J O U R N A L O F C H E M I S T R Y Materials Communication Metal chalcogenide–organic nanostructured composites from self-assembled organic amine templates Neeraj and C. N. R. Rao* Chemistry and Physics ofMaterials Unit, Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur Post, Bangalore 560 064, India hexagonal structure consistent with the XRD pattern in Fig. 1(a). The image shows the wall thickness to be ca. 2.0 nm, Hexagonal and lamellar nanostructured organic–metal chalcogenide composites have been prepared by the reaction of however, there is considerable disorder. When we employed a Cd(CH3CO2)25amine ratio of 152 metal salt aliphatic-amine nanostructured adducts with Na2S or Na2Se solution; nanostructured composites of CdS, SnS2, instead of 151, we obtained a lamellar structure as evident from the XRD pattern of an adduct with SA shown in Fig. 1(c) Sb2S3 and CdSe with long-chain aliphatic amines obtained in this manner have been characterized. with d-values of 5.0, 2.5 and 1.64 nm corresponding to the (001), (002) and (003) reflections, respectively. TG showed that the amine was completely removed at 623 K and the water removed at 393 K.The composition of the chalcogenide–SA adduct from TG gave the composition 9CdS·8SA·3.5H2O. A typical TEM image of the lamellar mesophase is shown in Braun et al.1 have recently described semiconductor–organic Fig. 2(b) which shows a well defined striped pattern with a nanostructured composites of hexagonal symmetry based on periodicity of ca. 5 nm. No change was observed on tilting the cadmium sulfide obtained by using non-ionic amphiphiles such particle perpendicular to the stripes, confirming the lamellar as poly(ethylene oxide). Such nanocomposites have been premorphology.When we employed thiourea instead of Na2S as pared by starting with diVerent cadmium salts.2 By employing the sulfiding agent, we obtained a lamellar nanostructure of hydrated polyol amphiphiles, Osenar et al.3 have obtained CdS with DA of composition 4CdS·3DA.The XRD pattern of lamellar, nanostructured cadmium sulfide. In all these prepthis adduct is shown in Fig. 1(d), with d values of 3.53, 1.74, arations, the nanostructured adduct of a cadmium salt with 1.17, 0.88 and 0.7 nm, respectively, due to (001), (002), (003), the amphiphiles was treated with H2S gas.Since the prep- (004) and (005) reflections. We also obtained excellent lamellar aration of the chalcogenide nanocomposites using amphiphiles mesophases by using long-chain thiols with Cd(CH3CO2)2. involves methods akin to those employed in the synthesis of For example, the adduct with dodecanethiol (DT) had the mesoporous metal oxides,4–6 we considered it important to composition 3Cd(CH3CO2)2·4DT. However, on heating this evolve a general method for the synthesis of mesostructured adduct we could not obtain pure CdS.semiconductor chalcogenide–organic nanostructures and characterize the materials suitably. By employing long-chain amines as the amphiphiles,7 we have prepared both hexagonal and lamellar nanostructures of CdS, SnS2, Sb2S3 and CdSe.The general procedure for the synthesis employed by us is as follows: to an aqueous solution of cadmium acetate (5 mmol) was added an alcoholic solution of the amphiphilic amine (5 mmol) and the mixture was stirred to obtain a gel. The gel was aged at ambient temperature for 18 h and dried. X-Ray diVraction (XRD) patterns of the gel indicated that nanostructured mesophases of the amine and Cd(CH3CO2)2 had indeed formed. To the gel, a concentrated aqueous solution of sodium sulfide was slowly added and the pH adjusted to 9.0–9.5.The resulting product was aged at 333 K for 18 h. The product thus obtained was washed first with water, followed by a ethanol–diethyl ether (50550) mixture and dried at 333 K. The X-ray diVraction pattern of the product was then recorded.Fig. 1(a) and (b) show the XRD patterns of the mesophases obtained