Morphology evolution from thin-hexapod to aggregated sphere of Cu2O microcrystals

A range of morphologies of Cu₂O microcrystals, such as thin-hexapod, thick-hexapod, truncated hexapod, truncated octahedron, cuboctahedron, and aggregated sphere were prepared by the reduction reaction from the mixed solution of CuCl₂, NaOH, glucose, and poly(ethylene) glycol. Monodispersed and well-crystallized Cu₂O microcrystals were prepared for only a few minutes using a conventional microwave oven. The amount of glucose and the microwave irradiation time play important roles in controlling the morphology of the Cu₂O microcrystals. The morphology of the Cu₂O microcrystals was changed from thin-hexapod to aggregated sphere by the glucose concentration. The morphology of Cu₂O microcrystals was changed from thick-hexapod to octahedron by increasing the microwave irradiation time. The crystal growth mechanism and morphology evolution of Cu₂O microcrystals are discussed.     

Self-assembled Cu2O flowerlike architecture: Polyol synthesis, photocatalytic activity and stability under simulated solar light

Self-assembled Cu₂O flowerlike architecture has been synthesized by polyol process with the presence of acetamide. The synthesized flowerlike architecture is composed of the petals assembled by small crystalline with size of 5-6 nm. The growth mechanism is proposed that the dissolution of the small particles in microsphere center and then the recrystallization on the surface of the microspheres with the increase of reaction time results in the formation of the final flowerlike architecture. The novel architecture shows a blue shift of absorption edge compared to Cu₂O nanocubes and good photocatalytic activity for the degradation of dye brilliant red X-3B under simulated solar light. Moreover, the flowerlike architecture is more stable than Cu₂O nanocubes during photocatalytic process since the photocatalytic activity of the second reused architecture sample is still twice as high as that of the original nanocubes. The Cu₂O flowerlike architecture may be a good photocatalyst candidate for wastewater treatment.     

Controllable synthesis of self-assembled Cu2S nanostructures through a template-free polyol process for the degradation of organic pollutant under visible light

Cu₂S nanostructures were fabricated by polyol method and then characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. The morphologically different Cu₂S nanostructures such as vertically nanorod arrays, nanoflowers assembled by nanorod arrays, nanoparticles and nanowires, can be successfully synthesized under different experimental conditions. The growth mechanism for the different nanostructures is proposed. The photocatalytic activity of the prepared samples was evaluated based on the degradation of organic pollutant, active brilliant red X-3B (X-3B), under visible light. Among the Cu₂S nanostructures, self-assembled nanoflowers have the highest photocatalytic activity. In addition, the prepared Cu₂S nanostructures are found to be able to decolorize X-3B with iron ions for the formation of Fenton reagent. This study provides a more choice to prepare self-assembled nanostructures for the application of environmental pollution control.     

Hydrothermal synthesis and characterization of TiO2 nanorod arrays on glass substrates

Large-scale, well-aligned single crystalline TiO₂ nanorod arrays were prepared on the pre-treated glass substrate by a hydrothermal approach. The as-prepared TiO₂ nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. X-ray diffraction results show that the main phase of TiO₂ is rutile. Scanning electron microscopy and transmission electron microscopy results demonstrate that the large-scale TiO₂ nanorod arrays grown on the pre-treated glass substrate are well-aligned single crystal and grow along [0 0 1] direction. The average diameter and length of the nanorods are approximately 21 and 400 nm, respectively. The photocatalytic activity of TiO₂ nanorod arrays was investigated by measuring the photodegradation rate of methyl blue aqueous solution under UV irradiation (254 nm). And the results indicate that TiO₂ nanorod arrays exhibit relatively higher photocatalytic activity.     

Facile fabrication of p–n heterojunctions for Cu2O submicroparticles deposited on anatase TiO2 nanobelts

In this paper, Cu₂O particle-deposited TiO₂ nanobelts with p–n semiconductor heterojunction structure were successfully prepared via a two-step preparation process to investigate electron-transfer performance between p-type Cu₂O and n-type TiO₂. Various measurement results confirm that the amount of pure Cu₂O submicroparticles, with diameters within the range of 200–400 nm and deposited on the surface of TiO₂ nanobelts, can be controlled, and that the purity of Cu₂O is heavily affected by reaction time. Visible-light photodegradation activities of Rhodamine B show that photocatalysts have little or no photocatalytic activities mainly due to their p–n heterojunction structure, indicating that there hardly appears any electron-transfer from Cu₂O to TiO₂.     

