氧化物與金屬奈米結構之設計與其化學感測及光催化應用

Abstract

由於奈米材料的尺寸原因，材料擁有許多特別的物理、化學以及光學特性，因此了解以及設計單一金屬與半導體材料，並將其結合成貴金屬-半導體異質結構是當今一個非常重要的課題。然而，現今許多製備材料的方法會加入對環境有傷害的化學物質，而限制了其實際應用性。因此如何發展綠色合成方法製備材料，並且有效提升其於感測器及光電轉換的表現，是個相當重要的挑戰。首先我們研究單一材料的特性及應用，再將其整合，製備出金屬-半導體奈米異質結構，因其能帶結構的差異，而產生高效載子分離性質與優越的光催化能力，可使用於產生各種太陽能源轉換應用。本論文主要針對如何利用綠色合成方法製備貴金屬、半導體以及貴金屬-半導體異質結構，並探討其光學性質與光電轉換應用等特性，本論文分為三部份主題進行探討: 在第一部份當中，我們發表不使用具高毒性化學品的晶種成長法來製備金奈米板做為研究材料，由於金奈米板結構上具有許多尖端的優勢，而擁有極佳的表面增強拉曼散射活性，利用這項特性使其可做為化學感測器，在實際應用於偵測芘(pyrene)時，也表現出其為具有高靈敏性以及重複使用性的化學感測器。 第二部份是使用超臨界二氧化碳輔助的電化學陰極沉積法製備氧化鋅以及二氧化鈦薄膜，不同形貌以及結晶性的材料可以被藉由電化學陰極沉積的參數調控，此外，此超臨界二氧化碳輔助的電化學陰極沉積法製備出的光陽極材料相對於一般製程的材料擁有極佳的太陽光水分解效能。此外，超臨界二氧化碳輔助製備出的氧化鋅也顯示出其應用在藥物釋放的潛力。 第三部份的主題則是將前述的貴金屬以及半導體材料接合在一起，製備貴金屬奈米顆粒修飾之半導體材料，研究貴金屬的表面電漿共振特性與光電化學性質的關聯性。我們將金奈米顆粒以及金@二氧化矽核殼結構修飾於二氧化鈦奈米線表面後，將此異質結構應用於光電化學水分解時，準確的調整二氧化矽厚度，可以調整金奈米顆粒與二氧化鈦奈米線表面的距離。以釐清金-二氧化鈦異質結構於太陽光照射下的水分解效率大幅提升之原理。我們發現金奈米顆粒經由表面電漿共振後可以局部增強其鄰近之電磁場強度，使得二氧化鈦奈米線可有效吸收太陽光，製造出更多的光激發載子，來提升太陽光照射下的水分解效率。另一方面，我們也利用綠色反溶劑法將貴金屬奈米顆粒(例如Au, Ag及Pd) 修飾於氧化鋅奈米晶體表面，由於貴金屬與氧化鋅能帶結構的差異，可產生高度載子分離特性與優異的光催化氧化還原能力。本研究也利用時間解析螢光光譜技術，來定量此異質結構界面的載子轉移行，以建立不同貴金屬之能帶結構對於界面載子動力學與載子被導出利用效率的關連性。

Understanding and designing noble metal and semiconductor nanostructures and heterostructures are quite crucial in developing nanotechnology, especially in the field of facile chemical sensor and effecient solar energy conversion. However, most of the synthetic approach for the fabrication of nanomaterials involved the use of environmentally harmful chemicals, which may hinder the applicability of the products. How to develope green environmentally friendly synthetic approach and enhance performance of practical applications for nanoheterostructures is important. Three individual yet relevant projects were included in the dissertation: First, we demonstrated the first successful demonstration of using Au nanoplate platform in practical SERS sensing toward a typical polycyclic aromatic hydrocarbons pollutant of pyrene. Au nanoplates were prepared using an environmentally benign seed-mediated growth approach. With the structural advantages of being sharp and straight, Au nanoplates may work as a promising surface-enhanced Raman scattering (SERS) platform for detection of Raman-sensitive analytes. It was found that Au nanoplates exhibited significantly enhanced SERS activities and achieved an extremely low detection limit toward pyrene molecules. Furthermore, the SERS activity of Au nanoplates can be fully recovered after repeatedly used and recycled in pyrene detection. These results manifest that the present Au nanoplates can serve as robust, recyclable SERS substrates that allow rapid detection of trace levels of analytes with a high degree of sensitivity and stability. In the second part, an clean, effective and favorable approach supercritical-CO2 (sc-CO2) emulsion-assisted electrochemical cathodic deposition was demonstrated to prepare ZnO and TiO2 nanocrystals thin films on conductive substrates directly. By precisely designing the experimental condition, the morphology and crystallinity of matrials could be manipulated. As compared to the structures prepared without the addition of sc-CO2, ZnO mesocrystals from sc-CO2 emulsion displayed greatly improved photoactivity toward photoelectrochemical water oxidation. As for TiO2 nanocrystals thin films, the enhanced photoactivity relies on the hydrobaric effect, in which the improved crystallinity of the deposited TiO2 was endowed by the exertion of high pressure created in the pressurized CO2. That revealled their promising potential as photoanodes in relevant photoelectrochemical processes. In addition, ZnO nanosheets prepared with sc-CO2 provided more active surface toward the release of DOX molecules, indicating it could be used as a potential drug delivery load. Last, we combined plasmonic noble metal nanoparticles (NPs) with semiconductors and studied the plasmonic effect of noble metal NPs on the photocatalytic property. We investigated and found out the mechanism of the SPR-enhanced photoactivity of Au NPs-decorated TiO2 nanowires in PEC water splitting. Subsequently, an environmentally friendly antisolvent process was proposed to fabricate noble metal NPs (Ag, Au, Pd) decorated ZnO nanocrystals (NCs). The electron transfer properties between ZnO and different types of noble metal NPs were quantitatively analyzed. The results of charge carrier dynamic were interpreted and correlated with those of the photocatalysis experiments.