Aniline In Aqueous Solution Research Articles

Fabrication of One Dimensional Polyaniline Nanofibers by UV-Assisted Polymerization in the Aqueous Phase

At the room temperature, a novel and environmental friendly approach for synthesizing polyaniline (PANI) nanofibers on a large scale is presented firstly in the aqueous phase by ultraviolet (UV)-assisted polymerization using cetyltrimethylammonium bromide (CTAB) as the "soft-template." It is obvious that the polymerization process can be accelerated under the illumination of UV light and the preliminary mechanism has been pointed out. Furthermore, it also can be noted that the lower concentrations of CTAB and HCl are helpful for the fabrication of smooth and uniform PANI nanofibers. As observed with FE-SEM and TEM, the as-synthesized PANI nanostructures under the appropriate conditions are composed of uniform nanofibers with the average diameter of about 100 nm and the length of several micrometers. Subsequently, the synthesized PANI nanostructures are characterized with UV-vis, FT-IR, XRD spectra, and the typical physical and chemical properties of PANI are displayed. In addition, the conductivity of the synthesized PANI nanofibers was also measured with the four probe method and the excellent conductivity was presented. In summary, the procedure presented here only involving exposure of an acidic aqueous solution of aniline to UV light illumination is so simple and the needed equipment is so low cost, from the viewpoint of technological applications, that the large-scale UV-assisted polymerization of PANI nanofibers from the monomer solution is feasible and promising.

Electrochemical Synthesis of Polyaniline as Ethylene Gas Sensor

The aim of this work is to fabricate an ethylene gas sensor based on polyaniline (PANi). The conductive layer of emeraldine base PANi was prepared by electrochemical synthesis. The aqueous aniline solution in sulfuric acid was electrolyzed by repeating potential cycling between -0.4 and 1.0 V relative to the silver reference electrode and platinum counter electrode. The conductive layers of PANi were deposited on patterned interdigited gold substrate. The numbers of repeated potential cycles on the amount of deposited layers of PANi were investigated for ethylene gas detection. The morphology of PANi films was investigated by scanning electron microscope (SEM). The ethylene gas sensing of PANi-H2SO4 was evaluated based on the changes in conductivity of PANi-H2SO4. The results revealed that the magnitude sensing provided a good sensitivity against ethylene with concentration in the parts per million (ppm) ranges. The effect of amount of deposited layer of PANi on ethylene gas sensing will be presented.

Photochemical removal of aniline in aqueous solutions: Switching from photocatalytic degradation to photo-enhanced polymerization recovery

Organic pollutants may be treated by either a degradation process or a recovery process in the view point of sustainable chemistry. Photocatalytic removal of aniline was investigated in aqueous solutions. It was found that the photocatalytic oxidation of aniline resulted in its degradation or polymerization, depending on its concentration. Hence a new treatment strategy was proposed in combination of photocatalytic degradation and polymerization, where the polymerization was in fact a recovery process. When aniline concentration was as low as 0.1 mmol L(-1), it was possible to photocatalytically degrade aniline, which could be further enhanced by increasing solution pH, modifying TiO(2) surface with the addition of anions, or coupling with the photoreduction of added oxidants. When aniline concentration was increased to about 1 mmol L(-1), the photocatalytic oxidation was observed to yield the polymerization of aniline, leading to nanocomposites of polyaniline (PAN) and TiO(2). Alternatively, the photo-enhanced chemical polymerization of aniline at higher concentrations (>or=50 mmol L(-1)) in the presence of chemical oxidants produced PAN nanostructures. The conversion of pollutant aniline to valuable PAN nanostructures or nano-PAN/TiO(2) composites is suggestive for possible applications in the treatment of aniline wastewaters as a sustainable environmental protection measure.

