微波輔助水熱製備氧化鈦奈米管：結構特性與光催化性質

Microwave-assisted hydrothermal preparation of titania nanotubes：Structure characteristics and photocatalytic performance

黃冠群(Kuan-Chun Huang)

指導教授 ： 簡淑華

國立臺灣大學/理學院/化學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.02625

摘要

本研究中利用微波輔助水熱法製備氧化鈦奈米管( titania nanotubes )分析其結構特性與評估光催化活性。探討以水熱溫度與鹼濃度之調控將二氧化鈦顆粒在鹼性環境下製備氧化鈦奈米管，並以不同晶型之二氧化鈦( Merck anatase TiO2、Aldrich rutileTiO2與Degussa P25 TiO2粉末 )、水熱溫度( 130 – 220℃ )與水熱時間對氧化鈦奈米管生成之影響。將各式TiO2顆粒與氫氧化鈉溶液混合，封入Teflon高壓反應斧中經微波水熱反應後，產物以去離子水與0.10 M硝酸溶液酸洗、過濾，在110℃乾燥後皆可製得氧化鈦奈米管。一般水熱製備氧化鈦奈米管需24小時以上，微波水熱製程可大為縮短製備之時間，如以Merck anatase TiO2於10 M氫氧化鈉溶液中220℃水熱反應20分鐘即形成奈米管。由TEM影像觀察奈米管之形態為中空開孔與多層壁結構，其管直徑約8 - 10奈米、內管徑為3 - 5奈米，長度可達數百奈米。奈米管之表面積及孔容積分別可高達330 m2/g與1.42 cm3/g，在催化反應上適合做為觸媒載體與光催化材料。
氧化鈦奈米管對光催化的活性評估，分別以紫外光與可見光進行有機染料的光催化脫色與一氧化氮( NO )光催化分解測試。在有機染料的光催化脫色反應中，奈米管的高表面積提供了優異的染料吸附能力與光催化活性，另外將碳包覆於氧化鈦奈米管上，修飾其在長波長可見光吸收能力，對於染料之光催化分解能力亦有很高的活性表現。在原位電子順磁共振( in situ EPR )光譜分析系統測試氧化鈦奈米管觸媒對一氧化氮的吸附及光催化分解活性中，顯示奈米管經高溫真空與氫氣活化處理後，通入NO氣體分子在活化過的奈米管上有強的NO吸附之EPR訊號，經紫外光照射後NO之吸附訊號幾乎全然消失，顯示氧化鈦奈米管對NO有極高的光催化分解活性。以殘餘氣體質譜分析儀分析NO光催化後氣體產物，結果顯示主要的分解產物為N2、N2O與O2，N2的選擇率可高達81%。

關鍵字

二氧化鈦 ； 氧化鈦奈米管 ； 微波輔助水熱法 ； 光催化 ； 染料 ； 一氧化氮 ； 原位電子順磁共振光譜

並列摘要

In this study, titania nanotubes (Tnt) was prepared by using microwave-assisted hydrothermal method, and the structure characteristics and photocatalytic performances were studied systematically. The titania nanotubes were prepared by hydrothermal treatment on commercial TiO2 particles ( Merck anatase TiO2, Aldrich rutile TiO2 and Degussa P25 TiO2 powder) in a concentrated aqueous NaOH solution. The effects of TiO2 precursor, alkaline concentration and hydrothermal temperature on the resultant nanostructure formation have been studied. Generally, the conventional hydrothermal treatment temperature, ranging from 110 to 150 °C in 10 M NaOH aqueous solution, yielded substantial particle-to-nanotube transformation after 24 h. Comparing to the above conventional method, the microwave-assisted hydrothermal process has an economical, rapid, and homogeneous heating process for preparation of the titania nanotube. For example, titania nanotubes were prepared using Merck anatase-TiO2 as a precursor that was dispersed in 10 M NaOH aqueous solution through microwave hydrothermally treated at 220 oC for 20 min. TEM images showed that the prepared nanotubes exhibit a multi-layered wall structure with open-end morphology, typical inner diameter of about 3 - 5 nm, outer diameter of about 8 - 10 nm, and length of several hundred nanometers. N2 adsorption/desorption isotherms at 77 K showed that the nanotube aggregations have high special surface area of ~ 330 m2/g and pore volume of ~ 1.42 cm3/g. Given above features, titania nanotube is suitable for utilization as catalyst supports or heterogeneous photocatalysts.
To further explore the photocatalytic performance, the activities of Tnt catalysts were investigated on the degradation of organic dyes and the decomposition of NO under UV and visible light irradiation. The Tnt catalysts exhibited high adsorption capacities and high degradation activities for cationic dyes. In situ EPR study was conducted to investigate the adsorption and photocatalytic decomposition of NO on Tnt catalysts. Results showed that the Tnt after the vacuum-thermal treatment or hydrogen-thermal treatment exhibited high photocatalytic activity for NO decomposition. Upon UV light irradiation, the EPR signal of NO adsorption completely disappeared. The reaction products were monitored by an on-line residual gas analyzer. The NO conversion reached nearly 100%, with the major products of N2, N2O and O2. The selectivity was as high as 81% toward N2 formation over the thermal-treated Tnt catalyst.

並列關鍵字

TiO2 ； Titania nanotubes ； Microwave-assisted hydrothermal method ； Photocatalysis ； Dye ； Nitric oxide ； In situ EPR

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