Electrochemical nitrite nanosensor developed with amine- and sulphate-functionalised polystyrene latex beads self-assembled on polyaniline

Aniline doped with polyvinyl sulphonate (PV-SO₃⁻) was electropolymerised on screen printed carbon (SPCE) and glassy carbon (GCE) electrodes. Then nano-structured polystyrene (PS_NP) latex beads functionalised with amine (PS_NP-NH₂) and sulphate (PS_NP-OSO₃⁻) were self-assembled on the modified SPCE and GCE. The resultant polyaniline nanocomposites (PANI|PS_NP-NH₂ or PANI|PS_NP-OSO₃⁻) were characterised by cyclic voltammetry (CV), UV-vis spectroscopy and scanning electron microscopy (SEM). Brown-Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations of the order of 10⁻⁸ mol cm⁻². UV-vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid π-π* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that are <100 nm in diameter. When applied as electrochemical nitrite sensor, sensitivity values of 60, 40 and 30 μA/mM were obtained for electrode systems containing PANI|PS_NP-NH₂, PANI and PANI|PS_NP-SO₃⁻, respectively. The corresponding limits of detection of the sensors were 7.4, 9.2 and 38.2 μM NO₂⁻.     

The role of DNA in PANI–DNA hybrid: Template and dopant

We exposed a novel method by using DNA as the dopant as well as template at the same time to prepare PANI–DNA hybrid micro/nanowires with conductivity as high as 10⁻² S cm⁻¹. The high conductivity is due to the co-doping function of DNA with HCl produced by FeCl₃. It is found that the morphology and conductivity of the PANI–DNA hybrids are affected by the [DNA]/[AN] ratio due to the co-operation and competition of DAN's dopant and template function, and the role of DNA in PANI–DNA hybrid varies with the changing of [DNA/[AN] ratios.     

Carboxylic acid-functionalized, core-shell polystyrene@polypyrrole microspheres as platforms for the attachment of CdS nanoparticles

Polypyrrole-coated polystyrene latex particles bearing N-carboxyl functional groups (PS@PPyCOOH) were prepared by the in-situ copolymerization of pyrrole (Py) and the active carboxyl-functionalized pyrrole (PyCOOH) in the presence of 390 nm diameter-sized polystyrene (PS) latex particles. Uncoated PS particles were prepared by emulsion polymerization of styrene. The initial comonomer fractions (in mol%) were 25/75, 50/50, 75/25 and 100/0 for pyrrole and PyCOOH, respectively. The PS@PPyCOOH_x particles, where x stands for the initial molar fraction of PyCOOH (x = 0, 25, 50 or 75%), were characterized in terms of particle size, surface morphology, chemical composition and electrochemical redox activity using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), FTIR, TGA and cyclic voltammetry respectively. TEM showed an increase of the latex particle diameter after coating by the conducting polymer layer, from 390 nm for uncoated PS to 430 nm for PS@PPyCOOH₅₀ particles, allowing an estimation of the PPyCOOH shell thickness to 20 nm. FTIR and XPS detected PyCOOH repeat units at the surface of the latex particles, indicating that this monomer had indeed copolymerized with pyrrole. The core-shell structure of the PS@PPyCOOH_x particles was confirmed by etching the polystyrene core in THF, leading to the formation of hollow conducting polymer capsules. Positively charged CdS nanoparticles were electrostatically assembled onto the surface of PS@PPyCOOH₅₀ particles, as a function of pH. It was found that, contrarily to unfunctionalized PPy-coated latex particles, PS@PPyCOOH₅₀ particles could be evenly decorated with stabilized CdS nanoparticles, at pH 5.The films of the PS@PPyCOOH@CdS-coated ITO electrodes are shown to be electroactive and electrochemically stable.     

