Room-Temperature Synthesis of Self-Assembled Sb2S3 Films andNanorings via a Two-Phase ApproachQiaofeng Han,*,† Yawen Yuan,† Xiaoheng Liu,† Xiaodong Wu,† Fengli Bei,† Xin Wang,*,†

and Kaijun Xu*,‡

†Key Laboratory for Soft Chemistry and Functional Materials, Ministry of Education, Nanjing University of Science and Technology,Nanjing 210094‡Physical Chemistry Lab, China Pharmaceutical University, Nanjing 210009, China

*S Supporting Information

ABSTRACT: The freestanding Sb2S3 films were easily synthesized at the interfaceof water and toluene at room temperature, where Na2S and (C2H5OCS2)3Sb(xanthate, O-ethyldithiocarbonate) acted as sulfur and antimony source,respectively. After 3 h of aging, the Sb2S3 films with a flat surface toward organicside and rough surface toward aqueous side were assembled by sheaflike Sb2S3nanowires. The Sb2S3 nanorings formed by end-to-end connection of the bundlednanowires appeared in the water layer when the reaction time reached 24 h. TheSb2S3 nanorings showed higher photocatalytic activity for methyl orangedegradation under visible light than the Sb2S3 films owing to broader spectrumresponse and better aqueous dispersion.

■ INTRODUCTIONOne-dimensional (1D) semiconductor nanostructures, such asnanowires, nanobelts, nanotubes, and nanorings, have becomeone of the most active research areas within the nanosciencecommunity due to their potential application.1 Controllablegrowth of 1D semiconductor nanostructures has been a crucialissue for nanoscale science. The approaches which have beendeveloped for preparing 1D structural semiconductor materialscan be placed into two categories, i.e., solution-phase2 andsolventless synthesis.3 The solution-phase method has beenwidely used due to its mild synthetic conditions. Particularly,liquid−liquid interfacial synthesis has been established as auseful alternative candidate to generate metal or semiconductornanoparticles because the interface possesses unique thermody-namic properties such as viscosity and density, the fluidity ofliquids may heal defects, and their rich phase separationbehavior may diversify the structural complexity.4 Thecontrolled interfacial self-assembly has been successfullyrealized by the proper design of the capping ligands on thenanocrystals.Among the 1D semiconductor nanostructures, nanorings are

especially interesting, because they can be an ideal system forinvestigating shape-related physical phenomena.5 The fabrica-tion of semiconductor nanorings was hindered owing to theirunique geometrical shapes which would require unconventionalsynthetic approaches. The reported nanorings were formed byself-coiling of the nanowires or nanobelts, colloidal lithography,and etching. The synthesis routes include lithography,molecular-beam epitaxy, molten salt synthesis, vapor−liquid−solid approach, template-assisted solution method, and so on.6

Most of the methods were complex and high cost. In this paper,

the Sb2S3 nanorings formed by end-to-end connection of thenanowires are easily obtained under ambient conditions.The Sb2S3 films have been attracting a great deal of attention

because of their potential applications in optoelectronic devices,solar cells, thermoelectric cooling technologies, fast ionconductors, and switching devices.7 The Sb2S3 thin films canbe obtained by a spray pyrolysis,8 vacuum evaporation,9

chemical bath deposition technique,10 and so on. However,the reported Sb2S3 films were prepared on substrates, thestructures and hence properties of the films were substrate-dependent, and in particular, the preparation of the films withhigh orientation required expensive substrates such as singlecrystals or highly functional substrates. The synthesis ofsubstrate-free semiconductor films still remains a key researchchallenge. The air−water interface has been exploited for thepreparation of self-supporting semiconductor films.11 Theliquid−liquid interface has not been investigated sufficiently.12

Herein, we demonstrate a facile liquid−liquid interfacial routeto synthesize substrate-free Sb2S3 films assembled by thenanowires.The synthesis for the nanostructured materials via an

organic−aqueous interfacial method primarily involves takinga metal organic compound in the organic layer and a reducing,a sulfiding, or an oxidizing agent in the aqueous layer. Thedevelopment of low-cost metal organic precursors is importantto the interfacial routes. O’Brien et al reported the synthesis ofPbS pyramids and Bi2S3 globules by using metal dithiocarba-mates as precursors at the water−toluene interface.13 Our

Received: January 17, 2012Revised: April 12, 2012Published: April 16, 2012

Letter

pubs.acs.org/Langmuir

© 2012 American Chemical Society 6726 dx.doi.org/10.1021/la300244c | Langmuir 2012, 28, 6726−6730

previous studies indicated that metal xanthate was also a goodprecursor to prepare chalcogenides with tunable size andcontrollable shape.14 In this communication, self-supportingSb2S3 films are synthesized at the interface between a toluenesolution of antimony xanthate and an aqueous Na2S solution atroom temperature over 3 h, and interestingly, unique Sb2S3nanorings were formed in the sediments when the aging timewas extended to 24 h.

