- 學位論文
金屬錯合氧活化反應之於超分子暨金屬硫硒化物奈米結構成長與性質研究
Synthesis and Properties of Metal-Complexed Supramolecular Nanotubes and Metal-Chalcogenide Nanostructures Formed with Metal-Complex Assisted Oxygenated Reactions
摘要
透過金屬錯合氧活化催化反應(metal-complex activation of dioxygen catalytic reaction)成功製備具有高結構規則性與尺寸可控性之超分子奈米管狀物。反應中金屬銅與錯合試劑十六碳胺(hexadecylamine)預加熱所生成之金屬錯合物(tetrahexadecylamine copper(II))，與空氣氧具有高反應性並會生成氧錯合物(dioxygen complex)，此生成之氧錯合物將能有效將空氣氧引入反應系統以形成一高活性循環氧催化反應；於此循環氧催化環境下，再藉由高溫裂解有機金屬前驅物(zinc hexadecylxanthate)，將可持續氧化生成構成超分子之組裝單元，即為dihexadecylamine μ-sulfato zinc(II) complex。經由多重分子間作用力驅使，包括有hydrophobic interaction、cross-linking type interaction，而此可藉由自組裝方式將組裝單元排列出具有高規則性的奈米管狀物。這種反應是首次被應用在超分子物質的製備上，而此獲得之超分子具有極佳的結構穩定性，同時其依尺寸大小則會顯現出尺寸效應所造成之獨特光學特性。 以金屬錯合物dihexadecylamine μ-sulfato zinc(II) complex為組裝單元之超分子奈米管，在電子束照射與高熱環境下被證實會有促使其自身結構趨於更穩定狀態之結構轉換過程(structure transformation)。實驗上，利用臨場觀測式電子顯微鏡(in-situ TEM)可以使分析物處於高能電子束與高溫狀態。超分子奈米管通常具有極高碳含量，且由於其具有極緊密之分子堆疊與高結構規則性，因此在結構上會存在有高應力。此狀態之物質在受到高能電子束照射下，會使其結構趨於不穩定狀態(dissipative state)，而在此狀態下，受到高溫的作用將有機會因更強的分子間作用力而驅動其進行自組裝式(self-assembly)結構轉換過程。未受電子束照射之奈米管，在受熱狀態下，由於沒有因電子束所造成之不穩定態，因此並無結構轉換過程。此分析物在接近773 K即會因受高熱而分解。反之，受電子束照射之奈米管在結構轉換後可使熱穩定性有效提升並可穩定存在於1273 K；此高熱穩定性是首次被發現在超分子系統上，而此將有助於提升其應用性。 利用金屬錯合物活化氧催化反應(metal-complex activation of dioxygen catalytic reaction)可成功在金屬基板上利用化學法製備多種金屬硫硒化物之奈米結構，包括有奈米線陣列(nanowire arrays)與奈米薄片(nanowall)結構。反應系統在鹼性環境下結合金屬錯合化學(metal chelation)、氧催化反應與強還原試劑聯胺(hydrazine)，所組成之氧還反應系統被首次證實可有效減低反應試劑與金屬基材間存在之高介面能(interfacial energy)，而此可依垂直於基板的方向(oriented)成長出奈米結構。同時利用強錯合試劑乙二胺(ethylenediamine)去溶解硫及硒以增加其對金屬基板之反應性；另一方面，在強鹼的環境下，也有助於硫及硒形成具有較高活性之陰離子狀態。再者，經由金屬與乙二胺形成之錯合物可以有效將空氣氧帶進反應系統，以形成氧催化循環；經由金屬基材持續的氧化反應與對活性硒硫離子的反應，而可成長出垂直於基板方向的金屬硫硒化物。這些硫硒化物具有良好的場發射(field-emission)與發光(cathodoluminescence)特性，而其將可應用於光電元件上。 利用擴散式水平爐管結合硫化鎘奈米粉末(CdS nanopowders)有效達到高溫低硫化速率(sulfidation rate)，並成功在金屬基板上成長出多種金屬含量較高之金屬硫化物奈米線(metal-rich sulfide nanowires)與奈米帯(nanobelt)，包括有金屬性質的Ni3S2及Co9S8。為有效降低金屬基板在高溫的硫化速率，首次選用硫化鎘奈米粉末作為硫化試劑，硫化鎘奈米粉被證實可以在較高溫環境下(773 K)釋放較少量S2氣體，其在高溫狀態下所造成的硫化速率比直接使用硫粉亦或是硫化氫(H2S)氣體較慢；同時在實驗建構上，我們進一步將硫化鎘奈米粉設置在水平爐管下游處(downstream side)，而待硫化之金屬基材則設置在上游處(upstream side)，如此以達到更低之金屬硫化速率。在持續通入含有還原氣氛的氣流下(carrier gas, Ar+H2)，除可有效避免氧化的反應外，導入之氫氣將會與硫化鎘奈米粉所釋出之含硫氣氛反應，而生成硫化氫氣氛並能更有效的促使奈米線生成。同時藉由控制溫度、擺放位置、氣流氣氛、反應時間與壓力等參數，可針對不同金屬基材達到硫化速率的控制，目前在銅及鈦金屬片上皆能成長出金屬含量高之硫化物奈米線，因此證實了可以有效達到高溫的低硫化速率，同時也顯示這個實驗的廣泛應用性。成長出的金屬奈米線，其所具有之良好導電性與場發特性，將可有效應用於微小導線組裝與場發元件上。
並列摘要
