Search Results (47)

First-principles density-functional theory (PBE, Quantum ESPRESSO) was employed to quantify how Fe substitution modulates the structural, elastic, electronic, and optical behaviour of cubic fluorite Fe_xZr_1−xO₂ (x = 0.00–1.00). The fluorite FeO₂ end member was treated as a hypothetical ambient-pressure limit to trace trends across the solid solution (experimental FeO₂ being stabilized in the high-pressure pyrite phase). Mechanical stability was verified via the cubic Born criteria, and composition-dependent stiffness and anisotropy were assessed through Voigt–Reuss–Hill moduli, Pugh ratio, and elastic indices. A strong band-gap narrowing was found—from 3.41 eV (x = 0) to ≈0.02 eV (x = 0.50)—which was accompanied by a visible–NIR red-shift, large absorption (α ≈ 10⁵ cm⁻¹ at higher x), and enhanced refractive index and permittivity; metallic-like response was indicated at high Fe content. Spin-polarized calculations converged to zero total and absolute magnetization, indicating a non-magnetic ground state at 0 K within PBE. The effect of oxygen vacancies (V₀)—expected under Fe³⁺ charge compensation—was explicitly considered: V₀ is anticipated to influence lattice metrics, elastic moduli (B, G, G/B), and sub-gap optical activity, potentially modifying stability and optical figures of merit. Stoichiometric (formal Fe⁴⁺) predictions were distinguished from V₀-rich scenarios. Absolute band gaps may be underestimated at the PBE level. Full article

A pyrochlore-type crystal structure photocatalytic nanomaterial, Ho₂FeSbO₇, was successfully synthesized using a hydrothermal method. Additionally, a fluorite-structured Bi_0.5Yb_0.5O_1.5 was prepared via rare earth Yb doping. Finally, a novel Ho₂FeSbO₇/Bi_0.5Yb_0.5O_1.5 heterojunction photocatalyst (HBHP) was fabricated using a solvothermal method. The crystal structure, surface morphology, and physicochemical properties of the samples were characterized using XRD, a micro-Raman spectrometer, FT-IR, XPS, ultraviolet photoelectron spectroscopy (UPS), TEM, and SEM. The results showed that Ho₂FeSbO₇ possessed a pyrochlore-type cubic crystal structure (space group Fd-3m, No. 227), while Bi_0.5Yb_0.5O_1.5 featured a fluorite-type cubic structure (space group Fm-3m, No. 225). The results of the degradation experiment indicated that when HBHP, Ho₂FeSbO₇, or Bi_0.5Yb_0.5O_1.5 was employed as a photocatalytic nanomaterial, following 140 min of visible light irradiation, the removal efficiency of ciprofloxacin (CIP) reached 99.82%, 86.15%, or 73.86%, respectively. This finding strongly evidenced the remarkable superiority of HBHP in terms of photocatalytic performance. Compared to the individual catalyst Ho₂FeSbO₇, Bi_0.5Yb_0.5O_1.5, or N-doped TiO₂, the removal efficiency of CIP by HBHP was 1.16 times, 1.36 times, or 2.52 times higher than that by Ho₂FeSbO₇, Bi_0.5Yb_0.5O_1.5, or N-doped TiO₂, respectively. The radical trapping experiments indicated that in the CIP degradation process, the hydroxyl radical owned the strongest oxidation ability, followed by the superoxide anion and the photoinduced hole. These studies are of great significance for the degradation of antibiotics and environmental protection. Full article

Tailoring the bandgap of a material is necessary for improving its optical properties. Here, the optical bandgap of high-entropy oxide Ce_0.2Gd_0.2Sm_0.2Y_0.2Zr_0.2O_2-δ (HEO) nanoparticles was modified using Pr³⁺. Various concentrations of Pr³⁺ (x = 0, 0.01, 0.02, 0.05, 0.075, 0.1, 0.15) were incorporated into the host high-entropy oxide using a gel combustion synthesis. After the gel combustion step, the powders were heat-treated at various temperatures (650 °C, 800 °C, 950 °C) for 2 h. The obtained Pr³⁺-incorporated HEO powders were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and UV–visible spectroscopy. The results indicate that, when the samples are calcined at 950 °C, a single-phase cubic fluorite structure is obtained without any phase separation or impurity. The optical absorbance red-shifts to higher wavelengths when the concentration of Pr³⁺ is increased. This reduces the bandgap of the material from 3.15 eV to 1.87 eV for Pr³⁺ concentrations of x = 0 (HEO-0) and x = 0.15 (HEO-6), respectively. The obtained HEOs can be suitable candidates for photocatalytic applications due to their absorbance in the visible region. Full article

