Microwave Irradiation Technique Research Articles

Preparation of Nickel Ferrite/Carbon Nanotubes Composite by Microwave Irradiation Technique for Use as Catalyst in Photo-Fenton Reaction

Nickel ferrite/multi-walled carbon nanotubes (NiFe2O4/MWCNTs) composite has been rapidly synthesized via microwave irradiation technique. The structural properties of the product was investigated by X-ray diffraction (XRD), N2 adsorption/desorption isotherms, thermogravimetric analysis (TGA), Raman spectroscopy and, scanning electron microscopy (SEM). Catalytic behavior of the composite material on the advanced photo-Fenton degradation of Amaranth dye was evaluated. The synthesis conditions employed on the microwave system were: temperature (235 °C), power (500 W), pressure (600 psi) and irradiation time (30 min) Characterization results showed the formation of hybrid material, containing a predominantly microporous structure, with surface area and total pore volume of 54 m2g-1 and 0.2249 cm3 g-1, respectively. The composite exhibited higher catalytic activity compared to the pure NiFe2O4, reaching 100% of decolorization at 60 min of reaction, which can be attributed to a synergism between NiFe2O4 and MWCNTs. Therefore, NiFe2 O4/MWCNTs composite can be used as a promising photo-Fenton catalyst to degrade Amaranth dye from aqueous solutions

Enhanced electrochemical performance of nickel-cobalt-oxide@reduced graphene oxide//activated carbon asymmetric supercapacitors by the addition of a redox-active electrolyte

Supercapacitors are an emerging energy-storage system with a wide range of potential applications. In this study, highly porous nickel-cobalt-oxide@reduced graphene oxide (Ni-Co-O@RGO-s) nanosheets were synthesized as an active material for supercapacitors using a surfactant-assisted microwave irradiation technique. The RGO-modified nanocomposite showed a larger specific area, better conductivity, and lower resistivity than the unmodified nanocomposite because the RGO facilitated faster ion diffusion/transport for improved redox activity. The synergistic effect of Ni-Co-O@RGO-s resulted in a high capacitance of 1903Fg−1 (at 0.8Ag−1) in a mixed KOH/redox active K3Fe(CN)6 electrolyte. The asymmetric Ni-Co-O@RGO-s//AC supercapacitor device yielded a high energy density and power density of 39Whkg−1 and 7500Wkg−1, respectively. The porous structure and combination of redox couples from both the electrode and electrolyte provided a highly synergistic effect, which improved the performance of the supercapacitor device.

Microwave assisted synthesis and characterization of a ternary flocculant from chitosan, acrylamide and lignin

Flocculant based on natural polymers has been given extensive attention recently in view of its rich source, low cost and eco-friendliness. In this study, a ternary graft copolymer (chitosan-acrylamide-lignin, CAML) was synthesized using combined microwave irradiation and chemical free radical initiator (K2S2O8/Na2S2O3) techniques. The synthesis process of dosage of initiator and microwave irradiation time was optimized with the initiator dosage of 1% (w/w) and microwave irradiation time of 18 min at the power of 280 W. Further, the flocculation performance of CAML was evaluated by the removal capacity of a synthetic dye (Acid black-172). The color removal efficiency was 97.1% at the dosage of 200 mg L−1 for 100 mg L−1 synthetic dye wastewater. CAML also revealed broad flocculation window and effective pH range. The possible flocculation mechanism for dye removal from wastewater was charge neutralization, bridging, and sweeping effects in various wastewater environments. The ternary copolymer showed the potential as an efficient flocculant.

Effect of microwave annealing on SOI MOSFETs: Post-metal annealing with low thermal budget

We investigate the effect of microwave irradiation (MWI) on silicon-on-insulator (SOI) based MOSFETs. The MWI technique is used for post-metal annealing (PMA) in air ambient, and compared with conventional thermal annealing in a forming gas ambient. This type of annealing not only constitutes a low cost, short time, low temperature, vacuum-free alternative to conventional post-metal annealing methods, but it also allows much lower thermal budgets, which, in turn, minimizes dopant motion, redistribution, and diffusion. The MWI treated MOSFETs showed superior electrical characteristics in terms of field effect mobility, on-off ratio, subthreshold swing, interface trap density, stability, and hot carrier effect immunity. Therefore, MWI technology is expected to become a promising annealing method for silicon-based processes, with low cost and low thermal budget.

