Microwave Assisted Sol Gel Technique Research Articles

High temperature photoluminescence dependence and energy migration of Tb3+-Incorporated K3Y(BO2)6 phosphors

This study investigates the structural and photoluminescence (PL) characteristics of Tb3+-incorporated K3Y(BO2)6 (KYBO) phosphors synthesized via a microwave-assisted sol-gel technique. X-ray diffraction (XRD) and Rietveld refinement confirmed the formation of a pure hexagonal phase, with lattice expansion due to Tb³⁺ doping. PL studies revealed strong green emissions centered at 541 nm, attributed to the ⁵D₄ → ⁷F₅ transitions of Tb³⁺ ions, with the highest intensity observed at 5 wt% Tb³⁺. A decrease in emission was observed at higher concentrations due to concentration quenching. Temperature-dependent PL measurements revealed reverse thermal quenching enhancing PL intensity. Chromaticity analysis based on CIE 1931 coordinates showed stable green emission across all concentrations, with a maximum color purity of 89.74% observed for the KYBO:3 wt% Tb³⁺ sample. The results, along with reverse thermal quenching behavior observed between 470K and 550K, suggest that these phosphors exhibit excellent potential for lighting and display technologies.

Temperature-dependent photoluminescence of novel Eu3+, Tb3+, and Dy3+ doped LaCa4O(BO3)3: Insights at low and room temperatures

This study explores the structural and optical qualities of LaCa4O(BO3)3 (LACOB) phosphors doped with Eu3+, Dy3+, and Tb3+ using a microwave-assisted sol-gel technique. It uncovers oxygen-related luminescence defects in LACOB, highlighting emission peaks at 489 and 585 nm for Dy3+, a distinct sharp peak at 611 nm for Eu3+ in the red spectrum, and a notable green emission for Tb3+ due to specific transitions. The photoluminescence (PL) analysis indicates that luminescence is optimized through precise doping, leveraging dipole interactions, and localized resonant energy transfer, which are influenced by dopant concentration and spatial configuration. Temperature studies show emission intensity variations, particularly noticeable below 100 K for Tb3+ doped samples, demonstrating the nuanced balance between thermal quenching and luminescence efficiency. This temperature dependency, alongside the identified optimal doping conditions, underscores the potential of these materials for advanced photonic applications, offering insights into their thermal behavior and emission mechanisms under different conditions.

A study on microwave synthesis of unique Zn1-3xCuxCexCrxO nanoparticles with efficient photocatalytic reactivity under visible sunlight irradiation

The study investigates the synthesis and characterization of Cu, Ce, and Cr co-doped ZnO nanoparticles (Zn1-3xCuxCexCrxO with x = 0.00, 0.03, and 0.05) using a microwave-assisted sol–gel technique. Powder X-ray diffraction confirmed the monoclinic structure of the nanocrystalline ZnO with an average crystallite size ranging from 41 nm to 47 nm. Fourier-transform infrared analysis revealed chemisorption of H2O and CO2 onto the ZnO surface upon exposure to the atmosphere. Energy-dispersive X-ray spectroscopy confirmed the presence of Zn, Cu, Ce, Cr, and O in the samples. Scanning electron microscopy images depicted agglomerated crystals with both agglomeration and non-agglomeration of smaller crystallites. Notably, a red shift in the UV–Vis spectrum was observed at a 3 % doping concentration, with an increase in photocatalytic efficiency from 56 % to 67 % compared to pure ZnO. Furthermore, an overall enhancement in photocatalytic performance was noted with increasing doping concentration, indicating potential applications in organic pollutant degradation. The study also highlighted a decrease in the band gap between pure and doped ZnO with escalating doping content, suggesting promising prospects for photocatalytic applications by suppressing carrier recombination.

