Unexpected oxidation behavior of Cu nanoparticles embedded in porous alumina films produced by molecular layer deposition

This work reports an unexpected oxidation behavior of Cu nanoparticles embedded in porous Al(2)O(3) confinements that are produced by annealing alucone (an organic-inorganic hybrid material) deposited by molecular layer deposition. An oxidation of such encapsulated Cu nanoparticles by annealing in air produces Cu oxide nanoparticles attached to the outer surface of the hollow Al(2)O(3) nanostructures, which is in strong contrast to bare or compact, nonporous Al(2)O(3)-coated Cu nanoparticles, which result in hollow oxide nanospheres or do not undergo oxidation, respectively. The conversion from encapsulated Cu to supported oxide nanoparticles is explained by a concerted pore-assisted diffusion and oxidation mechanism. The micropores in the films, having diameters of several angstroms, permit a selective out-diffusion of Cu atoms and prevent the inward diffusion of oxygen. The subsequent oxidation occurs at the pore entrances, which work as multiple nucleation sites for the formation of oxide nanoparticles with a small size and good dispersion.     

Synthesis of fluorescent and photovoltaic Cu(2)O nanocubes

Hollow and filled Cu(2)O nanocubes of about 28 ± 5?nm in edge length with a band gap ～2.42?eV have been prepared from cupric nitrate in alkaline aqueous solutions containing fructose and ascorbic acid at room temperature. To the best of our knowledge, this simple strategy demonstrates the first example of preparing high-quality Cu(2)O nanocubes (yield>95%) with sizes smaller than 30?nm. By controlling several important experimental parameters such as pH, concentrations of fructose, and molar ratios of fructose/copper (II), different Cu(2)O nanostructures were prepared. The cubic nanostructures were evidenced by the metal shadowing and transmission electron microscope (TEM) images. We confirmed that the Cu(2)O nanocubes were formed from hollow to filled structures by conducting time-evolution TEM measurements. The thus-prepared Cu(2)O nanocubes possess size-dependence absorption and luminescence characteristics; they absorb light at wavelengths 360 and 454?nm and fluoresce at 493?nm (quantum yield 6.6 × 10(-2)%) when excited at 360?nm. A film of Cu(2)O nanocubes provided a photocurrent density of ～80?mA?m(-2) at a biased voltage 3?V under sunlight illumination (100?mW?cm(-2)).     

Cu2O nanorod thin films prepared by CBD method with CTAB: Substrate effect,deposition mechanism and photoelectrochemical properties

Cuprous oxide (Cu₂O) films with different nanostructures are deposited on different substrates of fluorine-doped SnO₂ (FTO) glass, Cu and Ti foil respectively by using chemical bath deposition (CBD) technique with the presence of cetyltrimethylammonium bromide (CTAB). The samples are characterized by X-ray diffractmeter, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The results show that the prepared Cu₂O films are composed of nanorod arrays when there is CTAB in reaction system. Without CTAB, Cu₂O films with nanospheres are formed. The concentration of CTAB is crucial for the controllable synthesis of nanorod structured Cu₂O films with different length to diameter ratio and nanorod array density is dependent on both substrates and CTAB. A possible mechanism for the formation of Cu₂O nanorods is discussed. Additionally, the UV–vis absorption property for Cu₂O nanorods is much better than that for nanospheres. The photovoltage produced under visible light for Cu₂O nanorod films is higher than that for the nanospheres. Although Cu₂O nanorods on Ti foil can absorb the most visible light, those on Cu foil demonstrate better and more stable photoelectrochemical property than those on any other substrates. This study may be extremely useful for Cu₂O based device with nanostructures.     

Controlled synthesis of pentagonal gold nanotubes at room temperature

Large quantities of pentagonal gold nanotubes have been synthesized by reducing chloroauric acid with silver nanowires in an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) at room temperature. These gold nanotubes possess perfect structures, smooth surfaces, highly crystalline walls, and similar cross-sections to that of the silver template. In this process, the CTAB participation was found to be crucial for shape-controlled synthesis of pentagonal gold nanotubes. In the absence of CTAB, loose and hollow gold structures were routinely generated, while bundled gold nanotubes with rough surfaces were obtained by replacing the CTAB with poly(vinyl pyrrolidone) (PVP). The possible formation mechanism of pentagonal gold nanotubes has also been discussed on the basis of various growth stages studied by field-emission scanning electron microscopy (FE-SEM) images. In addition, the catalytic properties of these hollow nanostructures for hydrogen generation reaction from HCHO solution have also been investigated. They showed higher activity than that of spherical gold nanoparticles.     