Construction of Z-scheme type CdS–Au–TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The Z-scheme type CdS–Au–TiO₂ hollow nanorod arrays have been constructed on glass substrates by following these simple steps: firstly, highly ordered TiO₂ hollow nanorod arrays (THNAs) were synthesized by liquid phase deposition (LPD) using ZnO nanorod arrays as templates; then both Au core and CdS shell nanoparticles were achieved on the THNAs by in situ photodeposition. The prepared three-component films were characterized by field-emission scanning electron microscopy (FSEM), high-resolution transmission electron microscope (HRTEM), Raman scattering and ultraviolet–visible absorption spectrum. The results showed that Au–CdS core–shell nanoparticles were well dispersed on wall of anatase THNAs from top to bottom. The three-component nanojunction system was evaluated for their photocatalytic activity through the degradation of methylene blue (MB) in aqueous solution. It was found that the CdS–Au–TiO₂ three-component hollow nanorod arrays exhibited significantly enhanced photocatalytic activity compared with single (THNAs) and two components (Au-THNAs or CdS-THNAs) systems. Reasons for this enhanced photocatalytic activity were revealed by photoluminescence (PL) results of our samples.     

Preparation of polyaniline-poly (p-styrenesulfonic acid) composite by post-polymerization and application as positive active material for a rechargeable lithium battery

Polyaniline (PANI)-poly (p-styrenesulfonic acid) (PSS) composite was prepared by thermal post-polymerization of PANI-p-styrenesulfonic acid (SSA) composite. A PANI–SSA composite was prepared by mixing PANI/N-methyl-2-pyrrolidinone solution with SSA aqueous solution. The PANI–SSA composite film was prepared by casting the composite onto an ITO glass plate. The cast film was converted to PANI-PSS film by heating at 100°C for 3h (post-polymerization process). The PANI–PSS modified ITO electrode showed electrochemical responses based on the redox reaction of PANI–PSS composite in the organic electrolyte solution, for example, propylene carbonate containing 1moldm–3 LiClO4. The PANI–PSS composite was a cation -doping polymer composite. The composite was also modified on a porous carbon material (Reticulated Vitreous CarbonTM, RVC, Energy Research and Generation, Inc.). The PANI–PSS modified RVC electrode showed similar electrochemical behaviour as the PANI–PSS modified ITO electrode. Model secondary lithium cells, Li|1moldm–3 LiClO4-propylene carbonate|PANI–PSS modified RVC electrode, were constructed and charge–discharge cycling tests were carried out. The cell showed about 60% coulombic efficiency under high current density cycling conditions (3.8Ag–1, per gram of PANI–PSS modified RVC electrode).     

Stability of polyaniline synthesized by a doping–dedoping–redoping method

Stability, including thermal stability, conductivity stability in air and after thermal treatment (100–200°C), of the polyaniline (PANI) films synthesized by a doping–dedoping–redoping method was investigated. It was found that thermogravimetric analysis (TGA) curves undergo three steps: loss of water or solvent, dedoping and decomposition, and those depend on the counterions. Compared with PANI films doped with camphor sulfonic acid (CSA) in m‐cresol, the thermal stability of the doped PANI films is improved by the new method, and thermal stability in the order of PANI–H₃PO₄ > PANI–p‐TSA > PANI–H₂SO₄ > PANI–HCl, PANI–HClO₄ > PANI–CSA was observed. The conductivity of the doped PANI films at room temperature was reduced after thermal treatment, and it is dependent of the counterions. It was found that the conductivity stability of PANI–p‐TSA and PANI–CSA is the best below 200°C. When the doped PANI films were placed in air, their conductivity decrease slowly with time due to deproton, and also depends on the counterions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 615–621, 1999     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Preparation of mesoporous benzene–silica nanoparticles

Nanoparticles of periodic mesoporous organosilica (PMO) with benzene bridging groups were prepared using a 1,4-bis(triethoxysilyl)benzene organosilica precursor and mixed surfactant templates composed of a poly(ethylene oxide)–poly(dl-lactic acid-co-glycolic acid)–poly(ethylene oxide) (PEO–PLGA–PEO) triblock copolymer and a fluorocarbon surfactant under acidic conditions. Mesoporous organosilica particles clearly exhibited a nanoscale diameter of 50–1000 nm by scanning electron microscopy. Moreover, these particles possessed a mesostructure with uniform pores in the range of 6.3–6.6 nm and core-shell type spherical morphology, which were confirmed by Synchrotron small angle X-ray scattering, transmission electron microscopy, and nitrogen adsorption analysis. Benzene bridging groups linked covalently to Si atoms were analyzed by solid state ¹³C- and ²⁹Si MAS NMR.     

