Effect of fuel type on structural and physicochemical properties of solution combustion synthesized CoCr2O4 ceramic pigment nanoparticles

Due to importance and wide applications, CoCr₂O₄ ceramic pigment nanoparticles were synthesized via low-temperature solution combustion route by different fuels including ethylenediamine/oxalic acid, ethylenediamine/citric acid, oxalic acid/citric acid and ethylenediamine/oxalic acid/citric acid. Physicochemical properties of the synthesized samples were determined by different techniques such as fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX) and color/optical properties were evaluated based on CIELAB system by spectrophotometer. Moreover, thermodynamic considerations of combustion reactions for CoCr₂O₄ nanopigments formation in terms of calculated adiabatic flame temperature and enthalpy of combustion reaction were studied. The Comparison of results and data showed that cobalt chromite pigment nanoparticles synthesized by using ethylenediamine/citric acid and ethylenediamine/oxalic acid/citric acid fuels exhibited higher purity, smaller crystallite size and lower degree agglomeration.     

A novel approach for solution combustion synthesis of tungsten oxide nanoparticles for photocatalytic and electrochromic applications

Tungsten oxide (WO₃) and tungsten oxide hydrate (WO₃.H₂O) nanoparticles were synthesized via a novel solution combustion synthesis (SCS) method. Various organic fuels (i.e. oxalic acid, glycine, and citric acid) and heat sources were used to obtain different morphologies of nanoparticles. Combustion thermodynamic relations were explained based on propellant chemistry. Adiabatic temperature (T_ad) and specific impulse (I_sp) were also obtained. The synthesized nanoparticles were investigated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and UV–Visible spectrophotometer. XRD patterns indicated that the structures were transformed from orthorhombic and amorphous structures to monoclinic and tetragonal ones, respectively, upon combustion on the hot plate. Fourier-transform infrared (FTIR) spectra provided evidence of WO₆ octahedral. SEM images showed different microstructures from sponge or rock-like to fine spherical particles with up to 100 nm size. The obtained band gap of all samples was higher than 2.6 eV which is the band gap of bulk tungsten oxide. The synthesized WO₃ nanoparticles showed over 50% photocatalytic efficiency for the degradation of azo dye. The results exhibited that the nanoparticles can be used to make the electroactive layer for electrochromic applications.     

Hybrid composites of conductive polyaniline and nanocrystalline titanium oxide prepared via self-assembling and graft polymerization

After TiO₂ nanoparticles were surface modified, conductive polyaniline (PANI) layer was chemically grafted on the surface of the self-assembled monolayer (SAM) coated TiO₂ nanoparticles, resulting in PANI/SAM-TiO₂ composites. In the preparation process of the hybrid composites, γ-aminopropyltriethoxysilane was used as a coupling agent to form a dense aminopropylsilane monolayer with active sites for the graft polymerization of aniline. The resulted composite nanoparticles were characterized by using TEM, FTIR, TGA, and UV-vis-diffuse reflectance spectroscopy. The thermogravimetric analysis confirmed that the inserted SAM layer improved the thermal stability of the PANI-TiO₂ nanocomposites. Compared with neat-TiO₂ nanoparticles without any surface modification, moreover, the PANI/SAM-TiO₂ nanocomposites showed better photocatalytic activity in photodegradation of methyl orange under sunlight, which was partly attributed to the sensitizing effect of PANI.     

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.     

Fabrication of PMMA/PANI/Fe3O4 as a Novel Conducting Hybrid Coating

In this paper, an excellent new hybrid coating including poly(methyl methacrylate) (PMMA), polyaniline (PANI), and magnetite nanoparticles (Fe₃O₄) was obtained. Fe₃O₄ nanoparticles were synthesized using coprecipitation method, and then magnetite nanoparticles have been dispersed into the PANI to increase compatibility with PMMA. Also, PANI/Fe₃O₄ nanocomposites were synthesized through in situ emulsion polymerization, and then PMMA/PANI/Fe₃O₄ hybrid coating was successfully synthesized using batch emulsion polymerization method. Structure, morphology and thermal stability of the samples were characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermal gravimetric analysis (TGA). The synthesized samples were well distributed with an average diameter smaller than 20?nm. Microscopy and X-ray photoelectron spectroscopy results illustrated a great dispersion of magnetite nanoparticles in hybrid matrix. Moreover, the TGA results demonstrated that the PMMA/PANI/Fe₃O₄ hybrid coating nanoparticle is an excellent hybrid coating with high thermal resistance.     

