Citrate Sol Gel Method Research Articles

Preparation and Electrochemical Performance of Alkaline Earth Metal-Doped Nd2Ce2O7 Proton Conductor Hydrogen Separation Membranes

Nd2Ce2O7 is a rare earth oxide with a fluorite structure and exhibits proton conductivity. Alkaline earth metals (Mg, Ca, Sr, Ba) doped Nd2Ce2O7 powders were synthesized using the citrate sol-gel method. The doped samples retain the fluorite structure, and enhanced oxygen vacancy concentration. Notably, Nd1.85Mg0.15Ce2O7-δ exhibited the highest oxygen vacancy concentration, reaching an electrical conductivity of 2.91×10-2 S•cm-1 in a humid atmosphere of 20%H2 and 80%N2 at 900°C. Hydrogen separation membranes were fabricated using alkaline earth metal-doped Nd2Ce2O7 as the proton-conducting phase and Pt as the electron-conducting phase. The results indicated that Pt-Nd1.85Mg0.15Ce2O7-δ had the optimal hydrogen permeation flux, reaching 8.35×10-9 mol•cm-2•s-1 at 900°C. It demonstrated short-term stability in environments containing CO2 and H2O, and an increase in temperature and hydrogen partial pressure on the feed side enhanced hydrogen permeation, highlighting its potential as a hydrogen separation membrane material.

Enhanced photocatalytic and antimicrobial properties of nickel-doped barium M-type hexaferrites synthesized via citrate sol-gel method

Industrial activities release waste into aquatic sources, which is hazardous because of the pathogenic and cytotoxic behaviour of the contaminants present in the effluent. To address this issue, the citrate sol-gel auto-combustion method synthesized nickel-substituted barium M-type hexaferrites BaNixFe12−xO19 (x = 0.0, 0.1, 0.2) nanoparticles. The nanoparticles show the single-phase hexaferrite structure having a crystallite size of 52.47 to 49.30 nm with the space group P63/mmc. Magnetic study of nanoparticles indicates that increased nickel ions give rise to saturation magnetization, whereas coercivity decreases. The band gap values of the pure and Ni-doped barium hexaferrites determined by Tauc plots have been noticed to range from 1.42 eV to 1.26 eV. The photocatalytic activity of nanoparticles for methyl orange (MO) dye has been investigated. The nanoparticles have shown a dye degradation efficiency of 84.5 % within 100 min. The antimicrobial properties of the synthesized nanoparticles have also been studied. The effectiveness of synthesized nanoparticles against two types of bacteria, gram-positive Staphylococcus aureus and gram-negative Escherichia coli, as well as against two pathogenic fungi, Candida albicans and Aspergillus niger, has been investigated. The antibacterial effect has been demonstrated by all samples at all concentrations, with MIC values ranging from 1 to 4 mg/ml. Therefore, this study investigates the potential applications of nickel-doped barium M-type hexaferrites nanoparticles in real-world biological settings, suggesting their promising role in fighting against bacterial and fungal infections.

Impact of Ho substitution on structure, magnetic and electromagnetic properties hard-soft nanocomposites

This work presented the effect of Ho substitution on magnetic and electrodynamic properties of hard-soft SrBaHoxFe12-xO19@NiFe2O4 (x ≤ 0.06) nanocomposites (H/S Ho → SBFeO@NFO NCs) which were produced through one-pot citrate sol–gel method. The structure and morphology were explored using X-ray diffractometry (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM). By scrutinizing hysteresis curves at temperatures of 300 K (Room temperature, RT) and 10 K, the magnetic characteristics of H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs have been investigated. These materials display smooth, open hysteresis loops at both temperatures, indicating their ferrimagnetic nature and highlighting the presence of exchange-coupling interactions within the nanocomposites. The SQR (squareness ratio) values, below 0.5 at both high and low temperatures, indicate a multi-domain structure in the H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs. Magnetic parameters demonstrate fluctuations with growing Ho content. The introduction of Ho3+ ions notably reduce the coercivity of the undoped H/S Ho → SBFeO@NFO (x ≤ 0.06) NCs. Saturation magnetization (Ms) and magnetic moment show similarity between undoped and Ho-doped nanocomposites at all concentrations, except for x = 0.06, where a considerable decrease occurred at both temperatures. Our findings propose that by controlling the concentration of Ho3+ ions, the magnetic properties of H/S Ho → SBFeO@NFO NCs can be precisely adjusted. Electromagnetic properties of the H/S Ho → SBFeO@NFO NCs were investigated in the range 33–50 GHz. Frequency dispersions of the real/imaginary parts of permittivity and permeability were determined from S11 to S21 parameters. RL coefficient demonstrated intensive electromagnetic absorption with average level −16…−23 dB in this frequency range that corresponded to the absorption of the natural media.

