Synthesis of Au nanorods via autocatalytic growth of Au seeds formed by sonochemical reduction of Au(I): Relation between formation rate and characteristic of Au nanorods

The sonochemical formation of Au seeds and their autocatalytic growth to Au nanorods were investigated in a one-pot as a function of concentration of HAuCl₄, AgNO₃, and ascorbic acid (AA). The effects of ultrasonic power and irradiation time were also investigated. In addition, the formation rate of Au nanorods was analyzed by monitoring the extinction at 400 nm by UV–Vis spectroscopy and compared with the growth behavior of Au seeds to nanorods. Most of the reaction conditions affected the yield, size, and shape of Au nanorods formed. It was confirmed that the concentration balance between HAuCl₄ and AA was important to proceed the formation of Au seeds and nanorods effectively. The formation rate became faster with increasing AA concentration and dog-bone shaped nanorods were formed at high AA concentration. It was also confirmed a unique phenomenon that the shape of Au nanorods changed even after the completion of the reduction of Au(I) in the case of short-time ultrasonic irradiation for Au seed formation.     

Influence of amount of CTAB and ascorbic acid concentration on localized surface plasmon resonance property of gold nanorod

Gold nanorods (AuNRs) are prepared through seeded growth approach. Synthesis parameters of the amount of cetyltrimethylammonium bromide (CTAB), and concentration of ascorbic acid (AA) were studied. We were aiming for an aspect ratio of 3 which could be achieved by a nanorod feature in the range of 45 nm length and 15 nm width. The absorption spectra are observed with an UV–visible NIR spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse surface plasmon resonance (TSPR) and longitudinal surface plasmon resonance (LSPR), respectively. It is found that as the concentration of CTAB increases, the yield of NRs increases. As the concentration of AA increased from 0.05 to 0.2 M, LSP shifts to longer wavelength but upon further increasing the concentration, LSP shifts back to shorter wavelength. A linear relationship between LSPR wavelength and surrounding medium dielectric constant is obtained, which is in good agreement with the theoretical results.     

Shape and size transformation of gold nanorods (GNRs) via oxidation process: A reverse growth mechanism

The anisotropic shape transformation of gold nanorods (GNRs) with H₂O₂ was observed in the presence of “cethyl trimethylammonium bromide” (CTAB). The adequate oxidative dissolution of GNR is provided by the following autocatalytic scheme with H₂O₂: Au⁰ → Au⁺, Au⁰ + Auⁿ⁺ → 2Au³⁺, n = 1 and 3. The shape transformation of the GNRs was investigated by UV-vis spectroscopy and transmission electron microscopy (TEM). As-synthesised GNRs exhibit transverse plasmon band (TPB) at 523 nm and longitudinal plasmon band (LPB) at 731 nm. Upon H₂O₂ oxidation, the LPB showed a systematic hypsochromic (blue) shift, while TPB stays at ca. 523 nm. In addition, a new emerging peak observed at ca. 390 nm due to Au(III)-CTAB complex formation during the oxidation. TEM analysis of as-synthesised GNRs with H₂O₂ confirmed the shape transformation to spherical particles with 10 nm size in 2 h, whereas centrifuged nanorod solution showed no changes in the aspect ratio under the same condition. Au³⁺ ions produced from oxidation, complex with excess free CTAB and approach the nanorods preferentially at the end, leading to spatially directed oxidation. This work provides some information to the crystal stability and the growth mechanism of GNRs, as both growth and shortening reactions occur preferentially at the edge of single-crystalline GNRs, all directed by Br⁻ ions.     

In situ studies on free-standing synthesis of nanocatalysts via acoustic levitation coupled with pulsed laser irradiation

Acoustic levitation is a distinctive and versatile tool for levitating and processing free-standing single droplets and particles. Liquid droplets suspended in an acoustic standing wave provide container-free environments for understanding chemical reactions by avoiding boundary effects and solid surfaces. We attempted to use this strategy for the production of well-dispersed uniform catalytic nanomaterials in an ultraclean confined area without the addition of external reducing agents or surfactants. In this study, we report on the synthesis of gold and silver nanoparticles (NPs) via acoustic levitation coupled with pulsed laser irradiation (PLI). In situ UV–Visible and Raman spectroscopic techniques were performed to monitor the formation and growth of gold and silver NPs. The PLI was used for the photoreduction of targeted metal ions present in the levitated droplets to generate metal NPs. Additionally, the cavitation effect and bubble movement accelerate the nucleation and decrease the size of NPs. The synthesized Au NPs with ∼ 5 nm size showed excellent catalytic behavior towards the conversion of 4-nitrophenol to 4-aminophenol. This study may open a new door for synthesizing various functional nanocatalysts and for achieving new chemical reactions in suspended droplets.     