Room temperature operating sensitive and reproducible ammonia sensor based on PANI/hematite nanocomposite

ABSTRACT

A facile, ultra-sensitive, quickly recoverable, and room temperature operating ammonia sensor was developed by using polyaniline (PANI) and hematite (α-Fe₂O₃) hybrid nanocomposite. The hematite nanoparticles were obtained by template-free hydrothermal process. The PANI/α-Fe₂O₃ nanocomposite was synthesized by in situ chemical oxidative polymerization process of aniline in presence of α-Fe₂O₃ nanoparticles. The structural and morphological study and compositional analysis of PANI/α-Fe₂O₃ were performed by Fourier transform infrared spectroscopy, X-ray powder diffraction analysis, and scanning electron microscopy. The PANI/α-Fe₂O₃ sensor showed excellent reproducibility, ultra-fast response, and excellent sensitivity (46.72%) as compared to PANI (29.72%) sensor towards ammonia gas at room temperature.     

Diffuse reflectance behavior of the printed cotton/nylon blend fabrics treated with zirconium and cerium dioxide and citric acid in near- and short-wave IR radiation spectral ranges

Near- and short-wave IR emission spectra of printed cotton/nylon blend fabrics coated with inorganic compounds in order to tune their diffuse reflectance behavior to the ones with woodland and desert backgrounds are investigated. In this regard, cotton/nylon blend fabrics printed with a four-color digital pattern were used as the substrate, and different concentrations of zirconium and cerium dioxide (ZrO₂ and CeO₂) with and without citric acid as a cross-linker were loaded on these fabrics using the pad-dry-cure method. The diffuse reflectance of the coated fabrics with various concentrations of nanoparticles and a cross-linker was first measured by near-infrared (NIR) diffuse reflectance spectroscopy (DRS). Then, fabrics with an optimum concentration of nanoparticles and appropriate reflectivity profiles similar to woodland and desert were investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), washing, and rubbing fastness properties. In general, NIR and short-wave infrared (SWIR) reflectance of fabrics coated with ZrO₂ and CeO₂ nanoparticles in range of 1% to 1.5% (w/v [%]) was suitable for matching with different environments. According to the findings obtained from the durability test, it was concluded that the washing fastness of the treated fabrics with CeO₂ nanoparticles was excellent in both environments. FE-SEM images of the treated fabrics containing ZrO₂ and CeO₂ indicated that the presence of nanoparticles on the surface of fabrics in woodland patterns was greater than the desert ones. However, the coated fabrics with CeO₂ and citric acid in the woodland pattern have shown better dispersion with a mean particle size of 30 to 60 nm.     

Molybdate catalysts prepared by a novel impregnation method: Effect of citric acid as a ligand on the catalytic activities

Molybdate, nickel-molybdate and cobalt-molybdate/γ-alumina catalysts were prepared by an impregnation method using citric acid as well as ammonia as ligands. Molybdenum structures in the impregnating solutions and on the sulfided catalysts were characterized by EXAFS and XPS. Agglomerated molybdenum octahedra existed in the impregnating solutions containing citric acid, in contrast to the monomeric molybdenum tetrahedra obtained when using ammonia. The nickel-molybdenum catalyst prepared by using citric acid was inferior to the one prepared by using ammonia in terms of both hydrogenation and HDN activities, which might be due to a decrease in the amount of active Ni-Mo-S phase. On the other hand, the cobalt-molybdenum catalyst prepared using citric acid was superior to the one prepared using ammonia in terms of HDS activity. A decrease in the lateral size of MoS₂-like crystallites might attribute to an increase in the HDS activity.     

