Search Results (22)

Green chemistry seeks to find alternative synthesis routes that are less harsh to living organisms and the environment. In this communication, a microwave-assisted hydrothermal technique and a thermal annealing method were used in the reduction of graphene oxide (GO) to make reduced GO (rGO). Graphite powder was oxidised using the Improved Hummers’ method, exfoliated, and freeze-dried. Thereafter, an aqueous suspension of GO was reduced under microwave (MW) irradiation for 10 min at 600 W with and without the help of a reducing agent (hydrazine hydrate). Thermal annealing reduction was also conducted under a nitrogen atmosphere at 300 °C for 1 h. Prepared samples were analysed using Raman laser spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), the Brunauer–Emmett–Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). A successful reduction in the GO functional groups between the sheets was established using XRD. In the Raman analysis, the ratio of the intensity of the D and G band (I_D/I_G) in graphene sheets assisted in assessing the quality of the graphene films. An estimation of the number of structural defects was calculated using the I_D/I_G ratio. The Raman analysis showed an increase in the I_D/I_G ratio after both oxidation and reduction processes. The defect densities of both MW-treated samples were comparable while an increased defect density was evident in the thermally annealed sample. TEM micrographs confirmed the sheet-like morphology of the samples. The rGO sheets obtained from the MW-treated method appeared to be smaller when compared to the rGO ones obtained by thermal treatment. It was also evident from XRD analysis that thermal treatment promoted the coalition of graphitic layers, such that the estimated number of layers was larger than that of GO. The elemental analysis showed that the C/O ratio of GO increased from 2 to 7.8 after MW hydrazine reduction. Full article

The hydrogen economy, as an emerging paradigm for sustainable energy, relies on efficient hydrogen oxidation (HOR) and hydrogen evolution reactions (HER). These reactions require effective catalysts to enhance reaction kinetics and reduce costs. Platinum (Pt) is widely used but faces issues such as high cost and CO poisoning. Non-precious metal catalysts, particularly Ni-based alloys, are being explored as viable alternatives. This study introduces a ternary MoWNi alloy catalyst synthesized via microwave-assisted methods and annealing. The MoWNi alloy catalyst achieves a current density of 3.5 mA·cm⁻² at an overpotential of 100 mV in HOR and requires only 25 mV overpotential to reach a current density of 10 mA·cm⁻² in HER, making it comparable to commercial 20% Pt/C catalysts. Notably, the catalyst also exhibits superior stability and resistance to CO toxicity. These findings underscore the potential of MoWNi alloy catalysts in advancing hydrogen-based energy systems. Full article

Microwave annealing, an emerging annealing method known for its efficiency and low thermal budget, has established a foundational research base in the annealing of molybdenum disulfide (MoS₂) devices. Typically, to obtain high-quality MoS₂ devices, mechanical exfoliation is commonly employed. This method’s challenge lies in achieving uniform film thickness, which limits the use of extensive data for studying the effects of microwave annealing on the MoS₂ devices. In this experiment, we utilized a neural network approach based on the HSV (hue, saturation, value) color space to assist in distinguishing film thickness for the fabrication of numerous MoS₂ devices with enhanced uniformity and consistency. This method allowed us to precisely assess the impact of microwave annealing on device performance. We discovered a relationship between the device’s electrical performance and the annealing power. By analyzing the statistical data of these electrical parameters, we identified the optimal annealing power for MoS₂ devices as 700 W, providing insights and guidance for the microwave annealing process of two-dimensional materials. Full article

The NiMn₂O₄/graphene oxide (GO) nanocomposite material was in situ grown on the surface of a nickel foam 3D skeleton by combining the solvent method with the microwave-assisted hydrothermal method and annealing; then, its performance was investigated as a superior supercapacitor electrode material. When nickel foam was soaked in GO aqueous or treated in nickel ion and manganese ion solution by the microwave-assisted hydrothermal method and annealing, gauze GO film or flower-spherical NiMn₂O₄ was formed on the nickel foam surface. If the two processes were combined in a different order, the final products on the nickel surface had a remarkably different morphology and phase structure. When GO film was first formed, the final products on the nickel surface were the composite of NiO and Mn₃O₄, while NiMn₂O₄/GO nanocomposite material can be obtained if NiMn₂O₄ was first formed (immersed in 2.5 mg/L GO solution). In a 6M KOH solution, the specific capacitance of the latter reached 700 F/g at 1 A/g which was superior to that of the former (only 35 F/g). However, the latter’s specific capacitance was still inferior to that of in-situ grown NiMn₂O₄ on nickel foam (802 F/g). Though the gauze-formed GO film, almost covering the preformed flower-spherical NiMn₂O₄, can also contribute a certain specific capacitance, it also restricted the electrolyte diffusion and contact with NiMn₂O₄, accounting for the performance decrease of the NiMn₂O₄/GO nanocomposite. A convenient method was raised to fabricate the nanocomposite of carbon and double metal oxides. Full article

