Photocatalytic decomposition of methylene blue on nanocrystalline titania prepared by different methods

Nanocrystalline particles of pure anatase titania were prepared by two different methods. One is the sol-gel method at ambient temperature using ultrasonication (TiO₂-SG-US) and conventional stirring method (TiO₂-SG-S) and the other by surfactant assisted hydrothermal synthesis (TiO₂-HT). More uniform distribution/dispersion of the nanoparticles (SEM), marginally higher surface area, better thermal stability and phase purity are some of the advantages of preparation of nanocrystalline titania by sol gel ultrasonication method and hydrothermal synthesis method. The behavior of anatase titania in photocatalytic decomposition of methylene blue in aqueous medium was studied as a function of the method of preparation and the crystallite size. The nanoparticles prepared by ultrasonication method were more effective than both, the sample prepared by conventional stirring method and commercial Degussa P-25. The higher photocatalytic activity of TiO₂-SG-US is attributed to the more uniform size of the particles as compared to TiO₂-SG-S samples. Both TEM and XRD data on TiO₂-HT samples reveal a uniform and nanocrystalline TiO₂ particles, which showed photocatalytic activity in both UV and visible region although brookite phase was also present.     

Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Nanostructured zinc oxide films synthesized by successive chemical solution deposition for gas sensor applications

Nanostructured ZnO thin films have been deposited using a successive chemical solution deposition method. The structural, morphological, electrical and sensing properties of the films were studied for different concentrations of Al-dopant and were analyzed as a function of rapid photothermal processing temperatures. The films were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron and micro-Raman spectroscopy. Electrical and gas sensitivity measurements were conducted as well. The average grain size is 240 and 224 Å for undoped ZnO and Al-doped ZnO films, respectively. We demonstrate that rapid photothermal processing is an efficient method for improving the quality of nanostructured ZnO films. Nanostructured ZnO films doped with Al showed a higher sensitivity to carbon dioxide than undoped ZnO films. The correlations between material compositions, microstructures of the films and the properties of the gas sensors are discussed.     

Porous manganese oxide synthesized through organic-electrolyte templates and their catalytic applications

We report a facile approach to the preparation of porous manganese oxide materials by the organic-electrolyte templates based on strategy. The final products are thoroughly characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and Brunauer–Emmett–Teller (BET) techniques. The results reveal that porosity (pore size and distribution, surface area) of these manganese oxides has strong relationship with the templates used, which implies a simple way to obtain a series of porous materials. By comparing the catalytic effects of these manganese oxides in oxidation of indene and benzyl alcohol, we find that the pore size and distribution are also crucial to the catalytic properties of these porous materials.     

Growth and photocatalytic properties of one-dimensional ZnO nanostructures prepared by thermal evaporation

Aligned ZnO nanorods and nanotubes were grown on the silicon substrates by thermal evaporation of high pure zinc powders without any other metal catalyst. The morphology evolution of ZnO nanostructures with prolonged growth time suggested that the growth of the ZnO nanorods and nanotubes follows the vapor–liquid–solid mechanism. ZnO nanoneedle and nanoparticle films were also synthesized by the same way, and their photocatalytic performances were tested for the degradation of organic dye methylene blue. The ZnO nanoneedle films exhibited very high photocatalytic activities. The decomposition kinetics of the organic pollutant was discussed. Moreover, it is found that the ZnO nanoneedle films showed very stable photocatalytic activity.     

A simple template method for hierarchical dendrites of silver nanorods and their applications in catalysis

A novel strategy has been put forward to prepare hierarchical dendrites of silver nanorods via a simple integration method using “Devarda's template” as a reducing agent and architecture template with the assistance of ultrasonic waves, in which the template was firstly fabricated and employed. The individual silver dendrite is composed of a long central trunk with secondary branches, which preferentially grew in a parallel direction with a definite angle to the trunk. The results reveal that the dendrites are single crystalline in nature and interestingly prove that the silver single crystal has the preferential orientation in 〈1 1 1〉 direction in normal conditions. The contrast experiments demonstrated that both “Devarda's template” and the ultrasonic irradiation are necessary for building hierarchically silver dendrites in a water system. Moreover, the experimental results show that the dendrites of silver nanorods are the superior electrode materials for the electrochemical sensors to detect directly NO₂⁻ in aqueous solution.     

