Removal of toxic chromate ions by the films of poly(1,8-diaminonaphthalene)

Poly(1,8-diaminonaphthalene) films, p(1,8-DAN), were electrosynthesized on a Pt electrode to study their utility in extracting Cr(VI) (as dichromate ions) from acidic aqueous solution. The electrodeposition procedure was improved by acidification of the acetonitrile electropolymerisation bath with CCl₃COOH. Possible molecular structures of electrosynthesized poly(1,8-diaminonaphthalene) were determined by means of IR spectroscopy. The mechanism of dichromate ion removal was studied by potentiometric measurements in the system Ag/AgCl/Cl^– _(std)/0.1 M HClO₄/p(1,8-DAN)/Pt, upon addition of K₂Cr₂O₇ solution. The presence and oxidation state of chromium in the polymer matrix was explored by means of energy dispersive X-ray (EDX) spectrometry.     

Modulation of electrical properties in single-walled carbon nanotube/conducting polymer composites

The preparation and electrical characterization of a new class of composite layers formed by dispersing single-walled carbon nanotubes (SWNT) in 1,8-diaminonaphthalene polymer, the poly(1,8-DAN), are described.The material was grown on the surface of Pt plates by electropolymerization of 1,8-diaminonaphthalene (1,8-DAN) monomer in the presence of nanotubes. This synthesis method allows the simultaneous deposition of both the host polymer matrix and the filler nanotubes. A series of composite films were prepared using untreated nanotubes as well as nanotubes treated with KOH, HNO₃ and HNO₃/H₂SO₄ solutions. The structural features of the nanotubes and of the films produced have been investigated using Raman spectroscopy. Insight into the nature of nanotube dispersion and nanotube-polymer association was gained by AFM and STM analysis and by FE-SEM inspection after removing the outermost portion of composite films.The charge transport in composite films is found to be strongly enhanced by the nanotube insertion. Depending on the SWNTs processing, currents up to 30 mA, higher by a factor of about 140 than those of the pure poly(1,8-DAN) films, were measured with an applied voltage of 250 mV.     

Electrochemical quartz crystal microbalance studies of polymerization and redox process of poly(1,8-diaminocarbazole) in protic and aprotic solutions

Electropolymerization and doping/undoping process of poly(1,8-diaminocarbazole) (PDACz) were investigated by cyclic voltammetry combined with electrochemical quartz microbalance (EQCM), in aqueous solution of 0.1 M HClO₄ and in 0.1 M LiClO₄ in acetonitrile. The results demonstrated that protonation of the polymer in HClO₄ strongly influences the gravimetric response obtained during polymerization as well as the mechanism of redox process of the polymer in the monomer-free solution. The data are discussed in terms of the presence of protons and ClO₄⁻ counter ions in the reduced (neutral) polymer matrix. In aprotic acetonitrile containing LiClO₄ as the supporting electrolyte, the polymer doping/undoping occurs according to the simple mechanism with exchange of anions. The gravimetric results obtained in acidic aqueous solution allowed for some revision of the scheme of the redox process proposed by the authors in the previous paper.     

Adsorption of rhodium(III) ions onto poly(1,8-diaminonaphthalene) chelating polymer: Equilibrium,kinetic and thermodynamic study

In the present work, poly(1,8-diaminonaphthalene) (poly(1,8-DAN)) was synthesized by the reaction of 1,8-diaminonaphthalene (1,8-DAN) with ammonium persulfate (APS) and then the equilibrium, kinetics and thermodynamics of rhodium(III) adsorption onto poly(1,8-DAN) were studied. Poly(1,8-DAN), Rh(III)-poly(1,8-DAN) and Rh(III)-1,8-DAN complex were characterized by UV–vis. and FTIR spectroscopy, thermal analysis, potentiometric titration and electrical conductivity. In the adsorption studies, the effects of acidity, the temperature and the concentration of rhodium(III) were examined. It was found that poly(1,8-DAN) has Rh(III) adsorption capacity (q_m) of 11.11 mg/g polymer. The adsorption data fitted better to the Freundlich isotherm then the Langmuir isotherm, and the kinetics of the adsorption fitted to pseudo second order kinetic model. The ΔG° values were calculated as ?7.33 at 20 and ?11.31 kJ/mol at 60 °C. The enthalpy (ΔH°), entropy (ΔS°) and the activation energy (E_a) of the adsorption were found as 21.335 kJ/mol, 97.057 J/mol K and 70.210 kJ/mol, respectively. It was predicted that the adsorption of Rh(III) onto poly(1,8-DAN) was an endothermic chemical adsorption process governed by both ionic interaction and chelating mechanisms. It was also observed that the adsorption of Rh(III) lowered the electrical conductivity of the pol(1,8-DAN).     