This study focuses on fabricating cobalt particles deposited on graphitic carbon nitride (Co/gCN) using annealing, microwave-assisted and hydrothermal syntheses, and their employment in hydrogen and oxygen evolution (HER and OER) reactions. Composition, surface morphology, and structure were examined using inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The performance of Co-modified gCN composites for the HER and OER were investigated in an alkaline media (1 M KOH). Compared to the metal-free gCN, the modification of gCN with Co enhances the electrocatalytic activity towards the HER and OER. Additionally, thermal annealing of both Co(NO₃)₂ and melamine at 520 °C for 4 h results in the preparation of an effective bifunctional Co₃O₄/gCN catalyst for the HER with the lower E_onset of −0.24 V, a small overpotential of −294.1 mV at 10 mA cm⁻², and a low Tafel slope of −29.6 mV dec⁻¹ in a 1.0 M KOH solution and for the OER with the onset overpotential of 286.2 mV and overpotential of 422.3 mV to achieve a current density of 10 mA cm⁻² with the Tafel slope of 72.8 mV dec⁻¹. Full article

Magnesium oxide (MgO) was synthesized by three different methods: the sol–gel (SG), microwave-assisted sol–gel (MW), and hydrothermal (HT) methods for comparing the influence of the preparation conditions on the properties of the products. The powders were annealed at 450 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM/HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), BET specific surface area and porosity, photoluminescence, and UV–Vis spectroscopy. The samples consisted mainly of periclase as a crystalline phase, and the MW and HT preparation methods generated particles with higher specific surface areas. The powders had less-defined morphologies and high levels of aggregation. The optical band gaps of the samples were determined from UV DRS, and the photocatalytic activities of the magnesium oxides obtained by the three methods towards the degradation of methyl orange (MO) under UV light irradiation was evaluated. Full article

The tin-doped TiO₂ powders obtained by sol-gel and microwave-assisted sol-gel methods were investigated. The synthesis took place in a basic medium (pH 10, ammonium hydroxide, 25%) starting from tetrabutyl orthotitanate in its parental alcohol. In the case of the dopant, Tin(II) 2-ethylhexanoate as SnO₂ precursor was used in the amount of 1, 2, or 4 mol % SnO₂. Based on thermal analysis data, the powders were thermally treated in air, at 500 °C. The comparative investigation of the structure and morphology of the nanopowders annealed at 500 °C was performed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy with selected area electron diffraction (HRTEM/SAED), scanning transmission electron microscopy (STEM) coupled with EDX mapping, Fourier transmission infrared (FTIR), UV–Vis, Raman and photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), and X-ray florescence spectroscopy (XRF). The obtained materials were tested for the photocatalytic removal of methyl orange dye from aqueous solutions. High degradation efficiencies (around 90%) were obtained by Sn doping after 3 h of UV light irradiation. Full article

In this paper, we conducted a fundamental study concerning the effect of thermal treatment on the structure and morphology of 2 mol% vanadium doped ZnO nanopowders obtained by microwave assisted sol–gel method (MW). The samples were analyzed by DTA, FTIR, XRD, SEM, and UV–Vis spectroscopy. The DTA results showed that above 500 °C, there was no mass loss in the TG curves, and ZnO crystallization occurred. The XRD patterns of the thermally treated powders at 500 °C and 650 °C showed the crystallization of ZnO (zincite) belonging to the wurtzite-type structure. It was found that in the 650 °C thermally treated powder, aside from ZnO, traces of Zn₃(VO₄)₂ existed. FTIR spectra of the annealed samples confirmed the formation of the ZnO crystalline phase and V–O bands. The micrographs revealed that the temperature influenced the morphology. The increase in the annealing temperature led to the grain growth. The SEM images of the MW powder thermally treated at 650 °C showed two types of grains: hexagonal grains and cylindrical nanorods. UV–Vis spectra showed that the absorption band also increased with the increasing temperature of thermal treatment. The MW sample annealed at 650 °C had the highest absorption in ultraviolet domain. Full article

