Microwave-assisted Chemical Route Research Articles

Thermoelectric and power generation of 2D structured pieces of graphene-nanodiamonds nanocomposite.

Recently, the ultrafine 2D structured nanocomposite of graphene (Gr)-nanodiamonds (NDs) produced by a microwave-assisted chemical route was found to have attractive structural properties. This new 2D structured nanocomposite may be employed for a wide spectrum of applications including thermoelectricity (TE) applications. It is well established that TE materials should be highly effective to be used for designing operative devices for powering or cooling small devices. To fulfill such an objective, the functional TE material should possess a high-power factor and low thermal conductivity. In this study, NDs were successfully integrated into Gr with a magnificent structural alteration to the Gr layers/sheets. This structural modification was found to impact the TE final outcome above and below room temperature (RT). The obtained results showed that at 215 K the power factor value was increased from 4 μW m-1 K-2 for the pure Gr to ∼20 μW m-1 K-2 for the Gr-NDs nanocomposite. At higher T, e.g. 365 K, these values slightly decreased, but with clear superiority for the Gr-NDs nanocomposite. The thermal conductivity of the Gr-NDs nanocomposite was significantly reduced to ∼12% of that of the pure Gr, which could reflect a significant enhancement in the value of the figure of merit by >45 times. Furthermore, the output power generated by a single small leg module made of the Gr-NDs nanocomposite was measured and found to be measurable. The obtained values are still relatively low for practical application, but this newly produced material has great potential to be further developed for TE applications.

Anticancer potential of gold nanoparticles (AuNPs) using a battery of in vitro tests

Abstract This study synthesized gold nanoparticles (AuNPs) using a facile microwave-assisted chemical route and evaluated them as potential anticancer candidates against breast and colon cancer cell lines. Numerous spectral characterization tools were used to study the optical properties, structure, and morphology of the prepared AuNPs. UV-Vis spectroscopy showed a characteristic peak at 517 nm, which confirms the formation of AuNPs. The crystalline structure of NPs was studied by X-ray diffraction, and the NPs’ shape and size were calculated with Field emission transmission electron microscopy. The synthesized AuNPs were found to be uniform in size in the range of 2–6 nm. A variety of biological tests, including MTT, scratch, real time polymerase chain reaction (RT-PCR), and comet assays were adopted to assess the anticancer potential of these AuNPs in the studied cancer cell models. The findings suggested a cell-dependent cytotoxicity of AuNPs. Different cell viability of 40.3 and 66.4% were obtained for MCF-7 and HCT-116, respectively, at 5 µg/mL of AuNPs. The scratch assay showed AuNPs impede cell migration in a concentration-dependent manner in the MCF-7 cell line. On the other hand, real-time polymerase chain reaction (RT-PCR) of apoptotic (p53, Bax, and caspase-3) and anti-apoptotic (BCl-2) genes revealed upregulation and downregulation of these genes, respectively, probably leading to its cytotoxicity. At 5 µg/mL concentration of AuNPs, reactive oxygen species (ROS) production was found to be increased by 26.4 and 42.7%, respectively, in MCF-7 and HCT-116 cells. Similarly, comet assay demonstrated AuNPs induced DNA damage in the studied cancer cell lines. These findings suggest that the observed anticancer efficacy of AuNPs was driven by ROS generation. The synthesized AuNPs appeared to be a promising therapeutic against cancer cells. However, our in vitro data need to be confirmed and validated in ex vivo and in vivo models so that this NP can be further exploited for human use.

Structural, Morphological, Optical and Magnetic Studies of Cu-Doped ZnO Nanostructures.

In the present work, Cu-doped ZnO nanostructures (Cu% = 0, 1, 5) have been prepared using microwave-assisted chemical route synthesis. The synthesized nanostructures were investigated through structural, morphological, optical, and magnetic characterizations. The results of the X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), and selective area electron diffraction (SAED) patterns confirmed that all of the samples exhibit the single-phase polycrystalline hexagonal crystal structure. The XRD results infer a decrease in the lattice parameters (a/c) by increasing the Cu% doping into ZnO. The field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray (EDX) spectroscopic measurements revealed the formation of nanostructures, showing the major elemental presence of Zn and O in the samples. The photoluminescence (PL) spectra exhibited photoemission in the UV and blue-green regions. With the increase in the Cu%, the photoemission in the UV region is reduced, while it is enhanced in the blue-green region. Raman spectra of the Cu-doped ZnO nanostructures displayed a blue shift of the E2High mode and an increase in the peak intensity of E1(LO), indicating the doping of Cu ion in the ZnO lattice. The dc magnetization measurements demonstrated the ferromagnetic behavior of all of the samples with an enhanced ferromagnetic character with increasing Cu%.