Synthesis and antimicrobial evaluation of substituted fluoroquinolones under conventional and microwave irradiation conditions

A series of new fluoroquinolones analogs (3a-i) were prepared under conventional and microwave irradiation technique. Ethyl 1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylate (1) on reaction with boric acid and acetic anhydride in the presence of catalytic amount of zinc chloride under reflux, resulted in an unstable borate complex. Which was instantaneously treated with morpholine, piperidine, thiomorpholine, 2,6-dimethylmorpholine, 4,5,6,7-tetrahydrothieno[3,2-c]pyridine hydrochloride, 5,6,7,7a-tetrahydrothieno[3,2-c]pyridin-2(4 H )-one hydrochloride, 2,3-dichlorophenylpiperazine hydrochloride, 3-(piperidin-4-yl)benzo[d]isoxazole hydrochloride and 5,6,7,8-tetrahydro-[1,2,4] triazolo[4,3-a]pyrazine, in the presence of triethylamine to yield compounds 3a-i. The same compounds on the other hand synthesized using a microwave irradiation technique in the presence of triethylamine and adsorbed neutral alumina. The structures of the synthesized compounds were established on the basis of spectral and analytical data. The antimicrobial activity of newly synthesized compounds were evaluated against different microorganisms and found the compounds exhibited significant activity.

Dye-sensitized Solar Cell (DSSC) Utilizing TiO2 Films Prepared via Microwave Irradiation Technique: Effect of TiO2 Growth Time

This paper is concerned with the influence of TiO2 films growth time on the performance parameters of a DSSC. The films were prepared via microwave irradiation technique by varying growth times, 3, 5, 7, 10 and 12 minutes. The XRD results reveal that ana-tase phase exists at (101) and (004) plane with the biggest crystallite size was obtained at the growth time of 3 minutes. The FESEM ima-ges show that morphological shape of nanotablet was obtained at shorter irradiation time. The particle size and thickness were found to increase with growth time. However, the particle density decreases with growth time. The uncoated dye and coated dye samples grown at 10 minutes possesses the highest optical absorption and the broadest absorption window. The DSSC utilizing the TiO2 samples did not show rectification property. It was found that the photovoltaic parameters of the DSSC are greatly influenced by the growth time of TiO2 films. The DSSC utilizing the sample prepared for 10 minutes demonstrated the highest JSC, Voc and η of 2.60 mA cm-2, 0.62 V and 0.86%, respectively due to broadest absorption window, the highest recombination resistance (Rcr) and longest charge carrier lifetime (τ).

On the synthesis of RuSe oxygen reduction nano-catalysts for direct methanol fuel cells

Oxygen reduction reaction has a crucial role in energy conversion systems such as fuel cells. State-of-the-art Pt-based cathode catalysts suffer from low efficiency which is severely affected by poisoning of methanol fuel crossing the membrane that separates the electrodes and high cost. We have synthesized a non-platinum RuSe 3–15-nm in size catalysts using microwave irradiation technique, which produces nanomaterials at high efficiency and short time spans. Several Ru/Se atomic ratios of RuSe were prepared using both elemental Se powder and H2SeO3 as precursors. The structure and composition of the obtained materials were characterized using XRD, EDX, ICP-OES, and DSC/TGA. Electrochemical study of oxygen reduction reaction (ORR) on these catalysts was conducted using rotating disk electrode (RDE) technique, from which the Tafel slopes and exchanged current densities of ORR were calculated. The use of H2SeO3 as the Se source provides catalysts with controlled composition. All obtained materials show good electrocatalytic activity towards oxygen reduction and maintain high activity in the presence of high methanol contamination. A rigorous kinetic study of ORR on RuSe catalysts show that at Ru to Se ratio is 2 to 1, and the highest kinetic currents are attained. Stability tests at 0.4 V in strong acidic conditions and elevated temperatures, for over 600 hours, exhibit no degradation.

NiWO4-ZnO-NRGO ternary nanocomposite as an efficient photocatalyst for degradation of methylene blue and reduction of 4-nitro phenol

A novel NiWO4-ZnO-NRGO ternary nanocomposite has been efficiently synthesized by decorating nitrogen doped reduced graphene oxide (NRGO) with zinc oxide and nickel tungstate nanoparticles via a facile microwave irradiation technique and its capability to catalyze photodegradation of methylene blue (MB) dye in aqueous solution and reduction of 4-nitro phenol (4-NP) to 4-amino phenol (4-AP) using sodium borohydride was explored. The as-synthesized nanocomposite was characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) analysis, energy dispersive X-ray (EDX) analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and diffuse reflectance spectroscopy (DRS) techniques. The photocatalytic activity of the as-synthesized nanocomposite estimated through the photodegradation of MB under visible light irradiation showed 9 times improvement over pure NiWO4. It also showed excellent catalytic activity in reduction of 4-NP to 4-AP. The material also showed excellent stability and reusability. The entire study revealed that the novel NiWO4-ZnO-NRGO ternary nanocomposite can act as a promising bifunctional photocatalyst for environmental remediation and industrial application.