Highly sensitive tin oxide hollow microspheres and nanosheets to ethanol gas prepared by hydrothermal method

In this study, we synthesized tetragonal-phase SnO2 with a variety of well-crystallized morphologies as solid microspheres, hollow microspheres and mixture of hollow microspheres and nanosheets via the hydrothermal method. The synthesized samples were characterized with XRD, SEM, and BET. SnO2 hollow microsphere structures have been hydrothermally synthesized by using urea and SnCl2 as raw materials. With the addition of cetyltrimethylammonium bromide (CTAB), nanostructures with morphologies of hollow microspheres and nanosheets were obtained. Also, when CTAB was added in the reaction solution without urea, SnO2 microsphere with a solid interior composed of nanoparticles were obtained. A possible formation mechanism of these samples was briefly discussed. The gas sensing properties of sensors based on these samples were investigated. The result revealed that sample with morphology of hollow microsphere and nanosheet calcined at 600 degrees C showed the highest sensitivity to ethanol due to the special morphology and absence of SnO phase.     

Synthesis of core-shell nanostructures of Co3O4@SiO2 with controlled shell thickness (5-20 nm) and hollow shells of silica

Synthesis of uniform silica shell over Co3O4 nanoparticles was carried out using the colloidal solutions of Tergitol and cyclohexane. The shell could be controlled to a thickness of up to 20 nm by varying different parameters such as the amount of tetraethylorthosilicate, concentration of Co3O4 nanoparticles, reaction time and the presence of water and 1-octanol. Control of the amount of water (required for hydrolysis) appears to be the key factor for controlling the shell thickness. The methodology used is suitable to form shell over nanoparticles (present in powder form; synthesized at high temperature) which have high degree of agglomeration. Hollow shells of silica were obtained by the dissolution of the oxide core of Co3O4@SiO2 core-shell nanostructures. The composition of these core-shell nanostructures was confirmed by high-resolution transmission electron microscopy and elemental mapping by energy dispersive X-ray analysis. The hollow shells were characterized by using TEM, EDX and IR. Electron paramagnetic resonance studies of the core-shell nanostructures indicate the presence of free radicals on silica shell due to the presence of dangling bonds in the silica. Increase in the magnetic susceptibility was observed for these core-shell nanostructures.     

表面活性剂对FePt纳米颗粒形貌的影响

分别以乙酰丙酮铁(Fe(acac)3)和氯铂酸(H2PtCl6.6H2O)作为Fe源和Pt源,乙二醇作为还原剂和溶剂,通过多元醇还原法制备出单分散的FePt纳米颗粒,并研究了表面活性剂油酸油胺和CTAB对FePt纳米颗粒形貌和磁性能的影响。通过X射线衍射仪(XRD)、透射电子显微镜(TEM)和振动样品磁强计(VSM)对纳米颗粒进行表征。结果表明,表面活性剂油酸油胺和CTAB修饰的FePt纳米颗粒均为面心立方(FCC)结构,分散性良好,粒径分布较未使用表面活性剂时变窄;油酸油胺修饰的FePt形貌主要是球形,但是有四方形纳米结构出现;而CTAB修饰的FePt形貌有蠕虫状产生。VSM结果显示其矫顽力都趋近于零,呈现超顺磁性。     

树枝状与球状PbS纳米结构的组装合成及其形成机理研究

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂SDS单独作用和表面活性剂SDS和CTAB共同作用下可选择性地组装合成出颗粒以相同晶面粘连组装成的单晶树枝状PbS纳米结构和颗粒以不相同晶面粘连组装成的多晶球状PbS纳米结构,而且提高反应物浓度能起到调节树枝状和球状PbS纳米结构尺寸的作用.对树枝状和球状PbS纳米结构的形成机理进行了初探,发现SDS单独作用时其烷基链起到的软模板作用有利于PbS小颗粒组装成树枝状的PbS纳米结构.当反应溶液中再加入适量的CTAB时,它在溶液中形成微胶束起到了软模板作用,迫使颗粒粘连组装成球状PbS纳米结构,有效地限制树枝状结构的生长.     

Fabrication and highly sensitive gas sensors based on h-MoO3/SnO2 hollow nanostructures operated at low temperatures

Simulated by the synthesis of one dimensional hollow nanostructures with significant sensing, electrical, and optical properties, we have successfully synthesized 1D hollow nanostructures of h-MoO3/SnO2 with well-defined multi-side walls. These hollow nanostructured materials synthesized via a hydrothermal method with SnCl2.2H2O as the precursor and h-MoO3 as the template. SnO2 nanoparticles grew on the surface of h-MoO3 with preferential direction [001]. The morphological change was observed with variation of the growth conditions, such as HNO3, and h-MoO3 concentration. 1D hollow nanostructures of h-MoO3/SnO2 were studied and their growth mechanism was discussed. The result revealed that the existence of h-MoO3 caused to increase the sensor response to ethanol gas and downshift the sensor operating temperature at low temperatures.     

