土壤颗粒对纳米TiO_2悬浮稳定性作用机制的实验研究

在不含表面活性剂和含有表面活性剂两种条件下,研究了土壤颗粒对纳米TiO2(nTiO2)悬浮稳定性的影响.结果表明,土壤颗粒降低了nTiO2在水相中的悬浮稳定性.当体系中不含表面活性剂时,nTiO2在土壤大颗粒上的沉积是导致nTiO2脱稳沉淀的主要原因.在含有表面活性剂的溶液中,土壤颗粒降低nTiO2悬浮稳定性的作用变得更加明显了.一方面,表面活性剂加速了土壤颗粒本身的沉降从而增强了nTiO2在其中的沉降,另一方面,表面活性剂在土壤上的强烈吸附促进了表面活性剂-nTiO2在土壤上的沉积.扫描电镜显示,nTiO2不仅吸附在土壤大颗粒上,还会吸附在土壤小颗粒表面.3种表面活性剂中,十六烷基三甲基溴化铵(CTAB)悬浮的nTiO2与土壤颗粒共沉淀现象最明显.除了土壤对CTAB的吸附作用之外,XDLVO/DLVO能量计算显示CTAB体系中土壤颗粒与nTiO2之间存在显著第二极小值,表明nTiO2能够在第二极小值位置与土壤颗粒结合,从而与土壤颗粒一起快速沉淀.

Experimental study on the effecting mechanisms of soil particles on the stability of TiO2 nanoparticles

The effect of soil particles on the stability of TiO₂ nanoparticles (nTiO₂) both in the absence and in the presence of surfactants was systematically investigated. Results showed that soil particles significantly destabilize nTiO₂ in aqueous. In the absence of surfactnats, the adsorption of nTiO₂ on large soil particles was mainly responsible for the destabilization and sedimentation of nTiO₂. In the presence of surfactants, the destabilization of nTiO₂ by soil particles was significantly enhanced. On the one hand, surfactants enhanced the sedimentation rate of soil which led to the enhanced destabilization of nTiO₂. On the other hand, the large adsorption of surfactants on soil was also responsible for the co-deposition of surfactant and nTiO₂ on soil. SEM showed nTiO₂ did not only adsorb onto large soil particles, but also onto the fine particles. Among the three surfactants, the co-precipitation of nTiO₂ with soil particles in cetyl trimethylammonium bromide (CTAB) is the most obvious. Besides the adsorption of surfactant on soil, XDLVO/DLVO energy calculation revealed a significant secondary minimum between soil particles and nTiO₂, where hetero-aggregation of nTiO₂ with soil would probably occur.