Microwave Reduction Research Articles

Effects of Silver Nanoparticles Synthesize From Ficus Benjamina on Normal Cells and Cancer Cells

In this article we report the effect of silver nanoparticles which were synthesize from Ficus Benjamina leaves (Green Synthesis) which was administered to normal body cells (HEK293) and cervical cancer cells (HeLa) in vitro to evaluate its possible apoptotic (anti-cancer) potentials. Silver nanoparticles are obtained from its precursor; silver nitrate (AgNO3) by rapid reduction process using Ficus Benjamina leaves extract. Nanoparticles are found to be 20-30 nm in size and the reaction is accomplished by microwave reduction method and thermal heating method. Formation of silver and gold nanoparticles was confirmed by uv-vis spectrophotometer and scanning tunneling microscope. Keywords - Apoptosis, Cervical cancer cells, Ficus Benjamina, Silver nanoparticles.

Ionic liquid-assisted microwave reduction of graphite oxide for supercapacitors

We present a facile and scalable method for the rapid production of reduced graphene oxide (RG–O) by ionic liquid-assisted microwave chemistry. Microwave irradiation of graphite oxide (GO) in an ionic liquid (IL) enables the rapid reduction of GO within 15 s, producing RG–O containing the IL within their porous structures. The reduced graphene oxide prepared by IL-assisted microwave irradiation (mRG–O) electrodes exhibited a high specific capacitance of ∼135 F g−1, which can be attributed to the open architecture of the mRG–O filled with IL moieties. A supercapacitor made with mRG–O in an IL electrolyte operated at a voltage of 3.5 V and showed a high energy density (∼58 W h kg−1) and power density (∼246 kW kg−1).

Electrical Properties of Lanthanum Strontium Titanates Modified by Microwave Sintering

The pure perovskite La0.3Sr0.7Ti0.9Nb0.1O3 (LSTN) with high densification and conductivity was achieved by 1500°C conventional sintering (CS) in activated carbon reduction atmosphere. The low conductivity of porous LSTN was obtained for low sintering temperature 1300°C in same process. Porous and well-crystallized LSTN could be obtained by microwave reduction sintering (MS). The activated carbon post-treatment with long dwell time improved the conductivities of microwave sintered LSTN samples. The conductivity of microwave sintered LSTN increased fast in short post-reduction time and was higher than conventional sintered LSTN for same sintering temperature. The microwave sintering essentially modified the LSTN electrical properties.

Facile Microwave Process in Water for the Fabrication of Magnetic Nanorods

Magnetic nanorods were successfully prepared in water by a simple and fast method through microwave (MW) assisted reduction using akaganeite β-FeOOH nanorods and hydrazine as precursors and reductor, respectively. Elongated paramagnetic akaganeite precursors are synthesized for the first time using dopamine as green chemical shape-control agent. The nature and the growth mechanism are identified by XRD, Raman spectroscopy and HRTEM analysis. Fast MW reduction process induces a structural and magnetic change depending on MW irradiation cycles. After 2 min, MW reduction leads to iron oxide nanorods with aspect ratio 3.2. XRD and Raman spectroscopy indicate a heterogeneous composition with high proportion of maghemite. The FMR spectrum is characteristic of shape anisotropy and weak ferromagnetic behavior is observed from SQUID measurements.

