Controllable Synthesis of CuS Nanostructures from Self-Assembled

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J. Phys. Chem. C 2007, 111, 12181-12187

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Controllable Synthesis of CuS Nanostructures from Self-Assembled Precursors with Biomolecule Assistance Benxia Li, Yi Xie,* and Yi Xue Department of Nanomaterials and Nanochemistry, Hefei National Laboratory for Physical Sciences at Microscale, UniVersity of Science and Technology of China, Hefei, Anhui 230026, P. R. China ReceiVed: January 31, 2007; In Final Form: May 20, 2007

In this work, taking the preparation of CuS nanomaterials as an example, the multiple roles of L-cysteine in the formation of metal sulfide nanostructures were elucidated. First, the precursors captured from the initial reaction solutions were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy, which indicated that three typical precursors with different morphologies (dispersive flakes, flake-built spherical aggregations, and solid microspheres) have formed in the three initial reaction solutions with different ratios of L-cysteine to CuCl2‚2H2O. Then, the as-formed precursors decomposed as self-sacrificed templates under the hydrothermal condition to produce the interesting CuS nanostructures of highly ordered nanostructures (snowflake-like patterns and flower-like microspheres) and porous hollow microspheres. The mechanisms for the formation of the precursors and their transformation to the final CuS nanostructures have been discussed in detail. The UV-vis diffuse reflectance spectra of the as-obtained CuS nanomaterials with different morphologies have been investigated and discussed. Such work is meaningful in understanding the self-assembly of nanostructures and helpful to prepare novel functional nanomaterials.

Introduction In recent years, much effort has been focused on the selfassembly of lower dimensional (0D, 1D, and 2D) inorganic nanostructures into three-dimensional (3D) ordered superstructures because of the complexity of the possible arrangements, such as multipods,1 snowflakes,2 dendritic structures,3 and hierarchical structures.4 Controlled organization of primary building units into ordered superstructures represents another interest for materials’ self-assembly.5 Such a capability is attractive not only in understanding the concept of self-assembly with building blocks but also due to the importance in its potential applications.6 Hollow microspheres, as a special kind of 3D curved microstructures with inner cavities, are also important in many fields due to their unique properties of low density, high specific surface area, and good permeation.7 To obtain these fascinating structures with designed morphology, various organic templates and/or additives were usually employed in the reaction system to direct the formation of the nanostructures.8 Recently, biomolecule-assisted synthesis has been a new and promising focus in the preparation of various novel nanomaterials because biomolecules, as life’s basic building blocks, have special structures and fascinating self-assembling functions which make them templates of unmatched type for the design and synthesis of complicated structures in the nanometer or submicrometer regime.9 How to utilize biomolecules’ special structures and strong assembling functions to fabricate nanomaterials with desired shapes and to construct complicated superstructures is very important in all of biology, chemistry, and materials science. As an available small biomolecule, L-cysteine (HSCH2CH(NH2)COOH), has attracted researchers’ * To whom correspondence should be addressed. Tel.: 86-551-3603987. Fax: 86-551-3603987. E-mail: [email protected].

attention because of its simple hydrosulfide-group-included structure, which is not only versatile for the preparation of metal sulfides nanostructures10 but also generally utilized as a capping reagent for the synthesis of biofunctionalized semiconductor nanocrystals.11 In the previous reports on the synthesis of metal sulfides assisted by L-cysteine, the intermediates or precursors involved in the reaction process are rarely investigated in detail and the proposed formation mechanism for the as-obtained nanomaterials lacks favorable experimental evidence. Because there are three functional groups (-SH, -NH2, and -COOH) in L-cysteine molecule, the combination between L-cysteine and metal cations is diverse,12 which makes the reaction mechanism involved in the formation of metal sulfides nanostructures intricate but more interesting, and thus it deserves the further investigation. Herein, taking the preparation of CuS nanomaterials as an example, the cupric-cysteine system is elucidated on the basis of the special reaction between cupric salts and cysteine to give a precipitate of cystine and cuprous cysteine,13 in which the multiple roles of L-cysteine have attracted more of our attention. In the reaction solutions with different ratios of L-cysteine to CuCl2‚2H2O, the as-formed precursors were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). It was found that the precursors with different morphologies were assembled by the intermediates of cystine crystallites and Cu(I)-cysteine complexes. Such precursors with different morphologies would be applied as self-sacrificed templates for the following controllable fabrication of metal sulfide nanostructures. In addition, much interest has focused on copper sulfide because of its different unique properties14 as well as a wide range of well-established and prospective applications in numerous fields, such as the p-type semiconductors in solar cell