PEDOT/C Composites used as a Proton Exchange Membrane Fuel Cell Catalyst Support: Role of Carbon Amount

AbstractCarbon‐based support materials are mostly used in proton exchange membrane fuel cells (PEMFCs); however, they often suffer from degradation under the operating conditions. In this context, conducting polymers and their composites stand out as a good alternative support material thanks to their chemical stability, high electrical conductivity, and higher oxidation‐resistant properties, which fulfills the requirements for possible utilization as electrocatalyst in PEMFCs. This study reports the preparation of poly(3,4‐ethylenedioxythiophene)/carbon (PEDOT/C) composite‐supported Pt nanoparticles for PEMFC electrodes. First, PEDOT/C composites were prepared using different carbon amounts by in situ chemical oxidative polymerization of EDOT monomer on carbon particles. Then, Pt nanoparticles (about 20 % loading) were obtained by using a microwave irradiation technique as it is fast, inexpensive, energy and time saving, and ecofriendly. The successful synthesis was confirmed by XRD, TEM, and thermogravimetric analysis investigations. The surface area and pore structure of the PEDOT/C supports was also investigated by using the BET technique. The ex situ and in situ electrochemical analyses were performed by using cyclic voltammetry and PEMFC performance tests. The obtained results for the fuel cell open the way for the use of PEDOT/C composite support materials as electrocatalysts for fuel cells.

Fabrication and in vivo evaluation of hydroxyapatite/carbon nanotube electrospun fibers for biomedical/dental application

The aim was to synthesize bioactive electrospun fibers for biomedical and dental application with improved biocompatibility. In situ precipitation of nano-hydroxyapatite (nHA) was performed with various concentrations (0.5%, 1%, 2%, 3%, and 5% wt/wt) of functionalized multi-walled-carbon nanotubes (MWCNTs) by using microwave irradiation technique. The obtained composites were characterized by Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC), and the cylindrical discs were made for mechanical testing. The failure behavior was analyzed by Scanning Electron Microscope (SEM). CNT and HA/CNT were silanized with γ-methacryloxypropyl-trimethoxysilane (MPTS) and mixed with polyvinyl alcohol (10% wt./vol.) and electrospun to fabricate fibers. The biocompatibility of both fibers was accessed by their effects on angiogenesis in a chick chorioallantoic membrane (CAM) assay. The electrospun fibers were analyzed by SEM. FTIR confirmed the structural behavior of pre and post-silanized HA/CNT. XRD showed the phase purity and crystallinity before and after heat treatment. Mechanical properties showed that 3% loaded HA/CNT has higher compressive strength (100.5±5.9MPa) compared to others and the failure behavior exhibited dispersion of CNT in HA matrix. The HA/CNT electrospun fibers showed significantly more blood vessels formation compared to CNT fibers. These HA/CNT electrospun fibers showed promising results in terms of biocompatibility and with improved mechanical properties of CNT reinforced composites, they can be used in load bearing clinical applications.

Facile synthesis and characterization of Ti(1−x)CuxO2 nanoparticles for high efficiency dye sensitized solar cell applications

In this study, we demonstrate the facile synthesis of Ti(1−x)CuxO2 (x = 0.0, 0.03, 0.06 and 0.09) nanoparticles through solvothermal microwave irradiation (SMI) technique and explored their photocatalytic applications. A combined analysis of XRD, FESEM and TEM studies indicate that doping of Cu2+ in TiO2 lattice do not affect the microstructure of the particles. The UV–Vis. absorption study indicates that the introduction of Cu element lead to decrease in optical bandgap of TiO2 from 3.450 eV to 3.155 eV (for x = 0.0 to 0.09). By using Ti(1−x)CuxO2 nanoparticles photoanodes were prepared on transparent conductive fluorine doped tin oxide substrates by doctor-blade technique. The dye-sensitized solar cells (DSSCs) were assembled and an analysis was made to evaluate the variations in open-circuit voltage depending on the concentration of Cu in Ti(1−x)CuxO2. The optimum efficiency of 6.51% was found at Ti0.94Cu0.06O2 based DSSCs, which gives an efficiency improved by 4% compared with that of the cells based on pure TiO2 (6.26%). This work demonstrates that Ti(1−x)CuxO2 is a most fascinating material and has great potential for application in photoenergy conversion devices.

