Synthesis of palladium nanoparticles by sonochemical reduction of palladium(II) nitrate in aqueous solution

The sonochemical synthesis of stable palladium nanoparticles has been achieved by ultrasonic irradiation of palladium(II) nitrate solution. The starting solutions were prepared by the addition of different concentrations of palladium(II) nitrate in ethylene glycol and poly(vinylpyrrolidone) (PVP). The resulting mixtures were irradiated with ultrasonic 50 kHz waves in a glass vessel for 180 min. The UV-visible absorption spectroscopy and pH measurements revealed that the reduction of Pd(II) to metallic Pd has been successfully achieved and that the obtained suspensions have a long shelf life. The protective effect of PVP was studied using Fourier transform infrared (FT-IR) spectroscopy. It has been found that, in the presence of ethylene glycol, the stabilization of the nanoparticles results from the adsorption of the PVP chain on the palladium particle surface via the coordination of the PVP carbonyl group to the palladium atoms. The effect of the initial Pd(II) concentration on the Pd nanoparticle morphology has been investigated by transmission electron microscopy. It has been shown that the increase of the Pd(II)/PVP molar ratio from 0.13 x 10(-3) to 0.53 x 10(-3) decreases the number of palladium nanoparticles with a slight increase in particle size. For the highest Pd(II)/PVP value, 0.53 x 10(-3), the reduction reaction leads to the unexpected smallest nanoparticles in the form of aggregates.     

Self-assembly of ordered 3D Pd nanospheres at a liquid/liquid interface

A novel route for the self-assembly of nanoparticles to nanospheres at a liquid/liquid interface has been developed to prepare palladium nanospheres. It has proved that the interface offers an excellent site and plays a key role in the self-assembly of nanoparticles to nanospheres. The palladium nanospheres are characterized by electron microscopy, energy-dispersive X-ray analysis, UV-visible spectroscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy. The mechanism of the self-assembly process is also proposed.     

Synthesis and spectroscopic studies of stable aqueous dispersion of silver nanoparticles

A facile approach for the synthesis of stable aqueous dispersion of silver nanoparticles (AgNPs) using glucose as the reducing agent in water/micelles system, in which cetyltrimethylammonium bromide (CTAB) was used as capping agent (stabilizer) is described. The evolution of plasmon band of AgNPs was monitored under different conditions such as (a) concentration of sodium hydroxide, (b) concentration of glucose, (c) concentration of silver nitrate (d) concentration of CTAB, and (e) reaction time. AgNPs were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), fluorescence spectroscopy and FT-IR spectroscopy. The results revealed an easy and viable strategy for obtaining stable aqueous dispersion of AgNPs with well controlled shape and size below 30 nm in diameter.     

Flow-injection analysis of nitrate by reduction to nitrite and gas-phase molecular absorption spectrometry

Two flow-injection manifolds have been investigated for the determination of nitrate. These manifolds are based on the reduction of nitrate to nitrite and determination of nitrite by gas-phase molecular absorption spectrophotometry. Nitrate sample solution (300 microL) which is injected to the flow line, is reduced to nitrite by reaction with hydrazine or passage through the on-line copperized cadmium (Cd-Cu) reduction column. The nitrite produced reacts with a stream of hydrochloric acid and the evolved gases are purged into the stream of O2 carrier gas. The gaseous phase is separated from the liquid phase using a gas-liquid separator and then swept into a flow-through cell which has been positioned in the cell compartment of an UV-visible spectrophotometer. The absorbance of the gaseous phase is measured at 204.7 nm. A linear relationship was obtained between the intensity of absorption signals and concentration of nitrate when Cd-Cu reduction method was used, but a logarithmic relationship was obtained when the hydrazine reduction method was used. By use of the Cd-Cu reduction method, up to 330 microg of nitrate was determined. The limit of detection was 2.97 microg nitrate and the relative standard deviations for the determination of 12.0, 30.0 and 150 microg nitrate were 3.32, 3.87 and 3.6%, respectively. Maximum sampling rate was approximately 30 samples per hour. The Cd-Cu reduction method was applied to the determination of nitrate and the simultaneous determination of nitrate and nitrite in meat products, vegetables, urine, and a water sample.     

Application of a palladium hexacyanoferrate film-modified aluminum electrode to electrocatalytic oxidation of hydrazine.