Polyaniline–rhodium composites: Preparation,physicochemical characterization,and catalytic properties

In this work, polyaniline (PANI)–rhodium composites have been obtained for the first time. Their preparation procedure has involved reduction of Rh³⁺ ions in RhCl₃ aqueous solutions with NaBH₄ in the presence of PANI. Using UV–vis spectroscopy, it has been found that the reduction process is fast. X‐ray diffraction and Rh3d XPS studies have confirmed that metallic rhodium is incorporated into PANI matrix. SEM and TEM investigations allowed to establish that the sizes of Rh crystallites formed depend on the amount of metal in the composite as well as on the preparation conditions. It has been demonstrated that the composites containing Rh nanoparticles whose size is predominantly below 10 nm can be obtained. IR spectroscopy has proved that PANI chain is protonated in the Rh³⁺ reduction process. Catalytic properties of PANI–Rh composites have been investigated using isopropyl alcohol conversion as the test reaction. It has been found that the composites containing Rh nanoparticles show high redox activity. Catalytic activity of the composites in which larger, agglomerated metal particles have been present is about three times lower. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and Characterization of Conductive Polyaniline/Silver Nanocomposite Films and Their Antimicrobial Studies

Silver (Ag) nanoparticles are known to hold an important place in nanotechnology, and studies herein present the preparation and characterization of Ag metallic nanoparticles bearing antibacterial properties. In situ polymerization was used to prepare the conductive polymer polyaniline (PANI) and polyaniline/silver (PANI/Ag) nanocomposites. Increases in electrical conductivities of the nanocomposite films were observed compared to neat PANI, whereby these increases may be a result of the Ag doping effect or its complex formation. Spectroscopic techniques, such as, UV–Vis, FTIR, and photoluminescence were used for the characterizations of PANI and PANI/Ag nanocomposites. UV–Vis and FTIR data showed the quinoid units along the polymer chain being affected, such that strong interactions between Ag nanoparticles and quinoidal sites of PANI were presumed. The PANI/Ag nanocomposites showed higher photoluminescence intensities than neat PANI. TGA analyzes were used to determine weight losses and thermostabilities of PANI and PANI/Ag nanocomposites. Scanning electron microscopy was used for morphological evaluations of the nanoparticles and films, where the micrographs revealed that Ag nanoparticles were well dispersed and isolated in nanocomposite films. The presence and distribution of the Ag nanoparticles in PANI film matrix were analyzed by EDX. Antimicrobial properties of the nanocomposite films obtained were also explored. POLYM. ENG. SCI., 59:E182–E194, 2019. © 2018 Society of Plastics Engineers     

Thermodynamic modeling of the K2O-Al2O3 and K2O-MgO-Al2O3 systems with emphasis on β- and βʹʹ-aluminas

A critical evaluation and thermodynamic modeling study including key phase diagram experiments was performed to investigate the K₂O-Al₂O₃ and K₂O-MgO-Al₂O₃ systems. For the first time, potassium β- and β??-alumina solid solutions were described using the Compound Energy Formalism with accurate cation distributions in their sublattices. From the new experimental results, the stability of potassium β??-alumina was assured up to 1600?°C. A large discrepancy reported in the literature, the eutectic temperature between KAlO₂ and β-alumina in the K₂O-Al₂O₃ system, was resolved. A set of self-consistent Gibbs energy functions for all stable phases in the K₂O-MgO-Al₂O₃ system was obtained. As a result, any phase diagram sections and thermodynamic properties of the K₂O-MgO-Al₂O₃ system can be calculated from the optimized Gibbs energy functions. In particular, the cation distribution in the β- and β??-alumina solid solutions is calculated depending on the non-stoichiometry of solution and temperature.     

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.     