■ EXPERIMENTAL SECTIONSample Preparation. Yellow antimony O-ethyldithiocarbonate

precipitates were prepared according to our previous work.14 2.0 g (8.4mmol) of Na2S·9H2O dissolved in 20 mL of H2O was added dropwiseinto 40 mL toluene solution containing 1.0 g (2.0 mmol)

(C2H5OCS2)3Sb at the room temperature. The mixture was keptstill and aged for different times. The sheets at the liquid−liquidinterface were skimmed and rinsed with water and absolute ethanol,and dried spontaneously in air. The sediments were collected byfiltration, washing, and drying.

Characterization. The X-ray diffraction patterns (XRD) wererecorded on a Bruker D8 advanced X-ray diffractometer equipped withCu Kα radiation (λ = 0.1542 nm). The film were broken down andskimmed by carbon-coated copper grids for scanning electronmicroscopy (SEM) observation. SEM was carried out on a LEO-1530VP scanning electron microscope. Transmission electronmicroscopy (TEM) and the corresponding selected area electrondiffraction (SAED) were carried out on a JEM-2100 microscope(JEOL), equipped with an EDAX X-ray energy dispersivespectrometer. The films were crushed and dispersed in ethanol byultrasonication, and two or three drops of suspension was then put on

Figure 1. Digital pictures of the interfacial reactions with the different reaction time of (a) 0 h, (b) 0.5 h, and (c) 8 h.

Figure 2. TEM and SEM images of Sb2S3 nanowires and films collected at the liquid−liquid interface at different aging time: (a) 1 h, and (b−f) 3 h.

Langmuir Letter

dx.doi.org/10.1021/la300244c | Langmuir 2012, 28, 6726−67306727

a carbon-coated Cu grid and allowed to dry. The X-ray photoelectronspectra (XPS) were recorded on a Phi Quantera II SXM X-rayphotoelectron spectrometer, using a monochromatic Al Kα radiation(λ = 8.4 Å) as the exciting source. The diffuse reflection spectra weremeasured on a Shimadzu UV-2550 spectrophotometer equipped withan integrating sphere, using BaSO4 as a reference. Raman spectra ofSb2S3 nanorings were obtained using a Renishaw Invia spectrometer.Photocatalytic Activity Test. The photocatalytic reaction was

conducted in a reactor equipped with a 500 W Xe lamp and a 420 nmUV cutoff filter. A 200 mg quantity of catalyst was suspended in 200mL of 10 mg · L−1 methyl orange (MO) aqueous solution. Thesuspension was ultrasonated for 15 min and magnetically stirred in thedark for 1 h to ensure the establishment of an adsorption−desorptionequilibrium of the dye on the catalyst surface. Then, the suspensionwas stirred and illuminated by visible light. At given time intervals, 5mL of suspension was taken out from the reactor and centrifuged toremove the photocatalyst particles. The concentration of MO duringdegradation was determined on a UV−vis spectrometer and estimatedfrom the absorbance of the absorption maximum at 464 nm.

■ RESULTS AND DISCUSSIONAfter the addition of Na2S aqueous solution into toluenesolution of antimony xanthate was complete, the mixture wasleft without any disturbance, and about 30 min later, a brownthin layer appeared at the middle of the interface except for alittle attached to the beaker wall (Figure 1b, a bird’s-eye view),indicating that nucleation and growth first occurred at theinterface, which suggests that, within this emulsive region, asmall region with controlled supersaturation of reactants coexistproviding a site for nucleation.13 Transmission electronmicroscopy (TEM) image of the layer, transferred from theinterface, revealed the formation of randomly dispersednanowires (Supporting Information, Figure S1). With thereaction time extending, brown Sb2S3 particles were graduallydeposited to cover the whole interface (Supporting Informa-tion, Figure S2). When the reaction reached 1 h, bushlikestructures with dense roots at the interface and sparse branchesgrowing forward to the water layer were formed (Figure 2a).Bushlike nanowires changed more densely after 2 h(Supporting Information, Figure S3).When aging for 3 h, robust Sb2S3 films were formed at the