Cu induced catalytic growth of complex nanotubes has been demonstrated for the first time. With constituent unit of dihexadecylamine μ-sulfato zinc(II) complex, multi-hydrophobic interactions direct the self-assembly behavior and lead to the nanotube aggregates. Length-tunability has also been achieved simply by varying the precursor concentration. Intense light scattering resonance from nanotubes shows size-dependent optical properties. Due to highly-ordered packing inside our nanotubes, the enhanced structural stability promises possible device applications. Extraordinarily high thermal-resistance property of self-assembled supramolecular nanotubes has been discovered by in-situ transmission electron microscopy (in-situ TEM). By combining intense electron-beam irradiation and heating, structure transformation and 1273 K-sustainable thermal stability of the metal-complexed C32H70N2ZnSO4 nanotubes were directly observed. Associated chemical-bond breaking and self-organization process are considered as main factors for significant structural transformation. The reorganized concentric multi-wall nanotube structure with measured layer-spacing of ~2.7 nm is of such structural rigidity that it exhibits excellent thermal stability. The findings open new opportunities and show great significance of further investigations on diverse molecular-architectures with in-situ TEM platform for both fundamental and technological interests. A general solution method to oriented growth of diverse metal chalcogenides (MCs) has been developed. The oxidation scheme by combining ethylenediamine-chalcogens and hydrazine in alkali solution has been proved to have great advantages on metal-chalcogenides fabrications. By using metal-complex induced oxygenated catalytic reaction, controlled oxidation for the growth of MC nanostructures has been achieved. To our knowledge, the employment of this type of reaction on oriented growth of MC nanostructures is the first demonstrated example. This method is reliable and capable for large scale production. Field-emission measurement results revealed that Ni3S2 and Cu2S nanowire arrays are promising field-emitters. Furthermore, the cathodoluminescence results also show ZnS and Cu2Se to be potentially useful in light emitting devices. The diffusive vapor-transport furnace method for achieving low sulfidation rate at high temperature has been developed for the first time to fabricate sulfur-deficient metal sulfide nanostructures of Ni and Co. Ni3S2 and Co9S8 nanowires can be fabricated in high quality and high yield by combining diffusive vapor transport deposition with CdS nanopowders as sulfidation source. The as-grown nanowires possess properties that have been shown to be promising as interconnects and field emitters.