001) surface Γ–Γ band gaps always are smaller than their respective bulk Γ–Γ band gaps. The B–O ion chemical bond populations in the SrTiO3, CaTiO3 and BaZrO3 perovskite bulk are always smaller than at their nearby BO2-terminated (001) surfaces. On the contrary, the W–O and Re–O ion chemical bond populations in the WO3 (0.142e) and ReO3 (0.212e) bulk are slightly larger than at nearby the WO2- and ReO2-terminated WO3 and ReO3 (001) surfaces (0.108e and 0.170e). Nonetheless, the W–O and Re–O chemical bond populations between the W and Re ions located in the upper layer and the O ions located in the second layer of the WO2- and ReO2-terminated (001) surfaces (0.278e and 0.262e) are the absolutely largest bond populations in the WO3 and ReO3 crystals.

Refining perovskite structures to pair distribution function data using collective Glazer modes as a basis.

Structural modelling of octahedral tilts in perovskites is typically carried out using the symmetry constraints of the resulting space group. In most cases, this introduces more degrees of freedom than those strictly necessary to describe only the octahedral tilts. It can therefore be a challenge to disentangle the octahedral tilts from other structural distortions such as cation displacements and octahedral distortions. This paper reports the development of constraints for modelling pure octahedral tilts and implementation of the constraints in diffpy-CMI, a powerful package to analyse pair distribution function (PDF) data. The model in the program allows features in the PDF that come from rigid tilts to be separated from non-rigid relaxations, providing an intuitive picture of the tilting. The model has many fewer refinable variables than the unconstrained space group fits and provides robust and stable refinements of the tilt components. It further demonstrates the use of the model on the canonical tilted perovskite CaTiO3 which has the known Glazer tilt system α+β-β-. The Glazer model fits comparably to the corresponding space-group model Pnma below r = 14 Å and becomes progressively worse than the space-group model at higher r due to non-rigid distortions in the real material.

The factors controlling equilibrium inter-mineral Ca isotope fractionation: Insights from first-principles calculations

Equilibrium isotope fractionation factors are crucial to quantitatively interpreting Ca isotope data of natural samples. Recent studies have revealed significant equilibrium Ca isotope fractionation between minerals, but the controlling factors remain poorly understood. Using density functional theory, this study calculates the reduced partition function ratios (RPFRs) among amphiboles (richterite and tremolite), sorosilicates (akermanite and gehlenite), K-bearing carbonates (butschliite), Na-bearing diopside (jadeite), and other Ca-bearing minerals (fluorapatite, anhydrite, CaTiO3 perovskite, and fluorite) at 0 GPa. The RPFRs of diopside and anorthite over a pressure range from 0 to 5 GPa are calculated to investigate the pressure effect. The effect of force constant, bond length, coordination number, anion type, solid solution composition, and pressure on RPFRs are discussed by compiling the literature data. The RPFRs show good correlations with the force constant and bond length but have no clear correlation with the coordination number. This suggests that the bond length is more reliable than the coordination number for roughly predicting the signs and magnitudes of inter-mineral isotope fractionation. Na-bearing clinopyroxene (e.g., jadeite) has similar RPFR with Na-free clinopyroxene, suggesting that the jadeite effect should be insignificant in natural samples. The RPFR of anorthite is lower than that of diopside at low pressure, and the two minerals both show a positive correlation between RPFR and pressure. Notably, the heavy Ca isotope enrichment between these two minerals can be reversed at high pressure (>3 GPa at 1000 K) because anorthite’s RPFR changes more sharply with increasing pressure than that of diopside. However, such a reverse may not occur in Earth's modern crust due to the stability of anorthite at lower pressures. Combining the theoretical predictions of amphibole and plagioclase and natural sample observation on granitoids, we infer that the RPFR of granitic magma may be lower than that of basaltic magma.