Nanodiamonds as a knife for cutting graphene multilayers into ultrafine pieces under microwave irradiation

Graphene (Gr) has proved its potential as a successful material for various types of applications. However, poor dispersion due to the strong π–π stacking interactions between their layers limits its properties and potential as an effective material in some practical applications. In this work nanodiamonds (NDs) were successfully used under microwave irradiation for exfoliation/cutting Gr multi-layered sheets into ultrafine pieces of nanocomposite Gr-NDs of sizes less than 50 nm with a high yield of ∼ 93 %. A micro-mixing of xylene solution of NDs with a few Gr layers colloidal in dimethylformamide (DMF) were used without surfactant catalysts or other auxiliary substances. The nanocomposite hybrid material was prepared using the microwave-assisted chemical route at 1000 W for 30 mins. The new Gr-NDs nanocomposite was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Hence, we successfully fabricated 48.8 mg of Gr-NDs nanocomposite from 40 mL of the two solutions in the microwave digester, which might be useful for several applications including energy storage, electronics, sensors, etc.

Microwave irradiation for the production of graphene-nanodiamond composite carbon spheres

Structured spherically shaped carbon nanomaterials exhibit great application potential in various fields. In this work, sub-micron composite carbon spheres (CCSs) were successfully fabricated directly from graphite (Gra) and a small percentage of nanodiamonds (NDs) mixture under microwave irradiation. This was achieved using a scalable micro-mixing of xylene solution of NDs with a colloidal suspension of Gra in dimethylformamide (DMF), with no surfactants, catalysts, or other auxiliary chemicals. The diameters, shape, and yield of the produced CCSs were found to depend on the microwave operating parameters, including reaction time, power, and relative concentration of NDs to that of Gra. The structure of CCSs was established/optimized using the microwave-assisted chemical route at a fixed power of 1000 W for 30 min. These CCSs were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). This new composite structure might be useful for various applications including energy harvesting, storage, batteries, supercapacitors, etc.

Fabrication of Ag2O/WO3 based sensors for detection of hydrogen sulfide

Several metal oxides, such as tungsten oxide (WO3), are considered superior sensing materials for hydrogen sulfide (H2S) detection in the ambient environment. In this study, silver loaded tungsten oxide nanoparticles were prepared by microwave-assisted chemical route. Nanoparticle thin films were deposited on substrates with electrical electrodes to explore their gas sensing and electrical properties. The morphology, crystal structure, and chemical state were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). The sensing properties of the sample were tested at different temperatures varying from room temperature to 200 °C. The Ag2O/WO3 nanoparticles showed enhanced H2S sensing abilities at very low temperatures (close to room temperature) and concentrations as low as 10 ppm compared to bare WO3.Moreover, the effect of annealing and comparison with physical mixing was studied and showed that non-annealed Ag-loaded WO3 produced the best response. The results can be attributed to the decrease in the energy bandgap due to increasing the Ag content and the strong interaction between the Ag and WO3 and silver to silver oxide transformation at low annealing temperatures. This study demonstrates that Ag2O/WO3 sensors offer enhanced low-temperature sensing with reasonable response time, low operating power, and simple fabrication that can be promising sensors for H2S, which may be utilized as wearable devices and in the industrial setting.

The effect of morphological modification on the thermoelectric properties of ZnO nanomaterials

At present, huge research efforts are dedicated to improve the efficiency of thermoelectric (TE) materials. Nanostructuring is one of the suggested methods to improve their TE performance. However, the morphology of a nanomaterial might play a significant role on its TE properties. In this work, we demonstrated this effect by producing zinc oxide (ZnO) in two different morphologies using the microwave assisted chemical route. Nanoparticles (NPs) and nanorods (NRs) were synthesised by changing the molar ratios of the starting precursors. The obtained results show that the NRs have improved TE properties compared to those of the NPs, particularly at high temperature. At 673 K the Seebeck coefficient, electrical conductivity and power factor values of the ZnO NRs reached −1020 μV/K, 22 S/m and 23 μW/m.K2, respectively. The NPs have only recorded −850 μV/K, 3 S/m and 2.4 μW/m.K2 of these factors. Moreover, the thermal conductivity of the NRs was found to be three times lower than that of the NPs. As a result of these differences the Figure of Merit (zT) value of the NRs is around 0.012, while that of the NPs is only 0.001. Power generation characteristics of single leg modules made of the ZnO NPs and NRs, measured under the conditions of actual applications in an air atmosphere were also investigated. The output power of the ZnO NRs is found to be several times higher than that of the NPs. These results have clearly demonstrated the effect of nanostructures morphology on the TE performance, which might be important for future TE generators.

