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Novel Multilamellar Mesostructured Molybdenum Oxide Nanofibers and Nanobelts:

Synthesis and Characterization

Rui-Qi Song, An-Wu Xu,*,, Bin Deng, and Yue-Ping Fang

School of Chemistry and Chemical Engineering, Sun Yat-Sen UniVersity, Guangzhou 510275, China, andMax Planck Institute of Colloids and Interfaces, Department of Colloid Chemistry, MPI Research CampusGolm, D-14424, Potsdam, Germany

ReceiVed: June 21, 2005; In Final Form: September 30, 2005

One-dimensional molybdenum oxide nanostructures with layered mesostructures were prepared directly fromcommercial bulk MoO3crystals by a surfactant-templated hydrothermal process. X-ray diffraction, scanningelectron microscopy, transmission electron microscopy, infrared spectra, and thermal analyses have beenused to characterize the obtained molybdenum oxide nanomaterials. By use of cetyltrimethylammonium bromideas the structure-directing template, novel molybdenum oxide nanofibers with triple interlayer distances of2.84, 2.66, and 2.46 nm have been obtained. The nanofibers have diameters of 20 -100 nm and length up to20m. The growth of multilamellar molybdenum oxide nanofibers can be interpreted by the combination ofsurfactant/inorganic self-assembly process and host/guest intercalation chemistry. On the basis of the X-raydiffraction and infrared results, a possible arrangement of surfactant in the interlayer space of molybdenum

oxide by bilayer micelles with different tilt angles has been proposed. In addition, the thermal stability ofsurfactant has been improved by intercalation. Moreover, molybdenum oxide nanobelts with two kinds ofinterlayered structures were also produced in the presence ofn-alkylamines (n ) 12, 14, 16, and 18) followinga similar method, these nanobelts show length up to more than 10 m, width ranging between 200 and 600m, and width-to-thickness ratios of about 3-12. A linear relationship is observed between the interlayerdistance and the number of carbon atoms in n-alkyl chains.

Introduction

One-dimensional (1D) nanostructured inorganic materialsexhibit properties that differ from their corresponding bulkmaterials due to the reduced size and the large surface-to-volumeratios.1 Over the past decades, there has been considerable effort

devoted to fabricate 1D inorganic nanomaterials with differentmorphologies, such as nanowires, nanobelts, and nanotubes, tooptimize and utilize chemical and physical properties of thesematerials.2 Layered inorganic oxides have attracted continuinginterest with regard to their many applications resulting fromthe sorption properties and, therefore, for sorbents, productionof catalysts, ion exchangers, and electrochemical materials.3

Particularly, these materials have recently been investigated tobuild nanomaterials, in cases where 1D hollow nanostructureshave been fabricated by a high temperature-driven rollingprocess from 2D sheets of artificial lamellar structures.4

Molybdenum trioxide (MoO3), an important layered oxide,is especially attractive to be examined on the nanoscale, due toits layered crystal structure in the bulk and the multifaced

functional properties. It shows excellent catalytic activity inselective oxidation reactions, with applications not only inpetroleum refining and chemical production but also on pollutioncontrol industries.5 A wide range of application of MoO3andits derivatives can also be found in secondary batteries,electronic display devices, sensors, recording systems, andlubricants.6-9 For these applications, the efficient or sensitive

parameters have been found to be strongly dependent on thesurface area or interfacial properties of the MoO3 materials.Owing to the large aspect and surface-to-volume ratio, asignificantly large surface area could be expected when the sizerange of a material is downscaled to 1-100 nm in onedimension, as compared to its bulk counterpart. A variety of

techniques have been developed to control the architectures andmorphological patterns of MoO3materials. Examples includeelectrochemical process,10 carbon nanotubes template,11 acidi-fication of ammonium heptamolybdate tetrahydrate or molybdicacid,12,13 intercalation of neutral primary amine into molybdicacid,14 homogeneous solution reaction of sodium molybdate andperchloric acid,15 and infrared irradiation.16 Successful synthesisof 1D MoO3nanomaterials can be realized in these strategies;however, the study on the synthesis of MoO3nanofibers andnanobelts with multilamellar mesostructures based on surfactant/inorganic self-assembly process is still limited.