Lanthanide molybdates are materials known for their mixed proton–ionic conductivity. This study investigates the effects of Pr content and Nb-doping on the crystal structure and electrical properties of the La_5.4−xPr_xMo_1−yNb_yO_12−δ (x = 0, 1.35, 2.7, 4.05, 5.4; y = 0, 0.1) series. The research focuses on two primary objectives: (i) enhancing the electronic conductivity through the use of Pr⁴⁺/Pr³⁺ redox pairs and (ii) increasing the ionic conductivity through Nb⁵⁺ aliovalent doping. The materials were thoroughly characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission and scanning electron microscopy (TEM and SEM), and complex impedance spectroscopy. The average crystal structure of the materials depended significantly on the Pr content. In general, compositions with a higher Pr content crystallize in a cubic fluorite-type structure, whereas those with a lower Pr content stabilize a rhombohedral polymorph. However, detailed TEM studies reveal a more complex local crystal structure characterized by nanodomains and incommensurate modulations. The highest conductivity values were observed in a N₂ atmosphere for compositions with an elevated Pr content, with values of 0.17 and 204.4 mS cm⁻¹ for x = 0 and x = 5.4, respectively, at 700 °C, which is attributed to electronic conduction mediated by the Pr⁴⁺/Pr³⁺ redox pair, as confirmed by XPS. These findings highlight the potential of tailored doping strategies to optimize the conducting properties of lanthanide molybdates for specific high-temperature electrochemical applications. Full article

Mono- and di-substituted cerium oxide catalysts, viz. Ce_0.95Cu_0.05O_2-δ, Ce_0.90Cu_0.10O_2-δ, Ce_0.90 Cu_0.05Mn_0.05O_2-δ, Ce_0.85Cu_0.10Mn_0.05O_2-δ, and Ce_0.80Cu_0.10Mn_0.10O_2-δ, were synthesized via a one-step urea-assisted solution combustion method. The elemental composition and textural and structural properties of the catalysts were determined by various physical, electronic, and chemical characterization techniques. Hydrogen temperature-programmed reduction showed that co-doping of copper and manganese ions into the CeO_2-δ lattice improved the reducibility of copper. Powder XRD, XPS, HR-TEM, and Raman spectroscopy showed that the catalysts were a singled-phased, solid-solution metal oxide with a cerium oxide cubic fluorite (cerianite) structure, and evidence of oxygen vacancies was observed. Catalytic results in the preferential oxidation of CO in a hydrogen-rich stream showed that complete CO conversion occurred between 150 and 180 °C. Furthermore, at 150 °C, Ce_0.90Cu_0.05Mn_0.05O_2-δ, Ce_0.90 Cu_0.10O_2-δ, and Ce_0.85Cu_0.10Mn_0.05O_2-δ catalysts were the most active, achieving complete CO conversion and CO₂ selectivity of 81, 79, and 71%, respectively. The catalysts performed moderately in the presence of CO₂ and water, with the Ce_0.90Cu_0.05Mn_0.05O_2-δ catalyst giving a CO conversion of 80% in CO₂, which decreased to about 60% when water was added. Full article

