Hydrothermal synthesis and photocatalytic activity of anatase TiO2 nanofiber

TiO2 nanofiber consisting of 15 +/- 5 nm anatase grains was synthesized by hydrothermal treatment of fibrous hydrogen titanate precursor at 180 degrees C for 20 h. The hydrogen titanate precursor was synthesized by hydrothermal treatment of commercial P25 TiO2 powder in 10 M NaOH at 200 degrees C for 20 h followed by soaking in 0.1 M HNO3 to perform ion exchange between the as-synthesized Na titanate and H. By controlling pH of the solution during hydrothermal treatment of the hydrogen titanate precursor, pure anatase TiO2 nanofiber was obtained. Its band-gap energy determined from the onset of diffused reflectance spectrum was 3.19 eV which is equal to that of anatase TiO2 powder. The TiO2 nanofiber showed higher photodecomposition efficiency than the Cotiox KA-100 TiO2 but lower than the P25 TiO2. Photodegradation is the predominant process for 'Reactive blue 171' removal.     

Synthesis, characterization and catalytic activity of CdO nanocrystals

In this paper, we report the synthesis of nanocrystalline cadmium oxide (CdO) and its characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Its catalytic activity was investigated on the thermal decomposition of 1,2,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), ammonium perchlorate (AP), hydroxyl terminated polybutadiene (HTPB) and composite solid propellants (CSPs) using thermogravimetric analysis (TG), simultaneous thermogravimerty and differential scanning calorimetry (TG-DSC) and ignition delay measurements. Kinetics of thermal decomposition of AP + CdO has also been investigated using model free (isoconversional) and model-fitting approaches which have been applied to data for isothermal TG decomposition. All these studies show enhancement in the rate of decomposition of AP, HTPB and CSPs but no effect on HMX. The burning rate of CSPs has also been found to be increased with CdO nanocrystals.     

Hydrothermal synthesis of nanostructured TiO2 particles and characterization of their photocatalytic antimicrobial activity

Nanostructured titania particles were synthesized by using hydrothermal processing and the photocatalytic antimicrobial activities were characterized. Both sol-gel synthesized and commercial TiO2 (anatase) samples were processed with two step hydrothermal treatments, under alkaline and neutral conditions. Scanning Electron Microscope (SEM) images showed that alkaline treatment yields nanofibers and lamellar structured particles from the commercial anatase and sol-gel synthesized samples respectively. Further treatment of nanofibers and nanostructured lamellar particles with distilled water results with crystal growth and the formation of nano structured bipyramidal crystalline particles. The photocatalytic antimicrobial activities of the samples were determined against Escherichia coil under irradiation. It was observed that the samples treated under alkaline conditions have improved activity than the original anatase samples. Limited activity and resulting time lag in bacterial inactivation were observed for hydrothermally treated samples with distilled water. However, a post treatment comprising the UV irradiation in aqueous conditions enhanced the photocatalytic activity.     

Hydrothermal synthesis of HgTe rod-shaped nanocrystals

HgTe nanorods composed of crystalline particles with the diameter of 100-300 nm and length of up to 2-3 μm have been prepared by a hydrothermal method, and characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). It was found that ammonia played a key role in the formation of HgTe nanorods.     

Hydrothermal synthesis of SnO2/SnS2 nanocomposite with high visible light-driven photocatalytic activity

SnO₂/SnS₂ nanocomposite with a heterojunction structure (that is, SnO₂ nanoparticles-decorated SnS₂ nanoplates) was synthesized via the hydrothermal reaction between SnO₂ nanoparticles and thioacetamide in 5 vol.% acetic acid aqueous solution at 150 °C for 3 h, and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the hydrothermally synthesized SnO₂/SnS₂ nanocomposite was tested by degrading methyl orange in distilled water under visible light (λ > 420 nm) irradiation. It was found that the hydrothermally synthesized SnO₂/SnS₂ nanocomposite exhibited superior photocatalytic activity to SnO₂ nanoparticles, SnS₂ nanoplates and physically mixed SnO₂/SnS₂ nanocomposite. The heterojunction structure of the hydrothermally synthesized SnO₂/SnS₂ nanocomposite, which can facilitate interfacial electron transfer and reduce the self-agglomeration of two components, was considered to play an important role in achieving its higher photocatalytic activity.     

