Efficient one pot synthesis of chitosan-induced gold nanoparticles by microwave irradiation

An efficient and rapid method for the preparation of gold nanoparticles (AuNPs) within a few minutes has been developed by direct microwave irradiation of HAuCl₄ and chitosan mixed solution in one pot. Herein, chitosan molecules acted as both the reducing and stabilizing agent for the preparation of AuNPs. The obtained AuNPs have different shapes, such as the spherical nanoparticles, triangular nanoplates and nanorods, which were characterized by ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FTIR). Additionally, the results showed that microwave power could affect the required time for preparing the AuNPs arising from the distinction of heating rate, and long irradiation time was favorable for complete reduction of HAuCl₄ when a low microwave power was applied.     

Mechanistic aspects of formation of MgO nanoparticles under microwave irradiation and its catalytic application

This work reports a preparation of Mg(OH)₂ and MgO nanoparticles (NPs) using magnesium acetate in benzylamine and mechanistic study of its formation. The benzylamine acts as a solvent, base, promoter and capping agent in this reaction. The structure and morphology of particles were analyzed by X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), high resolution TEM (HRTEM), selected area energy dispersion (SAED), energy-dispersive X-ray spectroscopy (EDAX), thermogravimetric analysis (TGA), FT-IR, CO₂–temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) surface area analysis techniques. The application of as prepared MgO NPs was used in catalysis as a catalyst for the formylation of amines with recyclability studies of nanocatalyst.     

Prediction of aggregate shape using bubble size in suspension during microwave irradiation in the process of aggregation

To efficiently operate microwave assisted nanoparticle synthesis, thermal behavior around aggregate during irradiation must be well-understood to ensure stable operation. The key information in this regard are aggregate size and shape. In this study, aggregate size before the irradiation and maximum bubble size during the irradiation were measured at the different induction time and varying number density of primary particle. It was found that maximum bubble size is more closely related to the number density of aggregate than the number density of primary particles. Further analysis on the results indicates that aggregate size and shape can be estimated using known data of bubble size. These findings provide useful information on how microwave assisted nanoparticle formation can be better operated.     

Study of the degradation behaviour of dimethoate under microwave irradiation

In this work, the degradation of dimethoate under microwave irradiation assisted advanced oxidation processes (MW/oxidants) were studied. The efficiencies of the degradation of dimethoate in dilute aqueous solutions for a variety of oxidants with or without MW irradiation were compared. The results showed that the synergistic effects between MW and K(2)S(2)O(8) had high degradation efficiency for dimethoate. Simultaneously, UV/TiO(2)/K(2)S(2)O(8) photocatalytic oxidation degradation of dimethoate was investigated. The experimental results indicated that the method of microwave degradation of organic pollutants in the presence of oxidant could reduce reaction time and improve product yield. Microwave irradiation was an advisable choice for treating organic wastewaters and has a widely application perspective for non- or low-transparent and fuscous dye wastewaters.     

Synthesis of silver nanoparticles using N 1, N 2-diphenylbenzamidine by microwave irradiation method

Silver nanoparticles have been prepared under microwave irradiation from a solution of silver nitrate in the presence of N ¹,N ²-diphenylbenzamidine (DPBA) or simply amidine without any stabilizing agent. Different morphologies of silver colloids with charming colors could be obtained using N ¹,N ²-diphenylbenzamidine (DPBA). The structures of silver colloids were determined by TEM. UV-Vis spectroscopy was used to follow the reaction process and to characterize the optical properties of the resultant silver colloids. The influence of unconventional reducing agent on the morphology of silver was investigated.     

