Nanomaterials for Environmental Burden Reduction, Waste Treatment and Non-Point Source Pollution Control - Nanotechnologies for Water Environment Applications - page 456

immobilization of penicillin G acylase (PGA) biocatalysts. The results show that, under
optimized conditions, the relative loading amount and the total activity yield of the
immobilized enzyme (IME) were 97.20 % and 88.80 %, respectively (Xiao et al., 2006).
However, applications of nanomaterials or nanoparticles are often hampered by
difficulties in recovery and recycling (Tsang et al., 2006). Recently, the application of
magnetic nanoparticles as magnetically separable nano-vehicles for chemical or
biological species has become an area of intensive research for solving these problems.
Actually, magnetic nanoparticles were used to immobilize enzymes for use in magnetic
separation (Zeng et al., 2006). Magnetic nanoparticles as an enzyme immobilization
carrier can effectively inactivate glucose oxidase by gas bubbles (Betancor et al., 2005).
Moreover, the enhancement of intrinsically weak magnetic properties, avoidance of
magnetic interactions among particles, and improvement of the stability of the
nanoparticles, has been studied (Yu et al., 2007).
14.3.2 Adsorption and Photocatalytic Degradation of Dyes
Dye pollutants from industrial and agricultural wastes are often refractory and
carcinogenic. Different kinds of conventional treatment technologies for dye removal
have been investigated extensively, such as activated sludge, chemical coagulation,
adsorption, and photocatalytic degradation. Among these methods, the adsorption
process is fairly effective to produce a high-quality effluent without the formation of
harmful substances (Crini, 2007). The major challenge for the adsorption process is to
select the most promising adsorbents. At present, nanomaterials used as the adsorbents
are one of the best candidates for dye removal due to their large surface areas. For
example, chitosan-bound Fe 3 O 4 nanoparticles has very high adsorption capacities for
crocein orange G (1883 mg/g) and acid green 25 (1471mg/g) (Chang and Chen, 2005).
Moreover, the chitosan-bound Fe 3 O 4 nanoparticles can be conveniently separated by a
magnet. C ationic metalloporphyrin dyes can be removed by nano-clay sheets films
(Shiragami et al., 2006). At the dosages of nanoscale zerovalent iron (NZVI) between
0.16 and 0.33 g/L, the NZVI has an adsorptive capability of 609.4 mg/g for C.I. Acid
Black 24 under the conditions of the reaction time being 15-30 min, pH 4-9 and the
initial dye concentration of 25-100 mg/L (Shu et al., 2007). Hu et al. (2006) reported
that nano-chitosan adsorbents can remove Acid Green 27 at 2103.6 mg/g adsorbents,
which was significantly higher than that of the micron-sized chitosan.
Other than adsorption, dyes can be degraded photocatalytically by nanoparticles.
Acid Orange 7 (one of the widely used dyes) in wastewater can be degraded with TiO 2
nanoparticles (Li et al., 2007). Nanostructure Sn 4+ -doped TiO 2 based double layer thin
films have a very high photocatalytic performance for degradation of Malachite Green
dye in solution (Sayilkan et al., 2007). A textile azo dye, Reactive Orange 16, in aqueous