Angove Michael J, Wells John D, Johnson Bruce B
Colloid and Environmental Chemistry Laboratory, La Trobe University, P.O. Box 199, Bendigo, Victoria 3552, Australia.
Langmuir. 2006 Apr 25;22(9):4208-14. doi: 10.1021/la0534571.
The adsorption of mellitic acid (benzene-1,2,3,4,5,6-hexacarboxylic acid) onto kaolinite was investigated at five temperatures between 10 and 70 degrees C. Mellitic acid adsorption increased with increasing temperature at low pH (below pH 5.5), but at higher pH, the effect of increasing temperature was to reduce the amount adsorbed. Potentiometric titrations were conducted, adsorption isotherms were measured over the same temperature range, and the data obtained were used in conjunction with adsorption edge and ATR-FTIR spectroscopic data to develop an extended constant capacitance surface complexation model of mellitic acid adsorption. A single set of reactions was used to model all data at the five temperatures studied. The model indicates that mellitic acid sorbs via outer-sphere complexation to surface hydroxyl (SOH) groups on the kaolinite surface rather than to permanent charge sites. The reactions proposed are SOH + L6- + 2H+ <-->[(SOH2)+(LH)5-]4- and SOH + L(6-) <--> [(SOH)(L)6-]6-. Thermodynamic parameters calculated from the temperature dependence of the equilibrium constants for these reactions indicate that the adsorption of mellitic acid onto kaolinite is accompanied by a large entropy increase.
在10至70摄氏度之间的五个温度下，研究了苯六甲酸（苯 - 1,2,3,4,5,6 - 六羧酸）在高岭石上的吸附情况。在低pH值（低于pH 5.5）时，苯六甲酸的吸附量随温度升高而增加，但在较高pH值时，温度升高的影响是减少吸附量。进行了电位滴定，在相同温度范围内测量了吸附等温线，并将获得的数据与吸附边缘和ATR - FTIR光谱数据结合使用，以建立苯六甲酸吸附的扩展恒电容表面络合模型。使用一组反应对所研究的五个温度下的所有数据进行建模。该模型表明，苯六甲酸通过外层络合作用吸附到高岭石表面的表面羟基（SOH）基团上，而不是吸附到永久电荷位点上。提出的反应为SOH + L6- + 2H+ <-->[(SOH2)+(LH)5-]4- 和 SOH + L(6-) <--> [(SOH)(L)6-]6-。根据这些反应平衡常数的温度依赖性计算出的热力学参数表明，苯六甲酸在高岭石上的吸附伴随着大量的熵增加。
