Morphological and phase evolution of TiO2 nanocrystals prepared from peroxotitanate complex aqueous solution: Influence of acetic acid

Nanosized anatase and rutile TiO₂ having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H₂O₂) in water/isopropanol media by a facile sol-gel process. The TiO₂ nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO₂ are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given.     

Super crystal structures of octahedral c-In2O3 nanocrystals

The three-dimensional self-assembly of a nanocrystal superlattice, i.e., a super crystal, has attracted increasing attention. The small building blocks for assemblies are usually spherical nanocrystals. Recent progress indicates that it is possible to achieve a super crystal using cubic nanocrystals. We further analyze and describe two-dimensional and some three-dimensional assemblies of uniform cubic-phase In2O3 nanocrystals with an octahedral shape. In this article, we demonstrate our amazing observations on these kinds of super crystals (or superlattices) as a model system, report their scale in at least tens of microns, and show other interesting features such as steps, terraces, kinks, and vacancies which are similar to those from a single crystal. Based on electron microscopy observations, three types of well-defined octahedral nanocrystal packed structures in such super crystal systems are also identified. The investigation of octahedral super crystal systems provides an alternate direction in research that may extend the interest of superlattice study to a broad spectrum by enriching and varying the shape of elemental building blocks. This may potentially result in new concepts and more challenging applications such as soft X-ray photonics.     

Conversion of Cu2O nanocrystals into hollow Cu2-xSe nanocages with the preservation of morphologies

With the use of PVP (polyvinylpyrrolidone) as capping reagent, cubic, octahedral and spherical Cu2O nanocrystals were obtained in aqueous media when different reducing agents were applied. After adding selenium sources at room temperature, these nanocrystals could be converted (based on the Kirkendall effect) into hollow Cu2-xSe nanocages that keep their corresponding orignial morphologies.     

Enhanced solid-state electrochemiluminescence of CdS nanocrystals composited with carbon nanotubes in H2O2 solution

CdS nanoparticles composited with carbon nanotubes not only enhances their electrochemiluminescent intensity but also decreases their ECL starting potential; such a property would promote the application of quantum dots in fabricating sensors for chemical and biochemical analysis.     

Synthesis and characterization of single-crystalline In2O3 nanocrystals via solution dispersion

In this paper, In2O3 nanocrystals were prepared by solution dispersion from bulk indium. In2O3 nanocrystals with an average diameter of 30 nm have a single-crystalline phase and appear as a square or rhombohedral shape, and little spherical particles are also present. In addition, these nanocrystals show strong ultraviolet-blue emission.     

Fabrications of hollow nanocubes of Cu(2)O and Cu via reductive self-assembly of CuO nanocrystals

In this work, a template-free synthetic approach for generating single-crystalline hollow nanostructures has been described. Using the small optical band-gap cuprous oxide Cu(2)O as a model case, we demonstrate that, instead of normally known spherical aggregates, primary nanocrystalline particles can first self-aggregate into porous organized solids with a well-defined polyhedral shape according to the oriented attachment mechanism, during which chemical conversion can also be introduced. In contrast to the spherical aggregates, where the nanocrystallites are randomly joined together, the Cu(2)O nanocrystallites in the present case are well organized, maintaining a definite geometric shape and a global crystal symmetry. Due to the presence of intercrystallite space, hollowing and chemical conversion can also be carried out in order to create central space and change the chemical phase of nanostructured polyhedrons. It has been revealed that Ostwald ripening plays a key role in the solid evacuation process. Using this synthetic strategy, we have successfully prepared single-crystal-like Cu(2)O nanocubes and polycrystalline Cu nanocubes with hollow interiors. For the first time, we demonstrate that nanostructured polyhedrons of functional materials with desired interiors can be synthesized in solution via a combination of oriented attachment and Ostwald ripening processes.     

Size-controlled preparation of Cu2O octahedron nanocrystals and studies on their optical absorption

We report herein the size-controlled preparation of monodispersed cuprous oxide octahedron nanocrystals smaller than 100 nm. The method is based on the reduction of copper nitrate in Triton X-100 water-in-oil (w/o) microemulsions by gamma-irradiation. The average edge length of the octahedron-shaped nanocrystals varies from 45 to 95 nm as a function of the dose rate. The quantum confinement effect was illustrated by the blueshift in the optical absorption. In addition, the growth process was also traced by absorption spectra.     