10.1021/jp070861v CCC: $37.00 © 2007 American Chemical Society Published on Web 07/27/2007

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devices,15 superionic materials,16 and the materials in chemical sensors,17 etc. In this work, the highly ordered nanostructures (snowflake-like patterns and flower-like microspheres) and porous hollow microspheres of CuS were controllably synthesized by decomposing the self-assembled precursors with corresponding shapes under a simple hydrothermal condition. Such a facile route is undoubtedly interesting in understanding the self-assembly of nanostructures and helpful to prepare functional nanomaterials. The UV-vis diffuse reflectance spectra (DRS) of the as-obtained CuS nanomaterials with different morphologies have been investigated and discussed briefly. The variety of the products’ optical properties resulted from the different morphology should find applications in the optical and electronic devices. Experimental Section Chemicals. CuCl2‚2H2O and L-cysteine were used as the main reagents. All chemical reagents were purchased from the Shanghai Chemical Company, China. They were of analytical grade and used as received. Synthesis. Details of the experiment in this work are as follows. Under stirring, different amounts of L-cysteine (0.121 g, 1 mmol; 0.242 g, 2 mmol; 0.363 g, 3 mmol) were respectively dissolved in 10 mL of CuCl2‚2H2O aqueous solution (0.1 M), and deep-blue floccules occurred immediately. After 15 min of stirring, opaque floccules with different colors (deep-blue, whitish blue, and milk white) formed in the solutions with the corresponding amount of L-cysteine, respectively. Some of the floccules with different colors were centrifuged from the reaction solutions and dried under vacuum. Then, the solutions of the residual mixture were respectively transferred into Teflonlined stainless autoclaves (15 mL capacity), which were sealed and maintained at 160 °C for 12 h and then cooled to room temperature. The resulting products were collected, washed for several times using distilled water and absolute ethanol to remove the possible residues, centrifuged, and dried under vacuum at 50 °C for 4 h. Instruments and Characterization. The XRD patterns of the products were recorded by using a Rigaku Dmax Diffraction System with a Cu KR source (λ ) 0.154178 nm). The scanning electron microscopy (SEM) images were taken by using a JEOLJSM-6700F field-emitting scanning electron microscope (FESEM, 15 kV). The TEM images and electron diffraction (ED) patterns were obtained with a Hitachi Model H-800 instrument with a tungsten filament, using an accelerating voltage of 200 kV. For SEM and TEM observation, the samples were dispersed in ethanol by ultrasonic treatment and dropped on copper foils or carbon-copper grids, and they were allowed to air-dry. XPS measurements were performed on a VGESCALAB MKII X-ray photoelectron spectrometer with an exciting source of Mg KR ) 1253.6 eV. FTIR spectroscopic study was carried out with a Nicolet FT-IR-170SX spectrometer at room temperature, with the sample in a KBr disk. The UV-vis DRS of the products are obtained on an instrument (UV-3700) equipped with an integrating sphere and with BaSO4 as a reference. The spectra were recorded at room temperature in the wavelength range of 200-800 nm. Results and Discussion In order to understand the functions of L-cysteine in the formation of metal sulfide nanostructures, the phenomena occurring in the present solutions with different ratios of L-cysteine to CuCl2‚2H2O were observed. When different amounts of L-cysteine (1, 2, or 3 mmol) were respectively added

Figure 1. (a-c) Photos of the floccules in the solutions with the ratio of L-cysteine to CuCl2‚2H2O of (a) 1, (b) 2, and (c) 3, respectively; (a′-c′) TEM images of the as-formed precursors: (a′) precursor A, (b′) precursor B, (c′) precursor C.

