Formation and transformation of Al13 from freshly formed precipitate in partially neutralized Al(III) solution

Al13 is one of the novel nanospecies in partially neutralized Al(III) solution and Al-OH sol or precipitate could be generated simultaneously in the neutralization. Unfortunately, the precipitate is believed to be harmful to the formation of Al13 due to the consumption of Al(OH)4−, which was regarded as the precursor of Al13. In this paper, the feasibility and potential of transformation of freshly formed Al-OH precipitate into Al13 species were studied by using ferron colorimetric method and 27Al NMR spectroscopy. The Al-OH precipitates were produced by two ways: injection of base solution into Al(III) solution gradually and mixing of Al(III) and base solutions instantaneously. The re-dissolving behaviors of the freshly formed precipitates were examined under different basicities (OH/Al molar ratio) and temperatures. It has been shown that Al13 could be formed through the re-dissolution of intermediate Al-OH precipitate generated in partially neutralized Al(III) solution. A possible formation mechanism of Al13 was suggested. Easily transformable precipitate was developed when the OH/Al molar ratio was less than 2.5. Rapid re-dissolution of freshly formed precipitate was favorable for Al13 formation, which could be enhanced by heating.