liquid−liquid interface. The standalone Sb2S3 films werecomposed of unique nanowires, which grew forward to theaqueous solution (Figure 2b). A high-magnification TEMimage of a typical nanowire indicated its bundled structures(inset in Figure 2b), which may be because one-dimensionalantimony sulfide has a strong preference for attachment to itselfin the direction vertical to the growth direction.15 Differentfrom Rao’s report,4b our work showed that the side of the filmfacing the organic layer was smooth (Figure 2c), and a high-magnification SEM image revealed that the smooth sidecontained tightly packed nanowires (Figure 2e). While theside facing the water layer was rough with randomly dispersednanowires (Figure 2f), some were straight, standing perpen-dicular to the liquid−liquid interface, and others got curved(Supporting Information, Figure S4). The dense section of thefilm had a thickness of about 2 μm from the fracture edge-onprofile of the film (Figure 2d).As the reaction proceeded, the nanowires came closer to each

other and packed themselves at the interface to give pieces ofSb2S3. Because negatively charged xanthate ligands weretransferred from organic layer into aqueous layer, adsorbed tothe surface of the films and interacted with Sb3+ on the surfaceof the nanowires, the side of the films facing the aqueous layerappeared rough. The change of the color of the solution with

the aging time could further confirm this. At first, the color ofthe water phase was colorless and the color of the oil phase wasyellow due to the dissolution of antimony xanthate in toluene(Figure 1a). However, the color of the oil phase graduallychanged from yellow to colorless along with the reaction time,while the color of the water phase presented as yellow (Figure1c), which visually indicated that sodium xanthate and Sb2S3were generated by the reaction of antimony xanthate and Na2S,and as a result, Sb2S3 stayed at the interface and sodiumxanthate were transferred slowly from the oil to water phasedue to its high solubility in water.The thickness of films at the interface increased with time.

After 8 h of aging, brown flocculates began to fall down into thewater layer (Figure 1c), and 24 h later, a large amount ofsediments deposited at the bottom of the beaker (SupportingInformation, Figure S5). SEM images revealed the sedimentswith ring-like appearance and the yield of the nanorings wasvery high (>90%) (Figure 3a). The rings had typical diameters

of 1−2 μm and wall thickness of 50−200 nm (Figure 3b).From the fracture of an individual ring (Figure 3c; SupportingInformation Figure S10a), it can be speculated that thecomplete ring was made of bundled nanowires bent at thecurvature of the ring and connected by end to end, which wasdifferent from previously reported formation of the rings byloop-by-loop winding of nanobelt/nanowires, etching ofnanoplanes, or lithography strategy.5,6 The selected-areaelectron diffraction (SAED) revealed that the ring patternswere somewhat vague, and thus, the sample seemed to bearsome noncrystallinity (inset in Figure 3d). The presence ofseveral broad humps in XRD pattern also suggests that thenanorings appeared to be partially crystalline and thecrystallinity was not high (Supporting Information, FigureS6). The Raman spectra of Sb2S3 nanorings revealed two mainbands with maxima near 130 and 285 cm−1 (SupportingInformation, Figure S7), corresponding to two main structuralunits: SbS3 pyramids and Sb−Sb bonds in S2Sb-SbS2 structuralunits.16 The broad peaks showed the formation of poorlycrystallized products, which was consistent with the SAED and

Figure 3. SEM (a) and TEM (b−d) images of Sb2S3 nanorings in thesediments after a reaction of 24 h.

Langmuir Letter

dx.doi.org/10.1021/la300244c | Langmuir 2012, 28, 6726−67306728

XRD results. The chemical composition of Sb2S3 nanorings andfilms was determined by EDS in TEM, as shown in SupportingInformation S8, showing the present of the Sb and S elements.The surface composition of the as-prepared Sb2S3 nanorings

and films was further checked by the XPS spectra (SupportingInformation, Figure S9). The peaks at 529.8 and 539.2 eVcorresponded to the binding energies of Sb 3d5/2 and Sb 3d3/2core levels, respectively. The S 2p spectra were fitted to singlespin−orbit doublets at 161.8 and 163.2 eV, assigned to thebinding energies of S 2p3/2 and S 2p1/2, respectively (FigureS9b). All of the observed binding energy values for Sb 3d and S2p coincided with the reported data.17 Quantification of theXPS peaks gave the molar ratio of the products as 0.6:1.0 forSb:S, showing a slight excess of sulfur in contrast to the givenformula.With the aging time, the yield of Sb2S3 nanowires was too

