Synthesis of vanadium oxide nanofibers and tubes using polylactide fibers as template

doi:10.1016/j.materresbull.2004.10.005

Materials Research Bulletin

Volume 40, Issue 2, 15 February 2005, Pages 383-393

https://doi.org/10.1016/j.materresbull.2004.10.005 Get rights and content

Abstract

A new method to produce vanadium oxide nanofibers with dimensions <140 nm and tubes is reported. Vanadium oxide was coated on polylactide fibers by a sol–gel method using a reaction mix of ammonium vanadate and acetic acid as starting materials and water as solvent. Vanadium oxide tubes, of about 1 μm in diameter, were formed when this coated fiber was heated in nitrogen and oxygen at 300 and 250 °C for 1 h. Hydrothermal treatment of the polylactide fibers with the reaction mix at 160 °C for 12 h followed by heating in oxygen at 300 °C for 1 h formed vanadium oxide nanofibers, 60–140 nm in width and several microns in length. Electrochemical studies reveal that these vanadium oxide nanofibers are redox active and readily undergo reversible reactions with lithium in non-aqueous cells.

Introduction

We are exploring the synthesis and properties of vanadium oxide nanotubes and nanofibers. There is considerable interest in the development of new synthetic routes to nanostructured materials. Chemical structures and systems within the size range from 1 to 100 nm in one, two, or three dimensions are typical of such materials [1]. They attract considerable attention because of their novel and superior properties when compared with the bulk. It has been shown that transition metal oxide nanostructures possess enhanced device applications as a consequence of their size and topology [2]. Recently, transition metal oxide nanostructures have been prepared using different templates; namely, carbon nanotubes, alumina membrane and surfactant molecules. The preparation of metal oxide nanocomposites and oxide fibers using carbon nanotubes as removable templates have been reported previously since the technique was first developed by Ajayan et al. who prepared such materials based on V₂O₅ [3]. Metal oxide nanostructures have also been prepared by the use of sol–gel chemistry within the pores of alumina and polymer membranes [4], [5]. Micelle-based chemical synthesis is a known approach for preparing nanostructures with well-defined dimensions [6]. Recently, vanadium oxide nanotubes were prepared using surfactant templates [7]. These compounds contain δ-like vanadium oxide layers, with vanadium in VO₆ octahedra. This structure is particularly suitable for redox reactions [8], [9], [10]. The high specific surface area of V₂O₅ nanostructures could have significant implications with respect to energy storage devices based on electrochemically active sites and energy conversion devices depending on catalytic sites or defect structure.

Here, we report for the first time the synthesis of vanadium oxide nanofibers and tubes using polylactide fibers as a template. In the latter, the template induces important changes in morphology and growth of the nano-sized fibers, rather than acting as templates for gel particles to condense around. Further evidence for this is that the size of the polylactide template fibers is much larger than that of the V₂O₅ fibers formed. This new mode of formation of the nanofibers could constitute a new strategy of nano-structuring inorganic solids.

Section snippets

Synthesis

Acetic acid, hydrochloric acid, ammonium metavanadate, NH₄VO₃ (all from Fisher), dimethylformamide, methylenechloride and polylactide-PLA (Mw: 55,000) (Aldrich), were used without additional purification. PLA (2 g) was added to 50 ml of DMF/CH₂Cl₂ mixture (ratio by volume, 35:65). The mixture was stirred for 10 min at room temperature and then electron spun according to the literature [11], [12]. The PLA solution was put into a hypodermic syringe with a metallic needle. A positive potential of 0.8

Results and discussion

Polylactide (PLA) is a biodegradable polymer and can be synthesized from either a condensation polymerization of lactic acid or ring opening polymerization of lactide, a cyclic dimer of lactic acid. The electro spinning technique [13] has been used in the past decade to produce micro- and nanofibers from polymer solutions [14]. The morphology and diameters of the fibers are influenced by the solution viscosity, applied potential, and surface tension of the solution. For this work the PLA fibers

Conclusions

We have employed a fiber template-directed process to prepare vanadium oxide with novel fibrous and tubular morphology. This technique can be employed to prepare metal oxide nanostructures and thin films. The nanofiber electrochemical data show that it is possible to use a template method to prepare nanostructured electrodes with improved capacity and cyclability.

Acknowledgements

Financial support from the National Science Foundation, DMR-0313963, is gratefully acknowledged. We also thank Henry Eichelberger and Prof. Naslund for help with the SEM/TEM studies and DCP-AES measurements, respectively.

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Synthesis of vanadium oxide nanofibers and tubes using polylactide fibers as template

Abstract

Introduction

Section snippets

Synthesis

Results and discussion

Conclusions

Acknowledgements

Synth. Met.

Mater. Res. Bull.

Solid State Ionics

Adv. Mater.

Acc. Chem. Res.

Nature

J. Mater. Chem.

Appl. Phys. Lett.

Angew. Chem.

Chem. Mater.

J. Electrochem. Soc.