Microwave-assisted Wet Chemical Method Research Articles

β-Ni(OH)2 mediated redox catalysis for efficient hydrogen generation by reducing accumulation of bubbles in water splitting

The water-splitting efficiency depends on the design of electrodes, choice of electrode materials, and electrocatalysts for industrial and commercial use. Here, we report the design of screw pitch cylindrical electrodes deposited with β-Ni(OH)2 hexagonal nanostructures synthesized by microwave-assisted wet chemical method to overcome the accumulation of bubbles on the electrode surface. Further, β-Ni(OH)2/NiOOH coupled redox catalysis enhances electrocatalytic activities leading to a very low overpotential of 71 mV and 98 mV needed to obtain a current density of 10 mA/cm2 with a low Tafel slope of 41.2 and 32.27 mV/dec for hydrogen and oxygen evolution respectively. The remarkable hydrogen conversion efficiency of 40.39% is obtained over 250 h of electrochemical water splitting with less than 5% fluctuation. The result assures a promising method for the mass production of hydrogen fuel with high current density and long durability performance using naturally abundant materials.

Investigation on antibacterial and hemolytic properties of magnesium-doped hydroxyapatite nanocomposite

In this work, we have investigated the antibacterial and hemolytic efficacy of hydroxyapatite (HA) and Magnesium (Mg) incorporated hydroxyapatite (MHA), where the composite was synthesized by a rapid and cost-effective microwave-assisted wet chemical method. The synthesized MHA composite was characterized by using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), High-resolution transmission electron microscopy (HRTEM), in vitro antibacterial and anti-inflammatory activities. Also, the hemolytic activity of the sample was studied using the spectrophotometer technique. From the analysis, the XRD diffractogram confirms the presence of HA and MHA by the JCPDS card no: 09-0432. The chemical bonding confirmed the presence of Mg and HA in the nanocomposite and the HRTEM confirmed the spherical shape morphology of synthesized samples. The in vitro antibacterial activity of the nanocomposite was studied against the gram-positive bacteria Staphylococcus aureus and gram-negative bacteria Escherichia coli. Also, the in vitro anti-inflammatory activity of the sample was studied against the standard drug Diclofenac sodium and found to be compatible with the standard values. Further, the samples are investigated to be non-hemolytic according to the ASTM F756-00 (American Society for Testing and Materials Designation). Based on the studies, the prepared Mg-HA nanocomposite can be potential for the biomedical applications of dental, orthopaedic, and stem cell research.

A reliable chemiresistive sensor of nickel-doped tin oxide (Ni-SnO2) for sensing carbon dioxide gas and humidity

Herein, we report the chemiresistive gas and humidity sensing properties of pristine and nickel-doped tin oxide (Ni-SnO2) gas sensors prepared by a microwave-assisted wet chemical method. The structural and optical properties are characterised using X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, ultraviolet spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The structural elucidation and morphology analyses confirm a particle size of 32–46 nm, tetragonal rutile crystal structure and small cauliflower-type surface appearance. Nickel doping can tune the structure of NPs and morphology. The tested carbon dioxide gas and humidity sensing properties reveal a rapid sensing performance with high-to-moderate sensitivity. Also, the materials favour gas sensing because their sensitivity is enhanced with the increase in nickel concentration. The sensing results suggest that nickel is a vibrant metal additive to increase the gas sensitivity of the sensor. However, nickel doping decreases the electron density and increases the oxygen vacancies. Ultimately, the gas sensor produces highly rapid sensing with a response time of 4 s.

Microwave Assisted Synthesis of Titanium(IV) Doped Hydroxyapatite and its Antibacterial Activities

A rapid, efficient and cost-effective method for the synthesis of titanium(IV) doped hydroxyapatite using microwave assisted wet chemical method is reported. The synthesized hydroxyapatite and titanium(IV) doped hydroxyapatite (THA) samples were characterized by using XRD, FTIR and HR-TEM with EDAX. The antibacterial activity against Staphylococcus aureus and Escherichia coli was investigated by using the disc diffusion method showed good results. The anti-inflammatory activity by using the protein denaturation method proves to be less inflammable for in vivo applications. The hemolytic test showed that the samples are less hemolytic.

Synthesis and characterization of nickel antimonate nanoparticles: sensing properties in propane and carbon monoxide

Nickel antimonate (NiSb2O6) was synthesized by a microwave-assisted wet chemical method for its application as a potential gas sensor. The powders calcined at 600 °C were corroborated by X-ray diffraction. The microstructure of the material was analyzed by electron microscopy in its scanning and transmission versions, finding different morphologies. The average size of the nanoparticles was estimated at ~ 14.3 nm. X-ray photoelectron spectroscopy showed that the bond energies for Ni (2p) were of 855.2 and 872.9 eV, for Sb, they were of 530.28 and 539.66 eV, and for O(1s), it overlapped the Sb at 530.28 eV. Photoluminescence and UV–Vis spectroscopy measurements confirmed that the emission energy values were of 2.8 and 1.4 eV. Tests carried out in propane and CO atmospheres indicated that the NiSb2O6 nanoparticles possess good response at several concentrations and temperatures of both gases. According to our results, NiSb2O6 is a strong candidate to be applied as a gas sensor.

