Morphology‐Dependent Gas‐Sensing Properties of ZnO Nanostructures for Chlorophenol

The crystal‐plane effect of ZnO nanostructures on the toxic 2‐chlorophenol gas‐sensing properties was examined. Three kinds of single‐crystalline ZnO nanostructures including nanoawls, nanorods, and nanodisks were synthesized by using different capping agents via simple hydrothermal routes. Different crystal surfaces were expected for these ZnO nanostructures. The sensing tests results showed that ZnO nanodisks exhibited the greatest sensitivity for the detection of toxic 2‐chlorophenol. The results revealed that the sensitivity of these ZnO samples was heavily dependent on their exposed surfaces. The polar (0001) planes were most reactive and could be considered as the critical factor for the gas‐sensing performance. In addition, calculations using density functional theory were employed to simulate the gas‐sensing reaction involving surface reconstruction and charge transfer both of which result in the change of electronic conductance of ZnO.     

Length‐Dependent Charge Generation from Vertical Arrays of High‐Aspect‐Ratio ZnO Nanowires

Aqueous chemical growth of zinc oxide nanowires is a flexible and effective approach to obtain dense arrays of vertically oriented nanostructures with high aspect ratio. Herein we present a systematic study of the different synthesis parameters that influence the ZnO seed layer and thus the resulting morphological features of the free‐standing vertically oriented ZnO nanowires. We obtained a homogeneous coverage of transparent conductive substrates with high‐aspect‐ratio nanowire arrays (length/diameter ratio of up to 52). Such nanostructured vertical arrays were examined to assess their electric and piezoelectric properties, and showed an electric charge generation upon mechanical compressive stress. The principle of energy harvesting with these nanostructured ZnO arrays was demonstrated by connecting them to an electronic charge amplifier and storing the generated charge in a series of capacitors. We found that the generated charge and the electrical behavior of the ZnO nanowires are strictly dependent on the nanowire length. We have shown the importance of controlling the morphological properties of such ZnO nanostructures for optimizing a nanogenerator device.     

Analyses of the surfaces of concrete by Raman and FT‐IR spectroscopies: comparative study of hardened samples after demoulding and after organic post‐treatment

Concrete surfaces were studied by two spectroscopic techniques, FT‐IR (in ATR mode) and Raman, to establish a nondestructive method to analyze the distribution of hydrated and organic phases. The surface composition of ordinary clinker, polished concrete, concrete after demoulding, and coated concrete as used in building construction was studied. The clinker's mineral phases and the polished concrete were first analyzed by Raman spectroscopy to determine a spectrum database of the specific phases located on the surface of the concrete. Then, both spectroscopic techniques were used to analyze, directly, the surface of hardened concrete after demoulding. No impact of roughness or porosity was highlighted using Raman spectroscopy; many cementitious, or hydrated phases (alite, belite, tricalcium aluminate, ferrite, portlandite and ettringite) were clearly identified. FT‐IR in ATR mode only identified some hydrated phases: portlandite and CaO? SiO₂? H₂O (C? S? H), but organic residues from the demoulding oil were characterized by this technique. Furthermore, the convenience of using these techniques together was tested by analyzing the composition of concrete surfaces coated by different organic post‐treatments. FT‐IR spectroscopy was useful to identify the main organic groups at the concrete surface, whereas Raman spectroscopy was especially able to characterize the mineral/hydrated phases under a thick post‐treatment layer (constituted of polyester varnish). Due to their own specificities, these complementary techniques should be used together to easily identify all the mineral phases and organic residues/coatings on concrete surfaces. Copyright © 2010 John Wiley & Sons, Ltd.     

ZnSe Etching of Zn‐Rich Cu2ZnSnSe4: An Oxidation Route for Improved Solar‐Cell Efficiency