Construction of CaTiO3 nanosheets with boron nitride quantum dots as effective photogenerated hole extractor for boosting photocatalytic performance under simulated sunlight

Herein, titanate-based perovskite CaTiO3 nanosheets were successfully designed via boron nitride quantum dots (BNQDs) to fabricate CaTiO3/BNQDs catalyst. The as-fabricated composite catalysts were analysed by transmission electron microscope (TEM), scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), X-ray diffraction (XRD), UV–vis spectroscopy (UV-DRS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) techniques. SEM-Mapping analysis showed that the boron and nitrogen elements dispersed well over the CaTiO3 surface which was useful for building electronic channels for rapid transport of photo-induced charge pairs. TEM images verified the attachment of BNQDs around the surface of host CaTiO3 forming intimate interface while the distribution of chemical states was observed by XPS analysis demonstrating strong coupling effect between BNQDs and CaTiO3 through Ti–O–N and Ti–O–B bonds. Moreover, PL and light absorption properties enhanced with the quantum confinement effect of BNQDs. As expected, the photocatalytic degradation rate of CaTiO3/BNQDs was increased to kapp = 0.015 min− 1 with optimum BNQDs loading, which was 2.31 times folder than that of bare CaTiO3 (0.006 min− 1). The enhanced photocatalytic efficiency was observed for CaTiO3/BNQDs than pristine perovskite on account of formation of electron tapping sites, decreased band gap energy and hindered recombination rate. On the other hand, in the presence of H2O2, the degradation percentage increased from 88.5% to 92.1% at the end of 120 min of irradiation while 96.8% of TC was quickly degraded within 60 min after activating with peroxymonosulfate which created strong sulphate radicals. Radical trapping tests indicated that the photo-generated holes were the primary active species in the photocatalytic mechanism. Moreover, CaTiO3/BNQDs catalyst showed excellent stability in recycling tests. Besides, the possible degradation mechanism was proposed. This study shed light on the significance of BNQDs in the enhancement of the photocatalytic activities of titanate-based perovskite for effective degradation of tetracycline antibiotic in contaminated water.

Synergistic effects of Eu and Nb dual substitution on improving the thermoelectric performance of the natural perovskite CaTiO3

Driven by the development of sustainable and regenerable energy conversion materials, the mineral perovskite (CaTiO3) is considered to be a potential candidate for large-scale high-temperature applications owing to its abundance, light-weight, non-toxicity, and low cost. A series of compounds with the nominal composition Ca1–xEuxTi0.9Nb0.1O3 (0 ≤ x ≤ 0.4) has been synthesized and studied in this paper. The phase purities and crystal structures were evaluated by powder X-ray diffraction (XRD) and subsequent Rietveld analysis. Through X-ray photoelectron spectroscopy (XPS) characterization, the by far dominating valence states of Ti and Nb are confirmed to be +4 and + 5 in Ca1-xEuxTi0.9Nb0.1O3 compounds, respectively. Dual substitution by Nb and Eu yields a synergistic effect of improving electrical transport properties and simultaneously suppressing thermal conductivity. The former is mainly attributed to the d–f electron exchange induced by the strong hybridization of Eu 4f, Nb 4d, and Ti 3d orbitals. The latter is mostly attributed to the dominant phonon scattering by the mass fluctuation originating from the large mass contrast of Eu and Ca. The results demonstrate the evolution of insulating CaTiO3 to metallic-like conduction performance with increasing Eu content. Due to the largest power factor and lowest thermal conductivity, the sample Ca0.8Eu0.2Ti0.9Nb0.1O3 exhibits the maximum ZT of up to 0.3 at around 1173 K.

CO2 methanation activity of Ni-doped perovskites

Nickel-doped CaTiO3 (Ni@CTO) perovskites were prepared by sol–gel synthesis and compared to traditional CTO-supported Ni catalysts during the CO2 methanation reaction. All the prepared materials were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction and CO2 temperature programmed desorption. Both types of catalysts showed activity in the CO2 methanation, being the most active those that showed a particle size less than 10 nm. These samples showed a CO2 conversion around 80%, with 100% selectivity to CH4. In addition, the activity of doped catalyst began at lower temperature, possibly due to the enhanced CO2 adsorption sites related to the formation of oxygen vacancies in the perovskite after nickel doping, and to its higher specific surface area. In addition, the 10Ni@CTO catalyst shows a high stability at 40 h of reaction, with only a 1% decrease in CO2 conversion, while the selectivity remained constant. The results showed that Ni@CTO doped perovskites are promising catalysts for methanation.