into the three solutions containing the same amount of CuCl2‚ 2H2O (1 mmol) under stirring, deep-blue floccules occurred immediately. With the stirring continued, the color of the floccules in the solutions changed gradually. After about 15 min of stirring, the final color of the floccules in the solutions with the relevant amount of L-cysteine turned into deep-blue, whitish blue, and milk white, respectively, as displayed by the photos in Figure 1a-c, which suggested that different precursors possibly formed in these solutions. The three typical precursors prepared by dissolving L-cysteine and CuCl2‚2H2O with the different ratios (1, 2, and 3) are named as precursor A, precursor B, and precursor C, respectively. Then, to know the selfassembling morphologies of the precursors, TEM images of them are shown in Figure 1a′-c′. Precursor A is composed of some dispersive irregular flakes with widths of 100-200 nm and lengths of 200-400 nm (Figure 1a′); precursor B consists of spherical aggregations with diameters about 1.5 µm which are constructed by some rectangular flakes (Figure 1b′), and precursor C is the solid microspheres with diameters about 1 µm (Figure 1c′). The results indicate that the self-assembly of the intermediate is distinctly different in the solutions with different ratios of cysteine to CuCl2, and thus the morphology of the as-obtained precursor depends on the initial ratio of cysteine to CuCl2. It has been known that the reaction between cupric salts and cysteine gives a precipitate of cystine and cuprous cysteine.12 Moreover, considerable research has demonstrated that the oxidation-reduction reaction between the thiol (-SH) groups of cysteine molecules and Cu(II) ions in solution readily occurs to produce the disulfide (S-S bonds) and Cu(I) which immediately binds to the thiol groups of other cysteine molecules to form Cu(I)-cysteine complexes.18 To understand the structure and compositions of the precursors in the present system, XPS study on the as-obtained precursors has been carried out, especially on the binding energies of Cu 2p and S 2p because different states of Cu and S have different electron binding energies. Figure 2 shows the XPS spectra in the Cu 2p region and S 2p region of the precursors. In Figure 2a, peaks at 932.5 eV (Cu 2p3/2) and 952.4 eV (Cu 2p1/2) reveal that the oxidation state of Cu in the precursors is +1 rather than +2.18 The S region in Figure 2b consists of a slightly broad and asymmetric peak centered about 163.0 eV, which can be modeled by the S 2p3/2 peak at 162.1 eV and the S 2p1/2 peak at 163.5 eV corresponding to the thiolate (Cu-S bonds) and the disulfide

CuS Nanostructures from Self-Assembled Precursors

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Figure 2. XPS spectra of (a) Cu 2p and (b) S 2p regions of the as-formed precursors.

Figure 3. Schematic diagram of the formation of the three typical precursors with different morphologies.

(S-S bonds).19 No peak for the thiol group (S-H) is observed. In addition, XRD patterns of the precursors (Figure S1) clearly reveal that L-cystine crystallites have formed in these precursors. The disappearance of the characteristic signal of -SH in the FTIR spectra (Figure S2) of the precursors further validated the reactions between Cu(II) ions and cysteine. Thus, the reaction between cupric ions and cysteine to give a precipitate of cystine and the Cu(I)-cysteine complex can be illuminated by following equations:

Cu2+ + HOOCCH(NH2)CH2SH f Cu+ + HOOCCH (NH2)CH2S-SCH2CH(NH2)COOH (1) Cu+ + HOOCCH(NH2)CH2SH f HOOCCH (NH2)CH2S-Cu(I) (2) In the reaction system, one part of L-cysteine is oxidized into cystine by Cu2+ ions and the other part binds to the as-produced Cu(I) to form CuI-cysteine complex. On the basis of the asreported results and the preliminary experimental evidence, it can be concluded that the precursors are likely assembled by the small crystallites of cystine molecules and the amorphous CuI-cysteine complexes (HOOC-CH(NH2)-CH2S-CuI).20 The formation mechanism for the three typical precursors with different morphologies is described in Figure 3. Initially, the small crystallites of cystine molecules formed in the solutions and are simultaneously capped by the as-produced CuI-cysteine complexes. Then, the presence of amido (-NH2) and carboxyl

