Oriented growth of urchin-like zinc oxide micro/nano-scale structures in aqueous solution

The urchin-like ZnO microcrystals with high crystallinity decomposed from [Zn(OH)₄]^2? directly were obtained via a hydrothermal method. The morphology, particle size, crystalline structure and fluorescence of the as-prepared ZnO were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analyses. The results demonstrated that the urchin-like ZnO crystals with wurtzite structure had a narrow distribution in size, which could be adjusted in the range of 30–80 μm by varying reaction time. Broad visible light emission peak was also observed in the PL spectra of the synthesized ZnO products. A multistep growth process about how to form such a structure was proposed.     

Sonochemical synthesis and characterization of disk-like copper microcrystals

Disk-like Cu microcrystals were successfully synthesized with assistance of ultrasonic irradiation. The products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and thermogravimetric/differential thermal analysis (TGA/DTA). It was found that as-prepared Cu microcrystals were single crystals in nature and had a high crystallinity. They were mainly composed of disk-like and triangular Cu microcrystals with an average diameter of about 1 μm. There existed CuO on the outermost surface of the products, while a thin layer of Cu₂O was found between CuO and inner Cu microcrystals. Moreover, CTAB molecules were adsorbed on the surface of Cu microcrystals and they were desorbed while heated during TGA analysis. In addition, the influences of magnetic stirring, stillness, concentration of hexadecyltrimethylammonium bromide (CTAB) surfactant, and starting Cu salts on the morphology and size distribution of the final products have also been studied.     

Thermal decomposition synthesis of 3D urchin-like α-Fe2O3 superstructures

Urchin-like α-Fe₂O₃ superstructures have been deposited on Si substrate using thermal decomposition FeCl₃ solution at 200–600 °C in the oven. The morphologies and structures of the synthesized urchin-like superstructures have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that urchin-like α-Fe₂O₃ superstructures were a polycrystal with the rhombohedral structure and typical diameters of 16–20 nm and lengths up to 1.0 μm. The as-prepared α-Fe₂O₃ superstructures have a high Brunauer–Emmett–Teller (BET) surface area of about 60.24 m²/g. The photoluminescence spectrum of the urchin-like α-Fe₂O₃ superstructures consists of one weak emission peak at 548 nm (2.26 eV). A possible new mechanism for the formation of the urchin-like superstructures was also preliminarily discussed.     

Applications of Cu2O octahedral particles on ITO glass in photocatalytic degradation of dye pollutants under a halogen tungsten lamp

Cu₂O octahedral microcrystals were prepared on the ITO glass by galvanostatic electrodeposition in CuSO₄ solution with poly(vinylpryrrolidone) as the surfactant. By controlling the electrodeposition time, the microcrystals could be randomly distributed on the ITO glass and separated from each other, resulting in as many as possible {1 1 1} crystalline planes were exposed. Such microcrystals immobilized on ITO glass were employed in photodegradation of dye pollutants in the presence of H₂O₂ under a 150 W halogen tungsten lamp. The photodegradation of methylene blue was taken as an example to evaluate the photocatalytic activities of the octahedral Cu₂O microcrystals. Effects of electrodeposition time and H₂O₂ amount on the degradation efficiency was discussed, giving the optimum conditions and the corresponding degradation mechanism. The catalyst showed high ability in degradation of methylene blue, methyl orange, rhodamine B, eosin B and their mixtures under identical conditions.     

Synthesis of Cu2O nanocrystallites and their adsorption and photocatalysis behavior

Cuprous oxide (Cu₂O) nano-crystallites have been prepared via an electrochemical method by the anodic dissolution of copper in an alkaline solution of concentrated sodium chloride in a simple electrochemical cell. The effect of addition of glucose on the crystal size, structure and photocatalytic activity of Cu₂O particles was studied. Photocatalytic decolorization of MeO in aqueous Cu₂O suspensions was investigated. X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transformation infrared spectroscopy (FTIR) were used to characterize the samples. UV–vis Spectroscopy was employed to investigate the photocatalysis behavior of the Cu₂O samples. The adsorption performance of the Cu₂O samples showed that after adsorption of 2 h, the decolorization efficiencies of MO reached 11.81%, 95.24% and 56.53% for samples 1, 2 and 3, respectively, which proves that sample 2 has the highest adsorption capacity. The photocatalytic results showed that the as prepared Cu₂O on the addition of 5 g/L glucose was the best sample since it was photostable and decolorized 98.7% of MeO solution in 30 min without any further decrease in the photocatalytic efficiency with increase in the irradiation time for 120 min. Higher concentrations of glucose lead to the decrease of photocatalytic efficiencies of the Cu₂O particles.     

