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  • 學位論文

水相中快速合成出由八面體演繹至立方體硫化鉛奈米晶體 以及其不同形狀的排列結構研究

Fast Synthesis of PbS Nanocrystals in Aqueous Solution with Shape Evolution from Cubic to Octahedral Structures and Their Assembled Structures

指導教授 : 黃暄益

摘要


半導體奈米粒子時常是在有機相中及高溫下反應。如果能將奈米粒子的合成在水相中進行,則可以減少能量的消耗及能達到綠色化學的效果。根據文獻得知,若想要在水相中合成硫化鉛奈米晶體,則至少需要加熱12小時到24小時,而我們的實驗目的則是要能有效縮短反應時間且達到一系列的形狀變化。 在本次實驗中,我們在水相的環境中利用植晶方法,經由二次成核的方式長成硫化鉛奈米粒晶體,整個反應時間約2個半小時,合成的奈米粒子其大小範圍則介於30至60奈米之間。除此之外,可藉由硫代乙烯胺濃度從0.05 M至0.025 M的調整,使硫化鉛奈米晶體的形狀從立方體可以逐漸轉變成八面體。至於立方體及八面體的奈米粒子分別是由{100}和{111}晶面所組成的,而立方八面體是{100}和{111}晶面所組成的,經由粉末X-ray繞射的鑑定得知合成出的奈米晶體為硫化鉛,且其不同的形狀可得到具有擇優取向的訊號。此外藉由TEM選區電子繞射鑑定也可以做材料鑑定和得知奈米晶體的晶面。 除此之外,從SEM上還發現到截角立方體及八面體個別具有不同的單層與多層的排列情形,並藉由粉末X-ray繞射鑑定不同排列情形造成的擇優取向繞射圖。

關鍵字

硫化鉛 形狀演變 形貌 排列

並列摘要


Semiconductor nanoparticles are often synthesized in organic solvents with the use of high reaction temperatures. If nanoparticles can be synthesized in aqueous phase, it should reduce the energy cost and the process is more environmentally friendly. According to the literature, PbS nanocrystals are usually synthesized in organic solvents. When they are prepared in aqueous solutions, the reaction mixtures can frequently be heated for 12–24 hours. In this study, we have developed a seeding growth method to synthesize PbS nanocrystals in aqueous solution. The method involves addition of a small volume of preheated lead acetate and thioacetamide (TAA) mixture to an aqueous growth solution of lead acetate, thioacetamide, cetyltrimethylammonium bromide, and nitric acid. By varying the amount of thioacetamide added to the growth solution, PbS nanocrystals with different morphologies were generated in 2 h at 90 ºC. The PbS nanocrystals have sizes of 30–60 nm. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) patterns, and scanning electron microscopy (SEM) have been employed to characterize the nanocrystals. Nanocube sizes can also be tuned within a range. UV–vis absorption spectra of PbS cubes, cuboctahedra, and octahedra all show decreasing but continuous absorption from 300 nm to beyond 1000 nm. By monitoring the speed of darkening of solution color, particle growth rate was found to be fastest for nanocubes, followed by truncated cubes, cuboctahedra, and octahedra. The production of different particle morphologies of PbS nanocrystals is linked to their reaction rates. Lowering the concentration of TAA in the reaction mixture can retard the reaction rate, and this favors the formation of octahedra. These monodisperse nanocrystals can readily form self-assembled structures. Truncated cubes and octahedra forming monolayer and multilayer packing arrangements have been studied. PXRD was used to confirm these assembled structures. Intensities of certain peaks in the PXRD patterns are enhanced due to preferred orientations of the nanocrystal packing structures.

並列關鍵字

PbS shape evolution morphology assembly

參考文獻


(11) Wu, H.-L.; Tsai, H.-R.; Hung, Y.-T.; Lao, K.-U.; Liao, C.-W.; Chung, P.-J.; Huang, J.-S.; Chen, I.-C.; Huang, M. H. Inorg. Chem. 2011, 50, 8106–8111.
(8) Wu, H.-L.; Kuo, C.-H.; Huang, M. H. Langmuir 2010, 26, 12307–12313.
(30) Chen, F.; Qiu, W.; Chen, X.; Wang, M.; Chen, H. CrystEngComm 2010, 12, 1893–1898.
(31) Qiu, W.; Xu, M.; Chen, F.; Yang, X.; Nan, Y.; Chen, H. CrystEngComm 2011, 13, 4689–4694.
(3) Huang, W.-C.; Lyu, L.-M.; Yan, Y.-C.; Huang, M. H. J. Am. Chem. Soc. 2012, 134, 1261–1267.

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