Noerpel Matthew R, Lenhart John J
Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University, Columbus, OH 43210, USA.
Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University, Columbus, OH 43210, USA.
J Colloid Interface Sci. 2015 Dec 15;460:36-46. doi: 10.1016/j.jcis.2015.08.028. Epub 2015 Aug 15.
We investigated the adsorption of citric acid on the surface of two different sized hematite nanoparticles using batch adsorption experiments, Fourier-transform infrared spectroscopy, surface complexation modeling and computational molecular modeling. Citrate adsorption reached a maximum between pH approximately 2.5 and 5.5 and declined as the pH was increased or decreased from that range. At high surface loading conditions, the dominant adsorbed citrate structure was outer-sphere in nature with a protonation state that varied with pH. At low pH, there was also evidence of an inner-sphere complex consistent with a binuclear, bidentate structure where the hydroxyl group was deprotonated and played an active role in the adsorption. An inner-sphere complex was also detected at low citrate surface loading conditions. Surface-area normalized surface coverages were similar for both sizes of hematite, however, the inner sphere complex appeared to be slightly more prevalent on the smaller hematite. Based on these structures, a triple layer surface complexation model comprised of two outer-sphere complexes and one inner-sphere complex was used to describe the adsorption data for both hematite sizes across a range of solution conditions with a single set of surface area dependent equilibrium constants.
我们通过批量吸附实验、傅里叶变换红外光谱、表面络合模型和计算分子模型，研究了柠檬酸在两种不同尺寸赤铁矿纳米颗粒表面的吸附情况。柠檬酸盐吸附在pH约2.5至5.5之间达到最大值，当pH值从该范围升高或降低时，吸附量下降。在高表面负载条件下，占主导地位的吸附柠檬酸盐结构本质上是外层络合物，其质子化状态随pH值变化。在低pH值下，也有证据表明存在一种内层络合物，其结构与双核双齿结构一致，其中羟基去质子化并在吸附过程中起积极作用。在低柠檬酸盐表面负载条件下也检测到了内层络合物。两种尺寸的赤铁矿的比表面积归一化表面覆盖率相似，然而，内层络合物在较小尺寸的赤铁矿上似乎更为普遍。基于这些结构，使用由两个外层络合物和一个内层络合物组成的三层表面络合模型，通过一组与表面积相关的平衡常数，描述了在一系列溶液条件下两种尺寸赤铁矿的吸附数据。
