Nanosized Metal Oxide-Based Adsorbents for Heavy Metal Removal: A Review - Advanced Materials for Agriculture, Food and Environmental Safety - page 254

the number of adsorption sites to a large extent, which may be attributed
to an increase in surface charge due to the formation of magnesium oxide
on the bentonite surface.

9.3.2 Polymer-Supported Nano-Metal Oxide Nanocomposites

(P-NMOs)

Polymeric supports are attractive choices for nano-metal oxide sup-
port because of their controllable pore size and surface chemistry as
well as their excellent mechanical strength for long-term use. Zhao et al.
reviewed recent work on polymer-based nanocomposites for environmen-
tal application [75]. Su et al. prepared a new hybrid adsorbent HMO-001
by impregnating nanosized hydrous manganese dioxide (HMO) onto a
porous polystyrene cation exchanger resin (D-001) [76]. h e HMO-001
was tested for lead adsorption onto HMO-001 and the maximum capac-
ity of HMO-001 towards lead ion was about 395 mg/g. As compared to a
macroporous cation exchanger, D-001, HMO-001 exhibited highly selec-
tive lead retention from waters in the presence of competing Ca 2+, Mg 2+
and Na + at high concentration levels. Fixed-bed column adsorption of a
simulated water indicated that lead retention on HMO-001 resulted in a
signii cant decrease of this toxic metal from 1 mg/L to below 0.01 mg/L
(the drinking water standard recommended by WHO).

9.3.3 Zeolites-Supported Nano Metal Oxide Nanocomposites

(P-NMOs)

Zeolites of er an attractive and inexpensive alternative for e-removal of
organic and inorganic contaminants [77]. Natural zeolites are low cost and
act as cation exchangers for metallic contaminants. h e adsorption capac-
ity of zeolite-based nanocomposites results from their high surface area
and net negative charge on their channel structure, which causes an ai n-
ity for heavy metals [78]. h e NaY zeolites serve as potential adsorbent for
heavy metals with pore diameter of 0.78 nm, large surface area and high
cation exchange capacity [79, 80]. Oliveira et al. [81] prepared NaY zeolite
and magnetic iron oxides-based magnetic adsorbent. h e NaY zeolite:iron
oxide magnetic composites were prepared at a weight ratio of 3:1, which
was chosen to keep a relatively high content of iron oxide and thereat er
to avoid the decrease in adsorption capacity of the composites. h ey were
prepared by precipitation of iron oxides or hydroxides onto the zeolite sur-
face. Fe oxide in the composites had a smaller particle size of 25 nm for
pure Fe oxide and 16 nm for the composite. h e immobilized Fe oxides are