Anjali A. Athawale

Chloroform vapour sensor based on copper/polyaniline nanocomposite

Abstract Chemically synthesised copper/polyaniline (PANi) nanocomposite has been utilised as a chloroform sensor for ppm level vapour concentration. The response in terms of increase in dc electric resistance on exposure to chloroform vapours has been observed. The FT–IR spectra of nanocomposite on exposure to chloroform show remarkable modifications in the far IR region indicating the interaction of chloroform with metal cluster. It is believed that the sensing mechanism mainly involves adsorption–desorption of chloroform at metal cluster surfaces.

Polyaniline and its substituted derivatives as sensor for aliphatic alcohols

Abstract Polyaniline (PAni) as well as its substituted derivatives such as poly( o -toluidine) (Po-Tol), poly( o -anisidine) (Po-Anis), poly( N -methyl aniline) (PNMA), poly( N -ethyl aniline) (PNEA), poly(2,3 dimethyl aniline) (P2,3-DMA), poly(2,5 dimethyl aniline) (P2,5-DMA) and poly(diphenyl amine) (PDPA) were found to be sensitive to different alcohols such as methanol, ethanol, propanol, butanol and heptanol vapours. A negative change in resistance was observed upon exposing the polymers to methanol, ethanol or propanol vapours, whereas, a reverse trend has been observed for butanol and heptanol vapours. Although, the magnitude of change in resistance was found to be very high in many cases: poor response time was observed for most of the polymers. Rapid responses were exhibited only by P2,3-DMA and PAni for methanol and ethanol, respectively. High sensitivity value (>80%) have been obtained for saturated methanol vapours compared to other alcohols in all polymers. Further, measurable response (sensitivity ∼60%) has been obtained at lowest alcohol concentration of ∼3000 ppm with extended switching time. The results are explained on the basis of vapour induced change in the crystallinity of the polymer. The extent of change was found to be governed by the chain length of the alcohol and its chemical nature.

Exchanges of uranium(VI) species in amidoxime-functionalized sorbents.

Amidoxime (AO)-functionalized polymer sorbents used in this study were prepared by two different routes involving UV grafting and electron-beam grafting of acrylonitrile (AN) into poly(propylene) fibrous and microporous sheets, and subsequent conversion of AN to AO groups by reacting the precursor sorbent with hydroxylamine. The values of self-diffusion coefficient (D(s)) of UO(2)(2+) in fibrous and sheet AO sorbents were found to be 1.1 x 10(-6) and 2.3 x 10(-10) cm(2) s(-1), respectively. The higher diffusion mobility of UO(2)(2+) in the fibrous AO sorbent was attributed to its higher free volume as observed in scanning electron microscopic studies. The water content was also found to be maximum in AO-fibrous sorbent (165-200 wt %) and minimum in AO-sheet sorbent (70 wt %). In fibrous AO sorbent, the values of D(s) for Na(+) and Sr(2+) were found to be comparable to their self-diffusion coefficients in the aqueous medium. This indicated that the retardation in diffusion mobility of the ions was a minimum in the fibrous AO sorbent. However, D(s) of UO(2)(2+) in the fibrous membrane was found to be significantly lower than that of Sr(2+), which has a self-diffusion coefficient comparable to that of UO(2)(2+) in aqueous medium. This could be attributed to stronger binding of UO(2)(2+) with AO groups as compared to Sr(2+). To understand the parameters affecting the U(VI) sorption from seawater, the U(VI) exchange rates between fibrous AO sorbent (S) and seawater (aq) involving (H(+)/Na(+))(S) right harpoon over left harpoon ([UO(2)(CO(3))(3)](4-))(aq) and (UO(2)(2+))(S) right harpoon over left harpoon ([UO(2)(CO(3))(3)](4-))(aq) systems were experimentally measured. The exchange profiles thus obtained were found to be non-Fickian and much slower than (H(+))(S) right harpoon over left harpoon (UO(2)(2+))(aq) and (UO(2)(2+))(S) right harpoon over left harpoon (UO(2)(2+))(aq) exchanges. This seems to suggest that the reaction kinetics involved in decomplexation of [UO(2)(CO(3))(3)](4-) into UO(2)(2+), which forms a complex with AO groups, is the rate-determining step in sorption of U(VI) from seawater. The kinetics of U(VI) sorption in AO-gel and AO-fibrous sorbents followed the pseudo-second-order rate equation. The density of AO groups in the sorbents and their conditioning were found to influence the U(VI) sorption from seawater.

