Ferric Phosphate Hydroxide Microcrystals for Highly Efficient Visible‐Light‐Driven Photocatalysts

Fe₄(OH)₃(PO₄)₃ microcrystals are successfully synthesized by a simple hydrothermal method. Due to a possible self‐etching mechanism, different morphologies of Fe₄(OH)₃(PO₄)₃ microcrystals are obtained. Several reactions with different temperatures and times are performed to confirm the supposed self‐etching mechanism. Moreover, as a result of their different micro/nanostructures, these microcrystals present different photocatalytic activities for visible‐light‐driven photodegragadation of methylene blue.     

Hydrothermal Synthesis of Regular Octahedron Fe3O4 Microcrystals

Regular octahedron Fe₃O₄ microcrystals have been synthesized by a hydrothermal process on a large scale directly Fe substrates for the first time. X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to investigate the novel fractal microcrystals. The results show that the regular octahedron Fe₃O₄ microcrystals can be obtained using this simple method. The size of microcrystals is evaluated to be from 2 to 20 μm. Moreover, one key fact has been found that the reaction temperature has a vital effect on the morphologies of the products.     

Effect of crystal structure and ions concentration on luminescence in Yb and Tm codoped fluoride microcrystals

A facile hydrothermal method is used for the preparation of Tm³⁺/Yb³⁺ codoped fluoride microphosphors. The effect of crystal structure and ions concentration on the spectra and lifetimes of the radiative levels of Tm³⁺ ions in the different fluoride microcrystals is studied in detail. XRD analysis of Tm³⁺/Yb³⁺ codoped LaF₃ microcrystals shows that 20% Yb³⁺ doping is sufficient for hexagonal LaF₃ microparticles to crystallize completely in the orthorhombic phase. And lifetime analysis suggests that the average lifetimes of the radiative levels of Tm³⁺ ions increased when the matrix phase structure changing from orthorhombic phase to hexagonal phase with ytterbium dopant concentration changing.     

Unraveling Epitaxial Habits in the NaLnF4 System for Color Multiplexing at the Single‐Particle Level

We report an epitaxial growth technique for scalable production of hybrid sodium rare‐earth fluoride (NaLnF₄) microcrystals, including NaYF₄, NaYbF₄, and NaLuF₄ material systems. The single crystalline nature of the as‐synthesized products makes them strong upconversion emission. The freedom of combining a lanthanide activator (Er³⁺ or Tm³⁺) with a sensitizer (Yb³⁺) at various doping concentrations readily gives access to color multiplexing at the single‐particle level. Our kinetic and thermodynamic investigations on the epitaxial growth of core–shell microcrystals using NaLnF₄ particle seeds suggest that within a certain size regime it is plausible to exert precise control over shell thickness and growth orientation under hydrothermal conditions.     

High-pressure Raman scattering on Fe2(MoO4)3 microcrystals obtained by a hydrothermal method

This study reports on the effect of high hydrostatic pressure on the vibrational spectra of Fe₂(MoO₄)₃ microcrystals using Raman scattering in combination with a membrane diamond-anvil cell. The ferric molybdate was obtained by the conventional hydrothermal method, and the structural and morphological properties of the sample were characterized using additionally X-ray diffraction, scanning electron microscopy, as well as energy dispersive spectroscopy. The X-ray diffraction measurements have shown that the crystals have a monoclinic structure. At pressures higher than 4.8 GPa, the disappearance of external modes was observed, suggesting that pressure has induced a breakdown in the translational symmetry of the crystal system. The high-pressure amorphous phase is reversible and attributed to an incomplete crystal-amorphous transformation.     

Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

The development of technologically viable electrodes for the electrochemical oxygen evolution reaction (OER) is a major bottleneck in chemical energy conversion. This article describes a facile one‐step hydrothermal route to deposit microcrystals of a robust Dexter–Silverton polyoxometalate oxygen evolution catalyst, [Co_6.8Ni_1.2W₁₂O₄₂(OH)₄(H₂O)₈], on a commercial nickel foam electrode. The electrode shows efficient and sustained electrochemical oxygen evolution at low overpotentials (360 mV at 10 mA cm⁻² against RHE, Tafel slope 126 mV dec⁻¹, faradaic efficiency (96±5) %) in alkaline aqueous solution (pH 13). Post‐catalytic analyses show no mechanical or chemical degradation and no physical detachment of the microcrystals. The results provide a blueprint for the stable “wiring” of POM catalysts to commercial metal foam substrates, thus giving access to technologically relevant composite OER electrodes.     

