title: Effects of ionic strength and temperature on the aggregation and deposition of multi-walled carbon nanotubes.
abstract: 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 80mmol/L in NaCl and 1.3mmol/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 800nm. 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.
authors.affiliation: Environment Research Institute, Shandong University, Jinan 250100, China. Electronic address: lixinwangsdu@163.com.
authors.forename: Lixin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Environment Research Institute, Shandong University, Jinan 250100, China.
authors.forename: Xuezhi
authors.initials: X
authors.lastname: Yang
authors.affiliation: Environment Research Institute, Shandong University, Jinan 250100, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Environment Research Institute, Shandong University, Jinan 250100, China.
authors.forename: Yuxuan
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: Environment Research Institute, Shandong University, Jinan 250100, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Ding
authors.affiliation: Environment Research Institute, Shandong University, Jinan 250100, China. Electronic address: jiangw@sdu.edu.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
mesh_terms: D006812:Humic Substances; D007700:Kinetics; D008956:Models, Chemical; D037742:Nanotubes, Carbon / Q000032:analysis* / Q000737:chemistry; D009994:Osmolar Concentration; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D006812:Humic Substances; D037742:Nanotubes, Carbon; D014874:Water Pollutants, Chemical
keywords: Aggregation; Carbon nanotubes; Deposition; Electrolyte; Temperature