Synthesis and formation mechanism of Cu3V2O7(OH)2·2H2O nanowires

Cu₃V₂O₇(OH)₂·2H₂O nanowires have been synthesized in high yield through a simple and facile low-temperature hydrothermal approach without any template or surfactants. XRD, TG, FE-SEM, TEM and HRTEM were used to characterize the product. The results indicated that the product consisted of wirelike crystals about 80 nm in diameter and length up to several micrometers. The formation of wirelike structure of Cu₃V₂O₇(OH)₂·2H₂O depended crucially on the reaction time and pH value of the precursor suspensions. The optical absorption spectrum indicates that the Cu₃V₂O₇(OH)₂·2H₂O nanowires have a direct band gap of 1.94 eV.     

Facile synthesis of mesoporous core-shell TiO2 nanostructures from TiCl3

The present study reports the synthesis and formation process of mesoporous core-shell TiO₂ nanostructures by employing a glucose-assisted solvothermal process using water-ethanol mixture as solvent and subsequent calcination process at 550 °C for 4 h. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption analysis were used to investigate the structural properties of these nanostructures. By optimizing the preparation conditions, especially the contents of water and ethanol in the mixture solvent, mesoporous core-shell TiO₂ nanostructures were obtained. These mesoporous nanostructures have anatase phase and exhibit the superior photocatalytic activity. This synthesis route is facile due to the usage of stable and low-cost Ti precursor such as TiCl₃ and is thus applicable for large-scale production.     

Quasi-cube ZnFe2O4 nanocrystals: Hydrothermal synthesis and photocatalytic activity with TiO2 (Degussa P25) as nanocomposite

The fabrication and photocatalytic application of zinc ferrite nanocrystals were reported. Quasi-cube ZnFe₂O₄ nanocrystals with typical small sizes of 5-15 nm were successfully synthesized by a facile hydrothermal approach. ZnFe₂O₄/P25 nanocomposite was prepared by physically grinding the ZnFe₂O₄ nanocrystals with TiO₂ (commercial Degussa P25) at ambient temperature, and it exhibited excellent photocatalytic activity for the mineralization of Rhodamine B. UV-vis measurement and photocatalytic test results showed that ZnFe₂O₄ nanocrystals exhibited effective band-gap coupling to P25 nanopowders by simply physical grinding without any surface modification or high-energy balling, which is usually adopted in conventional mixture process. This phenomenon can be attributed to the high surface activities of the as-obtained tiny ZnFe₂O₄ nanocrystals and commercial P25 nanoparticles. It may imply that the mixing process of composite materials would be simplified by further lowering the grain sizes of their component particles.     

Hydrothermal transformation of titanate nanotubes into single-crystalline TiO2 nanomaterials with controlled phase composition and morphology

Single-crystalline TiO₂ nanomaterials were synthesized by hydrothermally treating suspensions of H-titanate nanotubes and characterized by XRD, TEM, and HRTEM. The effects of the pH values of the suspensions and the hydrothermal temperatures on the phase composition and morphology of the obtained TiO₂ nanomaterials were systematically investigated. The H-titanate nanotubes were predominately transformed into anatase nanoparticle with rhombic shape when the pH value was greater than or equal to 1.0, whereas primarily turned into rutile nanorod with two pyramidal ends at the pH value less than or equal to 0.5. We propose a possible mechanism for hydrothermal transformation of H-titanate nanotubes into single-crystalline TiO₂ nanomaterials. While the H-titanate nanotubes transform into tiny anatase nanocrystallites of ca. 3 nm in size, the formed nanocrystallites as an intermediate grow into the TiO₂ nanomaterials with controlled phase composition and morphology. This growth process involves the steps of protonation, oriented attachment, and Ostwald ripening.     

