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991.
Sonochemical Preparation of Hierarchical ZnO Hollow Spheres for Efficient Dye‐Sensitized Solar Cells
Chun‐Xiu He Bing‐Xin Lei Yu‐Fen Wang Cheng‐Yong Su Yue‐Ping Fang Dai‐Bin Kuang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(29):8757-8761
Hierarchical ZnO hollow spheres (400–500 nm in diameter) consisting of ZnO nanoparticles with a diameter of approximately 15 nm have been successfully prepared by a facile and rapid sonochemical process. The formation of hierarchical ZnO hollow spheres is attributed to the oriented attachment and subsequent Ostwald ripening process according to time‐dependent experiments. The as‐prepared ZnO hollow spheres are used as a photoanode in dye‐sensitized solar cells and exhibit a highly efficient power conversion efficiency of 4.33 %, with a short‐circuit current density of 9.56 mA cm?2, an open‐circuit voltage of 730 mV, and a fill factor of 0.62 under AM 1.5 G one sun (100 mW cm?2) illumination. Moreover, the photovoltaic performance (4.33 %) using the hierarchical ZnO hollow spheres is 38.8 % better than that of a ZnO nanoparticle photoelectrode (3.12 %), which is mainly attributed to the efficient light scattering for the former. 相似文献
992.
Marko Bitenc Peter Podbršček Dr. Pavo Dubček Dr. Sigrid Bernstorff Prof. Dr. Goran Dražić Prof. Dr. Bojan Orel Prof. Dr. Stane Pejovnik Dr. Zorica Crnjak Orel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(37):11481-11488
Layered ZnO microspheric particles were prepared by the thermal decomposition of layered hydrozincite (LZnHC), which was synthesized from zinc nitrate and urea in a water/PEG400 mixture. The influence of the starting reagents, their concentrations, and the amount of PEG in the water/PEG400 mixture on the particle growth was observed. The chemical aspect of the particle growth was proposed in the frame of the partial charge model (PCM), and the formation of [Zn(OH)2(OH2)4]0 and [Zn(OH)(HCO3)(OH2)3]0 was predicted for the solid phase. The assumed growth mechanism, which follows the “nonclassical crystallization” concept of a self‐assembling mechanism, was observed in situ by small‐angle X‐ray scattering (SAXS) and predicts the rapid formation of approximately 6 nm sized building units. The size of these nano building units, stable only in the reaction medium, remains nearly constant during the synthesis, as the concentration of the nano building units increases throughout the reaction. The nano building units connect into leaves of LZnHC with a thickness of 20 nm. These leaves of LZnHC are further agglomerated into porous, microsphere‐like particles with sizes up to 4 μm. 相似文献
993.
Basam M. Alzoubi Dr. Ralph Puchta Dr. Rudi van Eldik Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(24):7300-7308
The water‐exchange mechanisms of [Zn(H2O)4(L)]2+?2 H2O (L=imidazole, pyrazole, 1,2,4‐triazole, pyridine, 4‐cyanopyridine, 4‐aminopyridine, 2‐azaphosphole, 2‐azafuran, 2‐azathiophene, and 2‐azaselenophene) have been investigated by DFT calculations (RB3LYP/6‐311+G**). The results support limiting associative reaction pathways that involve the formation of six‐coordinate intermediates [Zn(H2O)5(L)]2+?H2O. The basicity of the coordinated heterocyclic ligands shows a good correlation with the activation barriers, structural parameters, and stability of the transition and intermediate states. 相似文献
994.
995.
Matthias Welker Simon Woodward Prof. Luis F. Veiros Prof. Maria José Calhorda Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5620-5629
Reaction of the cyclic thioacetal (RS)2CHCHO [R=1/2×? (CH2)3? ] with HCCCOMe, followed by treatment with TsCl/DABCO (Ts=tosyl, DABCO=1,4‐diazabicyclo[2.2.2]octane) affords the mono‐protected 1,4‐benzoquinone dithioacetal. The reactivity of this SR‐protected 1,4‐benzoquinone has been compared with the behavior of the analogous OR‐protected acetal in copper‐catalyzed additions of ZnMe2 by using chiral phosphoramidite ligands. The activation energy for 1,4‐methylation of the latter OR‐acetals with ZnMe2 (>95 % ee) has been determined for two CuX2 pre‐catalysts (X=OAc, 12.2 kcal mol?1; X=OTf, 6.7 kcal mol?1; Tf=triflate). The dithioacetal SR aromatizes in the presence of CuI/ZnMe2 giving 1,4‐HOC6H4S(CH2)3SMe through C? S bond formation. The disparate behavior of these two very closely related substrates is in accordance with the formation of closely related cuprate intermediates that were optimized by DFT calculations, supporting the synthetic and kinetic studies and thus defining the mechanisms of both pathways. 相似文献
996.