A palladium hexacyanoferrate (PdHCF) film as an electrocatalytic material was obtained at an aluminum (Al) electrode by a simple electroless dipping method. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of hydrazine. The electrocatalytic oxidation of hydrazine was studied by cyclic voltammetry and rotating disk electrode voltammetry techniques. A calibration graph obtained for the hydrazine consisted of two segments (localized at concentration ranges 0.39-10 and 20-75 mM). The rate constant k and transfer coefficient alpha for the catalytic reaction and the diffusion coefficient of hydrazine in the solution D, were found to be 3.11 x 10(3) M(-1) s(-1), 0.52 and 8.03 x 10(-6) cm2 s(-1) respectively. The modified electrode was used to amperometric determination of hydrazine in photographic developer. The interference of ascorbic acid and thiosulfate were investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level of stability during electrochemical experiments, making it particularly suitable for analytical purposes.     

Nitrogen photofixation on nanostructured iron titanate films

A nanostructured iron titanate thin film has been prepared by a sol-gel method from iron(III) chloride and titanium tetraisopropylate. Energy-dispersive X-ray analysis and M?ssbauer spectroscopy suggest the presence of a Fe(2)Ti(2)O(7) phase, which was previously obtained as an intermediary phase upon heating ilmenite. In the presence of ethanol or humic acids and traces of oxygen, the novel film photocatalyzes the fixation of dinitrogen to ammonia (17 microM) and nitrate (45 microM). In the first observable reaction step, hydrazine is produced and then undergoes further photoreduction to ammonia. Oxidation of the latter by oxygen affords nitrate as the final product. Since the reaction occurs also in air and with visible light (lambda>455 nm), and since the iron titanate phase may be formed by the weathering of ilmenite minerals, it may be a model for mutual nonenzymatic nitrogen fixation in nature.     

二氧化硅负载的胂钯(0)配合物作为丙烯酸丁酯和丙烯酰胺芳基化反应高活性和高立体选择性的催化剂

A silica-supported arsine palladium(O) complex has been prepared from y-chloropropyltriethoxysilane via immobilization on fumed silica, followed by reaction with potassium diphenylarsenide and palladium chloride, and then reduction with hydrazine hydrate. The complex has been characterized by X-ray photoelectron spectroscopy (XPS) and it is a highly active and stereoselective catalyst for arylation of butyl acrylate and acrylamide with aryl halides, affording a variety of tram-butyl cinnamates and trans-cinnamamides in high yields.     

PEDOT-supported Pd nanoparticles as a catalyst for hydrazine oxidation

Composite poly-3,4-ethylenedioxythiophene (PEDOT)/palladium (Pd) films were obtained by chemical deposition of dispersed palladium nanoparticles into PEDOT conducting polymer matrix. The amounts of palladium particles incorporated into PEDOT films were estimated by electrochemical quartz crystal microbalance measurements. It was shown that palladium loading depends on the time a PEDOT film is exposed in the solution, containing Pd(II)-ions, on the concentration of Pd(II) ions and the film thickness. X-ray photoelectron spectroscopy data have confirmed the presence of metallic palladium in the polymer. The morphology of pristine and composite films as well as the size of Pd nanoparticles and their distribution were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM images, it was found that Pd particles decorated PEDOT globular structures as quasi-spherical particles, and their mean size was dependent on synthesis conditions. The nanoparticles were non-uniformly dispersed on the polymer surface. The comparison of TEM images of composite PEDOT/Pd films obtained for different times of metal loading was made. The remarkable effect of loading time on the size of particles has been established: the mean size of dominating palladium particles was close to 6–10 nm for 30 s of metal deposition, and it was getting larger with the increase of deposition time (close to 15–30 nm for 120 s). It is most likely that with prolongation of synthesis time, the deposition of palladium predominantly proceeds on the already deposited palladium clusters, resulting in the extension growth of their size. Catalytic properties of PEDOT/Pd composite films were studied in respect to hydrazine oxidation by cyclic voltammetry and voltammetry on rotating disk electrode. The obtained data allow to conclude that the process of hydrazine oxidation on PEDOT/Pd composites takes place predominantly on palladium particles, located on the surface or in the near-surface layers of the polymer. The diffusion nature of the limiting current of hydrazine oxidation on composite PEDOT/Pd film in phosphate buffer solution рН = 6.86 was confirmed, and hydrazine diffusion coefficient was calculated. The increase of the limiting currents of hydrazine oxidation with the increase of Pd deposition time was observed, resulting from the increase of the active surface area of palladium particles, acting as microelectrodes. The electroanalytical applications of these nanocomposite materials for the determination of hydrazine were demonstrated.     

