Novel bulk synthesis of magnesium oxide nanobelts networks by microwave hydrothermal route

Novel magnesium oxide (MgO) nanobelt structures were successfully synthesized on a large scale, low cost and catalyst free by a microwave hydrothermal route using the magnesium metal and potassium hydroxide precursors at 200 °C for 10 min. The synthesized MgO nanobelts were systemically characterized by power X-ray diffraction (XRD), scanning electron microscopy, energy dispersion spectroscopy and transmission-high resolution electron microscopy. The XRD results indicate that the MgO nanobelts have the well-crystalline cubic phase. The detailed morphological studies revealed that the synthesized products were nanobelts and were grown in large quantity. The optical energy gap of MgO nanobelts was found to be 3.1 eV. The photoluminescence spectra of the MgO nanobelts show a strong and broad green emission band, a weak ultraviolet emission band, and a weak red emission band. This novel method will open new dimensions for synthesized 1-D metal oxide and can be easily extended to the synthesis and assembly of other inorganic nanocrystals.     

Surfactants for CNTs dispersion in zirconia-based ceramic matrix by sol–gel method

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO₂ matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.     

Temperature driven morphological changes of hydrothermally prepared copper oxide nanoparticles

The size and shape of nanocrystals have a strong effect on the optical, electrical and catalytic properties. Therefore, controlling the size, shape and structure of nanocrystals is technically important. The controlled synthesis of CuO nanostructures was achieved using a hydrothermal process by simply controlling the precipitation reaction temperature between copper nitrate trihydrate and sodium hydroxide. The Scanning Electron Microscopy (SEM), EDS, XRD, and FTIR analysis revealed that the synthesized product at 200 °C is of pure copper oxide particles. From Scherrer formula, the prepared CuO particles varied approximately 3–7 nm in size simply by varying the reaction temperature. The synthesized particles exhibited a regular flake like morphology and had a uniform size distribution. The morphology and size depend on the reaction conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Environmentally benign sol–gel derived nanocrystalline rod shaped calcium doped cerium phosphate yellow-green pigment

Nanocrystalline rod shaped calcium doped cerium phosphate yellow-green pigment particles having an average length of ~100 nm and aspect ratio 10 even after calcination at 600 °C have been realized through an aqueous sol–gel process. The morphology, particle size and identification of the phase are determined by using different analytical tools such as transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), Fourier-transform IR (FTIR) and X-ray diffraction (XRD). Brunauer–Emmett–Teller (BET) nitrogen adsorption analysis showed the pigment particles are mesoporous texture having specific surface area 42 m² g^?1 and average pore size 153 Å. Thermogravimetric (TG) analysis is used to explain the thermal phase stability of the pigment. UV–Visible spectroscopy and colorimetric analysis are also done. The typical yellow-green color has been obtained even after heating to as low as 600 °C, which is 300 °C lesser than reported. Systematic study on synthesis and effect of temperature on color are presented.     

Solvent-Free Synthesis of ZnO Nanoparticles by a Simple Thermal Decomposition Method

This paper reports on a novel processing route for producing ZnO nanoparticles by solid-state thermal decomposition of zinc(II) acetate nanostructures obtained by the sublimation of zinc(II) acetate powder. The sublimation process of the Zn(OAc)₂ powder was carried out in the temperature 150 °C for 2 h. In addition, nanoparticles of ZnO were obtained by solid-state thermal decomposition of the synthesized Zn(OAc)₂ nanostructures. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, and energy dispersive X-ray spectroscopy. The sublimation process of the Zn(OAc)₂ powder was carried out within the range of 150–180 °C. The XRD studies indicated the production of pure hexagonal ZnO nanoparticles after thermal decomposition.     

Sol–gel reactions of titanium alkoxides and water: influence of pH and alkoxy group on cluster formation and properties of the resulting products

In this work the effect of pH and the titanium precursor on the cluster and particle formation during titanium alkoxide based sol–gel processes was investigated using electrospray ionization mass spectrometry (ESI-MS) and dynamic light scattering (DLS). The influence of pH and the titanium precursor on the particle size, morphology, crystallinity and chemical composition of the resulting particles were investigated using differentiel scanning calometry (DSC), X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), BET-adsorption isotherms and high resolution transmission electron microscopy (HR-TEM). ESI-MS investigation of the titanium clusters present during the nucleation and growth period showed that the number of titanium atoms in the clusters varied dependent on the alkoxide used. Moreover, it was found that the titanium clusters formed using titanium tetraethoxide (TTE) were smaller than the clusters formed by titanium tetraisopropoxide (TTIP) and titanium tetrabutoxide (TTB) under similar conditions. pH was not found to influence the nature of the titanium clusters present in the sol–gel solution. HR-TEM investigation of the TiO₂ particles prepared at pH 7 and 10 showed that the primary particle size of the particles was around 3 nm. However, it was found that these primary particles aggregated to form larger secondary particles in the size order of 300–500 nm range. At pH 3 the particles grew significantly during the drying process due to destabilization of the colloidal solution leading to the formation of a gel. The highest specific surface area was found for particles synthesized under neutral or alkaline conditions based on TTIP. XRD analysis of the TiO₂ particles showed that the particles synthesized at 25 °C were amorphous. First after heating the samples to above 300 °C the formation of anatase were observed.     

