氧化鋅奈米線於光觸媒應用

Application of ZnO Nanowires in Photocatalysis

張展豪(Chang, Jan Hau)

指導教授 ： 林鶴南

國立清華大學/工學院/材料科學工程學系/博士(2014年)

摘要

本論文研究基板承載氧化鋅奈米線的光觸媒現象及增強效率之方法。論文中所使用的氧化鋅奈米線是利用無催化劑的熱蒸鍍成長法而得，而氧化鋅奈米線之光觸媒效率是利用氧化鋅奈米線照射紫外光分解50 uM羅丹明B(rhodamine B)進行評估。
在論文的第一部分，主要著重於基板導電性與奈米線結構缺陷對於光觸媒效率的影響。研究中發現，成長在導電性基板與內部缺陷較少之氧化鋅奈米線，其光觸媒效率可以有效增強。
在論文第二部份，氧化鋅奈米線的光催化動力學研究中可發現，分解50 M羅丹明B的光觸媒反應涉及零階與一階動力學機制，其機制轉變點發生在羅丹明B之濃度被分解低於10 uM的時候。未表面改質氧化鋅奈米線之反應常數分別為0.58 uMmin-1 (零階反應常數)與0.028 min-1(一階反應常數)，此光觸媒效率比其他文獻中成長條件相當的氧化鋅奈米線還要更好。
在論文第三部份，成功結合了氧化鋅奈米線的壓電性質與光觸媒性質。其中藉由製程方法不同可合成出無彎曲與彎曲之銀粒子改質氧化鋅奈米線。其光觸媒效率實驗中發現，比較其零階反應常數，彎曲之銀粒子改質氧化鋅奈米線光觸媒效率為無彎曲之銀粒子改質氧化鋅奈米線的1.4倍，並且為未改質氧化鋅奈米線的2.2倍。光觸媒效率之增強，主要原因是彎曲之氧化鋅奈米線可以產生內建電場，因而降低載子的再結合率。
在論文最後部分，利用氫處理的氧化鋅奈米線可增強光觸媒效率。於光致發光光譜(PL)實驗中可以得知，氫處理後氧化鋅奈米線的氧空缺濃度降低，因而減少載子的再結合率。而光觸媒效率實驗中，氫處理後之氧化鋅奈米線的零階反應常數為未氫處理之氧化鋅奈米線的2.5倍。

關鍵字

ZnO ； Nanowires ； Photocatalytic ； Nanocrystalline materials ； Piezoelectricity ； Photocatalysis

並列摘要

This thesis aims to investigate approaches to enhance the photocatalytic activity of substrate-supported ZnO nanowires (NWs). The employed NWs are grown on various substrates by thermal evaporation and have similar surface area. The NW photocatalytic activity is evaluated by degrading 50 uM rhodamine B with the use of UV light.
These results in the first part of thesis reveal that the photocatalytic activity can be enhanced by using a conductive substrate and NWs with less defects.
In the second part of thesis, the degradation kinetics has also been analyzed and indicates a combined zeroth-order and first-order reaction with a threshold concentration of 10 uM. The degradation constants of as-grown ZnO NWs are 0.58 uMmin-1 (zeroth-order) and 0.028 min-1 (first-order) and outperform reported values obtained from similar NWs.
In the third part of thesis is for an investigation of the photocatalytic activity of substrate-supported ZnO nanowires with Ag modification and induced bending. By degrading a 50 uM rhodamine B solution, it is found that the zeroth-order kinetic constant of Ag modified bent NWs is 1.4 and 2.2 times as high as that of Ag modified unbent NWs and unmodified as-grown NWs, respectively. The improvement due to bending is related to the piezoelectric property of ZnO that facilitates charge separation. This work demonstrates the usefulness of piezoelectricity for photocatalysis.
In the last part of the thesis, the photocatalytic activity of hydrogenated ZnO NWs is studied. Also, by degrading a 50 uM rhodamine B solution, it is found that the zeroth-order constant of hydrogenated ZnO NWs is around 2.5 times as high as that of as-grown ZnO NWs and the advantage of a low density of oxygen vacancies in ZnO NWs is apparent. Consequently, hydrogenated ZnO NWs enhance the photocatalytic activity significantly.

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