Microwave reduction of copper(II) oxide and malachite concentrate

The use of microwave radiation as an energy source in mineral processing and extractive metallurgy has demonstrated both the instantaneous generation of heat by microwaves in a number of compounds and minerals, and the achievement of high temperatures for an efficient time period enable the heating and reduction of metallic oxides and ores. In the present study, the carbothermic reduction of copper oxide (CuO) and one malachite [Cu 2CO 3(OH) 2] concentrate were investigated. To explore feasibility, the dielectric constants [real ( ε′) and imaginary ( ε″) permittivities] of both materials were measured at the frequencies of 2.45 GHz and 912 MHz, in the temperature range from 25 to 800 °C using the cavity perturbation method. The high ε″ values (between 1.9 and 36.3) observed in the case of CuO suggest strong microwave absorption, while the malachite concentrate values (between 0.1 and 0.4) indicate limited microwave absorption. Experiments showed the microwave heating rate of CuO was considerably higher than that of the malachite concentrate. The carbothermic reduction of CuO oxide was examined, and the effect of power supply, carbon source, carbon content and granularity of the reducing agent on the reduction rate was studied in detail. Using an 800 W power supply, and with addition of lignite as a reducing agent (with carbon content two times stoichiometric), almost complete reduction of 10 g of CuO was achieved in 4 min. The carbothermic reduction of one malachite concentrate was attempted with the same experimental procedure, but the reaction was not possible using only lignite as the reducing agent, since the poor microwave absorption of malachite concentrate–lignite mixture produced a maximum temperature of 200 °C. This difficulty was overcome by the addition of 5% by weight of graphite powder to the mixture. The rapid heating of the malachite concentrate–lignite–graphite mixture (800 °C after 2 min) resulted in sequential malachite calcination and CuO reduction reactions. After 8 min at a power supply of 800 W, the reduction degree of CuO produced by the calcination of malachite was about 90%.

Kinetics of Reduction Roasting of Hematite to Magnetite in Crude Niobium Concentrate under Microwave Irradiation

In this paper, the method of microwave reduction roasting was applied to investigate the heating and weight loss process from hematite to magnetite in crude niobium concentrate under the protection of argon. The kinetics of microwave reduction roasting of hematite in crude niobium concentrate were analyzed and calculated at the temperature range of 500°C ~850°C by way of non-isothermal thermogravimetry and isothermal gravimetric analysis. Results from this investigation demonstrated that the activation energy of microwave reduction roasting calculated by non-isothermal thermogravimetry was 26.5769kJ•mol-1, and the activation energy calculated by isothermal gravimetric analysis was 64.1203kJ•mol-1. Compared with the method of reduction roasting under resistance heating, the activation energy of microwave reduction roasting was small, and the reaction rate was fast.

Carbothermic Reduction of Panzhihua Oxidized Ilmenite in a Microwave Field

The reductions of Panzhihua coke bearing oxidized ilmenite pellets in a microwave field at the temperature ranging from 800 to 1100°C were studied. The reduction of composite pellets by conventional heating at 900 to 1200°C was also investigated as a comparison. A higher reduction reaction rate has obtained in the microwave field. Lower temperature and shorter time were demand for the microwave reduction of ilmenite due to the hotpots in the composite pellets inside the microwave field. The microwave irradiation has some special effect on phase and morphology change. The presence of crack and holes in composite pellets inside microwave field are beneficial due to the atmosphere diffusion and subsequent procedures such as separation of Fe metal and titanium oxide.

Non-Thermal Microwave Reduction of Pathogenic Cellular Population

Pathogenic bacterial cells have been proved to be destroyed by heat at specific parameters such as dry heat, moist heat, thermal radiation, etc. In the study that was undertaken, it was found that microwaves had shown the ability to destroy bacterial cells at specific parameters without causing heating of the substrate, when using low dielectric substrates such as a glass slide (originally devised method). It was found that the bacterial cells, when exposed to microwaves as a smear on glass slide were reduced in cell population using 2.45GHz microwaves at various power levels (Watts). The degrees of reduction of bacterial cells in smears were estimated by growing the exposed smears in routine bacterial media and by studying the surviving bacterial growth density in a spectrophotometer at 600nm.The study also revealed various parameters at which the selected pathogenic bacterial smear cells succumbed to microwave radiation, under such conditions.