Synthesis, FTIR Studies and Optical Properties of Aluminium Doped Chromium Oxide Nanoparticles by Microwave Irradiation at Different Concentrations

In this exposure, pure and aluminium (Al)doped chromium (III) oxide (Cr2O3) nanoparticles are synthesized by simple solvothermal microwave irradiation (SMI) technique. SMI technique is simple and low cost; it has the future to be produced on a huge scale. The effect of dopant (Al) concentration on the structural behavior of Cr2O3 nanoparticles was examined by X-ray diffraction. The average crystallite size of the synthesized nanoparticles was measured from XRD patterns using Scherrer equation and was decreased from 14.56 nm 10.86 nm with the increasing Al concentration in Cr2O3 from 0 to 5% (in steps of 0, 1, 2, 3, 5). Morphologies and compositional elements of the synthesized nanoparticles were observed by the field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) spectroscopy, respectively. The optical property of the samples was measured by ultraviolet - visible (UV-Vis.) absorption spectroscopy. The observed optical band gap value ranges from 2.12 eV to 1.90 eV for Al doped nanoparticles and was red shifted in comparison with that of the pure Cr2O3 (3.483 eV).

Controlled density of defects assisted perforated structure in reduced graphene oxide nanosheets-palladium hybrids for enhanced ethanol electro-oxidation

Controlled creation of defects in graphene based materials is a promising strategy to tailor the electrical, electrochemical, mechanical and other properties aiming at novel applications. In this work, we report a simple and reliable strategy for producing large-scale perforated graphene oxide nanosheets-Pd hybrids as promising catalytic material through in situ formation and insertion of palladium nanoparticles (Pd-NPs) employing continuous microwave irradiation technique. A tentative mechanism for obtained microstructures with controlled density of defects is proposed based on structural and morphological characterization of the synthesized material. During the treatment, high enough temperatures are achieved to allow melting of PD-NPs. Further, the particles migrate randomly over the graphene surface gradually dissolving carbon atoms at the defective sites, and eventually leading to the formation of holes of different sizes and shapes by perforation. These processes (particles formation and migration, perforation, etc.) can easily be controlled by tuning the parameters of the irradiation process. The synthesized hybrid material was used as catalysts with improved sensitivity for ethanol electro-oxidation with current density of 10 mA/cm2.

Structural, optical and magnetic properties of SnO2 quantum dot

High crystalline rutile nano sized tin oxide SnO2 nanoparticles have been synthesized by microwave irradiation technique with the assistance of Cetyl Tributyl Ammonium Bromide (CTAB). The addition of surfactant CTAB resulted in a strong variation of particle size. The presence of CTAB during the solvothermal synthesis considerably affects the morphology, band gap, fluorescence emission and magnetic property. The X-ray diffraction patterns reveal pure rutile-type tetragonal phase SnO2 nanoparticles. The transmission electron microscopy result shows the formation of spherical shaped SnO2 quantum dots of size about 4 nm. Noticeable morphological changes were observed by scanning electron microscopy. The functional groups were analyzed using Fourier Transform Infrared Spectroscopy studies. Optical studies were carried by UV–Visible Spectroscopy and Fluorescence Spectroscopy. Electron Paramagnetic resonance was used to calculate the Lande splitting factor ‘g’. The magnetic properties of the nanoparticles were studied by using Vibrating Sample Magnetometer.

Mineral-substituted hydroxyapatite reinforced poly(raffinose-citric acid)–polyethylene glycol nanocomposite enhances osteogenic differentiation and induces ectopic bone formation

Progress of biomimetic mineral-substituted hydroxyapatite reinforced poly(raffinose-citric acid)–polyethylene glycol–poly(raffinose-citric acid) for prospective ectopic bone formation.

Novel ZnWO<sub>4</sub>/RGO nanocomposite as high performance photocatalyst

In this study, we report the synthesis of nanocomposite material composed of zinc tungstate (ZnWO 4 ) and reduced graphene oxide (RGO) as photocatalyst by a simple microwave irradiation technique. The prepared nanocomposites have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FTIR), photoluminescence spectroscopy (PL) and UV-Visible spectroscopy. The photocatalytic activities of the prepared nanocomposites are evaluated in terms of the efficiencies of photodegradation of methylene blue (MB) dye in aqueous solution under visible light irradiation. The prepared nanocomposites showed excellent photodegradation efficiency compared to the commercial TiO 2 under visible light irradiation. The activity of the catalyst towards methyl orange (MO) and rhodamine B (RB) was also good. Further, in view of the low cost, simple preparation method and high catalytic activity of the material, it is expected that the prepared nanocomposite can serve as an environment friendly photocatalyst for treating the large scale industrial waste waters.