Structural, Optical, Electrical and Photocatalytic Investigation of n-Type Zn2+-Doped α-Bi2O3 Nanoparticles for Optoelectronics Applications.

Herein, n-type pure and Zn2+-doped monoclinic bismuth oxide nanoparticles were synthesized by the citrate sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) analysis, ultraviolet-visible (UV-vis) spectroscopy, and Hall effect measurements were used to study the effect of Zn2+ on the structural, optical, and electrical properties of nanoparticles. XRD revealed the monoclinic stable phase (α-Bi2O3) of all synthesized samples and the crystallite size of nanoparticles increased with increasing concentration of dopant. Optical analysis illustrated the red shift of absorption edge and blue shift of band gap with increasing concentration of dopant. Hall Effect measurements showed improved values (2.79 × 10-5 S cm-1 and 6.89 cm2/V·s) of conductivity and mobility, respectively, for Zn2+-doped α-Bi2O3 nanoparticles. The tuned optical band gap and improved electrical properties make Zn2+-doped α-Bi2O3 nanostructures promising candidates for optoelectronic devices. The degradation of methylene blue (MB, organic dye) in pure and zinc-doped α-Bi2O3 was investigated under solar irradiation. The optimum doping level of zinc (4.5% Zn2+-doped α-Bi2O3) reveals the attractive photocatalytic activity of α-Bi2O3 nanostructures due to electron trapping and detrapping for solar cells.

Ce-doped LaMnO3-δ perovskite as an efficient ozonation catalyst for the degradation of high-concentration phenol wastewater

In this study, a series of La1−xCexMnO3-δ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) perovskites with different Ce doping ratios were synthesized by the citrate sol-gel method for catalytic ozonation degradation of phenol at high concentration. Among them, the La0.9Ce0.1MnO3-δ catalyst showed the best catalytic performance, increasing COD removal nearly three times compared with ozonation alone. The COD removal of the catalysts was 0.1 > 0.3 > 0 > 0.5 > 0.7 > 0.9 > 1.0, which corresponded to COD removal of 67.56 %, 58.12 %, 57.94 %, 53.68 %, 52.18 %, 49.19 %, and 39.24 %, respectively. SEM, BET, and XRD characterized the structural performance of the catalysts. The two critical parameters of catalyst dosage and pH were also optimized. Simultaneous reproducibility experiments demonstrated the good reusability of the catalyst. In addition, the catalytic degradation mechanism was investigated by the qualitative and quantitative detection of free radicals, EPR, fluorescence detection, XPS and TPD/TPR tests, which indicated that the surface hydroxyl groups, oxygen vacancies, and Mn(Ⅲ)/Mn(Ⅳ) and Ce(Ⅲ)/Ce(Ⅳ) redox pairs on the surface of the catalysts were the potential active sites for the decomposition of ozone to ROSs. The doping of Ce can effectively increase the number of active sites and promote the electron cycling process, thus generating large amounts of •OH and O2-•, effectively mineralizing phenol.

Frequency tunable Ni–Ti‐substituted Ba–M hexaferrite for efficient electromagnetic wave absorption in 8.2–75 GHz range