Our group has published extensively on the fabrication of1D nanostructures by solid-liquid-solid (SLS) growth fromoxide bulk crystals under hydrothermal treatment.17-19 Rareearth hydroxide nanotubes,17 lithium manganese oxide nano-belts,18 and porous magnesium hydroxide nanoplates19 have beensynthesized by this method that dose offer advantages over othersynthetic approaches. One of the advantages is the low costand availability of raw materials, which favors scaled-upindustrial manufacturing. Another advantage is the simplicityof the hydrothermal process, which proceeds at a mild temper-ature in aqueous solution under a sealed environment. Wepresent here a novel approach to assemble commercial bulkMoO3into triple-layered MoO3nanofibers in aqueous solutionby using cetyltrimethylammonium bromide (CTAB) as the

* To whom correspondence should be addressed. E-mail: [email protected]. Phone: 49-331-5679505. Fax: 49-331-5679502.

Sun Yat-Sen University. Max Planck Institute of Colloids and Interfaces.

22758 J. Phys. Chem. B 2005, 109,22758-22766

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structure-directing template. The approach of hydrothermalsynthesis, in combination with the structure-directing propertiesof organic components, could be exploited in the isolation ofmetastable inorganic-organic composites that maintain thestructural elements of the synthetic precursors. Furthermore,MoO3nanobelts can also be formed together with two kinds ofinterlayers by the same method using aliphatic primary aminesas the template. A possible arrangement of surfactant in theinterlayer space of molybdenum oxide by bilayer micelles withdifferent tilt angles has been proposed.

Experimental Section

Preparation.In a typical synthesis, 0.8 g of MoO3powders(Shanghai Chinese Colloid Chemical Factory, 99.5% purity) was

mixed with CTAB (Alfa, 99.9% purity) at the required molarratio in 18 mL of distilled water under ambient stirring for 2 h.Then the mixture was transferred into a stainless Teflon-lined25-mL capacity autoclave. The autoclave was sealed andmaintained at 180 C for 4 days and then air cooled to roomtemperature. The resulting MoO3nanofibers were collected andwashed with ethanol and then dried at 80 C in air overnight.MoO3 nanobelts were prepared by the same method in thepresence of primary monoamines with different alkyl chainlength as the structure-directing agents.

Characterization. The low-angle and wide-angle X-raypowder diffraction (XRD) diagrams of all samples were carriedout on a D/Max-IIIA X-ray diffractometer using Cu KRradiation ( ) 1.5418 ), with the operation power maintained

Figure 1. SEM image (a) and XRD pattern (b) of the starting material (commercial bulk MoO3crystals).

Figure 2. SEM images of the products synthesized in the presence of CTAB by hydrothermal treatment. CTAB concentration: 1.1 10-2 M (a),1.5 10-2 M (b), 7.6 10-2 M (c), and 1.5 10-1 M (d).

Lamellar Molybdenum Oxide 1D Nanostructures J. Phys. Chem. B, Vol. 109, No. 48, 2005 22759
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at 3 kW. Scanning electron microscopy (SEM) images wereobtained with a JEOL JSM-6330F operated at a beam energy

of 10.0 kV. For SEM measurements, the samples were coatedwith platinum for higher magnification. Transmission electronmicroscopy (TEM), high-resolution TEM (HRTEM), and selected-area electron diffraction (SAED) were performed on a JEOLJEM-2010 operated at acceleration voltage of 200 kV. Samplegrids were prepared by sonicating dry samples in ethanol for15 min and depositing one drop of the suspension onto a carbonfoil supported on a copper grid for TEM investigations. Fouriertransformation infrared (FT-IR) spectra were recorded on pelletsof the samples mixed with KBr on a Bruker EQUINOX FT-IRspectrometer in the range of 500-4000 cm-1 at a resolution of2 cm-1. A NETZSCH TG-209 unit was used to carry out thethermogravimetric and differential thermal analyses (TGA andDTA) under nitrogen atmosphere with a heat rate of 5 Cmin-1.

