School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry of China and Key Laboratory of MOE for Life Science, Nanjing University, Nanjing 210093, China.
Environ Sci Technol. 2009 Dec 15;43(24):9281-6. doi: 10.1021/es901583m.
The water exchange reactions on the gibbsite surface have been investigated by density functional calculations (B3LYP/6-31G(d) level) combining the supermolecular model and PCM model in this paper, and the water exchange rate constants on the gibbsite surface have also been predicted. In the proposed reaction pathways, the clusters Al6(OH)18(H2O)6(0) and Al6(OH)12(H2O)12(6+) are used as the models of gibbsite surface and protonated gibbsite surface respectively to examine the effect of protonation of gibbsite surface on the water exchange rate constants. The activation energy barriers DeltaE(s) not equal to (aq) for Al6(OH)18(H2O)6(0) and Al6(OH)12(H2O)12(6+) are 28.6 and 27.2 kJ*mol-1, respectively. The reaction energies DeltaE(s) (aq) for Al6(OH)18(H2O)6(0) and Al6(OH)12(H2O)12(6+) are 2.9 and 14.4 kJ mol-1, respectively, indicating that hexacoordinate aluminum in the gibbsite surface is more stable. The log k(TST) for Al6(OH)18(H2O)6(0) and Al6(OH)12(H2O)12(6+) are 6.5 and 7.5 respectively, and the log k(ex) calculated by the given transmission coefficient for Al6(OH)18-(H2O)6(0) and Al6(OH)12(H2O)12(6+) are 2.4 and 3.4 respectively, indicating that the protonation of gibbsite surface promotes the water exchange reaction of gibbsite surface and accelerates the dissolution rate of gibbsite. The relationship between the calculated free energy and experimental rate constants was explored, and according to this relationship, the log k(ex) for Al6(OH)18(H2O)6(0) and Al6(OH)12(H2O)12(6+) are 2.5 and 3.1 respectively, close to the corresponding values calculated by the given transmission coefficient. The water exchange rate constant of gibbsite surface is close to those of K-MAl(12)(M = Al, Ga, and Ge) polyoxocations, but deviates from that of Al(H2O)6(3+), implying that the same reactions with similar structure have similar water exchange rate constants.
本文采用密度泛函理论（B3LYP/6-31G(d)水平）结合超分子模型和 PCM 模型研究了三水铝石表面的水交换反应，并预测了三水铝石表面的水交换速率常数。在所提出的反应途径中，分别以 Al6(OH)18(H2O)6(0)和 Al6(OH)12(H2O)12(6+)簇作为三水铝石表面和质子化三水铝石表面的模型，以考察质子化对水交换速率常数的影响。Al6(OH)18(H2O)6(0)和 Al6(OH)12(H2O)12(6+)的活化能垒 DeltaE(s) not equal (aq)分别为 28.6 和 27.2 kJ*mol-1。Al6(OH)18(H2O)6(0)和 Al6(OH)12(H2O)12(6+)的反应能 DeltaE(s) (aq)分别为 2.9 和 14.4 kJ mol-1，表明三水铝石表面的六配位铝更稳定。Al6(OH)18(H2O)6(0)和 Al6(OH)12(H2O)12(6+)的 log k(TST)分别为 6.5 和 7.5，Al6(OH)18-(H2O)6(0)和 Al6(OH)12(H2O)12(6+)的给定传递系数计算的 log k(ex)分别为 2.4 和 3.4，表明质子化三水铝石表面促进了三水铝石表面的水交换反应，加速了三水铝石的溶解速率。还探讨了计算得到的自由能与实验速率常数之间的关系，根据该关系，Al6(OH)18(H2O)6(0)和 Al6(OH)12(H2O)12(6+)的 log k(ex)分别为 2.5 和 3.1，与给定传递系数计算得到的值相近。三水铝石表面的水交换速率常数与 K-MAl(12)(M = Al、Ga 和 Ge)聚氧阳离子的水交换速率常数相近，但与 Al(H2O)6(3+)的水交换速率常数不同，表明具有相似结构的相同反应具有相似的水交换速率常数。