Cu₂ZnSnSe₄ kesterite compounds are some of the most promising materials for low‐cost thin‐film photovoltaics. However, the synthesis of absorbers for high‐performing devices is still a complex issue. So far, the best devices rely on absorbers grown in a Zn‐rich and Cu‐poor environment. These off‐stoichiometric conditions favor the presence of a ZnSe secondary phase, which has been proved to be highly detrimental for device performance. Therefore, an effective method for the selective removal of this phase is important. Previous attempts to remove this phase by using acidic etching or highly toxic organic compounds have been reported but so far with moderate impact on device performance. Herein, a new oxidizing route to ensure efficient removal of ZnSe is presented based on treatment with a mixture of an oxidizing agent and a mineral acid followed by treatment in an aqueous Na₂S solution. Three different oxidizing agents were tested: H₂O₂, KMnO₄, and K₂Cr₂O₇, combined with different concentrations of H₂SO₄. With all of these agents Se^2? from the ZnSe surface phase is selectively oxidized to Se⁰, forming an elemental Se phase, which is removed with the subsequent etching in Na₂S. Using KMnO₄ in a H₂SO₄‐based medium, a large improvement on the conversion efficiency of the devices is observed, related to an improvement of all the optoelectronic parameters of the cells. Improvement of short‐circuit current density (J_sc) and series resistance is directly related to the selective etching of the ZnSe surface phase, which has a demonstrated current‐blocking effect. In addition, a significant improvement of open‐circuit voltage (V_oc), shunt resistance (R_sh), and fill factor (FF) are attributed to a passivation effect of the kesterite absorber surface resulting from the chemical processes, an effect that likely leads to a reduction of nonradiative‐recombination states density and a subsequent improvement of the p–n junction.     

Energetic Materials Based on 5,5′‐Diamino‐4,4′‐dinitramino‐3,3′‐bi‐1,2,4‐triazole

A simple and straightforward synthesis of 5,5′‐diamino‐4,4′‐dinitramino‐3,3′‐bi‐1,2,4‐triazole by the selective nitration of 4,4′,5,5′‐tetraamino‐3,3′‐bi‐1,2,4‐triazole is presented. The interaction of the amino and nitramino groups improves the energetic properties of this functionalized bitriazole. For a deeper investigation of these properties, various nitrogen‐rich derivatives were synthesized. The new compounds were investigated and characterized by spectroscopy (¹H and ¹³C NMR, IR, Raman), elemental analysis, mass spectrometry, differential thermal analysis (DTA), X‐ray analysis, and impact and friction sensitivities (IS, FS). X‐ray analyses were performed and deliver insight into structural characteristics with which the stability of the compounds can be explained. The standard enthalpies of formation were calculated for all compounds at the CBS‐4M level of theory, revealing highly positive heats of formation. The energetic performance of the new molecules was predicted with the EXPLO5 V6.02 computer. A small‐scale shock reactivity test (SSRT) and a toxicity test gave a first impression of the performance and toxicity of selective compounds.     

基于ZnO纳米线的圆柱形微纳米跨尺度结构的制备与表征

基于水浴法在光纤纤芯上合成了ZnO纳米线, 得到了圆柱形微纳米跨尺度结构. 将纳米级的随机粗糙表面叠加到微米级的圆柱形基底上, 实现了对圆柱形跨尺度结构表面形貌的仿真分析. 采用扫描电子显微镜(SEM)并结合Matlab图像处理算子对跨尺度结构的表面形貌和ZnO纳米线的几何特征参数进行了表征. 与ZnO纳米线薄膜实际轮廓提取出的特征参数相同, 对均方根粗糙度为39.2 nm、偏斜度为0.1324及峭度为2.7146的圆柱形粗糙表面进行了仿真, 验证了仿真表面与实际轮廓的一致性. 建立了合成工艺参数对ZnO纳米线的长度、直径及长径比等几何特征参数的影响关系, 确定最佳工艺条件为: 种子层溶液Zn²⁺浓度为1.0 mmol/L, 生长液Zn²⁺浓度为0.03 mol/L, 生长时间为1.5 h, 水浴恒温90℃.     

Molten salt route toward the growth of ZnO nanowires in unusual growth directions

ZnO nanowires with unusual growth directions, such as the approximate 102 and the 100 directions, were prepared by using the LiCl molten salt synthetic method. Intrinsic crystallographic structures and the growth directions of the as-prepared ZnO nanowires were investigated by using selected area electron diffraction and high-resolution transmission electron microscopy. In the present case, Li+ and Cl- ions of molten salts may bind with O2- and Zn2+ ions, respectively, of the {101} and {001} polar surfaces of the ZnO crystals, resulting in the decrease of their surface energies and tuning the growth directions by blocking the growth on the polar surfaces. A combination of the growth along the <102>, <100>, and <210> directions may lead to the formation of complex tree like ZnO dendrites. Strong green light emission was observed from room-temperature PL spectra of the as-prepared ZnO nanowires. This molten-salt synthetic process could be extended to synthesize other kinds of unusual 1D nanomaterials with specific crystal structures and properties.     