Microwave-Reduced Uncapped Metal Nanoparticles on Graphene: Tuning Catalytic, Electrical, and Raman Properties

This work addresses a major challenge in liquid-phase catalysis by enabling the synthesis of solvent dispersible “uncapped” metal nanoparticles (NPs) with enhanced density of accessible catalytic sites. We demonstrate that graphene oxide’s (GO's) high density of accessible and bondable oxy-functional groups and the high steric hindrance from its micrometer-scale area covalently implant, stabilize, and support bare-surfaced gold nanoparticles (BSGNs) produced in situ by a unique microwave reduction process. Comparing the efficiency of catalytic reduction of p-nitroaniline (p-NA) by BSGNs and similar sized surfactant-capped gold NPs showed that the uncapped surface on GO-supported NPs, (a) opens up 258% more active sites, and (b) enhances the catalytic reduction of p-NA by 10−100 fold. Further, BSGN implantation on GO, (a) amplifies the Raman signal of bare GO by ∼3 fold, and (b) increases the conductivity of native p-type GO by >10 fold via injection of 1.328 × 1012 electrons/cm2, consequently transforming...

Advanced microwave-assisted production of hybrid electrodes for energy applications

Carbon nanotubes are one of the most prominent materials in research for creating electrodes for portable electronics. When coupled with metallic nanoparticles the performance of carbon nanotube electrodes can be dramatically improved. Microwave reduction is an extremely rapid method for producing carbon nanotube-metallic nanoparticle composites, however, this technique has so far been limited to carbon nanotube soot. An understanding of the microwave process and the interactions of metallic nanoparticles with carbon nanotubes have allowed us to extend this promising functionalisation route to pre-formed CNT electrode architectures. Nanoparticle reduction onto pre-formed architectures reduces metallic nanoparticle waste as particles are not formed where there is insufficient porosity for electrochemical processes. A two-fold increase in capacitive response, stable over 500 cycles, was observed for these composites, with a maximum capacitance of 300 F g−1 observed for a carbon Nanoweb electrode.

Microwave-Assisted Organic Synthesis and Transformations using Benign Reaction Media

A nonclassical heating technique using microwaves, termed "Bunsen burner of the 21st century", is rapidly becoming popular and is dramatically reducing reaction times. The significant outcomes of microwave (MW)-assisted green chemistry endeavors, which have resulted in the development of synthetic protocols for drugs and fine chemicals synthesis that are relatively more sustainable, are summarized. The use of emerging microwave-assisted chemistry techniques in conjunction with greener reaction media is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. A brief historic account of our own experiences in developing MW-assisted organic transformations, which involve various benign alternatives, such as solid-supported reagents, and greener reaction media, namely, aqueous, ionic liquid, and solvent-free, for the synthesis of various heterocycles, coupling reactions, oxidation-reduction reactions, and some name reactions are described. Synthesis of Heterocycles. The synthetic chemistry community has been under increased pressure to produce, in an environmentally benign fashion, the myriad of heterocyclic systems required by society in a short span of time, and one of the best options to accelerate these synthetic processes is to use MW technology. The efficient use of the MW heating approach for the synthesis of various heterocyclic compounds in aqueous and solvent-free medium is discussed. Organic Named Reactions. The application of MW chemistry for various named reaction such as the Prins reaction, the Suzuki reaction, the Heck reaction, the Aza-Michael reaction, Trost's gamma-addition, and the Cannizzaro reaction are summarized. Synthesis and Application of Ionic Liquids. Ionic liquids (ILs), being polar and ionic, in character couple with MW irradiation very efficiently and are, therefore, ideal MW-absorbing candidates for expediting chemical reactions. MW-assisted solvent-free synthesis and application of ILs are discussed. Oxidation-Reduction Reactions. MW protocols using mineral oxides such as alumina, silica, and clay to immobilize reagents on such solid supports have been extensively explored under "dry" media conditions. Various solvent-free examples of oxidation reactions are discussed that involve mixing of neat substrates with clay-supported iron(III) nitrate (clayfen) or iodobenzene diacetate (IBD) as an oxidant; some interesting MW reduction protocols using borohydrides are also discussed. Protection-Deprotection Reactions. The protection and deprotection of alcohols and amines are common events in multistep organic syntheses. Various protection and deprotection protocols under MW irradiation are discussed, including tetrahydropyranylation and (benzyloxycarbonyl) (Cbz)-protection, which are the most frequently employed methods.

