预处理条件对La2O3上过氧物种光诱导生成的影响

Effect of sample pretreatment conditions on the photo-induced formation of peroxide species over La_2O_3

采用原位显微Raman光谱技术详细考察了焙烧温度和焙烧时间对La(OH)3分解制备的La2O3结构以及过氧物种光诱导生成性能的影响,结果表明,经700℃焙烧所得La2O3样品较经800℃以上长时间焙烧的样品更有利于过氧物种的生成.对La(OH)3热分解过程的原位XRD测试结果表明,焙烧温度需达到近700℃才可使La(OH)3完全转化为La2O3.在700℃焙烧的样品上,除了六方相的La2O3外,还可检出介稳态的立方相La2O3.经800℃以上长时间(≥5 h)焙烧后,介稳态的立方相La2O3将转化为稳定的六方相La2O3物种.在相同的实验条件下,立方相的稀土倍半氧化物较六方相更有利于过氧物种的光诱导生成,其原因可能源于前者含更多氧空位,因而更有利于对分子氧的吸附和活化.

In situ microprobe Raman spectroscopy technique was used to study the photo-induced formation of peroxide species on the La2O3 prepared by thermal decomposition La（OH）3, with special attention focused on the effects of calcination temperature and calcination time on the structure and performance of the La2O3 samples for the photo-induced formation of peroxide species. It was found that the sample prepared by calcining La（OH）3 at 700℃ is more favorable to the photo-induced formation of peroxide species than those calcined at the temperature above 800℃ for 5 h. There results can be relating to the formation of La2O3 with different phase structures in the samples calcined under different conditions. The XRD patterns recorded during the La（OH）3 thermal decomposition process indicated that La（OH）3 was completely converted La2O3 at the temperature near 700℃. Both hexagonal and cubic La2O3 were detected on the sample calcined at 700℃. After calcining at the temperature above 800℃ for 5h, the metastable cubic La2O3 would finally convert to hexagonal La2O3 phase which was stable at high temperature. Compared with hexagonal lanthanide sesquioxide（Ln2O3）, cubic lanthanide sesquioxide is more favorable to the formation of peroxide specie under the same photo-irradiation condition. This phenomenon can be rational explained by that cubic Ln2O3 has more oxygen vacancies than the hexagonal one and thus is more conducive to the adsorption and activation of molecular oxygen.