利用微波水熱合成銅氮修飾鈦酸鹽奈米管光降解雙酚A之研究

Photocatalytic degradation of bisphenol A by Cu and N co-doped titanate nanotubes prepared by microwave-assisted hydrothermal method

廖軍懿(Chun-I Liao)

指導教授 ： 董瑞安

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2011年)

摘要

一維鈦酸鹽奈米管由於具有獨特的物化特性及製備方法簡單，已被視為一新型環境淨化材料，其中又以光催化降解新興汙染物最具應用潛力。傳統的水熱法最為廣泛應用於合成鈦酸鹽奈米管方法之一，最大優勢在於製備簡單，無需藉由模板即可合成。然而，水熱法所需反應時間過長，普遍需耗時一天以上。為了有效的縮短反應時間，本研究嘗試以微波輔助水熱法製備一維鈦酸鹽奈米管。而根據材料特性鑑定結果，利用微波功率600 W，維持150 °C三個小時的反應製備而成的鈦酸鹽奈米管具有比表面積約為376 m2/g；長度可達數百奈米及直徑約為6.1 nm。而奈米管藉由450 °C煅燒處理可轉化為銳鈦礦之晶型結構，後續以奈米管作為載體，利用二價銅離子修飾，通以氨氮混合氣體450 °C下煅燒，可合成具有金屬及半導體異質介面的銅氮共摻雜鈦酸鹽奈米管。經由XRD晶型分析結果，銅氮摻雜奈米管之晶型結構由銳鈦礦及金屬銅所組成。當銅附載於鈦酸鹽奈米管達到6 wt%，分別利用365 nm紫外光及400±20 nm近可見光照環境下進行光催化降解雙酚A，反應速率分別高達0.141及0.032 min-1，分別高於商用P25 TiO2粉末5及2.4倍。XPS物種分析結果顯示，氮存在於奈米管中主要以嵌入晶格縫隙及取代晶格中氧原子的方式存在，然而藉由光催化活性比對銅氮摻雜及單一金屬銅摻雜奈米管發現，金屬銅的參與是主要提升光催化活性的因素。金屬銅及二氧化鈦所形成的異質接面能夠有效的抑制電子電洞對的再結合，因此在光催化分解雙酚A過程中，與商用P25 TiO2比較，具有較佳的催化能力。然而在酸性條件下，由於金屬銅以離子態方式溶出而造成催化能力下降。此外，藉由Langmuir–Hinshelwood動力方程式模擬光催化降解雙酚A實驗可獲得在紫外光及可見光照射下不同濃度雙酚A之初始分解速率曲線，模擬結果顯示在紫外光及可見光分別照射下，銅氮共修飾鈦酸鹽奈米管對於降解雙酚A之速率常數分別為2.86及2.42×10-1 mg/L-min，此分解速率較商用二氧化鈦奈米材料高出3.45及1.8倍。本研究結果顯示，利用微波輔助水熱法所製備的鈦酸鹽奈米同樣具有傳統水熱製備之高比表面積，並且有效縮短由24小時的反應時間至3個小時，具有相當高的潛力能廣泛的應用於新穎環境材料上，也能符合綠色化學的概念。藉由銅氮摻雜及450°C鍛燒處理後產生二氧化鈦及金屬銅之異質結構，適合作為光催化材料應用於水體中汙染物的降解。
關鍵字: 鈦酸鹽奈米管、微波輔助水熱、雙酚A、光催化降解

關鍵字

鈦酸鹽奈米管 ； 微波輔助水熱 ； 雙酚A ； 光催化降解

並列摘要

One-dimensional (1D) titanate nanotubes (TNTs) have been considered as a novel material for environmental purification due to their novel physical and chemical properties and simple fabrication. One of the potential applications of TNTs is catalytic photodegradation of emerging pollutant. Conventional hydrothermal route is one of the most common methods for fabrication of template-free TNTs. However, the fabrication time is too long, and 24 h is necessary needed. In this study, microwave-assisted hydrothermal method was employed to effectively shorten the reaction time to 3 hr. The 1-D TNTs with areas of 376 m2/g; diameters of about 6.1 nm and lengths of several hundreds nanometers could be easily obtained. In addition, titanate form could be transformed into anatase phase after post heat treatment at 450 °C. Afterward, the as-prepared TNTs were used as a support to deposit Cu2+ ion followed by calcination under NH3/N2 atmosphere for fabrication of Cu-N/TNTs. XRD patterns showed that the crystallization of Cu-N/TNTs was composed of anatase TiO2 and zerovalent copper. The optimal copper loading was found to be at 6 wt%, and the pseudo-first-order rate constants (kobs) for PBA photodegradation by 6 wt% Cu-N/TNT were 0.141 and 0.032 min-1 under UV and visible lights, respectively, which were higher than those of TiO2 P25 by factors of 5.0 and 2.4, respectively. XPS results indicated that N is incorporated into the lattice of Cu-N/TNTs, and the presence of Cu(0) is the main factor to cause the efficient photocatalytic activity under visible illumination. The hetero-junction between metal (Cu0) and semiconductor (TiO2) could effectively suppress the recombination of electron (e-) and hole (h+) pair, resulting in the significant enhancement of the photodegradation efficiency of BPA. However, lower pH condition would cause the increase in copper leaching, followed by the decrease in photocatalytic activity. The photodegradation behavior of BPA followed Langmuir–Hinshelwood kinetics, and the intrinsic rate constant (kr) under UV and visible illumination for photodegradation of BPA were 2.86 and 2.42×10-1 mg/L-min, respectively, which were 3.45 and 1.8 times higher than those of P25. Results obtained in this study clearly demonstrate that TNTs with high surface area can be successfully fabrication within 3 h by microwave-assisted hydrothermal methods. This nanomaterial could serve as a green material for photocatalytic degradation of emerging pollutants.
Keyword: titanate nanotubes (TNTs); microwave-assisted hydrothermal method; bisphenol A; photodegradation; Cu-N codoped nanomaterials.

並列關鍵字

titanate nanotubes (TNTs) ； microwave-assisted hydrothermal method ； bisphenol A ； photodegradation ； Cu-N codoped nanomaterials

參考文獻

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