莴苣种子的生长与低温保存研究

文中主要介绍高原莴苣种子生长和低温保存时的相关性,为保护保存该种子提供理论和实验依据。种子在低温和适宜温度两种不同情况下培养,进行实验比较,得出低温预培养的种子对于低温保存无作用;快速降温下,DSC曲线出现两个波峰HTE和LTE,当温度低于LTE时,无种子发芽存活;慢速降温下,DSC曲线只有一个波峰HTE;随着温度降低,种子发芽率降低,当温度低于-40℃时,无种子存活。     

The effect of ultrasound on synthesis and energy storage mechanism of Ti3C2Tx MXene

Removal of aluminum (abbreviated to Al) accounts for the main step for synthesizing Ti₃C₂Tx MXene. To date, the synthesis of Ti₃C₂Tx MXene is hampered by the low removal efficiency of Al from Ti₃AlC₂. Ultrasound was therefore introduced to achieve efficient synthesis of Ti₃C₂Tx MXene by promoting the removal rate of Al from Ti₃AlC₂. It was found that ultrasonic aid can significantly boost the removal efficiency of Al. Additionally, distinct kinetics for the removal of Al was recognized as the advent of ultrasonic intervention: (i) the shrinking core model was used to describe the removal kinetics of Al in the case without ultrasound, whilst the shrinking particle model was capable for the case in presence of ultrasound; (ii) the activation energy for removal of Al with ultrasonic aid was 70.2 kJ/mol, indicating a chemical reaction-controlled process, whereas the corresponding value for the case without sonication was 28.1 kJ/mol, demonstrating a mixed kinetic feature of the removal process of Al. Morphological study showed that ultrasound can remove the surface-adhering reaction products and favors the formation of structures with flower-like morphology. The sample without sonication treatment exhibited typical capacitive behavior, whilst the contribution of diffusion-limited capacitance in addition to the capacitive behavior was readily observed for the sonication-treated sample. Surface chemistry study indicated the more prevalent oxidation of the sonication treated sample, which gave rise to a higher specific capacitance than those without sonication treatment.     

Facile sonochemical synthesis of tellurium and tellurium dioxide nanoparticles: Reducing Te(IV) to Te via ultrasonic irradiation in methanol

In this study, tellurium (Te) nanostructures were synthesized via a facile sonochemical method by reducing TeCl₄ to Te under ultrasonic irradiation in methanol. Moreover, by carrying out the reaction in an alkaline environment TeO₂ nanoparticles were produced. According to our knowledge, it is the first time that without secondary reducing agent Te⁴⁺ are reduced to Te. Also, the effects of ultrasonic power, irradiation time, solvent, and surfactant on the morphology and particle size of Te nanostructures were investigated. The obtained products were characterized by XRD, SEM, EDS, FT-IR and DRS.     

Large-scale synthesis and the roles of growth conditions on the formation of Zn2GeO4 nanorods

Large-scale Zn₂GeO₄ nanorods with a length of about 10 μm have been synthesized via a facile hydrothermal process in the absence of any surfactant. The synthesized nanorods are single crystals with a rhombohedral phase. The dependence on the growth conditions, such as reaction temperature, reaction time, compactness and GeO₂ concentration, of the formation, morphologies and sizes of the Zn₂GeO₄ nanostructures has been investigated. Proper selection and combination of the growth conditions are the key aspects to control the formation, morphologies and sizes of the Zn₂GeO₄ nanostructures. The nucleation and crystalline growth mechanism are proposed to explain the formation and growth of Zn₂GeO₄ nanorods. The photoluminescence spectrum of the Zn₂GeO₄ nanorods exhibits three fluorescence emission peaks centered at 421, 488 and 529 nm when the excitation wavelength is 235 nm.     

