La Doping Research Articles

Synergistic catalysis in Pd/La-CeO2 enhanced CH4 oxidation: The role of water and reactive oxygen species

The catalytic oxidation of methane (CH4) stands as an essential strategy for curtailing greenhouse gas emissions. This study advances CH4 oxidation using Pd on La-doped CeO2, where water (H2O) boosts oxidation efficiency. The temperature for obtaining 50 % CH4 conversion on Pd/La-CeO2 catalyst was reduced from 288 °C (without H2O) to 260 °C (with H2O), while that on CeO2 was 570 °C both under conditions with and without H2O. Operando DRIFTS analysis reveals the reaction pathway and intermediates during CH4 oxidation. Ce cations provide adsorption sites for CH4, leading to the generation of CH3 adsorbed species with the help of surface O2–. La doping creates oxygen vacancies essential for oxygen activation and foster the formation of reactive hydroxide (OH) from adsorbed H2O and O. Pd contributes to the formation of more reactive oxygen species that facilitate OH generation at La cations and the oxidation of CH4 adsorption species to CO2 and H2O. The synergistic interplay between Pd and La-CeO2 is particularly noteworthy, with H2O also playing a role in the gasification of surface carbonates, thereby enhancing the overall performance of CH4 oxidation. A kinetic model based on the Langmuir-Hinshelwood mechanism is proposed, offering an insight into CH4 oxidation.

Revealing La doping activation or inhibition of crystal facet effects in Co3O4 for catalytic combustion and water resistance improvement

It was challenging to enhance the catalytic activity and water resistance of transition metal oxides in the CH4 treatment process. Here, La with large atomic radii was doped onto Co3O4 on the (110), (111) and (100) crystal facets, respectively, and successfully doped into the (110) and (100) lattices, but accumulation occurs on the (111) crystal surface. Doping La into the Co3O4 lattice achieved a dual excitation effect for surface optimization and structural defects, causing lattice expansion, enhancing the electrophilicity of the O atoms in the vicinity of La, and significantly stimulating the Co-O bond. This significantly improved reactive oxygen species content, CH4 adsorption capacity, and gaseous oxygen activation and replenishment capability for higher catalytic activity. Conversely, the (111) facet with accumulated La showed an opposite trend. Meanwhile, La doping effectively improved the stability of Co3O4 and weakened its hydrophilicity, which effectively enhanced its water resistance. This research provided a viable strategy for designing high-performance and water-resistant Co3O4-based catalysts.

Effect of sintering temperature on the structural, morphological, optical and electrical properties of Ba1 − xLaxFe12O19

La substituted M-type Barium hexaferrite, Ba(1−x)La(x)Fe12O19, (x = 0.25 and 0.30) were synthesized using ball milling followed by heat treatment at 1150˚C and 1300˚C and the influence of sintering temperature as well as La doping were presented. X-ray diffraction, FESEM, dielectric spectroscopy, and ferroelectric measurements were performed to study the structural, morphological, dielectric, and ferroelectric properties of the prepared samples. Rietveld refinement on the X-ray diffraction measurement reveals the formation of a phase magnetoplumbite structure of barium hexaferrite only for the samples sintered at 1300˚C. The secondary phase, along with the major magnetoplumbite structure, was observed for the sample sintered at 1150˚C. Hexagonal plate-like grains of different sizes were observed, and samples sintered at 1300˚C showed large-size grains. Porosity was observed to decrease with La doping. Impedance spectroscopy reveals that Maxwell-Wagner-type polarisation occurs with the relaxation of mobile charges having long-range hopping. However, the ferroelectric property was suppressed for samples sintered at 1300˚C.

