The Aggregation And Deposition Of Carbon Nanotubes In Aqueous Solution

As an novel nanoscale materials, carbon nanotubes (CNTs) have caused rising attentions. Due to their unique physicochemical properties, CNTs have been an ideal ecomaterials for industrial application. The ever increasing demand and the decreasing cost make CNTs released into the natural waters inevitably. Once exposed to water environment, CNTs will gather the coexsited organic contaminations and easily penetrate into human body, thus becoming an latent threate to both environment and human health. However, the bioavailability and toxicity of carbon nanotubes largely depend on their aggregation and deposition behavior. Thus, the dispersion stability of CNTs is a key factor in determining their transport and fate in aquatic environment. Studies on the aggregation and deposition behavior of CNTs is of great significance to predict their environmental effects on water bodies.Current researches on the aggregation and depostion of CNTs in aquatic environment only focued on the homogeneous dispersed CNT solutions. Undoutly, homogeneous system is a suitable starting point for investigating the colloidal stability of CNTs since it is much simpler to systematically study in the laboratory. However, in natural waters, CNTs are usually heterogeneous in particle size ranged from nm to mm, and their fate is more likely to be controlled by aggregation between particles with heterogeneous sizes. In this paper, laser particle analysis and settling curve modeling method were established to describe the aggregation and depostion of CNTs with heterogeneous sizes in aquatic phase. The influence of physicochemical properties of CNTs, such as structure, length, diameter and oxygen functional groups, and the condition of sonication treatment, such as sonication time and power, were studied on the hydrodynamic diameter of sixteen kinds of carbon nanomaterials. The centrifugal sedimentation rate constant (ks) from settling curve profile was proved to be a practical and reliable quantitative index in the description of heterogeneous CNT suspension. The results from laser particle analysis and settling curve modeling method were proved to have consistency. Effects of solution pH, ionic strength, natural organic matter on the dispersion stability of CNTs were evaluated. The aggregation and deposition behavior of CNTs in three surface water specimens, waters from Yangtze River, Jiuxiang River, and Xuanwu Lake, were studied. The results demonstrate that in natural waters CNTs tend to be unstable and are prone to deposition, which were attributed to the bridging role of extracellular polymeric substances. Finally, the possible development of experimental research on the CNTs with heterogeneous sizes in the future was also put forward.