Octahedral iron phosphate hydroxide microcrystals: Fast microwave-hydrothermal preparation,influencing factors and the shape evolution

Octahedral Fe₄(PO₄)₃(OH)₃ microcrystals have been successfully prepared by a microwave-assisted hydrothermal route at 170 °C for 20 min, employing FeCl₃·6H₂O and NaH₂PO₄·2H₂O as the starting materials in the presence of proper amounts of Na₂SO₃ and acetic acid (HAc). The phase and morphology of the as-prepared product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Some factors influencing the formation of octahedral Fe₄(PO₄)₃(OH)₃ microcrystals were systematically investigated, including the reaction temperature, time, and the molar ratio of Na₂SO₃/HAc.     

Synthesis of copper and copper(I) oxide nanoparticles by thermal decomposition of a new precursor

The present investigation reports, the novel synthesis of nanoparticles Cu and Cu₂O using thermal decomposition and its physicochemical characterization. The nanoparticles copper powder have been prepared using [Bis(salicylidiminato)copper(II)], [Cu(sal)₂], as precursor. Cu nanoparticles are initially formed and subsequently oxidized to form Cu₂O. Transmission electron microscopy (TEM) analysis demonstrated nanoparticles Cu₂O with an average diameter of about 10 nm. As-prepared copper nano-particles were characterized by X-ray diffraction measurements (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), and Fourier transform infra-red spectroscopy (FTIR). XRD analysis revealed broad pattern for fcc crystal structure of copper metal and cubic cuprite structure for Cu₂O. Optical absorption measured by UV–visible spectroscopy was used to monitor oxidation course of Cu → Cu₂O and to determine the band-gap energy about 2.4 eV for Cu₂O nanoshells.     

Electrochemical synthesis and photocatalytic property of cuprous oxide nanoparticles

Cuprous oxide (Cu₂O) nanoparticles of 35 nm in crystal size have been successfully synthesized via electrochemical method in alkali NaCl solutions with copper as electrodes and K₂Cr₂O₇ as additive. Photocatalytic degradation of methyl orange (MeO) in aqueous Cu₂O solution was investigated under either ultraviolet (UV) light or sunlight. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–vis) and X-ray photoelectron spectroscopy (XPS) were introduced to characterize the samples. The results indicate that electric current shows no obvious effect on the growth of Cu₂O nanocrystals and that 97% of MeO can be decolorized under UV irradiation for 2 h or under sunlight for 3 h when amount of Cu₂O is 2 g/L. Recycling use of the catalyst revealed that Cu₂O still has a high photocatalytic efficiency when repeatedly used for four times. Cu₂O nanoparticles still kept its cubic crystal phase, but fractionally oxidized to be CuO after the photocatalysis. Compared with the original Cu₂O nanoparticles, there has 1 eV shift of Cu 2p electron and 1.6 eV shift of Cu Auger signals for the Cu₂O powders after four times photocatalysis. Some new peaks can also be observed at 401.1, 237.4 and 170.2 eV in the Cu₂O powders after photocatalysis.     

The effect of fabrication processes on the mechanical and interfacial properties of SiCf/Cu–matrix composites

Three groups of SiC_f/Ti/Cu composites were prepared under conditions of 650 °C + 105 min (sample 1#), 750 °C + 85 min (sample 2#) and 840 °C + 50 min (sample 3#), respectively, by foil-fiber-foil method (FFF), and their room temperature tensile strengths were established. The aim is to model the reactive bonding states between Ti and SiC fiber and between Ti and Cu when Ti is used as interfacial adhesion promoters in SiC_f/Cu–matrix composites. The fracture surfaces, SiC_f/Ti interfaces and Ti/Cu interfaces were investigated by scanning electron microscopy (SEM), optical microscopy and energy dispersive spectroscopy (EDS). The tensile tests show that the tensile strengths of samples 1# and 2# are not obviously enhanced due to the weak bonding strength between SiC fiber and Ti, while those of sample 3# are achieved above 90% of ROM (the rule of mixtures) strength because of excellent bonding between SiC fiber and Ti. However, there are distinct Ti/Cu interfacial reaction zones after the three processes, which are approximately 5.4, 9.0 and 13.3 μm thick, respectively. The Ti/Cu interfacial reaction products are mainly distributed in four layers. In samples 1# and 2#, the products are predicted to be Cu₄Ti, Cu₃Ti₂, CuTi and CuTi₂ according to their chemical compositions determined by EDS, while in sample 3#, the products are Cu₄Ti, Cu₄Ti₃, CuTi and CuTi₂. Additionally, the relationships between the thickness of Ti interlayer and its reaction with C and Cu are also discussed, and an optimal thickness of Ti is introduced.     

