Characteristics and optical properties of MgO nanowires synthesized by solvothermal method

Magnesium oxide (MgO) nanowires were synthesized by solvothermal method using magnesium nitrate hexahydrate and sodium hydroxide. Field emission scanning electron microscopy (FE-SEM) and transmission scanning electron microscopy (TEM) measurements indicate that the product consists of a large quantity of nanowires with average diameter of 20 nm and average length of several micrometers. Explorations of X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX), Fourier transformer infrared spectroscopy (FTIR), selected area electronic diffraction (SAED) and high-resolution transmission electron microscope (HRTEM) indicate that the product is high-quality cubic single-crystalline nanowires. The optical properties of the samples are investigated using UV–visible spectroscopy to study the refractive index and optical dielectric constant. The photoluminescence (PL) measurement suggests that the product has an intensive emission centered at 437 nm, showing that the product has potential application in optical devices. The advantages of our method lie in high yield, the easy availability of the starting materials and allowing their large-scale production at low cost.     

熔盐法合成BiFeO3粉体及其可见光光催化性能研究

以Bi2O3和Fe2O3为原料,NaCl和Na2SO4为熔盐,采用熔盐法合成了BiFeO3粉体,研究了合成温度和保温时间对合成粉体物相的影响,探讨了熔盐法合成BiFeO3粉体的形成过程。通过对甲基橙的降解,研究了合成BiFeO3粉体的可见光光催化性能。结果表明:在750℃的合成温度下保温30 min时,淬火后可得到几乎为BiFeO3纯相的粉体;相应合成的粉体具有最佳的可见光光催化性能,可见光光照120 min后,其对甲基橙的降解率达62.5%。     

溶剂热法制备立方钛酸钡纳米晶

将钛酸丁酯和适量乙醇混匀后,与氯化钡水溶液在溶剂热条件下反应制备立方钛酸钡纳米晶。结果表明:以KOH为矿化剂,r(Ba:Ti)为1.1,φ(乙醇)为25.0%和150℃反应12h,可得平均粒径为60nm左右、分散性较好的钛酸钡纳米晶。当乙醇用量增大时,产物的粒径减小,分散性降低;随着r(Ba:Ti)的增大,产物粒径减小。当r(Ba:Ti)为1.6时,产物的平均粒径可减小至35nm左右;矿化剂的种类、反应温度和反应时间对产物的形貌及晶体结构没有影响。     

Controlled synthesis of zinc oxide nanoflowers by succinate-assisted hydrothermal route and their morphology-dependent photocatalytic performance

Hierarchical flower-like zinc oxide (ZnO) nanostructures were successfully synthesized by using facile succinate and PEG assisted hydrothermal process. The as-prepared ZnO samples were characterized by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectroscopy and UV–visible spectroscopy. The effect of dilution of precursor concentration on the formation of distinctive morphology was systematically studied. The flower-like morphology of ZnO can be effectively tuned by simply varying the precursor concentrations. A plausible growth mechanism for the formation of different hierarchical nanostructures is also proposed. Further, photocatalytic activities of the as-prepared samples were studied by photodegradation of Rhodamine B (RhB).     

Visible light photocatalytic performance of hierarchical BiOBr microspheres synthesized via a reactable ionic liquid

Hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal process in the presence of ethylene glycol and 1-butyl-3-methylimidazolium bromide ([BMIM]Br) as a reactable ionic liquid. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance absorption spectra, nitrogen adsorption–desorption measurements, and photoluminescence spectroscopy. The photocatalytic activity of BiOBr microspheres was evaluated in terms of the degradation of Rhodamine B (RhB), methyl orange (MO), and 4-chlorophenol (4-CP) under visible light irradiation. We found that the solvothermal temperature had important effects on the crystallinity, crystallite size, optical property, adsorptive performance, and photocatalytic activity of BiOBr microspheres. BiOBr microspheres with a specific surface area of 15.7 m² g⁻¹ prepared at 160 °C exhibited the best adsorption and photocatalytic performance for RhB degradation in aqueous solution. However, this sample showed hardly any activity for photodegradation of 4-CP. Tests using radical scavengers confirmed that h⁺ and O₂⁻ were the main reactive species during RhB degradation. A possible mechanism for photocatalysis by BiOBr microspheres is proposed.     