Shielding and dielectric properties of sulfonic acid‐doped π‐conjugated polymer in 8.2–12.4 GHz frequency range

AbstractThis article deals with dielectric and electromagnetic interference shielding properties of the polyaniline doped with dodecyl benzene sulfonic acid (DBSA) synthesized by microemulsion polymerization of aniline in aqueous solution of DBSA. Dielectric constant and shielding effectiveness due to absorption (SEA) were calculated using S‐parameter obtained from the vector network analyzer in 8.2–12.4 GHz frequency range. Maximum SEA of 26 dB (>99%) was achieved for polymer sample. The real part ε′ of complex permittivity shows small variation, whereas the imaginary part ε″ is found to decrease with the increase in frequency. Different formulations have been performed to see the effect of monomer to dopant ratio on intrinsic properties of polyaniline. Further characterization of polymer was carried out by UV–visible and thermal gravimetric analysis, whereas the conductivity measurements were carried out by the four‐probe method.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Spectrophotometric determination of ionization constants of some organic compounds in aqueous solution

Ionization constants of some phenols and anilines in aqueous solution with a ionic strength of 0.01 were measured at 25°C by spectrophotometric method. The set of substrates was selected on the basis of the results of preliminary calculations of ionization constants in terms of an elemental linear empirical approach with account taken of the lack of the corresponding consistent published data.

Au nanoparticles-functionalized two-dimensional patterned conducting PANI nanobowl monolayer for gas sensor

A facile route for the generation of two-dimensional (2D) ordered, large-area, liftable, and patterned polyaniline (PANI) nanobowl monolayer containing Au nanoparticles has been demonstrated with the monolayer self-assembled polystyrene (PS) spheres at the aqueous/air interface as template. Tetrachloroauric acid has been used as an oxidizing agent for the polymerization of aniline in aqueous solution. The morphologies, compositions, and structure of the obtained samples were characterized by scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy and X-ray diffraction. Additionally, the sensor response to NH 3 of our products has been investigated and ultra-fast response and recovery behavior have been obtained, which endows our product in practical gas detector.

Permeation characteristics of 4-substituted phenols and anilines in aqueous solution during removal by a silicone rubber membrane

The objective of this study is to determine the correlation of permeability of phenols and anilines through the silicone rubber membrane (SRM) with hydrophobicity and acid–base properties and to gain insight into the permeation characteristics of phenols and anilines through the SRM. The permeation characteristics of 4-substituted phenols and anilines for a SRM in the permeation and chemical desorption (PCD) method were investigated. The phenols or anilines in aqueous solution were successfully recovered to aqueous NaOH or HCl solutions, respectively. Although permeation rates increased with alkyl chain length for both phenols and anilines, a marked difference was found in permeation characteristics based on molar volume. An increase in permeability of anilines through the SRM with increasing molar volume was significantly greater than that of the phenols. This was due to a greater membrane distribution coefficient ( m c) and a smaller reduction of diffusivity ( D) in the SRM with increasing molar volume of the anilines, as compared with the phenols. During permeation of the phenols and anilines through the SRM, their distribution process through the membrane had a significant influence. Hydrophobicity (log P OW: 1-octanol/water partition coefficient) and acid dissociation constant (p K a) values of the compounds played an important role in the distribution process. A regression equation was derived that related log m c of the compounds through the SRM, including log P OW and p K a values. The strong correlation indicates that the permeation rate of a target compound through the SRM using the PCD method may be predicted from known physical properties, such as P OW and p K a.

2P4-9 Sonochemical degradation of phenol and aniline in aqueous solution(Poster Session)

2P4-9 Sonochemical degradation of phenol and aniline in aqueous solution(Poster Session)

