二氧化鈦與鈣鈦礦化合物串疊薄膜之光催化特性研究

本文主要探討光觸媒材料二氧化鈦兩種不同的相:銳鈦礦(Anatase)與金紅石(Rutile)以及光觸媒鈣鈦礦化合物:鈮酸銀(AgNbO3)以及鈦酸鍶(SrTiO3)，利用溶膠凝膠法(sol-gel)搭配旋轉塗佈法(spin coating)後形成的複合串疊光觸媒薄膜，串疊基本概念遵從太陽能tandem cell的堆疊理念，並利用三極式電化學裝置量測薄膜光電流密度，而光電流密度值則代表光觸媒材料產氫的效率指標之一。本研究控制退火溫度於二氧化鈦銳鈦礦相至金紅石相之相轉變溫度區間內，將不同銳鈦礦-金紅石混相比例的同質接面薄膜制製備於FTO導電玻璃上。研究結果顯示，於550 oC可得到純銳鈦礦相的薄膜，於FTO導電玻璃之上限使用溫度700 oC則可得到接近純金紅石相之薄膜；搭配紫外光-可見光光譜儀(UV-Vis)以及紫外光電子能譜(UPS)可得到兩者接合之能帶結構關係。結果顯示，光致電子傾向由銳鈦礦傳至金紅石，光致電洞則傾向由金紅石傳至銳鈦礦。同樣的分析亦使用光觸媒材料鈮酸銀及鈦酸鍶上，最後建立四種不同材料的各自的能帶結構，將四種不同材料串疊而成異質接面薄膜，並利用形成之內建電場，使光致電子電洞對快速分離，減少載子再結合的可能性，進而提升光電流密度值。同時，此種由寬能隙依序串疊至窄能隙的方式能有效地利用光源波段區間，進而提升光電流密度；最後再進行光電流試片的穩定度量測，發現二氧化鈦會因長時間的照光下產生光致電洞衍生的光腐蝕(photocorrosion)現象而導致光電流密度的下降。本研究亦利用添加不同的PVP量的大小來調配鈦酸鍶薄膜的孔洞數量，進而控制表面態位(surface states)之數量，並探討光電流密度下降(photocurrent decay)與孔洞數量的關係。實驗結果顯示，當鈦酸鍶薄膜孔洞數量上升時，會使光電流密度下降比例上升。

關鍵字

二氧化鈦鈮酸銀；鈦酸鍶；異質接面；光電流密度；光腐蝕。

並列摘要

In this study, we mainly discuss photocatalyst materials: (1) titanium dioxide with two primary phases: anatase and rutile, (2) perovskite oxide: AgNbO3 and SrTiO3. Synthesizing with sol-gel process and spin-coating method, we try to make tandem thin film with anatase, rutile and perovskite oxide. Later, we measure photocurrent response of our thin film which represents the hydrogen production capability of photocatalyst. Initially, we control annealing temperature in the anatase to rutile phase transitition window. This action implies the different mix ratios of anatase/rutile homogeneous thin films successfully. The resuls shows we can make pure anatase thin film at 550 oC and nearly pure rutile thin film at 700 oC. Combining UV-Vis spectrum and UPS, we can get the band structure of anatase and rutile after they join together. The band structure implies photogenerated electrons transfer from anatase to rutile, and photogenerated holes transfer from rutile to anatase. Same characterizations are conducted on AgNbO3 and SrTiO3. We stack four materials to make them tandem films. Such design enhances the photocurrent response due to the built-in potential when we have the correct and preferred alignment. Besides, stacking sequence from large to small band gap also improves photocurrent by increase the usage of incident light. In order to verify the stability of our samples, we also conduct fatigue experiments by long-term light illumination. We surprisely find out the photogenerated holes induce photocorrosion of titanium dioxide anatase phase which will decay photocurrent density. Finally, we also create different amounts of pores in SrTiO3 thin films by varing addition amounts of PVP. With this idea, we verify the correlation between surfaces states and the decay phenomenon.

並列關鍵字

TiO2 ； AgNbO3 ； SrTiO3 ； Heterojunction ； Photocurrent ； Photocorrosion.

參考文獻

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二氧化鈦與鈣鈦礦化合物串疊薄膜之光催化特性研究

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