Sulfonated polyaniline–titanium dioxide nanocomposites synthesized by one-pot UV-curable polymerization method

Sulfonated polyaniline–titanium dioxide (SPAni–TiO₂) hybrid composites have been synthesized by using a new strategy in one-pot system of UV-cured polymerization method. Aqueous solution of aniline and orthoanilinic acid comonomers, a free-radical oxidant and titania precursor were irradiated by UV rays. Hydrolysis and reprecipitation of the titania precursor in aqueous aniline and orthoanilic acid lead to the formation of titanium dioxide particles which in turn catalyze oxidation of comonomers to sulfonated polyaniline. The resultant SPAni–TiO₂ composites were characterized by using different spectroscopy analyses like X-ray diffraction, UV–visible (UV–vis) and infrared spectroscopy. The UV–vis absorption bands revealed that SPAni–TiO₂ nanocomposites are optically active and the blue-shifted peaks due to the presence of titania within the SPAni matrix. Scanning electron microscopy and transmission electron microscopy of the nanocomposite showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the SPAni–TiO₂ composites have a good thermal stability than the pristine SPAni.     

Self-assembled polyaniline 12-tungstophosphate micro/nanostructures

Polyaniline (PANI) micro/nanostructures were synthesized by the external-template-free oxidative polymerization of aniline in aqueous solution of 12-tungstophosphoric acid (WPA), using ammonium peroxydisulfate (APS) as an oxidant and starting the oxidation of aniline from slightly acidic media (pH 5.4–5.9). The effect of the initial weight ratio of WPA to aniline on molecular structure, morphology, and physicochemical properties of polyaniline 12-tungstophosphate (PANI-WPA) was investigated by FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and conductivity measurements. The morphological change of polymerization products during a single polymerization process, from non-conducting submicro-/microspherical oligoaniline intermediates to semiconducting PANI-WPA consisted of self-assembled nanotubes and/or nanorods co-existing with submicro-/microspheres, has been revealed by SEM and TEM. The average diameter of nanorods in PANI-WPA samples decreased with increasing the initial WPA/aniline weight ratio. The incorporation of 12-tungstophosphate counter-ions into PANI matrix has been proved by FTIR, Raman and ICP-OES spectroscopies, TGA and DTA analysis. Electrical conductivity of PANI-WPA increased in the range (2.5–5.3) × 10^?3 S cm^?1 with the increase of the initial WPA/aniline weight ratio. The presence of branched structures and phenazine units besides the ordinary paramagnetic and diamagnetic emeraldine salt structural features in PANI-WPA was proved by FTIR and Raman spectroscopies.     

Gas sensing properties of layer-by-layer self-assembled ultrathin film of polyaniline/titanium dioxide

Electrostatic layer-by-layer (LbL) self-assembly (SA) was realized with processable polyaniline prepared with polystyrene sulfonic acid as a template (PANI-PSSA) and titanium dioxide sol as the starting materials, resulting in an ultrathin film of PANI-PSSA/TiO₂. The SA process was confirmed by UV–vis spectra and quartz crystal microbalance measurements. The composite ultrathin film was characterized by X-ray photoelectron spectroscopy, X-ray diffraction patterns, field-emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. It was revealed that the content of TiO₂ in the composite film was much higher than that of PANI-PSSA, and the doping level of PANI-PSSA was as high as 19.1%. Gas sensors were fabricated by depositing self-assembled ultrathin film of PANI-PSSA/TiO₂ on interdigital gold electrodes, then covering another layer of PANI-PSSA via dip-coating. Electrical response to NH₃ of the sensor was investigated at room temperature. Gas sensitivity of the sensor was found to closely relate to the number of self-assembled bilayers. Under optimal conditions, the sensor displayed high sensitivity (26.5% and 81.2% towards NH₃ of 10 and 100 ppm, respectively), fast response (response time ∼ 1 min; recovery time ∼ 2 min), good reversibility and repeatability.     

Formation of nanocomposites of platinum with nanotubular titanium dioxide

Metal oxide nanocomposites of platinized titania nanotube arrays (Pt-TNT) have been formed via electrochemical anodization-precipitation. Initially, the vertically aligned amorphous TiO₂ nanotube arrays (TNTs) were formed in accordance with potentiostatic electrochemical anodization of titanium with the use of 1 M H₂SO₄ + 0.3% HF electrolyte. Then, using the potentiostatic and pulse electrodeposition, precipitates of Pt on TNT were formed from 0.04 M solution of chloroplatinic acid (CPA). It has been shown with the use of SEM and Raman spectroscopy that, in order to prepare functional metal oxide Pt-TNT nanocomposites, pulse electrodeposition and subsequent annealing at 400°C are preferable, because they lead to TNTs that are homogeneously distributed along the surface and in bulk (with anatase structure) for platinized layers and conglomerates.     

