Ultrasonic pretreatment for hydrothermal synthesis of SAPO-34 nanocrystals

Synthesis of SAPO-34 nanocrystals which has been recently considered as a challenging task was successfully performed by sonochemical method using TEAOH as structure directing agent (SDA). The products were characterized by XRD, SEM, EDX, BET and TGA. The average crystal size of the final product prepared sonochemically is 50 nm that is much smaller than that of synthesized under hydrothermal condition and the morphology of the crystals changes from uniform spherical nanoparticles to spherical aggregates of cube type SAPO-34 crystals respectively. In the case of sample synthesized sonochemically with aid of hydrothermal condition, the surface area is significantly upper than that of obtained by the conventional static hydrothermal technology with almost the same crystallinity. SAPO-34 framework synthesized by just ultrasonic treatment is unstable and a significant part of SAPO-34 nanocrystals is transformed to the dense phase of AlPO₄ structure, i.e., Cristobalite. Contrary to hydrothermal method that at least 24 h of the synthesis time is required to obtain fully crystalline SAPO-34, sonochemical-assisted hydrothermal synthesis of samples leads to form fully crystalline SAPO-34 crystals taking only 1.5 h. In a sonochemical process, a huge density of energy for crystallization is provided by the collapse of bubbles which formed by ultrasonic waves. The fact that small SONO-SAPO-34 crystals could be prepared by the sonochemical method suggests a high nucleation density in the early stages of synthesis and slow crystal growth after nucleation.     

Hierarchically solvothermal synthesis of WO3-based nanocomposite: Nature-inspired structure and enhanced gas-sensing property

Composed of the heart, cardiac valves and blood vessels, the blood circulation system can manage the aggregation and the movement of the blood regularly and efficiently. Due to the analogical fluidity of the charge carrier and the blood, such system may act as the inspiration to design the advanced gas-sensing material. As a proof-of-concept, firstly, the porous WO₃ monomer was synthesized and recombined with the one-dimensional NiO monomer through the P-N junction to construct a similar structure. Subsequently, a series of gas-sensing tests towards the ethanol were measured. The obtained result indicates this nature-inspired nanocomposite indeed shows an enhanced gas-sensing property towards the ethanol, testifying the rationality of our design.     

Structural characteristics and chemical bonding states with temperature in barium titanate nanopowders prepared by using the solvothermal method

We report the structural characteristics and the chemical bonding states of nano-sized BaTiO₃ powders before and after having been heat treatment. We prepare BaTiO₃ nanopowders by using the solvothermal method at different reaction temperatures. We anneal the prepared powders at 400 and 600 °C, respectively, for 1 h. We examine the structures of the prepared powders by using the Rietveld analysis, and the chemical bonding states of the ions by using a fitting program with an assumption that the measured spectra are Gaussian. Then, we study the morphology of the nanopowders, and measure the ferroelectric properties with frequency and reaction temperature. We show that the BaTiO₃ nanopowders prepared by using the solvothermal method at lower reaction temperature exhibit the tetragonality and are useful for the electronic device applications.     

Synthesis and characterization of nano-sepiolite by solvothermal method

Nano-sepiolite with novel morphology has been fabricated by solvothermal method in different conditions. The nano-sepiolite was characterized by X-ray fluorescence analysis, X-ray powder diffraction, thermal gravimetry analysis, differential thermal analysis and infrared spectroscopy. Scanning electron microscopy observations revealed that using of solvothermal route led to nano-wires of sepiolite. The reactions have been performed in several conditions to find out the role of different factors such as the aging time and temperature of the reaction in the solvothermal on the size and morphology of the nano-structures.     

Phase and shape controlling of MnS nanocrystals in the solvothermal process

MnS nanocrystals with different phases and shapes were prepared through solvothermal synthesis. The products were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis absorption and photoluminescence (PL) spectra. The solvent and reaction time played an important role in controlling the phase and shape of MnS nanocrystals. The possible mechanism of the shape evolution was investigated, which revealed that the crystal growth along the unique c axis of γ-MnS resulted in the rod-like MnS at the primary period, and the tetrahedral crystal seed of β-MnS with zincblende structure resulted in the interlinking of MnS rods, so the zigzag and three-branched and palm-like MnS appeared; with increasing reactive time the thermodynamically stable spherical α-MnS was favored through the Ostwald ripening process. The PL results showed that the intensity of γ-MnS was much weaker than that of α-MnS, and the trap state emissions of γ-MnS at 470 and 482 nm, respectively, disappeared, which might be ascribed to the difference of the shapes between the sphere and the rod or branch.     

