Fabrication of Micrometer-Scaled Hierarchical Tubular Structures of CuS

Assembled by Nanoflake-builtMicrospheres Using an In Situ Formed Cu(I)

Complex as a Self-Sacrificed Templatelate

Zhenyu Yao, Xi Zhu, Changzheng Wu, Xuanjun Zhang, and Yi Xie*

Nano-materials and Nano-chemistry, Hefei National Laboratory for Physical Sciences at Microscale, UniVersity of Science &

Technology of China, Hefei, Anhui 230026, P. R. China ReceiVed December 14, 2006; ReVised Manuscript ReceiVed April 19, 2007

Advisor ： S.C.Wang

Student ： Shih-Kai Shu

OutlineOutlineIntroductionExperimental ProceduresResults and DiscussionConclusionFuture work

IntroductionIntroduction

Currently, hierarchical structures are of interest to chemists and materials scientists due to their unique functions in the development of advanced devices and systems.

For instance, Pt nanoshell tubes, CdS and CdSe nanotubes and nanowires, and hierarchically structured nanowires made of ZnO, ZnO/ In2O3, SnO, SnO2/Fe2O3, and V2O5/TiO2 have been synthesized via different routes including electrospinning and hydrothermal methods, and various characteristics of these special hierarchical structures have been studied.

In a word, investigation of hierarchical structures of functional materials is very important but challenging.

Moreover, in the past decade, owing to their important physical and chemical properties, transition metal chalcogenides with their special microstructure and nanoscaled size have attracted much attention in the field of material science.

For example, as a type of metal chalcogenide, copper sulfide has been found to be an important semiconductive material, which exhibits nearly ideal solar control characteristics and fast-ion conduction at high temperature. Covellite copper sulfide shows metallic conductivity and transforms into a superconductor at 1.6 K.

Many approaches have been used to synthesize transition metal chalcogenides, including sonochemical methods, microwave-assisted methods, hydrothermal methods, thermolysis, electrosynthesis, solid-state reactions, and chemical vapor deposition (CVD).

Micrometer-scaled hierarchical tubular structures of CuS assembled by nanoflake-built microspheres were first synthesized in high yield via a one-pot intermediate crystal templating process without surfactant or added templates, in which the intermediate complex Cu3(TAA)3Cl3 formed in situ and subsequently served as a self-sacrificed template.

Whereas the intermediate complex and final hierarchical structures were well characterized, the formation mechanism was preliminarily studied based on X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) observations by arresting the growth at a series of intermediate stages in the formation of the hierarchical tubular structures.

The benefits for the as-obtained nanostructures arise from their ultrahigh Brunauer-Emmett-Teller (BET) value and the potential capacity advantage for the catalyst industry and hydrogen storage.

Experimental ProceduresExperimental Procedures

Results and DiscussionResults and Discussion

Powder X-ray diffraction patterns of the as-prepared CuS product.

JCPDS Card File No. 06-0464

FESEM and TEM images of the CuS product prepared at 60 °C for 24 h. (A) FESEM image at low magnification (B) FESEM image at medium magnification (C) FESEM image at high magnification (D) FESEM image of a wall of a broken hierarchical tubular structure (E) TEM image of an individual CuS sphere composed by nanoflakes (F) TEM image of a single nanoflake (inset in F shows the SAED pattern).

FESEM images and XRD patterns of products prepared at 60 °C for different reaction times.

(a) An in-situ formed hexagonal prism-shaped Cu3(TAA)3Cl3 crystal (b) CuS nanoparticles appeared on the surface of intermediate prism (c) nanoparticles grew up to CuS microspheres composed of nanoflakes (d) CuS microspheres composed of nanoflakes covered over the intermediate

surface to form CuS shells (e) continuous consuming of intermediate cores and growing of CuS shells

made them transformed from hexagonal to nearly cylindrical (f) a hierarchical tubular structure formed after the exhaustion of the

intermediate core.

(a) The simulated XRD pattern of Cu3(TAA)3Cl3.

(b) the recorded XRD pattern of the intermediate prepared at 60 °C for 1 h.

(c) molecular illustration of cyclo-tri-í-thioacetamide-tris(chloro-copper(i)) (Cu3(TAA)3Cl3).

CuCl2 + TAA + H2O → Cu3(TAA)3Cl3 + H+ + NH4+ +Cl- + SO4

2- + H3COO-

Cu3(TAA)3Cl3 + O2 + H2O → CuS + NH4 + + H+ + Cl- + CH3COO-

CuCl2 + TAA + H2O + O2 → CuS + CH3COO- + NH4 + + H+ + Cl- + SO42-

FESEM images and XRD patterns of product at different reaction temperatures for 24 h.

FESEM image (a) and XRD pattern (b) of product at 60 °C for 24 h with continuous stirring.

UV-vis absorption spectra of product prepared at 60 °C for 24 h.

Surface areas of the samples were measured by the BET method.

The BET surface area of as-prepared CuS hierarchical tubular structures is 262 m2 g-1.

It is notable that the BET surface of CuS particles commonly used in the catalytic field is only 0.378 m2 g-1.

ConclusionConclusion

A one-pot in situ formed and self-sacrificed template route to synthesize micrometer-scaled hierarchical tubular structures of CuS assembled by nanoflake-built microspheres of high yield and purity at a rather low temperatures without surfactant or added templates has been developed; the intermediate complex Cu3(TAA)3Cl3 forms in situ and subsequently serves as a selfsacrificed template. While the intermediate complex and final hierarchical structures were well characterized, the formation mechanism was preliminarily studied.

An interesting transition in the Cu valence state from Cu(II) in raw material to Cu(I) in the intermediate complex then to Cu(II) in the product was observed and fully studied, which clarified the chemical component, crystal structure, morphology, and template effect of the intermediate complex in this CuCl2-TAA system and may be helpful in understanding of the similar TAA-based system.

The UV-vis spectra and BET measurements on nitrogen adsorption indicate special optical properties and the ultra-high specific surface area of the product, which may have potential applications, for example, in the optical industry, the catalysis industry, and hydrogen storage.

This one-pot intermediate crystal templating process may open the way for new routes to synthesize unconventional hierarchical nanostructures.

Further experimental, theoretical, and computational studies are now underway.

Future workFuture work

Paper review利用垂直基板和電化學沉積生成 CuS奈米線陣列，並於三月中進行 FIB的作業。