Compared with conventional silicon-based semiconductors, amorphous oxide semiconductors present several advantages, including the possibility of room-temperature fabrication, excellent uniformity, high transmittance, and high electron mobility. Notably, the application of oxide semiconductors to flexible electronic devices requires a low-temperature fabrication process. However, for the realization of semiconductor characteristics and stable products, the fabrication process requires annealing at temperatures of 300 °C or higher. To address this, a low-temperature microwave annealing method, which improves the electrical characteristics of a transistor and reduces the production time compared with the conventional annealing method, is presented herein. Microwave annealing is a well-known method of annealing that minimizes the heat energy transferred to a substrate via instantaneous heat transfer through the vibrations of the lattice in the material during microwave irradiation and is suitable as a low-temperature annealing method. In this study, we evaluate the electrical characteristics of devices subjected to conventional annealing at 200 °C and 300 °C for 1 h and microwave annealing at 200 °C for 10 min. For the device subjected to microwave annealing at 200 °C for 10 min, the threshold voltage, current on/off ratio, subthreshold swing, and saturation mobility are 13.9 V, 1.14 × 10⁵, 3.05 V/dec, and 4.23 cm²/V$·$s, respectively. These characteristic results are far superior to the characteristic results of the device subjected to conventional annealing at 200 °C for 1 h and are equivalent to those of the device treated at 300 °C for 1 h. Thus, this study develops a more effective annealing method, which facilitates low-temperature fabrication in a reduced period. Full article

The present study is focused on the synthesis of zirconium dioxide (ZrO₂) nanomaterials using the hydrothermal method assisted by microwave irradiation and solution combustion synthesis. Both synthesis techniques resulted in ZrO₂ powders with a mixture of tetragonal and monoclinic phases. For microwave synthesis, a further calcination treatment at 800 °C for 15 min was carried out to produce nanopowders with a dominant monoclinic ZrO₂ phase, as attested by X-ray diffraction (XRD) and Raman spectroscopy. The thermal behavior of the ZrO₂ nanopowder was investigated by in situ XRD measurements. From the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, the presence of near spherical nanoparticles was clear, and TEM confirmed the ZrO₂ phases that comprised the calcinated nanopowders, which include a residual tetragonal phase. The optical properties of these ZrO₂ nanopowders were assessed through photoluminescence (PL) and PL excitation (PLE) at room temperature (RT), revealing the presence of a broad emission band peaked in the visible spectral region, which suffers a redshift in its peak position, as well as intensity enhancement, after the calcination treatment. The powder resultant from the solution combustion synthesis was composed of plate-like structures with a micrometer size; however, ZrO₂ nanoparticles with different shapes were also observed. Thin films were also produced by solution combustion synthesis and deposited on silicon substrates to produce energy storage devices, i.e., ZrO₂ capacitors. The capacitors that were prepared from a 0.2 M zirconium nitrate-based precursor solution in 2-methoxyethanol and annealed at 350 °C exhibited an average dielectric constant (κ) of 11 ± 0.5 and low leakage current density of 3.9 ± 1.1 × 10⁻⁷ A/cm² at 1 MV/cm. This study demonstrates the simple and cost-effective aspects of both synthesis routes to produce ZrO₂ nanomaterials that can be applied to energy storage devices, such as capacitors. Full article

Efficient water electrolysis is one of the key issues in realizing a clean and renewable energy society based on hydrogen fuel. However, several obstacles remain to be solved for electrochemical water splitting catalysts, which are the high cost of noble metals and the high overpotential of alternative catalysts. Herein, we suggest Ni-based alternative catalysts that have comparable performances with precious metal-based catalysts and could be applied to both cathode and anode by precise phase control of the pristine catalyst. A facile microwave-assisted procedure was used for NiO nanoparticles anchored on reduced graphene oxide (NiO NPs/rGO) with uniform size distribution in ~1.8 nm. Subsequently, the Ni-NiO dual phase of the NPs (A-NiO NPs/rGO) could be obtained via tailored partial reduction of the NiO NPs/rGO. Moreover, we demonstrate from systematic HADDF-EDS and XPS analyses that metallic Ni could be formed in a local area of the NiO NP after the reductive annealing procedure. Indeed, the synergistic catalytic performance of the Ni-NiO phase of the A-NiO NPs/rGO promoted hydrogen evolution reaction activity with an overpotential as 201 mV at 10 mA cm⁻², whereas the NiO NPs/rGO showed 353 mV. Meanwhile, the NiO NPs/rGO exhibited the most excellent oxygen evolution reaction performance among all of the Ni-based catalysts, with an overpotential of 369 mV at 10 mA cm⁻², indicating that they could be selectively utilized in the overall water splitting. Furthermore, both catalysts retained their activities over 12 h with constant voltage and 1000 cycles under cyclic redox reaction, proving their high durability. Finally, the full cell capability for the overall water electrolysis system was confirmed by observing the generation of hydrogen and oxygen on the surface of the cathode and anode. Full article