The development of 5G telecommunication technology has seen a high demand for effective electromagnetic (EM) wave absorbers in the millimeter wave (mmWave) band. Because hexagonal M‐type ferrite is known to have high ferromagnetic resonance (FMR) in the 5G band frequency, it has attracted significant attention as a mmWave absorber. However, study of the relationship between magnetocrystalline anisotropy, FMR frequency, and EM wave absorption performance in the mmWave band remains insufficient. In this study, Ni–Ti‐substituted M‐type barium ferrite (Ba–M ferrite) was synthesized using the citrate sol–gel method, and the change in the magnetic properties caused by Ni–Ti substitution was analyzed. The complex permittivity, permeability, and reflection loss (RL) of the Ni–Ti‐substituted Ba–M ferrite composites in the 8.2–75 GHz broadband frequency range were also studied. The EM wave absorption frequency, which is governed by the FMR frequency, could be tuned by controlling the amount of substituted Ni–Ti ions in the Ba–M ferrite. The prepared EM wave absorber exhibited excellent EM wave absorption properties with an RL of −52 dB at 29.5 GHz and a matching thickness of 0.95 mm. This study provides insights into a frequency‐tunable EM wave absorber with enhanced absorption properties, attained by changing the magnetic properties of Ni–Ti‐substituted M‐type hexaferrites in the mmWave frequency band.

Inorganic Green Pigments Based on LaSr2AlO5

La1.03Sr1.97Al0.97M0.03O5 (M = Fe, Co, Ni, and Cu) samples were synthesized using a citrate sol–gel method to develop a novel environmentally friendly inorganic green pigment. Among them, the Co-doped sample exhibited a vivid yellow, but not green. Then, (La0.94Ca0.06)Sr2(Al0.97Mn0.03)O5 was synthesized and characterized with respect to the crystal structure, optical properties, and color. The sample was obtained in a single-phase form and the lattice volume was smaller than that of the (La0.94Ca0.06)Sr2AlO5 sample, indicating that Mn ions in the lattice of the sample were pentavalent. The sample exhibited optical absorption at a wavelength below 400 nm and around 650 nm. These absorptions were attributed to the ligand, the metal charge transfer (LMCT), and d-d transitions of Mn5+. Because the green light corresponding to 500 to 560 nm was reflected strongly, the synthesized sample exhibited a bright green color. (La0.94Ca0.06)Sr2(Al0.97Mn0.03)O5 showed high brightness (L* = 50.1) and greenness (a* = −20.8), and these values were as high as those of the conventional green pigments such as chromium oxide and cobalt green. Therefore, the (La0.94Ca0.06)Sr2(Al0.97Mn0.03)O5 pigment is a potential candidate for a novel environmentally friendly inorganic green pigment.

Ultrasound-induced PMS activation for acrylonitrile degradation with series LTZ perovskite-like catalysts: Synergistic and mechanistic insight

The degradation of toxic and refractory pollutants requires an efficient, environmentally friendly, and cost-effective treatment process to address the current challenges associated with wastewater. Herein, we present a hybrid system (LaTixZn1−xO3/PMS/US) that utilizes ultrasound irradiation to activate PMS (peroxymonosulfate) for the degradation of acrylonitrile. The system incorporates a series of perovskite-like catalysts LaTixZn1−xO3 (x = 0.2, 0.4, 0.6, 0.8, 1) fabricated using citric sol-gel method. The texture properties, surface morphology and composition of synthesized catalysts were analyzed by TEM, FESEM/EDS, FTIR, XRD and XPS. Furthermore, influences of operation parameters such as catalyst dose, PMS dose, pH, and US power, co-existing anions were investigated along with PMS utilization efficacy and its consumption rate. Under the optimal conditions, catalyst 0.75LTZ exhibited remarkable catalytic activity for acrylonitrile degradation (98.7%), with synergistic index value (3.363). The trapping experiments and EPR analysis revealed that ROS (SO4•− and •OH) both played a pivotal role in acrylonitrile removal, accordingly a rational mechanism was elucidated. The co-existing ions species HCO3– showed a strong inhibitory effect on acrylonitrile degradation compared to other ionic species (NO3–, Cl–, and SO42–). Based on the GC-MS analysis and existing literature, four possible pathways for the degradation of acrylonitrile were suggested. The treatment process incurred a cost of around 0.081$ per liter of wastewater in the 0.75LTZ/PMS/US system.

