Nature and charge properties of X-ray noncrystalline aluminosilicates as affected by citric acid
1989
Lou, G. | Huang, P.M.
The surface charge properties of X-ray noncrystalline alumino-silicates in relation to their structural distortion by citric acid during their formation were investigated. The precipitates formed from solutions containing monomeric orthosilicic acid and AlCl3 (Si/Al molar ratio 0.5 and OH/Al molar ratio 2.0) in the presence of citric acid (citrate/Al molar ratios of 0.02 and 0.025) exhibit an IR absorption maximum at 965 cm-1, a feature similar to that of "allophane-like constituents" or "ill-defined fraction of the allophane-imogolite complex" in soil. The complexation of citrate ligand with hydroxy-aluminosilicate ions or "proto-imogolite", the precursor of paracrystalline to X-ray noncrystalline aluminosilicates, promoted the development of structural defects apparently through perturbation of the regular linkage of hydroxy-aluminosilicate fragments. The pertubation effect of citrate ligands promoted the development of positive charge and resulted in a marked increase in the point of zero charge (PZC) due to the exposure of Al-OH2(0.5+) groups around the defect sites. The role of complexing organic ligands in influencing the surface properties of short-range ordered aluminosilicates through structural distortion thus deserves attention.
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