Investigating the synergistic effect of hybridized WO3-ZnS nanocomposite prepared by microwave-assisted wet chemical method for supercapacitor application

Several authors reported that the naked tungsten oxide (WO3) is basically poor in capacitance. In this report, we have made an attempt to enhance the capacitive performance of WO3 through compositing. The different ratios of ZnS (2wt%, 4wt%, 6wt%) was loaded with WO3 and hybridized WO3-ZnS nanocomposites were prepared by the microwave-assisted wet chemical method. The XRD analysis revealed the mixed state of the orthorhombic and monoclinic structure of WO3. In addition to that, some peaks corresponding to the cubic structure of ZnS was also observed. The average particle size was calculated as ±19nm. Microscopic studies like SEM and HRTEM analysis revealed that as-prepared nanocomposites consisted of irregular particles of relatively uniform size. The existences of functional groups are analyzed using FTIR and confirmed the chemical bonding nature and the phase shift between WO and Zn. The TGA/DTA analysis shows that as the prepared structure is stable up to 400°C temperature afterwards gradual weight loss was started. Finally, the electrochemical properties have been investigated in H2SO4 and KOH electrolyte by cyclic voltammetry and galvanic charge-discharge analysis. The maximum specific capacitances of as-synthesized samples were calculated as 44F/g, 105F/g, 120F/g and 215F/g correspondingly for the WO3 (a) particle and hybridized WO3-ZnS (b, c, d) nanocomposites in 20% KOH electrolyte. Similarly, in H2SO4 electrolyte, bare WO3 showed maximum capacitance of 246F/g and WO3-ZnS (d) exhibited a maximum capacitance of 17F/g, whereas remaining samples exhibited less than 10F/g. The long cyclic analysis showed that coulombic efficiency of WO3-ZnS composite in KOH electrolyte is more than 100% up to 4000cycles and capacitance retention is 71%.

Microwave-Assisted Fabrication of Bimetallic PdCu Nanocorals with Enhanced Peroxidase-Like Activity and Efficiency for Thiocyanate Sensing

Nanomaterials with enzyme-like characteristics (nanozymes) are an emerging alternative of traditional bioenzymes that holds great promise in a variety of fields. The activity and efficiency of most current nanozymes, however, are lower than those of natural enzymes, which will inevitably hinder their wider applications. Thus, the development of new nanozymes with favorable catalytic properties is urgently desired. In this work, we reported a coral-structured bimetallic PdCu nanozyme that exhibited enhanced peroxidase activity and efficiency. The coral-like nanozyme fabricated by a microwave-assisted wet-chemical method was composed of assembled PdCu branches. In a comparison with pure Pd, the bimetallic PdCu had an enhanced ability to catalyze the reaction of colorless tetramethylbenzidine (TMB) to its blue oxide (TMBox) in the presence of hydrogen peroxide (H2O2). X-ray photoelectron spectroscopy and theoretical calculation indicated that the insertion of Cu atoms into the Pd lattice would increase the P...

Structural and electrochemical studies of tungsten oxide (WO3) nanostructures prepared by microwave assisted wet-chemical technique for supercapacitor

Tungsten oxide (WO3) nanostructures were synthesised using the microwave-assisted wet chemical method without any addition of surfactant for three different microwave irradiation times (10, 20 and 30 min). Then as-prepared nanostructures were characterised using various characterization techniques to know their structural, morphology and optical properties. The monoclinic and orthorhombic (WO3) crystal structure was obtained from the as-prepared nanostructures by using X-ray diffraction analysis and its calculated crystalline size were found to be increased from 14 to 18 nm on increasing microwave irradiation time. The functional groups were investigated by using Fourier transform infrared spectroscopy analysis and the W–O chemical bonding nature was confirmed. The surface morphology was unclear using scanning electron microscope analysis, and a careful observation in high resolution transmission electron microscope studies shows that rod shaped structure. A blue-shifted optical absorption spectrum was observed by ultraviolet–visible spectroscopy analysis analysis and the bandgap energy value of WO3 was calculated as approximately 3.62 eV. The emission behaviours were investigated by using photoluminescence spectrofluorometer analysis and an enhanced defect reduced emission was obtained. Finally, the electrochemical properties were analyzed by using cyclic voltammogram and galvanostatic charge–discharge analysis analyses. The maximum capacitance was recorded at 264 F/g which was declined to 149 F/g with the growth of WO3 nanostructures size. Hence, the effect of microwave on structure and morphology, and consequent supercapacitor performances of WO3 were discussed in details.