This research focused on the synthesis of apatite, starting from a natural biogenic calcium source (egg-shells) and its chemical and morpho-structural characterization in comparison with two commercial xenografts used as a bone substitute in dentistry. The synthesis route for the hydroxyapatite powder was the microwave-assisted hydrothermal technique, starting from annealed egg-shells as the precursor for lime and di-base ammonium phosphate as the phosphate precursor. The powders were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), X-ray fluorescence spectroscopy (XRF), and cytotoxicity assay in contact with amniotic fluid stem cell (AFSC) cultures. Compositional and structural similarities or differences between the powder synthesized from egg-shells (HA1) and the two commercial xenograft powders—Bio-Oss^®, totally deproteinized cortical bovine bone, and Gen-Os^®, partially deproteinized porcine bone—were revealed. The HA1 specimen presented a single mineral phase as polycrystalline apatite with a high crystallinity (X_c 0.92), a crystallite size of 43.73 nm, preferential growth under the c axes (002) direction, where it mineralizes in bone, a nano-rod particle morphology, and average lengths up to 77.29 nm and diameters up to 21.74 nm. The surface of the HA1 nanoparticles and internal mesopores (mean size of 3.3 ± 1.6 nm), acquired from high-pressure hydrothermal maturation, along with the precursor’s nature, could be responsible for the improved biocompatibility, biomolecule adhesion, and osteoconductive abilities in bone substitute applications. The cytotoxicity assay showed a better AFSC cell viability for HA1 powder than the commercial xenografts did, similar oxidative stress to the control sample, and improved results compared with Gen-Os. The presented preliminary biocompatibility results are promising for bone tissue regeneration applications of HA1, and the study will continue with further tests on osteoblast differentiation and mineralization. Full article

In the present work, the structures and magnetic properties of (Nd, Pr, Ce) ₂Fe₁₄B/α-Fe nanocomposite magnets were thoroughly investigated. The microwave annealing was applied to achieve a uniform heating effect and uniform grains. Microwave annealing is more favorable to obtain α-Fe phase than conventional annealing, which leads to the enhanced coercivity of hysteresis loops. The coercivity of nanocomposite magnets was 245 kA/m after annealing at 2000 W for 10 min. Full article

In this study, we implemented a high-performance two-terminal memristor device with a metal/insulator/metal (MIM) structure using a solution-derived In-Ga-Zn-Oxide (IGZO)-based nanocomposite as a resistive switching (RS) layer. In order to secure stable memristive switching characteristics, IGZO:N nanocomposites were synthesized through the microwave-assisted nitridation of solution-derived IGZO thin films, and the resulting improvement in synaptic characteristics was systematically evaluated. The microwave-assisted nitridation of solution-derived IGZO films was clearly demonstrated by chemical etching, optical absorption coefficient analysis, and X-ray photoelectron spectroscopy. Two types of memristor devices were prepared using an IGZO or an IGZO:N nanocomposite film as an RS layer. As a result, the IGZO:N memristors showed excellent endurance and resistance distribution in the 10³ repeated cycling tests, while the IGZO memristors showed poor characteristics. Furthermore, in terms of electrical synaptic operation, the IGZO:N memristors possessed a highly stable nonvolatile multi-level resistance controllability and yielded better electric pulse-induced conductance modulation in 5 × 10² stimulation pulses. These findings demonstrate that the microwave annealing process is an effective synthesis strategy for the incorporation of chemical species into the nanocomposite framework, and that the microwave-assisted nitridation improves the memristive switching characteristics in the oxide-based RS layer. Full article

In this paper, a series of structurally modified silicate-substituted apatite co-doped with Sr²⁺ and Eu³⁺ ions were synthesized by a microwave-assisted hydrothermal method. The concentration of Sr²⁺ ions was set at 2 mol% and Eu³⁺ ions were established in the range of 0.5–2 mol% in a molar ratio of calcium ion amount. The XRD (X-ray powder diffraction) technique and infrared (FT-IR) spectroscopy were used to characterize the obtained materials. The Kröger–Vink notation was used to explain the possible charge compensation mechanism. Moreover, the study of the spectroscopic properties (emission, emission excitation and emission kinetics) of the obtained materials as a function of optically active ions and annealing temperature was carried out. The luminescence behavior of Eu³⁺ ions in the apatite matrix was verified by the Judd–Ofelt (J-O) theory and discussed in detail. The temperature-dependent emission spectra were recorded for the representative materials. Furthermore, the International Commission on Illumination (CIE) chromaticity coordinates and correlated color temperature were determined by the obtained results. Full article