The thermostability and reactivity of GaP nanocrystals in oxygen: from GaP nanocrystals to Ga2O3 nanocrystals

The thermostability and reactivity of GaP nanocrystals in O(2) were investigated using the thermogravimetric analysis (TGA), differential thermal analysis (DTA), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis techniques. alpha-Ga(2)O(3) nanoparticles, nano-hollow-particles, or nanorods and nanotubes can be separately obtained from the oxidation of nanocrystalline GaP at 400 degrees C for 30 min in dry O(2) atmosphere via manipulating different heating rates. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometry (EDX) analysis showed that the products were all alpha-Ga(2)O(3) but with different morphologies when different heating rates were applied. The formation mechanisms of the different morphological alpha-Ga(2)O(3) nanocrystals were discussed.     

Morphological evolution of Ba(NO3)2 supported on alpha-Al2O3(0001): an in situ TEM study

A key question for the BaO-based NOx storage/reduction catalyst system is the morphological evolution of the catalyst particles during the uptake and release of NOx. Notably, because the formed product during NOx uptake, Ba(NO3)2, requires a lattice expansion from BaO, one can anticipate that significant structural rearrangements are possible during the storage/reduction processes. Associated with the small crystallite size of high-surface area gamma-Al2O3, it is difficult to extract structural and morphological features of Ba(NO3)2 supported on gamma-Al2O3 by any direct imaging method, including transmission electron microscopy. In this work, by choosing a model system of Ba(NO3)2 particles supported on single-crystal alpha-Al2O3, we have investigated the structural and morphological features of Ba(NO3)2 as well as the formation of BaO from Ba(NO3)2 during the thermal release of NOx, using ex-situ and in-situ TEM imaging, electron diffraction, energy dispersive spectroscopy (EDS), and Wulff shape construction. We find that Ba(NO3)2 supported on alpha-Al2O3 possesses a platelet morphology, with the interface and facets being invariably the eight [111] planes. Formation of the platelet structure leads to an enlarged interface area between Ba(NO3)2 and alpha-Al2O3, indicating that the interfacial energy is lower than the Ba(NO3)2 surface free energy. In fact, Wulff shape constructions indicate that the interfacial energy is approximately 1/4 of the [111] surface free energy of Ba(NO3)2. The orientation relationship between Ba(NO3)2 and the alpha-Al2O3 is alpha-Al2O3[0001]//Ba(NO3)2[111] and alpha-Al2O3(1-210)//Ba(NO3)2(110). Thus, the results clearly demonstrate dramatic morphology changes in these materials during NOx release processes. Such changes are expected to have significant consequences for the operation of the practical NOx storage/reduction catalyst technology.     

Cu2ZnGeSe4 nanocrystals: synthesis and thermoelectric properties

A synthetic route for producing Cu(2)ZnGeSe(4) nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu(2)ZnGeSe(4) is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450 °C.     

Morphological aspects of sulfate-induced reconstruction of Cu(1 1 1) in sulfuric acid solution: in situ STM study

Using in situ STM the atomic structure and the morphology of a Cu(1 1 1) surface exposed to a dilute sulfuric acid solution have been studied depending on the applied electrode potential. At anodic potentials near the onset of copper dissolution the electrode surface is reconstructed (expanded) caused by the specific adsorption of sulfate anions. The extent of the surface reconstruction strongly depends on the sulfate adsorption rate. Fast sulfate adsorption results in a mainly disordered sulfate adlayer on an unreconstructed copper surface. Conversely, slow sulfate adsorption produces a mainly reconstructed copper surface with a highly ordered sulfate/water coadsorption layer. This adsorbate structure shows an additional long-range Moiré modulation, due to a misfit between the first reconstructed and the second unreconstructed copper layer. This is verified by spectroscopy-like STM experiments, which allow the imaging not only of the adsorbate overlayer, but also of the underlying reconstructed substrate. This type of adsorbate-induced reconstruction is characterized by an expansion of the topmost copper layer. The kinetically slow process of reconstruction can be easily followed by dynamic STM measurements revealing a mass transport out of the topmost copper layer during the slow sulfate adlayer formation. Characteristically, new copper islands nucleate and grow, while the sulfate Moiré adlayer expands over the electrode surface. At cathodic electrode potentials the desorption of the sulfate adlayer is accompanied by the lifting of the surface reconstruction and the massive formation of surface defects, such as small pits and vacancy islands. A continuous cycling of the electrode potential leads to an enormous roughening of the surface morphology.     