The effects of microwave irradiation on the floatability of chalcopyrite,pentlandite and pyrrhotite

Research into the application of microwave irradiation in the comminution of ores has made great progress in recent years, creating a demand to understand the effects of this technique on downstream processes, especially flotation. The present work investigated the floatability of untreated and microwave-treated chalcopyrite, pentlandite and pyrrhotite samples using potassium amyl xanthate and sodium oleate as collectors. The effects of the exposure time on each mineral’s recovery at different concentrations, pH and particle sizes were studied through microflotation, and the adsorption of the collectors was analyzed by electrophoretic zeta potential measurements. Microwave irradiation led to the decrease in the floatability of chalcopyrite and pyrrhotite in the presence of xanthate, at the pH values investigated, whereas no significant change was observed for pentlandite. The flotation of the microwave-treated minerals required greater sodium oleate concentration. The treated and non-treated pentlandite and pyrrhotite samples did not float at pH 10. Although the treated chalcopyrite and pentlandite displayed low recoveries at all pH values, the treated pyrrhotite displayed high floatability at acidic and neutral pH. The recovery of the microwave-treated sulphide minerals was more affected by the particle size in the tests with potassium amyl xanthate than with sodium oleate. The overall results presented by this work indicate potential conditions to achieve selectivity between the microwave-treated chalcopyrite, pentlandite and pyrrhotite.     

Synthesis of graphitic carbon particle chains at low temperatures under microwave irradiation

Chains of graphitic carbon particles were formed by microwave irradiation of polyethylene glycol at temperatures between 160 and 220 °C for 40 min, in the absence of a catalyst. Chains were comprised of individual particles ranging in size from 340 to 620 nm; particle size increased with synthesis temperature. The D/G ratio measured by Raman spectroscopy was 0.91, indicative of a mixture of amorphous and graphitic material. SEM, TEM and TGA measurements confirmed this. Our experiments show that the chains are an intermediate product, which when heated further under hydrothermal conditions, produce MWNTs.     

Influence of precursor preparation on the synthesis of WC under microwave irradiation

The role of precursor preparation in the microwave synthesis of tungsten carbide (WC) from tungsten, hydrogen peroxide (H₂O₂) and carbon is investigated. In this work, the influence of the conditions of precursor preparation on the synthesis reaction of WC is examined, with focus on evaporation temperature and concentration of the H₂O₂ solution. Precursors following different preparation conditions are compared in terms of phase and morphology. The evaporation step is shown to control the condition of the precursor in terms of its crystallinity and degree of hydration. These consequently affect the phase composition of the product. Slow evaporation, taking 8–12 h at temperatures below 100 °C (slow), led to crystalline flakes of hydrated tungsten oxide in the precursor. Vigorous evaporation, taking 10 min at a rapid heating rate (fast), resulted in amorphous tungsten oxide. When mixed intimately with carbon and microwaved, the latter precursor was more effectively carburised.     

Preparation of PbO nanoparticles by microwave irradiation and their application to Pb(II)-selective electrode based on cellulose acetate

Nanosized lead oxide particles were prepared by thermal decomposition of lead hydroxycarbonate synthesized under microwave irradiation. Urea and lead nitrate were used as the starting materials. Microstructure and morphology of the products were investigated by means of XRD, AFM, TEM, and IR absorption spectra. The results indicated that well crystallized, finely dispersed and spherical -PbO nanoparticles with a size of ca. 30 nm were obtained. Meanwhile, an orthogonal phase β-PbO with a size of ca. 38 nm was also obtained when the calcinations temperature was up to 600 °C. In addition, a Pb(II)-selective electrode based on cellulose acetate was prepared using nanosized -PbO powders synthesized. The electrode exhibited a Nernstian slope of 29±1 mV per decade in a linear range of 2.5×10⁻⁵ mol L⁻¹ to 1.0×10⁻¹ mol L⁻¹ for Pb²⁺ ion. The detection limit of this electrode is down to 8.0×10⁻⁶ mol L⁻¹. This sensor has a short response time of about 10 s and could be used in a pH range of 2.0–8.0. High selectivity was obtained over a wide variety of metal ions.     

Synthesis of amorphous Fe2O3 nanoparticles by microwave irradiation

Amorphous Fe₂O₃ nanoparticles of about 3–5 nm in size have been synthesized by microwave irradiation heating of an aqueous solution, containing ferric chloride, polyethylene glycol-2000 and urea. The Fe₂O₃ nanoparticles were characterized by the techniques of TEM, XRD, DSC, TGA and magnetization measurements.     