Polyaniline-carbon composite films as supports of Pt and PtRu particles for methanol electrooxidation

Vulcan XC-72 carbon black particles (average size: ca. 50 nm) was incorporated into polyaniline (PANI) matrix by an electrochemical codeposition technique during the electropolymerization process. The doping by carbon particles leads to a higher polymeric degree and a lower defect density in the PANI structure. Furthermore, the incorporation of carbon particles not only increases the electrochemical accessible surface areas (S_a) and electron conductivity of the PANI film, but also decreases charge transfer resistance at PANI/electrolyte interfaces. Therefore, as expected, a fabricated PANI + C composite film with dispersed Pt and PtRu particles exhibited excellent electrocatalytic activity for methanol oxidation due to better Pt dispersion and utilization. The PANI + C composite film is more promising as a support material in electrocatalysis than a PANI film. Meanwhile, a new application for regular carbon black as a doping material into conducting polymer for electrocatalysis was thus demonstrated.     

Investigation of Co–B–S system as anode material for secondary alkaline battery

A series of novel Co–S–B systems were prepared by simple chemical reduction method as the anode material for secondary alkaline batteries. The prepared samples were investigated by inductivity coupled plasma optical emission spectrum (ICP), Brunauer–Emmetr–Teller (BET) method, scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectroscopy (EDS) and charge–discharge method. It was found that the BET surface area of Co–S–B system increases and its particle size decreases with increasing the sulfur content. Sulfur incorporation suppresses initial capacity fading of Co–B compound due to irreversible dissolution of boron, and Co–S–B electrodes show enhanced electrochemical capacity and excellent cycle performance. The discharge capacity of Co_75.4B₁₇S_7.6 reaches 513.6 mAh/g at a moderate current density of 100 mA/g and 470 mAh/g after 60 cycles, which is about 1.5 times that of conventional AB₅-type alloy. A proper mechanism was proposed to explain the electrochemical reaction process of Co–S–B electrode.     

Monolayer and bilayer conducting polymer coatings for corrosion protection of steel in 1 M H2SO4 solution

In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H₂SO₄ solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings.     

Preparation of ordered porous SnO2 films by dip-drawing method with PS colloid crystal templates

Ordered macroporous SnO₂ thin films were fabricated by using colloid crystal template of polystyrene (PS) spheres. Efficient dip-drawing method was used in both PS template assembly and the fabrication of porous structure. The PS templates were orderly assembled on clean glass substrates through colloid crystallization of monodisperse PS latex spheres, which were synthesized by an emulsion polymerization technique. The porous SnO₂ thin films were prepared through filling SnO₂ precursor sol into the spaces among the close-packed PS templates, and then annealing at 500 °C to remove the PS spheres and form SnO₂ crystal wall. The forming mechanism of PS templates through dip-drawing method was explained based on three driving forces existing in the assembly processes. The SnO₂ sol concentration and PS sphere size had important effects on formation of ordered porous structure The X-ray diffraction (XRD) spectra indicated the thin film was rutile structure and consisted of nanometer grains. The transmittance spectrum showed that optical transmittance kept above 80% beyond the wavelength of 440 nm. Optical band-gap of the porous SnO₂ film was 3.68 eV.     

Performance of sol–gel Titanium Mixed Metal Oxide electrodes for electro-catalytic oxidation of phenol

Mixed metal oxides SnO₂–RuO₂–IrO₂, Ta₂O₅–IrO₂ and RhO₂–IrO₂ were immobilised on a Ti substrate using sol–gel techniques. The Ti mixed metal oxides were characterized in terms of morphology using scanning electron microscopy. Cyclic voltammetric responses of phenol at Ti/SnO₂–RuO₂–IrO₂, Ti/Ta₂O₅–IrO₂ and Ti/RhO₂–IrO₂ electrodes were evaluated and showed significantly low potentials for Ti/Ta₂O₅–IrO₂ (+100 mV), Ti/SnO₂–RuO₂–IrO₂ (+200 mV) and Ti/RhO₂–IrO₂ (−100 mV). The degradation of phenol in aqueous solution and its intermediates were investigated by bulk electrolysis and quantitatively assessed by HPLC analysis to elucidate the decomposition pathways and to develop a kinetic model for the electro-catalytic oxidation of phenol over Ti mixed metal oxides. Ring compounds, benzoquinone/hydroquinone, catechol, and short chain organics, carboxylic acids, have been identified as intermediate products for the electro-catalytic oxidation of phenol. Fundamental kinetic data were obtained for the conversion of phenol at these electrodes and was found to proceed in accordance with the pseudo-first-order kinetics with respect to the phenol concentration.     

Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Titanium dioxide nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method in hydrochloric acid solutions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectrum (XPS) and UV–vis spectra were carried out to characterize the composites with different PANI contents. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the modified catalysts. Results show that TiO₂ nanoparticles are deposited by PANI to mitigate TiO₂ particles agglomeration. The modification does not alter the crystalline structure of the TiO₂ nanoparticles according to the X-ray diffraction patterns. UV–vis spectra reveal that PANI-modified TiO₂ composites show stronger absorption than neat TiO₂ under the whole range of visible light. The resulting PANI-modified TiO₂ composites exhibit significantly higher photocatalytic activity than that of neat TiO₂ on degradation of phenol aqueous solution under visible light irradiation (λ ≥ 400 nm). An optimum of the synergetic effect is found for an initial molar ratio of aniline to TiO₂ equal to 1/100.     

Electrosynthesis of polyaniline–molybdate coating on steel and its corrosion protection performance

Electrosynthesis of polyaniline–molybdate (PANI–MoO₄²⁻) on mild steel was achieved in oxalic acid medium using cyclic voltammetry technique. Adherent and homogeneous PANI–MoO₄²⁻ coating was obtained. The corrosion behavior of steel with PANI–MoO₄²⁻ coatings in 1% NaCl solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The coating was characterized by SEM, XPS, EDAX and FTIR. The self-healing ability of PANI–MoO₄²⁻ coating was confirmed by SVET technique. It has been found that the PANI–MoO₄²⁻ coating is able to offer higher corrosion protection in comparison to that of pure PANI coating due to inhibitive nature of molybdate ions.     

Synthesis and properties of lithium disilicate glass-ceramics in the system SiO2–Al2O3–K2O–Li2O

The purpose of this study was the synthesis of lithium disilicate glass-ceramics in the system SiO₂–Al₂O₃–K₂O–Li₂O. A total of 8 compositions from three series were prepared. The starting glass compositions 1 and 2 were selected in the leucite–lithium disilicate system with leucite/lithium disilicate weight ratio of 50/50 and 25/75, respectively. Then, production of lithium disilicate glass-ceramics was attempted via solid-state reaction between Li₂SiO₃ (which was the main crystalline phase in compositions 1 and 2) and SiO₂. In the second series of compositions, silica was added to fine glass powders of the compositions 1 and 2 (in weight ratio of 20/100 and 30/100) resulting in the modified compositions 1–20, 1–30, 2–20, and 2–30. In the third series of compositions, excess of silica, in the amount of 30 wt.% and 20 wt.% with respect to the parent compositions 1 and 2, was introduced directly into the glass batch. Specimens, sintered at 800 °C, 850 °C and 900 °C, were tested for density (Archimedes’ method), Vickers hardness (H_V), flexural strength (3-point bending tests), and chemical durability. Field emission scanning electron microscopy and X-ray diffraction were employed for crystalline phase analysis of the glass-ceramics. Lithium disilicate precipitated as dominant crystalline phase in the crystallized modified compositions containing colloidal silica as well as in the glass-ceramics 3 and 4 after sintering at 850 °C and 900 °C. Self-glazed effect was observed in the glass-ceramics with compositions 3 and 4, whose 3-point bending strength and microhardness values were 165.3 (25.6) MPa and 201.4 (14.0) MPa, 5.27 (0.48) GPa and 5.34 (0.40) GPa, respectively.     

