Redox Intercalative Polymerization of Aniline in V₂O₅ Xerogel. The Postintercalative Intralamellar Polymer Growth in Polyaniline/Metal Oxide Nanocomposites Is Facilitated by Molecular Oxygen

Abstract

Polyaniline can be inserted in V2O5·nH2O xerogel by in situ oxidative polymerization/intercalation of aniline or anilinium in air. The reaction is facile and topotactic, forming polyaniline as the emeraldine salt. The interlayer separation (5.6 Å) is consistent with a monolayer of polymer chains in the V2O5 framework. Evidence is presented that oxygen acts as an electron acceptor both during the in situ reaction and long after intercalation is complete. The crucial role of oxygen in this reaction is probed and discussed. In an alternative route, anilinium is first intercalated and then, in a second step, is oxidatively polymerized in the xerogel upon exposure of the intercalate sample to air. Upon standing in air (aging), two processes occur independently in these materials: (a) the partial reoxidation of the reduced V2O5 framework and (b) further oxidative coupling of anilinium and aniline oligomers inside the V2O5 layers, leading to longer chain molecules. These observations are supported by several physicochemical data. The magnetic moment of (PANI) x V2O5·nH2O decreases gradually upon exposure to air, but it does not change when the sample is stored in vacuum. Gel permeation chromatography (GPC) analysis results show that the molecular weight of polyaniline extracted from aged (PANI) x V2O5·nH2O is larger than that extracted from the fresh samples. The thermal stability of polyaniline extracted from aged (PANI) x V2O5·nH2O is better than that extracted from fresh samples. All (PANI) x V2O5·nH2O samples are paramagnetic with a Curie−Weiss and a temperature-independent van Vleck contribution. Variable-temperature 2H-wide-line NMR of (PANI) x V2O5·nH2O shows that the polymer chains are sterically confined with respect to phenyl ring rotation. The room-temperature conductivity of the freshly prepared (PANI) x V2O5·nH2O samples is in the range 10-4−10-1 S/cm depending on the degree of polymerization inside the layers, but the conductivity of aged samples is always greater. Room temperature thermoelectric power is negative and varies (−30 to 200 μV/K) depending on the polymer content and the degree of polymerization.

Graphene-modified nanostructured vanadium pentoxide hybrids with extraordinary electrochemical performance for Li-ion batteries

“…At room temperature, the d-spacing of the V 2 O 5 -G is about 13.65 Å, which is much higher than that of the pure V 2 O 5 , 11.40 Å. Similar XRD results on the intercalation of polymers between V 2 O 5 layers in xerogel have been observed, suggesting that the interlayer spacing increased to between B12.0 and B15.0 Å, depending on the type of the polymer [46][47][48][49] . As the temperature increased, the (00l) reflection shifted to a higher 2-theta angle in a manner similar to that of the pure V 2 O 5 sample, but at a much slower rate.…”

Cathodes for lithium ion batteries: the benefits of using nanostructured materials

“…[55][56][57][58] Among these vanadium derivatives, the layered vanadium pentoxide, LiV 2 O 5 has been the most studied in spite of its low discharge voltage, low electric conductivity and slow diffusion kinetics of lithium ion. 59,60 To improve the performance of cells employing vanadium pentoxide as cathode several tricks have been tested, including the use of aerogels, 61-63 xerogels, [64][65][66] nanocomposites of LiV 2 O 5 with electronically conducting organic polymers 17,60,[67][68][69][70][71][72][73][74][75][76][77][78] and nanostructured materials (nanotubes, nanorods and nanoparticles). [79][80][81] In general, nanotubes of V 2 O 5 are prepared by sol-gel method from the hydrolysis of vanadium (V) triisopropoxide.…”

Transporte de carga em compósitos de polianilina/V2O5

“…A inserção de um caminho condutor paralelo às cadeias do V 2 O 5 provoca mudanças significativas no transporte eletrônico, uma vez que o transporte de cargas nestes materiais é governado pelos efeitos do espaço de cargas na interface situada entre a fase condutora (PANI) e as cadeias do óxido 52 . Graças às pontes de hidrogênio entre os dois componentes, envolvendo os átomos de oxigênio do V 2 O 5 e os áto-mos de hidrogênio da PANI (NH---O-V), suas cadeias são mantidas juntas, aumentando essa área interfacial e, conseqüentemente, provocando maiores efeitos na condutividade eletrônica 36 . O contato íntimo entre os componentes é observado a partir dos espectros de Ressonância Paramagnética de Elétrons, sugerindo uma grande aproximação (< 10 Å) entre os "polarons" da PANI e os centros V 4+ paramagnéticos 36 .…”

“…Graças às pontes de hidrogênio entre os dois componentes, envolvendo os átomos de oxigênio do V 2 O 5 e os áto-mos de hidrogênio da PANI (NH---O-V), suas cadeias são mantidas juntas, aumentando essa área interfacial e, conseqüentemente, provocando maiores efeitos na condutividade eletrônica 36 . O contato íntimo entre os componentes é observado a partir dos espectros de Ressonância Paramagnética de Elétrons, sugerindo uma grande aproximação (< 10 Å) entre os "polarons" da PANI e os centros V 4+ paramagnéticos 36 . 61 , caracterizando a formação de um nanocompósito.…”