Change in chirality of semiconducting single-walled carbon nanotubes can overcome anionic surfactant stabilisation: a systematic study of aggregation kinetics
Iftheker A. Khan A , Joseph R. V. Flora B , A. R. M. Nabiul Afrooz C , Nirupam Aich C , P. Ariette Schierz C , P. Lee Ferguson D , Tara Sabo-Attwood E and Navid B. Saleh C F
+ Author Affiliations
- Author Affiliations
A Department of Chemical Engineering, University of Rhode Island, Kingston, RI 02881,USA.
B Department of Civil and Environmental Engineering, University of South Carolina, Columbia, SC 29208, USA.
C Department of Civil, Architectural and Environmental Engineering, University of Texas, Austin, TX 78712, USA.
D Department of Civil and Environmental Engineering, Duke University, Durham, NC 27708, USA.
E Department of Environmental and Global Health, University of Florida, Gainesville, FL 32610, USA.
F Corresponding author. Email: navid.saleh@utexas.edu
Environmental Chemistry 12(6) 652-661 https://doi.org/10.1071/EN14176
Submitted: 5 September 2014 Accepted: 20 January 2015 Published: 20 May 2015
Environmental context. Chirally enriched semiconducting single-walled carbon nanotubes (SWNTs) are some of the most utilised nanomaterials. Although chirality of SWNTs is known to influence their electronic properties and interfacial interaction, the interplay between chirality and surfactant structure in SWNT stability is not well understood. This study investigates these interactions, providing data to better assess the environmental fate of SWNTs.
Abstract. Single-walled carbon nanotubes’ (SWNT) effectiveness in applications is enhanced by debundling or stabilisation. Anionic surfactants are known to effectively stabilise SWNTs. However, the role of specific chirality on surfactant-stabilised SWNT aggregation has not been studied to date. The aggregation behaviour of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalised with three anionic surfactants – sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and sodium deoxycholate – was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and divalent (CaCl2) electrolytes as well as a 2.5 mg total organic carbon (TOC) L–1 Suwannee River humic acid were used as background chemistry. Overall, sodium dodecyl benzene sulfonate showed the most effectiveness in stabilising SWNTs, followed by sodium deoxycholate and sodium dodecyl sulfate. However, the larger diameter (7,6) chirality tubes (compared to (6,5) diameter), compromised the surfactant stability due to enhanced van der Waals interaction. The presence of divalent electrolytes overshadowed the chirality effects and resulted in similar aggregation behaviour for both the SWNT samples. Molecular modelling results elucidated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of Suwannee River humic acid under 10 mM monovalent and mixed-electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilisation of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure.
Additional keywords: molecular dynamic simulation, stability.
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