Chandrappa, G.T.

Livage, J.

Steunou, N.

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3. Khush, G. S. Genome 42, 646–655 (1999). 4. Peng, J. et al. Nature 400, 256–261 (1999).5. Hooley, R. Plant Mol. Biol. 26, 1529–1555 (1994).6. Ross, J. J., Murfet, I. C. & Reid, J. B. Physiol. Plant. 100,550–560 (1997).7. Hedden, P. & Phillips, A. L. Trends Plant Sci. 12,523–530 (2000).8. Toyomasu, T. et al. Physiol. Plant. 99, 111–118 (1997).9. Xu, Y.-L. et al. Proc. Natl Acad. Sci. USA 92, 6640–6644 (1995).10.Maeda, H. et al. Breed. Sci. 47, 317–320 (1997).11.Zhang, W., McElroy, D. & Wu, R. Plant Cell 3,1155–1165 (1991).Competing financial interests: declared none.pounds, the bright yellow coloration of ourvanadium oxide foam indicates that all thevanadium ions are probably in their highestoxidation state (V5&). The hybrid foamscontain no water, even when dried at roomtemperature, and they have amphiphilicalkylamines intercalated between vanadiumoxide layers and are highly hydrophobic,separating readily at the surface of an aqueous solution. Vanadium oxide reacts with hydrogenperoxide to give V2O5.nH2O gels5 that havea layered structure composed of negativelycharged vanadium oxide ribbons. Thesegels can intercalate a wide variety of inorganic and organic species, such as protonated long-chain alkylamines6. In thefoaming process described here, gelationand intercalation both occur when the 1-hexadecylamine and hydrogen peroxidesolutions are added to vanadium oxidepowder. The intercalation of hexadecyl-amine between the V2O5 layers creates apasty solid, while the hydrogen peroxidedecomposes spontaneously in the presenceof vanadium oxide. Large pores are formedby oxygen gas released through the viscousgel in the presence of surfactants: as theyescape, the oxygen bubbles cause the form-ation of a voluminous polygonal foam,without destroying the crystalline structureof the oxide network of surfactant mol-ecules intercalated between the layers ofvanadium oxide. Meso- and macroporous solids are usually made in the presence of organictemplates which then have to be removedwithout damaging the inorganic shell7,8. Inthe foaming method we describe here,amines are simply intercalated betweenvanadium oxide planes and do not act astemplates for the formation of macropores.The experimental requirements are notcrucial — foams can form with amine/V2O5molar ratios ranging from 0.5 to 2.5, othersurfactants can be used and the process canbe extended to many different oxides (forexample, those of molybdenum (MoO3),titanium (TiO2) and zirconium (ZrO2)).G. T. Chandrappa*†, Nathalie Steunou*,Jacques Livage**Chimie de la Matière Condensée, Université Paris VI, 4 place Jussieu, 75252 Paris, Francee-mail: livage@ccr.jussieu.fr†Present address: Department of Chemistry,Bangalore University, 560001 Bangalore, India1. Mann, S. Angew. Chem. Int. Edn 39, 3392–3406 (2000).2. Mann, S. & Ozin, G. A. Nature 382, 313–318 (1996).3. Williams, R. J. P. in Biomineralization (eds Mann, S., Webb, J. &Williams, R. J. P.) 1–34 (VCH , New York, 1989).4. Livage, J. Chem. Mater. 3, 578–593 (1991).5. Alonso, B. & Livage, J. J. Solid State Chem. 148, 16–19 (1999).6. Liu, P., Moudrakovski, I. L., Liu, J. & Sayari, A. Chem. Mater. 9,2513–2520 (1997).7. Kresge, C. T., Leonowicz, M. E., Roth, W. J., Vartuli, J. C. &Beck, J. S. Nature 359, 710–712 (1992).8. Yang, P., Zhao, D., Margolese, D. I., Chmelka, B. F. & Stucky, G. D. Nature 396, 152–155 (1998).Competing financial interests: declared none.702 NATURE | VOL 416 | 18 APRIL 2002 | www.nature.com†Honda R&D, Wako Research Center, Wako 351-0193, Japan‡International Rice Research Institute, Manila,DAPO Box 7777, Philippines§BioResources Center and ¶Plant Molecular BiologyLaboratory, Riken, Tsukuba 305-0074, Japan 1. Hargrove, T. R. & Cabanilla, V. L. BioScience 29, 731–735 (1979).2. Dalrymple, D. G. Development and Spread of High-yielding RiceVarieties in Developing Countries (Bur. Sci. Tech., Agency Int.Dev., Washington DC, 1986). brief communicationsMaterials chemistryMacroporous crystallinevanadium oxide foamPorous inorganic solids can be syn-thesized in complex forms1,2, and herewe describe a simple method to create an ultralight, macroporous, crystallinevanadium oxide foam by bubbling oxygengas produced in situ through a viscous vana-dium oxide gel. This foaming process couldbe extended to other metal oxides. Vanadium oxide (V2O5) powder (1 g, or5.5210–3 mol) is mixed with a solution of along-chain alkylamine (1-hexadecylamine,C16H33NH2; 1.99 g, or 8.24210–3 mol) inacetone (3 ml).  A pasty material is formed,to which is added an aqueous solution ofhydrogen peroxide (50 ml, 30%). As H2O2decomposes, oxygen gas evolves and a voluminous bright yellow foam formsspontaneously (Fig. 1). The volume of thefoam increases rapidly and reaches 2.5 litresafter about 30 min. This new material isultralight, as only 1 g V2O5 is needed to generate the large volume of foam.Scanning electron microscopy of thefoam (Fig. 2a) reveals that it is highlyporous and has an irregular, honeycomb-like morphology. Large pores a fewmicrometres in diameter are surrounded byvanadium oxide walls about 1 mm thick.This unusual pattern resembles the hexago-nal cellular structures found in the skeletonsof some diatoms and radiolarians3. Themechanical properties of this porous materialare poor — the ultralight foam is brittle andcan easily be crushed into a powder. The vanadium oxide walls are crys-talline, and X-ray diffraction reveals fivesharp peaks that can be assigned to the 00lpeaks of a lamellar solid with a preferredorientation (Fig. 2b). The first 001 peakgives a basal distance, d, of 33.4 Å, which is much larger than the distance betweenvanadium oxide planes in the crystallineoxide or in V2O5,1.6H2O gels (d411.5 Å).This basal distance corresponds to thatnoted for hexadecylamine molecules inter-calated in vanadium oxide gels in whichthe alkyl chains are perpendicular to theoxide planes4. Contrary to observations of hybridorganic–inorganic vanadium oxide com-Figure 1 Light fantastic: up to 3 litres of a low-density, bright yellow vanadium oxide foam are formed when 1 g of V2O5 reactswith hydrogen peroxide in the presence of hexadecylamine.Figure 2 Structure of vanadium oxide foam. a, Scanning electron micrograph of vanadium oxide foam, showing its honeycomb-likestructure. b, The vanadium oxide walls are crystalline, as indicated by the 00l peaks of the X-ray diffraction diagram.04· 1038· 1031.2· 1041.6· 1044 8 12 16 202q  (deg)Counts (arbitrary units)a b© 2002 Macmillan Magazines Ltd

Materials chemistry - Macroporous crystalline vanadium oxide foam

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Materials chemistry - Macroporous crystalline vanadium oxide foam

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