Coating carbon nanotubes with humic acid using an eco-friendly
mechanochemical method: Application for Cu(II) ions removal from water
and aquatic ecotoxicity
SCIENCE OF THE TOTAL ENVIRONMENT, (2017)DOI: 10.1016/j.scitotenv.2017.07.045
Abstract
In this work, industrial grade multi-walled carbon nanotubes (MWCNT)
were coated with humic acid (HA) for the first time by means of a
milling process, which can be considered an eco-friendly mechanochemical
method to prepare materials and composites. The HA-MWCNT hybrid material
was characterized by atomic force microscopy (AFM), scanning electron
microscopies (SEM and STEM), X-ray photoelectron spectroscopy (XPS),
termogravimetric analysis (TGA), and Raman spectroscopy. STEM and AFM
images demonstrated that the MWCNTs were efficiently coated by the humic
acid, thus leading to an increase of 20% in the oxygen content at the
nanotube surface as observed by the XPS data. After the milling process,
the carbon nanotubes were shortened as unveiled by SEM images and the
values of ID/IG intensity ratio increased due to shortening of the
nanotubes and increasing in the number defects at the graphitic
structure of carbon nanotubes walls. The analysis of TGA data showed
that the quantity of the organic matter of HA on the nanotube surface
was 25%. The HA coating was responsible to favor the dispersion of
MWCNTs in ultrapure water (i.e. -42 mV, zeta-potential value) and to
improve their capacity for copper removal. HA-MWCNTs hybrid material
adsorbed 2.5 times more Cu(II) ions than oxidized MWCNTs with HNO3, thus
evidencing that it is a very efficient adsorbent material for removing
copper ions from reconstituted water. The HA-MWCNTs hybrid material did
not show acute ecotoxicity to the