Effects of ionic strength and temperature on the aggregation and deposition of multi-walled carbon nanotubes
Effects of ionic strength and temperature on the aggregation and deposition of multi-walled carbon nanotubes
复制标题
离子强度和温度对多壁碳纳米管聚集和沉积的影响
DOI：
10.1016/j.jes.2016.07.003
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发表时间：
2017
影响因子：
6.9
通讯作者：
Jiang Wei
中科院分区：
文献类型：
--
作者：
Wang Lixin;Yang Xuezhi;Wang Qi;Zeng Yuxuan;Ding Lei;Jiang Wei
碳纳米管在自然沃茨中的聚集和沉积决定了其在水体中的迁移和归宿。为此，采用时间分辨动态光散射技术研究了腐殖酸处理的多壁碳纳米管（HA-MWCNTs）在NaCl和CaCl 2电解质溶液中的聚集动力学。离子强度的增加诱导HA-MWCNT聚集，由于较少的负zeta电位和减少的静电排斥。HA-MWCNTs在NaCl和CaCl 2电解液中的临界凝聚浓度（CCC）分别为80 mmol/L和1.3 mmol/L，表明Ca 2+对HA-MWCNTs的凝聚作用比Na+更强。HA-MWCNTs的聚集行为符合Derjaguin-Landau-Verwey-Overbeek理论。通过在800 nm处的吸光度测量HA-MWCNTs的沉积动力学。HA-MWCNT在NaCl和CaCl 2溶液中的临界沉积浓度接近CCC值，因此在扩散限制聚集状态下，不能通过改变离子强度来增加沉积速率。沉积过程与聚集有关，因为较大的聚集体增加重力沉积，减少随机布朗扩散。在5、15和25°C下评估HA-MWCNT流体动力学直径。温度越高，由于静电斥力减小，随机布朗运动和碰撞频率增加，聚集速度越快。HA-MWCNTs在NaCl或CaCl 2电解液中，由于静电斥力的降低和随机布朗运动的增加，在较高温度下聚集更快。我们的研究结果表明，碳纳米管的聚集和沉积是两个相关的过程受电解质，和碳纳米管的运输有利于在低离子强度和低温。
The aggregation and deposition of carbon nanotubes (CNTs) determines their transport and fate in natural waters. Therefore, the aggregation kinetics of humic-acid treated multi-walled carbon nanotubes (HA-MWCNTs) was investigated by time-resolved dynamic light scattering in NaCl and CaCl2electrolyte solutions. Increased ionic strength induced HA-MWCNT aggregation due to the less negative zeta potential and the reduced electrostatic repulsion. The critical coagulation concentration (CCC) values of HA-MWCNTs were 80 mmol/L in NaCl and 1.3 mmol/L in CaCl2electrolyte, showing that Ca2 +causes more serious aggregation than Na+. The aggregation behavior of HA-MWCNTs was consistent with Derjaguin–Landau–Verwey–Overbeek theory. The deposition kinetics of HA-MWCNTs was measured by the optical absorbance at 800 nm. The critical deposition concentrations for HA-MWCNT in NaCl and CaCl2solutions were close to the CCC values, therefore the rate of deposition cannot be increased by changing the ionic strength in the diffusion-limited aggregation regime. The deposition process was correlated to the aggregation since larger aggregates increased gravitational deposition and decreased random Brownian diffusion. HA-MWCNTs hydrodynamic diameters were evaluated at 5, 15 and 25°C. Higher temperature caused faster aggregation due to the reduced electrostatic repulsion and increased random Brownian motion and collision frequency. HA-MWCNTs aggregate faster at higher temperature in either NaCl or CaCl2electrolyte due to the decreased electrostatic repulsion and increased random Brownian motion. Our results suggest that CNT aggregation and deposition are two correlated processes governed by the electrolyte, and CNT transport is favored at low ionic strength and low temperature.