Controllable synthesis of bifunctional material Ca2Ti2O6:Eu3+ and its comparative study on luminescence and photocatalytic properties with CaTiO3:Eu3+

Pure pyrochlore Ca2Ti2O6, perovskite CaTiO3, and their mixed crystalline phases with different proportions were controllably synthesized via a solvothermal method, followed by a subsequent calcination process. RIR (reference intensity ratio) data of Ca2Ti2O6 were first obtained by X-ray diffraction (XRD), which can be used to quantitatively analyze the phase composition. When Eu3+ is doped into these calcium titanium oxides, they can be used as luminescent and photocatalytic materials. The structure, luminescence, and photocatalytic properties of pure pyrochlore Ca2Ti2O6:Eu3+ and perovskite CaTiO3:Eu3+ were comparatively studied in detail. The relative intensities of the excitation peaks and the emission peaks in Ca2Ti2O6:Eu3+ and CaTiO3:Eu3+ are different, which is attributed to the different symmetries of Eu3+ inhabiting the two kinds of lattices. In addition, although the luminescence intensity of CaTiO3:3%Eu3+ is higher than that of Ca2Ti2O6:3%Eu3+ under excitation at 394 nm, the luminescence intensity of Ca2Ti2O6:3%Eu3+ is superior to that of CaTiO3:3%Eu3+ under excitation at 464 nm and 533 nm. Photocatalytic experiments show that Ca2Ti2O6:3%Eu3+ has better photocatalytic performance than CaTiO3:3%Eu3+, which is mainly due to its smaller crystallite size, higher specific surface area and pyrochlore structure. In addition, biphase (Ca2Ti2O6–CaTiO3):3%Eu3+ has the best photocatalytic activity compared with the single phase Ca2Ti2O6:3%Eu3+ and CaTiO3:3%Eu3+, owing to the presence of heterojunctions that significantly reduced the band gap. It is anticipated that the discovery of this bifunctional Ca2Ti2O6:Eu3+ would expand the application of rare earth-doped calcium titanium oxide materials.

Solution chemistry quasi-epitaxial growth of atomic CaTiO3 perovskite layers to stabilize and passivate TiO2 photoelectrodes for efficient water splitting

Perovskite oxides with unique crystal structures and high defect tolerance are promising as atomic surface passivation layers for photoelectrodes for efficient and stable water splitting. However, controllably depositing and crystalizing perovskite-type metal oxides at the atomic level remains challenging, as they usually crystalize at higher temperatures than regular metal oxides. Here, we report a mild solution chemistry approach for the quasi-epitaxial growth of an atomic CaTiO3 perovskite layer on rutile TiO2 nanorod arrays. The high-temperature crystallization of CaTiO3 perovskite is overcome by a sequential hydrothermal conversion of the atomic amorphous TiOx layer to CaTiO3 perovskite. The atomic quasi-epitaxial CaTiO3 layer passivated TiO2 nanorod arrays exhibit more efficient interface charge transfer and high photoelectrochemical performance for water splitting. Such a mild solution-based approach for the quasi-epitaxial growth of atomic metal oxide perovskite layers could be a promising strategy for both fabricating atomic perovskite layers and improving their photoelectrochemical properties.

Photocatalytic degradation of reactive anionic dyes RB5, RR198 and RY145 via rare earth element (REE) lanthanum substituted CaTiO3 perovskite catalysts

Water serves as a key component in the basis of life to function and evolve unceasingly. Excessive deterioration of fresh water resources through discarding enormous amounts of dye effluents is becoming a problem of concern. In this work we report a conventional solid-state technique improved with choline chloride: urea DES medium in 1:2 ratio for synthesizing pure calcium titanate (CTO) and lanthanum doped calcium titanate (LaxCa1-xTiO3; x = 0.0 and 0.5). Both the materials were subjected to photocatalytically degrade reactive dyes RB5, RR198 and RY145. La-doped calcium titanate showed effective degradation efficiency when compared to the pure calcium titanate. On increasing the concentration of the dye, the efficiency of degradation declined gradually. Also, the efficiency was assessed to be greatest for RY145 followed by RR198 and lastly RB5. Efficiency dependence on different pH exposed the enhanced degradation in acidic medium and comparatively lowered pH in basic medium. Recyclability was highly satisfying and promising to validate the real-time applicability of the catalyst.