Enhancing electrocatalytic nitrate reduction performance of Co3O4 nanoneedle arrays by La-doping

The excess emission of nitrate from human activities disturbs the global nitrogen cycle and thus needs to be remediated. In this work, we prepared a La-doped Co3O4 nanoneedle arrays catalyst for highly efficient electrocatalytic reduction of NO3− to NH3 at low concentration. The La-doped Co3O4 nanoneedle arrays exhibit remarkable activity with the highest Faradaic efficiency of 95.5% and an ammonia yield rate of 4.08 mg/(h·cm2) at −0.3 V versus RHE in 0.02 mol/L NO3−. Experiments and theoretical calculations show that the La doping not only facilitates the surface reconstruction to form active La-Co(OH)2, but also inhibits the hydrogen evolution reaction over Co sites, thus promoting the NH3 production. This work provides new insights into the promoting effect of the rare earth elements in transition metal-based electrocatalyst for nitrate reduction.

Influence of Ho, Gd, La Doping on Grain-Grain Boundary Characteristics and Minimization of Leakage Current in Nickel Ferrites

This study explores the impact of doping with Ho, Gd, and La on sol-gel-derived nickel ferrites through a comprehensive analysis using various analytical techniques. The combination of X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) spectra analysis, impedance spectroscopy, and I-V analysis enables a detailed exploration of the structural, compositional, and electrical characteristics of the samples. Williamson-Hall plots in XRD analysis reveal crucial insights into grain and grain boundary impacts, revealing a shift in trends for doped samples indicative of tensile strain and underscores the influence of dopant ions on lattice distortion. XRF study confirms the elemental composition of the samples, validating the experimental approach. Impedance spectroscopy sheds light on conduction mechanisms and charge transfer processes, while the modulus study identifies distinct relaxation peaks corresponding to grain and grain boundary relaxation mechanisms. IV analysis demonstrates a significant reduction in leakage current with rare Earth element doping, suggesting promising applications.

Dry Reforming of Methane on Ni/LaZrO2 Catalyst under External Electric Fields: A Combined First-Principles and Microkinetic Modeling Study.

Dry reforming of methane (DRM) reaction has great potential in reducing the greenhouse effect and solving energy problems. Herein, the DRM reaction mechanism and activity on Ni16/LaZrO2 catalyst under electric fields were comprehensively investigated by combining density functional theory calculations with microkinetic modeling. The results showed that La doping increases the interaction between Ni and ZrO2 by Ni cluster transfer of more electrons. The adsorption strength of species followed the order Ni16/ZrO2 > Ni16/LaZrO2, which is consistent with the results for the d-band center but opposite to the metal-support interaction. The best DRM reaction path on Ni16/LaZrO2 was the CH2-O pathway, which is different from the CH-O pathway on Ni(111) and Ni16/ZrO2. Both positive and negative electric fields of strong and weak metal-support interactions reduced the energy barrier of DRM reaction. Importantly, our results showed that the more dispersed and smaller Ni12/LaZrO2 model by considering the dispersing effect induced by La doping, which displayed very different results from that of Ni16/LaZrO2: reduced the energy barrier for methane decomposition, thereby promoting DRM reaction activity. Microkinetic results showed that the carbon deposition behavior of DRM becomes weaker on Ni16/LaZrO2 due to the suppression of methane decomposition in the presence of La doping compared to Ni16/ZrO2, but the opposite result is obtained on Ni12/LaZrO2. The order of DRM reactivity was Ni16/LaZrO2 < Ni16/ZrO2 < Ni12/LaZrO2, which is consistent with the experiment observations. The conversion of methane and CO2 was higher in positive electric fields than in negative electric fields at low temperatures, but the results were opposite at high temperature. Negative electric fields can improve the carbon deposition resistance of Ni-based catalysts compared to positive electric fields. The degree of rate control analysis showed that CHx* oxidation also plays an important role in the DRM reaction. We envision that this study could provide a deeper understanding for guiding the widespread application of electric field catalysis.

Wettability, electronic structure and optical properties of intrinsic, doped, and oxygen-deficient CeO2: A study using DFT+U and DFT+U-D3

Using density functional theory plus U (DFT + U) and considering dispersion correction with the DFT + U-D3 method, the wettability, electronic structure, and optical properties of MO2 (M = Ce, Ce0.75La0.25, Ce0.75Zr0.25, Ce0.75Y0.25) and CeO1.75 were investigated. The results showed that dispersion correction had a significant impact on the wetting behavior. Through comparison, we identified a calculation method for the water contact angle (WCA) that closely matched experimental values. All structures exhibited hydrophilic properties, but Y doping significantly increased the WCA. La and Y doping transformed CeO2 from semiconductor to exhibits metallic characteristics. Oxygen vacancies localized excess electrons by Ce, forming Ce-f gap states between the conduction and valence bands. Zr doping increased the transparency of CeO2. La doping, Y doping, and oxygen vacancies enhanced the extinction coefficients of CeO2 in infrared light and resulted in higher static refractive indices and static reflectivities.

