244
Metal oxide nanocrystals can be compressed into porous pellets without significantly compromising their surface area when moderate pressure is applied [16, 37].
The pore volume and pore size can be controlled by adjusting the consolidation pressure. Thus, they can be applied in forms of both fine powders and porous pellets,
which are the likely forms to be used in industry.
Metal-based nanomaterials have been explored to remove a variety of heavy metals such as arsenic, lead, mercury, copper, cadmium, chromium, and nickel, and
have shown great potential to outcompete activated carbon [38, 39]. Among them,
the application for arsenic removal has attracted much attention. Despite being a
good adsorbent for many organic and inorganic contaminants, activated carbon has
limited capacity for arsenic, especially for As(V). Several metal oxide nanomaterials including nanosized magnetite and TiO 2 have shown arsenic adsorption performance superior to activated carbon [40–42]. Metal (hydr)oxide nanoparticles can
also be impregnated onto the skeleton of activated carbon or other porous materials
to achieve simultaneous removal of arsenic and organic co- contaminants, which
favors point-of-use (POU) applications [43, 44].
Regeneration and Reuse
Metal oxide nano-adsorbents can be easily regenerated by changing solution pH
[39, 45]. In many cases, the adsorption capacity of metal oxide nano-adsorbents is
well maintained after several regeneration and reuse cycles [46, 47]. However,
reduced adsorption capacity after regeneration has also been reported [48, 49].
Above all, metal-based nano-adsorbents can be produced at relatively low cost.
The high adsorption capacity, low cost, easy separation, and regeneration make
metal-based nano-adsorbents technologically and economically advantageous.
Polymeric Nano-Adsorbents
Dendrimers are tailored adsorbents that are capable of removing both organics and
heavy metals. Their interior shells can be hydrophobic for sorption of organic compounds while the exterior branches can be tailored (e.g., hydroxyl- or amineterminated) for adsorption of heavy metals. The sorption can be based on
complexation, electrostatic interactions, hydrophobic effect, and hydrogen bonding
[50, 51]. A dendrimer-ultrafiltration system was designed to recover metal ions
from aqueous solutions [52, 53]. The system achieved almost complete removal of
Cu
2+
ions with initial concentration of 10 ppm and Cu
2+
-to-PAMAM dendrimerNH 2 ratio of 0.2. After adsorption, the metal ion-laden dendrimers were recovered
by ultrafiltration and regenerated by decreasing pH to 4.
13 Wastewater
Metal oxide nanocrystals can be compressed into porous pellets without significantly compromising their surface area when moderate pressure is applied [16, 37].
The pore volume and pore size can be controlled by adjusting the consolidation pressure. Thus, they can be applied in forms of both fine powders and porous pellets,
which are the likely forms to be used in industry.
Metal-based nanomaterials have been explored to remove a variety of heavy metals such as arsenic, lead, mercury, copper, cadmium, chromium, and nickel, and
have shown great potential to outcompete activated carbon [38, 39]. Among them,
the application for arsenic removal has attracted much attention. Despite being a
good adsorbent for many organic and inorganic contaminants, activated carbon has
limited capacity for arsenic, especially for As(V). Several metal oxide nanomaterials including nanosized magnetite and TiO 2 have shown arsenic adsorption performance superior to activated carbon [40–42]. Metal (hydr)oxide nanoparticles can
also be impregnated onto the skeleton of activated carbon or other porous materials
to achieve simultaneous removal of arsenic and organic co- contaminants, which
favors point-of-use (POU) applications [43, 44].
Regeneration and Reuse
Metal oxide nano-adsorbents can be easily regenerated by changing solution pH
[39, 45]. In many cases, the adsorption capacity of metal oxide nano-adsorbents is
well maintained after several regeneration and reuse cycles [46, 47]. However,
reduced adsorption capacity after regeneration has also been reported [48, 49].
Above all, metal-based nano-adsorbents can be produced at relatively low cost.
The high adsorption capacity, low cost, easy separation, and regeneration make
metal-based nano-adsorbents technologically and economically advantageous.
Polymeric Nano-Adsorbents
Dendrimers are tailored adsorbents that are capable of removing both organics and
heavy metals. Their interior shells can be hydrophobic for sorption of organic compounds while the exterior branches can be tailored (e.g., hydroxyl- or amineterminated) for adsorption of heavy metals. The sorption can be based on
complexation, electrostatic interactions, hydrophobic effect, and hydrogen bonding
[50, 51]. A dendrimer-ultrafiltration system was designed to recover metal ions
from aqueous solutions [52, 53]. The system achieved almost complete removal of
Cu
2+
ions with initial concentration of 10 ppm and Cu
2+
-to-PAMAM dendrimerNH 2 ratio of 0.2. After adsorption, the metal ion-laden dendrimers were recovered
by ultrafiltration and regenerated by decreasing pH to 4.
13 Wastewater