Upconversion in Er-doped Gd2O3 nanocrystals prepared by propellant synthesis and flame spray pyrolysis

In this study, monoclinic luminescent Gd₂O₃ nanocrystals doped with different concentrations of Er³⁺ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions was observed with increasing Er³⁺ concentration in the Gd₂O₃ nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er³⁺ concentration was increased, the intensity of the red (⁴F_9/2 → ⁴I_15/2) emission was observed to increase more rapidly in comparison to the green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP.     

Preparation of monodispersed cobalt-boron spherical nanoparticles and their behavior during the catalytic decomposition of hydrous hydrazine

Monodispersed cobalt-boron spherical nanoparticles have been prepared through solution plasma processing in the presence of hexadecyltrimethyl ammonium bromide for the first time. The particle size of cobalt-boron can be adjusted by changing either the plasma time or the concentration of hexadecyltrimethyl ammonium bromide. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. During the decomposition of hydrous hydrazine, the obtained monodispersed cobalt-boron spherical nanoparticles exhibit higher catalytic activity and hydrogen selectivity than regular cobalt-boron prepared by direct reduction of Co²⁺ with BH₄⁻. The experimental investigations indicate that hydrous hydrazine along with the monodispersed cobalt-boron spherical nanoparticles may find application in small-scale on-board hydrogen storage and supply.     

The catalytic behavior of zinc oxide prepared from various precursors and by different methods

Samples of zinc oxide were obtained by thermal decomposition of zinc salts (acetate and nitrate) and by precipitation (chloride and nitrate). The samples were characterized by S_BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM). XRD showed that ZnO crystals exhibited similar morphologies, while the crystal size and the particles morphology, availed by SEM, are dependent on the preparation method and the precursor salt utilized. The catalytic properties were evaluated to sec-butyl alcohol (SBA) reaction, using nitrogen, hydrogen and synthetic air as carrier gas. The catalytic properties of ZnO surface are strongly dependent on crystal size, atmosphere of reaction and zinc salts precursor. The activity to dehydrogenation of SBA in oxidant atmosphere is strongly sensitive to crystal size, while the selectivity to methyl ethyl ketone (MEK) is slightly sensitive. The activity to dehydrogenation and dehydration of SBA increases with change of atmosphere reaction from oxidant to reducing. High reaction temperatures and reducing environment for ZnO sample with small crystal size decrease significantly the selectivity to MEK. The ZnO crystal size has an important role to establish the properties of partial reduction of ZnO and catalytic properties.     

Preparation of Sm-doped ceria (SDC) nanowires and tubes by gas–liquid co-precipitation at room temperature

Sm-doped cerium dioxide (SDC) with fcc structure was formed using a gas–liquid chemical co-precipitation process at room temperature. Morphology and structure of the as-prepared samples were characterized using TG, XRD, TEM, HRTEM and SAED techniques. Under our specific experimental conditions, two kinds of 1D nano-structures SDC have been mainly obtained. SDC nanowires are 0.3–1.2 μm in lengths and 5–20 nm in diameters. SDC nanotubes have outer diameters in 10–40 nm with lengths up to 2 μm. The as-prepared SDC shows very strong UV absorption ability and the maximum absorption peak redshifts compared with that of SDC nanoparticles.     

Synthesis by an ionic liquid-assisted method and optical properties of nanoflower Y2O3

Flower-like Y₂O₃ nano-/microstructured phosphors without metal activators have successfully been fabricated by an ionic liquid (IL)-assisted method involving temperature (600 °C) annealing. In this paper, the effect of IL concentration on the morphology of the product has been investigated. The IL plays a crucial role in the formation of various morphologies of Y₂O₃. The structural and morphological features of the obtained samples have been characterized by means of X-ray powder diffraction (XRD) analysis, photoluminescence spectra (PL), Fourier-transform infrared (FT-IR) spectra and X-ray photoelectron spectra (XPS). The photoluminescence spectra of the products exhibit an intense bluish-white emission (ranging from 405 to 430 nm and centered at 418 nm). The luminescent mechanisms have been ascribed to the carbon impurities in the Y₂O₃ host. The effect of the ILs cation and the counter anions on the Y₂O₃ morphology of these nanostructures was studied experimentally. It was observed that Y₂O₃ morphology and PL of these nanostructures were strongly influenced by the type of cation and anion. As the length of the subsidiary chain of cation section of IL (imidaziole ione) reduces, the thickness of the nano-sheets increases. It is expected that the present method may easily be extended to similar nano-/microstructures of other oxide materials. Such investigations are currently underway.     