Detailed investigation on structural, optical, dielectric and magneto-dielectric properties with enhanced magneto-impedance characteristic of NdFeO3 nanoparticles

NdFeO3 (NFO) was synthesized using sol-gel citrate method and subsequent calcination at 1023 K. Utilizing Rietveld refinement analysis of the XRD pattern, it has been verified that NFO exhibits an orthorhombic crystal structure, with space group Pbnm. NFO grains were seen to be strongly agglomerated in a SEM image, despite their irregular shapes. The analysis of optical properties revealed a transmittance range of ∼20%–∼50% and an optical band gap of 2.15 eV for the NFO material. The dielectric properties of NFO were analyzed with respect to their dependence on frequency and temperature, while the ac electrical conductivity was studied in terms of its frequency variation. The dielectric dispersion behavior of NFO is explained by Maxwell Wagner-type polarization. A negative magneto-dielectric (MD) coupling of −19% and −35% was measured for ε and tanδ at 1 kHz for NFO. Magneto-impedance measurements on NFO showed positive magneto-resistance and both positive and negative magneto-capacitance, suggesting that the grain effect had a substantial role in the material's magnetic properties. These results suggest that NFO is an excellent choice for memory-based electronic devices with an appropriate band gap for optoelectronic applications having a large MD effect.

Synthesis, characterization, and feasibility investigation of dysprosium-doped samarium iron oxide nano-powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite for dynamic magneto-mechanical stability

In this study, the synthesis and characterization of a dysprosium-doped samarium iron oxide nano powder/polydimethylsiloxane (Dy-SmFeO/PDMS) nano-composite are described. The sol-gel citrate method was employed for the synthesis, yielding highly polycrystalline nano powders with a polymorphic distribution, as revealed by X-ray diffraction and Rietveld analysis. Raman spectroscopy was utilized to investigate the chemistry of the nano powders. Notably, the readings obtained using a vibrating sample magnetometer highlighted the intriguing ferromagnetic-to-antiferromagnetic coupling behavior of the samples. The field-emission scanning electron microscopy analysis indicated that the orthorhombic crystal surfaces were uniformly encapsulated by PDMS. Furthermore, a dynamic mechanical analysis was conducted under the influence of a magnetic field (1000 mT) revealed the excellent mechanical stability of the composite. This research highlights the potential of the Dy-SmFeO/PDMS composite as a promising magnetic material with desirable properties, opening up possibilities for various applications in fields such as micro-magnetic devices, sensors, spin valves, and actuators.

Investigation of magnetic properties and colossal magnetoresistance in nanocrystalline doped manganite

Here in, we report structural, magnetic, and magneto-transport properties of nanocrystalline La0.6Ag0.2Bi0.2MnO3 prepared using citrate sol–gel method. By using scanning and transmission electron microscopy measurements, the morphology and particle size of the sample have been confirmed. The Mn2p x-ray photoelectron spectroscopy spectra revealed the nanoparticles contained the coexistence of Mn3+ and Mn4+ ions with Mn3+/Mn4+ ratio of 2:1. Field-cooled and zero field-cooled magnetization protocols with temperature span of 5 K–300 K, confirm the paramagnetic (PM) to ferromagnetic (FM) phase transition at critical temperature, ∼ 146 K. The complete investigation of isothermal magnetization (), Arrott plots, and magnetocaloric effect as well as quantitative analysis of second-order phase transition has been studied. The criticality at the PM-FM transition was examined for the sample, and the obtained critical exponents were verified for their reliability through the utilization of the scaling hypothesis and Kouvel-Fisher plot. We observed a large magnetic entropy change (∼7 J-Kg−1K−1) at upon 5 T magnetic field strength. The renormalized magnetic entropy change plots are found to collapse onto a single curve, thus verifying the universality of the sample. Above the metal–insulator transitions the electrical resistivity shows a small polaron hopping conduction mechanism, however, at low temperatures scattering mechanism dominates and the whole range was explained by the universal percolation model. The colossal value of negative MR is found to be 88% at 168 K under an applied field strength of 2 T. As a result of our experimental data, we can grasp the intuitive understanding of magnetic as well as transport properties in Bi-doped manganite systems potential for magnetic sensors and spintronics applications.