(-COOH) functional groups in both the cystine molecules and the cysteine ligands leads to the formation of hydrogen bonds and thereby cross-linking of the small crystallites of cystine capped with CuI-cysteine complexes. Such a hydrogen bond mediated self-assembly has been found in the cysteine-capped colloidal metal particles and other small molecule systems.21 The hydrogen bonds in the present system act as an “adhesive” to facilitate the self-assembly of the small crystallites of cystine capped with CuI-cysteine complexes, which results in the formation of the precursors. It is understandable that the concentrations of the as-produced organic components (cystine molecules and CuI-cysteine complexes) in the solution directly affects their self-assembly state because the interactions among them strengthen with their increased concentrations. In the solution with the initial ratio of L-cysteine to CuCl2‚2H2O of 1, the amount of L-cysteine is so small that more than half of Cu2+ cations are superfluous to remain in the solution, which leads to the rather small amount of both CuI-cysteine complexes and cystine crystallites in the solution; as a result, the hydrogen bond interaction among the cystine crystallites capped with CuIcysteine complexes is so weak that only the dispersive flakes (precursor A) were produced by the self-assembly of the small crystallites. As the amount of L-cysteine added into the solution increased, more cystine crystallites capped with more CuIcysteine complexes formed in the solution. Thus, the flake-built spherical structure (precursor B) was organized into by these organic components via the hydrogen bond interaction. When the ratio of L-cysteine to CuCl2‚2H2O was further increased to 3, large numbers of cystine crystallites capped with more CuI-

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Figure 4. XRD patterns of the products prepared from the decomposition of (a) precursor A, (b) precursor B, and (c) precursor C. Figure 6. FESEM and TEM images of CuS flower-like microspheres from precursor B. (a, b) FESEM images with low and high magnification, respectively. (c, d) TEM image and SAED pattern of a flowerlike microsphere.

Figure 5. FESEM and TEM images of the CuS snowflake-like patterns from precursor A. (a) The panoramic FESEM image of the sample; (b) TEM image of some cracked snowflake-like patterns; (c-e) TEM images of three snowflake-like patterns with different details in their morphologies; (f) selected area ED (SAED) pattern taken on the snowflake-like pattern in (e).

cysteine complexes assembled into the solid microspheres (precursor C) due to their high concentration and the strong hydrogen bond interaction among them. Consequently, the precursors with different assemblies were formed in the solutions due to different concentrations of the cystine crystallites capped with CuI-cysteine complexes. Such special precursors with different assemblies are undoubtedly interesting and usable for the preparation of metal sulfide nanostructures with special morphologies. Thus, a facile precursor-decomposition route under hydrothermal condition was designed to synthesize three kinds of CuS nanostructures with interesting morphologies. The XRD patterns (Figure 4) of the as-prepared samples from the decomposition of the precursors indicate the formation of crystalline CuS, and all of them can be indexed as the reported hexagonal CuS (JCPDS Card No. 06-0464, a ) 3.792 Å and c ) 16.34 Å). No diffraction peaks of other phases or impurities were detected, further confirming that the precursors have been completely transformed into CuS nanostructures. The XPS analysis (Figure S4) on the as-obtained CuS samples provides some preliminary information about the surface atoms and electronic structure, and it further confirms its high purity. Figure 5 shows the FESEM and TEM images of the CuS sample from precursor A. As revealed in Figure 5a, the product consists of snowflake-like patterns of CuS. The TEM image in Figure 5b shows some cracked snowflake-like patterns, and their

branches are about 1.5 µm long. Three typical snowflake-like patterns shown in Figure 5c-e have a similar diameter of about 2.5 µm but different details in their shapes. The microstructure of the snowflake-like pattern in Figure 5c is semblable to that of the cracked ones in Figure 5b. Whereas both of the snowflake-like patterns in Figure 5d,e are assembled by many nanoparticles, the relevant selected area ED pattern (Figure 5f) presents discrete elongated bright dots for the {100} planes, unlike the usual polycrystalline diffraction rings, indicating that the nanocrystals aggregate along a highly oriented [100] crystallographic axis. FESEM and TEM images in Figure 6 visualize the CuS sample from precursor B. Observed from a panoramic FESEM image in Figure 6a, the product consists of many flower-like microspheres with the diameter about 2 µm which are constructed by nanoflakes. A magnified SEM image in Figure 6b demonstrates that the flower-like microspheres were built up of many interlaced nanoflakes with the thickness of 50 nm and lateral dimensions of several hundred nanometers. Careful observation finds that the nanoflakes in the spherical flowers have very rough fringes. The TEM image in Figure 6c further depicts the microstructures of the flowerlike microspheres. Numerous nanoflakes arrange compactly and spherically into a spherical microflower, and the selected area ED pattern (Figure 6d) taken on a microflower can be attributed to the diffraction of the polycrystalline hexagonal CuS. Figure 7 shows FESEM and TEM images of the CuS sample from precursor C. The panoramic FESEM image in Figure 7a indicates the sample is a large scale of microspheres with diameters between 1.0 and 1.5 µm. Several broken microspheres present in the image and the apparent cavities in them reveal that the microspheres are hollow and their shells could be fractured by the post-sonication. A typical broken microsphere in the magnified FESEM image (Figure 7b) shows that the thickness of the shell is about 100 nm and that the hollow interior occupies about 70% volume of a microsphere. In addition, it can be observed that the CuS hollow microspheres are built up of many nanoparticles with sizes between 10 and 30 nm, and the shells of the hollow microspheres present porous traits which are very similar to the TiO2 porous hollow microspheres prepared by using the ultrasonic spray pyrolysis (USP) method with a sacrificial colloidal silica template.22 The reported TiO2 porous hollow microspheres were obtained at 700-900 °C by using a USP apparatus, whereas our present

