フッ化物イオン処理によるアロフェンおよびイモゴライトの表面特性変化 : 表面酸性および陽イオン交換容量の増大と分子軌道法計算によるメカニズム解析

概要

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The purpose of this research is to improve the surface properties of allophane and imogolite which are frequently included in volcanic ash soils. Allophane and imogolite were respectively separated from the inner part and outer part of weathered pumice grains. These materials were treated with NH_4F solution. Surface acid strength and cation exchange capacity (CEC) were measured before and after the treatment. The measured values of CEC increased with the increasing concentration of NH_4F solution. The maximum values of the treated materials were 3 to 4.5 times higher for allophane and 22 times higher for imogolite than those of their untreated counterparts. The surface acidity measured by the Hammett indicator method was much stronger for allophane and imogolite treated with NH_4F solution than for those without treatment. The mechanism of the changes in CEC and surface acidity analyzed by infrared spectroscopy and molecular orbital method were as follows : Silanol groups (Si-OH) in the structures of allophane and imogolite interact at the electron level with fluorine taken into the structures. This interaction facilitates the dissociation of protons from the silanol groups, causing the enhancement of CEC and a strengthening of the acidity.
社団法人日本土壌肥料学会の論文
1998-10-05