Predicted double perovskite material Ca2ZrTiO6 with enhanced n-type thermoelectric performance

Herein, using first-principles calculations, we studied the electronic and thermoelectric properties of isolated perovskites CaTiO3, CaZrO3 and double perovskite Ca2ZrTiO6 crystal structure under ambient conditions, biaxial compression, and biaxial tensile strain. We used generalized gradient approximation and the Hubbard parameter (GGA ​+ ​U) to calculate exchange and correlation interactions. The isolated perovskite CaTiO3 and CaZrO3 are indirect bandgap (Γ ​− ​R) semiconductors of values 1.90 ​eV, 3.2 ​eV, respectively. The construction of a double perovskite Ca2ZrTiO6 results in a direct (Γ ​− ​Γ) bandgap semiconductor material. The bandgap values under 2% & 5% biaxial tensile strain and compressive strain are in the range of 2.3 ​eV and 2.2 ​eV. We studied the thermoelectric properties by taking the two chemical potential values (μ) equal to CBM and VBM, respectively. The thermoelectric properties of Ca2ZrTiO6 under 2% & 5% biaxial tensile strain were improved at CBM, while thermoelectric properties under 2% & 5% biaxial compression strain were enhanced at VBM as compared to thermoelectric properties under ambient conditions. At CBM, the maximum value of the figure of merit (ZT) is about 4.4 ​at 500 ​K, required for the next generation of the thermoelectric device. The ZT value shows that the novel double perovskite is a very suitable candidate for thermoelectric devices.

Effect of static local distortions vs. dynamic motions on the stability and band gaps of cubic oxide and halide perovskites

Ternary ABX3 perovskites made of corner-sharing BX6 octahedra have long featured prominently in solid-state chemistry and condensed matter physics. Still, the joint understanding of their two main subgroups—halides and oxides—has not been fully developed. Indeed, unlike the case in simpler compounds having a single, robust repeated motif (“monomorphous”), certain cubic perovskites can manifest a non-thermal (= intrinsic) distribution of local motifs (“polymorphous networks”). Such static deformations can include positional degrees of freedom (e.g., atomic displacements and octahedral tilting) or magnetic moment degrees of freedom in paramagnets. Unlike thermal motion, such static distortions do not time-average to zero, being an expression of the intrinsic symmetry breaking preference of the chemical bonding. The present study compares electronic structure features of oxide and halide perovskites starting from the static polymorphous distribution of motifs described by Density Functional Theory (DFT) minimization of the internal energy, continuing to finite temperature thermal disorder modeled via finite temperature DFT molecular dynamics. We find that (i) different oxide vs. halide ABX3 compounds adopt different energy-lowering symmetry-breaking modes. The calculated pair distribution function (PDF) of SrTiO3 from the first-principles agrees with recently measured PDF. (ii) In both oxides and halides, such static distortions lead to band gap blueshifts with respect to undistorted cubic Pm-3m structure. (iii) For oxide perovskites, high-temperature molecular dynamics simulations initiated from the statically distorted polymorphous structures reveal that the thermally-induced distortions can lead to a band gap redshift. (iv) In contrast, for cubic halide perovskite CsPbI3, both the intrinsic distortions and the thermal distortions contribute in tandem to band gap blueshift, the former, intrinsic effect being dominant. (v) In the oxide SrTiO3 and CaTiO3 (but not in halide) perovskites, octahedral tilting leads to the emergence of a distinct Γ–Γ direct band gap component as a secondary valley minimum to the well-known indirect R–Γ gap. Understanding such intrinsic vs. thermal effects on oxide vs. halide perovskites holds the potential for designing target electronic properties.

Insight into the spectroscopic and thermometric properties of titanate phosphors via a novel co-excited laser system

An approach to enhance the photophysical properties of Er3+-Nd3+-Yb3+ codoped CaTiO3 perovskite phosphors synthesized via solid state reaction technique under 808 nm and 980 nm co-excitation has been described. The band gap analysis and Rietveld refinement has been done on the basis of UV–Vis and XRD spectra. Frequency upconversion observed in the developed phosphors has been explained with the help of steady rate equations. Fluorescence intensity ratio (FIR) based temperature sensing study of the developed phosphors for different combination of thermally coupled Stark levels under co-excitation has been analysed over a range of 303–573 K. Consequently, the maximum sensitivity ~10.9 × 10−3 K−1 at room temperature (303 K) with an excellent thermal resolution (~0.4 K) due to Stark splitting thermally coupled (2H11/2(1) &4S3/2(2)) levels in comparison to the conventional 2H11/2 &4S3/2 levels has been reported.

