Molecular orbital study on the change in surface characteristics of allophane with oxo-acids adsorption.

活性氧酸（硫酸、磷酸、硼酸、钼酸和低分子量有机酸）在火山灰土活性粘土材料之一纳米球allophane上的吸附行为具有重要的环境保护和农业意义。通过理论量子化学计算和实验方法对吸附机理进行了详细的研究。实验结果表明，所有的氧化酸都是通过配体交换反应与表面羟基的硅- oh和铝- oh进行吸附的。虽然这类配体交换反应已有报道，但我们利用理论量子化学方法、分子轨道方法进一步发现了一些新的事实。新的发现说明如下：1。磷酸盐、钼酸盐和硼酸盐吸附在纳米球allophane上，并从allophane中释放Si。这被称为氧酸与Si.2的交换反应。在硼酸盐吸附的情况下，提出了一种特殊的键AT-OH-B。随着氧酸的吸附，氯烷的阳离子交换容量和表面酸度增加。这是由于硅烷醇基团在吸附位点附近的pKa （Brφnsted酸度增加）降低所致。4 .硅烷醇基团pKa的降低是由于吸附的氧酸的诱导作用引起的，其中对磷酸的诱导作用最大。氧酸的吸附也降低了附近Al-O和Si-O的结合强度，并且对盐酸、硝酸和硫酸等酸起怀疑作用。这对于最近的酸雨问题是很重要的。

Adsorption behavior of oxo-acids (sulfuric acid, phosphoric acid, boric acid, molybdic acid and low molecular weight organic acids) on nano-ball allophane, one of active clay mateials in volcanic ash soils, is important in view of environmental conservation and agriculture. We investigated the detailed adsorption mechanism with theoretical quantum chemical calculation in addition to with experimental methods.Experimental results showed that all of the oxo-acids were adsorbed on nano-ball allophane via ligand exchange reaction with surface hydroxy groups of allophane, Si-OH and Al-OH.Although this kind of ligand exchange reactions have been reported, we further found some new facts by utilizing thoretical quantum chemical method, molecular orbital method. The new findings are described below.1. The phosphate, molybdate and borate adsorbed on nano-ball allophane with releasing Si from allophane. This was called exchange reaction of oxo-acids with Si.2. In case of borate adsorption, a unusual bonding, AT-OH-B, was suggested.3. With oxo-acids adsorption, cation exchange capacity and surface acidity of allophane increased. This is due to decrease in pKa (increase in Brφnsted acidity) of silanol groups near the adsorption site.4. The decrease in pKa of the silanol groups was caused by inductive effect of the adsorbed oxo-acids, and the inductive effect was greatest for phosphate adsorption.5. The adsorption of oxo-acids also decresed bond strength of near Al-O and Si-O, and the allophane became suspective for acids such as hydrochloric, nitric and sulfuric acids. This is important in relation to the recent problem of acid rain.