Facile Synthesis And Assembly Of CuS Nano-flakes To Novel Hexagonal Prism Structures

In the past few decades, self-assembly of the nanoparticles into desired and higher-ordered architectures have been an extensively studied theme due to their unique properties and potential applications in many fields. Especially, copper sulfides as an important semiconductor semiconductor transition metal chalcogenides material evoke considerable interest. Copper sulfides are a particularly interesting class of metal sulfides owing to their ability to form various stoichiometries with complex structure and valence state, at least five phases of which are stable at room temperature: Cu-rich chalcocite (Cu2S), Cu1.96S (djurleite), Cu1.8S (digenite),Cu1.75S (anilite) and S-rich covellite (CuS).As a result, copper sulfides exhibit their unique physical and chemical properties. For instance,copper sulfide (covellite) CuS shows a metal-like electrical conductivity and transform at 1.6K into a superconductor and can be used as a cathode material in lithium rechargeable batteries.In addition, copper sulfide is found to possess nearly ideal characteristics for solar energy absorption. Recently, various morphologies of CuS have been fabricated by many techniques. However, to the best of our knowledge, there is no report on the large-scale synthesis of hexagonal prism structures of CuS assembled by nanoflakes through a facile and effective method up to now. In this paper, we demonstrate hexagonal prism structures of CuS assembled bynanoflakes can be successfully synthesized via a facile one step route. We use low toxic and low cost materials CuSO₄·5H₂O and Na₂S₂O₃·5H₂O as copper source and sulfur source, C6H12N4 (HMT) was introduced into the reaction system as capped agent, and the reaction temperature was lower(60°C). In the past, C6H12N4(HMT) was frequently used in the fabrication of ZnO nanostructures,but little attention was paid to employ to prepared metal chalcogenides. Herein, we demonstrate that C6H12N4(HMT)play an important role in controlling the morphology of the hexagonal prism CuS. Meanwhile, the influence of the temperature and reaction time on the final products was also investigated. The reaction temperature makes a significant contribution to the formation of various morphologies of the products. We do many experiments at different reaction temperatures with otherwise identical conditions, and we find 60℃is the most suitable synthetic temperature. No hexagonal prism copper sulfide(CuS) was found when the reaction temperatures at 40℃, 80℃, 90℃,100℃and120℃, only some nonuniform agglomerate ball-like structure.When the temperature increased to150℃and 200℃, plate-like structure of CuS began to be prepared. Therefore, temperature is an importance parameter of thermodynamics for synthesis of hexagonal prism structures CuS.The capping agents often play an important role in shape controlling synthesis of nanoarchitectures. In this work, we select HMT as a capping agent. On the one hand, HMT, as a nontoxic amine can hydrolyze and adjust the pH of reaction system.This can be beneficial to the nucleation and growth of CuS hexagonal prism structures.Additionally, HMT tends to selectively adhering to a particular nanosize precursor facet lower their surface energy, causing the nanoparticles get close to each other and facilitate ordered arrangement. Only when the the molar ratio of CuSO₄·5H₂O / Na₂S₂O₃·5H₂O / HMT was increased to 1:2:4, the perfect hexagonal prism structures CuS can be obtained. when no HMT was used(added), the molar ratio of( reagents) CuSO₄·5H₂O / Na₂S₂O₃·5H₂O / HMT was 1:2:0, only inhomogeneity platelike structure of CuS assembled by nanospheres were formed. With the increase of the ratio of HMT, spherelike nanoarchitectures were found when the molar ratio of reagents reached 1:2:2. When the the molar ratio of CuSO₄·5H₂O / Na₂S₂O₃·5H₂O / HMT was increased to 1:2:3, the obtained CuS became to form hexagonal prism structures while these structures were unperfect. Therefore, HMT had a crucial effect on controlling the morphology of CuS.The reaction time is also an importance parameter. We find the most suitable reaction time about obtaining the perfect hexagonal prism structures CuS is 35h. The possible mechanism for the formation of the interesting CuS structure was also proposed. The process of forming hexagonal prism structures includes three steps: the formation of the nano-sized primary particles , nano-sized primary particles aggregated rapidly, the nano-sized precursors rearrange and self-assemble into organized hexagonal prism structures . The UV-vis-NIR spectra and BET measurements indicate special optical properties and the preferable specific surface area of the product, which may have potential applications in related fields such as optical industry and the catalysis industry.Hence, compared with other methods, the outstanding advantage of such a reaction process is convenient, high yield, less energy, and environmentally friendly. Moreover, we prove nonspheres higher-ordered micrometerscale regular geometric shapes can be prepared by uniform nanoparticles selfassembley. Furthermore, the shape evolution process and the possible growth mechanism were also proposed.The results can make a significant contribution to further study on the fabrication of other products.