White-light emitting BaAl2O4/CaAl4O7:x% Dy3+ (0 ≤ x ≤ 3) mixed phase nanophosphors synthesized using citrate sol-gel method

Novel mixed phase BaAl2O4/CaAl4O7 (BC) and BC: x% Dy3+ (0 ≤ x ≤ 3) nanophosphors were synthesized by the citrate sol-gel method. The morphology changed as x%Dy3+ varied. The patterns showed that the BC nanophosphors matched well with the monoclinic CaAl4O7 and hexagonal BaAl2O4 structures. Moreover, the structure of BC was not influence by the dopant. The dopant is mainly located in the BaAl2O4 phase. The crystallite sizes were estimated to be in the nanoscale order. The photoluminescence (PL) results showed that the emission was quenched for BC: x% Dy3+ (x > 2.4) be due to the quadrupole-quadrupole interaction. The emission peaks at 325, 482 and (563 and 576) nm were assigned to the bandgap defects of BC, 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. The International commission on illumination (CIE) showed the dopant (Dy3+) had changed the emission color from blue to white. This showed that the BC: x% Dy3+ (1.2 ≤ x ≤ 3) nanophosphors were potential candidates for white-light LEDs.

The influence of partial substitution of Ce with K in CeMO3 (M = Mn, Fe, Co, Ni, Cu) perovskite catalysts on soot combustion performance

A series of Ce1−xKxMO3 (M = Mn, Fe, Co, Ni, Cu, and x = 0, 0.1, 0.2, 0.3, 0.4) perovskite catalysts were synthesized by citrate sol-gel method, in which A-site element Ce was partially substituted with K. The results showed that the catalytic performance could be significantly improved by partially substituting of Ce with K in CeCoO3 catalyst for soot combustion. Ce0.8K0.2CoO3 perovskite catalyst exhibited a superior catalytic activity, and its corresponding T10, T50, T90 and SmCO2 were 326, 383, 426 °C and 98.6%, respectively. The characterization results indicated that K+ had been successfully incorporated in the perovskite crystal structure. Partially substituting of Ce with K resulted in an increase in specific surface area. It also resulted in the formation of Co4+ in the perovskite catalysts together with abundant presence of oxygen vacancies on the surface. Moreover, it was of great significance to facilitate the activation of lattice oxygen species. In situ DRIFTS result showed that NO2 produced by thermal decomposition of monodentate nitrate species played a key role in soot combustion process.

Visible upconverted and NIR luminescence properties of Er3+ and Er3+/Yb3+-doped Lu3Sc2Ga3O12 nanocrystals

Trivalent erbium and ytterbium embedded in Lu3Sc2Ga3O12 nanocrystals in the garnet phase were synthesised employing the citrate sol-gel method. The crystalline phase and size, grain size, and effect of ion concentration and laser pump power on the photoluminescence properties of lanthanide ions were systematically characterised. XRD results showed that the present phosphor was in the cubic garnet phase with an average crystallite size of 27 nm and a lattice constant of 12.325 Å. Morphology images revealed the particles to be nearly spherical and agglomerated. Partial energy level diagrams have been constructed using diffused reflectance and excitation spectra. Stokes and anti-Stokes photoluminescence spectra were observed under 980 nm laser excitation. The near-infrared (NIR) photons (980 nm) were successfully converted into visible radiation. Upconverted luminescence spectra consisted of two strong peaks located in the green and red regions, corresponding to the 2H11/2,4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of the Er3+ ion. The intensity ratio of red to green emission bands increased with increasing Er3+ or Yb3+ concentrations as well as with the pump power of laser. Power-dependent photoluminescence spectra revealed that there were two photons involved in the upconversion mechanism. The decay profiles of the thermally coupled 2H11/2,4S3/2 levels of Er3+ showed a non-exponential nature accompanied by a shortening of lifetime as the concentration increased. CIE colour co-ordinates were located in the green region and shifted to the yellow region with increasing Yb3+ ion concentration. NIR emission spectra exhibited an intense peak at around 1535 nm, attributed to the 4I13/2 → 4I15/2 transition of Er3+ ion, the intensity of which was observed to increase with the incorporation of Yb3+ ions up to 5 mol%, confirming the existence of Yb3+-to-Er3+ energy transfer processes. Therefore, the present phosphors can be used for photovoltaic cells, solid-state light emitting diodes, and display devices.

Hydrogen-Rich Gas Production by Steam Reforming and Oxidative Steam Reforming of Methanol over La0.6Sr0.4CoO3-δ: Effects of Preparation, Operation Conditions, and Redox Cycles.