The effect of complexing agents on the oriented growth of electrodeposited microcrystalline cuprous oxide film

Three conventional complexing agents, including lactic acid, citric acid and EDTA, are applied in the electrodeposition of microcrystalline cuprous oxide (Cu₂O) film on indium tin oxide glass substrate. Both scanning electron microscopy and X-ray diffraction have been performed to characterize the morphology and texture of microcrystalline Cu₂O film. It is found that the stability constant of copper-based complex compound can obviously influence the deposition overpotential of Cu₂O, and the overpotential can significantly alter the growth priority of different planes, which results in oriented growth of Cu₂O grains. The quantitative relationships between the stability constant and the deposition overpotential of different complexing agents, as well as the relationship between the overpotential and the formation energy of microcrystalline cuprous oxide's (1 1 0), (1 1 1) and (2 0 0) planes are calculated, respectively.     

Hierarchical hollow microsphere and flower-like indium oxide: Controllable synthesis and application as H2S cataluminescence sensing materials

In the present work, In₂O₃ hierarchical hollow microsphere and flower-like microstructure were achieved controllably by a hydrothermal process in the sodium dodecyl sulfate (SDS)-N,N-dimethyl-formamide (DMF) system. XRD, SEM, HRTEM and N₂ adsorption measurements were used to characterize the as-prepared indium oxide materials and the possible mechanism for the microstructures formation was briefly discussed. The cataluminescence gas sensor based on the as-prepared In₂O₃ was utilized to detect H₂S concentrations in flowing air. Comparative gas sensing results revealed that the sensor based on hierarchical hollow microsphere exhibited much higher sensing sensitivity in detecting H₂S gas than the sensor based on flower-like microstructure. The present gas sensor had a fast response time of 5 s and a recovery time of less than 25 s, furthermore, the cataluminescence intensity vs. H₂S concentration was linear in range of 2–20 μg mL^?1 with a detection limit of 0.5 μg mL^?1. The present highly sensitive, fast-responding, and low-cost In₂O₃-based gas sensor for H₂S would have many practical applications.     

The effect of HNO3 on morphology,phase transformation,and luminescence properties of LaPO4:Eu3+ phosphors

LaPO₄:Eu³⁺ powders with different morphologies were hydrothermally constructed by adjusting the amount of HNO₃ without using a catalyst, surfactant, or template. The as-prepared products were characterized by photoluminescence spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), infrared (IR) spectra, and X-ray photoelectron spectroscopy. The SEM study revealed that the amount of HNO₃ played a crucial role in the morphology of the final products. The XRD results indicated that the as-prepared samples were in the monoclinic phase when 3 mL of HNO₃ was used. The HR-TEM micrographs and SAED results demonstrated that the prepared nanorods were single and crystalline in nature with HNO₃, and that they grew preferentially along the [0 1 2] direction. The emission spectra showed that the LaPO₄:Eu³⁺ samples had the strongest emission intensity when prepared with HNO₃.     

Biologically formed hollow cuprous oxide microspheres

Hollow cuprous oxide (Cu₂O) microspheres with a diameter of ca. 1.8 μm are prepared by using yeast as template. The possible mechanism for the formation of the hollow Cu₂O spheres is revealed. The biotemplated sample is investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible (UV–vis) absorption spectra. The sample consists of the crystalline Cu₂O microspheres with diameters of about 59.5 nm and lattice parameter of 4.264 Å. The observed optical band gap of the product indicates that the blue–shift effect occurs, which is attributed to the hollow Cu₂O microspheres.     

Effect of the mixing rate on the morphology and photocatalytic activity of ZnO powders prepared by a precipitation method

The urchin-like shape of ZnO powders was prepared by mixing of Zn²⁺ and NaOH solutions at various mixing rates. In this work, ε-Zn(OH)₂ was the first precipitant that was subsequently transformed to ZnO in the alkaline medium during heating. The size of the urchin-like shape of the ZnO powder decreased with a decrease of the mixing rate. The large urchin-like shape also had a large diameter of its hexagonal facet (0 0 0 1) and showed the highest photocatalytic degradative activity on methylene blue.     