Antimicrobial Activity of Ga-Doped Hydroxyapatite Nanostructures: Synthesis, Morphological, Spectroscopic, and Dielectric Properties

In the present paper, seven samples of hydroxyapatite (HAp) nanoparticles doped with different amounts (e.g., 0%, 1%, 3%, 6%, 9%, 12%, and 15% [wt.]) of Ga-ions were synthesized at low temperature using the microwave-assisted sol–gel technique. FT-Raman/Fourier-transform infrared (FTIR) technique, X-ray diffraction (XRD), dielectric/alternating current conductivity measurements, scanning electron microscopy, and antimicrobial tests were utilized in order to characterize the synthesized samples. The Ga content was observed to affect the crystallite size as well as the crystallinity of HAp. Variations were observed in the lattice parameters, lattice strain, and dislocation density. FTIR analysis revealed that HAp structure possessed the carbonate group. Thus all samples have promising medical applications, as this group improves the bioactivity of HAp. Dielectric properties, as well as the alternating current electrical conductivity, were also observed to be affected by the Ga content. Furthermore, the present study demonstrated that the Ga-doped HAp nanostructures exerted a considerable inhibitory effect on bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli) and fungi (Candida albicans). Therefore, the Gadoped HAp nanostructures are proposed as a promising candidate for applications in the field of bone cement engineering.

SOFT X-RAY IRRADIATION OF SILICATES: IMPLICATIONS FOR DUST EVOLUTION IN PROTOPLANETARY DISKS

ABSTRACT The processing of energetic photons on bare silicate grains was simulated experimentally on silicate films submitted to soft X-rays of energies up to 1.25 keV. The silicate material was prepared by means of a microwave assisted sol–gel technique. Its chemical composition reflects the Mg2SiO4 stoichiometry with residual impurities due to the synthesis method. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan. We found that soft X-ray irradiation induces structural changes that can be interpreted as an amorphization of the processed silicate material. The present results may have relevant implications in the evolution of silicate materials in X-ray-irradiated protoplanetary disks.

Studies on photocatalytic performance and photodegradation kinetics of zinc oxide nanoparticles prepared by microwave-assisted sol–gel technique using ethylene glycol

ZnO nanoparticles with an average particle size of 27 nm were fabricated using a microwave-assisted sol–gel method in the presence of ethylene glycol. The nanoparticles were characterized by X-ray diffraction, Monshi’s equation, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The band gap energy of the nanoparticles was measured to be 3.27 eV by UV–Vis absorption and reflection spectroscopy. Photocatalytic activity of the synthesized nanoparticles was assessed by degrading nitrophenol in aqueous solution under UV-C irradiation. The effects of initial nitrophenol concentration, amount of photocatalyst, and of pH on the photodegradation process were investigated. Degradation samples were analyzed by UV–Vis spectroscopy. Nitrophenol was removed by 98 % within 240 min. The degradation kinetics were studied and fitted well to pseudo-first-order and Langmuir–Hinshelwood models.

La-doped ZnO nanoflower as photocatalyst for methylene blue dye degradation under UV irradiation

Lanthanum doped ZnO flower-like structured nanoparticles were synthesized through microwave assisted sol–gel technique. X-ray diffraction, scanning electron microscopy, transmission electron microscopy analysis confirmed the size, structural morphology and successful compound formation of the samples. The band gap was calculated from Tauc’s plot using UV–Vis spectroscopy data. Lanthanum doped ZnO nanoparticles were used for the photocatalytic degradation of methylene blue dye under UV light irradiation. Compared to pure ZnO sample, La-doped samples exhibited higher photocatalytic dye degradation under UV light irradiation with short time duration. Among the different amounts of dopant, 3 mol% La-doped ZnO nano rods showed the highest degradation with short time UV light irradiation (60 min). Other factors such as particle size, morphology and defects also affect the photocatalytic activity. In our study, the main factor that influence photocatalytic activity is the separation of photo induced electron–hole pair due to defects formation in the sample. The 3 mol% sample has the appropriate electron–hole separation due to defects compared to pure ZnO. The influence of defects on the photocatalytic activity of all samples has been revealed using photoluminescence spectroscopy analysis. Furthermore, the effect of various operational parameters such as photocatalyst quantity, dye concentration and dopant concentrations were also optimized.

