(405c) Synthesis, Characterization, and Interfacial Properties of Lignin Coated Iron Oxide Magnetic Nanoparticles in Aqueous Solutions

Lignin is an abundant natural raw material on the planet with attractive properties, including high thermal stability, adsorbent properties, and antioxidant characteristics. However, lignin is a waste product with very low-value applications in the paper pulp industry. Ongoing studies are focusing on the development of value-added high-performance materials using lignin, which includes the development of nano- and micron-sized particles. In this study, core-shell nanostructures were synthesized using magnetic nanoparticles as the core functionalized by lignin macromolecules as the shell. In addition to the versatile properties of lignin, the hybrid nanostructure is attractive due to their ease of manipulation under the presence of a magnetic field and their inherent superparamagnetic properties. In this work, magnetic iron oxide-lignin nanoparticles were synthesized using two methods: a co-precipitation technique using iron salts to produce core-shell nanostructures (lignin@Fe₃O₄), and nanoprecipitation using ethanol/water solutions. For the co-precipitation technique, lignin was dissolved in ammonium hydroxide; whereas a lignin solution in ethanol was used for the nanoprecipitation method. Various concentrations of lignin were used to stabilize iron oxide nanoparticles, and the stabilization or the aggregation of the nanoparticles were characterized as a function of the weight ratios between lignin and the magnetic core for both synthetic routes. The nanoparticles were characterized by using a variety of experimental techniques including DLS, TEM, UV-Vis, FTIR, XRD, VSM and zeta potential analyses. The hybrid nanoparticles showed various sizes ranging from 17 -25 nm for single core-shell lignin@Fe₃O₄ nanostructures and from 100-200 nm for the aggregates. TEM images of the particles displayed encapsulation of iron oxide cluster within the lignin polymer matrixes at high concentrations of lignin. The surface tension of lignin@Fe₃0₄ nanoparticles in water and ethanol/water mixtures was measured at different nanoparticle concentrations using the pendant drop method. The results of this work show that superparamagnetic iron oxide nanoparticles coated with lignin were successfully synthesized. The outstanding properties of lignin as a renewable material, which could be used as antioxidant, emulsion stabilizer, UV adsorbent, antimicrobial properties, and preparation of biomaterials make the lignin-magnetic nanocomposite a unique substrate for a plethora of future investigations.