两步水热法合成Sn_2Nb_2O_7纳米晶及其高效可见光分解水制氢性能（英文）

铌基半导体光催化材料因其具有独特的晶体结构和能带结构在光催化分解水制氢领域受到科研工作者的高度关注.然而,大多数铌基半导体光催化剂仅能够在紫外光驱动下实现光催化分解水制氢,具有可见光响应的铌基半导体光催化剂不仅数量少而且活性较低,因此发展新型纳米铌基半导体光催化剂并实现其高效可见光催化分解水产氢具有重要的学术和实用意义.具有烧绿石构型的Sn_2Nb_2O_7材料由于具有较窄的禁带宽度(2.4 e V)和合适的导带和价带电势在可见光催化分解水制氢方面引起了科研人员广泛的兴趣.然而,目前报道的利用高温固相法制备的块体Sn_2Nb_2O_7材料由于颗粒尺寸较大和比表面积较小而导致光催化活性较差.因此,发展一种简便高效的制备方法实现纳米Sn_2Nb_2O_7材料的可控制备进而提高其可见光催化活性仍具有一定的挑战性.我们发展了一种简便的两步水热合成方法实现了Sn_2Nb_2O_7纳米晶的可控制备.扫描电镜和透射电镜测试结果表明,通过两步水热法得到的Sn_2Nb_2O_7纳米颗粒具有较好分散度,其平均颗粒尺寸为20 nm.X射线衍射测试结果也进一步证明,通过两步水热法可以实现Sn_2Nb_2O_7纳米晶的可控制备.比表面积测试结果表明,Sn_2Nb_2O_7纳米晶的比表面积约为52.2 m~2/g,远远大于固相法制备的块体Sn_2Nb_2O_7材料(2.3 m~2/g).大量研究表明,大的比表面积有利于半导体催化材料催化活性的提升.通过考查所制备的Sn_2Nb_2O_7纳米晶的可见光分解水制氢能力,对其催化性能进行了评价.研究结果表明,以乳酸为空穴消耗剂,负载0.3wt.%Pt纳米颗粒作为助催化剂的Sn_2Nb_2O_7纳米晶表现出优异的可见光催化分解水产氢性能,其产氢速率是块体Sn_2Nb_2O_7材料的5.5倍.Sn_2Nb_2O_7纳米晶可见光催化分解水产氢性能提高的主要原因是其具有高分散度的纳米颗粒、较大的比表面积和更正的价带电势.首先,颗粒尺寸的纳米化能够显著减小光生电子和空穴的迁移距离,实现光生载流子快速迁移到催化剂表面进而参与催化反应;其次,大的比表面积能够提供更多的催化活性位点,进而有利于催化活性的提高;最后,X射线光电子能谱测试表明,Sn_2Nb_2O_7纳米晶具有更正的价带电势,研究表明,价带电势越正,其光生空穴氧化能力越强.在光催化分解水制氢过程中,具有较强氧化能力的光生空穴通过与空穴牺牲剂乳酸快速反应而被消耗掉,抑制了光生电子与空穴的复合,进而导致其具有较高的光催化产氢活性.     

Surface facets dependent oxygen evolution reaction of single Cu2O nanoparticles

Understanding and establishing the structure-activity relation of nanoparticles is a prerequisite for rational design of high-performance electrocatalysts. Cu₂O nanoparticles enclosed with different crystal facets, namely, o-Cu₂O NPs with {111} facets, c-Cu₂O NPs with {100} facets are prepared and their electrocatalytic properties for oxygen evolution reaction (OER) in alkaline condition are evaluated at single nanoparticle level with a combination of scanning electrochemical cell microscopy and scanning electron microscopy. It is found that the o-Cu₂O NPs have significantly superior OER electrocatalytic activity compared to c-Cu₂O, which is almost inert. The estimated turnover frequency (TOF) at 1.97 V vs. RHE on {111} facet increases from 4 s^?1 to 115 s^?1 with the octahedron edge length decreasing from 1.3 µm to 100 nm. Deposition of carbon on c-Cu₂O surface barely promotes the activity, suggesting the inherent poor electric conductivity within the nanocrystal is most likely the reason for low activity. This work provides direct probing to single transition metal oxide crystals with dramatically different activity.     