The assistance of microwave process in sludge stabilization with sodium sulfide and sodium phosphate

After industrial wastewater sludge passed through an acid-extraction process to reclaim most of the copper ions in it, the residue may still need to be treated by stabilization technologies. The common method for the stabilization of hazardous waste in Taiwan is by cement solidification. However, this method has the disadvantage of an increase in waste volume. In this study, it was tried to combine the advantages of sulfur anions and phosphate anions with the characteristics of microwave energy to offer a new method which can avoid the disadvantage of cement solidification. From the results, it was found that the assistance of heating in sludge stabilization with additives was effective. Huge amounts of additives were saved. Compared with the assistance of the traditional electrical-heating in sludge stabilization with additives, that of the microwave process saved much time and was more powerful. However, when the reaction time was longer, a re-leaching situation would occur. The hybrid microwave process, a procedure of leading an inert gas into the microwave process, could overcome the disadvantage of the microwave process with regard to the long reaction time. Finally, a modified hybrid microwave process which reduced the use of gas was performed and recommended.     

Preparation and catalytic activity of Pt/C materials via microwave irradiation

Microwave heating was employed to prepare highly dispersed Pt/C catalyst. Uniform platinum nanoparticles with average diameter of about 3.0-5.0 nm dispersed on carbon materials (XC-72) were synthesized using a domestic microwave oven. Synthesized Pt/C materials were characterized by X-ray diffraction and transmission electron microscopy. The particle size and size distribution of Pt nanoparticles greatly depend on microwave irradiation duration, where the heating temperature rises rapidly as the process proceeds. Cyclic voltammetry demonstrates that Pt/C catalysts derived from microwave irradiation for 90 s exhibits higher catalytic activity than a commercial Pt/C catalyst (E-Tek) at room temperature. The improvement in electrocatalytic activity of synthesized Pt/C materials is attributed to uniformity of particle size, well dispersion and high surface area, which is obtained around 175 °C and irradiation for 90 s.     

Synthesis of gold nanoparticles using pluronic F127NF under microwave irradiation and catalytic effects

This study examined the synthesis of gold nanoparticles with pluronic F127NF and KAuCl4 in water under non-classical conditions. The gold nanoparticle products were well dispersed in water and characterized by ultraviolet-visible spectroscopy and transmission electron microscopy. The reaction time for the synthesis was investigated by monitoring the change in color and the peak of the UV-vis spectra under microwave conditions. The gold nanoparticles were used as a catalyst for the reduction of 4-nitrophenol to 4-aminophenol with NaBH4. The resulting product was confirmed by UV-vis spectroscopy and liquid chromatography-mass spectroscopy.     

Rhodium nanoparticles from cluster seeds: control of size and shape by precursor addition rate

The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticles with mean diameters ranging between 3-7 nm and multipod structures was accomplished using seeded growth methods. Isotropic PVP-capped 2.9 nm seeds were prepared by ligand exchange on rhodium-triphenylphosphine metal-organic clusters. Quantitative investigation of reaction parameters in ethylene glycol revealed that size and shape could be controlled at a single reaction temperature of 120 degrees C. The rate of rhodium monomer addition was found to be critical for monodispersity and shape control, regardless of thermodynamic factors. Solvent viscosity, varied by changing the polyol solvents, indicated that autocatalytic addition kinetics are responsible for isotropic versus anisotropic growth.     

Facile conversion of bulk metal surface to metal oxide single-crystalline nanostructures by microwave irradiation: Formation of pure or Cr-doped hematite nanostructure arrays

We report a method for converting the surfaces of bulk metal substrates (pure iron or stainless steel) to metal oxide (hematite or Cr-doped hematite) nanostructures using microwave irradiation. When microwave radiation (2.45 GHz, single-mode) was applied to a metal substrate under the flow of a gas mixture containing O₂ and Ar, metal oxide nanostructures formed and entirely covered the substrate. The nanostructures were single crystalline, and the atomic ratios of the substrate metals were preserved in the nanostructures. When a pure iron sheet was used as a substrate, hematite nanowires (1000 W microwave radiation) or nanosheets (1800 W microwave radiation) formed on the surface of the substrate. When a SUS410 sheet was used as a substrate, slightly curved rod-like nanostructures were synthesized. The oxidation states of Fe and Cr in these nanorods were Fe³⁺ and Cr³⁺. Quantitative analyses revealed an average Fe/Cr atomic ratio of 9.2, nearly identical to the ratio of the metals in the SUS410 substrate.     