Aniline as a stabilizer for metal nanoparticles

Palladium nanoparticles were synthesized by two different methods, i.e. reflux and γ-radiolysis in the presence of various monomers like aniline, N-ethyl aniline, N-methyl aniline, o-anisidine and o-toluidine as the stabilizing agent for the Pd nanoparticles. UV–Visible spectral analysis reveals that the aniline renders best stability to the Pd nanoparticles up to a period of 96 h. Nanocomposites were synthesized by polymerizing aniline stabilized Pd° nanoparticle solution by using ammonium persulphate as an oxidizing agent. The average particle size of the nanoparticles calculated from X-ray diffraction patterns were ∼24 nm (reflux method) and ∼28 nm (γ-irradiation method). The above results are supported by TEM analysis.

Photoemission and conductivity measurement of poly(N‐methyl aniline) and poly(N‐ethyl aniline) films

The studies involve the X-ray photoelectron spectroscopy (XPS) and conductivity measurements of poly(N-methyl aniline) and poly(N-ethyl aniline) films deposited electrochemically at different pH values of −0.96, 2.22, and 3.78 for N-methyl aniline and 1.10, 2.22, and 3.78 for N-ethyl aniline. The results obtained reveal significant differences in the film properties of the two matrices as a function of pH of solution. These differences are explained on the basis of the competitive reaction products formed during polymerization in the two matrices along with the differences in the electron-donating ability of the methyl and ethyl groups present on the nitrogen (N) atom. These results are further supported by the UV–Visible and IR data.

Acrylic acid-doped polyaniline sensitive to ammonia vapors

Acrylic acid and HCl-doped polyanilines were synthesized by chemical oxidative polymerization. The synthesized materials were used as sensors for ammonia. Comparison of the responses of the two polymers reveal that the acrylic acid-doped polymer exhibits higher sensitivity and reversibility. Further, the resistance is observed to decrease on exposing the acrylic acid-doped polyaniline to saturated ammonia vapors. A reversed trend is observed in the case of HCl-doped polyaniline. The results are explained in terms of the differences in the chemical interactions of the two polymers with respect to ammonia vapors. The proposed mechanism is further supported by the X-ray diffraction and FTIR analysis. The X-ray diffractogram of acrylic acid-doped polymer shows an enhancement in the crystallinity on exposure to ammonia vapors, while the HCl-doped polymer exhibits a loss in crystallinity. The FTIR spectra shows a higher doping level in acrylic acid doped polymer as observed from the intense peak of the dopant ion at 1158 cm−1, which is seen to be shifted to a lower wavenumber i.e. ∼1128 cm−1 on exposing the polymer to ammonia vapors. On the other hand, in HCl-doped polyaniline, the peak of the dopant ion ∼1120 cm−1 is initially less intense, which is further suppressed on exposure to ammonia. Conductivity measurements show a large vapor-induced increase in conductivity, in the case of ammonia-exposed acrylic acid-doped polyaniline, which results in the formation of a more crystalline-conducting phase. Exactly the opposite results were obtained in the case of HCl-doped polyaniline exposed to ammonia.

Uranium preconcentration from seawater using phosphate functionalized poly(propylene) fibrous membrane

ABSTRACT The poly(ethylene glycol methacrylate phosphate) macroporous membranes (PEGMPmembrane) were prepared by grafting of ethylene glycol methacrylate phosphate onto the poly(propylene) fibrous sheets using UV-irradiation and electron beam. The PEGMP-membrane samples thus prepared were characterized in terms of water uptake capacity, uranium uptake efficiency under seawater conditions, uranium distribution in the membrane samples, desorption and reusability of the membrane for uranium preconcentration. The uranium sorption capacity of the PEGMP membrane was found to be appropriate (1.4 × 10–3 mol/g) for using it in adsorptive mode for preconcentration of uranium from the lean aqueous feed. The functional group density based on the gravimetrically measured weight of PEGMP anchored in the membrane sample was calculated to be 3.2 × 10–3 mol/g. The comparison of expected functional group density and uranium uptake capacity seems to suggest that UO2 2+ forms complex with EGMP units in 1:2 proportion in the ...