Size,morphology and optical properties of SnO2 nanoparticles synthesized by facile surfactant-assisted solvothermal processing

Spherical and dumbbell-shaped SnO₂ nanoparticles were grown by a facile solvothermal using different amounts (0.5, 1 and 1.5 g) of three different surfactants (cetyltrimethylammonium bromide, polyethylene glycol and sodium dodecyl sulfate) in ethylenediamine, serving as both a coordinating and an alkaline reagent. The average particle size, measured by powder X-ray diffraction, was determined to be ∼3–6 nm and was confirmed by transmission electron microscopy. The chemical structure of products was studied by Fourier transform infrared spectroscopy. Morphologies and composition of products were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Optical properties of products were investigated by ultraviolet–visible (UV–vis) absorption and photoluminescence spectroscopies. Finally, the formation mechanism of SnO₂ nanoparticles is discussed.     

Photocatalytic properties of Bi2O2CO3 nanosheets synthesized via a surfactant-assisted hydrothermal method

Bi₂O₂CO₃ nanosheets were synthesized via a facile sodium dodecyl sulfate (SDS)-assisted hydrothermal process. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area analysis and UV-Vis diffuse reflectance spectroscopy techniques were used to investigate the phase structure, morphology and optical properties of the Bi₂O₂CO₃ products. The SDS surfactant played an important role in the formation of Bi₂O₂CO₃ nanosheets. As-synthesized Bi₂O₂CO₃ nanosheets exhibited excellent photocatalytic activity for RhB degradation under irradiation with simulated sunlight. O₂^? radicals are considered to be the dominant active oxygen species in the photodegradation process.     

Improvement of visible light photocatalytic activity over graphene oxide/CuInS2/ZnO nanocomposite synthesized by hydrothermal method

In this study, graphene oxide/CuInS₂/ZnO as a new photocatalyst with light absorption properties in the visible region were successfully synthesized via hydrothermal route. The UV–vis absorption spectra of the catalyst suggested that the graphene oxide/CuInS₂/ZnO is active under visible light. It was evaluated the photocatalytic activities of graphene oxide/CuInS₂/ZnO on the degradation of Rhodamine B under visible light irradiation and was found that the graphene oxide/CuInS₂/ZnO obtained exhibit photocatalytic activity higher than single ZnO and CuInS₂/ZnO. Presence of graphene oxide with high specific surface area and great conductivity make it as a good support for CuInS₂/ZnO and improves removal efficiency for degradation of Rhodamine B.     

二氧化锰纳米片的制备及其电化学性质

只利用MnSO_4和(NH_4)_2S_2O_8两种原料,采用水热法制得β-MnO_2纳米材料。分別采用场发射扫描电镜(FESEM)、X射线衍射(XRD)、同步热分析(TG/DSC)等测试技术对材料的形貌、结构及热稳定性做了表征。采用恒电流充放电、循环伏安、交流阻抗等方法对材料的电化学性质进行测试。结果表明:MnO_2纳米片材料具有优良的充放电性能,在电流密度为10×10~(-3)A/cm~2时,其比电容达到85.3F/g,很适合用于电化学电容器的电极材料。     

Enhanced photocatalytic degradation properties of zinc oxide nanoparticles synthesized by using plant extracts