Characterization of the visible-light-driven BiVO4 photocatalyst synthesized via a polymer-assisted hydrothermal method

BiVO₄ photocatalyst was synthesized by a polymer-assisted hydrothermal method at different temperatures and reaction times. Sodium carboxymethylcellulose was used in order to assist the formation of BiVO₄ oxide. The resulting samples were characterized by X-ray powder diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, and adsorption–desorption N₂ isotherms (BET). The predominant BiVO₄ phase of the system within the 160–200 °C range was the monoclinic crystalline structure, which was obtained in pure form only under certain experimental conditions. Short reaction times promoted the formation of linear arrays of BiVO₄ formed by particles with irregular form ranging in size between 100 and 200 nm. The photocatalytic activity of BiVO₄ samples was evaluated in the degradation of rhodamine B (rhB) under visible-light irradiation. The samples exhibited a higher activity when they were synthesized at higher temperatures and longer times of hydrothermal reaction. The total organic carbon analysis of a sample irradiated for 100 h revealed that mineralization of rhB by the BiVO₄ photocatalyst is feasible.     

Thermal analysis and phase evolution of nanocrystalline perovskite oxide materials synthesized via hydrothermal and self-combustion methods

Nanocrystalline perovskite oxide materials ABO₃ (where A = Ba, Ca, Mg, Sr; and B = Ce, Mn, and Ti) have been synthesized via sol-citrate combustion and hydrothermal-based methods with and without surfactant under mild conditions. Metal-titanates (ATiO₃) were prepared using synthesized anatase-TiO₂ nanotube powder, metal hydroxide/chloride solutions, and NaOH as raw materials. The stoichiometric amount of all reactants were put in polytetrafluoroethylene (PTFE)-lined stainless steel digestion reactor and were kept in convention oven at desired reaction conditions like mole composition, pH, temperature, and time, in range A/Ti = 0.9–1.1, 10–12, 150–170 °C for 24–48 h, respectively. The nanocrystalline barium cerium oxide (BaCeO₃) was synthesized using citric acid as polymerization agent in sol-combustion process, whereas barium manganite (BaMnO₃) was prepared via hydrothermal process using polyethyl glycol surfactant as structure directing agent. Thermal stability, phase evolution, and morphology of synthesized products were characterized by thermogravimetry and differential thermal analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD results revealed that synthesized CaTiO₃ and BaMnO₃ nanorods had an orthorhombic perovskite and hexagonal structure, respectively; whereas, the nanoparticle morphologies of BaTiO₃, Ba_0.5Sr_0.5TiO₃, and MgTiO₃, BaCeO₃ perovskite oxides were found strongly depended on pH of the precursor solutions. SEM images showed variety of morphological structures ranging from nanostructured surface with distinct particles morphology to nanowires and nanorods (length varies from nano to several micrometers) and uniform diameter ~<100 nm, depending upon the hydrothermal reaction conditions.     

The properties of silica nanoparticles with high monodispersity synthesized in the microreactor system

A new combined micromixer/microreactor/batch reactor system for the synthesis of monodisperse silica particles was demonstrated, which showed superiorities over the batch reactor. The silica nanoparticles with different sizes (ranging from 20 nm to 2 μm) and size distributions could be controllably synthesized by varying the reaction temperature and reaction time. The narrowest size distribution of the silica particles was synthesized at 60 °C. The transmission electron microscopy characterization showed that the sphericities of silica particles got better as the particle size increased. Thermal gravimetry–differential thermal analysis and Fourier transform infrared characterization indicated that the amount of ethoxy groups of silica particles decreased and the hydroxyl groups increased with the reaction time increasing. And the hydroxyl groups in silica particles increased with the reaction temperature rising.     