Oligoaniline intermediates in the aniline-peroxydisulfate system

Chemical oxidative polymerization of aniline using peroxydisulfate oxidant in aqueous pH 2.5–10.0 buffers yields electrically insulating brown powders that are believed to be mixtures of Michael-type adducts of benzoquinone monoimine and aniline at various stages of hydrolysis. A spectroscopically similar product is formed when solid 1,4-benzoquinone is added to an aqueous solution of aniline at room temperature in the absence of peroxydisulfate. This suggests that the peroxydisulfate oxidant in the aniline/S 2O 8 2− system provides a pathway for the formation of benzoquinone monoimine as an intermediate. Benzoquinone monoimine intermediate could be formed as a result of a Boyland–Sims rearrangement of aniline proceeding via the intermediacy of p-aminophenyl sulfate. Benzoquinone monoimine undergoes a series of conjugate 1,4-Michael-type addition/reoxidation/coupling steps with aniline or p-aminophenyl sulfate yielding the oligoaniline product. The precipitate that is isolated is also in the midst of two simultaneous pH dependent hydrolysis reactions: (i) hydrolysis of the imine groups to quinone, and (ii) hydrolysis of arylsulfates to phenols. The ratio of hydrolysis in each case was determined by the C/N ratio and sulfur elemental analysis values yielding analytical data that is consistent with experimentally determined values and also with our proposed reaction scheme. These findings offer a rationale for the high C/N ratios (>6.0) frequently observed in these systems while tracing the genesis of the residual sulfur in the product to unhydrolyzed arylsulfate. The oligoaniline product has previously been reported to have a novel poly-aza structure consisting of continuously linked –N–N–N– bonds, and alternately also reported to consist of phenazine-type linkages. This study is consistent with the latter and describes a pathway to phenazine coupling through a second and third stage hydrolysis of the arylsulfate and reoxidation with peroxydisulfate. There is no pathway for the formation of linear –N–N–N– linkages in the aniline/benzoquinone adduct and the striking similarity between its spectroscopic properties and the aniline/S 2O 8 2− adduct suggests that it is not a preferred pathway under these experimental conditions.

UV‐curing synthesis of sulfonated polyaniline‐silver nanocomposites by an in situ reduction method

AbstractSulfonated polyaniline‐silver (SPAni‐Ag) hybrid nanocomposites have been synthesized by the in situ reduction using a UV‐curing polymerization method without using any reducing or binding agent. An aqueous solution of aniline and orthoanilinic acid (OA) comonomers, a free‐radical oxidant and silver metal salts were irradiated by UV rays. Reduction of the silver salt in aqueous aniline and OA leads to the formation of silver particles which in turn catalyze the oxidation of comonomers to sulfonated polyaniline (SPAni). The resultant SPAni‐Ag nanocomposites were characterized by using different spectroscopy analyses like UV–visible (UV–Vis), X‐ray diffraction (XRD) and infrared spectroscopy. The absorption bands were revealed to be optically active and the peaks blue‐shifted due to the presence of metallic silver within the SPAni matrix. The XRD patterns displayed both the broad amorphous polymeric and sharp metallic peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposites showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the nanocomposites had a better thermal stability than the bulk SPAni. Copyright © 2008 John Wiley & Sons, Ltd.

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

Sulfonated polyaniline–titanium dioxide (SPAni–TiO 2) 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–TiO 2 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–TiO 2 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–TiO 2 composites have a good thermal stability than the pristine SPAni.

Polyaniline/silver nanocomposite preparation under extreme or non-classical conditions

Polyaniline (PANI) and polyaniline/silver nanocomposites have been synthesized by sonochemical and ionizing radiation technique. These composite materials were obtained through sonication and γ irradiation of an aqueous solution of aniline and silver nitrate at room temperature. The suggested mechanisms to explain the formation of these products are based on the fact that both methods produce hydroxyl radical OH and hydrogen radical H, which acts as an oxidizing agent for the polymerization process of aniline monomer and as reducing agent for silver ions, respectively. Spectroscopic, X-ray and scanning electron microscope (SEM) measures showed that polyaniline and silver nanoparticles of 40 nm of average diameter are obtained when ultrasonic technique is used whereas silver nanoparticles of 60 nm average, and highly fibrillar polyaniline network with diameter of 60 nm is obtained when γ radiation is used.