A facile microwave-assisted synthesis of novel ZnMn2O4 nanoparticles and their structural, morphological, optical, surface area, and dielectric studies

Spinel ZnMn2O4 nanoparticles (ZMONPs) were successfully synthesized using a microwave-assisted chemical route. X-ray diffraction (XRD) revealed the growth of ZMONPs along the (211) plane with a tetragonal structure. The crystallite size was ~ 14 nm, estimated using the XRD data. Vibrational analysis confirmed the tetragonal structure of ZMONPs. Scanning electron microscopy images showed nanometer-sized particles, which was in agreement with the XRD results. EDX investigation of the samples demonstrated the good stoichiometric ratio of Zn, Mn, and O (1:2:4). The surface area and pore radius were also investigated in detail through Brunauer–Emmett–Teller analysis and were found to be 10.385 m2/g and 16.24 A, respectively. The direct band gap for the ZMONPs was estimated using Tauc’s relation and was found to be 2.07 eV, which is larger than that of bulk ZMO (1.91 eV). Dielectric constant and loss values decreased with increasing frequency, while conductivity increased with increasing frequency. The dielectric constant was found to be in the range of 17–25 considering the entire testing range. The dielectric constant value was larger than expected, which could be the result of quantum confinement.

Structural and dielectric properties of Zr doped BaTiO3 synthesized by microwave assisted chemical route

Lead-free ferroelectric nano ceramics of BaZrxTi1-xO3 (x=0.1, 0.2 and 0.3) were prepared by means of microwave assisted chemical route. The structural, dielectric and electrical properties were examined. The crystalline structure of the specimens was studied by X-ray diffraction patterns. All the samples showed pure single phase of perovskite structure with space group of I4/mcm. X-ray diffraction data illustrated that there is no secondary phases exist. Structural and electrical properties of barium titanate ceramics are influenced significantly by small additions of Zr. The electrical conductivity showed higher values at x=0.2 and decreased at higher Zr content. The Hall charge mobility is found to decrease with Zr addition. The negative sign of the Hall coefficient RH confirms the dominant n-type conduction in all samples. The charge carrier concentration decreased with Zr content increase. Suggested potential application for this ceramics compound is in high storage multilayer capacitors and ferroelectric applications.

Influence of dopant concentration on the structural, optical and magnetic properties of nickel doped SnO2 nanoparticles

Nickel doped Tin oxide nanoparticles Sn1−xNixO2 (x = 0, 0.01, 0.02, 0.03, 0.04) have been prepared by microwave-assisted chemical route method. The prepared sample is annealed at 500 °C for 1 h for the formation of SnO2 phase. Structural properties investigated by XRD studies indicate the formation of tetragonal phase for the SnO2 nanoparticles, and the Ni doping does not transform the tetragonal structure of SnO2. The scanning electron microscope image shows the surface morphology of the synthesized nanopowder. Transmission electron microscope results illustrate the formation of tetragonal shaped and small sized spherical nanoparticles of diameter 11–19 nm. Photoluminescence emission measurements at room temperature exhibit that all the samples demonstrate photoluminescence in the visible region. VSM studies reveal the ferromagnetic behaviour at room temperature for our sample due to oxygen vacancy.

Effect of Ag on structural, optical and luminescence properties of ZnS nanoparticles synthesized by microwave-assisted chemical route

Silver (Ag)-doped (0, 5, 10 and 15%) ZnS nanoparticles are synthesized by microwave-assisted chemical route using polyvinylpyrrolidone (PVP). We study the compositional, structural, optical and luminescence properties by energy-dispersive analysis of X-rays (EDAX), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy and photoluminescence (PL) spectroscopy, respectively. Synthesized Ag-doped ZnS nanoparticles do not possess any impurity as seen from EDAX spectra. TEM images show particles to be in spherical shape with agglomeration, and corresponding selected area electron diffraction (SAED) pattern showed that they are polycrystalline in nature. Allowed LO and TO modes corresponding to cubic phase for all the samples are observed in Raman spectra. FTIR spectroscopy is used to study the interaction between PVP and as-synthesized nanoparticles. Blue shift can be seen in pure and Ag-doped ZnS nanoparticles compared to bulk ZnS as seen from absorption spectra. Green emission is observed in PL spectra due to Ag doping without showing any quenching behavior.