Optical and photoconductivity studies of Cu2O nanowires synthesized by solvothermal method

The solvothermal method has been employed to synthesize cuprous oxide (Cu₂O) nanowires using a precursor of cupric acetate monohydrate (CuAc₂) and ethylene glycol (EG) as the solvent. By optimizing the reaction temperature and reaction time, we have prepared Cu₂O nanowires with a diameter of approximately 7 nm and a length of several nanometers. The UV-visible absorption spectrum of the nanowires shows obvious blueshift compared to the bulk Cu₂O, which arises from the quantum confinement effect of the excitonic transition expected for Cu₂O nanowires. Here we also report the role of different excitation energies on the photoluminescence (PL) properties of the Cu₂O nanowires by steady-state and time-resolved PL spectroscopy. The decay times vary from nanoseconds to picoseconds. Decay kinetics indicates that the average lifetime 〈τ〉 of the nanowires increases with increasing excitation energy. The current-voltage (I-V) curves of the nanowires give the photocurrent density 16 times larger than the dark current density.     

Facile sonochemical synthesis of nanosized InP and GaP

A novel sonochemical method for the preparation of MP (M = Ga, In) nanocrystalline materials has been developed. The procedure consists of the in situ synthesis of sodium phosphide and its subsequent reaction with the appropriate metal chloride using ultrasound. The products were characterized by X-ray powder diffraction, electron microscopy, and energy dispersive X-ray microanalysis (EDX). The choice of solvent and the use of high-power ultrasound are both important in the formation of the products.     

Excimer laser accelerated hydrothermal synthesis of ZnO nanocrystals & their electrical properties

The synthesis of ZnO nanocrystals is reported using a hydrothermal chemical growth technique combined with 248 nm nanosecond excimer laser heating at fluences in the range 0-390 mJ cm⁻². The effect of laser heating in controlling the morphology of the nanocrystals is investigated using optical spectroscopy and electron microscopy characterization. Laser heating is shown to allow control of the crystal morphology from nanoparticles to nanorods as well as to modify the size distributions. The results indicate that not only does the laser accelerate the growth of nanocrystals, but can also produce crystals with a narrow size distribution possibly via photothermal size selection. An initial study of electrical conduction properties of ZnO nanocrystal thin films is also discussed.     

Facile alcohothermal synthesis of large-scale ceria nanowires with organic surfactant assistance

Well monodispersed and large-scaled ceria nanowires with cubic fluorite structure and high aspect ratios were successfully prepared at 80 °C without further sintering via a facile surfactant-assisted alcohothermal route. The X-ray diffraction, transmission electron microscopy with selected-area electron diffraction indicated that the as-prepared ceria nanowires had a cubic fluorite-structure and the morphologies of the products were uniform, with diameters of about 50–100 nm. The TG-DTA and XPS measurements revealed the existence of both trivalent and quadrivalent cerium and an oxidization process took place gradually with increase of the reaction time. Compared with as-reported method, the present process is more convenient and feasible.     

Sonochemical synthesis of a new nano-structures bismuth(III) supramolecular compound: New precursor for the preparation of bismuth(III) oxide nano-rods and bismuth(III) iodide nano-wires

A new nanostructured Bi(III) supramolecular compound, {[Bi₂(4,4′-Hbipy)_1.678(4,4′-Hbipy)_0.322(μ-I)₂I_5.678] (4,4′-bipy)} (1), 4,4′-bipy = 4,4′-bipyridine} was synthesized by a sonochemical method. The nano-structure of 1 was investigated using scanning electron microscopy, powder X-ray powder diffraction (XRD), IR spectroscopy and elemental analysis, and the crystal structure of compound 1 was determined by single-crystal X-ray diffraction. The thermal stability of bulk compound 1 and of nano sized particles was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Bi₂O₃ and BiI₃ nano-structures were obtained by calcinations of nano-structures of compound 1 at 400 °C under air and nitrogen atmospheres, respectively.     

Highly efficient cathodoluminescence of nanophosphors by solvothermal route

The low voltage excited nano-size of SrTiO₃: Pr, Al red cathodoluminescent phosphors is successfully prepared by hydrothermal and solvothermal processes. Crystal size does not have obvious growth after post-annealing process under the nucleation seeds control. The nanophosphors synthesized by the solvothermal process have a more stoichiometric and cubic SrTiO₃ structure than the hydrothermal ones. SrTiO₃: Pr, Al nanophosphors synthesized by the solvothermal process with 200 °C/24 h possess a cubic crystal size of about 50 nm. The red cathodoluminescent intensity of 200 °C/24 h-solvothermal phosphors is nine times that of the 250 °C/24 h-hydrothermal ones after 1000 °C/1 h heat treatment. The stoichiometric SrTiO₃: Pr, Al nanophosphors by solvothermal preparation need less amounts of Pr activator and Al dopant than when using conventional solid-oxide preparation and can achieve high cathodoluminescence at a wavelength of 615 nm exciting at a low accelerating voltage of 1 kV. The solvothermal process combined with the post-annealing process to synthesize nanophosphors distributes and excites the activator and the dopant more homogeneously and efficiently in the host structure of SrTiO₃, thus enhancing luminescence.     

