Nanosized Metal Oxide-Based Adsorbents for Heavy Metal Removal: A Review - Advanced Materials for Agriculture, Food and Environmental Safety - page 243

mostly through food and water, and to a lesser extent through inhalation
of polluted air. h us, how to ef ectively remove even deeply hidden metals
from water systems is a very important and challenging issue for environ-
mental engineers. Nowadays, numerous methods have been proposed for
ei cient heavy metal removal from waters, including chemical precipita-
tion, ion exchange, adsorption, membrane i ltration and electrochemical
technologies [3-5]. Among these methods, adsorption of ers l exibility
in design and operation and in many cases generates high-quality treated
el uent. In addition, due to the reversible nature of most adsorption pro-
cesses, the adsorbents can be regenerated by suitable desorption processes
for multiple use, and many desorption processes have low maintenance
costs, high ei ciency, and are easy to operate [6, 7]. h erefore, the adsorp-
tion process has come to the forefront as one of the major techniques for
heavy metal removal from wastewater.
Nanosized metal oxides (NMOs), including nanosized ferric oxides,
manganese oxides, aluminum oxides, titanium oxides, magnesium oxides
and cerium oxides are classii ed as promising for heavy metals removal
from wastewater [10, 11]. h is is because of their large surface areas and
high activities caused by the size-quantization ef ect [12]. During the last
decade, the research on metal oxide-based adsorbents for heavy metal
removal has been gaining importance (Figure 9.1). Recent studies have
suggested that many NMOs exhibit very favorable sorption to heavy met-
als in terms of high capacity and selectivity, which would result in deep
removal of toxic metals to meet increasingly strict regulations. However,
as the size of metal oxides is reduced from micrometer to nanometer lev-
els, the increased surface energy unavoidably leads to their poor stabil-
ity. Consequently, NMOs are prone to agglomeration. To improve the
Year
Figure 9.1 h e number of publications produced during the last ten years on the topic of
metal oxide-based adsorbents for heavy metal removal.