Immobilized CuO hollow nanospheres catalyzed alkyne-azide cycloadditions

An approach for gram-scale synthesis of uniform Cu2O nanocubes by a one-pot polyol process was used. The CuO hollow nanostructures were prepared by adding aqueous ammonia solutions with Cu2O nanocube colloidal solutions. CuO hollow nanospheres on acetylene black (CuO/AB), were synthesized and used for the catalytic [3+2] cycloaddition of azides with terminal alkynes to provide products in good yields with high regioselectivity. The CuO/AB was readily separated by centrifugation and could be reused ten times under the present reaction conditions without any loss of catalytic activity. Transition metals loaded onto acetylene black are useful reagents for a wide variety of organic transformations. Moreover, these heterogeneous systems are promising industrial catalysts.     

Synthesis of hollow silver nanostructures by a simple strategy

Various silver nanostructures with hollow interiors, including nanoscaled cubic or quasi-cubic boxes, tubes, triangular rings, trapeziform rings and hybrid structures composed of tubes and cubic boxes, were synthesized via an extremely simple route. The method involved the modification of the solid silver nanocrystals by dithiol, and subsequent dissolving of the interior metal and assembly of the outer surface. In the whole process, only one simple step of pretreatment was needed before the transformation from Ag solid nanostructures to their corresponding hollow nanostructures. According to the morphological, spectral and structural changes in the evolution from silver solid nanostructures to their corresponding hollow nanostructures, a layer-by-layer assembly mechanism was proposed. The method is believed to open up a simple and versatile route to the fabrication of metallic hollow nanostructures with various morphologies according to the starting templates.     

Functionalization of carbon nanotubes with magnetic nanoparticles: general nonaqueous synthesis and magnetic properties

A novel approach has been developed to synthesize magnetic nanoparticle and carbon nanotube (CNT) core-shell nanostructures, such as CoO/CNTs and Mn(3)O(4)/CNTs, by the nonaqueous solvothermal treatment of metal carbonyl on CNT templates using hexane as the solvent. The morphological and structural characterizations indicate that numerous cubic CoO or tetragonal Mn(3)O(4) nanoparticles are deposited on the surfaces of the CNTs to form CNT-based core-shell nanostructures. It is revealed that the hydrophobic interaction between nanoparticles and CNTs in hexane plays the critical role for the formation of CNT-based core-shell nanostructures. A physical property measurement system (PPMS-9, Quantum Design) analysis indicates that the CoO/CNT core-shell nanostructures show weak ferromagnetic performance at 300?K due to the ferromagnetic Co clusters and the uncompensated surface spin states, while the Mn(3)O(4)/CNT core-shell nanostructures display ferromagnetic behavior at low temperature (34.5?K), which transforms into paramagnetic behavior with increasing temperature.     

Shape controlled synthesis of iron-cobalt alloy magnetic nanoparticles using soft template method

Fe_xCo_1 − x alloy nanoparticles of spherical (x = 0.25, 0.68, 0.85), hollow spherical (x = 0.60) and sheet like (x = 0.60) shapes were prepared at room temperature by reduction of iron chloride tetrahydrate and cobalt chloride hexahydrate with sodium borohydride, using N-Cetyl-N,N,N-trimethyl ammonium bromide (CTAB)/water/hexanol system as soft template. The size and shapes of nanostructures were found to depend on the concentrations of CTAB and hexanol in water. Composition and shape dependence of magnetic properties of spherical, hollow spherical and sheet like Fe_xCo_1 − x alloy nanostructures were discussed. The highest saturation magnetization of 235 emu/g with a coercivity of 160 Oe was obtained for spherical Fe_0.68Co_0.32 nanoparticles.     

Anisotropic growth of gold clusters to gold nanocubes under UV irradiation

A chiral reagent, 2-naphthol, has been introduced under alkaline solution as a reductant for HAuCl(4) in CTAB micelle to produce exclusively cubic gold nanoparticles under UV photoactivation. Prolonged irradiation helped the digestion of the primarily evolved spherical particles into smaller gold nanocubes, which then act as tiny cubic seeds, leading to the formation of larger nanocubes. The smaller cubes take the assistance of CTAB under alkaline condition to serve as the seed in directing the transformation of all the spherical colloids into cubic shapes under continuous irradiation via Ostwald ripening. The shape transformation of the nanoparticles has been monitored by repetitive TEM imaging and absorption spectral analysis. The FTIR analysis proves that the gold nanocubes are capped by CTAB. The XRD pattern authenticates the formation of the fcc gold nanocubes. GCMS studies in turn confirmed the presence of hydroxylation of 2-naphthol in the course of the reaction, leaving exclusively cubic gold nanoparticles at the final stage of the photoactivation reaction.     