Results and Discussion

The SEM image and XRD patterns of the starting materialare shown in parts a and b of Figure l, respectively. The startingmaterial has irregular large particles with micrometer sizes andshows bulk orthorhombic MoO3polycrystalline, which matcheswell the standard JCPDS data (JCPDS 76-1003).

Figure 2 shows the morphology of the samples obtained byhydrothermal treatment of bulk MoO3crystals in the presenceof CTAB, measured by SEM. From this it can be clearly seenthat CTAB concentration has a significant effect on the growthof MoO3. The morphology changed dramatically with CTABconcentration variation. As shown in parts b and c of Figure 2,

MoO3nanofibers were obtained at CTAB concentrations rangingfrom 1.5 to 7.6 10-2 M, whereas excess CTAB in aqueous

solution led to exclusively entangled microsized fibers. CTABcould be responsible for the formation of the as-synthesizednanofibers due to the fact that no fibers can be observed in theabsence of CTAB. The reaction product consists almostexclusively of nanofibers when CTAB concentration wasincreased to 7.6 10-2 M. It is also found that the fibersbecome uniform in shape and warp slightly only in their endsat higher concentration of CTAB, accompanied by the decreasein the average diameter. The maximum length of the nanofibersobtained with CTAB concentration of 1.5 10-2 M is up to20m, and diameters range from several tenths to ca. 100 nm.

XRD patterns of the nanofibers formed by the hydrothermalprocess with different CTAB concentrations are shown in Figure3. Parts a and b of Figure 3 are the low-angle XRD patterns ofthe obtained products. It is interesting to note that tripleinterlayered mesostructures in MoO3nanofibers can be observed,which can be identified by the appearance of three groups of00lreflections. The peak (I) with the lowest intensity at 2 )3.05reflects one type of interlayer distance with dvalue of2.84 nm. The peak (II) with the intermediate intensity at 2 )3.27and the peak (III) with the highest intensity at 2 ) 3.56correspond to the other two types of interlayer distances withdvalues of 2.66 and 2.46 nm, respectively. The wide-angle XRDpattern of the sample is shown in Figure 3b and the inset inFigure 3c, with the reflections a little weaker than the 00lreflections in the corresponding low-angle XRD patterns. Alldiffraction peaks can be readily indexed to a pure orthorhombic

Figure 3. Low-angle (a) and wide-angle (b) XRD patterns of the product synthesized in the presence of 7.6 10-2 M CTAB. (c) Low-angle andwide-angle (the inset) XRD pattern of the product prepared at CTAB concentration of 1.5 10-2 M.

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phase (space group Pbnm62) with calculated lattice constantsR )3.965 , b )13.857 , and c )3.694 , in agreementwith the reported data (JCPDS 76-1003). It reveals that thecrystal phase of the MoO3 layers is the same as that of thestarting material.

TEM was also employed to provide further insight intostructure and morphology of the as synthesized MoO3nanofibersobtained in the presence of CTAB. Figure 4 shows therepresentative results of TEM characterization of the as-preparednanofibers, which confirms that the nanofibers are tripleinterlayered mesostructures. The selected ultralong nanofibershown in Figure 4c has a diameter of approximately 30 nm

and a respect ratio of 32. The walls appear as altering fringesof dark and bright contrast. The dark contrasts of narrow fringesrepresent the molybdenum oxide layers, between which theCTA+ cations are embedded. The layers of oxide in the selectednanofiber are separated by three characteristic distances of ca.2.9, 2.7, and 2.4 nm, respectively, as indicated in Figure 4c,which agree well with the results calculated from the dvaluesof the 00lreflections of the low angle XRD pattern. Figure 4bshows the corresponding SAED pattern taken from a singlenanofiber shown in Figure 4a. The SAED pattern supports thewell-crystallized structure inside the MoO3fiber walls. More-over, the lamellar structure is also confirmed by the multiplefringes observed in the image from the HRTEM investigationon the sample obtained at CTAB concentration of 1.5 10-2

