Development of Protein-Functionalized Magnetic Iron Oxide Nanoparticles: Potential Application in Water Treatment

Abstract: The treatment of water to make it safe for human consumption is a problem of immense concern, both in developing and developed countries. However, the production of clean water with chemicals as coagulants has several drawbacks associated with cost, health risks and complexity in sludge management. The application of nanotechnology in water treatment is a fast growing discipline proposed as an efficient alternative that will combat these hurdles. The aim of this thesis is to develop new water treatment strategies in a more eco-friendly manner based on a bottom-up approach using: (i) a natural coagulant protein from Moringa oleifera purified with nanoscale magnetic iron oxide nanoparticles for in situ treatment; and (ii) a protein-functionalized nanoparticle (MOCP-MNPs) system by means of binding the coagulant protein onto the nanoparticles in order to develop a potential reusable water treatment process.Magnetic iron oxide nanoparticles with different surface chemistry have been prepared from co-precipitation in aqueous solution and (water-in-oil and oil-in-water) microemulsion methods.  The prepared nanoparticles were studied in terms of size, morphology, magnetic behavior, structure, surface area including surface chemical structure and charges using different techniques such as TEM, VSM/SQUID, XRD, BET, FT-IR and zeta potential. The prepared nanoparticles exhibited a size ranging from 2-30 nm with superparamagnetic properties. The Moringa oleifera  coagulant protein (MOCP) with known molecular mass (6.5 kDa) was purified from the crude Moringa oleifera (MO) seed extracts using nanoparticles prepared from both methods. The obtained MOCP exhibits comparable coagulation activity with alum in terms of water turbidity removal, implying alternative replacement to chemical coagulants. This technique can be easily applied where natural materials are available locally.Studies on the interaction between MOCP and surface modified nanoparticles were essential to understand the binding mechanism for the development of a protein-functionalized nanoparticle. Based on in silico investigation, the overall molecular docking studies reveal the interactions between protein-ligand complexes by electrostatic, van der Waals and hydrogen-bonding; which imply, that there are at least two binding sites is i.e. one located at the core binding site (TEOS and APTES ligand) while the other located at the side chain residues (TSC and Si60-OH).This work underscores advancement in the development and use of MOCP-MNPs for potential water treatment. About 70% turbidity removal was achieved gravimetrically using MOCP-MNPs (60 min) in high and low turbid waters, whereas alum requires 180 min to reduce the turbidity especially in low turbid waters. The turbidity removal efficiency was enhanced by the use of MOCP-MNPs under the influence of an external magnetic field. More than 95% turbidity removal was achieved within 12 min in high and low turbid waters when MOCP-MNPs were used. The combination of natural coagulant protein and magnetic nanoparticles as well as the use of applied magnetic field enhanced the performance coagulating/flocculating properties in the water samples.These results suggest a successful development of MOCP-MNPs as demonstrated in the regeneration study. The data shown in this work represent novel potential water treatment strategies that could be cost-effective, simple, robust and environmentally friendly whilst utilizing biocompatible materials.