Journal
JOURNAL OF ENVIRONMENTAL SCIENCES
Volume 25, Issue 1, Pages 195-203Publisher
SCIENCE PRESS
DOI: 10.1016/S1001-0742(12)60023-0
Keywords
adsorption; lead; multi-walled carbon nanotube; diameter; surface oxygen content
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Funding
- National High Technology Research and Development Program (863) of China [2007AA06Z334]
- Ministry of Education
- Shanghai Jiao Tong University Innovation Fund for Postgraduates
- State Key Laboratory of Pollution Control and Resource Reuse Foundation [PCRRY11009]
- Program for Young Excellent Talents at Tongji University [2010KJ026]
- Scholarship Award for Excellent Doctoral Student
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The effects of different outer diameters and surface oxygen contents on the adsorption of heavy metals onto six types of multi-walled carbon nanotubes (MWCNTs) were investigated in an aqueous solution and lead was chosen as a model metal ion. The results indicated that the percentage removal and adsorption capacity of lead remarkably increased with decreasing outer diameter due to larger specific surface area (SSA). The SSA-normalized maximum adsorption capacity (q(m)/SSA) and SSA-normalized adsorption coefficient (K-d/SSA) were strongly positively correlated with surface oxygen content, implying that lead adsorption onto MWCNTs significantly increases with the rise of oxygen content and decreases with decreasing SSA. The calculated thermodynamic parameters indicated that adsorption of lead on MWCNTs was endothermic and spontaneous. When the oxygen content of MWCNTs increased from 2.0% to 5.9%, the standard free energy (Delta G degrees) became more negative, which implied that the oxygenated functional groups increased the adsorption affinity of MWCNTs for lead. Through calculation of enthalpy (Delta H degrees), Delta G degrees and free energy of adsorption (E-a), lead adsorption onto MWCNTs was recognized as a chemisorption process. The chemical interaction between lead and the phenolic groups of MWCNTs could be one of the main adsorption mechanisms due to highly positive correlations between the phenolic groups and K-d/SSA or q(m)/SSA.
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