Microwave-assisted sol–gel synthesis of BiFeO3 nanoparticles

Among the various multiferroic materials bismuth iron oxide is a promising candidate due to its relatively high antiferromagnetic Neel temperature and high ferroelectric Curie temperature as compared to all other multiferroic materials. However, synthesis of phase pure BiFeO3 is extremely difficult due to the volatile nature of Bi2O3 that leads to bismuth-deficient phases and if excess of bismuth is employed it gives rise to bismuth rich phases. Moreover, the synthesis of phase pure BiFeO3 requires high temperature annealing in the range of 400–700 °C. In order to overcome these difficulties, we here report microwave-assisted sol–gel synthesis of phase pure BiFeO3 nanoparticles. In the present study, power of microwaves is varied as 136, 264, 440, 616 and 800 W. XRD results show formation of phase pure BiFeO3 with rhombohedrally distorted perovskite structure at 264, 440 and 800 W. Crystallite size decreases to 21 nm with the increase in microwave power to 800 W. The presence of absorption bands at 470 and 580 cm−1 in FTIR spectra, corresponding to FeO6 and BiO6, indicate the formation of pure BiFeO3 phase. BiFeO3 nanoparticles show high dielectric constant (135 at 1 kHz) at 264 W. SEM images show the formation of spherical and cubic nanoparticles in the range of 100–150 nm with microwave powers of 136–440 W. Increasing the microwave power to 616 W gives spherical nanoparticles with sizes of 60 nm while further increasing the microwave power to 800 W results in nanoneedles with diameter of 30 nm. Ferromagnetic behavior, instead of antiferromagnetic nature of BiFeO3, is observed for the nanoparticles prepared at microwave power of 616 and 800 W. This demonstrates that microwave-assisted sol–gel technique gives phase pure BiFeO3 nanoparticles using low power and less time, along with excellent ferromagnetic and dielectric properties as compared to conventional heating method.

Low-temperature co-sintering of co-ionic conducting solid oxide fuel cells based on Ce0.8Sm0.2O1.9-BaCe0.8Sm0.2O2.9 composite electrolyte

A composite electrolyte Ce0.8Sm0.2O1.9-BaCe0.8Sm0.2O2.9 (SDC-BCS) material for co-ionic conducting solid oxide fuel cells was prepared by microwave-assisted sol-gel technique. The crystallization, morphology, and sintering characteristics were investigated by X-ray diffraction and scanning electron microscopy. The obtained SDC-BCS composite electrolyte powders distribute uniformly, and SDC and BCS crystalline grains play a role as matrix for each other in the composite electrolyte. Anode-supported solid oxide fuel cells of NiO-Ce0.8Sm0.2O1.9/Ce0.8Sm0.2O1.9-BaCe0.8Sm0.2O2.9/Ce0.8Sm0.2O1.9-SrCo0.9Ti0.1O2.55 (NiO-SDC/SDC-BCS/SDC-SCT) were fabricated based on the nanocomposite electrolyte powders. The electrochemical performances were tested at 500–650 °C using humidified hydrogen as fuel. Results demonstrated that the anode-supported half cells could be sintered at 1,300 °C with a dense electrolyte layer and a porous anode structure. Moreover, the single cell with 40-μm-thick electrolyte layer achieved an open-circuit voltage (OCV) of 0.77 V and a maximum power density of 621 mW cm−2 at 650 °C.

Visible light responsive Ag/TiO2/MCM-41 nanocomposite films synthesized by a microwave assisted sol–gel technique

A convenient and inexpensive method for the preparation of visible light responsive nanocomposite film was introduced in this study. Silver doped TiO2 was incorporated into as-synthesized MCM-41, via a microwave assisted sol–gel technique. The nanocomposite film was formed by dip coating on a glass substrate. The characterization results displayed high adsorbability and photocatalytic properties of the Ag and MCM-41 enhanced TiO2 photocatalyst. Performance of the nanocomposite film was tested by photocatalytic decolorization of MB dye, under UV and visible light irradiation. Ag/Ti/Si (0.1/1/2) exhibited the highest photocatalytic decolorization of methylene blue, with an efficiency of 81% under UV, and 30% under visible light irradiation. The kinetic rate constant of MB dye on the composite films followed pseudo first-order reaction law (R2>0.9), arranged in the order of Ag/Ti/Si (0.1/1/2)>Ag/Ti/Si (0.1/1/1)>Ag/Ti/Si (0.1/1/0.5)>Ag/Ti/Si (0.1/1/0)>TiO2.