A b initio calculation of the growth of Te nanorods and Bi2Te3 nanoplatelets

In this paper the growth mechanism of a Te/Bi2Te3 novel structure is studied by ab-initio calculations. The results show that the growth of Te nanorods is determined by the adsorption energy of Te atoms on different crystalline Te surfaces. The adsorption energy of Te on the Te （001） surface is 3.29 eV, which is about 0.25 eV higher than that of Te on the Te （110）. This energy difference makes the preferential growth direction along the 〈 001 〉 direction. In addition, the higher surface energy of Bi2Te3 （110） and the lattice misfit between crystalline Bi2We3 and Te along 〈 001 〉 direction are considered to explain the growth of the Bi2Te3 nanoplatelets, in which Volmer-Weber model is used. The theoretical results are in agreement with experimental observation.     

Sonochemical immobilization of noble metal nanoparticles on the surface of maghemite: mechanism and morphological control of the products

Aqueous sample solutions containing noble metal ions (HAuCl₄, Na₂PdCl₄, H₂PtCl₆), polyethyleneglycol monostearate, and magnetic maghemite nanoparticles were irradiated with high power ultrasound. Analyses of the products showed that noble metal ions were reduced by the effects of ultrasound, and the formed noble metal nanoparticles were uniformly immobilized on the surface of the maghemite. The present “one pot process” significantly simplifies the immobilization of noble metal nanoparticles on the surface of supports, compared with the conventional impregnation method. The average diameter of immobilized Au was 7–13 nm, and the diameters of Pd and Pt were several nm. The diameters depended upon the concentration of polyethyleneglycol monostearate and the concentration of noble metal ions, but not upon the maghemite concentration, indicating the possibility of the morphological controls of the products by adjusting these preparation conditions. The measurements of the average diameters and the numbers of immobilized Au nanoparticles obtained under various conditions suggest that the nucleation of Au does not occur on the surface of maghemite, but it might occur in the homogeneous bulk solution.     

Ab initio calculation of the growth of Te nanorods and Bi2Te3 nanoplatelets

In this paper the growth mechanism of a Te/Bi$_{2}$Te$_{3}$ novel structure is studied by \textit{ab-initio} calculations. The results show that the growth of Te nanorods is determined by the adsorption energy of Te atoms on different crystalline Te surfaces. The adsorption energy of Te on the Te (001) surface is 3.29 eV, which is about 0.25 eV higher than that of Te on the Te (110). This energy difference makes the preferential growth direction along the $<001>$ direction. In addition, the higher surface energy of Bi$_{2}$Te$_{3}$ (110) and the lattice misfit between crystalline Bi$_{2}$Te$_{3}$ and Te along $<001>$ direction are considered to explain the growth of the Bi$_{2}$Te$_{3}$ nanoplatelets, in which Volmer--Weber model is used. The theoretical results are in agreement with experimental observation.     

光照法在玻璃基底上原位生长金纳米结构及其光谱性质

 以硅烷化后吸附粒径小于10 nm的金种子的玻璃片为基底,聚乙烯吡咯烷酮为还原剂,在荧光灯照射条件下还原氯金酸,制备出表面具有金纳米粒子聚集结构的基底。用原子力显微镜、扫描电镜、X射线衍射、吸收和荧光光谱研究了基底的性质。结果表明：随着光照时间增加至20 h,金种子长大为平均粒径140 nm的不规则状多晶粒子,且出现双层粒子堆叠。基底的吸收光谱上出现了由金粒子的表面等离子体激元偶极子耦合引发的强烈吸收峰,随着粒子粒径增大,耦合峰在600~800 nm波段内连续红移升高,表明耦合程度不断增强。在223 nm紫外光的激发下,基底的荧光光谱上在405 nm处出现发射峰,是由金粒子表面激发电子和空穴的复合辐射造成的,发光强度随着基底上粒子平均尺度增加而减弱。     

Inexpensive and highly controlled growth of zinc oxide nanowire: Impacts of substrate temperature and growth time on synthesis and physical properties