Effects of initial precursor and microwave irradiation on step-by-step synthesis of zinc oxide nano-architectures

ZnO nano-architectures were produced with the aid of a fast, simple and low cost microwave-assisted synthesis method. Solid semispherical ZnO nanoparticles on the order of 600 nm in diameter along with rice-like ZnO nanorods 95 nm thick were produced from butanol, triethanolamine (TEA), and zinc acetate dihydrate. Solid spherical ZnO nano-architectures with an average diameter of 250 nm were produced from the same starting materials in addition to NaOH. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to characterize the ZnO nano-architectures as well as the precursor. This method is cheap, fast and simple; capable of producing large quantities of each ZnO nanostructure. Investigation of the step-by-step formation mechanism for each ZnO nanostructure was conducted.     

Preparation and catalytic activity of Ni/CNTs nanocomposites using microwave irradiation heating method

Ni nanoparticles supported on carbon nanotubes were prepared by microwave-assisted heating hydrazine reduction in ethylene glycol. The Ni/CNTs nanocomposites by microwave-irradiation method (MIM-Ni/CNTs) were characterized by XRD, SEM, EDS and BET. The results indicated that MIM-Ni/CNTs had compact coating, high nickel loading and large BET surface area. The catalytic activity of obtained products on the thermal decomposition of ammonium perchlorate (AP) was carried out by DTA. The burning rate of the propellant modified by MIM-Ni/CNTs was measured by strand burner method. Moreover, the experimental results showed that the obtained products could play a catalytic role in the thermal decomposition of AP and combustion of AP-based propellant.     

Fabrication and characteristics of porous NiTi shape memory alloy synthesized by microwave sintering

Porous nickel titanium (NiTi) shape memory alloy (SMA) was successfully fabricated by microwave sintering method. This method allows formation of porous structures without using any pore-forming agents. Moreover, microwave sintering of NiTi SMA can be successfully performed at a relatively low sintering temperature of 850 °C and a short sintering time of 15 min. The pore characteristics, microstructure, phase transformation and stress-strain behavior of the porous NiTi SMA were investigated. The porous NiTi SMA exhibited porosity ratios from 27% to 48% and pore sizes range from 50 to 200 μm when using different sintering temperatures and holding times. The predominant B2 (NiTi) and B19′ (NiTi) phases were identified in the porous NiTi SMA. A multi-step phase transformation took place on heating and a two-step phase transformation took place on cooling of the porous NiTi SMA. The irrecoverable strains decreased with increasing sintering temperature, but the holding time had little effect on the stress-strain behavior at 60 °C.     

Facile synthesis of highly uniform ZnO multipods as the supports of Au and Ag nanoparticles

Through the direct reaction of the aqueous solutions of zinc salts and KOH, highly uniform ZnO multipods consisted of rod-shaped branches are synthesized in an extremely high yield. The synthesis is conducted at low temperature, does not require any organic capping agents to affect the crystal habit, and is independent on the species of zinc sources. Moreover, by changing the reaction temperature from 25 to 70 °C, the tips of the multipods can be adjusted from taper to regular hexagon. The mechanism responsible for the formation of ZnO multipods is the self-regulation growth guided by the inherently asymmetric structure of hexagonal ZnO along the c-axis. After the surface modification with amino groups, ZnO multipods show good affinity to Ag and Au nanoparticles, which results in the spontaneous migration of Au and Ag nanoparticles to the surface of ZnO to form well-defined Au/ZnO and Ag/ZnO heterostructures. The fabricated hybrids are found to be effective surface-enhanced Raman scattering (SERS) substrates because of their distinct geometrical shape, large surface area, and the ability to create a strong local electromagnetic field by the metal–semiconductor heterojunction.