X-ray crystallinity of different soil nanoclays in relation to phosphatase adsorption

Nanoclays, which are active component of soils, play a very important role for enzyme adsorption. To study the effect of nanoclays on enzyme adsorption, these were isolated from three genetically different Indian soils, i.e. black soil (Vertisols), red soil (Alfisols) and recent alluvial soil (Inceptisols). Then X-ray coherent particle sizes of different nanoclays (with and without amorphous aluminosilicates) before and after acid phosphatase adsorption were studied. Result showed that basal spacing of smectite present in nanoclays increased due to intercalation of enzyme molecules, whereas 'd' spacing in kaolinite did not change due to enzyme immobilization. Average particle size, calculated by Scherrer equation, increased due to enzyme immobilization for all nanoclays. In case of kaolinite, enzyme molecules acted as linkers and bind more than one particle together, which resulted in increased apparent particle size. Crystallite size of kaolinite was also more than that of mica or smectite. Increased average particle size after enzyme immobilization was confirmed from transmission electron microscopy (TEM) images.