Wurtzite Cu2ZnSnS4 nanocrystals: a novel quaternary semiconductor

A new wurtzite phase Cu(2)ZnSnS(4) was discovered and the corresponding nanocrystals have been successfully synthesized. They have been characterized in detail and showed the photoelectric response, which demonstrated their potential in the application of photovoltaic devices.     

Hydrothermal Syntheses of CuO,CuO/Cu2O,Cu2O,Cu2O/Cu and Cu Microcrystals Using Ionic Liquids

In this paper, CuO, CuO/Cu₂O, Cu₂O, Cu₂O/Cu and Cu microcrystals were synthesized via a hydrothermal method by mixing Cu(NO₃)₂·3H₂O and NaOH together in the presence of an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate([BMIM]BF₄) or 1-butyl-3-methylimidazolium chloride([BMIM]Cl). The structures and the morphologies of the obtained products were characterized by means of X-ray diffractometer(XRD), field-emission scanning electron microscopy/energy-dispersive spectroscopy(FESEM/EDS), transmission electron microscopy/selected area electron diffraction(TEM/SAED) and Raman spectroscopy. The result of XRD indicates that Cu₂O and Cu microcrystals are cubic phase and the Raman spectra confirm the presence of carbon. The results of FESEM and TEM images show Cu₂O microcrystals as rule cubes of 2 μm in length and Cu particles of 5 μm in diameter. According to the difference between crystal structures, bi-component and single component products were synthesized by adjusting the reaction conditions. A possible formation mechanism of Cu₂O and Cu was proposed in[BMIM]BF₄.     

Tetragonal nanocrystals from the Zr0.5Ce0.5O2 solid solution by hydrothermal method

The formation of tetragonal Zr(0.5)Ce(0.5)O(2) solid solution nanocrystallites of 5 +/- 1 nm size by a hydrothermal method at 120 degrees C for 6 h was confirmed by careful Raman and XRD studies for the first time. It was characterized as the t' '-form with an axial ratio of c/a = 1 but with oxygen ion displacements. The as-prepared sample was hydrous in nature, which is responsible for the lattice expansion. However, most of the water held in the structure can be expelled by heating the sample above 600 degrees C. Above 1050 +/- 50 degrees C the t' '-form of tetragonal Zr(0.5)Ce(0.5)O(2) solid solution dissociates into two phases, cubic phase and the t-form of tetragonal phases.     

Shape evolution of Cu2O nanostructures via kinetic and thermodynamic controlled growth

We report the shape evolution process of Cu(2)O nanocrystals upon slow oxidation of Cu under ambient conditions, yielding novel hexagonal and triangular platelike morphologies. The shape of the obtained nanocrystals evolves from hexagonal to triangular to octahedral; the growth patterns are governed by kinetically and thermodynamically controlled growth. Preferential adsorption of I(-) on {111} planes of Cu(2)O nanoparticles induced the selective crystal growth of metastable platelike structures with {111} faces as the basal planes. On aging, the growth process appeared to shift into the thermodynamic regime and the thermodynamically stable octahedral shape is obtained. The possible growth mechanisms were investigated by varying the synthetic conditions. The band gap of Cu(2)O nanooctahedrons was determined by the classical Tauc approach to be 2.24 eV, which is blue shifted with respect to the bulk Cu(2)O value (2.17 eV). Results suggest that the slow oxidation process and use of crystallographic selective surfactants are essential for the appearance of anisotropic metastable shapes. In general, surface energy control by surfactant molecules might provide a convenient channel for tailoring nanocrystal shapes of metal oxides.     

Ferromagnetism in malonato-bridged copper(II) complexes. Synthesis,crystal structures,and magnetic properties of [[Cu(H2O)3][Cu(mal)2(H2O)]]n and [[Cu(H2O)4]2[Cu(mal)2(H2O)]][Cu(mal)2(H2O)2][[Cu(H2O)4][Cu(mal)2(H2O)2][(H2mal = malonic acid)