Noncovalent imprinted microspheres: Preparation,evaluation and selectivity of DBU template

1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) imprinted polymer was prepared as microspheres by precipitation polymerization method to obtain molecular recognition systems based on the noncovalent interactions between DBU template, methacrylic acid (MAA), and ethylene .glycol dimethacrylate (EDMA) in acetonitrile. ¹H NMR analysis of DBU/MAA mixture has been performed and hydrogen bonding interactions have been established. Microspheres have been characterized by FTIR studies with evidence of DBU linkage in polymer particles and by Scanning Electron Microscopy (SEM) to study their morphological properties. How pH values affect the binding capacity of imprinted polymer during the binding stage has been also discussed and results suggest that imprinted poly‐(MAA‐EDMA) behavior is related to the influence of DBU basicity during rebinding processes and the optimum pH value for binding has been found around neutral range. Binding ability of the imprinted polymer towards different concentration of DBU buffered solutions has been evaluated and compared with binding ability of the non‐imprinted polymer. A more sensitive response to the template in the imprinted system suggests that a reasonable number of specific binding sites is formed. Finally, differential selectivity towards other less strong than DBU nitrogen bases, such as pyridine, imidazole, and 1,5‐diazabicyclo[4.3.0]non‐5‐ene (DBN) has been also discussed. Our results indicate that both specific sites and basic properties are involved in the rebinding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Laterally Controlled Template Electrodeposition of Polyaniline

Polyaniline (PANi) was electrodeposited in gold-coated nanoporous alumina membranes (NAMs) by anodic polymerization of aniline. PANi deposition was followed by cathodic deposition of Ag or Cu, to form a layer of PANi–metal segmented nanowires in the NAM. The compact PANi nanowires fill the entire pore volume, providing a sharp transition from the polymer to the metal segment. The deposited metal layer enables SEM visualization of the PANi nanowire length in the membrane. Deposition of Cu on PANi nanowires occurs at potentials where the PANi is in its reduced leucoemeraldine state, with no evidence for penetration of the metal into the polymer matrix. The mechanism of metal ion reduction on the nonconducting polymer wires is not yet clear. Free-standing segmented PANi–Ag and PANi–Cu nanowires obtained by membrane dissolution show a sharp heterojunction between the polymer and metal phases and are mechanically stable. Aniline electropolymerization in the insulating NAM under a lateral potential gradient generated a thickness gradient of the PANi deposit, revealed by subsequent Cu deposition. The potential-dependent length of the PANi nanowires follows the PANi conductivity pattern, reaching a maximum in the region of stability of the conducting emeraldine phase. The results demonstrate the possibility of obtaining nonlinear graded materials using electrochemical systems showing a complex current–voltage behavior.     