Microwave-assisted synthesis and characterization of Ti 1 − x V xO 2 (x = 0.0–0.10) nanopowders

Ti 1 − x V xO 2 (x = 0.0–0.10) nanopowders were successfully synthesized by a microwave-assisted sol–gel technique and their crystal structure and electronic structure were investigated. The products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV–Vis spectroscopy. The results revealed that TiO 2 powders maintained the anatase phase for calcination temperature below 600 °C, but gradually changed to the rutile phase above 800 °C. The formation of the rutile phase was completed at 1000 °C. For Ti 1 − x V xO 2 (x = 0.05) powders, the phase transformation appeared at 600 °C. The absorption edge of Ti 1 − x V xO 2 (x > 0) powders broadened to the visible region with increasing V concentration and a strong visible light absorption was obtained with 10% V doping. V doping and subsequent coexistence of both anatase and rutile phases in our Ti 1 − x V xO 2 nanoparticles are considered to be responsible for the enhanced absorption of visible light up to 800 nm.

TiO2–SiO2 hard coating on polycarbonate substrate by microwave assisted sol–gel technique

To enhance the poor scratch resistance of polycarbonate, a silica (SiO2) and titania (TiO2) transparent inorganic coatings was designed and synthesized using a microwave assisted sol–gel heating. Due to the transparency of PC to microwave, the idea was to obtain a localized heating only on the coating film. The obtained films were fully characterized to mainly evaluate the effect of titania content, added both as nanoparticles and from tetraethyl orthotitanate, TEOT, on scratch resistance and surface morphology. Particular attention was paid to preserve the transparency of the final product. The results allowed to define that TEOT addition enhances the adhesion between coating and polycarbonate, even if the optimized quantity have to be defined in order to avoid a decrease of coating mechanical resistance. In this work optimized TEOT level results to be the associated to 5 wt% of TiO2, which enable the better balancing between adhesion and mechanical resistance performances.

Influence of the OH groups on the photocatalytic activity and photoinduced hydrophilicity of microwave assisted sol–gel TiO 2 film

In the present work the influence of the OH groups on the photocatalytic activity and the photoinduced hydrophilicity of microwave assisted sol–gel TiO 2 films was investigated. The prepared TiO 2 films were characterized using XRD and AFM. Furthermore, the surface of the TiO 2 films was examined by help of XPS in order to determine the amount of OH groups before and after UV irradiation at different humidities. The activity of the TiO 2 films was determined using stearic acid as a model compound and the photoinduced superhydrophilicity was investigated through contact angle measurements. The results of this investigation showed that the microwave assisted sol–gel technique produces highly homogeneous and efficient TiO 2 films without the need for heat treatment for crystallization. Based on the conducted experiments it is suggested that the amount of OH groups on the TiO 2 surface highly influence the photocatalytic activity and the photoinduced superhydrophilicity and that the two mechanisms may be closely related. It is suggested that the superhydrophilicity is obtained through a combination of photocatalytic degradation of organic contaminants and surface structural changes in form of an increased amount of OH-groups.

Surface properties and photocatalytic activity of nanocrystalline titania films

In this work the efficiency and physicochemical details of a thin film produced by help of a microwave assisted sol gel technique is compared to different commercial powders (Degussa P25 and Hombikat UV100) deposited on glass substrates. Furthermore, a supercritical produced TiO 2 powder (SC 134) was included in the comparison. The prepared TiO 2 films were characterized using XRD, XPS, AFM, DSC and DLS. The photocatalytic activity was determined using stearic acid as a model compound. Investigation of the prepared films showed that the Degussa P25 film and the sol–gel film were the most photocatalytic active films. The activity of the films was found to be related to the crystallinity of the TiO 2 film and the amount of surface area and surface hydroxyl groups. Based on the XPS investigation of the films before and after UV irradiation it was suggested that the photocatalytic destruction of organic matter on TiO 2 films proceeds partly through formation of hydroxyl radicals which are formed from surface hydroxyl groups created by interactions between adsorbed water and vacancies on the TiO 2 surface. Furthermore a correlation between the amount of OH groups on the surface of the different TiO 2 films and the photocatalytic activity was found.