Self-assembled necklace-like polyaniline nanochains from elliptical nanoparticles

High quality necklace-like polyaniline nanochains assembled by elliptical nanoparticles have been synthesized in chitosan aqueous solution by a facile dispersion polymerization method. The synthetic procedure is very simple and easy to scale up. The necklace-like nanochains coated by a layer of chitosan are typical doped polyaniline in its emeraldine salt form, which is easy to form stable polyaniline dispersion in water. Open-circuit potential measurements show that the rate of polymerization of aniline has a substantial decrease due to the steric effects of chitosan. The synthetic parameters, such as reaction times, and the concentrations of chitosan, aniline, and dopant acid, have profound influences on the sizes and morphologies of polyaniline nanostructures. A new self-assembly process of elliptical nanoparticles has been proposed for the formation of necklace-like polyaniline nanochains with fluctuant diameters, which is different from that of other one-dimensional polyaniline nanostructures including nanofibers and nanotubes.     

Synthesis, characterization and microwave absorption property of doped polyaniline nanocomposites containing TiO2 nanoparticles and carbon nanotubes

As nanomaterial possessing moderate conductivity, magnetic and dielectric property, novel hexanoic acid (HA)-doped polyaniline (PAni) nanocomposites containing TiO₂ nanoparticles (dielectric filler) and carbon nanotubes, CNTs (magnetic fillers such as single-walled carbon nanotube, SWNT and multi-walled carbon nanotube, MWNT) were prepared by template free method. The PAni were characterized by UV, FTIR, X-ray diffraction (XRD), thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses. Conductivity, magnetization, dielectric and microwave absorption properties of PAni were also investigated. The resulted nanorods/tubes as shown in SEM images clearly show that polymerization is proceeded in micelle/water interface through elongation. During template free method, TiO₂ and CNT exist in the center of Ani/HA micelle. The SEM images show that some of the CNT enwrapped with PAni layer indicate CNT are just packed underneath the PAni and never attacked by PAni. PAni/HA/TiO₂/SWNT with 20% of SWNT exhibits the best microwave absorption property (99.2% absorption) with reflection loss of −21.7 dB at 6 GHz due to its moderate conductivity (1.27 S/cm), magnetization (M_s = 1.01 emu/g), highest tan δ and heterogeneity.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Electrochemical preparation of chiral polyaniline nanocomposites

Optically active polyaniline colloids have been generated in high yield via the electrohydrodynamic polymerisation of aniline in the presence of 1.0 mol dm⁻³ (+)- or (−)-camphorsulfonic acid as dopant using colloidal silica (5% w/w) as dispersant and an applied potential of +0.8 V (vs. Ag/AgCl). Both the rate of polymer formation and the degree of chiral induction in the polyaniline chains were enhanced compared to colloid formation using polystyrenesulfonate (PSS) as steric stabiliser. Higher chiral induction was achieved using 10% w/w silica as dispersant, while lower silica concentrations (e.g., 2.5% w/w) led to over-oxidation. Lower (+)-HCSA concentrations (≤0.5 mol dm⁻³) also caused over-oxidation. The dispersions using 5 and 10% w/w silica were very stable, showing unchanged chiroptical properties after 3–4 months. The particle size (300–600 nm) increased with increasing polymerisation time. Transmission electron micrographs (TEM) studies on the dried PAn.(+)-HCSA/silica colloid also showed large (200–600 nm diameter) particles, which on high magnification were seen to be nanocomposites consisting of individual polymer-coated silica particles (ca. 20 nm) fused together to give a raspberry-like morphology.     

Melt blending of carbon nanotubes/polyaniline/polypropylene compounds and their melt spinning to conductive fibres

Blends of polypropylene with polyaniline and multi-walled carbon nanotubes have been prepared and melt spun to fibre filaments. The resulted filaments have been characterised regarding conductivity, morphology, thermal and mechanical properties. DSC suggests that carbon nanotubes act as nucleating sites for PP/polyaniline blend. Electrical conductivity has been measured for blends with extruded rod shape, as-spun fibre filaments and fibres made under draw ratio of four. Polypropylene containing 20 wt% polyaniline polymer modified with 7.5 wt% carbon nanotubes shows the maximum conductivity among all the samples, about 0.16 S/cm.     