Hydrothermal synthesis of NaEuF4 spindle-like nanocrystals

NaEuF₄ spindle-like nanocrystals have been synthesized through a simple hydrothermal method. The nanocrystals were well crystallized and exhibited fine morphology, as indicated by X-ray diffraction, transmission electron microscope and selected area electron diffractometer. The luminescence properties of these NaEuF₄ products were investigated.     

Hydrothermal synthesis of hierarchical flower-like α-CNTs/SnO2 architectures with enhanced photocatalytic activity

The hierarchical flower-like α-CNTs/SnO₂ architectures composed of curved sheets are synthesized with hydrothermal method at 160?°C for 8?h. The α-CNTs/SnO₂ composite was doped with α-CNTs during preparation, the photocatalytic activity of α-CNTs/SnO₂ was evaluated by photodegradation of Rhodamine B (RhB) under simulated visible light. The results showed that the photocatalytic activity of α-CNTs/SnO₂ for degradation of RhB was up to 90.35% within 120?min, which was much higher than that of pure compound. It was significantly found that the introduction of α-CNTs, which may suppressed the recombination of photogenerated electron-hole pairs on the interface of SnO₂, leading to enhanced photocatalytic activity.     

Synthesis and photocatalytic activity of sea urchin-shaped rutile TiO2 nanocrystals

Sea urchin-shaped rutile nanostructures (SUR NSs) with abundant {110} surfaces are synthesized at 60 °C under atmospheric pressure. The SUR NSs were ~ 420 nm in diameter and contain a number of needle-like rutile single crystals grown parallel to the (110) face from a single nucleus in a radial fashion. The photocatalytic activity of the SUR NSs is significantly higher than that of commercial rutile nanoparticles with the same specific surface area. This demonstrates that {110} facets are effective in enhancing photoactivity.     

NaTaO_3光催化剂的水热合成与催化性能研究

以Ta2O5和NaOH为原料,采用简单水热合成法在低温制备结晶性能良好的纳米NaTaO3光催化剂.并利用XRD、TEM、SEM、UV-vis等分析检测手段对样品的结构和形貌等进行表征.同时研究了制备的钽酸钠光催化降解染料罗丹明B的性能.结果表明,水热反应温度为120℃,反应时间12h可以合成了结晶良好,尺寸约为150～200nto的立方体NaTaO3颗粒.光催化降解罗丹明B的实验显示,制备的Na-TaO3具有较高的光催化活性.     

纳米晶MnFe2O4的水热法合成及其磁性能

采用水热法制备了软磁材料MnFezO4纳米晶,借助XRD、IR、SEM和VSM对产物进行了表征,着重研究了水热条件如温度和时间等对MnFe2O4纳米晶的形成及其结构和磁性能的影响。结果表明水热温度较低时的产物晶化度和纯度低,表现出较差的磁性能,温度为120℃的产物其饱和磁化强度为15．34emu／g,剩磁比为0．08,矫顽力为8lOe,而在200℃下水热产物饱和磁化强度为51．49emu／g,剩磁比达到0．14,矫顽力为121Oe。     

Hydrothermal synthesis of Eu3+-doped Y2Sn2O7 nanocrystals

Fine powders of Y₂Sn₂O₇ nanocrystals with pyrochlore structure have been successfully synthesized by the hydrothermal method in an alkaline system. The samples were characterized by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. Furthermore, photoluminescence characterization of the Y₂Sn₂O₇ nanocrystals doped with 5 mol% Eu³⁺ was carried out, and the results show that there were some intense and prevailing emission peaks located at 580–635 nm.     

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.     

Glycerol as an efficient mesopore-controlling agent for synthesis of mesoporous-assembled TiO2 nanocrystals and their remarkable photocatalytic H2 production activity

In this work, the mesoporous-assembled TiO₂ nanocrystals were successfully synthesized by a modified sol–gel process under mild conditions with the aid of glycerol, which is a main by-product from biodiesel production via the transesterification of vegetable oils. The synthesized TiO₂ nanocrystals were characterized by various techniques, i.e. N₂ adsorption–desorption, SEM, high resolution TEM, and XRD. The characterization results clearly showed that the glycerol could behave as an efficient mesopore-controlling agent, which induced the mesoporous-assembled characteristic of the synthesized TiO₂ nanocrystals with very narrow pore size distribution. The synthesized mesoporous-assembled TiO₂ nanocrystals were applied for hydrogen production from the photocatalytic water splitting. The photocatalytic activity results revealed that the synthesized mesoporous-assembled TiO₂ nanocrystals possessed much higher hydrogen production activity than the commercially available P-25 TiO₂ and ST-01 TiO₂ powders.     