A Soft Solution Process to Synthesize Nanocrystalline Barium Zirconate via Reactive Solid State Precursors

Barium zirconate, a perovskite oxide has been synthesized by a new procedure using solid state metathesis reaction precursors subjected to sonication. We report the lowest temperature of synthesis with particle size ranging from 20 to 30 nm. The initial stage involves formation of composite hydroxide nanoparticles by the solid state reaction of precursor salts with KOH at ambient temperature followed by sonication. BaZrO3 formation as a consequence of ultrasonicator output power variation and ultrasonic time variation has been studied. Results indicate that the process is convenient, low energy, environmentally benign and having narrow particle size distribution of BaZrO3.

Quaternary ammonium bearing hyper-crosslinked polymer encapsulation on Fe3O4 nanoparticles

The Gibbs free energy involved in the transfer of ions from water to a hydrophobic medium with ion-exchange sites changes the selectivity pattern expected from the electrostatic interactions. Oxyanions are less hydrated and, therefore, their exchange with more hydrated anions at the ion-exchange sites of a hydrophobic matrix in contact with aqueous solution is energetically more favorable. This gives rise to a possibility of separating the highly toxic monovalent oxyanions such as HCrO4−, MnO4−, TcO4− and ClO4− etc. by the Gibbs free energy of the transfer controlled anion-exchange process. In the present work, hydrophobic anion-exchange polymer encapsulation was anchored on Fe3O4 particles by a simple and reproducible method for studying the selectivity pattern. The choice of Fe3O4 nanoparticles (NPs) as the host matrix was based on their higher dispersion, larger surface area, and easy retrieval using an external magnetic field that is best suited for treating a large volume of an aqueous stream and developing sustainable technology. The anion-exchange polymer encapsulation was formed by first coating Fe3O4 NPs with (3-aminopropyl)triethoxysilane, and subsequently reacting these precursor particles in a sequence with poly(vinylbenzyl chloride) (PVBCl), 1,4-diazabicyclo[2.2.2]octane (DABCO), and 1,8-dibromooctane (DBO). Each step involved in the chemical treatments was monitored by C, H and N analyses. Energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were used to confirm the expected chemical structure of the encapsulation on the Fe3O4 NPs. This sequence of chemical treatments resulted in the formation of hyper-crosslinked, hydrophobic, and high fixed positive charge density polymer encapsulation on the Fe3O4 NPs. The analyses of the images obtained from field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) indicated that the sizes of the Fe3O4 NPs were increased from 13 ± 3 nm to 33 ± 3 nm due to the formation of polymer encapsulation and inter-particle crosslinking. Although a very dilute solution and ultrasonication were used, there was a possibility of crosslinking between the particles. However, the thus encapsulated Fe3O4 NPs retained their superparamagnetic properties having a reasonably good magnetic saturation (30 emu g−1). The anion-exchange capacity was found to be 0.65 ± 0.03 meq g−1. The Fe3O4@PVB–DABCO–DBO particles exhibited a selectivity pattern corresponding to the Hofmeister series, i.e. the least hydrated anions were adsorbed preferentially. For example, the least hydrated representative TcO4− anions adsorbed quantitatively in the Fe3O4@PVB–DABCO–DBO particles from aqueous solutions such as ground water, seawater, and 0.5 mol L−1 HNO3 with efficiencies of 98%, 80% and 75%, respectively.

Ag Dispersed Conducting Polyaniline Nanocomposite as a Selective Sensor for Ammonia

Silver nanoparticles were synthesized by irradiating silver nitrate solution (10-4 M) (methanol:water as a solvent) with different concentrations of aniline as a stabilizer in a 60Co g-ray source at a dose rate of 1.1 kGy. The particles exhibiting maximum stability up to a period of 7 days were obtained at the concentration of 0.1M aniline. The average particle size of the nanoparticles as estimated from XRD and TEM was found to be ~23 nm. Silver-Polyaniline (Ag-Pani) nanocomposite was prepared by oxidative polymerization of aniline. The applicability of synthesized nanocomposite as a sensor was tested by exposing the same to different chemical vapors viz. alcohols, amines, ammonia, chloroform etc. The results revealed its selectivity towards ammonia vapors and a long term stability of response is observed up to a period of two months. The above results are well supported by FT-IR spectroscopy.