Electrospinning and alignment of polyaniline‐based nanowires and nanotubes

Polyaniline (PANi) nanowires and nanotubes are processed by electrospinning. Nanowires are electrospinned using PANi/PEO and PANi/PMMA polymer blends. The morphology and composition of these nanofibers are determined by scanning electron microscopy (SEM) and Nano‐Secondary Ion Mass Spectrometry (Nano‐SIMS). The conductive polymer seems more homogeneously distributed for the PANi/PEO than for the PANi/PMMA blend nanowires, which exhibit a phase separation. On the other hand, pure PANi nanotubes are prepared using PMMA nanowires as a template. The synthesis is followed by X‐ray photoelectron spectroscopy (XPS), SEM and Nano‐SIMS. Moreover, a simple method based on electrostatic steering allows us to align these fibers on a substrate. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

In-situ polymerization of styrene in AAO nanocavities

One of the most promising aspects of the anodic aluminium oxide (AAO) template is the ability to generate a variety of different hierarchical one-dimensional (1D) polymer morphologies with structural definition on the nanometric scale. In-situ polymerization of monomers in reduced space of porous AAO template nanocavities can give rise to the direct production of versatile polymer nanostructures. In this work, porous AAO devices of 35 nm of diameter have been obtained by a two-step electrochemical anodization process and used as a nanoreactor to study the radical polymerization kinetics of styrene (St) in confinement and the results compared to those of polymerization in bulk. SEM morphological study has been conducted to establish the final structure of obtained polymer nanostructures. Confocal Raman microscopy has been performed to study the formation of the polymer through the AAO cavities as a function of time and with this methodology it has been possible to establish the monomer conversion for styrenic polymerization in AAO devices. Polystyrene obtained in the nanoreactor was characterized by SEC, NMR, TGA and DSC and the properties compared with those of bulk polymer. It was found that both the average molecular weights and polydispersity index of nanostructured polymer are lower than those obtained for bulk polymer. NMR studies have shown that the use of a reactor with nanometric size dimensions gave the obtained polystyrene greater stereospecificity than that obtained in bulk. Thermal stability and glass transition temperature (T_g) values are higher for nanostructured than bulk polymers. Moreover, the methodology proposed in this work, using AAO nanocavities as nanoreactors for polymerization reaction, can be generalized and applied to obtain polymer nanostructures of very different chemical nature and morphology by choosing the appropriate monomer or monomer reactants and by tailoring the dimension of AAO cylindrical nanocavities, that is, diameter from 20 to 400 nm and length from a few to hundreds of microns.     

High thermal conductivity of polyethylene nanowire arrays fabricated by an improved nanoporous template wetting technique

Generally polymer bulk structures and nanostructures are thermally insulative. In this study, we show that an improved nanoporous template wetting technique can prepare thermally conductive polymer nanowire arrays. The thermal conductivities of the fabricated high-density polyethylene (HDPE) nanowire arrays with diameters of 100 nm and 200 nm, measured by a laser flash method, are about 2 orders of magnitude higher than their bulk counterparts. The estimated thermal conductivity of a single HDPE nanowire is as high as 26.5 W/mK at room temperature. The high orientation of chains of the HDPE nanowires may arise from the integrative effects of shear rate, vibrational perturbation, translocation, nanoconfinement and crystallization. Findings in this study provide useful strategies on enhancing the intrinsic thermal properties of polymer nanostructures.     

溶剂交换法制备一维有机纳米材料

利用溶剂交换法制备了几种有机小分子化合物的一维纳米材料,并分别用SEM、TEM、XRD等对其结构进行了表征.分析了纳米材料的生长过程,讨论了有关的机理,并研究了其吸收光谱和荧光光谱等光物理行为.结果显示,有机纳米结构的形貌和尺寸对分子聚集体的光谱性质具有调制作用,使得它们展示出不同于溶液和体材料的优良纳米特性.     

Formation of polymer nanowires through electropolymerization of polybithiophene from mixed electrolyte solutions of tetrabutylammonium hexafluorophosphate and tetrabutylammonium chloride

Preparation of one-dimensional conducting polymer structures such as nanowires and nanotubes require anisotropic growth conditions. Usually, such conditions are achieved by applying a certain template or by patterning the substrate. In this work, we employ a new approach to facilitate the anisotropic growth of electrochemically deposited polybithiophene through variations of the conductivity of the growing material. If the deposited material varies in conductivity, the areas with less conducting material will sustain little or no electrochemical current and only the areas with sufficient conductivity will experience further growth. In this work, the conductivity variations and the resulting anisotropic growth are achieved by performing electropolymerization in mixed electrolyte solutions of tetrabutylammonium hexafluorophosphate and tetrabutylammonium chloride. No growth can be observed in pure tetrabutylammonium chloride because the resulting films are insulating. However, addition of small amounts of tetrabutylammonium hexafluorophosphate was found to selectively activate local nanometer-sized areas of the polymer surface where polymer nanowire growth was observed. The latter was confirmed by atomic-force microscopy (AFM). The local properties of the polymer nanostructures obtained with varying contents of tetrabutylammonium hexafluorophosphate were characterized.     