Synthesis of nanosized ceria with controlled particle sizes and bandgap widths

The formation dynamics of nanosized ceria in cerium nitrate(III) and hexamethylenetetramine (HMTA) solutions has been studied for the first time using UV-visible spectroscopy. The bandgap width and particle size of CeO₂ are controlled by the synthesis duration, reaction temperature, and the concentrations and molar ratio of the reagents.     

Elaboration by high-energy ball milling of copper/palladium composite materials – characterization and electrocatalytic activity for the reduction of nitrate in alkaline medium

In this study, an original approach was explored to decorate copper particles with palladium and well-defined bimetallic copper/palladium powders were elaborated through a two-step ball milling procedure. First, copper powder was milled with previously determined optimal conditions (ball-to-powder mass ratio of 2, milling duration of 6 h under argon) in order to obtain spherical nanocrystalline copper particles with an average diameter of 800 μm. Then, an additional milling in presence of 1 at.% of palladium powder was performed, leading to the formation of Cu–Pd composite materials. Palladium surface concentrations from 3 to 62 at.% were obtained by varying both the ball-to-powder mass ratio (2:1 or 10:1) and the milling duration (from 5 to 30 min). Scanning electron microscopy, optical microscopy, X-ray photoelectron spectroscopy and X-ray diffraction analyses confirmed that the more intense the milling is, the easier the palladium diffuses into the copper matrix and smaller the palladium concentration on copper particles is. Cyclic voltammetry and electrolysis experiments showed that palladium inclusions on copper improve greatly the electrocatalytic activity for nitrate reduction in alkaline media. The key role of Pd in the Pd–Cu composite electrodes is to accelerate the reduction of nitrite, formed by the electrochemical reduction of nitrate on Cu sites. Also different nitrate electroreduction behaviors were observed at copper and copper–palladium electrodes leading to the preferential formation of nitrite or ammonia depending on the applied potential and the Pd surface concentration.     

Fabrication of a covalently attached self-assembly multilayer film based on CdTe nanoparticles

A precursor film has been fabricated from TGA (thiolglycolic acid)-stabilized CdTe nanoparticles and NDR (nitro-containing diazoresin) using electrostatic interactions and the standard layer-by-layer assembly method; covalent bonds are formed under ultraviolet irradiation. XPS provided evidence for the presence of CdTe nanoparticles within the polymer ultrathin films. UV-visible spectroscopy and FTIR spectroscopy provide evidence for the formation of a covalent linkage. Moreover, the UV-visible spectroscopy and AFM measurement support the improvement of the stability of the hybrid organic/inorganic film toward polar solvents when the linkages between the nanoparticles and polymer changed from ionic bonds to covalent bonds.     

Nucleation and growth of palladium nanoparticles stabilized by polymers and layer silicates

Palladium nanoparticles were synthesized in aqueous medium via reduction by hydrazine using various polymers (polyvinylpyrrolidone and polystyrene sulfonate) and the clay mineral hectorite as stabilizers. The kinetics of homogeneous and heterogeneous nucleation processes was studied by UV-visible spectrophotometry. The effect of the polymer and concentration of the silicate and palladium ions on particle formation rate was investigated. The size of the nanoparticles were determined by transmission electron microscopy. Both polymers and the silicate lamellae were found to be capable of stabilizing the particles. The rate of reduction is decreased by increasing amounts of stabilizing agents and increased by increasing concentrations of precursor ions. The kinetics of heterogeneous nucleation was determined by the adsorption of the palladium species at the clay mineral particles and the viscosity of the hectorite dispersion.     

硫化物纳米级粒子化膜的形成与气相性质的影响

采有偏振光反光度，紫外及可见光谱，电子显微镜形貌观察，粒子大小测定及电子衍射等方法以加系统研究硫化锌钠米级粒子化膜的制备与气相性质的影响。     

Polyaniline film formation in hexadecyl trimethyl ammonium bromide admicelles on hydrous zirconia surface

Formation of a thin polyaniline film on hydrous zirconia (ZrO2) surface was carried out using adsorbed surfactant bilayers on ZrO2 as reaction sites. Aniline was adsolubilized in hexadecyltrimethylammonium bromide (HDTAB) admicelles formed on the surface of ZrO2 by adsorption. Subsequent polymerization of the adsolubilized aniline monomer showed effective conversion of aniline to polyaniline. The formation of the polyaniline coated ZrO2 has been confirmed by UV-visible spectroscopy, FT-IR spectroscopy, and conductivity measurements. Various parameters involved during the adsorption process were studied. Selection of pH 9.0 as the pH of all experimental feed solutions was governed by the knowledge of point of zero charge (PZC) of ZrO2. Effect of aniline concentration on HDTAB adsorption was studied and it was observed that increase in aniline concentration decreased the amount of HDTAB adsorbed on ZrO2. Addition of salt (0.05 M NaCl) in the feed solution increased HDTAB adsorption and drastically reduced the effect of aniline concentration on HDTAB adsorption.     