Zinc oxide nanowires (ZnO NWs) were synthesized using a simple reactive-evaporation method without the use of catalysts. The NWs growth was precisely controlled by adjusting the experimental conditions mainly growth times and substrate temperatures. These experimental parameters are crucial for the growth of NWs. The typical diameter and length of the highly crystalline NWs obtained are several tens and several hundred nanometers, respectively. The nature of early-stages growth, morphology, structure and photoluminescent properties of the NWs grown at low temperatures have been explained and give the basic reasons behind these growth mechanisms. Self-organized ZnO nuclei are primarily formed on FTO pits due to high density of Zn atoms. It can be ascribed to vapour-solid with an area selected growth of NWs which provide a continuous pathway for carrier transport due to direct contact with the substrate. These features are crucial for the application of electronic devices, solar cells, etc.     

Sonochemical synthesis,characterization, and effects of temperature,power ultrasound and reaction time on the morphological properties of two new nanostructured mercury(II) coordination supramolecule compounds

Two new mercury(II) coordination supramolecular compounds (CSCs) (1D and 0D), [Hg(L)(I)₂]_n (1) and [Hg₂(L′)₂(SCN)₂]·2H₂O (2) (L = 2-amino-4-methylpyridine and L′ = 2,6-pyridinedicarboxlic acid), have been synthesized under different experimental conditions. Micrometric crystals (bulk) or nano-sized materials have been obtained depending on using the branch tube method or sonochemical irradiation. All materials have been characterized by field emission scanning electron microscope (FESEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Single crystal X-ray analyses on compounds 1 and 2 show that Hg²⁺ ions are 4-coordinated and 5-coordinated, respectively. Topological analysis shows that the compound 1 and 2 have 2C1, sql net. The thermal stability of compounds 1 and 2 in bulk and nano-size has been studied by thermal gravimetric (TG), differential thermal analyses (DTA) for 1 and differential scanning calorimetry (DSC) for 2, respectively. Also, by changing counter ions were obtained various structures 1 and 2 (1D and 0D, respectively). The role of different parameters like power of ultrasound irradiation, reaction time and temperature on the growth and morphology of the nano-structures are studied. Results suggest that increasing power ultrasound irradiation and temperature together with reducing reaction time and concentration of initial reagents leads to a decrease in particle size.     

The effect of KI on the formation of Tl2E (E=S, Se) nanorods via solvothermal route

Tl₂E (E=S or Se) nanorods were synthesized via solvothermal route with the addition of KI. The products were characterized with X-ray powder diffraction patterns and transmission electron microscope images. Their optical properties were studied by UV-vis transmittance and photoluminescence spectrum. The band gap of direct forbidden transitions was found larger than that of bulk materials, because of the blue shift caused by nanometer-scale crystalline particles due to quantum confinement effects. A possible growth mechanism is proposed.     

Ultrasound assisted chitosan coated iron oxide nanoparticles: Influence of ultrasonic irradiation on the crystallinity,stability, toxicity and magnetization of the functionalized nanoparticles

Due to unique reaction conditions of the acoustic cavitation process, ultrasound-assisted synthesis of nanoparticles has attracted increased research attention. In this study, we demonstrate the effect of ultrasonic irradiation on the crystallinity, stability, biocompatibility, and magnetic properties of chitosan-coated superparamagnetic iron oxide nanoparticles (CS-SPIONs). CS solution and colloidal suspension of SPIONs were mixed and sonicated using an ultrasonic probe of 1.3 cm tip size horn, frequency (20 kHz), and power (750 W). Different samples were sonicated for 1.5, 5, and 10 min with corresponding acoustic powers of 67, 40 and 36 W, and the samples were denoted S_1.5, S_5, and S₁₀, respectively. The samples were characterized using X-ray diffractometer (XRD), Energy dispersive X-ray (EDX), Transmission electronic microscope (TEM), Fourier transform infrared spectroscopy (FTIR), Zeta sizer, and vibrating sample magnetometer (VSM). Cell cytotoxicity and cell uptake were investigated with human embryonic kidney 293 (HEK-293) cells through MTT assay and Prussian blue staining, respectively. The sharp peaks of the XRD pattern were disappearing with an increase in the sonication period but a decrease in acoustic power. EDX analysis also demonstrates that atomic and weight percentages of the various elements in the samples were decreasing with an increase in the sonication period. However, the Zeta potential (ζ) values increase with an increase in the sonication period.The saturation magnetization (M_s) of the S_1.5 before and after the coating is 62.95 and 86.93 emu/g, respectively. Cell cytotoxicity and uptake of the S_1.5 show that above 70% of cells were viable at the highest concentration and the longest incubation duration. Importantly, the CS-SPIONs synthesized by the sonochemical method are non-toxic and biocompatible.     