Electrochemical synthesis of CdS nanowires by underpotential deposition in anodic alumina membrane templates

Cadmium sulfide (CdS) nanowires were electrosynthesized within the pores of the anodic alumina membranes (AAM) using underpotential deposition (UPD) through an electrochemical co-deposition at room temperature (25 °C). The nanowire arrays were grown from an aqueous solution of CdSO₄, ethylenediaminetetraacetic acid (EDTA), and Na₂S at pH 4.0. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis absorption spectroscopy, and energy dispersive spectroscopy (EDS) were employed to characterize the nanowires. These nanowires have uniform diameters of approximately 90 nm, and their lengths are up to 7 μm. XRD analysis reveals that the electrosynthesized nanowires deposited at −500 mV (vs. Ag/AgCl) have a preferential orientation along (1 1 0) direction for hexagonal crystal. Electrochemical and EDS results of the deposits confirm that the atomic ratio of Cd to S is very close to 1:1 stoichiometry. UV-vis absorption measurement shows a blue-shifted absorption at 488 nm because of the quantum confinement at low dimensions.     

Template-assisted nanostructure fabrication by glancing angle deposition: a molecular dynamics study

In the present work, we investigate the pre-existing template-assisted glancing angle deposition of Al columnar structures on Cu substrate by means of molecular dynamics simulations, with a focus on examining the effect of deposition-induced template deformation on the morphologies of the fabricated structures. Our simulations demonstrate that the pre-existing templates significantly intensify the shadowing effect, which thus facilitates the formation of columnar structures under small deposition flux. The underlying deformation modes of the templates under different deposition configurations are analyzed and are correlated to the geometrical characteristics of the columnar structures. It is found that the template height-dependent deformation behavior of the templates strongly influences the morphologies of the fabricated columnar structures. Our findings provide design and fabrication guidelines for the fabrication of one-dimensional nanostructures by the template-assisted deposition technique.     

The effect of electroless bath pH on the surface properties of one-dimensional Ni–P nanomaterials

In this research, the one-dimensional Ni–P nanomaterials was formed on alumina substrate. The effect of electroless bath pH on the surface properties of one-dimensional Ni–P nanostructures was investigated. For evaluation of morphological properties and chemical composition of deposits, scanning electron microscopy (SEM) analysis, which coupled with energy disperse spectroscopy (EDS) were used. Two-step anodization for alumina substrate was selected as the best sample for producing the one-dimensional Ni–P nanomaterials. The electroless coating was carried out at different pH = 4.5, 5.5 and 6.5 values. The results showed that in all samples, due to the high Ni–P deposition rate, the Ni–P nanomaterials does not fill the entire channel path. By increasing the pH value, the one-dimensional nanomaterials were changed from nanowire to nanotube type. Also, by increasing the pH value, despite increasing the length of Ni–P nanomaterials, but the compactness of this material was reduced. So, the optimum pH value for producing the one-dimensional Ni–P materials was 4.5. On the other hand, by reducing the pH value, the crystallinity degree of Ni–P deposits was increased. The pH content trends along the nanomaterials length were indicated that the phosphorus content toward the bottom of channel was increased.     

Polymerization of hexamethyldisiloxane by plasma on activated charcoal: Investigation of parameters

The polymerization of hexamethyldisiloxane by plasma (glow discharge) on activated charcoal was investigated. The effects of discharge power, discharge duration, and monomer flow rate on polymer deposition were examined. Maximum deposition was observed when the applied power, monomer flow rate, and discharge duration were 20 W, 50 cm³/min, and 1 h, respectively. The deposited film was investigated by IR, SEM, and ESCA. The same tests were also carried out for plasma-induced polymer deposits.     

