物理化学学报 >> 2020, Vol. 36 >> Issue (4): 1905021.doi: 10.3866/PKU.WHXB201905021

所属专题： 固体核磁共振

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部分还原二氧化钛的NMR和EPR研究

李玉红1,2,吴新平3,刘聪1,王萌1,宋本腾2,郁桂云4,杨刚1,侯文华2,龚学庆3,彭路明2,*()   

  1. 1 常熟理工学院化学与材料工程学院，苏州市功能陶瓷材料重点实验室，江苏 常熟 215500
    2 南京大学化学化工学院，介观化学教育部重点实验室，南京 210023
    3 华东理工大学工业催化研究所，先进材料重点实验室，计算化学中心，上海 200237
    4 盐城工学院化学与生物工程学院，江苏 盐城 224051
  • 收稿日期:2019-05-05 录用日期:2019-06-21 发布日期:2019-06-27
  • 通讯作者: 彭路明 E-mail:luming@nju.edu.cn
  • 基金资助:
    江苏省自然科学基金(BK20170435);国家自然科学基金(91745202);国家自然科学基金(21573103)

NMR and EPR Studies of Partially Reduced TiO2

Yuhong Li1,2,Xin-Ping Wu3,Cong Liu1,Meng Wang1,Benteng Song2,Guiyun Yu4,Gang Yang1,Wenhua Hou2,Xue-Qing Gong3,Luming Peng2,*()   

  1. 1 Suzhou Key Laboratory of Functional Ceramic Materials, School of Chemistry and Material Engineering, Changshu Institute of Technology, Changshu 215500, Jiangsu Province, P. R. China
    2 Key Laboratory of Mesoscopic Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, P. R. China
    3 Key Laboratory for Advanced Materials, Centre for Computational Chemistry, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China
    4 School of Chemical and Biological Engineering, Yancheng Institute of Technology, Yancheng 224051, Jiangsu Province, P. R. China
  • Received:2019-05-05 Accepted:2019-06-21 Published:2019-06-27
  • Contact: Luming Peng E-mail:luming@nju.edu.cn
  • Supported by:
    the Natural Science Foundation of Jiangsu Province, China(BK20170435);the National Natural Science Foundation of China(91745202);the National Natural Science Foundation of China(21573103)

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摘要：

部分还原TiO2纳米材料由于具备可见光催化及降解活性而引起广泛研究关注。本研究采用17O和1H魔角旋转固体核磁共振(MAS NMR)谱学，结合电子顺磁共振(EPR)谱学研究了锐钛矿型部分还原TiO2(Re-A-TiO2)纳米颗粒的表面结构，并与非还原样品(A-TiO2)作了对比。EPR结果显示，Re-A-TiO2的顺磁物种(氧空位(OV)和Ti3+)含量远高于A-TiO2，并且EPR信号的强度受吸附水含量的显著影响，我们结合1H NMR数据，探讨了这一过程中的结构变化。17O NMR谱中，两种样品除了表面2配位氧(μ2-O)的信号有明显差异外，还发现在Re-A-TiO2表面有更多的羟基(OH)，显示该样品表面有较高比例的(001)晶面暴露。综合EPR和NMR数据，可推断羟基主要来源于顺磁中心与吸附水分子反应。1H→17O交叉极化(CP)-MAS和二维异核相关(2D HETCOR)NMR谱确认了强吸附的水物种和一种羟基的归属，另外位于约11 ppm的1H NMR信号可归属为分子内氢键中的氢物种。这些表面结构的差异应与两种材料光降解甲基橙性能差别直接相关。

关键词: 部分还原TiO2, 固体核磁共振, 17O核磁谱, 1H核磁谱, 电子顺磁共振, 羟基, 氢键, 可见光降解

Abstract:

Partially reduced TiO2 nanomaterials have attracted significant interest because of their visible-light activity for catalysis and photodegradation. Herein, we prepared a partially reduced anatase TiO2 (Re-A-TiO2) nanoparticle material using a fast combustion method, demonstrating good activity toward decomposing methyl orange under visible light irradiation. The surface structure of the prepared material, after being surface-selectively 17O-labeled with H217O (17O-enriched water), was studied via 17O and 1H solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, and the obtained results were compared to those of non-reduced anatase TiO2 (A-TiO2). The EPR results showed that the concentrations of paramagnetic species (i.e., oxygen vacancies (OV) and Ti3+) in Re-A-TiO2 were much higher than that in A-TiO2, while the former was associated with a higher OV/Ti3+ ratio. The intensities of the EPR signals were significantly affected by the adsorbed water, and this phenomenon was explored in combination with 1H NMR spectroscopy. The 1H species on Re-A-TiO2 appeared at larger chemical shifts, denoting the increased acidity of the sample, and these 1H species on Re-A-TiO2 were more difficult to remove than those on A-TiO2. On the other hand, different features were observed for the signals arising from the two-coordinated oxygen atoms (μ2-O) in 17O NMR, suggesting a typical anatase TiO2(101) surface on A-TiO2, but a more complex surface environment for Re-A-TiO2. Furthermore, a larger amount of hydroxyl groups (OH) were observed on Re-A-TiO2 compared to that on A-TiO2, indicating a larger proportion of exposed (001) facets on Re-A-TiO2. However, the μ2-O signals broadened and became similar when the drying temperature was increased to 100 ℃, indicating a non-faceted anatase TiO2 surface in such conditions. Based on the EPR and NMR results, a significant fraction of the OH species is believed to be formed from the reaction of the paramagnetic centers and adsorbed water molecules. The 1H→17O cross polarization (CP) MAS and two-dimensional heteronuclear correlation (2D HETCOR) NMR spectra were used to verify the spatial proximity of the hydrogen and oxygen species, confirming the spectral assignments of a strongly adsorbed water and one type of surface OH species. In particular, the 1H NMR signals at approximately 11 ppm were ascribed to the hydrogen species in the intramolecular hydrogen bond. In summary, this study investigated the paramagnetic species and surface structure of anatase TiO2 materials by combining EPR along with 1H and 17O solid-state NMR spectroscopy. The differences in the surface structures of Re-A-TiO2 and A-TiO2 should be closely related to their different properties toward the photodegradation of methyl orange.

Key words: Partially reduced TiO2, Solid-state NMR, 17O NMR spectrum, 1H NMR spectrum, EPR, Hydroxyl group, Hydrogen bond, Visible light degradation

MSC2000: 

  • O641