TiO2 결정과 이를 기반으로 한 혼합 산화물 촉매의 합성과 그 촉매 반응성에 대한 연구
Study on the synthesis and catalytic activity of TiO2 nanocrystals and their modification with metals
초록/요약
This study was focused on various TiO2-based catalysts such as titania nanotube (TNT), anatase TiO2 nanosheet, gold nanoparticles deposited on TiO2, transition metal-doped TiO2, and graphene oxide (GO)-TiO2 composite to identify their roles in catalytic reactions. The as-synthesized catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Raman spectroscopy, UV-vis diffuse reflectance spectra (DRS), and electron paramagnetic resonance (EPR) techniques. It was observed that the surface oxygen atoms of titania nanotubes were replaced by nitrogen atoms after cycles of NH3 temperature programmed desorption (TPD) in vacuum. This procedure resulted in a change in the surface chemical composition and the surface bonding structure of the as-synthesized titania nanotubes, which had a strong influence on their photocatalytic activity. Au/TiO2 catalysts showed a high catalytic activity in ethanol decomposition into a number of reaction product such as ethylene, acetaldehyde, and many other coupled reaction products. Doping of transition metals induced new color centers or oxygen vacancies in the lattice of TiO2, which affected their physical properties as well as their catalytic activities.
more초록/요약
본 연구에서는 TiO2를 기반으로 한 타이타늄 나노튜브 (TNT), 나노시트, 금 입자 혹은 산화형태의 그래핀이 결합된 다양한 촉매 등에 대하여, 촉매 반응시의 그들의 역할 규명에 대해 초점을 맞췄다. 합성된 촉매들은 투과전자현미경 (TEM), X-선 회절 (XRD), 에너지분광 (EDS), 라만 분광, 자외선-가시광선 산란반사 (UV-vis DRS), 전자상자성공명 (EPR) 방법들로 분석되었다. 여러 번에 걸쳐 암모니아 가스(NH3)가 처리된 진공에서의 온도가 조절된 탈착 분석 (TPD) 결과들로부터, 타이타늄 나노튜브 표면의 산소 원자들이 질소 원자들로 자리 교환되는 현상이 관찰 되었다. 이러한 과정들은 결국 합성된 타이타늄 나노튜브 표면의 화학적 구성과 결합 구조의 변화를 일으켰고, 이로 인하여 해당 표면에서의 광촉매 반응성에 강한 영향을 끼쳤다. Au/TiO2 촉매는 에탄올이 분해되어 에틸렌, 아세트알데하이드 그 외 여러 결합 형태의 생성물 형성에 대하여 매우 큰 반응성을 보였다. 또한, TiO2의 격자구조에 대한 전이금속 도핑은 그들의 격자구조 내에 새로운 색 중심 혹은 산소 결핍을 형성하였으며, 이는 물성의 변화만큼이나 촉매 반응성에도 영향을 끼쳤다.
more목차
Chapter I. Synthesis of titania nanotubes and photocatalytic water splitting activity
1. Introduction
2. Synthesis and characterization of titania nanotubes 2.1) Sample preparation
2.2) TEM, XRD, and Raman spectroscopy analyses 2.3) Surface area and UV-vis DRS analyses
3. Surface modification on titania nanotubes by NH3 treatment
3.1) Cyclic NH3 treatment on titania nanotubes by Temperature programmed desorption
3.2) H2 evolution by photocatalytic water splitting
4. Conclusion
5. References
Chapter II. Ethanol partial oxidation reactions over Au/TiO2 catalyst
1. Introduction
2. Synthesis and characterization of Au/TiO2
2.1) Sample preparation
2.2) TEM and XRD analyses
3. TPR and GC analyses of Au/TiO2
3.1) Partial oxidation reactions of ethanol over Au/TiO2
3.2) Reactions of acetaldehyde over Au/TiO2
3.3) Substrate surface area effect of Au/TiO2
4. Conclusion
5. References
Appendix
A. Empirical quantitative calibration method
B. Calibrated profile dimension conversion
Chapter III. Synthesis of doped TiO2 nanocrystals and Graphene oxide-TiO2 composite
1. Introduction
2. {001}facet-exposed TiO2 nanosheet
3. Growth of anatase TiO2 nanotube arrays
4. Transition metal-doped TiO2 by sol-gel method
5. Graphene oxide-TiO2 composite by sol-gel with Hummers method
6. References