Studies of structural,optical, and electrical properties associated with defects in sodium-doped copper oxide (CuO/Na) nanostructures

In the present paper, we report a detailed study on the sodium (Na) doping-induced modifications in the copper oxide (CuO) nanostructure and its properties. A facile and sustainable sol–gel synthesis approach was employed for the preparation of high-quality pristine CuO- and Na-doped CuO nanostructures(1.0, 3.0, 5.0 and 7.0 mol% doping levels, CuO/Na) with controlled shape and composition. Due to the remarkable difference in the ionic radii of Cu²⁺ (0.73 Å) and Na⁺ (1.02 Å), Na⁺ substitution in place of Cu²⁺ generates strain/distortions in CuO lattice. The XRD analysis reveal the structural alteration from monoclinic to cubic symmetry with increase in doping level and also reveal the phase purity up to 3% doping level, and beyond this (i.e., for 5 and 7% doping level) small amount of impurity phase corresponding to Na₂O was observed. The FTIR results further confirmed the presence of the Na–Cu–O stretching vibrations at higher Na-doped samples. Morphology of the samples indicates that the Na-doped CuO nanostructures exhibit less agglomeration compared to pristine CuO nanoparticles. The presence of Na in CuO lattice were found to greatly enhances optical and electrical properties owing to the formation of defects like copper vacancies and oxygen vacancies at the grain boundaries of the nanoparticles with increased doping of Na.     

Formation and stability of small well-defined Cu- and Ni oxide particles

Well-defined and -structured Cu/Cu₂O and Ni/NiO composite nanoparticles have been prepared by physical-vapor deposition on vacuum-cleaved NaCl(001) single crystal facets. Epitaxial growth has been observed due to the close crystallographic matching of the respective cubic crystal lattices. Distinct particle morphologies have only been obtained for the Ni/NiO particles, comprising truncated half-octahedral, rhombohedral- and pentagonal-shaped outlines. Oxidation of the particles in the temperature range 473–673 K in both cases led to the formation of well-defined CuO and NiO particles with distinct morphologies. Whereas CuO possibly adopts its thermodynamical equilibrium shape, NiO formation is accompanied by entering a Kirkendall-like state, that is, a hollow core–shell structure is obtained. The difference in the formation of the oxides is also reflected by their stability under reducing conditions. CuO transforms back to a polycrystalline mixture of Cu metal, Cu₂O and CuO after reduction in hydrogen at 673 K. In contrast, as expected from theoretical stability considerations, the formation of the hollow NiO structure is reversed upon annealing in hydrogen at 673 K and moreover results in the formation of a Ni-rich silicide structure Ni₃Si₂. The discussed systems present a convenient way to tackle and investigate various problems in nanotechnology or catalysis, including phase transformations, establishing structure/activity relationships or monitoring intermetallic particles, starting from well-defined and simple models.     

Large-scale synthesis of high-content Fe nanotubes/nanorings with high magnetization by H2 reduction process

High-content Fe hollow nanostructures from nanotubes (NTs) to nanorings (NRs) have been successfully fabricated by reduction of α-Fe₂O₃ hollow nanostructures at designated temperature. We investigated the influence of reduction condition on the structure and property of the products. With increasing reduction temperature, α-Fe₂O₃ with rhombohedral phase could be converted to cubic inverse spinel phase Fe₃O₄. Thereafter the phase was converted to the dominant cubic Fe preserving the same morphology. The highest M_s is 126 emu/g and 123 emu/g for 70 nm NRs and NTs reduced at 450 °C, respectively. Our results provide a general strategy of reducing single-crystalline α-Fe₂O₃ hollow nanostructures to get high magnetization which is required for many applications.     

Synthesis of hollow spheres with mesoporous silica nanoparticles shell

Hollow spheres with mesoporous silica nanoparticles shell were synthesized with the use of cetyltrimethylammonium bromide (CTAB) and polystyrene (PS) hollow spheres as dual templates. The key to this study is that the uneven surface of the template provides nucleation sites for mesoporous nanoparticles, resulting in the formation of hollow spheres with mesoporous silica nanoparticles shell. The final products with hierarchical mesopores can be obtained through a simple one-step approach.     

Selected synthesis of CuS nanotubes and hollow nanospheres at room temperature

A solution route has been developed to synthesize covellite (CuS) nanostructures through the precitation reaction of CuCl2.2H2O, thiourea (Tu), and NaHCO3 in distilled water at room temperature. By regulating the concentration of Tu, CuS nanotubes and hollow nanospheres with diameters of 100-200 nm have been selectively prepared. Structural characterizations indicate that both nanotubes and hollow spheres are composed of CuS nanoparticles with diameters of about 5-10 nm. UV-Vis absorption and room temperature photoluminescence (PL) spectra display different morphology-related absorption phenomena for nanotubes and hollow nanospheres. A systematic investigation has been carried out to understand the factors influencing the CuS morphology. Two different routes are identified to explain the formation of the nanotubes and hollow nanospheres herein.