La0.6Sr0.4CoO3-δ (LSC) perovskite, as a potential catalyst precursor for hydrogen (H2)-rich production by steam reforming of methanol (SRM) and oxidative steam reforming of methanol (OSRM), was investigated. For this purpose, LSC was synthesized by the citrate sol-gel method and characterized by complementary analytical techniques. The catalytic activity was studied for the as-prepared and prereduced LSC and compared with the undoped LaCoO3-δ (LCO) at several feed gas compositions. Furthermore, the degradation and regeneration of LSC under repeated redox cycles were studied. The results evidenced that the increase in the water/methanol ratio under SRM, and the O2 addition under OSRM, increased the CO2 formation and decreased both the H2 selectivity and catalyst deactivation caused by carbon deposition. Methanol conversion of the prereduced LSC was significantly enhanced at a lower temperature than that of as-prepared LSC and undoped LCO. This was attributed to the performance of metallic cobalt nanoparticles highly dispersed under reducing atmospheres. The reoxidation program in repetitive redox cycles played a crucial role in the regeneration of catalysts, which could be regenerated to the initial perovskite structure under a specific thermal treatment, minimizing the degradation of the catalytic activity and surface.

Promising Directions in Chemical Processing of Methane from Coal Industry. Part 2. Development of Catalysts

For the creation of new highly active and stable catalysts for the complete processing of coal methane, different methods for designing catalytic systems are being applied, including the use of the effects of mutual strengthening of the action of metals and modifying the composition of the supports. Different chemical synthesis approaches were considered for obtaining supported Ni nanoparticles with controllable compositions and sizes. For the citrate sol-gel method, it was found that with an increase in the citric acid/metals molar ratio from 0 to 1, the textural characteristics (specific surface area: 76→100 m2/g) of Сe0.2Ni0.8O1.2/Al2O3 catalysts, dispersion (average particle size: 10→5 nm) and reducibility (temperature of maximum H2 consumption: 580→530 °C) of the Ni-containing species improved. For calcined in air at 500 °C catalysts it was shown that Ni2+ cations stabilized in NiO or in the Ce-Ni-O solid solution. The proportion of the latter was maximum at a citric acid/metal molar ratio equal to 0.25, which was chosen as the optimal value in the investigated range of 0.25–1.0. An increase in the calcination temperature from 500 to 900 °C contributes to the stabilization of Ni2+ in the Al-Ni-O solid solution, which leads to a slight deterioration in the textural properties of the samples and a significant difficulty in their reducibility. After reductive activation at 800 °C of Сe0.2Ni0.8O1.2/Al2O3 samples, catalytically active metal Nio nanoparticles of ~7 nm in size were formed for effective reforming of coal industry methane into synthesis gas.

Tuneable blue-green co-activated CaAl2O4: 0.1 mol% Tb3+, x mol% Sm3+ (0 ≤ x ≤ 2) nanophosphor prepared by citrate sol-gel method

This study reports the analysis of tuneable blue-green phosphor of calcium aluminate (CaAl2O4) co-doped with terbium (Tb3+) and varying concentration of samarium (Sm3+) (0 ≤ x ≤ 2). The powder samples were synthesized by using the citrate sol-gel method and annealed at 900 °C for 2 h (h) for all samples. The X-ray powder diffraction (XRD) results revealed a developing amorphous monoclinic structure of CaAl2O4. Co-doping with Tb3+ and Sm3+ slightly affected the structure of synthesized CaAl2O4. Scanning electron microscope (SEM) results showed that co-doping the host material of CaAl2O4 slightly affected the morphology of the synthesized nanopowders. The transition electron microscope (TEM) images showed that the particle sizes of the host material were affected by doping. Ultraviolet–visible (UV–Vis) reflection spectroscopy suggested that the band gap of co-doped CaAl2O4:0.1 mol% Tb3+, x% Sm3+ (0 ≤ x ≤ 2) ranges between 5.05 and 5.20 eV. The photoluminescence (PL) results showed several emission peaks located at 420, 440, 484, 548, 558, 562, 584, 603 and 654 nm. Emission peaks at 420, 440, 484 and 558 nm were attributed to the host material. The peaks at 548 and 558 nm are originating from 5D4→7F6 and 5D4→7F5 transitions of Tb3+ while the peaks at 562, 603 and 654 nm seems to be originating from the dopant of Sm3+ which may be assigned to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 transitions of Sm3+, respectively. CIE coordinates results suggested that the emission colour can be tuned from bluish to greenish as x% Sm3+ concentration is varied.