Polyaniline-coated halloysite nanotubes via in-situ chemical polymerization

Polyaniline coated halloysite nanotubes (PANI/HNTs) were prepared by the in-situ soapless emulsion polymerization of the anilinium chloride adsorbed halloysite nanotubes (HNTs), obtained by the dispersion of HNTs in acidic aqueous solution of aniline with magnetic stirring and ultrasonic irradiation, by using ammonium persulfate (APS) as oxidant. The effect of the acidities of the polymerizing media on the crystal structure of the nanotubes was investigated with X-ray diffraction (XRD) technique. The surface conducting coatings of the hybrids were characterized with X-ray photoelectron spectroscopy (XPS). The morphological analyses showed that the polyaniline coated halloysite nanotubes via the in-situ chemical oxidation polymerization with ultrasonic irradiation had the better well-defined structures, by the transmission electron microscopy (TEM). The conductivities of the PANI/HNTs hybrids increased with the increasing of the amounts of HCl dopant added in the emulsion polymerization.

Influence of pH on the specific surface area of polyaniline matrices

AbstractWe report the successful measurement of the specific surface area of chemically synthesized and treated polyaniline (PANI) and its composite PANI/silica (SiO2). PANI was synthesized chemically from an aqueous solution of aniline and hydrochloric acid (HCl) in the presence of an oxidant, ammonium peroxydisulfate [(NH4)2S2O8]. In the synthesis of PANI/SiO2, SiO2 was incorporated from its colloidal solution contained in the solution for the polymerization of PANI. PANI and PANI/SiO2 thus synthesized were pretreated with double‐distilled water (pH = 6.95), aqueous HCl (pH = 1.09), and aqueous ammonia (pH = 10.15) solutions to control their pH levels. Surface morphologies of the treated PANI and PANI/SiO2 matrices were investigated with scanning electron microscopy. The successful incorporation of SiO2 into the PANI/SiO2 composite was confirmed by the characteristic infrared absorption band at 1096 cm−1. The adsorption of methylene blue, which was found to follow the Langmuir isotherm, onto the prepared materials was probed to estimate the real surface area. The base‐treated PANI matrix showed a higher surface area than the acidic and neutral ones. The incorporation of SiO2 into the PANI matrix yielded a larger surface area. However, the treated PANI/SiO2 showed the same trend as the treated PANI matrices. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Adsorption of aniline onto hexagonal mesoporous silicate monoliths (HOM-2)

Hexagonally highly ordered monolithic mesoporous silica and aluminosilicate composites (HOM-2 and Al/HOM-2, respectively) were used as adsorbents for removal of aniline in aqueous solution. These HOM-adsorbents were fabricated by using a simple, reproducible and direct synthesis strategy in which instantly preformed liquid crystalline phase of Brij 56 (C16EO10) surfactant was used as templates. Extensive characterisation studies showed that Al/HOM-2 composites revealed higher surface area, smaller pore sizes and thicker pore wall than those of unloaded-HOM-2 monoliths, indicating that Al might be impregnated into the inner pores and the wall frameworks of HOM-2 silica monoliths. The adsorption experiments of aniline were investigated by using batch techniques. The results obtained showed that the aniline molecule strongly adsorbed onto the aluminosilicate mesostructures. In addition, the HOM-adsorbent exhibited high efficiency for aniline removal after several uses without loss of structural ordering, permitting the reusability for further selective separation of organic molecules from water.

Improvement of conductivity of electrochemically synthesized polyaniline

AbstractThe electrochemical polymerization of aqueous solution of aniline and HCl was carried out in a single compartment electrochemical cell. After 2 h of the polymerization reaction, polarity of the electrodes was reversed and kept for 1 h. By this process the conductivity of the polyaniline (PAni) formed was found to increase dramatically from 1.1 × 10−4 to 3.0 × 10−1 S/cm. The PAni samples obtained both by reversing the polarity (“PANI‐R”) and without reversing the polarity (“PANI”) were characterized by the infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), ultraviolet spectroscopy (UV), Hall effect experiment, X‐ray analysis (XRD) and scanning electron microscope (SEM). The results show that the increase in the conductivity of PAni through the reversion of polarity is due to the partial reduction of over oxidized sample giving more emeraldine base and hence more polaron formation with increased charge carrier density and its mobility. The degree of crystallinity and the crystallite size is decreased marginally and the d‐spacing is increased marginally due to this reduction. The PAni behaves like a p‐type semiconductor that means the majority current carriers are holes. A plausible reduction mechanism due to reversal of polarity during electrochemical polymerization is also proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Conductive polymer preparation under extreme or non-classical conditions