Effects of octahedral tilting on the site of substitution of manganese in CaTiO3

Electron paramagnetic resonance (EPR) and X-ray absorption fine structure measurements were combined with first principles calculations to investigate the substitutional behavior of Mn ions in perovskite CaTiO3 ceramics. While transition-metal dopants in perovskite-structured oxides often act as aliovalent defects, Mn in CaTiO3 is amphoteric and concurrently occupies both Ca and Ti sites as Mn2+ and Mn4+, respectively. Contrary to the behavior of Mn in SrTiO3 and BaTiO3, which exhibit larger geometric perovskite tolerance factors, in CaTiO3, it is determined that Mn2+ prefers A-site substitution. Density functional theory (DFT) calculations provide insight to the unique defect chemistry of Mn-doped CaTiO3 compared to SrTiO3 and BaTiO3, highlighting the role of octahedral rotations which accommodate ionic size mismatch between the larger host and smaller dopant cations on the cuboctahedral sites without significant dopant-ion displacements. Superposition models of the EPR zero-field splitting parameters for multiple types of Mn defect centers were considered based on the structural parameters of DFT calculations, and these results, combined with the EPR, DFT, and X-ray absorption analysis, were used to determine the point defect substitution mechanisms of Mn-CaTiO3.

Enhanced photoluminescence in a Eu3+ doped CaTiO3 perovskite phosphor via incorporation of alkali ions for white LEDs

Intense red photoluminescence has been observed in Eu3+/Z+ (Z+ = Li+, Na+ & K+) co-doped CaTiO3 perovskite phosphor materials, synthesized through high temperature solid-state reaction technique. The phosphor materials are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. All the compounds are crystalline with the orthorhombic phase. The crystallite and particle size of phosphor increase via incorporation of alkali ions. The vibrational groups in phosphor materials are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra showed a number of peaks in the UV–visible regions due to different transitions of Eu3+ ion. The band gap (Eg) of the phosphor decreases on incorporation of alkali ions. The phosphor materials emit intense red color at 613 nm due to 5D0 → 7F2 transition of Eu3+ ion upon 398 nm and 466 nm excitation wavelengths. The intensity of red emission increases upto 12 mol% concentration of Eu3+ ions. On incorporation of alkali ions in the 12 mol% Eu3+: CaTiO3 phosphor, the emission intensity increases further due to crystallinity, charge compensation and the asymmetry created around the Eu3+ ions in the phosphor. The emission intensity is largest for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The asymmetric ratio is higher for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The lifetime of 5D0 level is enhanced via incorporation of alkali ions and it is also larger for the 12Eu3+/10Na+ co-doped CaTiO3 phosphor. The CIE color coordinates, correlated color temperature (CCT), color purity and color rendering index (CRI) calculations of the phosphors have also been carried out, which show pure red color in warm light region. Therefore, these synthesized perovskite phosphor materials can be advantageous for display devices, NUV excited red phosphors for making the tricolor phosphor converted WLEDs and blue LED chip-based WLEDs for solid state lighting applications.

Upconversion and downshifting emissions of Ho3+-Yb3+ co-doped ATiO3 perovskite phosphors with temperature sensing properties in Ho3+-Yb3+ co-doped BaTiO3 phosphor

In this work, we report a comparative study on upconversion and downshifting properties of Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors for the first time. The phosphor samples are prepared via solid state reaction method in a programmable furnace at 1523 K. The phosphor samples are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The EDS analyses show the presence of the desired elements used in the synthesis. The vibrational structures of the phosphor samples are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to Ho3+ and Yb3+ ions. The optical band gap (Eg) is calculated using Wood and Tauc relation and its values are found to be 3.61, 3.20 and 3.32 eV for the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphor samples, respectively. The upconversion emission spectra are monitored by exciting these phosphor samples at 980 nm. The phosphor samples give intense green emission in all the cases. However, the UC emission intensity is higher for the Ho3+-Yb3+ co-doped CaTiO3 perovskite phosphor. These phosphor samples also give intense green downshifting emission upon 419 and 452 nm excitations. The Ho3+-Yb3+ co-doped BaTiO3 perovskite produces relatively larger emission intensity among these phosphors. The lifetime of green emitting level (5F4) of Ho3+ ion shows temporal behavior of these perovskite phosphors. Furthermore, the temperature versus UC emission intensities of the green thermally coupled levels of Ho3+-Yb3+ co-doped BaTiO3 phosphor gives the fluorescence intensity ratio (FIR) and FIR-based relative (SR) and absolute (SA) temperature sensor sensitivities are obtained as 0.0034 K-1 and 0.0050 K-1, respectively at 305 K. Thus, the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors may be found suitable in display devices, solid state lighting, upconversion based devices and temperature sensing devices.