ZnO nanoparticles were successfully prepared by biological synthesis using aqueous extracts of Allium sativum (garlic), Allium cepa (onion) and Petroselinum crispum (parsley). For all ZnO samples, the XRD studies reveal a hexagonal wurtzite structure, without supplementary diffraction lines. The particle size is influenced by the type of plant extract used and varies between 14 and 70 nm. The biomolecules involved in the biosynthetic procedure was evidenced by FTIR spectroscopy. The presence of Mn and Fe in ZnO powders synthesized by using plant extracts was highlighted by ICP-MS. The EPR spectroscopy confirms the presence of Fe³⁺ and Mn²⁺ ions in ZnO samples and its variation depending on the plant extract. Also, Zn vacancy complexes and oxygen vacancies are present in all analyzed samples. A narrowing of the band gap for the ZnO prepared with plant extracts was observed as compared to that of the ZnO, prepared using solely ultrapure water. The photodegradation studies conducted in the presence of UV light irradiation indicated that ZnO nanoparticles prepared using garlic extract exhibit the highest efficiency in the photodegradation of methylene blue dye.     

The preparation of BiOCl photocatalyst and its performance of photodegradation on dyes

The photocatalyst BiOCl was prepared by a facile hydrolysis method and employed to study the phase structure, morphology and optical properties via X-ray diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of BiOCl was tested on the degradation of the selected four kinds of dyes under UV and visible light irradiation. The results showed that four dyes molecules could be efficiently degraded over BiOCl under UV light irradiation. Most of all, rhodamine B was thoroughly degraded after visible light irradiation in 60 min and this was ascribed to the dye photosensitization mechanism. The decomposition efficiency of RhB was apparently reduced by adding silver nitrate solution to capture electron of the LUMO orbit. This study demonstrated that electron of the LUMO level of dye molecules played an important role in the dye photosensitization reaction.     

Enhanced photocatalytic activity of zinc oxide synthesized by calcination of zinc sulfide precursor

ZnO nanoparticles were synthesized by calcination of ZnS precursor in an air atmosphere, in which ZnS had been firstly synthesized through precipitation with sodium sulfide (Na₂S) as the precipitator. Detailed structure and morphology of the samples were characterized by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, and transmission electronic microscopy. Optical properties were examined by UV–vis absorption spectroscopy. Photocatalytic activities of the samples were evaluated by degradation of Reactive Blue 14 (KGL). The results indicate that ZnS precursor converted into pure ZnO stepwise via calcination at a temperature range of 400–800 °C, and pure ZnO can be achieved above 700 °C. ZnO obtained by calcination at 700 °C had an average crystalline size around 45 nm and exhibited the highest photocatalytic activity, degrading KGL by almost 97.1% after 60 min under ultraviolet irradiation, which was superior to that of the directly synthesized and commercial ZnO. The inherent correlation between different samples and their photocatalytic activities was discussed. The phase, crystalline size, specific surface area and oxygen vacancy defects of the samples were proposed to affect their photocatalytic activity.     

Facile preparation of Sn-doped BiOCl photocatalyst with enhanced photocatalytic activity for benzoic acid and rhodamine B degradation

A series of Sn-doped BiOCl photocatalysts were successfully synthesized at room temperature via a facile oxidation-reduction method. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoemission spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) emission spectroscopy measurements. The results showed that the as-prepared samples exhibited tetragonal crystal structure, lamellar morphology and band gap energy of 3.12 eV and 2.91 eV for BiOCl and Sn(10%)-doped BiOCl, respectively. XPS results showed that Sn was in the form of tetra-valence. The photocatalytic activities of as-synthesized samples were evaluated by the degradation of benzoic acid (BA) and rhodamine B (RhB) in an aqueous solution. The results revealed that the Sn doping could enhance the photocatalytic performance of BiOCl and the highest photocatalytic activity was achieved by the Sn(10%)-doped BiOCl, in addition, the optimum dosage of Sn(10%)-doped BiOCl was 0.4 mg/L in degrading BA. The improved photocatalytic activity of Sn-doped BiOCl could be attributed to the narrower band gap energy (2.91 eV) than pure BiOCl. Furthermore, scavenger experimental results indicated that h⁺ played the pivotal role in BA photocatalytic degradation. What is more, the as-synthesized Sn(10%)-doped BiOCl photocatalyst exhibited a good stability during the photodegradation of BA and RhB, revealing its promising prospect in the practical application of the treatment of organic wastewaters.     