Polyaniline (PANI) emeraldine salt form and PANI/silver composites have been synthesized by sonochemical and ionizing radiation methods. These composite materials were obtained through sonication and γ irradiation of an aqueous solution of aniline and silver nitrate, in room temperature, respectively. The mechanisms suggested to explain the formation of these products are based on the fact that both methods produce hydroxyl radical •OH and hydrogen radical •H, where hydroxyl radical •OH acts as an oxidizing agent in the polymerization process of aniline monomer; and hydrogen radical •H, as a reducing agent for silver ions. Spectroscopic, X-ray, and SEM measures show that PANI and silver nano particles of 40 nm average diameter are produced with ultrasonic methods, whereas silver nano particles of 60 nm average, and fibrillar, highly network morphology for PANI with 60 nm fibrillar diameter average are obtained using γ radiation).

Effect of addition of organic solvents on properties of the chemically synthesized polyaniline in aqueous solutions

AbstractIn the process of polymerization of aniline in aqueous solution, different kinds or volumes of organic solvents were added. The effects of the organic solvents on the morphology, structure, conductivity and water-dispersity of the resulting polyaniline (PANI) were investigated with the aid of SEM, UV-Vis, FT-IR and Raman spectra and conductivity measurements. The results showed that the weak H-bond interactions between PANI and the solvents might play an important role in forming uniform nanofibers with relatively high conductivity and good waterdispersity. However, excessive addition of organic solvents led to the aggregation of the nanofibers and the corresponding PANI had a bad water-dispersity.

Synthesis of core‐shell silver–polyaniline nanocomposites by gamma radiolysis method

AbstractCore‐shell silver (Ag)–polyaniline (PAni) nanocomposites have been synthesized by the in‐situ gamma radiation‐induced chemical polymerization method. Aqueous solution of aniline, a free‐radical oxidant, and/or silver metal salt were irradiated by γ‐rays. Reduction of the silver salt in aqueous aniline leads to the formation of silver nanoparticles which in turn catalyze oxidation of aniline to polyaniline. The resultant Ag‐PAni nanocomposites were characterized by using different spectroscopy analyses like X‐ray photoelectron, UV–visible, and infrared spectroscopy. The optical absorption bands revealed that the bands at about 400 nm are due to the presence of nanosilver and the blue‐shifted peak at ∼ 555 nm is due to the presence of metallic silver within the PAni matrix. X‐ray diffraction pattern clearly indicates the broad amorphous polymer and the sharp metal peaks. 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 composites have a higher degradation temperature than polyaniline alone. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5741–5747, 2007

The Degradation Products of Aniline in the Solutions with Ozone and Kinetic Investigations

Aromatic compounds are extensively used in several industries and can cause pollution in water sources. This work aims at examining the degradability of aniline in aqueous solutions by ozone-induced cleavage, and at determining the kinetics of the cited cleavage reactions. Aniline was prepared in four different concentrations and the flow rate of ozone supplied to each solution was selected. Aniline solutions were ozonated at low and high pH, so as to compare both molecular and hydroxyl free radical mechanisms, respectively. The main identified aromatic by-products were nitrobenzene and azobenzene when the experiment was carried out at acidic pH. Formation of nitrobenzene, azobenzene, azoxybenzene and 2-pyridine carboxylic acid (picolinic acid) was observed when the ozonization was carried out at basic pH. All the aromatic by-products found were less toxic than the raw materials. The pseudo-first-order constants in aniline concentrations were calculated.