Preparation of Gold Microcrystal-Doped TiO2, ZrO2 and Al2O3 Films Through Sol-Gel Process

Au-microcrystal-doped TiO₂, ZrO₂ and Al₂O₃ films were made by sol-gel dip-coating method using titanium, zirconium and aluminum alkoxides with HAuCl₄ · 4H₂O. The influence of the oxide matrix composition on the maximum amount of the Au microcrystals that can be incorporated in the oxide film was examined. Some amount of Au microcrystals were exhausted to the surface of Au microcrystal-doped oxide films when an excess amount of HAuCl₄ · 4H₂O was dissolved in the coating solution. The maximum amount of Au that can be incorporated in the oxide film was found to increase with the increase of the pH point at zero charge (PZC) of the matrix oxide. This should be due to the fact that AuCl ₄ ^- ions are charged negative and also Au microcrystals tend to charge negative, so that the oxide gel with high PZC, which has a tendency to charge positive, may fix the ions and/or microcrystals to its interior. A maximum amount of Au microcrystals as high as 12.6 vol% was attained in an Au:Al₂O₃ film.     

Aqueous mineralization process to synthesize uniform shuttle-like BaMoO4 microcrystals at room temperature

Single-crystalline BaMoO₄ microcrystals with uniform shuttle-like morphology have been successfully prepared via a facile aqueous solution mineralization process at room temperature. It was found that the pH value and the reaction temperature had important influences on the formation of the BaMoO₄ microcrystals. The shuttle-like microcrystals can be obtained in alkaline aqueous solution (pH=9-14), and when the pH value was adjusted to 6-7, cocoon-like microcrystals appeared. A possible two-stage growth process has been proposed, and the Ostwald ripening was responsible for the formation of the shuttle-like BaMoO₄ microcrystals. The products were characterized by XRD, XPS, FESEM, HRTEM and Raman spectroscopy. Room-temperature photoluminescence indicated that the as-prepared BaMoO₄ microcrystals had a strong blue emission peak centered at 438 nm.     

Electron microscopy of V2O5 microcrystals in the V2O5-NH3-H2O colloid system

Summary The formation of V₂O₅ fibrous microcrystals in the V₂O₅-NH₃-H₂O system has been investigated by electron microscopy. The morphology of these microcrystals is dependent on the concentration of the particular components in the colloidal system and on the time of aging. In some colloid systems the orientation of V₂O₅ fibrous crystals with their long axes parallel to one another is also possible. The microcrystal growth in these systems can be attributed to very effective conditions for the recrystallization of vanadium pentoxide crystals in equilibrium with ammonium vanadate in solution.With 3 figures     

Carrier dynamics in CsPbI3 perovskite microcrystals synthesized in solution phase

Carrier diffusion and recombination kinetics in all-inorganic CsPbI₃ perovskite microcrystals directly synthesized in solution phase are reported.     

Solvothermal synthesis and photoluminescence properties of BiPO4 nano-cocoons and nanorods with different phases

Hexagonal phase BiPO₄ nano-cocoons and monoclinic phase BiPO₄ nanorods have been synthesized in the mixed solvents of glycerol and distilled water with the volume ratio of 2:1 at 200 °C. The solvothermal evolution process from hexagonal phase BiPO₄ nano-cocoons to monoclinic phase BiPO₄ nanorods was observed by varying the reaction time from 1 to 3 h. In the hydrothermal condition at 160 °C, the similar phase transformation from hexagonal phase BiPO₄ to monoclinic phase BiPO₄ was also observed, accompanying with a morphology transformation from nanorods to octahedron-like microcrystals. It was found that the volume ratio of glycerol to water in the solvothermal condition had a great impact on the shapes of products, while it had no influence on the formation of different phases. The fluorescence spectra of hexagonal phase BiPO₄ nano-cocoons and monoclinic phase BiPO₄ nanorods were also studied.     