High-strength long-length single-mode fiber synthesized by the VAD method

Long-length high-strength single-mode fibers were fabricated from large preforms made by the VAD process. The longest piece lengths produced at 2-percent (1.4 GPa) strain prooftesting and 5-percent (3.5 GPa) strain prooftesting are 41.7 km and 15.6 km, respectively. These are the longest length fibers in the world at their respective strain prooftesting levels. The transmission losses for the 41.7-km fiber are 0.36 dB/km at 1.3 μm and 0.22 dB/km at 1.55 μm.     

Enhanced photocatalytic and antibacterial activities of sol–gel synthesized ZnO and Ag-ZnO

Nanocrystalline ZnO and Ag-ZnO (0.1 at%) have been synthesized by sol–gel method and characterized by X-ray diffraction, energy dispersive X-ray spectrum, scanning electron micrographs and UV–vis diffuse reflectance, photoluminescence and electrochemical impedance spectra. Doping ZnO with Ag reduces the average crystal size, sharpens the band gap absorption and decreases the charge-transfer resistance. The bactericidal and photocatalytic activities of sol–gel synthesized ZnO, tested, respectively, with Escherichia coli and cyanide ion, are larger than those of commercial ZnO nanoparticles. Ag doping by sol–gel method enhances the antibacterial and photocatalytic activities; the latter has been tested using methylene blue, methyl orange and rhodamine B.     

Effects of reaction conditions on the structural,morphological and optical properties of solvothermal synthesized ZnS nanostructures

Structural and morphological controlled ZnS nanostructures were synthesized with solvothermal method by using the mixed solvent of ethylenediamine (En) and deionized water. ZnS nanowires were synthesized successfully. The mechanism of the morphological evolution of ZnS nanostructures was concluded by studying the influences of different synthetical conditions on the properties of ZnS nanowires, which included the volume ratios of En and deionized water, the mole ratios of two precursors, different zinc precursors, reaction temperatures and times. The optical properties of ZnS nanostructures were also examined by photoluminescence and absorption spectra.     

Morphology and crystalline phase-controllable synthesis of titania nanoparticles via acrylamide gel method and their photocatalytic properties

Titanium dioxide nanoparticles with average particle size of about 5 nm to 60 nm were readily synthesized via a simple, fast and low cost method; polyacrylamide gel method. Furthermore, the effect of the used acid and solvent together with calcination temperature, on crystallite size, morphology, band gaps of resultant material were investigated. The products were characterized by means of thermo gravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy analysis. The XRD results show that the presence of different anions in the precursor solution leads to the formation of samples with different anatase/rutile ratios. Their photocatalytic activities were evaluated by photocatalytic degradation of Yellow GX aqueous solution under ultraviolet radiation. The results show that the photocatalyst (TEPC_I), containing 79% anatase exhibits the highest photocatalytic activity, which is due to a synergistic effect between anatase and rutile.     

A simple method for preparing ZnO foam/carbon quantum dots nanocomposite and their photocatalytic applications

ZnO foam/carbon quantum dots (CQDs) nanocomposite has been successfully synthesized by a facile process which ZnO foam prepared by combustion method was dispersed in CQDs solution. It is found that the ZnO foam is constructed by a large number of ZnO nanoparticles filling in irregular, hierarchical pores. The foam structure originates from a large amounts of gas produced in the combustion process. The obtained ZnO foam/CQDs nanocomposite shows excellent photocatalytic activities on degrading Rhodamine B (RhB), Methyl orange (MO) and Methylene blue (MB) under UV and visible light irradiation. The order of degradation efficiency is MB>RhB>MO. It is attributed to the synergistic effect of several factors, including the light-trapping effect of ZnO foam, the up-converted photoluminescence behavior and photo-induced electron transfer property of CQDs.