Hydrothermal synthesis, characterization, and influence factors of PbTe nanocrystals

In the present paper, we successfully prepared PbTe nanocrystals in a simple aqueous system via the hydrothermal route employing PbO, Te powders and N₂H₄·H₂O as the starting reactants at 150 °C for 14 h. Some factors affecting the morphologies of the PbTe nanocrystals, such as the reaction temperature, time, the amount of NaOH, sorts of reductants and Pb²⁺ ion sources, were systematically investigated. Experimental results indicated that, under keeping the other experimental conditions constant: raising the reaction temperature, the shapes of the as-obtained PbTe hardly changed, while decreasing the temperature, some PbTe dendrites were obtained; the short reaction time availed to obtain cubes with a hole in the center of each face; more amounts of NaOH were favorable to the formation of regular PbTe nanocuboids. When NaBH₄ was used as the reductant, a large amount of near spherical PbTe nanocrystals was produced; while NaH₂PO₂ was used, many PbTe crystals with hollow framework structures were obtained. When Pb(CH₃COO)₂ was used as the Pb²⁺ ion source, some dendrites made of many irregular particles were generated; while PbSO₄ was employed, many PbTe nanocuboids were produced. A possible formation mechanism of PbTe nanocrystals was proposed based on the experimental results.     

Sm掺杂K_4Nb_6O_(17)的制备及其光催化性能

以KOH、Nb_2O_5和Sm(NO_3)_3为原料,采用水热合成法制备掺杂不同物质的量的Sm的片层状K_4Nb_6O_(17)光催化剂;采用X射线衍射、扫描电子显微镜、能量色散X射线光谱,高分辨率透射电子显微镜和X射线光电子能谱等测试技术对其结构和形貌进行表征,考察Sm掺杂K_4Nb_6O_(17)复合材料对有机染料罗丹明的降解性能。结果表明,Sm的掺杂提高了K_4Nb_6O_(17)的结晶度,Sm以Sm_2O_3的形式高度分散在K_4Nb_6O_(17)中;当Sm与Nb的物质的量比为0.01时,K_4Nb_6O_(17)具有最佳的光催化活性,在80 min内能使质量浓度为20 mg/L的罗丹明染料溶液100 mL完全脱色。     

Low-temperature hydrothermal synthesis of phase-pure rutile titania nanocrystals: Time temperature tuning of morphology and photocatalytic activity

In this paper, a simple and efficient methodology for the low-temperature synthesis of phase-pure nanocrystalline rutile TiO₂ with tuned morphology is reported. Control on morphology has been achieved by simple variation of the hydrothermal process, starting with titanium-tetrachloride without using mineralizers, additives or templating agents. The X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns showed no other phases of TiO₂ establishing the formation of phase-pure rutile titania in the entire temperature range of synthesis (40-150 °C) and most noticeably even at a considerably low temperature (40 °C). Fourier transform infrared (FT-IR) spectra strongly indicated the presence of hydroxyl group or surface adsorbed water and the thermogravimetry and differential thermo-gravimetry (TG-DTG) showed no phase change up to 1000 °C. A combination of reaction parameters (temperature, time) with a thorough transmission electron microscopy (TEM) study demonstrated the formation of phase-pure rutile titania nanocrystals as nano-rods, bunched nano-spindles or spherical nanoparticles depending on the hydrothermal reaction conditions. The photocatalytic activity of the synthesized nanocrystals has been successfully evaluated on the photodegradation of methyl orange (MO), a well-known pollutant azo-dye, as a model reaction.     

Hydrothermal growth of wheatear-shaped ZnO microstructures and their photocatalytic activity

A facile hydrothermal process was developed to synthesize novel wheatear-shaped ZnO microstructures at a low temperature (\(85^{\circ }\hbox {C}\)) without the assistance of any template agent. X-ray diffraction and field emission scanning electron microscopy were used to characterize the structure and morphology of the samples. Results showed that the length of the ‘wheatear’ was about \(5.8~\upmu \!\hbox {m}\) and the section width was \(1.2~\upmu \!\hbox {m}\). The particles consisted of closely packed nanorods with average diameter of 100 nm. The growth of wheatear-shaped ZnO is very rapid and can be achieved in only 5 min. \(\hbox {OH}^{-}\)-driven oriented aggregation and multistep nucleation resulted in the formation of wheatear-shaped ZnO microstructures. The product had assembled open structures and it exhibited excellent photocatalytic activity in the degradation of methyl orange under UV-light irradiation.