Pyroelectric Thermal Energy Harvester Based on Sol‐Gel‐Derived PLZT Films

The present work focuses on studying the pyroelectric properties of chemical solution deposition‐grown Pb1−xLax(Zr0.4Ti0.6)O3 films on nickel substrate which are annealed at constant temperature of 650 °C with lanthanum concentrations ranging from x = 2–8% respectively. Structural studies reveal polycrystalline nature in all the PLZT films. The dielectric constant values rise from 497 to 1048 as La doping concentration rises from 2% to 6% at a constant frequency of 1 MHz, reaching a maximum value of 1048 for 6% La doping with little variation in dielectric loss between 0.03 and 0.05. As La doping level increases from 2% to 6%, the remnant (Pr) and saturation (Ps) polarization values increase from 12 to 47 μC cm−2 and 18 to 53 μC cm−2 respectively. The leakage current is found to be 2.68 × 10−8 A for 2%‐doped PZT film and it reduces to 2.94 × 10−10 A for PLZT (6% doping) film. The influence of lanthanum doping on the pyroelectric properties has been studied in detail. The value of pyroelectric coefficient (p) is varied from 240 × 10−3 to 980 × 10−3 Cm−2 K−1 and current responsivity is varied from 960 × 10−10 to 3920 × 10−10 mV−1 with the variation in lanthanum content from 2% to 6%, respectively. The promising pyroelectric results found in PLZT films encourage these films in energy applications field.

La‐doped ZnCr‐layered Double Hydroxide with Enhanced Photocatalytic Activity for Tetracycline Hydrochloride Removal

AbstractA series of lanthanum‐doped ZnCr‐layered double hydroxide (La/ZnCr‐LDH) photocatalysts were successfully synthesized by a facial hydrothermal method and their photocatalytic activity for degradation tetracycline hydrochloride (TCH) were evaluated under visible light irradiation. The structure and physicochemical properties of the as‐synthesized photocatalysts were well characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer‐Emmett‐Teller (BET), X‐ray photoelectron spectrometer (XPS), and UV‐vis absorption spectroscopy. The photocatalyst with La doping content of 10 % (molar ratio La3+/(La3++Cr3+), La/ZnCr‐LDH‐10) has optimal performance for TCH removal (87.2 %) among all synthesized photocatalysts. Radical trapping experiments and Valence Band‐XPS (VB‐XPS) were used to propose a possible photocatalytic degradation process for TCH by La/ZnCr‐LDH‐10 photocatalyst. This strategy can be used to modify other photocatalysts for efficient removal of organic pollution in the environment.

CO2 electrolysis to multi-carbon products in strong acid at ampere-current levels on La-Cu spheres with channels

Achieving satisfactory multi-carbon (C2+) products selectivity and current density under acidic condition is a key issue for practical application of electrochemical CO2 reduction reaction (CO2RR), but is challenging. Herein, we demonstrate that combining microenvironment modulation by porous channel structure and intrinsic catalytic activity enhancement via doping effect could promote efficient CO2RR toward C2+ products in acidic electrolyte (pH ≤ 1). The La-doped Cu hollow sphere with channels exhibits a C2+ products Faradaic efficiency (FE) of 86.2% with a partial current density of −775.8 mA cm−2. CO2 single-pass conversion efficiency for C2+ products can reach 52.8% at −900 mA cm−2. Moreover, the catalyst still maintains a high C2+ FE of 81.3% at −1 A cm−2. The channel structure plays a crucial role in accumulating K+ and OH- species near the catalyst surface and within the channels, which effectively suppresses the undesired hydrogen evolution and promotes C–C coupling. Additionally, the La doping enhances the generation of *CO intermediate, and also facilitates C2+ products formation.