Structural, optical and impedance properties of SnO2 nanoparticles

Tin oxide (SnO2) nanoparticles have been synthesized by microwave assisted chemical route method. The as-prepared sample was annealed at 550 °C for 1 h for the formation of SnO2 phase. The crystal structure, morphology, optical band gap of SnO2 nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, UV–visible spectroscopy, Fourier transform infra-red spectroscopy. XRD result shows that the annealed SnO2 samples exhibited tetragonal crystalline structure with crystallite size ranging from 13 to 25 nm. The optical band gap value of SnO2 nano particles was calculated to be 3.78 eV. The impedance properties of SnO2 nanoparticles were analysed for different temperatures varying between 110 and 150 °C and the dielectric properties and ac conductivity are discussed.

Structural and optical properties of Ag doped tungsten oxide (WO3) by microwave-assisted chemical route

The present study explores, the pure and silver (Ag) doped WO3 nanoparticles synthesized by microwave irradiation method. Powder X-ray diffraction results reveal that the WO3 doped with Ag concentration from 0 to 10 wt% crystallizes in monoclinic structure. TEM analysis shows both pristine and silver doped WO3 nanoparticles. They are having spherical morphology with a average size from 30 to 40 nm. Scanning electron microscopy studies depicts that both the pristine and Ag doped WO3 form in spherical shaped morphology with an average diameter of 40–30 nm, which is in proper agreement with the average crystallite sizes calculated by Scherrer’s formula. A considerable red shift in the absorbing band edge and a decrease in the band gap energy from 3.00 to 2.85 eV for Ag doped samples were observed by using UV–DRS spectra analysis. The defects in crystal and oxygen deficiencies were analyzed by photoluminescence spectra analysis.

Mixed valence nanostructured Mn3O4 for supercapacitor applications

Nanostructured Mn3O4 with an average crystallite size of ∼19 nm was synthesized through a microwave-assisted chemical route. Structural characterization was carried out using X-ray diffraction analysis and transmission electron microscopy. Observed change in the ratio of lattice constants, c/a for the sample compared with single-crystalline Mn3O4 points to the presence of Mn4+ ions at the octahedral sites. This is attributed to the presence of cation vacancies. X-ray photoelectron spectroscopic studies confirm the presence of Mn4+ ions. Specific capacitance value of 665.08 F g−1 was obtained for symmetric supercapacitor with Mn3O4 active material at slow scan rate. Reasonably high power and energy density values, viz., 4.27 kW kg−1 and 4.36 × 10−2 Wh kg−1, respectively, were obtained for charge–discharge cycles at a constant current of 12.74 mA cm−2.

Structural, morphological and optical properties of Bi-doped ZnO nanoparticles synthesized by a microwave irradiation method

In this work, the effect of Bi doping (up to 5 wt%) on the structural, morphological and optical properties of ZnO nanoparticles prepared by a microwave assisted chemical route has been investigated. The synthesized Bi-doped (BZO) samples were widely characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. BZO samples were found to be polycrystallines with a hexagonal wurtzite structure. The presence of Bi modified the morphology as well as the average particles size. The optical and photoluminescence properties of BZO samples were also investigated showing a decrease of the band gap energy (Eg) values with Bi doping level and a modifications of the photoluminescence pattern.

Effect of transition Metal (Co, Ni and Cu) doping on lattice volume, band gap, morphology and saturation magnetization of ZnO nanostructures

Herein, the effect of different TM (Co, Ni and Cu) doping on structural, optical and magnetic properties of ZnO nanostructures has been studied. Zn1−xTMxO (TM=Co, Ni and Cu) nanostructures were prepared by a microwave assisted chemical route and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy (TEM), Raman spectroscopy, UV-Vis and magnetization measurements. XRD and TEM analyses showed that the TM-doped ZnO nanostructures had single phase nature with the wurtzite structure. Changes in the lattice volume, bandgap energy, morphology and the saturation magnetization of Zn1−xTMxO nanostructures were found to be dependent on the type of TM dopants. Lattice volume, bondlength and bandgap determined from XRD and UV-Vis, respectively, were found to decrease as the atomic number of the dopant increased from Co to Cu. Magnetic studies showed that all the TM-doped ZnO exhibited room temperature ferromagnetism and the decreasing trend of saturation magnetization was observed with the increase of 3d electrons number from Co to Cu.