Microwave assisted synthesis of 3D network of Mn/Zn bimetallic oxide-high performance electrodes for supercapacitors

Electrode materials with high efficiency in ionic and electronic transport are essential for high performance supercapacitors. Even though MnO2 is demonstrated as a promising material for supercapacitors due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by the electrochemical activity and electrical conductivity of ZnO, a highly porous three dimensional nanostructure of Mn/Zn bimetallic oxide was synthesized by microwave irradiation technique for the first time. The crystal structure, morphology and chemical composition and electrochemical properties of the Mn/Zn bimetallic oxide were investigated. The bimetallic oxide exhibits a high specific capacitance of about 250 F g−1 even after 5000 charge/discharge cycles at current density of 0.5 A g−1. A possible correlation of the structure of the bimetallic oxide to its electrochemical performance is also proposed.

High performance catalytic activity of pure and silver (Ag) doped TiO2 nanoparticles by a novel microwave irradiation technique

This work reports the pure and silver doped-titanium dioxide (Ag-TiO2) nanoparticles prepared by a novel one step microwave irradiation method. The results from powder X-ray diffraction indicate that both pure and Ag-TiO2 nanoparticles are in anatase phase. The measured average crystallite sizes were found to be around 31 and 21 nm respectively. Transmission electron microscope observations revealed a uniform size distribution of spherical particles. The UV absorption edges are estimated from the UV–Vis absorption spectra by using UV–visible absorption spectroscopy. The results prove that the UV radiation absorption of prepared nanoparticles is improved and the absorption edge shifted towards longer wavelength. The photocatalytic degradation of different dyes such as azo-Methyl Red, Congo Red, and Orange G were investigated by using pure and Ag-TiO2 catalyst under UV light irradiation. The result showed that the photocatalytic property is significantly enhanced by doping silver. This is due to charge separation and charge transfer between electron and hole of the Ag-TiO2 catalyst. The samples were further characterized by photoluminescence and Fourier Transform infrared spectra analysis. Moreover, the method is simple, cost effective and high yields compared with other methods.

Microwave assisted synthesis of CuS-reduced graphene oxide nanocomposite with efficient photocatalytic activity towards azo dye degradation

Semiconductor based CuS-rGO nanocomposite materials have drawn a considerable attention towards photodegradation of organic dye molecules due to the low band gap (∼2.5eV) of CuS nanoparticles. Presence of reduced graphene oxide (rGO) in CuS-rGO nanocomposite induced synergistic effect between CuS and rGO sheets which led towards better photocatalytic degradation efficiency as compared to CuS nanoparticles (without rGO support) and rGO alone. In this study CuS-rGO nanocomposite was synthesized by a simple microwave irradiation technique and characterized by High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Photoluminescence (PL) spectroscopy studies. The synthesized nanocomposite behaved as efficient photocatalyst towards diazo Congo Red (CR) dye molecule under natural sunlight irradiation with a maximum degradation efficiency of 98.76%. Effect of initial dye concentration, catalyst loading, pH of the reaction medium and role of different inorganic ions as well as the amount of graphene content in the photocatalyst on photocatalytic degradation of CR dye molecule was investigated in this study. The present study also focussed on the effect of different inorganic ions on the surface potential of the photocatalyst and their effect on the degradation process.

Strong NIR luminescent Ag2S@ZnS core-shells synthesized by a novel one pot pulsed microwave irradiation

Synthesis of Ag2S quantum dots (QDs) in water with increasing both Near Infrared (NIR) emission and nontoxicity of Ag2S quantum dots (QDs) have been a great challenge in nano-biotechnology. To reconcile these issues synthesis of Ag2S@ZnS in water with high quantum yield has been a great challenge. In this report, we have synthesized high quality and ultrafine Ag2S@ZnS core-shells in water with a fast and facile microwave irradiation technique. Thioglycolic acid (TGA) was employed as capping agent for the synthesis of Ag2S@ZnS in water for the first time. The prepared core-shells were optimized based on different experimental parameters and verified using UV–vis and PL spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. It was found that the core-shells show a strong absorption at 805nm and emission located at 857nm with a narrow width of 60nm. The quantum yield of prepared core-shells was found to be 5.3% which is the highest value reported yet.