| Summary: | In soil science has been recognized two categories of minerals are crystalline and amorphous. Amorphous mineral was once defined as minerals that do not have a clear shape or structure. Having found X-Ray Diffraction (XRD) it is known that the mineral has a short peak that can be categorized as a short-range order aluminosilicate. At the recent developments after discovery of Transmission Electron Microscope (TEM), it is known that the amorphous mineral has an obvious morphology, Allofan shaped hollow spheres (nano-ball) and Imogolit shaped nano-tube (such as a long pipe). Imogolite is one of the amorphous minerals commonly found in soils developed from volcanic ash or other weathered pyroclastic deposits. Imogolite is an important paracrystalline hydrous aluminosilicate with a unique nanofiber structure. Imogolite have nano-tubular morphology with a diameter of 1 nm and the outer 2 nm. Its length can reach several hundred nm. The imogolite struture has a composition of Al2(OH)3SiO3OH with a Si/Al ratio of 0.5. The tube walls consist of a single continuous A1(OH)3 (gibbsite) sheet with the inner hydroxyl surface of the gibbsite replaced by O3SiOH groups. The formation of imogolite is believed to occur in a gibbsite sheet through the displacement of three hydroxylgroups surrounding a vacant octahedral site by an orthosilicate anion. Molecular orbital calculation results proved that the dissociation or undissociated form of the Si–OH has an important role in formation of imogolite. When the Si–OH was undissociated, the shape of proto-imogolite model was transformed to asymmetrical in molecular configuration. This caused curling of the proto-imogolite model, which lead to formation of imogolite tube. The surface charge properties of imogolite are controlled by the outer –Al2OH groups is higher than the inner –Al2OHSiO3 groups. Consequently, the outer tube walls are unreactive towards ions. On the inside of the tube -SiOH groups can be a source of negative charge. Imogolit probably also able to strongly adsorb oxyanions (phosphate and sulphate) but only occurs at the end of the tube which has -AlOH1/2- groups (singly coordinated OH).
Key Words: X-RD, TEM, Imogolite, short-range order aluminosilicate, and nano-tube
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