掺入氮之奈米氧化鋅可見光光觸媒與奈米氧化鋅-銀其形成之方法和多功能特性研究

Syntheses and Characterization of Multi-functional N-doped Nano-ZnO Visible Light Photocatalyst and ZnO-Ag Nano-composite Particles

洪松慰(Sung-Wei Hung)

指導教授 ： 王錫九 ； 陳志恆

國立臺北科技大學/工程學院/材料科學與工程研究所/碩士(2007年)

https://doi.org/10.6841/NTUT.2007.00208

摘要

在本研究中，運用直流熱電漿法可大量生產出掺入氮之氧化鋅奈米粉體，其形態為棒狀(rod-like)與四角狀(tetrapod-like)的混合。掺入氮之氧化鋅奈米粉體在波長420 nm附近有很強的能量吸收，並且在波長450 nm到650 nm的可見光範圍有明顯的能量吸收。利用硼氫化鈉化學還原法可合成奈米銀膠體，並且在還原合成銀膠體的過程中因有同時加入檸檬酸根離子，其作用可修飾銀粒子的表面性質。將掺入氮之氧化鋅奈米粉體加入奈米銀膠體中，此時掺入氮之氧化鋅奈米粒子與銀奈米粒子的表面因分別帶正電荷和負電荷而產生吸引，其銀奈米粒子可附著於掺入氮之氧化鋅奈米粒子上。實驗結果顯示氧化鋅-銀奈米複合粒子其界面屬於半整合型(semi-coherent)，並且附著在掺入氮之氧化鋅奈米粒子表面的銀粒子含量，是與掺入氮之氧化鋅奈米粒子表面的正電荷密度有關，而在銀奈米粒子表面的檸檬酸根離子扮演著與掺入氮之氧化鋅奈米粒子產生選擇性吸附位址的角色。
雖然掺入氮之氧化鋅奈米粒子其亞甲基藍的分解效率在UV (365nm)波段並不因掺入氮之含量而有所不同；但在可見光波段，較高含氮量(1800 ppm)的氧化鋅奈米粒子，其亞甲基藍的分解效率較含氮量1200 ppm的氧化鋅奈米粒子好，因掺入氮所引起的氧空缺會提昇電子-電洞的復合壽命(recombination life)。氧化鋅-銀奈米複合粒子在UV(365nm)波段照射，其亞甲基藍的分解效率明顯優於掺入氮之氧化鋅奈米粒子，因銀粒子扮演電子補捉(trap)的角色，而使得電子-電洞的復合壽命大幅提昇；但在可見光波段的照射，氧化鋅-銀奈米複合粒子與掺入氮之氧化鋅奈米粒子兩者之亞甲基藍的分解效率幾乎沒什麼差別。銀奈米粒子在UV波段和在可見光波段對掺入氮之氧化鋅奈米粒子所伴演的角色不完全相同，此原因是跟銀奈米粒子的表面電漿子共振(SPR)吸收有關。
較高含氮量(1800 ppm)的氧化鋅奈米粒子，其殺菌能力較含氮量1200 ppm的氧化鋅奈米粒子好，其原因是跟掺入氮引起的氧空缺所提昇的電子-電洞復合壽命有關；並且掺入氮之氧化鋅奈米粒子在可見光照射下，其殺菌能力是優於商業上的氧化鋅奈米粒子。掺入氮之氧化鋅奈米粒子，展現出額外的光觸媒活性殺菌的能力。氧化鋅-銀奈米複合粒子其在可見光543 nm波長三小時的照射下，表現出跟掺入氮( 1800 ppm)之氧化鋅奈米粒子一樣好的殺菌能力，但氧化鋅-銀奈米複合粒子在黑暗區的殺菌能力比掺入氮( 1800 ppm)之氧化鋅奈米粒子大兩個級數。另外抗霉測試顯示掺入氮( 1800 ppm)之氧化鋅奈米粒子具有零級(zero level)優越的抗霉能力。

關鍵字

奈米複合粒子 ； 掺入氮之氧化鋅奈米粒子 ； 銀奈米粒子 ； 可見光光觸媒 ； 氧空缺

並列摘要

In this study, N-doped ZnO nanoparticles with rod-like and tetrapod-like morphologies were synthesized on a mass scale using the DC thermal plasma approach. The N-doped ZnO nanoparticle has a strong absorption below 420 nm and significant absorption in the visible range from 450 to 650 nm. Ag nano-colloids were prepared by chemical reduction with the presence of citrate ion, which modified the surface properties of Ag nanoparticle. After complete mixing, the Ag nanoparticles can adhere to the surface of N-doped ZnO nanoparticle to form ZnO-Ag nano-composite particles (NCPs) due to the attraction between the positively charged ZnO surface and the negatively charged Ag surface. The experimental results indicate that ZnO-Ag composite has semicoherent interface boundary. The amount of Ag nanoparticles absorbed on the surface of N-doped ZnO nanoparticle, is related to the surface charge density of the N-doped ZnO nanoparticle. Citrate ions play the role of selective absorption site on N-doped ZnO nanoparticle surface.
Although decomposition efficiency of methylene blue (MB) under UV irradiation does not appear to differ from each other, ZnO with a higher N-doped concentration has better decomposition performance under visible light illumination. This is due to that oxygen vacancies prolong the recombination of electron and hole. The decomposition performance of methylene blue (MB) by ZnO-Ag NCPs significantly exceeded that by N-doped ZnO nanoparticles under UV irradiation, because the Ag nanoparticles act as electron traps, which enhances electron-hole separation. However, there is almost no difference in methylene blue (MB) decomposition efficiency between the ZnO-Ag NCPs and the N-doped ZnO nanoparticles under visible light. The Ag nanoparticles behave incompletely equivalent under UV irradiation and visible light due to the surface plasmon resonance absorption of Ag nanoparticles, which is only induced by visible light. Ag nanoparticles can decompose methylene blue (MB) during illumination with visible light.
Increasing the N-dopant concentration of ZnO nanoparticles improves anti-bacterial performance because oxygen vacancies prolong the recombination of electron and hole. The anti-bacterial performance of N-doped ZnO nanoparticles under visible light is better than that of commercial ZnO nanoparticles. The N-doped ZnO nanoparticles exhibit additionally the intrinsic photocatalytic activity for anti-bacterial performance. N-doped ZnO nanoparticles modified with a coating of Ag nano-dots on their surface perform as well as N-doped ZnO nanoparticles do, during 3 hours of illumination with visible light with a wavelength of 543 nm. However, the performance of ZnO-Ag NCPs is improved by approximately two orders of magnitude in the dark. Mildew resistance tests indicate N-doped ZnO nanoparticles has excellent performance of zero-level.

並列關鍵字

nano-composite particles(NCPs) ； N-doped zinc oxide nanoparticle ； silver nanoparticle ； visible light photocatalyst ； oxygen vacancy

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