with dodecylamine (DA) and stearylamine (SA), respectively. The diVraction patterns are characteristic of a hexagonal mesophase with d100 values of 4.1 and 5.5 nm, respectively, for DA and SA. EDX analysis of these products gave a Cd5S ratio of 151 (see inset of Fig. 1) showing that the sulfide had the expected composition.Thermogravimetry (TG) showed that the amine template was completely removed below 573 K while the water of hydration, if any, was removed at 393 K. TG gave the compositions of the chalcogenide amine adducts as 3CdS·DA and 7CdS·6SA·9H2O for DA and SA, Fig. 1 X-Ray diVraction patterns of (Cu-Ka radiation) CdS–amine respectively. The hexagonal nature of the CdS–amine adducts nanostructures.Hexagonal phases obtained with (a) dodecylamine and was also confirmed by recording transmission electron micro- (b) stearylamine. Lamellar phases obtained with (c) stearylamine and scope (TEM) images. The TEM image of the adduct of CdS (d) using thiourea as the sulfiding agent. Inset shows EDX of an adduct with dodecylamine. with DA shown in Fig. 2(a) suggests that the mesophase has a J.Mater. Chem., 1998, 8(2), 279–280 279Fig. 3 X-Ray diVraction patterns of metal chalcogenide–amine nanostructures: (a) SnS2–dodecylamine, (b) Sb2S3–dodecylamine, (c) CdSe– Fig. 2 TEM images of CdS–amine nanostructures: (a) hexagonal phase dodecylamine. The EDX results are shown alongside the XRD patterns. with dodecylamine, (b) lamellar phase with stearylamine Cd(CH3CO2)2–amine gel.Fig. 3(c) shows the XRD pattern of On heating the hexagonal CdS adduct with DA at 473 K the hexagonal mesophase of the CdSe–DA adduct with d for 2 h, the mesostructure collapsed, but the resulting sulfide values of 3.66, 1.9 and 1.75 nm for the (100), (110) and (200) exhibited high surface area (90 m2 g-1). We have been able to reflections, respectively.The adduct had the composition remove amine partly from the hexagonal phase of the CdS 9CdSe·4DA and the amine could be removed completely at adduct with SA by heating it slowly at 448 K for 2 h. The 573 K. We have also been able to obtain CdSe–amine nano- XRD pattern of the product showed a feature corresponding structures by employing sodium selenosulfate as a seleniding to a d100 value of ca. 5.5 nm, although somewhat weaker in agent instead of Na2Se; Na2Se however appears to be a better intensity compared to the adduct. seleniding agent. We have also been able to synthesize metal sulfide–organic amphiphile nanostructures of tin and antimony by starting References from SnCl4·2H2O and SbCl3·5H2O, respectively, and keeping the metal salt5amine ratio at 151.XRD patterns of the 1 P. V. Braun, P. Osenar and S. I. Stupp, Nature (L ondon), 1996, hexagonal mesophases of the adducts of SnS2 and Sb2S3 with 380, 325. DA are shown in Fig. 3(a) and (b), respectively, with d100 values 2 V. Tohver, P. V. Braun, M. U. Pralle and S. I. Stupp, Chem. Mater., of 3.12 and 3.57 nm. The d110 and d200 reflections are also 1997, 9, 1495. 3 P.Osenar, P. V. Braun and S. I. Stupp, Adv.Mater., 1996, 8, 1022. observed at larger angles. The composition of the sulfides was 4 J. S. Beck and J. C. Vartuli, Curr. Opinion Solid State Mater. Sci., confirmed by EDX analysis (see insets of Fig. 3). TG indicated 1996, 1, 76. the adduct compositions to be 2SnS2·3DA·H2O and 5 P. Behrens, Angew. Chem., Int. Ed. Engl., 1996, 35, 515. 5Sb2S3·7DA·H2O. TEM images showed that the adducts pos- 6 S. Ayyappan and C. N. R. Rao, Chem. Commun., 1997, 575. sessed disordered hexagonal structures. 7 P. T. Tanev and T. J. Pinnavaia, Science, 1995, 267, 365. In order to prepare CdSe–amine nanostructures, we 8 N. Ulagappan, Neeraj, B. V. N. Raju and C. N. R. Rao, Chem. Commun., 1996, 2243. employed a procedure similar to that with CdS, except that an aqueous solution of Na2Se was reacted with the Communication 7/07690H; Received 24th October, 1997 280 J. Mater. Chem., 1998, 8(2), 279–280