Experimental data of CaTiO3 photocatalyst for degradation of organic pollutants (Brilliant green dye) - Green synthesis, characterization and kinetic study.

The data presented here focuses on the physicochemical characterization of perovskite CaTiO3 nanoparticles (orthorhombic) as photocatalyts and the kinetic study of their photodegradation performance toward organic pollutant, i.e. brilliant green (BG) which is azo derivatives dye. The CaTiO3 nanoparticles was synthesized using chicken eggshell-derived CaCO3 and anatase TiO2 with molar ratio of (1:1), (1:3), (2:5), and (2:7). The physical and microstructural properties of CaTiO3 were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), Fourier Transform Infrared (FTIR) and UV/vis spectrometer. The effect of initial dye concentration, catalyst composition, and catalyst dosage on the adsorption mechanism of dye on CaTiO3 was investigated in jacketed photoreactor under UV irradiation. The analysis reveals that BG molecules are efficiently chemisorbed, as indicated by pseudo first order kinetic, and degraded within 120 min. Considering the low-cost preparation process and high photocatalytic performance, the resultant CaTiO3 can further be used as an efficient photocatalyst for organic pollutant removal from aqueous and industrial wastewater.

Correlation of hydrogen generation and optical emission properties of plasma in water photolysis on perovskite photocatalysts

Photocatalytic decomposition of organic materials-contained aqueous solution is assessed using a plasma discharged into the liquid directly. The correlation of H2 generation and optical emission spectroscopy is discussed in terms of photocatalytic H2 production using plasma and photocatalysts. Variations of the active species are evaluated according to the conditions of the plasma in the liquid phase. The optical emission spectra vary according to the plasma discharging conditions in the liquid phase. The intensities of the OH· peaks at 309 nm increase with the addition of ethanol or acetaldehyde in water. The highest intensities and rate of H2 evolution are observed at a 10% acetaldehyde concentration in the aqueous solution. The rates of H2 evolution in the ethanol or acetaldehyde solution correspond to the concentration of OH· in the solution. The photocatalytic reaction using liquid plasma generates hydrogen at the same time as the decomposition of the organic chemicals. The rate of hydrogen evolution in aqueous solutions containing the organic chemicals is higher than that in pure water. This is because hydrogen is further generated due to hydrogen generation by photolysis of the organic chemicals. CaTiO3 perovskite photocatalyst shows better photocatalytic activity than TiO2. Ni loading on the photocatalyst lead to an increase in H2 production.

Electronic and optical behaviour of lanthanum doped CaTiO3 perovskite

To improve the efficiency of perovskite based solar cells, doping of heavier elements in Perovskite materials (ABX3) can modulate its electronic and optical properties significantly. Thus it is important to understand the possible microscopic origin of the band gap modification and optical enhancement after heavier element doping using first-principles studies. Here we investigate the effect of La doping, while substituting the Ca atom, on the electronic and optical properties in CaTiO3 perovskite material using generalized gradient approximation within density functional theory. We observe a decrease in lattice constants and bond lengths in LaxCa1−xTiO3, mainly due to re-distribution of electronic charge density between La and Oxygen, as confirmed by charge density contour. We further notice a widening of electronic band gap and an upward shift of Fermi level into the conduction band, thus characterizing LaxCa1−xTiO3 as an n-type material. DOS diagram attributes this shift mainly due to the appearance of La p-DOS and d-DOS and their repulsion with N p-DOS, when La enters into the host lattice at Ca site. Investigation of optical properties upon La Doping in CaTiO3 exhibits further shifting of polarization and refractive index to lower values as compared to its pure counterpart, due to dominating semiconducting behavior and hence one observes a blue shift in absorption and reflection spectrum accordingly. Energy loss function is found to be consistent with absorption and extinction coefficient measured in case of LaxCa1−xTiO3. All these results are found to be consistent with the existing experimental and first-principles studies.

Fe and Co-doped (Ba, Ca)TiO3 Perovskite as Potential Electrocatalysts for Glutamate Sensing

Fe and Co-doped (Ba, Ca)TiO3 Perovskite as Potential Electrocatalysts for Glutamate Sensing