Nanosized Metal Oxide-Based Adsorbents for Heavy Metal Removal: A Review - Advanced Materials for Agriculture, Food and Environmental Safety - page 251

9.3 Hybrid Adsorbents

Nanosized metal oxides emerge as ef ective and adsorbent for heavy metal
removal from aqueous phase. However, they are usually present as i ne or
ultrai ne particles, which ot en lead to problems such as activity loss due to
agglomeration and dii cult separation [63]. An ef ective way to overcome
these technical bottlenecks is to fabricate hybrid adsorbents by impreg-
nating or coating NMOs particles into/onto porous materials of larger
size [64]. h e widely used supports include natural hosts such as benton-
ite [65], sand [66], montmorillonite [21] metallic oxide materials such as
Al 2 O 3 membrane [67] and porous manganese oxide complex [68], and syn-
thetic polymer supports such as crosslinked ion-exchange resins [69, 70].
Some of the hybrid adsorbents are classii ed in Table 9.3.

9.3.1 Bentonite-Based Hybrid Nano-Metal Oxide

Nanocomposites (B-NMOs)

Bentonite is a natural clay with a basic structural unit of two tetrahedrally
coordinated sheets of silicon ions surrounding a sandwiched octahedrally
coordinated sheet of aluminum ions with net negative surface charge [71].
Also, bentonite has a high exchange capacity, amphoteric pH-dependent
surfaces and dif erent modes of aggregation [72], which makes it a poten-
tial adsorbent for adsorption of heavy metals from aqueous solutions [73].
h e iron oxide-coated bentonite (ICB) and magnesium oxide-coated ben-
tonite (MCB) were prepared by precipitating the metal ions with sodium
hydroxide on the surface of raw bentonite, followed by thermal treatment.
h e BET surface areas follow an order as ICB > RB > MCB. h e ICB, RB
and MCB were tested for the removal of Pb(II) from aqueous phase. h e
Langmuir monolayer adsorption capacities of RB, ICB and MCB toward
Pb(II) from 0.1 M KNO3 solution were found to be 16.70, 22.20 and 31.86
mg/g, respectively. Both bentonite samples showed an increased uptake
of Pb(II) with gradually increasing pH because H + can compete for the
exchange site with Pb(II). Increasing the ionic strength from 0.01 to 0.1
M led to a signii cant decrease in Pb(II) adsorption. Eren et al. [74] also
investigated magnesium oxide-coated bentonite for the removal of copper
ions from aqueous solution. h e adsorption of Cu(II) ions depends upon
both the nature of the adsorbent surface as well as the Cu(II) species dis-
tribution solution, which are greatly af ected by the pH of the system. h e
Langmuir monolayer adsorption capacity of MCB in 0.1 M KNO 3 solution
was estimated to be 58.44 mg/g, whereas the adsorption capacity of RB was
42.41 mg/g, indicating that the treatment with magnesium oxide increased