Photoluminescence of Fe2O3 nanoparticles prepared by laser oxidation of Fe catalysts in carbon nanotubes

Iron oxide nanoparticles have been produced on the top surface of aligned multi-walled carbon nanotubes by CO₂ laser processing. They were characterized to be Fe₂O₃ nanoparticles by X-ray photoelectron spectroscopy, X-ray diffraction and high resolution scanning electronic microscopy. Absorption bands in the visible region were found to be redshifted compared with the absorption of Fe₂O₃ nanoparticles prepared by traditional chemical methods. Photoluminescence from these Fe₂O₃ nanoparticles shows a broad emission band in the near infrared region for both excitations at 514 and 633 nm. Particle size is considered to be responsible for the unique optical properties of the Fe₂O₃ nanoparticles.     

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.     

Fabrication of TiO2 hollow fibers with surface nanostructure

Polyvinyl alcohol-TiO₂ (PVA-TiO₂) core sheath nanofibers were fabricated by electrospinning an aqueous solution of PVA and introducing the thread-like droplets directly into a titanium tetraisopropoxide (TTIP)/hexane solution. Rod-like and sheet-like structures of lepidocrocite-type layered titanate formed on the surface of the TiO₂ sheath of the nanofibers by alkaline treatment in 1 mol L⁻¹ aqueous NaOH solution at 363 K. The nanofibers were converted to hollow TiO₂ nanofibers with surface nanostructure and anatase crystallinity by acid treatment to remove sodium ions and heat treatment at 773 K. The surface nanostructures enhanced the crystallinity and external surface area of the nanofiber and contributed to the improvement of photocatalytic oxidation activity.     

FTIR study of the photocatalytic degradation of gaseous benzene over UV-irradiated TiO2 nanoballs synthesized by hydrothermal treatment in alkaline solution

In this study, photocatalysts of TiO₂ nanoballs were obtained via a hydrothermal treating of commercial P25 in alkaline solution, and then characterized with SEM, XRD, BET and surface photovoltage spectroscopy techniques. The UV-assisted photodegradation of gaseous benzene over P25 and the prepared TiO₂ nanoballs was monitored by an in situ infrared technique. The results demonstrated that the prepared TiO₂ nanoballs in anatase form were more active than commercial P25 in photocatalytic oxidation of gaseous benzene. The promoted activity of the hydrothermal-treated TiO₂ is attributed to the increasing specific surface area and larger band gap induced by the reduced crystallite size. The spectra of FTIR indicated that weakly adsorbed phenol was formed as the reaction progress. Hydroxyl groups on the surface of TiO₂ nanoballs are able to react with photo-produced phenol, which is then retained on the catalyst surface leading to the progressive deactivation of the catalyst in the gas-solid system.     

Preparation of Fe-doped TiO2 nanotube arrays and their photocatalytic activities under visible light

Fe-doped TiO₂ nanotube arrays have been prepared by the template-based liquid phase deposition method. Their morphologies, structures and optical properties were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV-vis absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of methylene blue under visible light. The UV-vis absorption spectra of the Fe-doped TiO₂ nanotube arrays showed a red shift and an enhancement of the absorption in the visible region compared to the undoped sample. The Fe-doped TiO₂ nanotube arrays exhibited good photocatalytic activities under visible light irradiation, and the optimum dopant amount was found to be 5.9 at% in our experiments.     

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.     

Studies on the structural and optical properties of zinc oxide nanobushes and Co-doped ZnO self-aggregated nanorods synthesized by simple thermal decomposition route

Pure and Co-doped zinc oxide nanomaterials were prepared by a simple low temperature synthesis and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), diffused reflectance spectroscopy (DRS) and electron paramagnetic resonance (EPR) techniques. The results showed the formation of nanobushes that consists of several nanowires for pure ZnO and the nanorods formed by self-aggregation for Co-doped ZnO. The presence of Co²⁺ ions replacing some of the Zn²⁺ in the ZnO lattice was confirmed by EPR and DRS studies. The mechanism for the formation of self-aggregated and self-aligned ZnO rods after the incorporation of cobalt in the lattice by the building block units is discussed in this study. Morphological studies were carried out using SEM and HR-TEM, which supports the validity of the proposed mechanism for the formation of ZnO nanobushes and Co-doped ZnO nanorods. The synthesized nanomaterials were found to have good optoelectronic properties.     

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.