Improved photocatalytic properties of WO3 nanoparticles for Malachite green dye degradation under visible light irradiation: An effect of La doping

Abstract Doped materials have received substantial attention due to their increased usefulness in photocatalytic applications. Within this context, the present study was dedicated to investigating the potential of the precipitation technique for producing La-doped tungsten oxide (WO3). To comprehensively characterize the synthesized La-doped WO3, scanning electron microscopy and X-ray diffraction were judiciously employed. The focal point of the investigation encompassed an examination of the impact of varying La concentrations on multiple fronts: the photocatalytic activities (PCAs), as well as any associated structural and morphological modifications. This holistic approach aimed to uncover the intricate relationship between La incorporation and the resulting properties of the WO3 matrix. Through the degradation of Malachite green dye within an aqueous medium, PCA of the La-doped WO3 samples was quantitatively evaluated. Remarkably, over 180 min under irradiation of visible light irradiation, the achieved levels of dye degradation were remarkable, amounting to 81.165, 83.11, and 83.85% for the respective samples. These findings firmly underscore the potential of La-doped WO3 as a proficient photocatalyst, particularly in color removal from wastewater. This study paves the way for enhanced wastewater treatment approaches by utilizing doped WO3 materials.

Influence of Surface Basic Sites and Oxygen Vacancies on the Performance of Metal-Modified Rod-Like Ceria Catalysts for Low-Temperature Hydrolysis of Carbonyl Sulfide.

This study utilized a hydrothermal method to synthesize various metal-modified rod-like ceria catalysts (Fe, Co, Cu, Ni, La), achieving efficient COS removal at low temperatures. The research identified surface oxygen vacancies and basic sites as critical factors that influence the catalytic performance of COS hydrolysis. The addition of different metals to pristine ceria rods increased the specific surface area, oxygen vacancy content (Ov), and basicity, which enhanced the catalysts' sulfur resistance and stability. Among all the catalysts tested, 10La-CeO2 demonstrated the highest COS removal rate. This is because La doping significantly augmented Ov, providing more H2O adsorption and activation sites. Furthermore, 10La-CeO2 showed enhanced Lewis basicity, making it easier for COS to adsorb and promote hydrolysis. The in situ DRIFTS results confirmed that appropriate oxygen vacancies and basic sites favored the formation of intermediates such as HCO3 - and HSCO2 -, promoting the decomposition of COS into H2S and CO2.

Tailoring perovskite ceramics for improved structure, vibrational behaviors and radiation protection: The role of lanthanum in PbTiO3

This study investigates the characteristics of lanthanum (La)-doped lead titanate (PbLaxTi(1-3x/4)O3 where, x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1), a type of perovskite ceramic. It specifically focuses on analyzing its structure, vibrational properties, and efficacy in shielding against radiation. The prepared samples are investigated by X-ray diffraction (XRD), which clarified that the small doping of La (x ≤ 0.06) produced the required phase, and increasing the La doping (x > 0.06) produced nonrequired phases (secondary phase). Also, increasing the La doping converted the crystal symmetry from tetragonal to cubic, which was confirmed by the tetragonality raio (c/a) calculations. Also, the samples are investigated by Fourier transform infrared (FTIR) spectroscopy to confirm the XRD results. Transmission electron microscopy (TEM) examination clarified that the prepared samples were in the nanoscale range with a maximum crystallite size value of around 70 nm. In addition, the shielding effectiveness of all the prepared samples was theoretically evaluated using the Phy-X/PDS program by considering characteristics such as the linear attenuation coefficient (GLAC), mean free path (GMFP), transmission factor (TF), and radiation protection efficiency (RPE). Increasing the La concentration increases the theoretical density to 4.98 gm/cm3 at x = 0.1, leading to low TF and GMFP values and high GLAC values. This produces samples with high attenuation to radiation and high shielding effectiveness.