Upconversion nanoparticles (UCNPs) are well-reported for bioimaging. However, their applications are limited by low luminescence intensity. To enhance the intensity, often the UCNPs are coated with macromolecules or excited with high laser power, which is detrimental to their long-term biological applications. Herein, we report a novel approach to prepare co-doped CaF₂:Yb³⁺ (20%), Er³⁺ with varying concentrations of Er (2%, 2.5%, 3%, and 5%) at ambient temperature with minimal surfactant and high-pressure homogenization. Strong luminescence and effective red emission of the UCNPs were seen even at low power and without functionalization. X-ray diffraction (XRD) of UCNPs revealed the formation of highly crystalline, single-phase cubic fluorite-type nanostructures, and transmission electron microscopy (TEM) showed co-doped UCNPs are of $~$12 nm. The successful doping of Yb and Er was evident from TEM–energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy (XPS) studies. Photoluminescence studies of UCNPs revealed the effect of phonon coupling between host lattice (CaF₂), sensitizer (Yb³⁺), and activator (Er³⁺). They exhibited tunable upconversion luminescence (UCL) under irradiation of near-infrared (NIR) light (980 nm) at low laser powers (0.28–0.7 W). The UCL properties increased until 3% doping of Er³⁺ ions, after which quenching of UCL was observed with higher Er³⁺ ion concentration, probably due to non-radiative energy transfer and cross-relaxation between Yb³⁺-Er³⁺ and Er³⁺-Er³⁺ ions. The decay studies aligned with the above observation and showed the dependence of UCL on Er³⁺ concentration. Further, the UCNPs exhibited strong red emission under irradiation of 980 nm light and retained their red luminescence upon internalization into cancer cell lines, as evident from confocal microscopic imaging. The present study demonstrated an effective approach to designing UCNPs with tunable luminescence properties and their capability for cellular imaging under low laser power. Full article

The present study explores an environmentally friendly green approach to obtain cerium oxide nanoparticles via a biomediated route using Mellisa officinalis and Hypericum perforatum plant extracts as reducing agents. The as-prepared nanoparticles were studied for their structural and morphological characteristics using XRD diffractometry, scanning electron microscopy, Raman, fluorescence and electronic absorption spectra, and X-ray photoelectron spectroscopy (XPS). The XRD pattern has shown the centered fluorite crystal structure of cerium oxide nanoparticles with average crystallite size below 10 nm. These observations were in agreement with the STEM data. The cubic fluorite structure of the cerium oxide nanoparticles was confirmed by the vibrational mode around 462 cm⁻¹ due to the Ce-08 unit. The optical band gap was estimated from UV-Vis reflectance spectra, which was found to decrease from 3.24 eV to 2.98 eV. A higher specific area was determined for the sample using M. officinalis aqueous extract. The EDX data indicated that only cerium and oxygen are present in the green synthesized nanoparticles. Full article

Crystals based on alkaline earth metal difluorides are widely used optical materials. In this study, in order to expand the range of optical matrices, multicomponent Pb_1−x−yCd_xSr_yF₂ (0.27 < x < 0.55, 0.06 < y < 0.18) solid solution crystals with a fluorite structure (sp. gr. Fm-3m) were grown from melt using the vertical directional crystallization technique for the first time. The densities and refractive indices of the grown crystals vary depending on the quantitative content components (x and y) in the ranges of 6.6039(5)–7.5232(5) g/cm³ and 1.6403–1.7084, respectively. The optical transmission and electrochemical impedance spectra were studied. The homogenous composition regions of non-cellular crystallization of this ternary solid solution at a crystallization rate of 6 mm/h and an interface temperature gradient of 80 deg/cm were experimentally determined as 0.30 < x < 0.35, 0 < y < 0.6. These grown crystalline materials may be of interest as high-density highly refractive cubic isomorphic hosts and low-temperature ionic conductors (~2 × 10⁻⁵ S/cm at room temperature) for various applications. Full article

A cubic fluorite-type CeO₂ with mesoporous multilayered morphology was synthesized by the solvothermal method followed by calcination in air, and its oxygen storage capacity (OSC) was quantified by the amount of O₂ consumption per gram of CeO₂ based on hydrogen temperature programmed reduction (H₂–TPR) measurements. Doping CeO₂ with ytterbium (Yb) and nitrogen (N) ions proved to be an effective route to improving its OSC in this work. The OSC of undoped CeO₂ was 0.115 mmol O₂/g and reached as high as 0.222 mmol O₂/g upon the addition of 5 mol.% Yb(NO₃)₃∙5H₂O, further enhanced to 0.274 mmol O₂/g with the introduction of 20 mol.% triethanolamine. Both the introductions of Yb cations and N anions into the CeO₂ lattice were conducive to the formation of more non-stoichiometric oxygen vacancy (V_O) defects and reducible–reoxidizable Ceⁿ⁺ ions. To determine the structure performance relationships, the partial least squares method was employed to construct two linear functions for the doping level vs. lattice parameter and [V_O] vs. OSC/S_BET. Full article