CuS Nanostructures from Self-Assembled Precursors

Figure 7. FESEM and TEM images of CuS porous hollow microspheres from precursor C. (a, b) FESEM images with low and high magnification, respectively. (c) TEM image and (d) SAED pattern taken on a hollow microsphere.

precursor-decomposition route was achieved at quite a low temperature and did not require the additional process to remove the templates. The obvious contrast between the dark edge and the relatively bright center in TEM image (Figure 7c) further validates their hollow trait, and the ED pattern (Figure 7d) taken on the hollow microsphere exhibits a polycrystalline characteristic of the hexagonal CuS, confirming that the hollow microspheres are assembled by well-crystalline CuS nanoparticles. Thus, the results indicate that this precursor-decomposition route is efficient for the synthesis of both highly ordered nanostructures and porous hollow microspheres of CuS nanomaterial. Our accessorial experiment has indicated that the reaction between L-cystine and CuCl2 under the present hydrothermal condition could produce CuS product, which can be described by following equation: 160 °C

C6H12N2O4S2 + Cu2+ + H2O 98 CuS + NH3 + some carbonous compounds (3) According to the foregoing discussion, some Cu2+ ions have remained in the two reaction systems with the initial ratio (Lcysteine to CuCl2‚2H2O) of 1 and 2, whereas the Cu2+ ions in the reaction system with the initial ratio of 3 have completely transferred into CuI-cysteine complex via the reactions in eq 1 and eq 2. Thus, the formation mechanisms for CuS products from the decomposition of precursor A and precursor B were a little different from that of precursor C, which is illuminated in Figure 8. For the decomposition of precursor A and precursor B, the final CuS products result from both the decomposition of the CuI-cysteine complex and the reaction between the cystine in the precursors and the residual Cu2+ in the solution. Because the reaction between cystine and Cu2+ ions is confined in the precursor aggregations, the self-sacrificed templates of precursor A and precursor B function well in the formation of CuS nanostructures. For the decomposition of precursor C, the precursor directly acted as both the copper source and the sulfur source; the final CuS product entirely came from the decomposition of the CuI-cysteine complex in the precursor: 160 °C

C3H6NO2SCu + O2 + H2O 98 CuS + NH3 + some carbonous compounds (4)

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Figure 8. Schematic diagram of the formation of CuS nanostructures from three precursors.

