Sorption of organophosphate esters by carbon nanotubes.
Insights from the molecular-level mechanism of sorption of organophosphate esters (OPEs) on carbon nanotubes (CNTs) can further our understanding of the fate and transport of OPEs in the environment. The motivation for our study was to explore the sorption process of OPEs on multi-walled CNTs (MWCNTs), single-walled CNTs (SWCNTs) and their oxidized counterparts (O-MWCNTs and O-SWCNTs), and its molecular mechanism over a wide concentration range. The sorption isotherm results revealed that the hydrophobicity of OPEs dominated their affinities on a given CNT and the π-π electron donor-acceptor (EDA) interaction also played an important role in the sorption of aromatic OPEs. This π-π EDA interaction, verified with Raman and FT-IR spectroscopy, could restrict the radial vibration of SWCNTs and affect the deformation vibration γ(CH) bands of OPE molecules. The OPE surface coverage on CNTs, estimated using the nonlinear Dubinin-Ashtakhov model, indicated that the oxygen-containing functional groups on CNTs could interact with water molecules by H-bonding, resulting in a decrease in effective sorption sites. In addition, FTIR analysis also confirmed the occurrence of Brønsted acid-base interactions between OPEs and surface OH groups of SWCNTs. Our results should provide mechanistic insights into the sorption mechanism of OPE contaminants on CNTs.
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Wei
W
Yan
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Li
L
Yan
School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
Jinming
J
Duan
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: cyjing@rcees.ac.cn.
Chuanyong
C
Jing
D000327:Adsorption; D004785:Environmental Pollutants / Q000737:chemistry*; D004952:Esters; D037742:Nanotubes, Carbon / Q000737:chemistry*; D010755:Organophosphates / Q000737:chemistry*; D010084:Oxidation-Reduction; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman
D004785:Environmental Pollutants; D004952:Esters; D037742:Nanotubes, Carbon; D010755:Organophosphates
Carbon nanotubes; FTIR; Organophosphate esters; Raman spectroscopy; Sorption