Abstract
M.Sc. (Chemistry)
Zero-valent nanoscale metal, especially iron nanoparticles have attracted significant attention with
regards to remediation of organochlorinated compounds in drinking water. For a more rapid and
complete dechlorination, a second and usually electronegative element is often added, resulting in
the formationof bimetallic nanoparticles. However, in the absence of surfactants,the bimetallic
nanoparticles easily aggregate into large particles (if they are not anchored on solid supports) with
wide size distributions, thus losing their reactivity. This work reports an in-situ synthesis method of
bimetallic nanoparticles immobilized on L-lysine functionalized microfiltration membranes by
chemical reduction of metal ions chelated by amine and hydroxyl functional groups of L-lysine on
the composite. The immobilization of the nanoparticles on membranes offers many advantages:
reduction of particle loss, prevention of particle agglomeration and application under convective
flow.
The objective of this research wasto produce catalytic filtration membranes for dechlorination of
organic compound, PCB-77. This was achieved first by (i) the modification of commercial PVDF
to introduce functional groups that render the membrane more hydrophilic and have the ability to
capture metal ions through chelation, and secondly (ii) the controlled introduction of catalytic
nanoparticles onto the composite membrane surface, anchored through chelation to the surface
functional groups. This approach was selected with aview to produce uniform surface distribution
of monodispersed bimetallic nanoparticles that are resistant to leaching during the reduction
reactions. The modification of the PVDF membrane was achieved by firstly performing an in situ
polymerization of acrylic acid followed by covalently bonded L-lysine to the polymerized acrylic
acid chains using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). The Fe
ions were introduced to the composite by L-lysine chelation and subsequently reduced to Fe0 with
NaBH4, and finally deposition of Ni2+ which later were also reduced to Ni0 with NaBH4. The Fe/Ni
bimetallic NPs system was chosen based on its proven ability for the total dechlorination of
chlorinated organic compounds. Systematic characterization of the composite was performed using
ATR-FTIR, FESEM, EDS, HRTEM, XRD, AFM and Contact Angle measurements. A relatively
uniform distribution of Fe/Ni nanoparticles was found in L-lysine/PAA/PVDF membrane. The
diameter of Fe/Ni nanoparticles was predominantly within the range 20-30 nm.
Furthermore, the mechanism of the catalytic dechlorination of the model compound, PCB 77, was
investigated by careful analysis of the reaction products. It is generally known that zero-valent iron
undergoes corrosion to provide hydrogen atoms and electrons for the reductive catalytic
hydrodechlorination reaction. The second metal in the bimetallic system on the other hand, acts as...