Critical evaluation of adsorption-desorption hysteresis of heavy metal ions from carbon nanotubes: influence of wall number and surface functionalization.
Single-, double-, and multi-walled carbon nanotubes (SWCNTs, DWCNTs, and MWCNTs), and two oxidized MWCNTs with different oxygen contents (2.51 wt % and 3.5 wt %) were used to study the effect of the wall number and surface functionalization of CNTs on their adsorption capacity and adsorption-desorption hysteresis for heavy metal ions (Ni(II), Cd(II), and Pb(II)). Metal ions adsorbed on CNTs could be desorbed by lowering the solution pH. Adsoprtion of heavy metal ions was not completely reversible when the supernatant was replaced with metal ion-free electrolyte solution. With increasing wall number and amount of surface functional groups, CNTs had more surface defects and exhibited higher adsorption capacity and higher adsorption-desorption hysteresis index (HI) values. The coverage of heavy metal ions on the surface of CNTs, solution pH, and temperature affect the metal ion adsorption-desorption hysteresis. A possible shift in the adsorption mechanism from mainly irreversible to largely reversible processes may take place, as the amount of metal ions adsorbed on CNTs increases. Heavy metal ions may be irreversibly adsorbed on defect sites.
Key Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 Hefei (PR China).
Jie
J
Li
Changlun
C
Chen
Shouwei
S
Zhang
Xuemei
X
Ren
Xiaoli
X
Tan
Xiangke
X
Wang
adsorption-desorption hysteresis; heavy metal ions; nanotubes; surface functionalization; wall number