- 學位論文
金屬/金屬氧化物複合材料於環境及能源之應用
Metal/Metal Oxide Composites for Environmental and Energy Applications
摘要
本篇論文著重在金屬與金屬氧化物奈米複合材料的合成，並使用於環境修復及能源相關應用。本論文共分成五個部分，第一章先介紹了奈米材料與奈米科技的發展，簡述了金屬氧化物光觸媒的發展，也介紹了可用於去除重金屬離子與作為直接甲醇燃料電池催化之奈米材料。第二章介紹了具光催化性的二氧化鈦-金奈米球體（TiO2-Au NSs），其在紫外光的照射下具有高催化活性，能夠將亞甲基藍（MB）降解與將六價鉻離子（Cr6+）還原為三價鉻離子（Cr3+），其降解MB與還原Cr6+離子的反應分別可在15分鐘與60分鐘內完成。此外，以TiO2-Au NSs所發展出具有高靈敏性與高選擇性之用於檢測汞離子（Hg2+）的比色檢測法，在Hg2+濃度範圍10.0-100.0 nM時有良好的線性關係（R2 = 0.98），其偵測極限為1.5 nM。上述方法結合低成本的智慧型手機應用程式，根據照片顏色的三原色光數值（RGB），來偵測含有Hg2+離子的MB溶液顏色變化(ΔRGB)，其偵測Hg2+離子與甲基汞離子（CH3Hg+）的偵測極限分別為2.0 nM與5.0 nM。第三章則是在討論以氧化鐵/氧化鋁（Fe2O3/Al2O3）所製備的微立方體，其立方結構之邊長為1 ± 0.09 µm，並具有大的比表面積（208.3 m2 g-1）與高吸附量（216 mg g-1），再加上兩種金屬氧化物的協同效應，可用以去除自來水、湖水及番茄汁中的Hg2+離子（100 ppm），其去除效率分別為98.2 ± 0.4、98.5 ± 0.3與97.1 ± 0.5%。第四章介紹了可應用於氧氣還原反應的矽奈米片-石墨烯量子點複合奈米結構（Si–GQD NCs）催化劑，其可藉由在25 °C下將矽奈米片（Si NSs）與石墨烯量子點（GQD）混合2個小時後製備而成。Si–GQD NCs電極的開路電壓為-0.33 V (參考電極為銀/氯化銀電極)，其電流密度為2.61 ± 0.27 mA cm-2，顯示其具有好的電催化活性。此環境友善、具催化活性、高穩定度與低成本的Si–GQD NCs，有很大的潛力可應用於直接甲醇燃料電池中。最後一章討論了用於電化學還原二氧化碳反應的還原氧化石墨烯-氧化亞銅-聚乙酸乙烯酯（RGO-Cu2O-PVA）薄膜，低成本且穩定的RGO-Cu2O-PVA薄膜能夠將二氧化碳選擇性還原為甲醇，並在-0.85 V電壓下具有電流密度9.04 mA cm-2與96%的法拉第效率。金屬/金屬氧化物為主的奈米材料的發展提供了進一步的能源與環境相關應用的潛力，如能源儲存與轉換、淨水與污染修復等應用。
並列摘要
This thesis focuses on synthesizing metal/metal oxide and graphene based low-dimensional materials for use in environmental remediation and energy applications. The thesis is divided into five parts. Chapter one introduces the rise of nanomaterials and nanotechnology and also provides an overview of the metal oxide photocatalysts that have been developed. Also introduced are nanomaterials used in removing heavy metals and green nanomaterials that can be used as an alternative to direct methanol fuel cells (DMFCs). In chapter two, photocatalytic titanium dioxide- gold nanospheres (TiO2-Au NSs) are used for the degradation of toxic dyes such as methylene blue (MB) and to reduce inorganic pollutants such as Cr6+ to Cr3+. Under UV irradiation, TiO2–Au NSs provide high catalytic activity for the degradation of MB and reduction of Cr6+ within 15 and 60 min, respectively. It can also be used for highly sensitive, selective and colorimetric detection of mercury (Hg). The method provides linearity (R2 = 0.98) for Hg2+ over a concentration range of 10.0 to 100.0 nM, with a limit of detection (LOD) of 1.5 nM. Using a low-cost smartphone APP that records the color changes (ΔRGB) of MB solution based on the Red-Blue-Green (RGB) component values, this TiO2-Au NSs/MB approach provides LOD of 2.0 nM for Hg2+ and 5.0 nM for CH3Hg+, respectively. In chapter three, we talk about the development of stable absorbents made of iron oxide/aluminum oxide microboxes (Fe2O3/Al2O3). The microboxes with a cubic structure (1 ± 0.09 µm) possess large specific surface area (208.3 m2 g-1) and high adsorption capacity (216 mg g-1) and were used for the removal of Hg2+ (100 ppm) from various samples, including tap water, lake water and tomato juice, with efficiencies of 98.2 ± 0.4, 98.5 ± 0.3 and 97.1 ± 0.5%, respectively. The microboxes are efficient adsorbents mainly because of a synergetic effect provided by the two metal oxides and high surface area. Chapter four explains the work done on the development of alternative catalysts for oxygen reduction reactions (ORR). Hybrid silicon nanosheets (NSs)–graphene quantum dot nanocomposites (Si–GQD NCs) were prepared from a mixture of GQDs and Si NSs in ethanol at 25 °C for 2 h. The onset potential of the Si–GQD NC electrode is -0.33 V (versus Ag/AgCl) with a current density of 2.61 ± 0.27 mA cm-2, showing greater electrocatalytic activity. The environmentally-friendly, active, stable and inexpensive Si–GQD NCs hold great potential for DMFCs. The final chapter talks about free-standing reduced graphene oxide-copper oxide-polyvinyl alcohol (RGO-Cu2O-PVA) film that has been developed for the reducing carbon dioxide (CO2) electrochemically. The low-cost and stable RGO-PVA-Cu2O film allows selective reduction of CO2 to CH3OH, with a current density of 9.04 mA cm-2 at -0.85 V and 96% Faradaic efficiency. The development of metal/ metal oxide and graphene based low-dimensional materials offers potentials for further energy and environment-related applications such as energy storage and conversion, clean water, and pollution remediation among others.