M, as shown in Figure 4d. It is also found that most layerswithin the fibers are indeed unequally separated from each other.The repeat varying interlayer spacings between corresponding

planes in the fiber wall structure give rise to strong reflectionsat the low-angle XRD pattern.There has long been much interest in the use of MoO3because

of the ability of this material to act as host for intercalationchemistry, in which guest molecules are believed to insert intothe host lattice by electron transfer. In general, when smallercations, such as alkalis, silver, and ammonium, are present inthe reaction system, tunnel structures or three-dimensionallattices are formed.20 For the intermediate size cations such astetramethylammonium, layered structures as well as Keggin-like cluster complexes dominate. For the larger cations, suchas C12H25N+(CH3)3, flakelike layered microcrystals are found.In contrast, the combination of hydrothermal treatment with theuse of CTAB here permits to promote the formation of MoO3

nanofibers with high aspect ratios. On the other hand, the as-synthesized fibers have unique wall structures consisting ofMoO3 layers that are separated by triple interlayer spacings.

In the cationic surfactant-inorganic layered solid intercalatingsystems, the cationic headgroup is believed to be tethered tothe internal surface of the galleries of the layered inorganic hostsby Coulomb forces.21 The surfactant molecules can adopt avariety of structures in the galleries, such as monolayer, bilayer,and paraffin-type monolayer, depending on the grafting densityand the structure of the surfactant methylene tail. In addition,the methylene chain can behave as the trans or gaucheconformer, which differ from each other distinctively in theirvibrational modes.22 FT-IR spectroscopy has been used as asensitive tool to probe the structure and organization of alkyl

chain assemblies.The room-temperature FT-IR spectra in the 500-4000-cm-1

region of solid CTAB, lamellar MoO3nanofibers prepared withCTAB concentration of 1.5 10-2 M and bulk MoO3crystalare shown in Figure 5. On the basis of the literature values, themolybdenum oxide lattice vibrations appear at 553, 858, and994 cm-1, respectively. The IR contour in Figure 5c indicatesthe signals of three bands at 550, 853, and 996 cm-1, whichcan be assigned to the lattice vibration mode of MoO3. Becauseof the presence of CTAB in the synthetic process, it is reasonableto expect the appearance of the relevant CTAB bands, especiallytogether with XRD results. It has been reported that theantisymmetric and symmetric deformation modes pertaining toC16H33(CH3)3N+ of the CTAB headgroup appear at around 1390

Figure 4. Typical TEM image (a), SAED pattern of an individualnanofiber (b), and HRTEM image (c) of the obtained molybdenumoxide nanofibers at CTAB concentration of 7.6 10-2 M. (d) HRTEMimage of lamellar MoO3nanofibers obtained at CTAB concentration

of 1.5 10-2 M.

Figure 5. FTIR spectra of reagent crystalline CTAB (a), MoO3 aspurchased (b), and the product prepared in the presence of 1.5 10-2

M CTAB (c).

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and 1490 cm-l.22 In fact, from Figure 5 it can be seen that thebands shift to lower frequency as layered MoO3nanofibers wereformed. Two intense bands appear at 2846 and 2920 cm -1 inthe IR spectrum of the multilamellar MoO3nanofibers, whichcan be attributed to the antisymmetric and symmetric C-Hstretching modes of the methylene groups, respectively. Thesefrequencies are almost identical to those for the correspondingbands of solid CTAB, indicating that trans conformers dominatein the methylene chains.23 The absence of splitting of the 720

cm-

1 band also supports the large distance between chains oftrans conformers, leading to weaker lateral interchain interac-tions than those of the gauche conformers. Additional bands inthe regions of 3250-3750 cm-1 can be also observed in allsamples sets, indicating the presence of hydration of the cationicheadgroup of the surfactant.