Under the hydrothermal condition, the ligands in the CuIcysteine complexes were attacked by the strong nucleophilic O atoms of H2O molecules, leading to the weakening and break of C-S bonds;23 then CuI was oxidized to CuII by a small amount of oxygen in the solution, and CuS was produced. The organic ligands in CuI-cysteine complexes and the cystine molecules were removed by decomposing into some dissoluble carbonous compounds as byproducts to be eliminated. The FTIR spectrum of the final CuS product (Figure S3) confirmed the complete elimination of the organic compositions in the precursors. For the snowflake-like CuS patterns from precursor A, the decomposition of the dispersive flakes (precursor A) via the reactions in eqs 3 and 4 would first produce some CuS naoparticles which then assembled into the snowflake-like patterns during the ripening process under the hydrothermal condition. The formation of CuS snowflake-like structures had been commonly reported previously, and it should be a characteristic growth habit for the hexagonal CuS in solution.24 For the flower-like CuS microspheres from precursor B, the flake-built spherical aggregations (precursor B) acted as selfsacrificed templates during the hydrothermal process, in which the CuI-cysteine complexes in situ decompose and part of the cystine molecules react with the Cu2+ ions from the solution. The in situ decomposition and the self-sacrificed role result in the formation of the flower-like CuS microspheres which inherit well the morphology of their precursors. As for the formation of the porous CuS hollow microspheres, CuS nanoparticles would first appear on the surface of precursor C and cover over the solid microspheres to form CuS shells due to the decomposition of the CuI-cysteine complexes. While the CuS-covered intermediate cores were consumed continuously, the laterproduced CuS nanoparticles aggregate to the surfaces, and more closely packed shells form. Finally, CuS hollow microspheres are shaped after the exhaustion of the intermediate cores. In addition, it is understandable that the removal of these organic compositions with relative large volumes will lead to the polycrystallinity and porosity of the final CuS nanostructures. Moreover, as more organic components in the precursor are released, more obvious porosity will present in the final CuS nanostructure. As a result, the porous CuS hollow microspheres are obtained from the precursor C that contains large numbers of CuI-cysteine complexes and cystine molecules. Consequently, three typical CuS nanostructures of snowflake-like patterns, flower-like microspheres, and porous hollow microspheres were obtained through the decomposition of the precursors (dispersive

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Li et al. spectra of the as-obtained CuS nanostructures with different morphologies have been investigated and discussed briefly. These novel CuS nanostructures may find potential applications in catalysis fields, chemical sensors, and high-energy batteries, as well as the study of structure-property relationships. Acknowledgment. This work was financially supported by the National Natural Science Foundation of China (No. 20621061) and the state key project of fundamental research for nanomaterials and nanostructures (2005CB623601). Supporting Information Available: XRD patterns, FTIR spectra, and XPS spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

Figure 9. Diffuse reflectance spectra of the as-prepared (a) CuS snowflake-like patterns, (b) CuS flower-like microspheres, and (c) CuS hollow microspheres.

flakes, flake-built spherical aggregations, and dense microspheres), respectively. The study of the optical property of the materials provides a simple and effective method to explain some features concerning the band structure. To examine the effect of the products’ morphology on their optical property, the UV-vis DRS of the as-obtained CuS nanomaterials with three different morphologies was investigated and is discussed briefly here. Figure 9 represents the diffuse reflectance spectra in the range of 200800 nm of the as-prepared CuS nanomaterials of snowflakelike patterns, flower-like microspheres, and hollow microspheres. The spectra of the three CuS nanostructures (snowflakelike patterns, Figure 9a; flower-like microspheres, Figure 9b; and hollow microspheres, Figure 9c) display similar diffuse reflectance and optical absorption. It is shown that the three CuS nanostructures have two absorption regions of 300-400 nm and 620-720 nm, which is in accordance with the characteristic absorption of covellite (CuS).25 Differently, the absorption ranges of the CuS hollow microspheres are narrower and more obvious than those of the CuS snowflake-like patterns and CuS flower-like microspheres. The results suggest that the variety in the morphology of the materials can lead to some subtle distinction in their optical absorption but overall absorption spectrum is not affected by the shapes of the products.26 Conclusion In summary, the multiple roles of L-cysteine in the formation of CuS nanostructures were elucidated in detail by characterizing the precursors captured from the reaction solutions. In the special reactions between cupric salts and L-cysteine, one part of L-cysteine was oxidized into cystine by Cu(II) and the other part bound to the as-produced Cu(I) to form CuI-cysteine complex, which gave a precipitate of cystine and cuprous cysteine. The as-formed precursors in the present system were assembled by cystine molecules and Cu(I)-cysteine complexes via the hydrogen bond interaction. Moreover, three typical precursors with different assemblies (dispersive flakes, flakebuilt spherical aggregations, and dense microspheres) formed in the three initial reaction solutions with different ratios of L-cysteine to CuCl2‚2H2O. Subsequently, the highly ordered nanostructures (snowflake-like patterns and flower-like microspheres) and porous hollow microspheres of CuS have been synthesized by the precursor-decomposition route, in which the precursors acted as self-sacrificed templates as well as both Cu and S sources. Such a route is interesting in understanding the self-assembly of nanostructures and helpful to prepare inorganic functional nanomaterials. The UV-vis diffuse reflectance

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