high for the interface to support owing to the small interfacialattachment energy, and so they fell down from the interface.The appropriate surface hydrophobicity of the nanowires dueto the coordination interaction of Sb3+ with xanthate and lowdensity made them fall down slowly. These were crucial for thenanowires to roll into ring-like structures. The ends of thenanowires were even (Figure 3c; Supporting Information,Figure S10), and dangling bonds of the ends may be eliminatedby the end to end interaction, forming stable nanorings. Therolling process of the lamellar structures has been proposed asthe usual mechanism involved in the formation of nanowires ornanotubes.18 Herein, the exact formation mechanism for thenanorings by end-to-end joining of the nanowires is stillunclear, and further investigation is underway.The reagent concentration was a key factor capable of

causing changes to the nature of crystal growth at the interfaceexcept for the reaction time. A nearly saturated toluene solutionof (C2H5OCS2)3Sb was necessary to form Sb2S3 films at theinterface and subsequent nanorings in the sediments. If theconcentration of antimony xanthate in toluene was dilutedtwice, no Sb2S3 was produced. However, if the solution wasstirred, highly dispersed Sb2S3 bundled nanowires wereproduced with 2 h of reaction (Supporting Information, FigureS11). Different from O’Brien’s work, herein, the height of thetoluene column did not exert an obvious influence on thenature of the interfacial deposition.In summary, the self-assembled Sb2S3 films and freestanding

nanorings were easily synthesized via a two-phase approach byusing Na2S and antimony xanthate as sulfur and antimonysource, respectively. The Sb2S3 nanorings presented higherphotocatalytic activity for methyl orange (MO) degradationunder visible-light irradiation than the Sb2S3 films (SupportingInformation, Figure S12A-C). Since both Sb2S3 nanorings andfilms were poorly crystallized (Supporting Information, FigureS6), better aqueous dispersion of the nanorings compared withrobust films, as well as broader spectrum response (SupportingInformation, Figure S12D), should be responsible for thephotoactivity.

■ ASSOCIATED CONTENT

*S Supporting InformationDetailed XRD patterns, TEM images, Raman spectra, XPSspectra, diffuse reflectance spectra, and photocatalytic activity ofSb2S3 films and nanorings can be obtained. This material isavailable free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: qiaofenghan@yahoo.com; xukaijun_62@163.com.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe work was supported by NUST Research Funding(2011YBXM62 and 2011ZDJH03), National Natural ScienceFoundation of China (No. 20974045) and Natural ScienceFoundation of Jiangsu Province (BK2011024).