Supercapacitive behavior of polyaniline thin films deposited on fluorine doped tin oxide (FTO) substrates by microwave-assisted chemical route

Simple and quick microwave assisted synthesis is used for the preparation of polyaniline (PANI) thin films on fluorine doped tin oxide (FTO) substrates. Aniline monomer and ammonium persulphate are used as precursors for the preparation of PANI thin films. The PANI thin films are characterized for their structural and morphological studies by employing X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) techniques. The wettability study is carried out using water contact angle meter. The supercapacitive behavior of PANI thin film electrode is studied in 1MH2SO4 electrolyte using cyclic voltammetry (CV) technique. The amorphous nature is observed from the XRD pattern. Morphological study reveals the well-dispersed agglomerated fibrils of PANI over the substrate. The PANI thin film shows hydrophilic nature with water contact angle of 29°. The maximum specific capacitance of PANI thin film electrode is found to be 546Fg−1 at the scan rate of 5mVs−1. The charge–discharge study of PANI thin film electrode carried out at 2mAcm−2 constant current density. The specific power, specific energy and coulombic efficiency of PANI thin film electrode are found to be 8.09kWkg−1, 38.2Whkg−1 and 89%, respectively from the charge–discharge curves.

Carbonaceous nickel oxide nano-composites: As electrode materials in electrochemical capacitor applications

Carbonaceous nickel oxide powder samples have been synthesized from an adducted nickel β-ketoester complex used as a “single source precursor” through a solution-based microwave-assisted chemical route. Comprehensive analysis of the resulting powder material has been carried out using various characterization techniques. These analysis reveal that, depending on the solvent used, either NiO/C or Ni/NiO/C composites are formed, wherein Ni and/or NiO nanocrystals are enveloped in amorphous carbon. As the components emerge from the same molecular source, the composites are homogeneous on a fine scale, making them promising electrode materials for supercapacitors. Electrochemical capacitive behavior of these oxide composites is studied in a three-electrode configuration. With a specific capacitance of 113 F g−1, Ni/NiO/C is superior to NiO/C as capacitor electrode material, in 0.1 M Na2SO4 electrolyte. This is confirmed by impedance measurements, which show that charge-transfer resistance and equivalent series resistance are lower in Ni/NiO/C than in NiO/C, presumably because of the presence of metallic nickel in the former. The cyclic voltammograms are nearly rectangular and the electrodes display excellent cyclability in different electrolytes: Na2SO4, KOH and Ca(NO3)2·4H2O. Specific capacitance as high as 143 F g−1 is measured in Ca(NO3)2·4H2O electrolyte.

Microwave Assisted Growth of ZnO Nanorods and Nanopolypods Nanostructure Thin Films for Gas and Explosives Sensing

The growth of uniformly distributed and densely packed array of zinc oxide (ZnO) nanorods (NRs) and nanorods (NRs)/nanopolypods (NPPs) was successfully achieved through microwave-assisted chemical route at low temperature. The ZnO NRs and NRs/NPPs were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), and UV-Vis absorption spectroscopy. The ZnO NRs were of 100–150 nm diameter and 0.5–1 μm length, while the NPPs were of diameter about 150–200 nm and 1.5–2 μm pod length. The prepared films are polycrystalline in nature and highly oriented along (002) plane with a hexagonal wurtzite structure. These films were studied for the sensing properties of liquefied petroleum gas (LPG), oxygen, and hazardous explosives, that is, 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramines (RDX), in the temperature ranges of 25–425 °C and 100–200 °C, respectively. The grown nanostructure films showed reliable stable response to several on-off cycles, and reduction in sensor recovery time was found with the increase in temperature. ZnO NRs and NRs/NPPs showed better sensitivity and recovery time for both LPG and oxygen, as compared to the literature-reported results for ZnO thin films.

A multiferroic behavior of TbMnO3 nanorods prepared by microwave-assisted chemical route

TbMnO3 rods-like morphology were prepared by the microwave-assisted chemical route. The samples were synthesized at different microwave heating conditions. We synthesized nanorods of size 100 nm in diameter and length in several micrometers. SEM and TEM confirmed the morphology and size of the samples. Orthorhombic phase was indexed from XRD data. The temperature profile of the magnetization (M) at H = 50 Oe indicates well defined feature around 8 K for almost all samples. Temperature dependence of dielectric constant demonstrates an upward rise in dielectric constant start near 50 K and continues up to 23 K and lowering near 10 K. Magnetization and dielectric constant (e) was observed to be strongly influenced by microwave power level used for synthesis of the samples.