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Abstract: Understanding the dispersion and aggregation of carbon nanotubes (CNTs) in the aqueous environment are critical for the fate, bioavailability, and the environment and health risk assessment of them because the better suspended CNTs display a higher mobility and could transfer to a longer distance in the environment to possibly pose greater ecological and environmental risks. In this study, we have found that bulk single-walled carbon nanotubes (SWCNTs) could not be dispersed and stably suspended in water and sodium dodecylbenzene sulfonate (SDBS) solution by shaking at 140 r/min, although they could be stably suspended in SDBS solution by sonication. Even through sonication, SWCNTs suspended in SDBS solution do not remain stable at the presence of environmentally relevant cations (e.g., Na⁺, K⁺, Ca²⁺, and Mg²⁺) after dilution. These observations suggest that SWCNTs will not travel long distances in significant concentrations in the natural environment to pose great ecological and environmental risks. We also observed that the re-aggregation of suspended SWCNTs in the presence of cations was dependent on the SDBS concentration rather than the SWCNT concentration in the suspension. Both SDBS and sonication play important roles in the dispersion of SWCNTs, with sonication breaking down large aggregates of SWCNTs, while SDBS adsorbed on the SWCNTs inhibits the coagulation and aggregation by steric/electrostatic repulsion to maintain the stability of the suspension in water.

单壁碳纳米管在阴离子表面活性剂溶液中的分散悬浮和团聚沉降性能研究

研究目的：纳米颗粒在水中的悬浮和团聚性能是决定它们在环境中迁移行为及潜在健康和环境风险影响范围的关键。表面活性剂不仅在环境中普遍存在，而且是工业制备纳米颗粒稳定悬浮液的主要分散剂。本文以单壁纳米碳管为代表，研究震荡扰动及稀释等模拟环境条件下其在阴离子表面活性剂溶液中的分散悬浮和团聚沉降性能，为评价纳米颗粒排放进入环境后的潜在风险提供依据。
创新要点：现有研究认为，纳米颗粒由于能在水中稳定悬浮，其排放到环境中会产生长距离迁移并存在造成大范围污染的可能性和生态健康风险。在本文中，震荡扰动及稀释等模拟环境条件的研究表明，单壁碳纳米管在环境中长距离迁移并造成大范围污染的可能性和风险较小。
研究方法：通过比较震荡扰动（模拟环境条件）和超声辅助两种分散悬浮方式及有无添加十二烷基苯磺酸钠（SDBS）阴离子表面活性剂条件下的单壁碳纳米管在水中的悬浮性能（图1），研究单壁碳纳米管能否在环境中被分散悬浮。通过研究Na+，K+，Ca2+和Mg2+等环境主要阳离子存在时SDBS稳定悬浮的单壁碳纳米管悬浮性能及与SDBS浓度等的相关性 （图6和8），探明稳定悬浮的单壁碳纳米管能否在环境稀释过程中和环境阳离子存在下保持稳定悬浮。
重要结论：在超声辅助下，单壁碳纳米管可以在SDBS阴离子表面活性剂溶液中稳定分散悬浮，但不能在水中稳定分散悬浮。在无超声辅助、仅通过机械震荡的情况下，单壁碳纳米管无法在水中和SDBS溶液中稳定分散悬浮。对于已经在SDBS溶液中稳定悬浮的单壁碳纳米管，它们在Na+，K+，Ca2+和Mg2+等环境主要阳离子存在时也会脱稳形成团聚沉降，且该团聚沉降行为取决于悬浮溶液中SDBS的浓度。当SDBS稳定悬浮的单壁碳纳米管在环境中被稀释时，SDBS浓度被稀释降低，会迅速导致单壁碳纳米管团聚沉降。因此，单壁碳纳米管很难在环境中被分散悬浮，即使是已经稳定分散悬浮的单壁碳纳米管，也会在环境稀释和环境阳离子的作用下快速团聚沉降。由此可见，单壁碳纳米管在环境中长距离迁移并造成大范围污染的可能性和风险较小。
分散悬浮；团聚沉降；单壁碳纳米管；阴离子表面活性剂；超声

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