纳米氧化锌粒子分散性对其吸收光谱的影响

Influence of Polydispersity on the Absorbance Spectra of ZnO Nanoparticles

在异丙醇中用氢氧化钠分别与醋酸锌及溴化锌反应制备了纳米氧化锌粒子.分别用高分辨率电子显微镜及原位紫外吸收光谱测定了粒子大小及分布.实验结果表明,粒子的增大服从LSW(Lifshitz-Slyozov-Wagner)模型,即粒子体积随老化时间线性增大;但粒子的分布不符合LSW模型,这与他人的研究结果不一致.用计算机数值模拟确定了纳米氧化锌分布函数对其紫外吸收光谱的影响,发现在紫外吸收边附近光谱发生弯曲,且随粒子分布标准方差(SD)的增大,弯曲更显著,引起紫外吸收光谱红移,这将导致用吸收边计算氧化锌粒子大小时产生正误差.就单分散(SD/■<5%,■是粒子的平均半径)纳米氧化锌而言,这种正误差仅为2%,但当粒子分布的SD/■达到15%时,所产生的正误差可高达15.1%.

Influence of polydispersity on UV absorption spectra of ZnO nanoparticles, which were prepared from zinc bromide and sodium hydroxide as well as zinc acetate and sodium hydroxide in 2-propanol, had been studied. The particle size was measured with UV absorption spectrometry in-situ and high resolution transmission electron microscope （HRTEM）. The growth kinetics ofZnO nanoparticles was in agreement with LSW（Lifshitz-Slyozov-Wagner） model for coarsening where the particle volume was proportional to aging time. However, the particle size distribution was found to be inconsistent with the LSW model, which has been reported previously for other systems. Computer numerical calculation was used to determine the effect of the distribution function on the UV absorption spectra of ZnO suspension. It was found that absorption＇spectra bent near the UV absorption edge and shifted with the increase of standard deviation （SD） of normal distribution function, which can lead to an over-estimation of the particle size from UV spectra. For monodispersed ZnO suspensions （SD√γ 〈 5%）, the over-estimation of particle size is only about 2%. ff SD√γ of the particle is 15%, the over-estimation can be as high as 15.1%.