具形狀序列演變的氧化銀奈米粒子之合成、其不同晶面對化學蝕刻的相對穩定性、及藉由氧化銀奈米模版來形成硫化銀奈米籠

Synthesis of Ag2O Nanocrystals with Systematic Shape Evolution, Investigation of Their Facet Stability to Chemical Etching, and the Formation of Ag2S Nanocages Using the Ag2O Nanocrystal Templates

呂煉明(Lian-Ming Lyu)

指導教授 ： 黃暄益

國立清華大學/理學院/化學系/博士(2012年)

https://doi.org/10.6843/NTHU.2012.00212

摘要

氧化銀為能隙1.46 eV的p-型半導體材料。氧化銀具有與氧化亞銅一樣的晶體結構，同為立方體的赤銅礦晶體。在此論文研究過程我們首先成功運用簡單的合成方法:固定氫氧化鈉、硝酸銀與硝酸銨之間的莫爾濃度比例，再調整試劑使用量，可以得到從立方體到八面體與六足體之間的序列演變。經由X-ray繞射、掃描式電子顯微鏡與穿透式電子顯微鏡鑑定，確定其結晶性與表面晶面。這是文獻中第一次能夠製備出如此具豐富形貌演變的氧化銀奈米晶體。
我們進一步利用氧化銀的正方體、菱形立方八面體、八面體與長六足體來了解其不同晶面在氨水環境下的相對穩定性。實驗在蝕刻劑為氨水的鹼性環境下進行。利用精準控制氨水注射量，發現可以有具特定晶面的選擇性蝕刻，進而產生新的氧化銀奈米結構。銀銨錯合物的生成，是驅使蝕刻反應進行的動力，氫氧化鈉則扮演穩定晶面的角色。在設定的條件下，氧化銀表面晶面的穩定性由高到低分別為{111}晶面、{110}晶面和{100}晶面。換言之，{100}晶面最容易被侵蝕。
在第三個工作中，採用氧化銀奈米結構當作模版，經由Kirkendall效應可將氧原子置換成硫原子，形成氧化銀–硫化銀的核殼結構與硫化銀的奈米籠。立方體與六足體的硫化銀奈米籠，都可經由相對應的氧化銀模版得到。另外也對立方體的氧化銀與氧化銀–硫化銀核殼結構進行循環電位量測，並結合掃描式電子顯微鏡觀測，第一次觀察到電化學氧化還原反應對化合物成分與形貌的影響。

關鍵字

氧化銀 ； 硫化銀 ； 系列性 ； 蝕刻 ； 模板 ； 奈米

並列摘要

Silver(I) oxide (Ag2O) is a p-type semiconductor with a reported band gap of 1.46 eV. Ag2O has the same cubic cuprite crystal structure as that of Cu2O. In the first project, we have successfully developed a facile procedure for the synthesis of Ag2O nanocrystals with systematic shape evolution from cubic to octahedral and hexapod structures by adjusting the amounts of NH4NO3, AgNO3, and NaOH solutions added to make the reaction mixture, while keeping their molar ratios constant. The crystals are mostly sub-micrometer-sized. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization have been used to determine their crystalline facets. This work represents one of the first reports to achieve synthesis of Ag2O nanocrystals with systematic shape evolution.
In the next study, we used Ag2O nanocubes, rhombicuboctahedra, octahedra, and extended hexapods to examine the relative stability of different crystal faces of Ag2O by selectively etching the least stable faces. NH3 was used as the etchant. By carefully controlling the volume of NH3 solution injected, only a specific face was etched, resulting in the formation of new Ag2O nanostructures. Ag(NH3)2+ formed from dissolved silver ions should drive the etching process while NaOH tunes the reaction equilibrium to control morphology of the etched nanocrystals. The order of facet stability in this reaction was found to be {111} > {110} > {100}. The {100} faces are most easily etched.
In the third work, the use of these Ag2O heterostructures as templates for the formation of Ag2O–Ag2S core–shell structures and Ag2S cages with morphology control via nanoscale Kirkendall effect was considered. Cubic and hexapod-shaped Ag2S nanocages were produced from Ag2O nanocrystals of corresponding shapes. Cyclic voltammetry curves and scanning electron microscopy images were taken on cubic Ag2O crystals and cubic Ag2O–Ag2S core–shell structures to examine the effects of electrochemical redox processes on the morphology and composition integrity of the initial particles for the first time.

並列關鍵字

Ag2O ； Ag2S ； systematic ； etching ； template ； nano

參考文獻

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Chapter 1