The research on CO oxidation over Ce–Mn oxides: The preparation method effects and oxidation mechanism

A series of CeO2-MnOx for highly efficient catalytical oxidation of carbon monoxide were prepared by citrate sol-gel (C), hydrothermal (H) and hydrothermal-citrate complexation (CH) methods. The outcome indicates that the catalyst generated using the CH technique (CH-1:8) demonstrated the greatest catalytic performance for CO oxidation with a T50 of 98 °C, and also good stability in 1400 min. Compared to the catalysts prepared by C and H method, CH-1:8 has the highest specific surface of 156.1 m2 g−1, and the better reducibility of CH-1:8 was also observed in CO-TPR. It is also observed the high ratio of adsorbed oxygen/lattice oxygen (1.5) in the XPS result. Moreover, characterizations by the TOF-SIMS method indicated that obtained catalyst CH–Ce/Mn = 1:8 had stronger interactions between Ce and Mn oxides, and the redox cycle of Mn3++Ce4+ ↔ Mn4++Ce3+ was a key process for CO adsorption and oxidation process. According to in-situ FTIR, the possible reaction pathway for CO was deduced in three ways. CO directly oxidize with O2 to CO2, CO adsorbed on Mn4+ and Ce3+ reacts with O to form intermediates (COO−) (T > 50 °C) and carbonates (T > 90 °C), which are further oxidized into CO2.

Tunable magnetic and microwave absorption properties of barium ferrite particles by site-selective Co2+-Zr4+ Co-doping

Co2+-Zr4+ ion-doped barium ferrite (BaFe12–2x(CoZr)xO19, x = 0.3, 0.4, 0.5) particles were prepared by a citrate sol-gel method. It is found that a single M-type barium ferrite phase exists in particles fabricated with a relatively high ion doping amount, which indicates Co2+ ions can balance the system valence and aid the entry of high-valent Zr4+ ions. With the increase in doping amount, the lattice constant and the particle size gradually increase. Moreover, the content of Fe2+ is at a lower level, and the oxygen vacancy concentration first increases and then plateaus. According to the results of first-principles calculation and Mössbauer spectral analysis, doping ions tend to replace Fe3+ at 4 f2, 4 f1, and 2b sites, continuously decreasing the coercivity and saturation magnetization. Multi-doping effectively introduces dual magnetic resonances and multiple polarization, and reduces the natural resonance frequency. In addition, it improves the impedance matching performance and the electromagnetic attenuation capabilities, leading to an excellent absorption performance in the Ku-band. The co-doped barium ferrites produce obvious interference cancellation at a specific thickness, further improving the absorption ability. The BaFe11Co0.5Zr0.5O19 can achieve the maximum microwave absorption bandwidth of 6.08 GHz, covering the entire Ku-band. When the matching thickness is 2.05 mm, it also exhibits the minimum reflection loss of − 48.16 dB at 11.94 GHz. The above results suggest that this co-doped barium ferrite possesses great potential in microwave absorption applications.

Synthesis of p-LaFeO3–n-BaTiO3 Heterojunctions and Their Room Temperature Methanol Sensing Applications

LaFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LFO) and BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BT) were prepared by citrate sol gel method. X-ray diffraction pattern of developed materials were recorded to confirm their crystalline phase formation and for the strain calculations in these materials. (x)LaFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -(1-x)BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (x = 0.10, 0.30, 0.50 and 1.0) composites were developed by solid state method. SEM images of the developed composites confirms their mesoporous structure formation. P-n heterojunctions films of (x)LaFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -(1-x)BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were prepared on integrated digitized electrodes using spin coating technique. These were further investigated for methanol sensing properties at room temperature (40°C) based on the I-V characteristics. The developed heterojunctions films using these materials are found to exhibit fast response and recovery times (i.e., 4.7 sec. and 3.7 sec respectively).