Document Type

Thesis

Date of Degree Completion

Spring 2024

Degree Name

Master of Science (MS)

Department

Chemistry

Committee Chair

Samuel Lohse

Second Committee Member

Anthony Diaz

Third Committee Member

Yingbin Ge

Abstract

This study investigates the surface chemistry and molecular-level interactions between lignin, a special type of natural organic matter, and polymer-capped gold nanoparticles, shedding light on the strength of adsorption between lignin and nanoscale polymer surfaces. Specifically, the study presents a variety of nanoscale polymer surfaces displaying different charged functional groups, using layer-by-layer assembly of three polyelectrolytes (polyallylamine hydrochloride (PAH)), polyacrylic acid (PAA), and poly(diallyldimethylammonium chloride (PDADMAC)) on 90 nm citrate-stabilized gold nanoparticles (AuNPs). This approach provides a library of polymer-encapsulated AuNPs for investigating the binding interactions of lignin to nanoscale polymers via spectroscopic techniques. ζ-potential, dynamic light scattering (DLS), and infrared spectroscopy (FTIR) measurements confirmed the successful wrapping of the AuNPs with polyelectrolytes. The interactions of the AuNPs with lignin were investigated using UV-visible absorbance spectroscopy, fluorescence spectroscopy, and DLS. Fluorescence quenching titrations indicated that lignin's binding affinity (Ka) was significantly higher for PDADMAC-AuNP than others. Ka for PAA-AuNP, Cit-AuNP, PAH-AuNP, and PDADMAC-AuNP were 87 ± 8 nM-1, 92 ± 11 nM-1, 107 ± 13 nM-1, and 240 ± 13 nM-1 respectively. UV-vis absorbance spectroscopy was not generally effective in determining Ka values for lignin-AuNP by absorbance titration; however, citrate-stabilized AuNP showed significant binding affinity to lignin in absorbance spectroscopy titrations. DLS analysis data indicated that the particles' hydrodynamic diameter (Dh) generally increases after interaction with lignin, supporting the formation of a lignin eco-corona around the AuNPs.

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