Hybrid solvothermal/sonochemical-mediated synthesis of ZnO NPs generative of OH radicals: Photoluminescent approach to evaluate OH scavenging activity of Egyptian and Yemeni Punica granatum arils extract

Zinc oxide NPs were synthesized solvothermally within sonochemical mediation and characterized by XRD, FTIR, SEM, EDX, elemental mapping, TEM and UV–vis. spectrophotometry. To evaluate the hydroxyl radicals (OH) scavenging activity of arils extract of Egyptian (EGY-PAM) and Yemeni Punica granatum (YEM-PAM), the developed zinc oxide nano particles (ZnO NPs) as a highly productive source of hydroxyl radicals (under Solar-illumination) was used. The yield of OH was trapped and probed via fluorimetric monitoring. This suits the first sensitive/selective photoluminescent avenue to evaluate the OH scavenging activity. The high percentage of DPPH radical scavenging reflected higher contents of phenolics, flavonoids, and anthocyanins that were found in EGY-PAM and YEM-PAM. Although, some secondary metabolites contents were significantly different in EGY-PAM and YEM-PAM, the traditional DPPH radical scavenging methodology revealed insignificant IC₅₀. Unlike, the developed fluorimetric probing, sensitively discriminated the OH scavenging activity with IC₅₀ (105.7 µg/mL) and lower rate of OH productivity (k = 0.031 min⁻¹) in case of EGY-PAM in comparison to IC₅₀ (153.4 µg/mL) and higher rate of OH productivity (k = 0.053 min⁻¹) for YEM-PAM. Our findings are interestingly superior to the TBHQ that is synthetic antioxidant. Moreover, our developed methodology for fluorimetric probing of OH radicals scavenging, recommends EGY-PAM as OH radicals scavenger for diabetic patients while YEM-PAM exhibited a better OH radicals scavenging appropriate for high blood pressure patients. More interestingly, EGY-PAM and YEM-PAM exhibited high anticancer potentiality. The aforementioned OH and DPPH scavenging activities as well as the anticancer potentiality present EGY-PAM and YEM-PAM as promising sources of natural antioxidants, that may have crucial roles in some chronic diseases such as diabetics and hypertension in addition to cancer therapeutic protocols.     

Structure and optical properties of polyvinyle alcohol capped GaAs nanocrystals

Polyvinyl alcohol capped GaAs nanocrystals, assembled in thin film form, have been synthesized by a simple electrochemical technique. Transmission electron microscopy (TEM) study reveals the presence of 20–50 nm size GaAs nanoparticles embedded in the polymer host. Selected area diffraction pattern contains a series of spotted rings indicative of textured nature of the thin film. The excitonic peak broadening and the blue shift of its spectral position with respect to the bulk band gap depend upon the concentration of the polyvinyle alcohol. The X-ray photoelectron spectrum shows C(1s) peak corresponding to the surface bonded polyvinyl alcohol along with the Ga3d and As3d peaks of the GaAs core. Room temperature micro-Raman spectrum shows one surface phonon mode that shifts to the lower energy side with decrease in the crystallite size.     

Optical properties of GaN nanocrystals embedded into silica matrices

The purpose of this work was to obtain GaN nanocrystals (GaN-nc) embedded into silica-based matrix and to investigate their optical properties by photoluminescence (PL) spectroscopy. GaN-nc have been obtained both by the sol–gel chemistry and by the combustion method (CM). The GaN-nc obtained by CM have been introduced into the silica-based matrix during the formation of the film in the spin-on technique. Strong emission at 3.4 eV has been observed for the films doped by GaN-nc whereas no emission in UV has been observed for GaN-nc obtained by sol–gel chemistry.     

Synthesis of photocatalytic active fibrous titania by the solvothermal reactions

Abstract

Fibrous titania was synthesized by the solvothermal reactions of H₁Ti₄O₉ nH₂in different media. H₂Ti₄O₉·nH₂O transformed in steps to H₂Ti₈O₁₇, monoclinic TiO_z, anatase and rutile. The phase transformation temperature and microstructure of the products changed significantly depending on the heating environment. The critical temperature at which anatase appeared in liquid media was much lower than that in air. The titania fibers consisted of nanocrystals of TiO₂. The crystallite size and crystallinity of titania decreased with decreasing the dielectric constant of the reaction medium. Consequently, the photocatalytic activity of titania changed with heat treatment media in the following sequence: ethanol, methanol > water > air, i.e., fibrous titania possessing excellent photocatalytic activity could be obtained by the solvothermal reactions using alcohol such as methanol and ethanol. Titania powders crystallized by the solvothermal reaction in methanol also possessed excellent thermal stability.     