Synthesis and characterization of polyaniline co-doped with nitric acid and dodecyl benzene sulfonic acid

Polyaniline (PANI) co-doped with nitric acid (HNO₃) and dodecyl benzene sulfonic acid (DBSA) was directly prepared by the chemical oxidative polymerization of aniline in an aqueous solution. When the molar ratio of HNO₃/DBSA was 0.3:7, the resulted co-doped PANI (PANI_H0.3D7) reached a maximum electrical conductivity of 7.98 S/cm. When the molar ratio of HNO₃/DBSA was 0.4:6, the resulted co-doped PANI (PANI_H0.4D6) exhibited a maximum yield of 70.09%. Thermogravimetric analysis (TGA) results illustrated that there were four weight loss stages in the co-doped PANI. These weight losses were resulted from the evaporation of moisture, HNO₃, DBSA, and PANI respectively. TGA results also indicated that approximately 10.04 and 3.32 repeating units of PANI were doped with one HNO₃ molecule and one DBSA molecule in the co-doped PANI_H0.3D7, respectively. Fourier transform infrared (FTIR) results showed that the absorption peaks of the ?C═C? and ?C_aromatic?N? stretching vibrations in the emeraldine salt (ES) PANI were all shifted to the lower wavenumbers than those in the emeraldine base (EB) PANI. It was worth noting that the morphology of PANI was strongly affected by polymerization conditions.     

Impact of molecular mass on the elastic modulus of thin polystyrene films

Surface wrinkling was used to determine the elastic modulus at ambient temperature of polystyrene (PS) films of varying thickness and relative molecular mass (M_n). A range of M_n from 1.2 kg/mol to 990 kg/mol was examined to determine if the molecular size impacts the mechanical properties at the nanoscale. Ultrathin films exhibited a decrease in modulus for all molecular masses studied here compared to the bulk value. For M_n > 3.2 kg/mol, the fractional change in modulus was statistically independent of molecular mass and the modulus began to deviate from the bulk as the thickness is decreased below ≈50 nm. An order of magnitude decrease in the elastic modulus was found when the film thickness was ≈15 nm, irrespective of M_n. However, an increase in the length scale for nanoconfinement was observed as the molecular mass was decreased below this threshold. The modulus of thin PS films with a molecular mass of 1.2 kg/mol deviated from bulk behavior when the film thickness was decreased below ≈100 nm. This result illustrates that the modulus of thin PS films does not scale with molecular size. Rather, the quench depth into the glass appears to correlate well with the length scale at which the modulus of the films deviates from the bulk, in agreement with molecular simulations from de Pablo and coworkers [31] and recent experimental work [35].     

Synthesis and performances of Ni–SDC cermets for IT-SOFC anode

NiO–SDC (samaria-doped ceria) composite powders were synthesized using a urea-combustion technique. The structure, electrical conducting, thermal expansion and mechanical properties of the Ni–samaria-doped ceria (Ni–SDC) cermets have been investigated with respect to the volume contents of Ni. No chemical reaction product between the two constituents was detected for the cermets sintered at 1200–1300 °C for 4 h in air and reduced at 800 °C for 2 h in a 60%N₂ + 40%H₂ atmosphere. A porous microstructure consisting of homogeneously distributed Ni and SDC phases together with well-connected grains was observed. It was found that the open porosity, electrical conductivity, thermal expansion and bending strength of the cermets are sensitive to the volume content of Ni. The Ni–SDC cermets containing 50–60 vol.% Ni were ascertained to be the optimum composition. These compositions offer sufficient open porosity of more than 30%, superior electrical conductivities of over 1000 S/cm at intermediate temperatures (600–800 °C), a moderate average thermal coefficient of 12.6–13.5 × 10⁻⁶ between 100 and 800 °C and excellent bending strength of around 100 MPa.     

Narrow multi-walled carbon nanotubes produced by chemical vapor deposition using graphene layer encapsulated catalytic metal particles

The use of graphene layer encapsulated catalytic metal particles for the growth of narrower multi-walled carbon nanotubes (MWCNTs) has been studied using plasma-enhanced chemical vapor deposition and conventional thermal CVD. Ni–C or Fe–C composite nanoclusters were fabricated using the dc arc discharge technique with metal–graphite composite electrodes carrying a current of 100–200 A in a stainless-steel chamber filled with He and CH₄ mixture gas at 27 kPa. Nano-sized grains with diameters less than 10 nm were fabricated and deposited on a Si substrate, and were used as a catalyst for MWCNT growth. Structural analyses of the composite nanoclusters and MWCNTs were carried out using transmission electron microscopy. The results show that the diameters of the MWCNTs were reduced from 50–100 nm for a conventional Ni thin film-evaporated Si substrate to a minimum of roughly 2–4 nm in the present study.