贵金属对稀土倍半氧化物表面过氧物种光诱导生成的促进作用及其机理研究

The aim of this project is to explore the role and the underlying mechanism of noble metal nanoparticles in promoting the formation of peroxide species via the reaction of molecular oxygen with the lattice oxygen of lanthanide sesquioxides (Ln2O3) under photo irradiation condition. By using in situ Raman spectroscopy as a major tool, combined with O2/CO2-TPD and 18O2 isotopic tracer techniques, the effects of various factors such as O2 partial pressure, temperature and photo irradiation power on the formation of peroxide species over the M/Ln2O3 samples with different noble metals (Ag, Ru, Rh, Pd, Pt or Ir) supported on the Ln2O3 with different crystal structure (cubic, hexagonal and monoclinic) are to be systematically investigated. On these basis, further investigations on the photo-induced formation of peroxide species over the M/Ln2O3 samples with metal nanoparticles of different morphology (facet) and size as well as with different thickness of the surface covering layer under the irradiation of lasers of different wavelengths are to be carried out, aiming at revealing the factors such as surface-plasomon-driven hot election and enhancement in the electric field as well as oxygen adsorption properties of the metal nanoparticle with different facets on the activation of molecular and lattice oxygen species, and their correlation with the promotion mechanism of noble metal nanoparticles during the peroxide formation.

本项目以探究贵金属纳米粒子对分子氧在光照下与稀土倍半氧化物(Ln2O3)的晶格氧反应生成过氧物种的促进作用及其机理为目的，主要采用原位Raman光谱技术，结合O2/CO2−TPD和18O2同位素示踪等实验手段，在分子氧存在下系统考察负载了Au以及其他贵金属组分(如Ag、Ru、Rh、Pd、Pt或Ir)的立方、六方和单斜等结构的Ln2O3表面过氧物种的光诱导生成情况，探明O2分压、样品温度、照射光功率等因素对相关样品表面过氧物种光诱导生成的影响规律；在此基础上，通过合成不同形貌(晶面)和尺寸以及不同表面覆盖层厚度的金属纳米粒子并将其负载到Ln2O3上，结合改变照射激光的波长等，探究由金属纳米粒子表面等离子共振激发的热电子和产生的电磁场增强等效应以及不同晶面吸附氧性能的差异等因素对分子氧和晶格氧活化以及过氧物种生成的影响，揭示金属纳米粒子对稀土倍半氧化物上过氧物种光诱导生成的促进作用本质。

采用燃烧法成功制备出立方和单斜Sm2O3、Eu2O3和Gd2O3。以325 nm激光为激发源，原位Raman光谱为主要工具详细考察了相关样品上过氧物种的光诱导生成及其影响因素，研究表明立方相样品比单斜相样品更容易吸附和活化分子氧，样品表面晶格氧的碱性也更强，因而更有利于分子氧与晶格氧反应生成过氧物种，单斜相样品上生成的过氧物种的热稳定性略高于立方相样品。在光照条件下成功捕获到分子氧在Sm2O3表面活化生成的超氧和单态氧等活性氧物种，为阐明过氧物种的光诱导生成机理提供了实验证据。Au、Ag、Pd和Pt等贵金属的负载均可显著促进稀土倍半氧化物上过氧物种的光诱导生成性能，且除了325 nm紫外激光外，457和514 nm等可见激光在室温下也可诱导过氧的生成，对过氧光诱导生成具有促进作用的是金属态的纳米粒子，对于3-10 nm的Au纳米粒子，粒径越小，促进作用越大。负载了Au纳米粒子后不仅有助于增强分子氧在稀土倍半氧化物表面的物理和化学吸附，也有助于抑制光生电子和空穴的复合，Au纳米粒子作为等离激元还能在可见光作用下通过SPR效应产生热电子，这些因素均有助于提高分子氧活化生成单态氧的效率，进而促进过氧物种的生成。上述研究成果为温和条件下分子氧在氧化物体系上的活化提供了新途径，也为相关体系在光催化氧化方面的潜在应用提供了科学基础。