Fe3O4八面体微晶的水热法制备与表征

在乙二醇与水( ＝5∶8)的混合溶剂中, 通过K₄[Fe(CN)₆]与NaOH在200 ℃水热反应12 h, 制备了Fe₃O₄的八面体. 采用X射线衍射仪、扫描电镜和透射电子显微镜对产物进行表征, 并在室温下测试了它的磁学性能, 结果表明, Fe₃O₄八面体为单晶面心立方相结构, 尺寸约为0.7～6.3 μm. 它的矫顽力(H_c)为77.5 Oe, 饱和磁化强度(M_s)为98.53 emu/g, 剩余磁化强度(M_r)为6.27 emu/g. 研究了乙二醇, NaOH的浓度, 反应温度和时间对产物形貌的影响, 结果表明乙二醇在Fe₃O₄八面体的形成过程中起着关键作用, 并提出了可能的生长机理.     

NH<Subscript>4</Subscript>V<Subscript>3</Subscript>O<Subscript>7</Subscript>: Synthesis,morphology, and optical properties

The effect of the method used for the synthesis of NH₄V₃O₇ on its morphology, textural parameters, and optical properties was studied. Ammonium vanadate NH₄V₃O₇ was prepared by treating NH₄VO₃ in the presence of citric acid under hydrothermal (4.0 ≤ pH ≤ 5.5, T = 180–200°C, 48 h) and microwave–hydrothermal (3.5 ≤ pH ≤ 5.0, T = 180–220°C, 20 min) conditions. Self-assembled NH₄V₃O₇ microcrystals crystallizing in monoclinic system with unit cell parameters a = 12.247(5) Å, b = 3.4233(1) Å, c = 13.899(4) Å, β = 89.72(3)°, and V = 582.3(4) ų (space group P2₁) were shown to be formed independently of the method used to treat the reaction mixture. The morphology of NH₄V₃O₇ particles was shown to depend on рН of the reaction mass and the method of synthesis. The structural features of NH₄V₃O₇ were studied by IR, UV, and Vis spectroscopy, and the optical bandgap was determined.     

Morphology Engineering of Fullerene[C70] Microcrystals: From Perfect Cubes,Defective Hoppers to Novel Cruciform-Pillars

Controlled crystallization of fullerene molecules into ordered molecular assemblies is important for their applications. However, the morphology engineering of fullerene[C₇₀] assemblies is challenging, and complicated architectures have rarely been reported due to the low molecular symmetry of C₇₀ molecules, which makes their crystallization difficult to control and the low production yield as well. Herein, with the assistance of solvent intercalation, a general reprecipitation approach is reported to prepare morphologically controllable C₇₀ microcrystals with mesitylene as a good solvent and n-propanol as a poor solvent in one solvent system without replacing specific solvents. A series of C₇₀ microcrystals with high uniformity from perfect cubes and defective hoppers to novel cruciform-pillars are obtained by intentionally tuning C₇₀ concentration and the volume ratio of mesitylene to n-propanol. Among them, novel cruciform-pillar-shaped microcrystals are obtained for the first time by further decreasing the amount of mesitylene in the solvent-intercalated microcrystals. Notably, the C₇₀ concentration is a key parameter for the selective growth of C₇₀ hopper, rather than the volume ratio of mesitylene to n-propanol. Interestingly, the hopper-shaped microcrystals exhibit excellent photoluminescence properties relative to those of cubes and cruciform-pillars owing to the enhanced light absorption, proving their potential applications in optoelectronic devices. This study offers new insights into the morphology-controlled synthesis of other micro/nanostructured organic microcrystals and the fine tuning of photoluminescence properties of organic crystals.     

Selected-control solution-phase route to multiple-dendritic and cuboidal structures of PbSe

Well-crystalline PbSe multiple-dendritic hierarchical structures have been prepared through a facile hydrothermal process in an alkaline glycerol/water solution system using SeO₂ as selenium source and hydrous hydrazine as reducing agent at 160 °C for 12 h. The obtained products were characterized by X-ray powder diffraction, field emission scanning electron microscopy and transmission electron microscopy, which showed that the obtained products were face-centered cubic PbSe multiple-dendritic superstructures with length of each dendrite ranging from 1.0 to 1.5 μm. Additionally, cuboidal PbSe microcrystals with different concave faces can be obtained through a similar process except for using Se powders instead of SeO₂ as selenium source and without hydrous hydrazine. The edge lengths of these cuboidal microcrystals range from 1.0 to 2.5 μm observed by field emission scanning electron microscopy. The influencing factors for the formation of the two kinds of PbSe microstructures were discussed and the possible growth mechanisms were proposed from the point of crystallographic and kinetic views. The studies on the corresponding photoluminescence (PL) properties of the two kinds of PbSe structures are also carried out.     