The presence of CTA+ cations is most likely responsible forthe anisotropic growth and the appearance of the three distinctinterlayer spacings. The c-axis interlayer spacings of thenanosized fiberlike MoO3intercalate, as calculated from the 00lreflections in the XRD patterns in Figure 3a, are 2.84, 2.66,and 2.46 nm, respectively. This corresponds to intercalationswith lattice expansions of 2.15, 1.97, and 1.77 nm, comparedto those of MoO3 bulk crystal.24 By comparison with the

expansions in dspacing with the length of the fully stretchedCTA+ cations, 2.2 nm,25 it is concluded that the intercalatedCTA+ cations adopt bilayer structures with different tilt anglesbetween the MoO3 layers. Figure 6a shows the possiblearrangements of the intercalated CTA+ cation that can accountfor the observed occurrence of three different expansions ininterlayer spacings. Three panels as shown in Figure 6a havethree tilted bilayers inserted without interdigitation, in whichtwo all-trans methylene chains sandwich between the internal

surfaces of the opposing oxide layers. The value of the tilt anglesis determined from the X-ray lattice expansions assuming thatthe chains are all trans and that there is no interdigitation in theintercalated CTA+ cations bilayer.

It is well known that surfactant molecules in aqueous solutionabove a critical micelle concentration self-aggregate to formmicelles.26 And in our synthetic system, the bilayer micellesformed by CTAB serve as template and direct the formation ofthe MoO3nanofibers. As shown in Figure 1b, the precursor isindexed to the orthorhombic phase of MoO3. By considerationof the structural particularity of MoO3, a selective adsorptionmechanism is employed to interpret the formation of MoO3nanofibers assisted by CTAB. As shown in Figure 6b, theorthorhombic structured MoO3has a distinct layered structure,

Figure 6. (a) Cartoon illustrating the formation of CTAB-mediated assembly of multilamellar structured MoO 3nanofibers. (b) Structure model ofMoO

3sheets as seen along the [010] direction.

Figure 7. TGA and DTA curves collected from the pure CTAB (a) and the as-synthesized MoO 3 nanofibers in the presence of 7.6 10-2 MCTAB (b). In all graphs, dashed lines correspond to the DTA curves and solid lines correspond to the TG curves.

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in which one monolayer is one layer of MoO6octahedrons withcorner sharing along the [100] direction and edge sharing alongthe [001] direction. And two MoO3 monolayers have the

structure in which one of the slabs orient perpendicular to the[010] direction.27 Charge sensitivity analysis and periodicboundary density functional calculation have been developedto identify reactivity trends and chemisorption activity of MoO3surfaces. It is proposed that the (010) MoO3 surfaces exhibitstronger preference for adsorption and catalytic activity.28 Duringthe 1D anisotropic growth, the oxide bulk crystals dissolvedand recrystallized under hydrothermal conditions, further re-nucleated at the selected surfactant-inorganic interfaces. CTABmicelles would play capping effect on the (010) MoO3surfacesowing to the stronger activity and higher selectivity of thesurfaces for the adsorption of CTAB. This inhibits crystal growthalong the [010] direction. On the other hand, the bondingsituations for MoO6along the [100] direction is different from

that along the [001] direction.29 Two Mo-O bonds will beformed if the octahedron grow along the [001] direction, whileonly one Mo-O bond forms in case of the growth along the[100] direction. From the point of energy view, the greaterenergy released in the growth along the [001] direction isfavorable for the anisotropic growth along the [001] direction.Hence, the formation of the nanofibers is preferred. And thesurfactant micelles are suggested to behave as glue that holdsnanocrystals together with different lamellar spacings by stericand electrostatic interaction. As to different morphologies subjectto variation in CTAB concentration, the main reason can beattributed to the competition between formation and stabilizationof surfactant micelle structures, which is controlled by thecounterion condensation. Prior to the addition of oxide precursor,

the surfactant molecules are in a dynamic equilibrium betweenmicelles and single molecules. Upon the addition of oxide, thenumber density of nanofibers increases with the strong growthof micelles of the surfactant. A bilayer of CTA+ should makethe MoO3layers positively charged. Thus, the growth into 1Dnanostructures could be significantly restricted due to the highercondensation of Br- on the micelle surfaces with the incrementin the size of surfactant micelle, as the solution becomes moreconcentrated.