La implanted band engineering of ZnO nanorods for enhanced photoelectrochemical water splitting performance

In the quest to improve photoelectrochemical water-splitting performance, we have doped lanthanum (La) in highly crystalline zinc oxide (ZnO) nanorods (NRs) using a facile and low-temperature hydrothermal route and successful substitution of La3+ at the Zn2+ site is confirmed from structural and chemical analysis. The tapered NRs morphology gained after La doping resulted in lower optical bandgap of 3.17 eV, enhanced visible light trapping, and multiphoton absorption, which assist in achieving good PEC activity. The La doping also offered higher Urbach energy (EU), subsidizing the number of oxygen vacancies. The UPS spectra show that La doping reduces conduction band energy level and endorses smooth charge transportation. The La-doped ZnO exhibits two times enhancement in photocurrent (1.54 mA·cm−2) compared to pristine ZnO (0.81 mA·cm−2). The higher applied bias to the photon conversion efficiency of ∼1.14% for La-doped ZnO confirms the efficient utilization of solar energy. The EIS measurements demonstrated reduction in charge transfer resistance with La-doping. Mott-Schottky analysis shows that La doping lowers the flat-band potential and enhances charge transportation, making it a potential photoanode for PEC water-splitting applications.

High response chemiresistive room temperature ammonia gas sensor based on La-doped ZnO samples

The current study describes the excellent sensing properties of zinc oxide samples with varying La doping concentrations (1, 3, and 5 %). The X-ray diffraction (XRD) study suggests that the produced ZnO samples exhibit hexagonal structure. Due to varying concentrations of La, a notable difference in the morphological image of the samples was observed using a Field Emission Scanning Electron Microscope (FESEM). The existence of La, Zn, and O elements in the sample was analyzed by Energy Dispersive X-Ray Analysis (EDX). The Fourier Transform Infrared Spectroscopy (FTIR) studies validate the sample's structure and functional group. The UV–Vis results showed that the maximum optical reflectance of 90 % was attained in the visible region and the obtained band gap values for the samples were in the range of 3.27–3.33 eV. At ambient temperature, the La-doped samples demonstrated high sensitivity towards ammonia (NH3) and had the highest response value of 1940 % for the 250 ppm. According to the results, an excellent operating stability, and response/recovery time were obtained for the ZnO:La1% sample which suggests that the sample can serve as the most appropriate metal oxide for the detection of NH3 at room temperature.

Impact of La doping on the optoelectronic and structural properties of CsPbIBr2 perovskite solar cell

Inorganic lead halide perovskite solar cells (IPSC) have high power conversion efficiency (PCE). Currently, heteroatom substitution is a promising method for enhancing the properties of perovskite materials and the performance of associated devices. This study outlines the production process of a perovskite solar cell made from inorganic CsPbIBr2 with a 4 % La doping. The cubic crystal structure with large grain size and small band gap energy is observed at 4 % La–CsPbIBr2. The optoelectronic and structural characteristics of CsPbIBr2 perovskite solar cells have been substantiated through various methodologies, such as the determination of space charge restricted current, examination of the photoluminescence decay profile, assessment of charge transfer resistance, and utilization of Mott Schottky analysis. The incorporation of lanthanum-doped cesium lead iodide bromide (La-doped CsPbIBr2) resulted in a notable enhancement in both the open circuit voltage (Voc), and the short circuit current density (Jsc), leading to a much higher overall efficiency of 9.89 % compared to the pristine counterpart, which exhibited an efficiency of 8.62 %.

Luminescence studies and Judd Ofelt parameterization of Dy3+ activated La2(WO4)3 yellow phosphor

The synthesis and detailed luminescence studies of a series of La2-xDyx(WO4)3 (x = 0.02, 0.1, 0.2, 0.4, 0.6, 0.8) phosphors synthesized via microwave-assisted co-precipitation technique is reported in this paper. The XRD analysis confirmed that the phosphors were crystalized in a monoclinic structure with space group C2/c and FTIR analysis identified the characteristic vibrational modes. Morphological studies were conducted using FESEM analysis, and the EDS technique substantiated the effective incorporation of Dy3+ ions in La2(WO4)3. The photoluminescence excitation and emission spectra of varying concentrations of Dy3+ ions were recorded and an optimum concentration of 10% exhibited the highest intensity. The emission spectra of all phosphors were dominated by peaks at 484 nm and 574 nm. The radiative properties were evaluated using Judd-Ofelt analysis and the JO intensity parameters followed the trend Ω2 > Ω6 > Ω4. The gradual decrease in the decay lifetime value of 4F9/2 excited level with an increase in doping concentration elucidates concentration quenching phenomena due to dipole – quadrupole interaction. The emission data were also analyzed by calculating CIE coordinates and concluded that Dy3+ doped La2(WO4)3 phosphors have potential applications in yellow light generation.