Synthesis of crystal MFe2O4 (M = Mg,Cu, Ni) microspheres

A low-temperature solvothermal synthetic method was developed for the large-scale synthesis of uniform-sized ferrite MFe₂O₄ (M = Mg, Cu, Ni) microspheres. The size of the as-prepared ferrite MFe₂O₄ microspheres could be controlled to be diameters 300–800 nm in diameter by adjusting some growth parameters, such as reaction time and concentration. The structures of the as-prepared ferrite MFe₂O₄ microspheres were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The magnetic properties of the ferrite MFe₂O₄ microspheres were also investigated.     

Morphology and phase selective synthesis of CuxO (x = 1, 2) nanostructures and their catalytic degradation activity

Cu_xO (x = 1, 2) nanocrystals have been synthesized by the composite-hydroxide-mediated approach. The obtained nanocrystals were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrum. The morphology of the nanocrystals changed from sphere-shaped nanostructures to flower-shaped nanostructures, and finally to nanowires associated with phase transformation from CuO to Cu₂O by increasing the temperature. The possible phase transformation mechanism was discussed. The catalytic degradation activity of the Cu_xO (x = 1, 2) nanocrystals to methyl orange was also investigated. The photocatalytic ability of the sphere-shaped nanostructures is much higher than that of the nanowires, owing to its absorption of wider range of light energy. This work provides a new facile synthesis route of Cu_xO (x = 1, 2) nanocrystals and suggests their possible application in organic pollutants removal.     

Compressive strength and microstructural characteristics of class C fly ash geopolymer

Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO₂/Na₂O was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na₂O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were cured at 75 °C for 8 h followed by curing at 23 °C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm^?1 have been attributed to asymmetric stretching of Al–O/Si–O bonds, while those at 747 cm^?1 are due to the Si–O–Si/Si–O–Al bending band. The main geopolymeric gel and calcium silicate hydrate (C–S–H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM–EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern.     

Microstructural and mechanical characteristics of Cu–Cu2O composites compacted with pulsed electric current sintering and hot isostatic pressing

This paper reports the influence of applied sintering process – pulsed electric current sintering (PECS) and hot isostatic pressing (HIP) – on the microstructure and mechanical properties of Cu–Cu₂O composites. In PECS fine-grained structure was obtained while in HIPing the grain growth was more noticeable, mostly due to the longer process time. The studies also showed that Cu₂O-phase distributed in Cu-matrix increased microhardness; at a fixed grains size Cu–Cu₂O structure had higher hardness than Cu so that 20% higher microhardness was obtained when Cu₂O was doubled from 19.1 to 37.2 vol%. At best, 99.1% density with 690 nm grain size and 1.35 GPa hardness were achieved by PECS whereas by HIP the same density with 1860 nm grain size gave 1.02 GPa hardness. The grain growth and the effect of second phase clustering on the grain growth were evaluated experimentally.     

Novel synthesis and characterization of bismuth nano/microcrystals with sodium hypophosphite as reductant

In this paper, we report on the low temperature solution reduction method employed in the synthesis of large quantities of nano/micro-sized bismuth (Bi) crystals with sodium hypophosphite (NaH₂PO₂·H₂O) as reductant in acidic solutions. The achieved Bi crystals exhibited plate-like (100 nm in size and few nanometers in thickness) or polyhedral (500 nm in size) shapes. Bi nanocrystals transformed to octahedron-like Bi microcrystals only by prolonging the reaction time. The assembly and oriented growth should be the reason. To understand the growth mechanism, we also discussed the possible growth of the Bi nanocrystals exhibits influence of experimental parameters such as reaction time, NaH₂PO₂·H₂O concentration, and pH value. The resulting Bi crystals were characterized by using scanning electron microscopy, X-ray powder diffraction and differential thermal analysis and thermogravimetry. Optical properties of the samples were studied by ultraviolet–visible spectroscopy.     

Characterization of ordered Cu2O nanowire arrays prepared by heat treated Cu/PAM composite

Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu₂O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (?180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu₂O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu₂O phase with the space limitation of the PAM template. Single-crystal Cu₂O nanowire arrays were also obtained under the template embedded.