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Insight into the Segregation Phenomenon in Metal-Cation-Doped Aluminum Sol during the Drying Process with NO3鈥?/sup> as Counterions
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文摘
The segregation mechanism of metal ions (Na+, K+, Mg2+, Ca2+, Co2+, Ni2+, La3+, Y3+) in 纬-AlOOH was investigated during the sol鈥揼el process by a combination of experiments and density functional theory (DFT) calculations. The DFT calculations showed that all of the adsorption energies of metal ions were smaller than the hydrogen ion in neutral conditions, and the metal ions even could not be adsorbed on the protonated 纬-AlOOH surface due to electrostatic repulsion. The segregation of metal ions in 纬-AlOOH sol during the drying process was caused by weak adsorption of metal ions on the 纬-AlOOH surface in acidic conditions and mainly occurred at the late period of drying with the removal of adsorbed water. The computational segregation sequence of metal ions was consistent with experimental results, which was La3+ 鈮?Y3+ > Ni2+ 鈮?Co2+ > Mg2+ 鈮?Ca2+ > K+ 鈮?Na+. According to the segregation mechanism during sol鈥搙erogel transition, it is speculated that an additive which could strengthen the combination between metal ions and the protonated 纬-AlOOH surface could diminish the segregation. On the basis of this speculation, citric acid was added into the 纬-AlOOH sol, and the segregation percentage of La3+ decreased to 3.54% from 16.4%.

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