Raman studies of semiconductor alloy microcrystals prepared by rf co-sputtering

A rf co-sputtering technique was applied to prepare CdS_xSe_1–x and Si_xGe_1–x alloy microcrystals embedded in SiO₂ matrices. Raman spectra of the samples clearly demonstrated the growth of the alloy microcrystals. Our novel sputtering arrangement allows us to obtain alloy microcrystals with the composition varying continuously on a single substrate.     

Phonon properties of nanosized MnWO4 with different size and morphology

Highly hierarchical barlike and flowerlike MnWO₄ microcrystals have been synthesized for the first time by a hydrothermal method, where ethanolamine (EA) and cetyltrimethylamonnium bromide (CTAB) play important roles in directing growth and self-assembly of these structures. The possible formation process has been proposed. In addition, platelike nanosized MnWO₄ was also synthesized by annealing of a precursor obtained by coprecipitation method. The obtained samples were characterized by XRD, SEM, TEM, Raman and IR methods. Raman spectra showed relatively weak dependence on particle size and morphology of the particles. In contrast to this behavior, IR-active bands showed pronounced shifts and changes in relative intensities on particle size and the morphology. Origin of this behavior is discussed.     

Inorganic ion exchange membranes consisting of microcrystals of zirconium phosphate supported by Kynar®

Membranes consisting of insoluble acid salts of tetravalent metals are attractive for their potential use in some technological processes where organic ion exchange membranes cannot be employed because of their degradability under drastic conditions (e.g. high temperature, high doses of ionizing radiation, high concentration of oxidizing agents, etc.). p]A brief survey of crystalline insoluble acid salts of tetravalent metals and membranes consisting of these compounds is presented, and Zr(HPO₄)₂ · H₂O— Kynar® membranes are examined in detail. Although the ratio of surface protons to internal protons is small (～10^?3), the mobility of the protons in the surface of microcrystals is much higher than that of internal protons (≥ 10⁴ times), so that most of the electric transport occurs at the surface. Thus, these heterogeneous membranes behave as homogeneous porous membranes, the pores being the free spaces between adjacent flat microcrystals of Zr(HPO₄)₂ · H₂O. For this reason the concentration potential depends essentially on the nature of the counterions present in the surface. This was confirmed by preparing membranes with microcrystals of Zr(HPO₄)₂ · H₂O whose surface protons were partially or totally replaced by Cs⁺ions. An equation has been derived which fits the experimental data and permits a calculation of the counterion composition at the surface of the microcrystals from measurements of membrane potential. Some possibilities for enhancing the internal transport are discussed.     

Photochromic Coatings Containing Ag(Cl1−xBrx) Microcrystals

Photochromic ormosil coatings containing Ag(Cl_1–x Br _x ) microcrystals were formed on a glass substrate via the sol-gel process. Methyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane were used as starting materials of the ormosil matrices. 3-chloropropyltrimethoxysilane and bromophenyltrimethoxysilane were added as halogen sources and silver colloidal dispersion was introduced into the precursor sol. The coated glass became transparent and photosensitive after Ag(Cl_1–x Br _x ) microcrystals were precipitated in the coatings above 300°C. Insertion of a SiO₂ buffer layer between the substrate and photochromic layer was effective in preventing Ag⁺ migration into the substrate. Photochromic performances were improved by the substitution of Cl with Br and the incorporation of a minute amount of Cu.     

Temperature-dependent six-photon upconversion fluorescence of Er

Yb³⁺/Er³⁺ codoped β-NaYF₄ microcrystals were synthesized through a facile EDTA-assisted hydrothermal method. Under 980 nm excitation, 244, 256, and 276 nm upconversion (UC) emissions were observed in NaYF₄:Yb³⁺/Er³⁺ microcrystals, which were assigned to the ²I_11/2 → ⁴I_15/2, ⁴D_7/2 → ⁴I_15/2, and ⁴G_9/2 → ⁴I_15/2 transitions of Er³⁺ ions, respectively. Successive energy transfers (ETs) from Yb³⁺ to Er³⁺ played crucial roles in populating the high-energy states of Er³⁺ ions. Power dependence analysis exhibited that 244 and 256 nm UC emissions came from six-photon processes. Temperature-dependent UC emissions of ⁴D_7/2 → ⁴I_15/2 and ²I_11/2 → ⁴I_15/2 transitions of Er³⁺ were discussed and the nonradiative relaxation (NR) process of ²I_11/2 → ⁴D_7/2 was confirmed.