Citric Acid Crosslinking of Cellulose Using TiO2 Catalyst by Pad-Dry-Cure Method

TiO₂ was used as a catalyst for crosslinking of cellulose using citric acid by pad-dry-cure method. Different factors affecting crosslinking were studied, including TiO₂ concentration, curing temperature, curing time, and citric acid concentration. The results obtained indicate that TiO₂ has the ability to catalyze crosslinking of cellulose with citric acid. Crease recovery angle increases with increasing TiO₂ concentration; the optimum concentration was 0.6% TiO₂. Also, crease recovery angle increases with increased curing time, curing temperature, and citric acid concentration. The results of whiteness index and roughness were found to be better than those obtained when using a sodium hypophosphite catalyst. The crosslinking was confirmed by FT-IR spectroscopy. It was also found that crosslinking in the presence of TiO₂ has an adverse effect on the samples dyed with reactive and direct dyes.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Using modified Pechini method to synthesize α-Al2O3 nanoparticles of high surface area

A modified Pechini method for the preparation of a high surface area α-alumina is proposed. The synthesis of these nanoparticles was carried out using a polymer as a chelating agent. The polymer was prepared from citric acid and acrylic acid by the melt blending method. The resulting α-alumina (98.16%) after calcination at 900 °C consisted of cylindrical nanoparticles of 100–200 nm in length and <25 nm in diameter with a relatively high surface area (18 m² g^?1).     

The effects of carboxylic acids on the aqueous dispersion and electrophoretic deposition of ZrO2

The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO₂ with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO₂ suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO₂ surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability.     

In situ preparation of monodispersed Ag/polyaniline/Fe3O4 nanoparticles via heterogeneous nucleation

Acrylic acid and styrene were polymerized onto monodispersed Fe₃O₄ nanoparticles using a grafting copolymerization method. Aniline molecules were then bonded onto the Fe₃O₄ nanoparticles by electrostatic self-assembly and further polymerized to obtain uniform polyaniline/Fe₃O₄ (PANI/Fe₃O₄) nanoparticles (approximately 35 nm). Finally, monodispersed Ag/PANI/Fe₃O₄ nanoparticles were prepared by an in situ reduction reaction between emeraldine PANI and silver nitrate. Fourier transform infrared and UV-visible spectrometers and a transmission electron microscope were used to characterize both the chemical structure and the morphology of the resulting nanoparticles.     

Hydrothermal synthesis of monoclinic zirconia sol

In this study, we demonstrate a synthetic method of zirconia sol using ZrO(NO₃)₂·xH₂O as Zr⁴⁺ precursor, tetramethylammonium hydroxide as mineralizer, and oxalic acid as a complexing agent. X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and UV–vis adsorption spectroscopy were used to characterize the nanocrystals. The effect of oxalic acid content on the growth of zirconia nanocrystals was investigated. Zirconia sol cannot be synthesized without oxalic acid. The oxalic acid content has no obvious effect on the phase formation of monoclinic zirconia. The transparent and monoclinic zirconia sol with particle size <10 nm was synthesized. This provides a new hydrothermal system for the synthesis of zirconia sol.     

Preparation of high pure α-Al2O3 nanoparticles at low temperatures using Pechini method

A Pechini process was successfully used to synthesize alpha-alumina (98.95% mass fraction) at relatively low calcination temperature (925 °C). The synthesis of these nanoparticles was carried out using a polymer prepared from citric acid and ethylene glycol by the melt blending method. This polymer worked as a chelating agent for aluminum cations. The final products were produced after a dual-stages thermal treatment. The resulting α-alumina consisted of nanoparticles of 8–16 nm in diameters with a surface area (～8 m² g^?1). The mass fraction of α-alumina was dependent on the concentration of aluminum salt and polymer precursor's solutions, while the surface area of the final product was dependent on the mass fraction of θ-alumina.     

Synthesis and characterization of BGO with different chelating compounds by the polymeric precursor method,and their effect on luminescence properties

In the present work, Bi₃Ge₄O₁₂ (BGO) was synthesized by the polymeric precursor method using different chelating agents. We present a comparative analysis of each chelate formation and how the physicochemical properties of the BGO were affected, specifically its luminescence. In this work we used citric acid (CTR), ethylenediaminetetraacetic acid (EDTA), ethylene glycol (EG), nitrilotriacetic acid (NTA) and tartaric acid (TA), since they are the most reported chelating agents for this type of synthesis. The BGO materials were characterized by scanning electron spectroscopy (SEM), X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and photoluminescence (PL), and showed that the luminescence properties of the synthesized BGO was affected by the formation of secondary phases. The changes in the BGO luminescence properties with the use of each chelating agent are discussed.