Heats of interaction of hydrogen with gold and platinum powders and its effect on the subsequent adsorptions of oxygen and noble gases

Exposure of pure gold powders to hydrogen flow at 125 °C and atmospheric pressure causes heat evolution accompanied by hydrogen adsorption. The exposure takes place in a flow-through microcalorimeter, in which the metal powders are purged by nitrogen flow used as an inert carrier gas. The adsorbed hydrogen is slowly desorbed by nitrogen flow. The heats of hydrogen adsorption and its uptake by the gold powder are greatly increased by its sequential treatments with micromole quantities of oxygen and noble gases, such as helium and argon. This increase does not take place if the gold treatment is confined only to oxygen, or only to pure noble gases. The radically increased hydrogen adsorption by gold is caused by a combination of its treatments with oxygen and the noble gases. Similar results were obtained with pure platinum powder exposed to hydrogen at room temperatures. Gold powder containing adsorbed hydrogen reacts very strongly with molecular oxygen/argon mixtures, generating heats of adsorption several times higher than the heat of formation of water. The heat evolution is very rapid and is not accompanied by the formation of water. These intense interactions are not observed after complete desorption of hydrogen from the gold surfaces.     

The bonding geometry of alkylsilanes on gold: Relation to surface pattern development and STM image contrast

The adsorption of methylsilane (MeSiH₃) on Au(1 1 1) was investigated using density functional theory (DFT) within a generalized gradient approximation (GGA). Two preferred chemisorption sites are identified: the hollow site and an atop site with an ejected gold substrate atom. Both of these configurations result in a tetracoordinate Si with a distorted tetrahedral geometry. The energy of adsorption is calculated allowing an analysis of the preferred binding geometry as a function of coverage. The relation of the supermolecular length scale pattern that emerges from a spinodal decomposition of the two phases arising from the two binding geometries is discussed. The pattern observed in the STM images is shown to be consistent with the local density of states calculated for the two different binding geometries.     

The effect of surface symmetry on the adsorption energetics of SCH3 on gold surfaces studied using Density Functional Theory

Adsorption of methanethiol onto the three, high symmetry gold surfaces has been studied at the density functional level using a linear combination of atomic orbitals approach. In all three cases the bond energy between the thiolate radical and surface is typical of a covalent bond, and is of the order of 40 kcal mol⁻¹. For the (1 1 1) surface the fcc hollow site is slightly more stable than the bridge site. For the (1 0 0) surfaces the four-fold hollow is clearly the most stable, and for the reconstructed (1 1 0) surface the bridge/edge sites either side of the first layer atoms are preferred. The calculated differences in binding energy between the three surfaces indicate that the thiolate will preferentially bind to the Au(1 1 0) or (1 0 0) before (1 1 1) surface, by about 10 kcal mol⁻¹. The (1 1 0) surface is slightly more favourable than the (1 0 0), although the energy difference is only 3 kcal mol⁻¹. The results suggest the possibility of selectively functionalising the different facets offered by a gold nanoparticle.     

The cooperative effect of electromigration and non-equilibrium vacancies on reactive phase growth

Phase formation under a direct current was analysed for a binary system with non-equilibrium vacancy distribution. It was shown that the non-equilibrium vacancy distribution diminishes the effect of electromigration on the phase formation process: if the electric current augments the phase growth, the resulting vacancy concentration gradient delays it; if the current opposes phase growth, the vacancy concentration gradient maintains it. A comparative analysis is presented involving the results obtained within Gösele and Tu theory (taking into consideration the finiteness of the reaction rate at interfaces).