Earth‐Abundant Oxygen Evolution Catalysts Coupled onto ZnO Nanowire Arrays for Efficient Photoelectrochemical Water Cleavage

ZnO has long been considered as a model UV‐driven photoanode for photoelectrochemical water splitting, but its performance has been limited by fast charge‐carrier recombination, extremely poor stability in aqueous solution, and slow kinetics of water oxidation. These issues were addressed by applying a strategy of optimization and passivation of hydrothermally grown 1D ZnO nanowire arrays. The length and diameter of bare ZnO nanowires were optimized by varying the growth time and precursor concentration to achieve optimal photoelectrochemical performance. The addition of earth‐abundant cobalt phosphate (Co‐Pi) and nickel borate (Ni‐B) oxygen evolution catalysts onto ZnO nanowires resulted in substantial cathodic shifts in onset potential to as low as about 0.3 V versus the reversible hydrogen electrode (RHE) for Ni‐B/ZnO, for which a maximum photocurrent density of 1.1 mA cm^?2 at 0.9 V (vs. RHE) with applied bias photon‐to‐current efficiency of 0.4 % and an unprecedented near‐unity incident photon‐to‐current efficiency at 370 nm. In addition the potential required for saturated photocurrent was dramatically reduced from 1.6 to 0.9 V versus RHE. Furthermore, the stability of these ZnO nanowires was significantly enhanced by using Ni‐B compared to Co‐Pi due to its superior chemical robustness, and it thus has additional functionality as a stable protecting layer on the ZnO surface. These remarkable enhancements in both photocatalytic activity and stability directly address the current severe limitations in the use of ZnO‐based photoelectrodes for water‐splitting applications, and can be applied to other photoanodes for efficient solar‐driven fuel synthesis.     

籽晶层制备方式对氧化锌纳米棒阵列的影响

采用3种不同的方式制备ZnO薄膜籽晶层:旋涂、喷雾热解和脉冲激光沉积。对于每一种制备方式,其薄膜的晶体结构、形貌、表面粗糙度等性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)进行了表征。之后,通过水热合成方法,在3种籽晶层衬底上制备得到具有不同结构和形貌特征的ZnO纳米棒阵列。结果表明,ZnO纳米棒生长和籽晶层制备方式具有极强的相关性。最后,对两者相关性的生长机理进行了解释。     

Study on the Preparation of Cr‐based Catalysts Doped by Zn using Sol–Gel Auto‐Combustion Method and Its Application for Synthesis of 1‐Chloro‐2,3,3,4,4,5,5‐heptafluorocyclopentene

High‐surface‐area chromium‐based catalysts in the presence of a small amount of zinc were prepared via a sol–gel auto‐combustion method using chromic nitrate, zinc nitrate, and citric acid. First, the auto‐combustion behavior of the dried gel was investigated by derivative thermogravimetry and (DTG)‐TG and infrared (IR) techniques. The results revealed that the dried gel exhibited self‐propagating combustion properties. Second, the as‐burnt powders were characterized by IR , X‐ray diffraction (XRD) , Brunauer–Emmett–Teller analysis (BET) , and scanning electron microscopy (SEM) . The findings showed that the gels were directly converted into CrZn ‐O nanoparticles with high surface area during the auto‐combustion process. Third, the pre‐fluorination Cr‐Zn catalysts were characterized by XRD , BET , SEM , X‐ray photoelectron spectroscopy (XPS) , and Fourier transform (FT)‐IR spectroscopy of pyridine adsorption techniques. It was found that the presence of zinc led to significant structural changes in the catalyst, the particle size was smaller, the surface area became larger, and more active sites appeared. Finally, the catalytic activities of the samples were tested for the fluorination of 1,2‐dichlorohexafluorocyclopentene (1,2‐F6 ) with anhydrous hydrogen fluoride. The obtained results indicated that the pre‐fluorination activated Cr‐Zn catalysts prepared by this sol–gel auto‐combustion method exhibited high efficiency in the synthesis of cyclic hydrofluorocarbons.     

Large-scale synthesis and microstructure of SnO2 nanowires coated with quantum-sized ZnO nanocrystals on a mesh substrate