Clean energy devices are essential in today’s environment to combat climate change and work towards sustainable development. In this paper, the potential materials A₂Ce₂O_7−δ (A = La⁺³, Nd⁺³, Bi⁺³) were analyzed for clean energy devices, specifically for conventional and single-component solid oxide fuel cells (SC-SOFCs). The wet chemical route has been followed for the preparation of samples. X-ray diffraction patterns showed that all three samples exhibited a defected fluorite cubic structure. It also revealed the presence of dopants in the ceria, which was confirmed by the fingerprint region of FTIR. The optical behavior, fuel cell performance and electrochemical behavior were studied by UV–vis, fuel cell testing apparatus and EIS, respectively. The SEM results showed that all samples had irregular polygons. In Raman spectra, the F_2g mode corresponding to the space group (Fm3m) confirms the fluorite structure. The Raman spectra showed that A₂Ce₂O_7−δ (A = La⁺³, Nd⁺³, Bi⁺³) have different trends. The conventional fuel cell performance showed that the maximum power density of Bi₂Ce₂O₇ was 0.65 Wcm⁻² at 600 °C. The performance of A₂Ce₂O_7−δ (A = La³⁺, Nd³⁺, Bi³⁺) as a single-component fuel cell revealed that Nd₂Ce₂O_7−δ is the best choice with semiconductors conductors ZnO and NCAL. The highest power density (Pmax) of the Nd₂Ce₂O₇/ZnO was 0.58 Wcm⁻², while the maximum power output (Pmax) of the Nd₂Ce₂O₇/NCAL was 0.348 Wcm⁻² at 650 °C. All the samples showed good agreement with the ZnO as compared to NCAL for SC-SOFCs. Full article

CSZM compounds were synthesized by dry chemistry route with 5, 10, and 15% dopant of Mg dopants in the Ce _0.8−2x Sm _0.2 Zr_x Mg_x O_2−d, {x = 0.05, 0.1 & 0.15}. The newly investigated materials were physically, chemically, and electrochemically studied and have shown promising results. The CSZM was crystalized in a fluorite structure with a pure cubic phase in a space group Fm3m and cell parameter a = 5.401742 $°A$ and theoretical density from 7.6 to 8.9 after firing in the air with a final temperature of 1400 °C. Characterization of the structure and indexing of electrolyte materials were made after X-ray diffraction (XRD) testing. A Scanning electron microscope (SEM) morphological analysis was used to examine the microstructure details. Electrochemical impedance spectroscopy (EIS) measurements were performed from 400 °C to 700 °C which show the highest conductivity value of 1.0461 × 10⁺¹ S/cm at 700 °C. In comparison, the minimum value was 2.7329 × 10⁻² S/cm at 400 °C, and the total activation energy (E_a$°A$) was found to be 0.6865 eV under 5% H₂/Ar. Full article

Biomass lignin can be used to produce vanillin through an oxidation process. Although its purity is high, the processing time and separation efficiency are not ideal. This research aims to produce vanillin directly from Kenaf stalks without separating the lignin first from the lignocellulosic biomass. This method is greener because it does not require the separation of cellulose and hemicellulose from the biomass, thus minimizing the use of acid and alkaline solutions and saving time. A high oxygen storage capacity and release capacity of ceria as an oxidation catalyst contribute to the reversable redox properties between Ce⁴⁺ and Ce³⁺ in ceria lattice. Cerium oxide nanostructures were synthesized using a hydrothermal method treated under alkaline NaOH, followed by drying at 120 °C for 16 h and calcining at different temperatures between 400 and 600 °C for the direct oxidation of Kenaf stalks to vanillin under microwave irradiation. The catalysts were characterized for their physicochemical properties using XRD, N₂ adsorption–desorption isotherms and TEM. All synthesized CeO₂ nanostructures showed the presence of diffraction peaks assigned to the presence of cubic fluorite. The N₂ adsorption–desorption isotherms showed that all catalysts possess a Type IV isotherm, indicating a mesoporous structure. The TEM image shows the uniform shape of the CeO₂ nanostructures, while HRTEM images show that the CeO₂ nanostructures are single-crystalline in nature. All catalysts were tested for the direct oxidation of Kenaf stalks using H₂O₂ as the oxidizing agent in temperatures ranging from 160 to 180 °C for 10–30 min with 0.1–0.3 g catalyst loading under 100–500 W of microwave irradiation. The CeO₂-Nps-400 catalyst produced the highest vanillin yields of 3.84% and 4.32% for the direct oxidation of Kenaf stalks and extraction of lignin from Kenaf stalks, respectively. Compared to our earlier study, the highest vanillin yields of 2.90% and 3.70% for direct biomass and extracted lignin were achieved using a Ce/MgO catalyst. Full article