Figure 8. SEM images of the MoO3nanobelts with lamellar structures prepared by hydrothermal treatment in the presence of dodecylamine (a),tetradecylamine (b), hexadecylamine (c), and octadecylamine (d).

Figure 9. Low-angle XRD pattern of the nanobelts prepared withequivalent molar ratio of MoO3and dodecylamine under hydrothermaltreatment at 180 C for 7 days. Inset: wide-angle XRD pattern of thecorresponding nanobelts.

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Thermal stability of the as-synthesized nanofibers was alsoinvestigated to further comprehend the formation process of thenanofibers. Figure 7 shows the TGA and DTA curves of pureCTAB and the as-synthesized MoO3nanofibers. As expected,the TGA-DTA of pure solid CTAB exhibits a single mass loss,a distinct exothermic peak accompanied by 100% mass lossoccurred at temperatures in the range of 200-270 C. On theother hand, the TGA curve of obtained MoO3nanofibers canbe divided into three stages. In the first stage, no othercomponents but lattice H2O molecules were released before 300C with a mass loss of 1.27%. Two sequential exothermic peaksbetween 300 and 400 C with a general mass loss of 24.0%could be attributed to the CTA+ decomposition and theelimination of bromide species. The fact that the synthesized

MoO3nanofibers is thermally stable until 300

C, suggestingthe affinity between the CTA+ cations and the bonding sites of

the oxide layers, which is effective in improving the thermalstability of CTAB.

In addition to the CTAB-directing 1D MoO3multilamellarnanofibers described in this report, assembly of bulk MoO3crystals into 1D nanobelts with lamellar mesostructures was alsorealized by using neutral long-chain primary amine (CnH2+1-NH2,n ) 12, 14, 16, and 18) as the structure-directing templateinstead of CTAB. Following the same scenario in the fabricationof MoO3 nanofibers, layered MoO3 nanobelts were obtained

by hydrothermal treatment of commercial bulk MoO3crystalsin the presence of monoamines. SEM images corresponding tothe samples prepared by using dodecylamine, tetracylamine,hexacylamine, and octacylamine are shown in Figure 8,respectively. It shows that nanobelts were formed from bulkMoO3crystals by hydrothermal treatment at 180 C for 7 days.It is found that the quantity of alkylamines is an important factorin determining the morphology of the final products. Well-defined 1D nanobelts can be grown at equivalent molar ratioof MoO3to amines. As shown in Figure 8, some nanobelts werescrolled to form interesting morphologies such as water pipefor fire protection when dodecylamine or tetracylamine was usedas the template. The length of the obtained nanobelts is usuallyseveral tenths of micrometers, and their widths are typically

200-600 nm, significantly wider and longer than those of MoO 3nanofibers obtained in the presence of CTAB. As a result, width-to-thickness ratios of the nanobelts are usually in the range ofca. 3-12. These lamellar mesostructures were formed by theintercalation of surfactant into MoO3layers, and lamellar sheetswere further rolled into the nanobelts under the certain condi-tions.

It should be noted that the low-angle XRD patterns for theproducts obtained by the use ofn-alkylamines have two groupsof 00l reflections, as similarly observed for the case in thepresence of CTAB. Taking the intercalation of dodecylaminein MoO3as an example, Figure 9 shows the XRD patterns ofthe corresponding products with morphology as shown in Figure

8a. After assembly of MoO3 directed by dodecylamine, thereflections of MoO3 bate and a new phase appears with two

Figure 10. A linear relationship between interlayer distance and thenumber of carbon atoms in alkylamines. Interlayer distances weredetermined from thedvalue of the two groups of 00lreflections in theXRD patterns of the MoO3nanobelts obtained by using alkylaminesas the template.