Processing and photocatalytic properties of Cu-grafted TiO2 powder from acid treated BaTiO3

The respective influences of calcination, drying methods, and washing conditions on the morphologies, surface properties, and photocatalytic activities of TiO₂ powders prepared from acid treatments of BaTiO₃ were investigated. Rutile powder was obtained using the treatment under strong acid conditions. It possesses a bundle-like shape and comprises rutile nanorods. After calcination, characteristic voids were observed in the particles. Anatase powder was obtained by adjusting pH values of a BaTiO₃ suspension to 2.5-3. Drying at 110 °C engendered the formation of spheroidal anatase, although freeze-dried anatase particles assembled into a flake-like shape. The freeze-dried samples show lower crystallinity. With grafting Cu ions, rutile exhibited better photocatalytic performance for the decomposition of gaseous 2-propanol (IPA) under visible light, although it did not work effectively for anatase.     

Co-electrospinning fabrication and photocatalytic performance of TiO2/SiO2 core/sheath nanofibers with tunable sheath thickness

In this paper, core/sheath TiO₂/SiO₂ nanofibers with tunable sheath thickness were directly fabricated via a facile co-electrospinning technique with subsequent calcination at 500 °C. The morphologies and structures of core/sheath TiO₂/SiO₂ nanofibers were characterized by TGA, FESEM, TEM, FTIR, XPS and BET. It was found that the 1D core/sheath nanofibers are made up of anatase–rutile TiO₂ core and amorphous SiO₂ sheath. The influences of SiO₂ sheath and its thickness on the photoreactivity were evaluated by observing photo-degradation of methylene blue aqueous solution under the irradiation of UV light. Compared with pure TiO₂ nanofibers, the core/sheath TiO₂/SiO₂ nanofibers performed a better catalytic performance. That was attributed to not only efficient separation of hole–electron pairs resulting from the formation of heterojunction but also larger surface area and surface silanol group which will be useful to provide higher capacity for oxygen adsorption to generate more hydroxyl radicals. And the optimized core/sheath TiO₂/SiO₂ nanofibers with a sheath thickness of 37 nm exhibited the best photocatalytic performance.     

CuO-CeO2 binary oxide nanoplates: Synthesis, characterization, and catalytic performance for benzene oxidation

This work reports the first synthesis of CuO-CeO₂ binary oxides with a plate-like morphology by a solvothermal method. The as-prepared CuO-CeO₂ nanoplates calcined at 400 °C were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectrum, and tested for catalytic oxidation of dilute benzene in air. Various structural characterizations showed that large amounts of copper species were exposed on the CuO-CeO₂ nanoplate surface. The effect of the synthesis conditions on the structure of the product, as well as the growth process of the nanoplates, has been studied and discussed. The CuO-CeO₂ nanoplates exhibited an excellent catalytic activity for benzene oxidation despite its relatively low surface area and could catalyze the complete oxidation of benzene at a temperature as low as 240 °C.     

Soft chemistry synthesis and crystal structure of MgxCu3−xV2O6(OH)4·2H2O

Mg_xCu_3−xV₂O₆(OH)₄·2H₂O (x ∼ 1), with similar crystal structure as volborthite Cu₃V₂O₇(OH)₂·2H₂O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V₂O₅ with few mL of 30 vol.% H₂O₂ followed by addition of distilled water). When ammonium hydroxide NH₄OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO₄ to trigonal bipyramidal VO₅, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu₃V₂O₈ phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu₃V₂O₈ phases.     

Deposition-precipitation with Urea to prepare Au/Mg(OH)2 catalysts: Influence of the preparation conditions on metal size and load

Deposition-precipitation with Urea method to prepare Au/Mg(OH)₂ was investigated. The preparation was carried out at 80 °C using an aqueous solution of HAuCl₄ and Urea in presence of MgO as support precursor. The pH of the solution was 9.5-10 owing to the rapid hydration of MgO to Mg(OH)₂. The influence of the preparation conditions (Urea concentration, preparation procedure, addition of magnesium citrate) on the gold load and particle size distribution was evaluated. The structural characterization of preparations was carried out by means of X-ray diffractometry and transmission electron microscopy. Among the parameters investigated, the preparation procedure, that is the control of the interaction between gold species and the support, is the main step for the deposition of the highest amount of gold (> 80% of the theoretical amount) having small size and a narrow distribution (d = 4.1 nm, σ = ±1.1 nm). The synthesized catalysts were tested in the CO oxidation reaction.     