Pd-Ni/MWCNT Electrocatalysts for Ethylene Glycol Electro-oxidation in Alkaline Medium

The MWCNT (multi-walled carbon nanotube) electrocatalysts with different Pd/Ni atomic ratios were prepared by microwave reduction method. XRD, TEM, and EDS measurements were used to characterize the composition, particle size, and crystallinity of the catalysts. It showed that the Pd-Ni nanoparticles supported on MWCNTs were small and well dispersed on the surface of MWCNTs. The electrocatalytic oxidation of ethylene glycol (EG) was studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impendance spectroscopy (EIS). It was found that the performance of ethylene glycol electro-oxidation on Pd-Ni/MWCNT electrocatalysts with a Pd/Ni atomic ratio of 3∶1 was the best.

Sequential determination of Se(IV) and Se(VI) by flow injection-hydride generation-atomic absorption spectrometry with HCl/HBr microwave aided pre-reduction of Se(VI) to Se(IV)

In this study a flow injection (FI) system used in conjunction with hydride generation (HG), atomic absorption spectrometry (AAS) and microwave (MW) aided pre-reduction of selenite (Se(IV)) to selenate (Se(IV)) with HCl:HBr has been developed in order to differentiate both inorganic selenium species. As full control of the MW reduction step is possible, the experimental approach allows the use of milder acidic conditions (10% v/v of HCl and HBr) than those conventionally accomplished with hydrochloric acid alone (≥50% v/v). Experimental parameters were optimized by the univariate optimization method. In either case, the linear range was from 1.0 to 30 μg l −1. The detection limits based on 3σ of the blank signal were 0.25 μg l −1 for Se(IV) and 0.30 μg l −1 for Se(VI). The reproducibility, about 3% RSD and recoveries of different amounts of Se(VI) and Se(IV) added to water and orange juice samples (97–103%) were good. The main advantage of the proposed method is that the sequential determination of Se(IV) and Se(VI) is performed at a high sampling frequency (ca. 50 samples per h) in a closed system without Se losses, and with a minimum sample waste, operator attention, and sample manipulation.

Optimization of microwave digestion for determination of selenium in human urine by flow injection-hydride generation-atomic absorption spectrometry

A microwave digestion program, which completely decomposes and oxidizes selenium compounds in urine to selenate, was developed by monitoring the pressure and the temperature during microwave digestion. The efficient decomposition and quantitative recovery of trimethylselenonium iodide spiked into urine was achieved in 18 min using the optimized microwave program reaching 200 °C and 8 bar. The selenate in the digest was reduced to selenite by hydrochloric acid with the aid of microwave energy. Urea was found useful to eliminate NOx fumes, which might be absorbed in the digest and interfere in the determination of selenium by flow injection-hydride generation-atomic absorption spectrometry (FI-HG-AAS). The recovery of trimethylselenonium iodide, selenomethionine, and selenoethionine added to urine was 96.5–105%. The whole procedure, FI-HG-AAS determination following microwave digestion of urine sample and microwave reduction of selenate in the digests into selenite, was checked with two Standard Reference Materials 2670 (toxic metals in human urine). The results showed good agreement with the certified values (normal level 30 ± 8 µg Se l–1 and elevated level 460 ± 30 µg Se l–1. The detection limit of the whole procedure was 3 µg Se l–1 urine. Selenomethionine and selenoethionine were found unstable during the microwave heating used to reduce selenate to selenite. Such a microwave reduction procedure should be cautioulsy used to distinguish selenate from selenite in the matrices which might contain organic selenium compounds.