Large-quantity single-crystal SnO(2) nanowires coated with quantum-sized ZnO nanocrystals (nc-ZnO/SnO(2) nanowires) were directly synthesized by thermal evaporation of SnO powder and a mixture of basic ZnCO(3) and graphite powders. A common stainless steel mesh was used to collect the products. The microstructure and possible growth mechanism of the nc-ZnO/SnO(2) nanowires were investigated. Results showed that tetragonal structured SnO(2) nanowires were obtained, whose surfaces were coated with single-layer ZnO nanocrystals with an average diameter of less than 5 nm. The nanowires had cross-rectangle section with width-to-thickness aspect ratio ranging from 2:1 to 5:1. The lengths of the nanowires were several tens of micrometers. ZnO nanocrystals were single crystalline wurtzite structures, which coated the whole nanowires and distributed uniformly. The possible growth mechanism of the composite nanowires may be enucleated that Zn atoms in the source vapor will replace the Sn atoms on the surface of the formed SnO(2) nanowires due to the higher reducibility of Zn than Sn. Two strong Raman scattering peaks at 626 and 656 cm(-1) appeared in the micro-Raman spectrum of nc-ZnO/SnO(2) nanowires. The origins of the peaks were discussed. Most importantly, the method can be extended to other composite oxide nanowires that are synthesized by oxidizing two kinds of metals, such as high reducibility elements Mg, Al, Zn, and Ti, and low reducibility elements In, Ge, Ga, etc.     

Development of the Headspace SPME/ATR‐IR Method for Detection of Chlorinated Aromatic Compounds in Soils

In this paper, a new method based on attenuated total reflection infrared (ATR‐IR) spectroscopy was developed to detect chlorinated aromatic compounds in soil. To eliminate the problems associated in inspection of soil samples by the ATR‐IR method, chlorinated compounds were evaporated from soil matrices and detected in the headspace. The sensing device was constructed by an internal reflection element (IRE) coated with a hydrophobic film to attract and concentrate chlorinated compounds evaporated to the headspace. Factors that influence the analytical signals were studied such as the moisture content, volatilities of analytes, and effect of heating temperature. Results indicated that the addition of thermal energy to the soil sample resulted in an increase of IR signal. However, the IRE was also warmed up and caused a slight decrease of the IR signals after a long detection time. The studies of the influence of moisture indicated that a small amount of water present in soils could tremendously increase the intensity of detected IR signals. The further increase of moisture contents resulted in a decrease of the analytical signals, and the optimal signal was found when soil samples contained 5% (v/w) water. Results in analyses of compounds with different volatilities indicated that even with vapor pressure lower than 0.017 Torrs, quality IR spectra could still be obtained. Using the optimal conditions found in this work, the results in determination of five compounds in soil samples indicated that the linear regression coefficients (R‐square) were higher than 0.992 with detection limits around a few hundreds of ppb.     

A complete set of self‐consistent charge density‐functional tight‐binding parametrization of zinc chalcogenides (ZnX; X=O,S, Se,and Te)

We have developed a complete set of self‐consistent charge density‐functional tight‐binding parameters for Zn? X (X = Zn, O, S, Se, Te, Cd, H, C, and N). The transferability of the derived parameters has been tested against Pseudo Potential‐Perdew, Burke and Ernzerhof (PP‐PBE) calculations and experimental values (whenever available) for corresponding bulk systems (e.g., hexagonal close packing, zinc‐blende, and wurtzite(wz)), various kinds of nanostructures (such as nanowires, surfaces, and nanoclusters), and also some small molecular systems. Our results show that the derived parameters reproduce the structural and energetic properties of the above‐mentioned systems very well. With the derived parameter set, one can study zinc‐chalcogenide nanostructures of relatively large size which was otherwise prohibited by other methods. The Zn‐Cd parametrization developed in this article will help in studying large semiconductor hetero‐nanostructures of Zn and Cd chalcogenides such as ZnX/CdX core/shell nanoparticles, nanotubes, nanowires, and nanoalloys. © 2012 Wiley Periodicals, Inc.     

Surface Engineering of Poly(DL‐lactic acid) by Entrapment of Biomacromolecules

Alginate, chitosan and gelatin were deposited on the surface of PDL‐LA films via an entrapment method. ATR‐FT‐IR, XPS and contact‐angle analyses revealed the formation of stable thin biomacromolecule layers on the PDL‐LA film, thus enhancing the hydrophilicity of the films. Confocal laser scanning microscopy showed the existence of entrapment areas of approximately 10–20 μm in depth. This simple surface‐treatment method may have the potential for many biomedical applications.     

Organic‐Stabilizer‐Free Polyol Synthesis of Silver Nanowires for Electrode Applications

The polyol reduction of a Ag precursor in the presence of an organic stabilizer, such as poly(vinylpyrrolidone), is a widely used method for the production of Ag nanowires (NWs). However, organic capping molecules introduce insulating layers around each NW. Herein we demonstrate that Ag NWs can be produced in high yield without any organic stabilizers simply by introducing trace amounts of NaCl and Fe(NO₃)₃ during low‐temperature polyol synthesis. The heterogeneous nucleation and growth of Ag NWs on initially formed AgCl particles, combined with oxidative etching of unwanted Ag nanoparticles, resulted in the selective formation of long NWs with an average length of about 40 μm in the absence of a capping or stabilizing effect provided by surface‐adsorbing molecules. These organic‐stabilizer‐free Ag NWs were directly used for the fabrication of high‐performance transparent or stretchable electrodes without a complicated process for the removal of capping molecules from the NW surface.     