Synthesis of Cu2O nanoboxes, nanocubes and nanospheres by polyol process and their adsorption characteristic

Nanoboxes, nanocubes and nanospheres of cuprous oxides were readily synthesized by reducing Cu(CH₃COO)₂·H₂O with ethylene glycol at different concentrations of poly(vinyl pyrrolidone); the formation mechanism of as-synthesized Cu₂O nanostructures was investigated. Moreover, we report the highly selective adsorption characteristic of as-synthesized Cu₂O nanostructures to anionic dyes and suggest the mechanism is electrostatic adsorption.     

New compounds Cu2MnTi3S8 and Cu2NiTi3S8 with thiospinel structure

Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈ compounds were prepared by high-temperature synthesis. The crystal structure of these quaternary phases was investigated by X-ray powder diffraction. The compounds are described in the thiospinel structure (space group ) with the lattice constants a = 1.00353(1) nm (Cu₂MnTi₃S₈) and a = 0.99716(1) nm (Cu₂NiTi₃S₈). The atomic parameters were calculated in anisotropic approximation (R_I = 0.0456 and R_I = 0.0520 for Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈, respectively).     

Synthesis of shape-controlled Nb3O7F/NbB2 heterostructure: A new idea to synthesize binary hybrid materials by incomplete reaction

Niobium oxide fluoride/niobium diboride (Nb₃O₇F/NbB₂) heterostructures with urchin-like and nanowall-like morphologies were synthesized by a facile hydrothermal approach. The high-density one-dimensional Nb₃O₇F nanoneedle arrays and two-dimensional Nb₃O₇F nanosheets stand on the surface of NbB₂ cores. Here a new idea is proposed to synthesize binary heterostructure by in situ “incomplete reaction”. Ultraviolet-visible spectra showed that such heterostructure has a wide absorption peak at around 270 nm and the absorption edge of the products synthesized at higher temperature shifts to longer wavelength because of stronger nanometric effect.     

A low-temperature process to synthesize rutile phase TiO2 and mixed phase TiO2 composites

This works employed K₂Ti₄O₉, a novel Ti source, to prepare TiO₂ powders. By a “low-temperature dissolution-reprecipitation process” (LTDRP), rutile phase TiO₂ was successfully synthesized after reacting at 50 °C for 48 h. The obtained sample showed a specific surface area about 45 m²/g, and excellent activity in photo-destruction of NO_x gas. The coupling of rutile phase TiO₂ with commercial anatase TiO₂ showed significant effect in further enhancing the photocatalytic activity.     

One step synthesis of Bi@Bi2O3@carboxylate-rich carbon spheres with enhanced photocatalytic performance

Bi@Bi₂O₃@carboxylate-rich carbon core-shell nanosturctures (Bi@Bi₂O₃@CRCSs) have been synthesized via a one-step method. The core–shell nanosturctures of the as-prepared samples were confirmed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Raman spectroscopy. The formation of Bi@Bi₂O₃@CRCSs core–shell nanosturctures should attribute to the synergetic roles of different functional groups of sodium gluconate. Bi@Bi₂O₃@CRCSs exhibits significant enhanced photocatalytic activity under visible light irradiation (λ > 420 nm) and shows an O₂-dependent feature. According to trapping experiments of radicals and holes, hydroxyl radicals were not the main active oxidative species in the photocatalytic degradation of MB, but O₂⁻ are the main active oxidative species.     

Control over the morphology and structure of manganese oxide by tuning reaction conditions and catalytic performance for formaldehyde oxidation

Flower-like manganese oxide nanospheres as assembled by layered MnO₂ sheets have been successfully fabricated via a facile route using a hydrothermal treatment at 120 °C for 12 h. XRD, FE-SEM, TEM and BET were used to investigate the crystalline structure, morphology, specific surface area, and porosity of the products. The products have a BET surface area of ca. 94.6 m²/g. Effects of preparation conditions including hydrothermal temperature, reaction time, pH value and kinds of anion were investigated on the morphology, structure and crystalline phase. It was found that control over the morphology and structure of product can be achieved by tuning reaction conditions. On the basis of experimental results, the formation mechanism of the products was investigated and discussed. The manganese oxide nanomaterials showed high catalytic activities for oxidative decomposition of formaldehyde. The crystallographic structure of the products had great influence on the catalytic performance in formaldehyde oxidation. Thereinto, the catalytic activity of the cryptomelane-type MnO₂ was higher than other crystalline manganese oxides below 120 °C.