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A. Srivastava
17.3.3 Carbon Nanotubes (CNT)
CNTs are the allotropes of carbon having structure similar to graphite but exhibit
different adsorption features that vary on the extent of whorl, the diameter, internal
geometry, physical and chemical properties, the making of the original sheet, and
the treatment process which has been used for synthesis (Ahmed and Theydan 2012;
Ji et al. 2010a, b, Wu et al. 2012a, b and Zhang et al. 2010). Usually, these tubes
are classified on the basis of their internal diameter (i.d.) as single-walled nanotubes
(SWNT), if the i.d. is 1 nm (Lara et al. 2014 and Ren et al. 2011) and multi-walled
nanotubes (MWNT), if numerous concentric tubes or laminated graphene layers
are present together (Ren et al. 2011 and Kim et al 2014). The carbon materials
differ according to their treatment for production, which is apparent by comparing
the performance of CNTs, AC, and biochar. The surface area of CNTs also has an
important role in their performance for removing of ECs. Single- or multi-walled
CNTs structures result in different removal rates when used for the same contaminant.
For instance, despite the same experimental conditions being adopted, Ji et al. (2010a,
b), were able to achieve to remove 92% of tetracycline using SWNT but only 16%
with MWNT. However, in the removal of other ECs, MWNT worked fairly well.
For example, amoxicillin (>90%) and ibuprofen/triclosan (100%) were effectively
removed by the use of MWNT (Teixidó et al. 2011; Mitchell et al. 2015 and Zheng
et al. 2013). In the same way, 100% of norfloxacin was removed by using singlewalled CNTs (Peng et al. 2012), but only 35% of norfloxacin could be removed
by the use of MWCNTs (Yang et al. 2012). MWCNTs can be made from singlewalled CNTs by the use of some extra chemical processes that enhance the contact
region by several folds and the number of active sites for adsorption which results in
better contaminant removal efficiency. Though these chemical treatments result in
increasing the adsorption power of CNTS, it has been reported that all these features
may not essentially improve the performance of CNTs because of the molecular
sieving effects that occur in MWNTs (Cho et al. 2011 and Zhang et al. 2011). The
removal of ECs by the use of CNTS is a vital area for advanced research because
studies currently available are only limited, and therefore, more experimental support
is needed to express the previously reported trends. On comparing the performance
of single- and multi-walled CNTs, it has been found that the former show better
performance than the latter and quite often ambiguous results are given by the use
of the similar type of CNTs, in the removal of the same contaminant. The adsorptive
nature of CNTs can be utilized in combination with other reactive nanomaterials
for effective removal of ECs. It is an area of great importance and requires further
research.
A. Srivastava
17.3.3 Carbon Nanotubes (CNT)
CNTs are the allotropes of carbon having structure similar to graphite but exhibit
different adsorption features that vary on the extent of whorl, the diameter, internal
geometry, physical and chemical properties, the making of the original sheet, and
the treatment process which has been used for synthesis (Ahmed and Theydan 2012;
Ji et al. 2010a, b, Wu et al. 2012a, b and Zhang et al. 2010). Usually, these tubes
are classified on the basis of their internal diameter (i.d.) as single-walled nanotubes
(SWNT), if the i.d. is 1 nm (Lara et al. 2014 and Ren et al. 2011) and multi-walled
nanotubes (MWNT), if numerous concentric tubes or laminated graphene layers
are present together (Ren et al. 2011 and Kim et al 2014). The carbon materials
differ according to their treatment for production, which is apparent by comparing
the performance of CNTs, AC, and biochar. The surface area of CNTs also has an
important role in their performance for removing of ECs. Single- or multi-walled
CNTs structures result in different removal rates when used for the same contaminant.
For instance, despite the same experimental conditions being adopted, Ji et al. (2010a,
b), were able to achieve to remove 92% of tetracycline using SWNT but only 16%
with MWNT. However, in the removal of other ECs, MWNT worked fairly well.
For example, amoxicillin (>90%) and ibuprofen/triclosan (100%) were effectively
removed by the use of MWNT (Teixidó et al. 2011; Mitchell et al. 2015 and Zheng
et al. 2013). In the same way, 100% of norfloxacin was removed by using singlewalled CNTs (Peng et al. 2012), but only 35% of norfloxacin could be removed
by the use of MWCNTs (Yang et al. 2012). MWCNTs can be made from singlewalled CNTs by the use of some extra chemical processes that enhance the contact
region by several folds and the number of active sites for adsorption which results in
better contaminant removal efficiency. Though these chemical treatments result in
increasing the adsorption power of CNTS, it has been reported that all these features
may not essentially improve the performance of CNTs because of the molecular
sieving effects that occur in MWNTs (Cho et al. 2011 and Zhang et al. 2011). The
removal of ECs by the use of CNTS is a vital area for advanced research because
studies currently available are only limited, and therefore, more experimental support
is needed to express the previously reported trends. On comparing the performance
of single- and multi-walled CNTs, it has been found that the former show better
performance than the latter and quite often ambiguous results are given by the use
of the similar type of CNTs, in the removal of the same contaminant. The adsorptive
nature of CNTs can be utilized in combination with other reactive nanomaterials
for effective removal of ECs. It is an area of great importance and requires further
research.