Reduction of iron ore with coal by microwave heating

Microwave heating was investigated because it would largely solve the problem of slow heat transfer during reduction inherent in conventional reduction processes. Microwave heating and reduction tests were run on composite green balls made from coal and magnetite concentrate. Bench scale tests were run using a 15 KW microwave generator on both powdered and pelletized feeds. A significant increase in the reduction rate was obtained. Over 90% reduction of the iron ore can be achieved in about 10 minutes at temperatures about 1,000 C with 20% excess stoichiometric carbon in the mix. The reduction of iron ore with coal by microwave heating produces a pure, dust-free, and high Btu flue gas that can be used in related thermal operations. Depending upon the purity, the reduced iron product could be fed directly to electric arc furnaces for melting. Removal of a slag phase to remove excess silica and alumina may be required in some cases.

Microwave reduction of oxidised ilmenite concentrates

This paper covers preliminary investigations into the novel use of microwave energy as a heat source for the partial reduction of oxidised ilmenite (FeTiO 3) concentrates. Microwave energy has potential for the speedy and efficient heating of minerals and in a commerical context may provide savings in both time and energy. The oxidation and reduction of iron in ilmenite concentrates between the ferrous and ferric states has been found to greatly enhance its chemical activity. When reduced to the correct extent, iron can be preferentially extracted to yield a titanium rich beneficiate suitable for use as a feed for the production of titanium dioxide (TiO 2) pigments via the Chloride Process. Two ilmenite concentrates were first oxidised in a conventional muffle furnace at 1000°C. The ferric iron was then reduced back to ferrous iron by heating with a fine carbon powder under an inert nitrogen atmosphere. The reduction process was carried out in a variable power (0 to 1500 kW), 2.45 GHz microwave oven. Duplicate control samples were reduced at temperatures over the range 700 to 1000°C in a conventional muffle furnace. The mineral phase changes occurring during the oxidation and reduction stages were detected by X-ray diffraction techniques. Changes in the surface morphology of the concentrate particles were detected by scanning electron microscopy and quantitatively described through changes in the specific surface area. Samples were leached with 25% hydrochloric acid to detect changes in the activity of both iron and titanium components.

Selenium speciation using high-performance liquid chromatography-hydride generation atomic fluorescence with on-line microwave reduction

This paper describes an on-line method for the determination of inorganic selenium species in aqueous samples. Separation of the species is achieved using high-performance liquid chromatography, after which the analyte is acidified before flowing through an on-line microwave system. This latter stage leaves the selenium (iv) unaltered, but transforms selenium(vi) to selenium (iv) and thus converts it into a suitable oxidation state to undergo hydride generation. The selenium hydride is then determined using an atomic fluorescence detector. The method was validated by the analysis of a standard reference material (NIST SRM 1643c Trace Elements in H2O).

Selenium speciation—a flow injection approach employing on-line microwave reduction followed by hydride generation–quartz furnace atomic absorption spectrometry

Trace and ultra-trace levels of selenium are routinely determined in many laboratories using hydride generation–quartz furnace atomic absorption spectrometry. However, as more is understood about the role of selenium in toxicity and dietary studies, there is an increasing need to provide species-specific information from complex biological and environmental samples. As the hydride generation process requires the selenium to be in the selenium(IV) oxidation state, prior reduction of any selenium(VI) present in the sample is necessary. This step is conventionally accomplished by maintaining the sample at an elevated temperature in the presence of hydrochloric acid, although this approach suffers from a number of disadvantages, including the loss of information on the original selenium species present in the sample. This paper describes an on-line system for the determination of inorganic selenium species in which the sample is first analysed for selenium(IV), and then microwave energy is then used to reduce selenium(VI) and provide a total selenium measurement. As full control of the microwave reduction step is possible, the approach lends itself to a totally automated selenium speciation system. Detection limits and precision are unaffected by the on-line reduction step.