Dielectric behavior of polyaniline synthesized by different techniques

Polyaniline doped with dodecylbenzenesulfonic acid (Pani.DBSA) was synthesized by different procedures: by a dedoping-redoping process, by one step inverted emulsion polymerization and by one step aqueous dispersion polymerization. The effect of these different techniques on the electric properties (dielectric constant, dielectric losses, and complex electric modulus) of the corresponding emeraldine base has been studied by thermal dielectric analyzer (DETA) in the temperature range −130 °C to 200 °C and in frequency range 0.03-10⁵ Hz. It was found that the preparation technique has significant influence on the dielectric properties of Pani. The different synthetic routes give rise to polyaniline with different distribution of electric relaxation process, indicating different chain structure. Emeraldine base from Pani.DBSA prepared by one step aqueous dispersion polymerization exhibits one single relaxation peak with narrow distribution whereas that prepared by inverted emulsion polymerization exhibits two relaxation peaks, indicating two-phase structure as indicated by a bimodal distribution of relaxation process. Emeraldine base from Pani.DBSA prepared by dedoping-redoping process presents an intermediary behavior. Percentage crystallinity of Pani.DBSA samples has also been investigated using wide-angle X-ray diffraction analysis. Pani.DBSA prepared by aqueous dispersion exhibited higher crystallinity degree, which agrees with the higher conductivity.     

Synthesis and characterization of polyaniline nanoparticles in the presence of magnetic field and samarium chloride

A new and economical method of preparing polyaniline (PANI) nanoparticles will be introduced in this article. Compared with conventional methods, this method is much more simple and convenient. Scanning electron microscope (SEM) shows that the diameter of particles are between 30 and 50 nm, which is in good agreement with the results of a transmission electron microscope (TEM). Polyaniline/SmCl₃/Bp, polyaniline/SmCl₃ and polyaniline/HCl were prepared in a solution containing 1.0 mol dm⁻³ aniline, 1.0 mol dm⁻³ HCl with and without 0.5 mol dm⁻³ SmCl₃, in the presence and in the absence of a magnetic field, respectively. Their conductivity, UV-vis spectra, FTIR spectra, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were investigated. Changes in UV-vis and FTIR spectra indicate a strong interaction between Samarium ions (SmCl₃) and polyaniline chains. The conductivity of PANI depends on magnetization and concentration of Sm³⁺. Polyaniline/SmCl₃/Bp has the higher degree of crystallinity than that of polyaniline/HCl.     

Enhancement of photovoltaic performance of polyaniline/graphene composite-based dye-sensitized solar cells by adding TiO2 nanoparticles

Polyaniline (PANi)-graphene composites and polyaniline-graphene/TiO₂ composites were prepared by ex-situ approach. Systematic investigation was carried out to explore photovoltaic (PV) properties of PANi-graphene and PANi-graphene/TiO₂ composite. The prepared composites were characterized using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Raman Spectroscopy and Ultraviolet–Visible (UV–Vis) Spectroscopy. The PV properties of dye-sensitized solar cells (DSSCs) prepared composites investigated by assembling materials in ITO/PANi-graphene/Al and ITO/PANi-graphene/TiO₂/Al architecture. Different PV parameters such as short circuit current, open circuit voltage, fill factor and power conversion efficiency were determined from the (Current-Voltage) IV characteristics of PV cell. The 15 wt% PANi loaded graphene composite based PV cell shows optimized power conversion efficiency of the order 6.47%. The main accomplishment of present work is that efficiency associated with 15 wt% PANi loaded graphene composite, improved further by addition of TiO₂ nanoparticles. The composite system between PANi-graphene/TiO₂ for 1 wt% of TiO₂ nanoparticles shows optimized power conversion efficiency of the order 8.63%.     

Morphology evolution of ZrB2 nanoparticles synthesized by sol-gel method

Zirconium diboride (ZrB₂) nanoparticles were synthesized by sol-gel method using zirconium n-propoxide (Zr(OPr)₄), boric acid (H₃BO₃), sucrose (C₁₂H₂₂O₁₁), and acetic acid (AcOH). Clearly, it was a non-aqueous solution system at the very beginning of the reactions. Here, AcOH was used as both chemical modifier and solvent to control Zr(OPr)₄ hydrolysis. Actually, AcOH could dominate the hydrolysis by self-produced water of the chemical propulsion, rather than the help of outer water. C₁₂H₂₂O₁₁ was selected, since it can be completely decomposed to carbon. Thus, carbon might be accounted precisely for the carbothermal reduction reaction. Furthermore, we investigated the influence of the gelation temperature on the morphology of ZrB₂ particles. Increasing the gelation temperature, the particle shapes changed from sphere-like particles at 65 °C to a particle chain at 75 °C, and then form rod-like particles at 85 °C. An in-depth HRTEM observation revealed that the nanoparticles of ZrB₂ were gradually fused together to evolve into a particle chain, finally into a rod-like shape. These crystalline nature of ZrB₂ related to the gelation temperature obeyed the “oriented attachment mechanism” of crystallography.     

Enhancing extraction rate in solid-phase microextraction by using nano-structured polyaniline coating

The decrement of equilibrium extraction time without losing extraction efficiency in solid-phase microextraction (SPME) was achieved using nano-structured coating. Polyaniline (PANI) was used as an extraction phase for the comparison of extraction capacity and equilibrium extraction time of nano- and micro-structured coatings. Polychlorinated biphenyls (PCBs) were used as model compounds to examine the extraction properties of nano- and micro-structured coatings. The results revealed that nano-structured PANI coating showed higher extraction rate and shorter desorption time than micro-structured coating, because of the larger surface area. In order to evaluate the extraction capability of prepared nano-structured PANI coating, headspace-SPME method was used for the determination of PCBs in sediment samples by GC-electron capture detector. The proposed method was validated using the certified reference material.     