997.
Wei Song Xiaoxia Han Lei Chen Youming Yang Bin Tang Wei Ji Weidong Ruan Weiqing Xu Bing Zhao Yukihiro Ozaki 《Journal of Raman spectroscopy : JRS》2010,41(9):907-913
A controllable heterostructure consisting of ZnO nanorod arrays with attached Ag nanoparticles at only one end has been synthesized via a facile and convenient galvanic reduction method. Scanning electron microscopic images of these nanostructures showed good selectivity of Ag deposition on the tip of ZnO nanorod arrays. The formation of these regular Ag ZnO heterogeneous nanorod arrays can be explained by a localization of the electrons at the ends of the ZnO nanorods after the electron transfer step. By tuning the reaction time and the concentration of silver nitrate, the density of Ag nanoparticles on the tip of ZnO nanorods can be well controlled. Owing to the introduction of Ag nanoparticles with different densities, the resulting Ag ZnO heterogeneous nanorod arrays have been proved to be a versatile substrate for surface‐enhanced Raman scattering not only for common organic molecules but also for label‐free protein detection. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
998.
A new coating system of under layer for hot dip zinc coating was explored as an effective coating for steel especially for application in relatively high aggressive environments. The influence of different barrier layers formed prior to hot dip galvanization was investigated to optimize high performance protective galvanic coatings. The deposition of ZnO and Ni-P inner layers and characteristics of hotdip zinc coatings were explored in this study. The coating morphology was characterized by scanning electron microscope (SEM) analysis. The hot dip zinc coatings containing under layer showed substantial improvement in their properties such as good adhesion, and high hardness. In addition, a decrease in the thickness of the coating layer and an enhancement of the corrosion resistance were found. Open circuit potential (OCP) of different galvanized layers in different corrosive media viz. 5% NaCl and 0.5 M H2SO4 solutions at 25 ± 1 °C was measured as a function of time. A nobler OCP was exhibited for samples treated with ZnO and Ni than sample of pure Zn; this indicates a dissolution process followed by passivation due to the surface oxide formation. The high negative OCP can be attributed to the better alloying reaction between Zn and Fe and to the sacrificial nature of the top pure zinc layer. 相似文献
999.
Chandrasekar M. S. Shanmugasigamani Srinivasan Malathy Pushpavanam 《Journal of Solid State Electrochemistry》2009,13(5):781-789
Zinc–cobalt (Zn–Co) and zinc–nickel (Zn–Ni) alloy electrodeposits each prepared from acid and alkaline formulations were compared
for their properties. Compared to alkaline baths, acid baths offer higher metal percent of the alloying element and higher
current efficiency. In alkaline baths, the variation of metal percent in deposit with current density is less significant,
but that of current efficiency with current density is more. Electrolyte pH does not change significantly in alkaline solutions
compared to acid solutions. X-ray diffraction evaluation of Zn–Co deposits from both electrolytes indicated their presence
in the η-phase, while Zn–Ni shows pure γ-phase for deposits obtained from alkaline solutions and the existence of γ-phase
with traces of η-phase of zinc for deposits obtained from the acid electrolytes. Scanning electron microscope examination
shows finer grain structure for deposits obtained from alkaline solutions, and atomic force microscope studies confirm their
nanostructure with reduced surface roughness. Deposits obtained from the alkaline baths exhibited higher corrosion resistance
probably due to their nanostructure. 相似文献
1000.
Jung‐tak Jang Hyunsoo Nah Jae‐Hyun Lee Seung Ho Moon Min Gyu Kim Dr. Jinwoo Cheon Prof. 《Angewandte Chemie (International ed. in English)》2009,48(7):1234-1238
Doped up : The incorporation of Zn2+ dopants in tetrahedral sites leads to the successful magnetism tuning of spinel metal ferrite nanoparticles (see picture). (Zn0.4Mn0.6)Fe2O4 nanoparticles exhibit the highest magnetization value among the metal ferrite nanoparticles. Such high magnetism results in the largest MRI contrast effects (r2=860 mm?1 s?1) reported to date and also huge hyperthermic effects.