Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 345

term filtration showed that the 10%wt C 60 -poly (2, 6-dimethyl-1, 4-phenylene oxide)
membrane was able to maintain its excellent removal performance of at least 95% (Jin et
al., 2007).
11.2.2.3 Carbon Nanotubes
A carbon nanotube (CNT, a synthetic, nano-sized tube made up of graphene
sheets) is one of the most fascinating carbon allotropes. A typical image of CNT is
shown in Figure 11.13. In spite of having a simple chemical composition and atomic
bonding configuration, it possesses a tremendous strength, an extreme aspect ratio, as
well as excellent thermal and electronic properties. This makes it a unique material of
interest in fundamental science. Based on their structure, CNTs are basically divided
into two groups: the multi-wall carbon nanotube (MWNT), which is an array of
cylindrical graphene sheets wrapped one over the other; whereas the single-wall carbon
nanotube (SWNT) consists of a single graphene sheet tube with a single atomic layer
wall (Figure 11.13). Since its discovery in 1991 (Iijima, 1991), it has been the subject of
an increasing number of experimental and theoretical studies due to their unique
morphologies and various potential applications (Meunier and Lambin, 2000). Because
of the extremely high specific area (~1500m 2 /g), CNTs have attracted researcher's
interest as a new type of adsorbent. Here, we summarize recent development of CNTs
and their derivatives for the application of water treatment.
Long and Yang (Long and Yang, 2001) first reported that CNTs can be more
efficient for the removal of dioxins than activated carbon. Li et al. (2002) found that
acid-refluxed CNTs can be good Pb adsorbents and have great application potential in
environmental protection (Li et al., 2002). They also prepared amorphous Al 2 O 3
supported on carbon nanotubes (Al 2 O 3 /CNTs) and found that it has a much higher
adsorption capacity for fluoride than c-Al 2 O 3 and predicted that it is very suitable for
potential applications in fluoride removal from water (Li et al., 2001). Peng et al. (2005)
evaluated high surface area ( 189 m 2 /g) CNTs (CeO 2 -CNTs) for arsenate removal from
water. The experiments show that the CeO 2 -CNT is an effective adsorbent for arsenate,
and the adsorption is pH-dependent. Ca 2+ and Mg 2+ significantly enhanced its adsorption
capacity, which suggests that it is a promising adsorbent for drinking water purification.
Under natural pH conditions, an increase from 0 to 10 mg/L in the concentration of Ca 2+
and Mg 2+ results in an increase from 10 to 81.9 and 78.8 mg/g in the amount of As(V)
adsorbed, respectively. The loaded adsorbent can be efficiently regenerated by diluted
NaOH, and a regeneration efficiency of 94% was achieved using 0.1 mol/L NaOH (Peng
et al., 2005). Peng et al. (2003) have evaluated the sorption of 1,2-dichlorobenzene
(DCB) onto CNTs. It takes only 40 min for DCB sorption onto the CNTs to reach
equilibrium with a maximum sorption capacity of 30.8 mg/g (Peng et al., 2003).
Thermodynamic calculations indicated that the adsorption reaction is spontaneous with a
high affinity, and the adsorption is an endothermic reaction.