A simple route to porous ZnO and ZnCdO nanowires

Porous ZnO nanowires were obtained in an inexpensive and simple way by thermally oxidizing ZnSe nanowires in air. The morphologies of the precursor and resulted nanowires are almost identical. X-ray diffraction and energy-dispersive X-ray spectroscopy reveal that the zinc blende ZnSe nanowires were transformed into wurtzite ZnO nanowires after oxidation. Transmission electron microscope measurements indicate that the ZnO nanowires are polycrystalline and are composed of nanoparticles and nanopores. ZnCdO nanowires, which were seldom reported previously, have also been prepared in this way. Just like the ZnO nanowires, the ZnCdO nanowires also show the porous structure. Photoluminescence studies on both ZnO and ZnCdO nanowires show intense near-band edge emissions at room temperature. The transition from one kind of nanowires to another by simple thermal oxidization described in this paper may be applicable to some other compound semiconductors and may open a practical route to yield nanowires.     

ZnO/ZnSe复合纳米结构的制备及可见光光催化性能

通过热水解法, 以氧化锌为模板, 成功制备出形貌均一的ZnO/ZnSe复合纳米结构. 为了对比不同O/Se比对光催化性能的影响, 保持其它反应参数不变, 调节还原剂水合肼的用量, 得到不同硒化程度的ZnO/ZnSe复合纳米结构. 采用场发射扫描电子显微镜、 X射线衍射仪和透射电子显微镜对样品的形貌及结构进行了表征, 通过测试该复合结构对亚甲基蓝的可见光催化降解评估了其光催化效率. 结果表明, 与纯ZnO比, ZnO/ZnSe复合结构在可见光区域和紫外光区域的光吸收范围变宽, 显示出较高的光催化效率. 原因在于ZnSe导带上的电子在扩散势能的作用下迁移到ZnO的导带上, 而空穴仍保留在ZnSe价带, 这样有助于光生电子和空穴对的分离, 降低其复合机率, 从而提高ZnO的光催化效率.     

Fabrication of zinc oxide nanowires/polymer composites by two‐photon polymerization

We present an approach to fabricate ZnO nanowires/polymer composite into three‐dimensional microstructures, based on two‐photon polymerization direct laser writing, a fabrication method that allows submicrometric spatial resolution. The structural integrity of the structures was inferred by scanning electron microscopy, while the presence and distribution of ZnO nanowires was investigated by energy dispersive X‐ray, Raman spectroscopy, and X‐ray diffraction. The optical properties of the produced composite microstructures were verified by imaging the characteristic ZnO emission using a fluorescence microscope. Hence, such approach can be used to develop composite microstructures containing ZnO nanowires aiming at technological applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 333–337     

Control of the ZnO nanowires nucleation site using microfluidic channels

We report on the growth of uniquely shaped ZnO nanowires with high surface area and patterned over large areas by using a poly(dimethylsiloxane) (PDMS) microfluidic channel technique. The synthesis uses first a patterned seed template fabricated by zinc acetate solution flowing though a microfluidic channel and then growth of ZnO nanowire at the seed using thermal chemical vapor deposition on a silicon substrate. Variations the ZnO nanowire by seed pattern formed within the microfluidic channel were also observed for different substrates and concentrations of the zinc acetate solution. The photocurrent properties of the patterned ZnO nanowires with high surface area, due to their unique shape, were also investigated. These specialized shapes and patterning technique increase the possibility of realizing one-dimensional nanostructure devices such as sensors and optoelectric devices.     

Polymer‐Decorated Carbon Nanotubes as Transducers for Label‐Free Photonic Biosensors

A biosensor taking advantage of the optical properties of sorted carbon nanotubes has been developed. A polyfluorene polymer bearing azido groups was synthesized and used for the selective extraction of semi‐conducting nanotubes from the bulk population. The resulting polymer‐decorated nanotubes were then conjugated by click‐chemistry to a ligand unit (biotin), and the sensing properties of the biotinylated nanotubes were investigated by photoluminescence measurements, upon interaction with the streptavidin target.