A series of 5%Ni/Ce_1-xTi_xO₂ catalysts was prepared with nickel impregnation of mixed Ce–Ti oxides obtained via synthesis in supercritical isopropanol. All oxides have a cubic fluorite phase structure. Ti is incorporated into the fluorite structure. Small amounts of impurities of TiO₂ or mixed Ce–Ti oxides appear with Ti introduction. Supported Ni is presented as the NiO or NiTiO₃ perovskite phase. Ti introduction increases total samples reducibility and results in stronger interaction of supported Ni with the oxide support. The fraction of rapidly replaced oxygen and the average tracer diffusion coefficient also increase. The number of metallic nickel sites decreased with increasing Ti content. All catalysts except Ni-CeTi0.45 demonstrate close activity in tests of dry reforming of methane. The lower activity of Ni-CeTi0.45 can be connected to Ni decoration with species of the oxide support. The incorporation of Ti prevents detachment of Ni particles from the surface and their sintering during dry reforming of methane. Full article

Cerium oxide nanoparticles were obtained using aqueous extracts of Chelidonium majus and Viscum album. X-ray diffractometry analysis confirmed the crystalline structure of the synthesized cerium oxide nanoparticles calcined at 600 °C. Scanning electron microscopy, UV-Vis reflectance and Raman spectroscopy, XPS, and fluorescence studies were utilized to interpret the morphological and optical properties of these nanoparticles. The STEM images revealed the spherical shape of the nanoparticles and that they were predominantly uniform in size. The optical band gap of our cerium nanoparticles was determined to be 3.3 and 3.0 eV from reflectance measurements using the Tauc plots. The nanoparticle sizes evaluated from the Raman band at 464 cm⁻¹ due to the $F_{2g}$ mode of the cubic fluorite structure of cerium oxide are close to those determined from the XRD and STEM data. The fluorescence results showed emission bands at 425, 446, 467, and 480 nm. The electronic absorption spectra have exhibited an absorption band around 325 nm. The antioxidant potential of the cerium oxide nanoparticles was estimated by DPPH scavenging assay. Full article

Aedes aegypti mosquito is responsible for the transmission of some of the most serious vector-borne diseases affecting humans, including dengue fever, chikungunya, and Zika. The only effective method for minimizing their transmission is vector control. In this work, an environmentally friendly method for synthesizing cerium oxide nanoparticles (CeO₂ NPs) is highlighted, and the larvicidal activity against Ae. aegypti was studied. This method uses the aqueous extract of Bruguiera cylindrica leaves (BL) as an oxidizer and stabilizing agent. UV–Vis spectroscopy presented a distinctive absorbance band at 303 nm for CeO₂ NPs with a band gap of 3.17 eV. The functional groups from the plant extract connected to CeO₂ NPs were identified by FT-IR analysis, while X-ray diffraction revealed the cubic fluorite orientation of CeO₂ NPs. Zeta potential revealed a surface charge of −20.7 mV on NPs. The formation of CeO₂ NPs was confirmed by an energy dispersive spectral analysis, and TEM and DLS revealed an average diameter of 40–60 nm. The LC₅₀ of synthesized CeO₂ against Ae. aegypti fourth instar larvae was reported to be 46.28 μg/mL in 24 h. Acetylcholinesterase (47%) and glutathione S-transferase (13.51%) activity were significantly decreased in Ae. aegypti larvae exposed to synthesized CeO₂ NPs versus the control larvae. All these findings propose the potential for using B. cylindrica leaves-synthesized CeO₂ NPs as an efficient substitute for insecticides in the management of mosquitoes. Full article