製備具一系列形狀控制的氧化銀晶體並探討晶面效應對其光催化活性與電性的影響

Synthesis of Diverse Ag2O Crystals for Facet-Dependent Photocatalytic Activity and Electrical Conductivity Measurements

陳映瑞(Chen, Ying Jui)

指導教授 ： 黃暄益

國立清華大學/理學院/化學系/碩士(2016年)

摘要

論文摘要
氧化銀具有與氧化亞銅相同的晶體結構，而氧化亞銅之晶面效應已經由不同形狀之單一晶面氧化亞銅藉由光催化、表面化學侵蝕以及導電性等實驗中被發現與證實。因此，在本論文研究中，我們在水溶液的系統下，簡單的調控硝酸銨、氫氧化鈉與硝酸銀之間的莫爾比例，藉此控制反應速率，在室溫下簡易且快速的合成一系列具立方體、菱形12面體以及八面體等不同形狀的氧化銀晶體，並進行晶面效應的實驗分析。各式氧化銀晶體的形狀可在場發式電子顯微鏡下清楚的被觀察到，透過粉末式X光繞射、X射線光電子能譜分析與固態UV-vis光譜的分析，可了解氧化銀晶體的成分與表面特性。在光催化降解甲基橙有機染料的實驗中發現，以立方體氧化銀當催化劑的效果最佳，在90分鐘內降解了85%，次之是八面體，最後是菱形十二面體只降解了15%。而利用電子自旋共振分析，我們偵測到光催化下產生的自由基並發現光照氧化銀晶體時所產生的自由基濃度與光催化效率的結果相符。雖然在光催化反應後氧化銀晶體形狀發生崩解的情況，但藉由X射線光電子能譜的分析我們可以確定在此催化過程中沒有金屬銀的產生。在氧化銀單一晶體的導電性分析，我們發現不同晶面的氧化銀，會得到截然不同的導電性，八面體導電性最佳，立方體次之，菱形十二面體不導電，此結果與氧化亞銅晶體一致。

關鍵字

氧化銀 ； 晶面效應 ； 光催化活性 ； 導電性量測

並列摘要

Abstract
Sub- to micrometer-sized Ag2O cubes, great rhombicuboctahedra, cuboctahedra, corner-truncated octahedra, octahedra, and rhombic dodecahedra have been synthesized at room temperature using simple molar ratios of NH4NO3, NaOH, and AgNO3 solutions with a short reaction time. In addition, tuning the concentration of NH3 in the solution can provide more particle morphologies including edge- and corner-truncated cubes, small rhombicuboctahedra, and edge-truncated octahedra to enrich Ag2O shape diversity. X-ray photoelectron spectroscopy (XPS) spectra indicate surface composition of various crystals as pure Ag2O. Diffuse reflectance spectra have been used to determine the band gap of Ag2O cubes. Ag2O cubes, octahedra, and rhombic dodecahedra having the same total particle surface area were used for facet-dependent photocatalytic activity comparison in the degradation of methyl orange. Cubes are comparably highly active for this reaction, while octahedra and rhombic dodecahedra give moderate and low catalytic activities, respectively. Electron paramagnetic resonance (EPR) measurements confirm this reactivity order. Although all Ag2O samples show significant etching during photocatalysis, metallic silver is not produced. Furthermore, the facet-dependent electrical conductivity behaviors have also been measured for the three different faces of Ag2O. The Ag2O {111} faces are most electrically conductive, the {100} faces only moderately conductive at high applied voltages, and the {110} faces are non-conductive. The results are the same as those obtained for Cu2O crystals.

並列關鍵字

Silver oxide ； Facet-dependent properties ； Photocatalytic activity ； Electrical conductivity measurement

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