Unravelling the La dopant induced physicochemical changes and the electrical behaviour on BaFeO3 under oxidising and reducing atmospheres

Electroceramic oxides like La-doped BaFeO3 garner greater interest owing to their tunability of mixed ionic conduction. However, reports on the effect of La on the microstructural changes, the type of conduction mechanism under different atmospheres and the negative charge transfer influenced by the Fe-O hybridization in Ba1−xLaxFeO3−δ are hardly available. Doping La induces cation vacancies and Fe reduction, creating nanorod decorated surface after the high-temperature treatment. Conductivity studies expose the rate-limiting steps for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) as the ohmic resistances and Ba segregation effects. Among the samples studied, Ba0.9La0.1FeO3−δ performs better at 800 °C with an activation energy of ∼0.35 eV under both oxidizing and reducing atmospheres. Surface analysis after EIS reveals Fe and O with different oxidation states that enhance the total conductivity. The amount of hydroxyl species retained (23.66% for Ba0.9La0.1FeO3−δ ) and the ratio of the adsorbed to the lattice oxygen (15.33% for Ba0.9La0.1FeO3−δ ) gives insight on HOR and ORR activities. Also, computational studies validated the negative charge transfer mechanism of the samples under thermally assisted oxidation. The results indicate Ba0.9La0.1FeO3−δ as a tuneable electrode for solid oxide cells.

Effects of La-N Co-Doping of BaTiO3 on Its Electron-Optical Properties for Photocatalysis: A DFT Study.

In cation-anion co-doping, rare earth elements excel at regulating the electronic structure of perovskites, leading to their improved photocatalytic performance. In this regard, the impact of co-doping rare earth elements at the Ba and Ti sites in BaTiO3 on its electronic and photocatalytic properties was thoroughly investigated based on 2 × 2 × 2 supercell structures of BaTiO3 with different La concentrations of 12.5% and 25% using DFT calculations. The band structure, density of states, charge density difference, optical properties, and the redox band edge of the co-doped models mentioned above were analyzed. The results indicated that the BaTiO3 structure co-doped with 25% La at the Ti site exhibited higher absorption in the visible range and displayed a remarkable photocatalytic water-splitting performance. The introduced La dopant at the Ti site effectively reduced the energy required for electronic transitions by introducing intermediate energy levels within the bandgap. Our calculations and findings of this study provide theoretical support and reliable predictions for the exploration of BaTiO3 perovskites with superior photocatalytic performances.

Exploring the influence of lanthanum doping on pyroelectric and pyrocatalytic Characteristics in NBT-BT-2Zn ceramics

The present work investigates the pyroelectric properties of 0.94Na1/2Bi1/2TiO3-0.06BaTiO3-0.02Zn-xLa (NBT-6BT-2Zn-xLa; x = 0, 0.25, 0.5 and 1 in mole %) and its use in methylene blue (MB) dye degradation in wastewater. La doping is used to enhance the pyroelectric properties of NBT-6BT-2Zn for energy harvesting and pyrocatalysis applications. The 0.25 mol % La-doped sample consists of a maximum pyroelectric coefficient of 3.8 × 10−4 C m−2 °C−1 and shows a 55% MB dye decomposition. The presence of •OHandO2•− is confirmed by scavengers and radical trapping experiments. The repeatability test ensures the reusability of the NBT-6BT-2Zn-0.25La as a pyrocatalyst for dye degradation. The bulk form of NBT-6BT-2Zn-0.25La is also investigated to overcome the limitations of powder recovery in dye degradation.