Synthesis of (K,Na)NbO3 particles by traditional hydrothermal method and high-temperature mixing method under hydrothermal�Csolvothermal conditions

Pure (K,Na)NbO₃ (KNN) powders have been successfully prepared by using traditional hydrothermal method and high-temperature mixing method (HTMM) under solvothermal and hydrothermal conditions. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to show the change of phase, morphology, and size of the as-prepared particles with the alkalinity of the starting solution. Compared with the traditional hydrothermal method, smaller particles with higher phase purity are prepared using HTMM under hydrothermal conditions. It is found that the alkalinity has significant effects on the crystal size. The KNN grain size first increases and then decreases with increasing alkalinity. Typical samples solvothermally synthesized in a mixed solvent with isopropanol/deionized water ratio of 50/50 by volume were made of well-crystallized single-crystalline nanoparticles with size of about 500 nm.     

Dynamic hydrothermal synthesis of xonotlite from acid-extracting residues of circulating fluidized bed fly ash

This investigation was made to examine how the conditions of hydrothermal synthesis influence the crystal structure of xonotlite and its morphology. For synthesis, we used acid residues after extracting the alumina from circulating fluidized bed fly ash as raw material, as far as we know, that no one used before. Staring with Ca/Si = 1, hydrothermal temperatures were between 180 and 260 °C. The samples were characterized in terms of mineralogical composition (XRD), morphological analysis (SEM), and thermal gravimetric and differential thermal analyses. During the 72 h synthesis at 240 °C, well formed xonotlite fibers of 10–15 μm long were obtained. Under the same conditions, but at 200 °C, the obtained xonotlite was poorly formed. The results indicated that the residue could be used to prepare pure xonotlite. Different hydrothermal temperatures and holding times have a great impact on crystallinity and morphology of xonotlite.     

Synthesis of sodium titanium phosphate at ultra-low temperature

Powders of the Nasicon material NaTi₂(PO₄)₃ were directly synthesized at ultra-low temperature. NaTi₂(PO₄)₃ was obtained by mixing the initial reagents titanium hydroxide, 85 % H₃PO₄, and NaH₂PO₄·2H₂O at 85 °C for 3.5 h or at 125 °C for 1.5 h. The raw materials and synthesized products were characterized for purity, crystal structure, particle size, and powder morphology by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), and UV–visible diffuse reflectance spectroscopy. XRD results revealed that NaTi₂(PO₄)₃ powders with rhombohedral crystal structure were synthesized at 85 and 125 °C. SEM patterns showed that the as-prepared products were agglomerated and that each of the agglomerations consisted of many small grains 50–80 nm in diameter.     

Synthesis of ZnO/NiO nanocomposites from ethanol solutions

We propose a process for the synthesis of ZnO/NiO nanocomposites from ethanolic solutions by means of consecutive generation of ZnO and NiO nanoparticles. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) show that in the range 400–900°C, nanocomposites are two-phase mixtures of particles of hexagonal and cubic phases with ZnO dissolved in NiO; at 1000°C, Ni_0.5Zn_0.5O single-phase solid solution is generated. The mean particle size determined from TEM data and diffraction peak broadening increases with rising temperature. In the cathodoluminescence spectrum of a sample annealed at 400°C, the luminescence peak shifts to the UV. Specific magnetization versus magnetic field measurements in nanocomposites show hysteresis; the coercive force reaches 200 Oe.     

Optical and kinetic studies of CdS:Cu nanoparticles

CdS:Cu nanoparticles were successfully synthesized by a coprecipitation method using mercaptoethanol as a capping agent. Thermoluminescence (TL) spectra of CdS:Cu nanoparticles were studied for different exposure time. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectrometry. XRD and SEM measurements showed that the size of the crystallites was in the range 8–17 nm. Optical measurements indicated a blue-shift in the absorption band edge upon Cu doping. The direct allowed bandgap of undoped and Cu-doped CdS nanoparticles was 2.53 and 2.64 eV, respectively. We also calculated the kinetic parameters for Cu-doped CdS nanoparticles from the TL glow curves measured at 254, 249, and 244 °C with variation of the ultra-violet (UV) exposure time. The glow curve shows general order kinetics, and its kinetic parameters are calculated.     

Preparation of rhodium nano-particles using microwaves

A new process for synthesizing rhodium (Rh) nano-particles by sol–gel processing using acrylamide and microwaves is reported and discussed. Three heat treatments were applied: the first required the use of microwaves, with an inert gas (Ar) flux, to decompose the organic material; the second and third treatments, respectively, were carried out into a furnace in air at temperatures of 600 and 1,000 °C. This procedure ensured the removal of by-products produced during the sol–gel reaction. The synthesis of a pure nano-Rh was confirmed by X-ray diffraction (XRD), where the presence of a cubic structure was observed (PDF file 089-7383), and EDX. Thermogravimetric analysis (TGA), in addition to determining the decomposition temperatures, enabled the heat treatment conditions needed to obtain pure nano- Rh to be elucidated. Furthermore, the morphology was observed with a scanning electron microscope (SEM). After the heat treatment at 1,000 °C, SEM images showed grain sizes between 3 and 200 nm. High-resolution transmission electron microscopy (HR-TEM) confirmed the production of those nano- particles, and the beginning of the formation of clusters as a consequence of the high temperature applied to the system.     