■ REFERENCES(1) Yang, P.; Yan, R.; Fardy, M. Semiconductor Nanowire: What’sNext? Nano Lett. 2010, 10, 1529−1536.(2) (a) Chen, L. Y.; Yin, Y. T.; Chen, C. H. Influence ofPolyethyleneimine and Ammonium on the Growth of ZnO Nanowiresby Hydrothermal Method. J. Phys. Chem. C 2011, 115, 20913−20919.(b) Zhang, S.; Pelligra, C. I.; Keskar, G. Liquid Crystalline Order andMagnetocrystalline Anisotropy in Magnetically Doped Semiconduct-ing ZnO Nanowires. ACS Nano 2011, 5, 8357−8364.(3) (a) Wang, S.; Yang, S. Growth of Crystalline Cu2S NanowireArrays on Copper Surface: Effect of Copper Surface Structure, ReagentGas Composition, and Reaction Temperature. Chem. Mater. 2001, 13,4794−4799. (b) Han, Q.; Sun, S.; Li, J.; Wang, X. Growth of CopperSulfide Dendrites and Nanowires from Elemental Sulfur on TEM CuGrids under Ambient Conditions. Nanotechnology 2011, 22, 155607.(c) Convertino, A.; Cuscuna, M.; Nicotra, G.; Spinella, C.; Felisari, L.;Fortunato, G.; Martelli, F. Low-Temperature Growth of In-AssistedSilicon Nanowires. J. Cryst. Growth 2011, 335, 10−16.(4) (a) Hou, L.; Chen, L.; Chen, S. Interfacial Self-AssembledFabrication of Petal-Like CdS/Dodecylamine Hybrids towardEnhanced Photoluminescence. Langmuir 2009, 25, 2869−2874.(b) Rao, C. N. R.; Kalyanikutty, K. P. The Liquid−Liquid Interfaceas a Medium to Generate Nanocrystalline Films of Inorganic Materials.Acc. Chem. Res. 2008, 41, 489−499. (c) Pan, D.; Ji, X.; An, L.; Lu, Y.Observation of Nucleation and Growth of CdS Nanocrystals in a Two-Phase System. Chem. Mater. 2008, 20, 3560−3566. (d) Wang, X.;Peng, Q.; Li, Y. Interface-Mediated Growth of MonodispersedNanostructures. Acc. Chem. Res. 2007, 40, 635−643. (e) Wang, J.;Wang, D.; Sobal, N. S.; Giersig, M.; Jiang, M.; Mohwald, H. StepwiseDirecting of Nanocrystals to Self-Assemble at Water/Oil Interfaces.Angew. Chem., Int. Ed. 2006, 45, 7963−7966. (f) Sathaye, S. D.; Patil,K. P.; Paranjape, D. V.; Mitra, A.; Awate, S. V.; Mandale, A. B.Preparation of Q-Cadmium Sulfide Ultrathin Films by a New Liquid-Liquid Interface Reaction Technique (LLIRT). Langmuir 2000, 16,3487−3490.(5) (a) Kong, X. Y.; Ding, Y.; Yang, R.; Wang, Z. L. Single-CrystalNanorings Formed by Epitaxial Self-Coiling of Polar Nanobelts.Science 2004, 303, 1348−1351. (b) Wang, Z. L.; Kong, X. Y.; Zuo, J.M. Scanning Electron Microscope Image of Double-Sided ″Nano-combs″ Grown by a Solid-Vapor Process. Phys. Rev. Lett. 2003, 91,185502−185505. (c) Hughes, W. L.; Wang, Z. L. Formation ofPiezoelectric Single-Crystal Nanorings and Nanobows. J. Am. Chem.Soc. 2004, 126, 6703−6709. (d) Leung, Y. P.; Choy, W. C. H.;Markov, I.; Pang, G. K. H.; Ong, H. C.; Yuk, T. I. Synthesis ofWurtzite ZnSe Nanorings by Thermal Evaporation. Appl. Phys. Lett.2006, 88, 183110−183112. (e) Sun, Z.; Li, Y.; Zhang, J.; Li, Y.; Zhao,Z.; Zhang, K.; Zhang, G.; Guo, J.; Yang, B. A Universal Approach toFabricate Various Nanoring Arrays Based on a Colloidal-Crystal-Assisted-Lithography Strategy. Adv. Funct. Mater. 2008, 18, 4036−4042. (f) Ji, R.; Lee, W.; Scholz, R.; Gosele, U.; Nielsch, K. TemplatedFabrication of Nanowire and Nanoring Arrays Based on InterferenceLithography and Electrochemical Deposition. Adv. Mater. 2006, 18,2593−2596.(6) (a) Shen, G. Z.; Chen, D. Self-Coiling of Ag2V4O11 Nanobeltsinto Perfect Nanorings and Microloops. J. Am. Chem. Soc. 2006, 128,