In-vitro hemolytic activity and free radical scavenging by sol-gel synthesized Fe3O4 stabilized ZrO2 nanoparticles

Zirconia ceramics have attained much consideration owing to the amazing mechanical strength and white color. These properties provide an opportunity for the use in biomedical applications. In the present study, an application oriented sol-gel route was adapted for synthesis of zirconia nanoparticles. ZrOCl₂·8H₂O was used as a precursor, iron oxide (Fe₃O₄) nanoparticles (pH 2 & pH 9) as a stabilizer and de-ionized water was used as a solvent. Sol-gel synthesized iron oxide stabilized zirconia nanoparticles were prepared by varying concentrations of iron oxide nanoparticles in the range of 2–10 wt%. X-ray diffraction results showed mixed phases at all wt% with acidic pH value, while pure tetragonal phase of zirconia was observed for stabilization with 6 wt% basic iron oxide. Maximum value of dielectric constant (~80 at log f = 4) and minimum value of tangent loss (~0.66 at log f = 4) were observed for zirconia stabilized with basic 6 wt% iron oxide. Maximum value of hardness (1410 ± 10 HV) along with high fracture toughness were observed with optimized stabilization. Very weak hemolytic activity and maximum scavenging (~76) antioxidant activity was observed under optimized conditions. Thus, it can be suggested that optimized nanoparticles, i.e. tetragonal zirconia stabilized with 6 wt% of basic Fe₃O₄, can be further useful for therapeutical and pharmaceutical applications.     

Sorption of Cu2+ ions by chitin and chitosan from aqueous solutions. Molecular structure of complexes formed

The sorption of Cu²⁺ ions by chitin and chitosan from aqueous solutions has been investigated, as well as the molecular structure of the complexes formed. The static exchange capacities have been determined, equal to 3.5 and 0.25 mmole/g for chitosan and chitin, respectively, and the partition coefficients (5000 and 70 g/ml). It has been shown that in complex formation a bond with the amino group is formed as the result of the substitution of a proton in the latter. The EPR spectra of these complexes have been obtained and their radiospectroscopic parameters determined (g = 2.334,g = 2.054,A = 0.0156 cm^–1, andB = 0.0028 cm^–1 for chitin, andg = 2.231,g = 2.048,A = 0.0192 cm^–1, andB = 0.0025 cm^–1 for chitosan). For chitosan the ligands are two nitrogen atoms of the amino groups and two oxygen atoms of the hydroxyl groups in the position C³ of adjacent glucosamine rings; for chitin, the oxygen atoms of the acetyl groups take part in addition in the complex formation. The analysis of the radiospectroscopic parameters and their comparison with published data lead to the conclusion that the Cu²⁺ complex with chitosan has a tetragonal symmetry, while the complex with chitin most probably has an octahedral structure.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2305–2311, October, 1992.     

Polymerization of aniline derivatives by K2Cr2O7 and production of Cr2O3 nanoparticles

Oxidative polymerization of aniline, anthranilic acid, and aniline‐co‐anthranilic acid by potassium dichromate Cr(VI) as an oxidant in acidic medium was investigated. In this study, the polymerization process of aniline, o‐anthranilic acid as well as aniline/o‐anthranlic acid using K₂Cr₂O₇ produced, coordinated Cr(III)/polyaniline (PANI), Cr(III)/polyanthranilic acid (PAA) and Cr(III)/poly aniline‐co‐anthranilic acid (PANAA). The mechanism of polymerization reaction in the presence of dichromate was hypothesized. The precursor chromium doped polymers were characterized by TGA, FT‐IR, UV‐visible, XRD analyses. Cr₂O₃ nanoparticles size were determined using TEM analysis. The calcinations process of synthesized chromium doped PANI, PAA and PANAA yields Cr₂O₃ nanoparticles 26%, 31%, and 34% wt. respectively. Rhombohedral phase of Cr₂O₃ particles in the range from 33 to 61 nm was produced from chromium/polyanthranilic acid (PAA) and chromium/poly(aniline‐co‐anthranilic acid) PANAA. UV‐ visible analysis showed that optical band gaps (E_g) of doped poly aniline and its derivatives are in the range from1.55 to 1.80 using Tacu's law. The band gap values reveal that the doped chromium emeraldine base can be used as semiconductor materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterization and optical properties of mechanochemically synthesized molybdenum-doped rutile nanoparticles and their electronic structure studies by density functional theory

The optical and electronic properties of molybdenum (Mo) doped rutile TiO₂ prepared by the mechanochemical method were studied both experimentally and using density functional theory (DFT). The synthesized nanoparticles were characterized by XRD, TEM, EDS-MAP, and XPS. The XRD results showed the successful incorporation of Mo in the rutile crystal lattice. High-resolution TEM images illustrated a decreasing trend in the (110) d-spacing for samples doped up to 3 at%. The shift toward higher binding energies in the XPS spectra was due to the higher oxidization tendencies of Mo⁵⁺ and Mo⁶⁺ substituted in Ti⁴⁺ sites. The optical behavior of samples was examined by UV–Vis and photoluminescence spectroscopy. The bandgap energy value of rutile was reduced from 3.0 eV to 2.4 eV by 2 at% Mo doping. The DFT calculations showed a reduction of bandgap energy value of rutile to 2.35 eV with 2 at% Mo, which is in harmony with the experimental results. The creation of energy states below the conduction band because of Mo doping was identified as the reason for reducing the bandgap energy and photoluminescence emission of rutile.