Preparation and characterization of polyaniline micro/nanotubes with dopant acid mordant dark yellow GG

Polyaniline(PANI) micro/nanotubes doped with novel dopant acid mordant dark yellow GG (AMY GG) were prepared by soft template method in the presence of ammonium persulfate (APS) as an oxidant. It was found that the molar ratio of HCl to aniline and washing method of the products played key roles in the formation of PANI micro/nanotubes. Changing the molar ratio of HCl to aniline, the typical morphology of PANI could be changed from nanotubes to microtubes. In order to get the final product, different solvents were tried to wash away the by-products. After the by-products were removed by water/methonal/ether, the PANI micro/nanotubes appeared. The morphology of PANI micro/nanotubes was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical structure and thermal stability of PANI micro/nanotubes were examined by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) and the thermogravimetric analysis (TGA). The formation mechanism of PANI micro/nanotubes was also discussed.     

Morphological development of nanofibrillar composites of polyaniline and carbon nanotubes

Nanofibrillar composite of polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) is readily synthesized by means of conventional in situ polymerization process. It is found that the MWNT loading during polymerization has a significant influence on both the micro- and macro-scale morphological properties of the composites. At low MWNT loadings, PANI/MWNTs are formed as individual nanofibers, similar to that of the neat PANI in the absence of MWNTs. With the increase in MWNT loading, the composite exhibits granular form and becomes a continuous porous matrix at higher MWNT loadings. A possible mechanism is proposed to account for the structural variation of the composites caused by MWNTs at the different loadings.     

Preparation of titanium dioxide/silver sulfate powder and its antibacterial activity

Antibacterial powders of titanium dioxide/silver sulfate were produced by heat-treatment of the metatitanic acid, as precursor, into which the silver nitrate was added. The influences of heating temperature on the structure and composition of the product were investigated through XRD and SEM. The results show that the powder is spherical in the phase of TiO2-Ag2 SO4. The granularity of the particles increases from 10.7 nm to 28.7 nm with the temperature of heat-treatment increasing from 300 ℃ to 800 ℃. The antibacterial activity of the powder was judged in the way of the minimum inhibitory contents (MiCs). When the content of silver sulfate is less than 2%, the photocatalysis of titanium dioxide and silver ions cooperate to kill bacteria. And the MiCs decrease and keep around 1.0× 10-4- 1.5 × 10-4 constantly with the increase of silver content. Furthermore, the MiCs decrease with the increase of temperature of heat-treatment when the temperature is lower than 500 ℃. But when the temperature is beyond 600 ℃ the MiCs increase quickly, which shows the inferior antibacterial performance.     

超声波辐照对水合二氧化钛晶体结构和煅烧二氧化钛粒度的影响

介绍在硫酸氧钛水解过程初期引入超声波辐照,采用透射电子显微镜、X射线衍射仪和激光粒度测试技术对水解产物-水合二氧化钛及其在650℃的煅烧产物二氧化钛进行表征.结果表明:超声波辐照作用不仅促进了硫酸氧钛的水解过程而且使水解产物的晶格参数发生改变,特别是锐钛型四方晶胞的c轴从0.951 4 nm缩短到0.918 1 nm,同时,晶胞体积缩小,晶粒度减小.在煅烧以后,c轴伸长明显使原有的晶格畸变消失.与未受超声波辐照的水解产物不同,受过超声波作用的水合二氧化钛在煅烧之后其平均颗粒度减小的趋势达10%,从水合二氧化钛的0.712μm减小为0.639 μm.     

Evaluation of dispersion state and thermal conductivity measurement of carbon nanotubes/UV-curable resin nanocomposites

We describe (i) the evaluation of bundled degrees of single-walled carbon nanotubes (SWNTs) in SWNT/UV-curable resin composite films based on the intensity change in the radial breading mode (RBM) of their Raman spectra at a 785-nm excitation, and (ii) the thermal conductivity measurements of the composites films using the temperature wave analysis method. The homogeneous dispersion of the SWNTs produced a gradual increase in the thermal conductivity with an increase in the SWNT loading up to 5.0 wt%. This observed behavior is quite different from that of the electric conductivity of the composite films, in which the electric conductivities dramatically decrease at around only a 0.05 wt%-SWNT loading as previously reported.     