Langmuir Letter

dx.doi.org/10.1021/la300244c | Langmuir 2012, 28, 6726−67306729

11762−11763. (b) Yang, W.; Cheng, X.; Wang, H.; Xie, Z.; Xing, F.;An, L. Bundled Silicon Nitride Nanorings. Cryst. Growth Des. 2008, 8,3921−3923. (c) Yada, M.; Sakai, S.; Torikai, T.; Watari, T.; Furuta, S.;Katsuki, H. Cerium Compound Nanowires and Nanorings Templatedby Mixed Organic Molecules. Adv. Mater. 2004, 16, 1222−1226.(d) Zhang, J.; Li, Y.; Zhang, X.; Yang, B. Colloidal Self-AssemblyMeets Nanofabrication: From Two-Dimensional Colloidal Crystals toNanostructure Arrays. Adv. Mater. 2010, 22, 4249−4269. (e) Yan, C.;Singh, N.; Lee, P. S. Kinking-Induced Structural Evolution of MetalOxide Nanowires into Single-Crystalline Nanorings. ACS Nano 2010,4, 5350−5356.(7) Rodriguez-Castro, J.; Dale, P.; Mahon, M. F.; Molloy, K. C.;Peter, L. M. Deposition of Antimony Sulfide Thin Films from Single-Source Antimony Thiolate Precursors. Chem. Mater. 2007, 19, 3219−3226.(8) Rajpure, K. Y.; Lokhande, C. D.; Bhosale, C. H. A ComparativeStudy of Concentration Effect of Complexing Agent on the Propertiesof Spray Deposited Sb2S3 Thin Films and Precipitated Powders. Mater.Chem. Phys. 1997, 51, 252−257.(9) (a) Ghosh, C.; Verma, B. P. Some Optical Properties ofAmorphous and Crystalline Antimony Trisulphide Thin Films. SolidState Commun. 1979, 31, 683−686. (b) Droichi, M. S.; Vaillant, F.;Bustrarret, E.; Jousse, D. Study of Localized States in AmorphousChalcogenide Sb2S3 Films. J. Noncryst. Solid 1988, 101, 151−155.(10) (a) Desai, J. D.; Lokhande, C. D. Alkaline Bath ChemicalDeposition of Antimony (III) Sulphide Thin Films. Thin Solid Films1994, 237, 29−31. (b) Nair, M. T. S.; Pena, Y.; Campos, J.; Garcia, V.M.; Nair, P. K. Chemically Deposited Sb2S3 and Sb2S3-CuS ThinFilms. J. Electrochem. Soc. 1998, 145, 2113−2120.(11) Masuda, Y.; Kato, K. High c-Axis Oriented Stand-Alone ZnOSelf-Assembled Film. Cryst. Growth Des. 2008, 8, 275−279.(12) (a) Agrawal, V. V.; Mahalakshmi, P.; Kulkarni, G. U.; Rao, C. N.R. Nanocrystalline Films of Au−Ag, Au−Cu, and Au−Ag−Cu AlloysFormed at the Organic−Aqueous Interface. Langmuir 2006, 22, 1846−1851. (b) Gautam, U. K.; Ghosh, M.; Rao, C. N. R. A Strategy for theSynthesis of Nanocrystal Films of Metal Chalcogenides and Oxides byEmploying the Liquid-Liquid Interface. Chem. Phys. Lett. 2003, 381,1−6. (c) Kalyanikutty, K. P.; Gautam, U. K.; Rao, C. N. R. Ultra-ThinCrystalline Films of ZnS and PbS Formed at the Organic−AqueousInterface. Solid State Sci. 2006, 8, 296−302.(13) (a) Fan, D.; Thomas, P. J.; O’Brien, P. Pyramidal Lead SulfideCrystallites With High Energy {113} Facets. J. Am. Chem. Soc. 2008,130, 10892−10894. (b) Fan, D.; Thomas, P. J.; O’Brien, P. Synthesisand Assembly of Bi2S3 Nanoparticles at the Water-Toluene Interface.Chem. Phys. Lett. 2008, 465, 110−114.(14) (a) Han, Q.; Chen, J.; Yang, X.; Lu, L.; Wang, X. Preparation ofUniform Bi2S3 Nanorods Using Xanthate Complexes of Bismuth (III).J. Phys. Chem. C 2007, 111, 14072−14077. (b) Han, Q.; Sun, S.; Sun,D.; Zhu, J.; Wang, X. Room-Temperature Synthesis from MolecularPrecursors and Photocatalytic Activities of Ultralong Sb2S3 Nanowires.RSC Adv. 2011, 1, 1364−1369.(15) Park, K. H.; Choi, J.; Kim, H. J.; Lee, J. B.; Son, S. U. Synthesisof Antimony Sulfide Nanotubes with Ultrathin Walls via GradualAspect Ratio Control of Nanoribbons. Chem. Mater. 2007, 19, 3861−3863.(16) Frumarova, B.; Bílkova, M.; Frumar, M.; Repka, M.; Jedelsky, J.Thin Films of Sb2S3 Doped by Sm3+ Ions. J. Non-Cryst. Solids 2003,326/327, 348−352.(17) Zakaznova-Herzog, V. P.; Harmer, S. L.; Nesbitt, H. W.;Bancroft, G. M.; Flemming, R.; Pratt, A. R. High Resolution XPSStudy of the Large-Band-Gap Semiconductor Stibnite (Sb2S3):Structural Contributions and Surface Reconstruction. Surf. Sci. 2006,600, 348−356.(18) Wang, X.; Li, Y. Synthesis and Formation Mechanism ofManganese Dioxide Nanowires/Nanorods. Chem.Eur. J. 2003, 9,300−306.

Langmuir Letter

dx.doi.org/10.1021/la300244c | Langmuir 2012, 28, 6726−67306730