Nanosized Metal Oxide-Based Adsorbents for Heavy Metal Removal: A Review - Advanced Materials for Agriculture, Food and Environmental Safety - page 244

applicability of NMOs in real wastewater treatment, they were impreg-
nated in porous supports of large size to obtain composite adsorbents [13].
h e widely used porous supports include activated carbon, natural materi-
als, synthetic polymeric hosts, etc.
h is chapter presents a brief overview of several NMOs, including their
synthesis and their sorption behavior towards heavy metals from aqueous
systems under varying experimental conditions, the underlying mecha-
nism responsible for the sorption, as well as their reusability.

9.2 Nanosized Metal Oxide

For adsorptional removal of heavy metals from aqueous systems, the most
widely investigated NMOs include iron oxides, manganese oxides, alumi-
num oxides, and titanium oxides. h e size and shape of NMOs are both
important factors that af ect their adsorption performance. During the
last decades, facile synthetic methods have been widely applied to obtain
shape-controlled, highly stable, and monodisperse metal oxide nanoma-
terials [14]. Generally, the synthesis methods can be classii ed into two
categories: (1) physical methods, including inert gas condensation, severe
plastic deformation, high-energy ball milling, ultrasound shot peening,
and (2) chemical methods, including controlled chemical co-precipita-
tion, chemical vapor condensation, pulse electrode position, liquid l ame
spray, liquid-phase reduction, etc. Among these synthesis protocols, co-
precipitation, thermal decomposition and/or reduction, and hydrother-
mal synthesis techniques are used widely and are easily scalable with high
yields [15-18]. h e following section includes the synthesis, characteriza-
tion, and application perspectives of NMOs.

9.2.1 Nano Ferric Oxides (NFeOs)

Iron is one of the most abundant elements found in earth. Availability of
resources and environmental friendliness make iron a suitable adsorbent
for heavy metal removal. h e intensive NFeOs for heavy metal removal
include hematite (α-Fe 2 O 4 ) [19], goethite α(-FeOOH) [20], and amorphous
hydrous Fe oxides [21] (Table 9.2). Hydrous ferric oxide (HFO) could be
prepared by precipitation of ammonia with ferric chloride or nitrate solu-
tions in carbonate-free environment by purging with N 2 [22]. Dzombak
and Morel [23] prepared HFO with mean pore diameter of 3.8 nm and sur-
face area of 600 m 2 /g. h e sorption of heavy metals to HFO seems poorly
sensitive to the variation of ionic strength. For example, Swallow et al. [24]