Rare-Earth Free Self-Activated Graphene Quantum Dots and Copper-Cysteamine Phosphors for Enhanced White Light-Emitting-Diodes under Single Excitation

Rare-earth (RE) based phosphors are attractive due to their potential applications. However, owing to the resource issue, these kinds of phosphors are expensive and costly. On the contrary, as for phosphor-convert white light-emitting-diodes (pc-WLEDs), a solution-processed tunable warm white emission LED composite is fabricated in this study under single excitation, with both RE free phosphors graphene quantum dots (GQDs) and Copper-Cysteamine (Cu-Cy). By using microwave-assisted wet-chemical method and with graphite as raw material, cold white fluorescence of the GQDs is obtained. Cu-Cy which shows intense photoluminescence in the red region has the structure where both the thio and amine groups connected with copper and forming cysteamine. Warm white light is achieved by mixing the two self-activated RE free phosphors at the weight ratio of 1: 1.7 under the excitation at 365 nm. The designed optimal LED device has the properties of CIE (x, y) = (0.341, 0.327), T = 4436 K, R = 87.9 EQE = 0.31%. The experimental results demonstrate that RE free phosphor(s) excited under a single chip can open up a new avenue to develop much lower device for warm WLEDs.

Preparation and thermoelectric properties of Bi2SexTe3−x bulk materials

Bi2Te3 and Bi2Se3 nanoplates were synthesized by a microwave-assisted wet chemical method, and Bi2SexTe3−x (x=1, 2, 3) bulk nanocomposites were then prepared by hot pressing the Bi2Te3 and Bi2Se3 nanoplates at 80MPa and 723K in vacuum. The phase composition and microstructures of the bulk samples were characterized by powder X-ray diffraction and field-emission scanning electron microscopy, respectively. The electrical conductivity of the Bi2SexTe3−x bulk nanocomposites increases with increasing Se content, and the Seebeck coefficient value is negative, showing n-type conduction. The absolute Seebeck coefficient value decreases with increasing Se content. A highest power factor, 24.5µWcm−1K−2, is achieved from the sample of x=1 at 369K among the studied samples.

Preparation and thermoelectric properties of MoS2/Bi2Te3 nanocomposites

MoS2 nanosheets with size of several-hundred nanometers were prepared by a hydrothermal intercalation/exfoliation method, then MoS2/Bi2Te3 composite nanopowders were prepared by a microwave-assisted wet chemical method using the MoS2 nanosheets, TeO2, Bi(NO3)3·5H2O, KOH and ethylene glycol as raw materials. Bulk MoS2/Bi2Te3 nanocomposites were prepared by hot pressing the MoS2/Bi2Te3 composite nanopowders with MoS2 nanosheet content ranging from 0 to 17wt% at 80MPa and 648K in vacuum. X-ray photoelectron spectroscopy and X-ray diffraction analyses indicate that MoS2 and Bi2Te3 did not react each other during the hot pressing. FESEM observation reveals that the MoS2/Bi2Te3 composite samples had a more compact microstructure than the pristine Bi2Te3 bulk sample. The MoS2 phase was relatively randomly dispersed in the composite. At a given temperature, the electrical conductivity of the composites increases first then decreases as the MoS2 content increases, whereas the Seebeck coefficient of the bulk nanocomposites does not change much. A highest power factor, ~18.3μWcm−1K−2 which is about 30% higher than that of pristine Bi2Te3 sample, at 319K has been achieved from a nanocomposite sample containing 6wt% MoS2.

Synthesis via a Microwave-Assisted Wet Chemical Method and Characterization of Bi2Te3 with Various Morphologies

Bi2Te3 with various morphologies, such as microrods, nanoplates, and nanoflowers, has been successfully fabricated by a microwave-assisted method in ethylene glycol solution without any surfactant. The structures and morphologies of the obtained products have been characterized by powder x-ray diffraction and field-emission scanning electron microscopy. Based on time-dependent experiments, a possible formation mechanism of the Bi2Te3 has been proposed. The concentration of KOH in the solution controls the rate of the disproportionation reaction of Te and plays an important role in the formation of the various morphologies of Bi2Te3. The electrical properties of bulk Bi2Te3 materials obtained by cold pressing and then vacuum heat treatment of the Bi2Te3 nanostructures with various morphologies have also been investigated. The highest power factor among the studied samples, ∼17.3 μW cm−1 K−2, was achieved using Bi2Te3 nanoflowers.

Bi2Te3 hexagonal nanoplates and thermoelectric properties of n-type Bi2Te3 nanocomposites

Bi2Te3 plate-like crystals with homogeneous hexagonal morphology were rapidly synthesized using a microwave assisted wet chemical method in 30 min. These Bi2Te3 nanoplates possessed a fixed edge with a length of ∼0.5–2 µm, and the thickness was less than ∼100 nm. The n-type Bi2Te3 nanocomposites were prepared by consolidating mixtures of these nanoplates and mechanically alloyed powders using plasma activated sintering, and the effect of nanoplate addition on the thermoelectric properties of the nanocomposites was investigated. When the content of the doped nanoplates was 15 wt%, the lattice thermal conductivity of the Bi2Te3 nanocomposites decreased by 18% compared with that of the undoped compounds. A preliminary investigation showed that nanopowder addition was an effective way to decrease the thermal conductivity and increase the thermoelectric efficiency.