Application of Zero-valent Iron Nanoparticles for Environmental Clean Up - Advanced Materials for Agriculture, Food and Environmental Safety - page 405

nFe 0 /Pd

nFe 0

Catalytic
hydrodechlorination Reduction

RH + Cl -

RCI

Pd---Cl---R

RH + Cl -

Co-precipitation

RCI

Pd

Me-Fe-OOH
Me n+

Fe 0 Fe 2+ + 2e -

H

Adsorption and
Reduction

Me (n-m)+

H 2

Me n+

Me n+ H 2 O

Core

Adsorption

Shell (iron
oxides/hydroxides)

Figure 14.1 Schematic diagram of mechanisms involved in contaminant degradation in
presence of nFe 0 (let portion) and nFe 0 /Pd (right portion).

bimetallic nFe 0 . h e let and right portion represent direct reduction of an
organochlorine by nFe 0 and catalytic reductive dechlorination respectively.

Fe 0 + 2H + Fe 2+ + H 2 (in acidic solution) (14.13)

Fe 0 + 2H + Fe 2+ + H 2 + 2OH - (in alkaline solution) (14.14)

Fe 0 + RCl + H + Fe 2+ + RH + 2Cl - (direct reduction) (14.15)

M + H 2 M.H 2

(14.16)

M + RCl M…Cl…R (14.17)

M.H 2 + M…Cl…R RH + H + + Cl - + M (14.18)

Reduction and precipitation of metal ions by nFe 0 depend on transport
of the dissolved metal ions to the surface and electron transfer (ET) to the
metal ion. Potential ET pathways from the surface to the sorbed ions/mol-
ecules may include:

i. Direct electron transfer (DET) from nFe 0 through defects
such as pits or pinholes, where the oxide layer is interpreted
as a simple physical barrier.
ii. Indirect electron transfer (IET) from nFe 0 through the oxide
layer via the oxide conduction band, impurity bands or
localized bands.
iii. Electron transfer from sorbed or lattice Fe 2+ surface site.