脉冲电沉积制备InSb/Sb超晶格纳米线阵列

采用脉冲电沉积技术在氧化铝模板中制备得到直径60 nm的InSb/Sb超晶格纳米线阵列,并运用扫描电镜、透射电镜和电子能谱仪对其形貌与结构进行了表征与测试。高度有序的InSb/Sb超晶格纳米线长度约为40 μm,其长径比超过600。实验中,通过改变沉积电压与时间达到了对超晶格纳米线组分与结构的控制, 纳米线阵列中In与Sb的原子质量比接近于1/2,在每个周期中,InSb的厚度为12 nm,Sb相似文献   

多元氧化物纳米丝阵列的电泳沉积

以多孔氧化铝(porous alumina)为模板,用电泳沉积技术组装了高度有序的钛酸钡(BaTiO3)、钛酸锶(SrTiO3)、锆钛酸铅(lead zirconate titanate,PZT)等多元氧化物纳米丝阵列.用扫描电镜(scanning electron microscope,SEM)、透射电镜(transmission electron microscope,TEM)、选区电子衍射(selected area electron diffraction,SAED)、X射线衍射(x-ray diffraction,XRD)等手段表征多元氧化物纳米丝阵列.SEM照片显示:所得纳米丝连续、致密,纳米丝直径略小于模板孔径且模板填充率很高.XRD和SAED显示:纳米丝为多晶钙钛矿型结构.因此,电泳沉积法是一种很有发展前途的制备氧化物纳米丝阵列的方法.     

Towards TiO2-conducting polymer hybrid materials for lithium ion batteries

Nanocomposites of TiO₂ (anatase) with polypyrrole (Ppy) or poly(3,4-ethylenedioxythiophene) (PEDOT) were prepared via electrochemical routes. The deposition process of the conducting polymer films was performed in the presence of perchlorate, p-toluenesulphonate (TOS) or bis(trifluoromethylsulphonyl)imide (TFSI) anions in propylene carbonate (PC). The obtained electrode materials were characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). An improvement of lithium ion intercalation/de-intercalation properties of titanium(IV) oxide as a result of its interfacing with the polymers is evidenced. This effect was strongly dependent on the thickness of the polymer layer and closely related to the polymer facility for transporting of lithium ion. Polypyrrole properties, in contrast to the PEDOT case, are very sensitive to selection of the substrate material (Pt or Pt/TiO₂) during electropolymerization. Polypyrrole deposited on a rough surface exhibits an improvement in its ion exchange abilities. The impact of underlying TiO₂ layers on Ppy properties has an indirect (synergic) influence on the effectiveness of lithium ion intercalation into the oxide too. The properties of the composites were discussed also in view of the comparative electrochemical quartz crystal microbalance (EQCM) study focussing on ion transport properties of Ppy and PEDOT.     

Influence of electrodeposition techniques on Ni nanostructures

Different Ni nanostructure arrays were fabricated by pulsed electrodeposition from a Watts bath inside the pores of anodic alumina membrane (AAM) templates. Under a trapezoidal waveform of potential, consisting of fast linear sweeps between 0 and −3 V (SCE) interleaved by delay times at 0 (10 s) and −3 V (0.1 s), Ni nanowires were grown. The rate of nanowires growth was constant up to 60 min of deposition. For longer times, the growth of nanowires was not uniform, and after about 180 min some nanowires reached the template surface exposed to the electrolyte. Under square potential pulses between the same potentials (pulse length 1 s), nanotubes of Ni are obtained. Morphological analysis of these nanostructures at different lengths revealed that the inner profile of nanotubes evolved from cylindrical to conical with increasing deposition time. The possibility to grow either nanowires or nanotubes in dependence of the potential waveform, as well as the growth rate of nanostructures were discussed taking into account the reaction of hydrogen evolution, occurring simultaneously with Ni electrodeposition.