Sterrer Martin, Berger Thomas, Stankic Slavica, Diwald Oliver, Knözinger Erich
Institut für Materialchemie, Technische Universität Wien, Veterinärplatz 1/GA, 1210 Wien, Austria.
Chemphyschem. 2004 Nov 12;5(11):1695-703. doi: 10.1002/cphc.200400266.
To characterise electron-trapping sites on the surface of MgO nanoparticles, surface colour centres were generated using UV light in conjunction with selected hydrogen-based electron sources. Four different colour-centre species, including the characteristic (e-)(H+) or F(S)+(H) centre, were identified due to the distinct shape of the respective electron paramagnetic resonance (EPR) signals. The analysis of the EPR saturation behaviour down to microwave powers of 5 x 10(-3) mW reveals an enhanced spin-relaxation probability of the (e-)(H+) centre compared to all other F(S)+ centres that do not exhibit significant magnetic interactions with hydroxylic protons. Beside the dipolar magnetic interaction in the (e-)(H+) centre observed by EPR, the electronic interaction between the unpaired electron and the proton of a closely spaced OH group produces a redshift of the OH stretching band by about 70 to 170 cm(-1), as observed by infrared spectroscopy. EPR and IR spectroscopic data obtained after the selective address of individual reaction channels for surface colour-centre formation point to the fact that (e-)(H+) centres are formed by trapping electrons from H atoms. Consequently, the underlying surface defect does not belong to the sites of the MgO surface, which chemisorb hydrogen via a heterolytic splitting process.
为了表征氧化镁纳米颗粒表面的电子俘获位点，使用紫外线结合选定的氢基电子源生成表面色心。由于各自电子顺磁共振（EPR）信号的独特形状，鉴定出了四种不同的色心种类，包括特征性的（e -）（H +）或F（S）+（H）中心。对低至5×10（-3）mW微波功率的EPR饱和行为分析表明，与所有其他与羟基质子没有显著磁相互作用的F（S）+中心相比，（e -）（H +）中心的自旋弛豫概率增强。除了通过EPR观察到的（e -）（H +）中心的偶极磁相互作用外，未成对电子与紧密间隔的OH基团的质子之间的电子相互作用使OH伸缩带发生约70至170 cm（-1）的红移，这是通过红外光谱观察到的。在选择性寻址表面色心形成的各个反应通道后获得的EPR和红外光谱数据表明，（e -）（H +）中心是通过俘获来自H原子的电子形成的。因此，潜在的表面缺陷不属于氧化镁表面通过异裂分裂过程化学吸附氢的位点。