Opportunities in the electrowinning of molten titanium from titanium dioxide

The value chain of titanium products shows that the difference between the cost of titanium ingot and titanium dioxide is about $9/kg titanium. In contrast, the price of aluminum, which is produced in a similar way, is only about $1.7/kg. Electrowinning of molten titanium from titanium dioxide is therefore believed to have significant potential to reduce the cost of titanium products. The process is hampered by the high operating temperatures and sophisticated materials of construction required; the high affinity of titanium for carbon, oxygen, and nitrogen; and physical and chemical properties of the different titanium oxide species when reducing titanium from Ti₄₊ to metallic titanium. For more information, contact D.S. van Vuuren, CSIR, Materials and Manufacturing Technology Department, Meiring Naude Road, Pretoria, Gauteng 0181, South Africa; +27 12-841 2375; fax +27 841 2135; e-mail dvvuuren@csir.co.za.     

Magnetic properties of hydrophilic iron oxide/polyaniline nanocomposites synthesized by in situ chemical oxidative polymerization

This work describes the preparation and characterization of polyaniline (PANI)/hydrophilic iron oxide nanocomposites synthesized from monodispersed 13 nm iron oxide (Fe₃O₄) nanoparticles and aniline monomer in HCl solution by in situ chemical oxidative polymerization. Hydrophilic 13 nm spherical Fe₃O₄ nanoparticles fabricated using the thermal decomposition process were modified using 11-aminoundecanoic acid tetramethylammonium salt. The modified Fe₃O₄ nanoparticles that served as cores were dispersed in an aqueous solution with anionic surfactant dodecylbenzenesulfonic acid sodium salt to form spherical templates and the PANI/Fe₃O₄ nanocomposites were then synthesized via in situ chemical oxidative polymerization on the surface of spherical templates. Structural and morphological analysis using X-ray diffraction and high-resolution transmission electron microscopy showed that the fabricated PANI/Fe₃O₄ nanocomposites are core (Fe₃O₄)-shell (PANI) structures. The magnetic properties of PANI/Fe₃O₄ nanocomposites exhibit supermagnetism with saturation magnetization in the range of 0.23–0.91 emu/g, depending on the amount of 13 nm Fe₃O₄ nanoparticles.     

Novel Al-matrix nanocomposites reinforced with multi-walled carbon nanotubes

Novel Al-based nanocomposites reinforced with multi-walled carbon nanotubes were produced by mechanical milling followed by pressure-less sintering at 823 K under vacuum. The interface between Al matrix and the multi-walled carbon nanotubes was examined using transmission electron microscopy. These observation showed that the multi-walled carbon nanotubes were not damaged during the preparation of the nanocomposite and that no reaction products were detected after sintering. The mechanical properties of sintered nanocomposites specimens were evaluated by a compression test. The yield stress (σ_y) and the maximum strength (σ_max) obtained were considerably higher than those reported in the literature for pure Al prepared by the same route. The values for σ_y and σ_max increase as the volume fraction of multi-walled carbon nanotubes increases. The milling time and the concentration of multi-walled carbon nanotubes have an important effect on the mechanical properties of the nanocomposite.     

Actuation behaviour of layered composites of polyaniline,carbon nanotubes and polypyrrole

Layered composites of polyaniline (PAn), single-walled carbon nanotubes (CNTs) and polypyrrole (PPy) were produced by coating PAn or PAn/CNT on a PPy hollow fibre containing a platinum (Pt) helix. The actuation behaviour of PAn/PPy and PAn/CNT/PPy composites was compared with that of neat PPy. The Pt helix reduces the IR drop along the fibre, thus enhancing the actuation strain. Components of the composite with low actuation strain such as PAn and/or CNT restrict the actuation displacement of the PPy substrate causing a reduced strain in the composite. In particular, a minimal quantity of CNT (1.3 wt.%) in the composite leads to a discernible decrease in actuation strain but also increases the Young's modulus and tensile strength of the composite. Sodium nitrate (1 M) aqueous solution used as an electrolyte gives good actuation stability where the actuation strain is almost independent of applied stress (5–12 MPa). This can be explained by the unchanged Young's modulus at the reduced (contracted) and oxidized (expanded) states during the actuation process. The polyaniline/polypyrrole composite produced the highest work-per-cycle reported to date under isotonic conditions.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.