Batlouni Hazar, Al-Ghoul Mazen
Department of Chemistry, American University of Beirut, P.O. Box 11-0236, 1107 2020 Riad El Solh, Beirut, Lebanon.
J Phys Chem A. 2008 Sep 4;112(35):8038-45. doi: 10.1021/jp803118r. Epub 2008 Aug 9.
In this paper we study the temporal dynamics of the Co(OH) 2/NH 4OH Liesegang system with redissolution by complex formation with ammonia using UV-vis spectrophotometry with a special setup. The formation of precipitate bands is accompanied with band redissolution at the top, and because of such precipitation-redissoultion dynamics, the bands appear as a propagating wave. The spectrophotometric technique developed in this study allows us to study at the kinetics of formation of the bands and their redissolution in great details. The formation, growth, and dissolution of multiple bands are monitored by the time evolution of the absorbance. It was found that the individual band formation is sudden and takes between 15 min to half an hour to form before the next band appears. The speed of formation of bands was different for different bands and the maxima of these speeds fit a Gaussian curve. The content of cobalt hydroxide in these bands was calculated and is shown to increase to a maximum away from the interface and then decreases. The bands later grow by further precipitation. This growth was demonstrated to be nonlinear in time. On the other hand, the dissolution of bands was shown to take place simultaneously and collectively among the multiple bands under study. The effect of the concentration of Co (+2) ions on the dynamics of band formation and dissolution was studied. A time law for this Liesegang system was also determined. The system was also found to be very sensitive to temperature fluctuations.
在本文中，我们使用具有特殊装置的紫外可见分光光度法，研究了通过与氨形成络合物而发生再溶解的Co(OH)₂/NH₄OH Liesegang体系的时间动态。沉淀带的形成伴随着顶部的带再溶解，并且由于这种沉淀 - 再溶解动态，这些带呈现为传播波。本研究中开发的分光光度技术使我们能够详细研究带的形成动力学及其再溶解。通过吸光度随时间的变化来监测多个带的形成、生长和溶解。发现单个带的形成是突然的，在下一个带出现之前需要15分钟到半小时的时间来形成。不同带的形成速度不同，这些速度的最大值拟合高斯曲线。计算了这些带中氢氧化钴的含量，结果表明其远离界面处增加到最大值，然后下降。这些带随后通过进一步沉淀而生长。这种生长在时间上被证明是非线性的。另一方面，研究表明带的溶解在多个研究带中同时且共同发生。研究了Co(+2)离子浓度对带形成和溶解动力学的影响。还确定了该Liesegang体系的时间规律。还发现该体系对温度波动非常敏感。