硫化物纳米级粒子化膜的形成与气相性质的影响

采用偏振光反光度、紫外及可见光谱、电子显微镜形貌观察、粒子大小测定及电子衍射等方法加以系统研究硫化锌纳米级粒子化膜的制备与气相性质的影响．     

Carbonyl allylation of aldehydes catalyzed by a silica-supported poly-γ-diphenylarsinopropylsiloxane palladium(0) complex

A silica-supported poly-γ-diphenylarsinopropylsiloxane palladium(0) complex has been prepared from γ-chloropropyltriethoxysilane via immobilization on fumed silica, followed by reacting with potassium diphenylarsenide and palladium chloride, and then the reduction with hydrazine hydrate. The palladium(0) complex has been found to catalyze the allylation of aldehydes via the formation of π-allylpalladium complexes, using allylic chlorides as allylating agent and SnCl₂ as reducing agent. This polymeric palladium complex can be recovered and reused.     

聚N-乙烯咔唑光敏片的研制及其成像原理

对聚N-乙烯咔唑(PVK)和四溴化碳体系的电荷转移复合物在紫外光照射下光解的化学过程反应进行了研究。顺磁共振谱证明,这种光化学反应是属自由基反应过程。这种光解反应生成聚N-乙烯咔唑阳离子自由基和四溴化碳阴离子自由基,同时放出质子酸H⁺·聚N-乙烯咔唑阳离子自由基与四溴化碳进一步反应产生3-溴代聚N-乙烯咔唑。利用这些光化学反应,我们以聚N-乙烯咔唑为主要原料研制出一种光敏显示材料——PVK光敏片,其中PVK是经过改性的,成本比较便宜。采用不同的酸敏指示剂可获得多种变色片。     

Pd-Ag合金纳米线的可见光辅助简易合成及其对乙醇的电催化氧化

以硝酸钯和硝酸银为金属前驱体,乙醇和柠檬酸钠作为还原剂,聚乙烯吡咯烷酮作为稳定剂和导向剂,以普通市售白炽灯作为光源,采用简易可见光辅助液相法合成了Pd-Ag合金纳米线。通过FESEM、TEM、HRTEM、PXRD和UV-Vis等技术对样品的形貌、晶体结构和光学性质进行了表征,并通过循环伏安法和计时电流法研究了Pd-Ag合金纳米线修饰玻碳电极对乙醇的电催化氧化。与相同条件下制备的纳米钯材料相比,Pd-Ag合金纳米线具有更好的电催化活性、抗中毒性和稳定性。     

Pd-Ag合金纳米线的可见光辅助简易合成及其对乙醇的电催化氧化

以硝酸钯和硝酸银为金属前驱体,乙醇和柠檬酸钠作为还原剂,聚乙烯吡咯烷酮作为稳定剂和导向剂,以普通市售白炽灯作为光源,采用简易可见光辅助液相法合成了Pd-Ag合金纳米线。通过FESEM、TEM、HRTEM、PXRD和UV-Vis等技术对样品的形貌、晶体结构和光学性质进行了表征,并通过循环伏安法和计时电流法研究了Pd-Ag合金纳米线修饰玻碳电极对乙醇的电催化氧化。与相同条件下制备的纳米钯材料相比,Pd-Ag合金纳米线具有更好的电催化活性、抗中毒性和稳定性。     

二氧化硅负载胂钯(0)配合物催化酰氯和芳基碘与四苯硼化钠的苯基化反应

氯丙基三乙氧基硅烷依次与气相法二氧化硅、二苯胂钾、氯化钯作用, 再用水合肼还原, 合成了二氧化硅负载的胂钯(0)配合物. 该配合物是酰氯及芳基碘化物与四苯硼化钠苯基化反应的有效催化剂, 为苯基酮及不对称联苯的合成提供了简便且实用的新方法.