CO gas sensing of CuO nanostructures, synthesized by an assisted solvothermal wet chemical route

CuO nanostructures with different morphologies and sizes were grown in a controlled manner using a simple low-temperature hydrothermal technique. By controlling the pH of reaction mixture, spherical nanoparticles and cloudlike CuO structures were synthesized at 100-150 °C with excellent efficiency. These CuO nanostructures have been tested for CO gas monitoring by depositing them as thick films on an interdigitated alumina substrate and evaluated the surface resistance of the deposited layer as a function of operating temperature and CO concentrations. The gas sensitivity tests have demonstrated that the CuO nanostructures, especially cloudlike morphology, exhibit high sensitivity to CO proving their applicability in gas sensors. The role of the nanostructure on the sensing properties of CuO is also discussed.     

Fabrication and characterization of Pd/Ag alloy hollow spheres by the solvothermal method

Pd/Ag alloy hollow spheres have been synthesized in ethylene glycol solution by the solvothermal method and have been characterized extensively. TEM results have revealed the formation of Pd/Ag hollow spheres. Moreover, HRTEM results confirmed the formation of Pd/Ag alloy spheres, where the lattice fringe spacing is 0.229 nm corresponding to the (111) plane of Pd/Ag alloy. SEM, XRD and UV–vis results have further suggested the formation of alloy hollow spheres. The preliminary results showed the reaction time may be an importance factor influencing the formation of Pd/Ag alloy hollow spheres.     

Hydrothermal synthesis of TiO2 nanocrystals in different basic pHs and their applications in dye sensitized solar cells

In this research TiO₂ nanocrystals with sizes about 11–70 nm were grown by hydrothermal method. The process was performed in basic autoclaving pH in the range of 8.0–12.0. The synthesized anatase phase TiO₂ nanocrystals were then applied in the phtoanode of the dye sensitized solar cells. It was shown that the final average size of the nanocrystals was larger when the growth was carried out in higher autoclaving pHs. The photoanodes made of TiO₂ nanocrystals prepared in the pHs of 8.0 and 9.0 represented low amounts of dye adsorption and light scattering. The performance of the corresponding dye sensitized solar cells was also not acceptable. Nevertheless, the energy conversion efficiency was better for the state of pH of 9.0. For the photoanodes made of TiO₂ nanocrystals prepared at autoclaving pH of 10.0, the dye adsorption and light scattering were quite higher. The photovoltaic characteristics of the best cell in this state were 15.25 mA/cm², 740 mV, 0.6 and 6.8% for the short-circuit current density, open-circuit voltage, fill factor and efficiency, respectively. The photoanodes composed of TiO₂ nanocrystals prepared in autoclaving pHs of 11.0 and 12.0 demonstrated lower amount of dye adsorption and higher light scattering. This was quite considerable for the state of pH of 12.0. The energy conversion efficiencies were consequently decreased compared to that of the pH of 10.0. The optimum situation was finally discussed based on the nanocrystals size and its influence on the sensitization and light harvesting efficiency.     

Charge retention in quantized energy levels of nanocrystals

Understanding charging mechanisms and charge retention dynamics of nanocrystal (NC) memory devices is important in optimization of device design. Capacitance spectroscopy on PECVD grown germanium NCs embedded in a silicon oxide matrix was performed. Dynamic measurements of discharge dynamics are carried out. Charge decay is modelled by assuming storage of carriers in the ground states of NCs and that the decay is dominated by direct tunnelling. Discharge rates are calculated using the theoretical model for different NC sizes and densities and are compared with experimental data. Experimental results agree well with the proposed model and suggest that charge is indeed stored in the quantized energy levels of the NCs.     

Magnetic phases of bismuth ferrite

We have recently shown that BiFeO₃ has at least four different magnetic phases, contrary to the conventional wisdom. Below room temperature it undergoes spin reorientation transitions at T₂=200 K and T₁=140 K analogous to those in orthoferrites; and above room temperature it undergoes a structural transition near 185°C first reported by Polomska et al. This may help explain the apparent linear magnetoelectric effect at 20°C reported by D. Lebeugle et al. [Phys. Rev. Lett. 100, 227602 (2008)] which is nominally forbidden due to the long wavelength cycloidal spin structure assumed. We also find evidence of an unusual acentric spin glass below ca. 200 K, related not to T_N but to T₁ and T₂.