of nanosized pores in the synthesized membranes as most of the naturally occurring
materials like graphene and MoS 2 are impermeable to water (Surwade et al. 2015;
Killingsworth 2012). The ability to adjust pore size in the membrane is a crucial
step in nanoporous desalination as a variation of few angstroms in pore size can be
the difference between a properly functioning pore and an inefficient one
(Killingsworth 2012). Recently, experimental studies have begun to explore a
wide variety of methods for introducing nanopores in desalination membranes.
Earlier approaches relied on electron beam exposure, but in recent times methods
like diblock copolymer templating, helium ion beam drilling, and chemical etching
are preferred to achieve both higher porosity and precise pore size distribution
(Killingsworth 2012; Chua et al. 2013).
4.4 Synthesis Methods
4.4.1 Focused Electron Beam Induced Etching
In focused electron beam induced etching (FEBIE), a beam of electrons is projected
onto the surface of the synthesized membrane. The beam interacts with the pressurized gas on top of the membrane which then bonds with the material’s atoms and
thus corrodes the surface. FEBIE was considered as a promising tool for the
synthesis of nanopores with controlled shape and size (Yemini et al. 2009). The
diameter of the pores depends on the pressure of the gas, acceleration voltage (Liebes
et al. 2011), and electron beam exposure time (Killingsworth 2012). Pore diameter
and peripheral-etched region can be reduced by increasing the applied acceleration
voltage (Liebes et al. 2011; Pan et al. 2006). The use of highly focused energetic
electron beam as a source makes this method comparably accessible leading to the
widespread fabrication of nanopores (Liebes et al. 2011). This technique provides
improved lateral resolution at shorter fabrication times when compared to multi-step
Fig. 4.7 Computational
simulation showing the
desalination across
nanoporous membrane
(Wang and Karnik 2012)
4 Functional Properties of Nanoporous Membranes for the Desalination of Water
139
materials like graphene and MoS 2 are impermeable to water (Surwade et al. 2015;
Killingsworth 2012). The ability to adjust pore size in the membrane is a crucial
step in nanoporous desalination as a variation of few angstroms in pore size can be
the difference between a properly functioning pore and an inefficient one
(Killingsworth 2012). Recently, experimental studies have begun to explore a
wide variety of methods for introducing nanopores in desalination membranes.
Earlier approaches relied on electron beam exposure, but in recent times methods
like diblock copolymer templating, helium ion beam drilling, and chemical etching
are preferred to achieve both higher porosity and precise pore size distribution
(Killingsworth 2012; Chua et al. 2013).
4.4 Synthesis Methods
4.4.1 Focused Electron Beam Induced Etching
In focused electron beam induced etching (FEBIE), a beam of electrons is projected
onto the surface of the synthesized membrane. The beam interacts with the pressurized gas on top of the membrane which then bonds with the material’s atoms and
thus corrodes the surface. FEBIE was considered as a promising tool for the
synthesis of nanopores with controlled shape and size (Yemini et al. 2009). The
diameter of the pores depends on the pressure of the gas, acceleration voltage (Liebes
et al. 2011), and electron beam exposure time (Killingsworth 2012). Pore diameter
and peripheral-etched region can be reduced by increasing the applied acceleration
voltage (Liebes et al. 2011; Pan et al. 2006). The use of highly focused energetic
electron beam as a source makes this method comparably accessible leading to the
widespread fabrication of nanopores (Liebes et al. 2011). This technique provides
improved lateral resolution at shorter fabrication times when compared to multi-step
Fig. 4.7 Computational
simulation showing the
desalination across
nanoporous membrane
(Wang and Karnik 2012)
4 Functional Properties of Nanoporous Membranes for the Desalination of Water
139