Tamura H, Tanaka A, Mita Ky, Furuichi R
Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628, Japan
J Colloid Interface Sci. 1999 Jan 1;209(1):225-231. doi: 10.1006/jcis.1998.5877.
Hydroxyl groups on metal oxide in water are the sites for ion exchange, and the surface hydroxyl site density on oxides is a measure of the ion-exchange capacity. Here, the Grignard reagent method was applied to determine the surface hydroxyl site density of oxide samples. The results were similar to those reported for different oxides with other methods (dehydration by heating, tritium exchange, crystallographic calculations, etc.), and they are comparable with those calculated from the closest packing of hydroxide ions. A mechanism of hydroxylation is proposed: lattice oxide ions (extremely strong bases) are exposed to aqueous solutions and are neutralized by water to become hydroxide ions. Also, the saturated deprotonation method was applied to hematite, and it was found that all the acid hydroxyl groups on hematite were deprotonated in very high concentrations of alkali solutions ( approximately 5 mol dm-3 NaOH), and from the saturated amount of OH- consumed by deprotonation, the same result as that by the Grignard method was obtained. It is shown that all hydroxyl groups take part in ion exchange and that the unusually small values reported elsewhere with the saturated (de)protonation method may contain errors. Hetero- or homogeneity of hydroxyl groups in contact with water as ion-exchange sites is also discussed. It is suggested that intensely hydrated layers at the oxide/water interface may result in homogeneous discrete sites. The development of microstructures in the oxides was suggested from the measured values of specific surface areas, and the effect of the microstructure environments on the reactivity of internal surface hydroxyl sites is discussed. Copyright 1999 Academic Press.
水中金属氧化物上的羟基是离子交换的位点，氧化物表面的羟基位点密度是离子交换容量的一种度量。在此，采用格氏试剂法测定氧化物样品的表面羟基位点密度。结果与用其他方法（加热脱水、氚交换、晶体学计算等）报道的不同氧化物的结果相似，并且与由氢氧根离子紧密堆积计算得到的结果具有可比性。提出了一种羟基化机理：晶格氧化物离子（极强的碱）暴露于水溶液中并被水中和形成氢氧根离子。此外，对赤铁矿应用了饱和去质子化方法，发现在非常高浓度的碱溶液（约5 mol dm⁻³ NaOH）中赤铁矿上所有的酸性羟基都被去质子化，并且从去质子化消耗的OH⁻饱和量得到了与格氏法相同的结果。结果表明所有羟基都参与离子交换，并且其他地方用饱和（去）质子化方法报道的异常小的值可能存在误差。还讨论了作为离子交换位点与水接触的羟基的异质性或同质性。有人认为氧化物/水界面处强烈水合的层可能导致均匀的离散位点。从比表面积的测量值推测了氧化物中微观结构的发展，并讨论了微观结构环境对内表面羟基位点反应性的影响。版权所有1999年学术出版社。