Figure 11. TEM images of the beltlike MoO3with lamellar structures prepared by the hydrothermal method using different neutral amines as thetemplate at 180 C for 7 days with 1:1 molar ratio of MoO 3 to amines: (a) dodecylamine, (b) tetradecylamine, (c) hexadecylamine.

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interlayer dspacings of 2.88 and 3.04 nm, resulting from theconcurrent adsorption and insertion of dodecylamine in theMoO3 sheets during the hydrothermal process. As shown inFigure 9, the two distinct interlayer distances correspond to twodifferent orientations of the bilayers formed by dodecylaminesbetween the adjacent oxide layers. The inset shows less intensepeaks at smallerdvalues, corresponding to the structure withinthe layers. The diffusing reflections can be indexed to ortho-rhombic phase MoO3.

Figure 10 shows the variations in the distance between thelayers, caused by varying template with different alkyl chains.It indicates that the interlayer distance increases proportionalto alkyl length of the n-alkylamine. The 00lpeaks shift slightlyto lower angles, reflecting an increase in the lamellar spacingwith increasing the number of carbon atoms in then-alkylaminetemplates chosen for study here. Although the reflections oftype 00lmove to largerdvalues with the increment of the alkylchain length, the reflections in wide-angle XRD patterns of thecorresponding products are independent of the alkylaminetemplates. The result suggests that template has no effect onthe wall structure within the layers.

TEM images of the beltlike products obtained using neutralamines with alkyl chains of different lengths are presented in

Figure 11. It is evident from the images that the lamellarstructures could be formed across long distance independent ofthe alkyl length of the amines. The warped shape of thenanobelts might be attributed to mechanical stress caused byincreased interlayer expansion due to the insertion of n-alkylamines between two adjacent oxide layers, as comparedto the case for CTAB-templated assembly of nanofibers. Thereason might lie in that neutral long-chain primary amines havelower steric effects than CTAB with respect to few branchedgroups.

Conclusions

Our present study shows that 1D MoO3 nanofibers and

nanobelts with multilamellar mesostructures can be synthesizedfrom commercial bulky MoO3crystals by a surfactant-templatedhydrothermal process. The combination of hydrothermal treat-ment with the use of surfactant promotes the anisotropic growthvia SLS transformation. CTAB can be successfully inserted intoMoO3layers with three tilt angles to form a novel intercalationstructure with three interlayer distances in aqueous solution, andthese lamellar sheets are further grown into 1D nanostructures.The as-synthesized fiber-shaped oxide with CTA+ cationsintercalated in improves the thermal stability of the surfactant.The choice of surfactants and their concentration greatlyinfluence the morphology and structure of the resultant products.MoO3 nanobelts with bilamellar mesostructures were alsoprepared by the same method employing neutral amine with

long alkyl chain as intercalating template. Well-developednanobelts with two interlayer distances can be obtained withequivalent molar ratio of Mo/alkylamines after duration inaqueous solution. The interlayer distances can be easilycontrolled by using monoamines with different length of alkylchains.

The present work provides much inspiration toward theformation of a target structure with desired morphologies,arrangements, and even improved functional properties. Theflexible strategy reported herein is being expanded to prepareother 1D nanostructured materials. For example, starting frombulk Co2O3 crystals with the use of alkylamines, we haveprepared cobalt oxide nanowires. Tungsten oxide nanosheetshave also been obtained from bulk WO3crystals in the presence

of alkylamines. Surfactant-assisted hydrothermal synthesis of1D binary oxidic nanomaterials from the corresponding com-mercial bulk powders is also in progress.

Acknowledgment. We are grateful to the National NaturalScience Foundation of China (20371053) and the NaturalScience Foundation of Guangdong Province (031574, 04300770)for financial support. A.-W. Xu thanks the Alexander vonHumboldt Foundation for granting a research fellowship. This

work was also supported by the Young Teacher Starting Projectof Sun Yat-Sen University (for R.-Q. Song).

References and Notes

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