Easy Synthesis of Surface-Tunable
Carbon-Encapsulated
Magnetic Nanoparticles: Adsorbents for Selective Isolation and Preconcentration
of Organic Pollutants
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Abstract
We have prepared core/shell structured carbon-encapsulated
magnetic
nanoparticles (CMNPs) with a simple method by using inorganic iron
salt and glucose solution as precursor substance. The synthetic procedure
does not require the use of organic solvents. We have utilized X-ray
photoelectron spectroscopy, infrared spectroscopy, X-ray diffraction,
and Raman analysis to examine the surface properties of CMNPs prepared
at different temperature. The specific surface areas, magnetization
and contents of graphitized carbon on carbon shell of CMNPs increase
with heat treatment temperature. The obtained CMNPs are used to adsorb
or preconcentrate bisphenol A (BPA), 4-n-nonylphenol (4-NP), 4-tert-octylphenol
(4-OP), diethyl phthalate (DEP), dipropyl phthalate (DPP), dibutyl
phthalate (DBP) dicyclohexyl phthalate (DCHP), dioctyl phthalate (DOP),
sulfonamide, tetracyclines, and quinolones antibiotics organic compounds
from water samples. The adsorption of analytes is mainly based on
π–π stacking interaction, hydrophobic interaction
and hydrogen bonds between analytes and graphitic carbon. As a result,
the adsorption or extraction behaviors of CMNPs to analytes are controlled
by the content of oxygen-containing species and graphitized carbon
on carbon shell of CMNPs. CMNPs prepared at 200 °C have ample
oxygen-containing species (80%) on surface and favor the adsorption
and extraction of quinolones antibiotics. CMNPs heated at 300–500
°C with the graphitization efficiency of carbon shell lower than
50% exhibit great preconcentration performance to BPA, 4-NP, 4-OP,
DBP, DCHP, DOP, tetracyclines, and quinolones antibiotics. CMNPs prepared
at 850 °C are highly graphitized (80%) and have strong adsorption
affinity to all model analytes; however, they can quantitatively extract
only highly polar sulfonamide antibiotics and moderately polar DEP,
DPP because of hard desorption of other model analytes. We suggest
that the appropriate adsorbent to certain organic contaminants can
be obtained with this technique just by tuning the heat temperature
without any post-treatment