Preparation of Nanosized Perovskite‐type Oxides via Polyol Method

Several perovskite‐type nanosized oxides were prepared via polyol‐mediated synthesis. The crystallinity of the materials was analysed by X‐ray diffraction (XRD). While the “as synthesized” materials are amorphous or show very poor crystallinity, highly ordered materials could be obtained by annealing at 700 °C. Morphology of the materials was analysed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Particle size of the materials lay between 20 and 200 nm.     

Synthesis and characterization of high surface area nanosilica from rice husk ash by surfactant-free sol–gel method

A nanosilica powder was obtained by thermal treatment of rice husk ash using the sol–gel method without adding any extra surfactant, and was characterized by several techniques. Fourier transform infrared measurements revealed the similarity of the absorption curves of both standard nanosilica and synthesized nanosilica. From the nitrogen adsorption–desorption analysis followed that the nanosilica showed very high surface area of 653 m²/g, total pore volume of 0.64647 mL/g, and narrow pore radius of about 1.98 nm. Scanning electron microscopy of the nanosilica sample dried at 120 °C showed separated particles, while the particles of the sample sintered at 700 °C were aggregated. The analysis of transmission electron microscopy (TEM) micrographs and showed that about 69 % of particles had their sizes in the range of 20–25 nm. X-ray diffraction measurements showed the amorphous nature of the synthesized silica. Applying the Debye–Scherrer formula provided the value of the mean crystallite size around 26 nm which agreed with the one determined from TEM. The purity of the prepared nanosilica was higher than 95 % silica which was confirmed by means of energy dispersive X-ray analysis.     

Solution-based fabrication of a graphene–ZnO nanocomposite

Graphene-based composites represent a new class of materials with potential for many applications. Graphene can be attached to a metal, a semiconductor, or any polymer. In this work, our approach was to attach graphene to a well-known semiconductor, ZnO. We synthesized graphene–ZnO composites by a simple, low-cost, environmentally friendly solvothermal method, carrying out the reaction in different conditions in order to discover the optimum condition, and also to obtain a high-quality product. Our research demonstrated that the optimum temperature to obtain a high-quality product is 180 °C for 20 h. All obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy, electron dispersion spectrometry, X-ray photoelectron spectrometry, Raman spectroscopy, Fourier transform infrared spectrometry, UV–visible spectrophotometry, and thermogravimetric analysis. The XRD confirmed that the crystal structure of the ZnO in the nanocomposite was wurtzite type. The prepared composite was stable to 800 °C with its 80 % weight.     

Synthesis and characterization of NaA zeolite powder/film deposited on alumina beads by dip-coating method

Linde Type A (LTA) zeolites have been synthesized in the current study by simple sol–gel technique. The crystal growth has been controlled by varying the hydrogel synthesis time and annealing temperature. The resulting products obtained at various crystallization times and temperatures have been studied using X-ray powder diffraction (XRD) method, High resolution transmission electron microscopy images, scanning electron microscopy (SEM) micrographs, energy dispersive study and Brunauer–Emmett–Teller (BET) analysis. The TEM images of the final LTA zeolite annealed at 500 °C revealed the formation of cubic structure. XRD analysis revealed that the crystallinity improved with annealing. BET analysis revealed that the synthesized LTA is a well crystallized 4A zeolite. LTA zeolites were dispersed in poly ethylene glycol in the ratio 3:100 and 5:100 and coated on porous alumina beads for the formation of membrane. The SEM images revealed excellent formation of fine structure LTA zeolite membrane with uniform coating. The membrane consisted of a top layer with thickness of 1.14–2.0 µm. Crystals in the top layer showed cubic morphology and amorphous phase was observed at the grain boundaries present between LTA zeolite and alumina substrate.     

Effect of synthesis conditions on the preparation of titanium dioxides from peroxotitanate solution and their photocatalytic activity

Nanosized TiO₂ particles were prepared by the hydrothermal method from the amorphous powders which were precipitated in an aqueous peroxotitanate solution. The physical properties of the nanosized TiO₂ particles prepared were investigated. We also examined the activity of TiO₂ particles as a photocatalyst on the decomposition of orange II. The titania sol can be successfully crystallized to the anatase phase through hydrothermal aging at temperatures higher than 160°C. The particle size increases from 18 to 26 nm as the synthesis temperature increases from 140 to 200°C. Titania particles prepared at 180°C show the highest activity, and titania particles calcined at 400°C show also the highest activity on the photocatalytic decomposition of orange II.