chemical, indirect or reactive ion etching-based synthesis techniques (Liebes et al.
2011). However, even though this technique was one of the earlier approaches for
the synthesis of nanometer-sized pores, FEBIE is currently not used for wide range
of applications because of its inaccuracy in generating uniform-sized pores with
functional groups (Fig. 4.8).
4.4.2 Diblock Copolymer Templating
The template method is generally used for synthesizing nanomaterials, especially
nanotubes and nanowires (Yu et al. 2003). Diblock copolymer templating is an
advanced method to create nanoporous membrane with tunable pore size (Yu et al.
2003), high selectivity, and membrane stability at high pressure (Yang et al. 2008).
In this method a suitable template is used in the synthesis of copolymer which is
subjected to selective etching (Olson et al. 2007). The pore size and the thickness of
the pore in the template membrane can be optimized by this method (Yu et al. 2003).
The patterns in the membranes are designed based on its ability to self-assemble into
micro-domains, and these patterns can be manipulated by various physical and
chemical activations. Inorganic nanoporous membranes like nitrogen-containing
mesoporous carbonaceous polymers synthesized using copolymer templating are
found to be defect-free which make them suitable for enhanced desalination
(McGovern et al. 2014; Yang et al. 2010). Oxygen plasma etching method is done
by exposing suspended monolayers to oxygen plasma that causes etching and also
allows the size of the pores to be tuned. The intensity of plasma etching is directly
proportional to the size and density of pores in the membranes and time of exposure.
Maintenance of uniformity is the foremost constraint during the process, and it can
be resolved by optimizing the process parameters of the operating system. The
resulting membrane exhibits salt rejection rate of nearly 100% with increasing rate
Fig. 4.8 Focused electron
beam induced etching
(Killingsworth 2012)
140
J. Ganesan et al.
2011). However, even though this technique was one of the earlier approaches for
the synthesis of nanometer-sized pores, FEBIE is currently not used for wide range
of applications because of its inaccuracy in generating uniform-sized pores with
functional groups (Fig. 4.8).
4.4.2 Diblock Copolymer Templating
The template method is generally used for synthesizing nanomaterials, especially
nanotubes and nanowires (Yu et al. 2003). Diblock copolymer templating is an
advanced method to create nanoporous membrane with tunable pore size (Yu et al.
2003), high selectivity, and membrane stability at high pressure (Yang et al. 2008).
In this method a suitable template is used in the synthesis of copolymer which is
subjected to selective etching (Olson et al. 2007). The pore size and the thickness of
the pore in the template membrane can be optimized by this method (Yu et al. 2003).
The patterns in the membranes are designed based on its ability to self-assemble into
micro-domains, and these patterns can be manipulated by various physical and
chemical activations. Inorganic nanoporous membranes like nitrogen-containing
mesoporous carbonaceous polymers synthesized using copolymer templating are
found to be defect-free which make them suitable for enhanced desalination
(McGovern et al. 2014; Yang et al. 2010). Oxygen plasma etching method is done
by exposing suspended monolayers to oxygen plasma that causes etching and also
allows the size of the pores to be tuned. The intensity of plasma etching is directly
proportional to the size and density of pores in the membranes and time of exposure.
Maintenance of uniformity is the foremost constraint during the process, and it can
be resolved by optimizing the process parameters of the operating system. The
resulting membrane exhibits salt rejection rate of nearly 100% with increasing rate
Fig. 4.8 Focused electron
beam induced etching
(Killingsworth 2012)
140
J. Ganesan et al.