Three malonato-bridged copper(II) complexes of the formulas [[Cu(H2O)3][Cu(C3H2O4)2(H2O)]]n (1), [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]] [Cu(C3H2O4)2(H2O)2][[Cu(H2O)4][Cu(C3H2O4)2(H2O)2]] (2), and [Cu(H2O)4][Cu(C3H2O4)2(H2O)2] (3) (C3H2O4 = malonate dianion) have been prepared, and the structures of the two former have been solved by X-ray diffraction methods. The structure of compound 3 was already known. Complex 1 crystallizes in the orthorhombic space group Pcab, Z = 8, with unit cell parameters of a = 10.339(1) A, b = 13.222(2) A, and c = 17.394(4) A. Complex 2 crystallizes in the monoclinic space group P2/c, Z = 4, with unit cell parameters of a = 21.100(4) A, b = 21.088(4) A, c = 14.007(2) A, and beta = 115.93(2) degrees. Complex 1 is a chain compound with a regular alternation of aquabis(malonato)copper(II) and triaquacopper(II) units developing along the z axis. The aquabis(malonato)copper(II) unit acts as a bridging ligand through two slightly different trans-carboxylato groups exhibiting an anti-syn coordination mode. The four carboxylate oxygens, in the basal plane, and the one water molecule, in the apical position, describe a distorted square pyramid around Cu1, whereas the same metal surroundings are observed around Cu2 but with three water molecules and one carboxylate oxygen building the equatorial plane and a carboxylate oxygen from another malonato filling the apical site. Complex 2 is made up of discrete mono-, di-, and trinuclear copper(II) complexes of the formulas [Cu(C3H2O4)2(H2O)2]2-, [[Cu(H2O)4] [Cu(C3H2O4)2(H2O)2]], and [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]]2+, respectively, which coexist in a single crystal. The copper environment in the mononuclear unit is that of an elongated octahedron with four carboxylate oxygens building the equatorial plane and two water molecules assuming the axial positions. The neutral dinuclear unit contains two types of copper atoms, one that is six-coordinated, as in the mononuclear entity, and another that is distorted square pyramidal with four water molecules building the basal plane and a carboxylate oxygen in the apical position. The overall structure of this dinuclear entity is nearly identical to that of compound 3. Finally, the cationic trimer consists of an aquabis(malonato)copper(II) complex that acts as a bismonodentate ligand through two cis-carboxylato groups (anti-syn coordination mode) toward two tetraaqua-copper(II) terminal units. The environment of the copper atoms is distorted square pyramidal with four carboxylate oxygens (four water molecules) building the basal plane of the central (terminal) copper atom and a water molecule (a carboxylate oxygen) filling the axial position. The magnetic properties of 1-3 have been investigated in the temperature range 1.9-290 K. Overall, ferromagnetic behavior is observed in the three cases: two weak, alternating intrachain ferromagnetic interactions (J = 3.0 cm-1 and alpha J = 1.9 cm-1 with H = -J sigma i[S2i.S2i-1 + alpha S2i.S2i+1]) occur in 1, whereas the magnetic behavior of 2 is the sum of a magnetically isolated spin doublet and ferromagnetically coupled di- (J3 = 1.8 cm-1 from the magnetic study of the model complex 3) and trinuclear (J = 1.2 cm-1 with H = -J (S1.S2 + S1.S3) copper(II) units. The exchange pathway that accounts for the ferromagnetic coupling, through an anti-syn carboxylato bridge, is discussed in the light of the available magneto-structural data.     

Molecular dynamics simulation of the interaction between methyl benzotriazole and Cu2O crystal

In circulating water system , methyl benzotriazole (TTA) is one of the common corrosion inhibitors for copper. But the inhibition mechanisms have not been clearly understood so far. In different number of water molecules, the interaction between TTA and Cu₂O (copper surface) was investigated with molecular dynamics (MD) method. The results showed that the MD simulation result with water was more consistent with the experiment results. In different number of water molecules, the sequence of the interaction energies between TTA and Cu₂O (001) was ? E ₁ (150H₂O) > ? E ₁(200H₂O) > ? E ₁(100H₂O) > ? E ₁(50H₂O) > ? E ₁(0H₂O). The number of water molecules had an important influence on the interaction between corrosion inhibitors and Cu₂O crystal. From non‐bond energy and pair correlation functions, the interaction energies of the model system were mainly contributed by the non‐bond interaction. Strong adsorption could be raised by the Coulomb interaction between the negatively charged functional groups in TTA and the positive copper ions in the Cu₂O (001) face, and further interaction between aggressive media and copper could be restricted. So, copper corrosion could be avoided. Chemical bonds and non‐bond interactions were formed between TTA and Cu₂O (001) in different number of water molecules. Water molecules could not be ignored during the MD simulation, too. The results obtained here may provide theoretical supports for developing new corrosion inhibitors.