Analysis of defect energy level of titanium(IV) oxide particles by double-beam infrared photoacoustic spectroscopy

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K06019
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Inorganic industrial materials
• Research Institution: Kyushu Institute of Technology
• Principal Investigator: Murakami Naoya 九州工業大学, 大学院工学研究院, 准教授 (10452822)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 光音響 / 酸化チタン(IV) / 半導体粒子

Outline of Final Research Achievements

Energy level of trapped electrons in titanium(IV) oxide particles were studied by photoacoustic (PA) Fourier transform near- and mid-infrared spectroscopy. PA measurements enabled in situ observation of the energy levels of electron trapping sites in wide energy levels (0.1–1.9 eV) below the bottom of the conduction band. During ultraviolet (UV) irradiation, PA intensity increased depending on the wavenumber, and changes in the PA spectra were observed as a result of electrons accumulated at trapping sites. Moreover, the PA spectral shape during UV irradiation was different between the crystal structures, and it greatly depended on the crystal structure rather than other properties. The results for various samples suggest that the main energy level of the trapping sites is deep in the order of brookite > rutile > anatase. Thus, the present PA technique is an effective method for measurements of energy levels of electron trapping sites in semiconductor photocatalysts.

Free Research Field

光触媒

Academic Significance and Societal Importance of the Research Achievements

従来，粒子の赤外分光によく用いられる全反射測定法では，観測領域や測定できる粒子サイズなどの制限があり，多様な試料・条件で測定を行うには限界があった．一方で，本研究の赤外光音響分光法は試料の制限が少なく，幅広い試料に対応することができ，粒子内部のバルクの情報も抽出できるため，新たな知見が得られるとともに系統的な解析が可能である．光触媒の研究においてはこれまで半導体粒子中の欠陥の量のみが評価・議論されてきたが，本研究によりエネルギー準位の分布も解析可能になることで，水分解による水素製造や二酸化炭素の資源化を可能にするようなエネルギー変換型の光触媒材料の設計にも役立つと考えられる．