Nanomaterials for Environmental Burden Reduction, Waste Treatment and Non-Point Source Pollution Control - Nanotechnologies for Water Environment Applications - page 458

color components (Frank et al., 2002), while RO can also be used for desalinization. The
major properties of these three membrane processes are listed in Table 14.3.

Table 14.3 Properties of three major membrane processes.
Category

RO NF UF

Pore Size (nm)
Cut-off Molar Mass (Da)
KCl Retention (%)
Working Pressure (kPa)

0.1-1.0
<1000
90-100
850-7000

< 2
1000-3000
20-90
500-1000

2-50
> 3000
< 20
70-700

DeFriend et al. (2003) fabricated alumina UF membranes using acetic acid
surface stabilized alumina nanoparticles which has a molecular weight cut-off in the
range of < 1000 g/mol and shows good selectivity to a range of synthetic dyes. Ericsson
et al. (1996) reported that the removal of color and organic matter was almost complete
(undetectable levels) with NF. Removal of pesticides, viruses and bacteria with NF has
been reported by many authors (e.g., see ven der Bruggen and Vandecasteele, 2003).
Ultra low pressure reverse osmosis (ULPRO) processes use NF membranes with a
hydrophilic layer attached to a hydrophobic UF support membrane. Due to the active
surface layers, ULPRO and NF membranes allow the desalination of brackish water at
pressures comparable to those applied in NF; they also have improved fouling resistance
against hydrophobic colloids, oils, proteins and other organics (Hassan et al., 2000;
Ozaki et al., 2000; Matsuura, 2001). Dendrimer-enhance UF (DEUF) was used to
recover Cu(II) from aqueous solutions; dendrimer-Cu(II) complexes could be efficiently
separated from aqueous solutions by UF (Diallo et al., 2004). Christen (2004) reported a
chemically modified nanoporous ceramic that can remove contaminants from all types
of waste streams faster and at a significantly lower cost than conventional technologies
such as ion exchange resins and activated carbon filters. Binder et al. (1992) invented a
nanofilter membrane that can be used to filter the outflow of a food processing stream
which begins with starch slurry and ends with glucose syrup which, in its preferred
form, is about 95% dextrose and 5% di- and trisaccharides. The nanofilter membrane is
able to pass the dextrose while retaining the di- and trisaccharides. As a result, a purity
of over 99 % of dextrose is produced.

Carbon nanotube (CNT) membranes have been made and tested recently for the
transport of Ru(NH 3 ) 6 3+ (Hinds et al., 2004), multiple components of heavy
hydrocarbons from petroleum, bacteria (Srivastava et al., 2004), water, ethanol, iso -
propanol, hexane, and decane (Majumder et al., 2005a). Using the CNT membrane (pore
diameter = ~7 nm, membrane thickness = 34-126 m, density = 3.4 x 10 9 /cm 2 ),
Majumder et al. (2005a) found that, normalized at 1 bar, water flux was 10 4 -10 5 times
the flux predicted by Hagen-Poiseuille (H-P) equation (see Eq. 1 below); the slip length
L s (see Eqs. 3 and 4 below) was 108 m for KCl, 39-68 for water, 3.4 for decane, and
28 for ethanol. Holt et al. (2006) used the CNT membrane (pore diameter = ~2 nm,
membrane thickness = 2-3 m, density = 2.5 x 10 11 /cm 2 ) to study the transport of gas