State Key Laboratory of Physical Chemistry of Solid State Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian Province, P. R. China
Three Nd2O3 samples with cubic phase being the main component phase, denoted as Nd2O3-H, Nd2O3-HT, and Nd2O3-C, were synthesized by hydrolysis, hydrothermal, and combustion methods, respectively. A comparative study of the photo-induced formation of peroxide species on the three Nd2O3 samples was carried out using Raman spectroscopy with a 325 nm laser as the excitation source. After irradiation with the laser of the Raman spectrometer at room temperature in air, peroxide species was detected in all Nd2O3 samples. However, the rate of peroxide formation over Nd2O3-C was much greater than that over the other two samples. This observation can be explained by the differences in the structure and basicity of the surface lattice oxygen (O2-) species of the samples. As evidenced by the results of O2-and CO2-temperature-programmed desorption (TPD) characterizations, the Nd2O3-C sample contains greater number of surface lattice oxygen (O2-) species with low coordination numbers than the other two samples. Moreover, the basicity of the surface O2- species in Nd2O3-C is stronger than that in the Nd2O3-H and Nd2O3-HT samples. Both these factors are in favor of the reaction of lattice oxygen with molecular oxygen to generate peroxide species under photo irradiation.
Fund: the National Key Basic Research Program of China (973)(2013CB933102);National Natural Science Foundation of China(21173173);National Natural Science Foundation of China(21473144);Program for Innovative Research Team in University, China(IRT_14R31)
Wei-Zheng WENG,Hui-Lin WAN
Fig 1 Raman spectra of the peroxide formation induced by 325 nm laser (5.5 mW) at 25 ℃ under air over the Nd2O3 synthesized by (a) hydrolysis (Nd2O3-H), (b) hydrothermal (Nd2O3-HT) and (c) combustion (Nd2O3-C) methods, and (d) the intensity ratio of the Raman peaks at 833 and 336 cm-1 (I833/I336) as a function of photo irradiation time for the above three samples.
Table 1BET surface area (ABET) of the Nd2O3 samples synthesized by hydrolysis (Nd2O3-H), hydrothermal (Nd2O3-HT) and combustion (Nd2O3-C) methods.
Fig 2 XRD patterns of the Nd2O3 synthesized by hydrolysis (Nd2O3-H), hydrothermal (Nd2O3-HT) and combustion (Nd2O3-C) methods.
Fig 3 Raman spectra of the Nd2O3 synthesized by (a) hydrolysis, (b) hydrothermal and (c) combustion methods.
Fig 4 SEM images of the Nd2O3 synthesized by (a) hydrolysis, (b) hydrothermal and (c) combustion methods.
Fig 5 CO2-TPD profiles of the Nd2O3 synthesized by hydrolysis (Nd2O3-H), hydrothermal (Nd2O3-HT) and combustion (Nd2O3-C) methods.
Fig 6 O2-TPD profiles of the Nd2O3 synthesized by hydrolysis (Nd2O3-H), hydrothermal (Nd2O3-HT) and combustion (Nd2O3-C) methods.
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