Nanoparticles for Treatment of Arsenic - Nanotechnologies for Water Environment Applications - page 132

concentrations in the solution at any reaction time is almost equal to the initial DMA
concentration of 10 mg-As/L. The methyl groups in MMA and DMA are transformed
into organic carbon, including formic acid and possibly methanol, also through
photochemical reactions. The results showed that nanocrystalline TiO 2 can be used for
the photocatalytical degradation of MMA and DMA and subsequent removal of the
converted As(V), since the high adsorption capacity of the material for inorganic arsenic
species has been demonstrated in previous sections.

5.4 Treatment of Arsenic Using Nanoparticles Other Than TiO 2

The zero-valent iron (ZVI) has been used for the rapid treatment of As(III) and
As(V) in the subsurface environment (Bang et al., 2005a; Bang et al., 2005b). The
removal is mainly caused by adsorption on ferric hydroxides formed readily in-situ
during ZVI oxidation (corrosion). The reactivity of ZVI has been improved significantly
by the development of nanoscale zero-valent iron (nZVI) during the past few years. A
simple and robust method for large-scale and cost-effective production of nZVI has been
introduced by mixing 1:1 volume ratio of 0.25 M sodium borohydride with 0.045 M
ferric chloride solution (Wang and Zhang, 1997). The nZVI exhibits a core-shell
structure with a layer of iron oxides on the surface. The average particle size of the nZVI
produced is approximately 60 nm with the majority (>90%) in the nano-domain (1-100
nm). The average BET surface area is about 30-35 m 2 /g. Iso-electric point (IEP) is in the
range of pH 8.1-8.3 (Li et al., 2006; Sun et al., 2006).

The application of nZVI in arsenic treatment has been reported recently (Kanel et
al., 2005, 2006). The removal of As occurs rapidly on a scale of minutes and follows a
pseudo-first-order kinetics. The maximum As(III) adsorption capacity in batch
experiments is about 3.5 mg of As(III)/g of nZVI (Kanel et al., 2005). Yuan and Lien
(2006) reported a maximum As(V) adsorption capacity at 38.8 mg/g. However, the nZVI
tends to aggregate during oxidative corrosion to Fe(III) oxide/hydroxide which could
limit the effective transport and delivery of nZVI for in-situ groundwater remediation.
To overcome this limitation, surface modified nZVI has been synthesized using
stabilizers recently (Kanel et al., 2007). This surface modification by surfactant resulted
in fully dispersed nZVI in aqueous solution that is mobile in a simulated sandy
groundwater aquifer treatment of As(III).

Other iron-based nanoparticles for arsenic removal include akaganeite (-
FeO(OH)) (Deliyanni et al., 2003; Solozhenkin et al., 2003) and magnetite (Fe 3 O 4 ). The
akaganeite is synthesized by precipitation of iron(III) and ammonium carbonate. The
produced average particle size is 2.6 nm with a BET surface area of 330 m 2 /g. The
maximum adsorption capacity is about 100-120 mg As(V) per g of -FeO(OH). Recent
studies show that laboratory-synthesized 12 nm Fe 3 O 4 nanoparticles can remove over