Stabilization of highly sensitive noble metal nanoparticles is essential for their practical application. Bionanocomposites in which various types of noble metal nanoparticles, especially anisotropic noble metal nanoparticles, are immobilized into a macroscopic biomaterial membrane show promising applications in biomedical, catalytic, and environmental fields. This research focuses on developing two fabrication methods to generate novel bionanocomposite materials by immobilizing gold (Au) or silver (Ag) nanoparticles onto a "green" biomaterial, namely an eggshell membrane (ESM). Furthermore, the applications of the resulting bionanocomposite materials were demonstrated by studying their use as catalysts for environmental pollutant conversion and for the detection of two pollutant chemicals.
The first fabrication method immobilizes ex situ synthesized nanoparticles onto a chemically modified ESM. Disulfide originating from the ESM was reduced by dithiothreitol into free thiol groups for binding to Au nanoparticles with different morphologies. The immobilization of Au nanoparticles greatly enhances their stability, making it possible to apply the resulting bionanocomposites for catalyzing the reduction reaction to convert pollutant p-nitrophenol (PNP) to p-aminophenol (PAP), with a great increase in their lifetime use from 2 to 10 reaction cycles.
The second fabrication method utilizes the zwitterionic property of the protein based ESM for binding with Ag nanoparticles to form bionanocomposites. A seed mediated nanoparticle synthesis method originally performed in suspension was modified and adapted for the in situ synthesis of Ag nanodisks in this research. Ag nanoseeds were first immobilized onto an eggshell membrane using the static interaction between the nanoseeds and the membrane. Subsequently, Ag nanodisks were further grown directly on the Ag nanoseeds on the ESM. The final distribution density of Ag nanodisks can be adjusted by tuning the distribution density of Ag nanoseeds immobilized on the ESM. The performance of the resulting bionanocomposites were evaluated for both catalysis, and their application as substrates for surface enhanced Raman spectroscopy (SERS). The material performance was found to depend on the final distribution density of the Ag nanodisks on the ESM, offering the possibility to optimize bionanocomposite material performance by adjusting this density.
A SERS based technique was further developed for detecting pollutant chemical species using the Ag nanodisks/ESM bionanocomposite material as a SERS substrate. Direct detection of thiram, a commonly used pesticide, was achieved at a concentration that is lower than that regulated by the US EPA. By using crystal violet as a SERS probe molecule, mercury, a heavy metal without an intrinsic Raman fingerprint, was indirectly detected not only at a limit of detection lower than most reported in the scientific literature, but also with a selectivity against a group of metal ions including Ba, Cu, Ca, Co, Mg, Mn, Ni, and Zn. It was also found that the detection sensitivity can be optimized by adjusting the Ag nanodisk distribution density on the ESM.
The development of the fabrication approach and the use of ESM as a matrix material for immobilizing noble metal nanoparticles to form bionanocomposite materials demonstrates a novel strategy for meeting the needs of a variety of applications. The development of bionanocomposites for detecting pollutant species with different SERS activities by simply tuning the nanoparticle distribution density on the surface of the substrate, is a novel discovery, as it does not appear to have been previously reported in the literature. / Doctor of Philosophy / Noble metal nanoparticles exhibit special physical and chemical properties, which are totally different from the bulk material, making them promising candidates for use as novel materials in broad applications, such as catalysis, pollutant detection, antibacterial materials, etc. However, due to their high activity and poor colloidal stability (having high tendency to aggregate and lose activity), the nanoparticles require stabilization when being exploited for practical applications. A promising method to achieve this goal is to immobilize highly active noble metal nanoparticles onto a macroscopic membrane to form a nanocomposite. In this research, a "green" biomaterial, eggshell membrane (ESM), was utilized to immobilize noble metal nanoparticles. The resulting bionanocomposite materials were applied for catalyzing a reduction reaction to convert an environmental pollutant p-nitrophenol (PNP) to p-aminophenol (PAP) for environmental cleaning purposes, as well as detecting pollutant chemicals such as pesticide thiram and heavy metal mercury.
General physical and chemical properties of the proteins in the ESM include rich chemical functional groups on the amino acid residue, and a zwitterionic property that allows the surface charge of the ESM to be changed under different pH levels. These properties, which have not been unleashed to immobilize noble metal nanoparticles in this field as of yet, were exploited in this research to create strong interactions between the noble metal nanoparticles and the ESM. This resulted in the formation of a bionanocomposite where the ESM served as a matrix for stably immobilizing the nanoparticles.
Different bionanocomposites were fabricated using gold (Au) or silver (Ag) nanoparticles. The resulting bionanocomposite materials with gold nanoparticles were applied for catalyzing a reduction reaction for the conversion of p-nitrophenol, a commonly used chemical in the pharmaceutical photographic industries. The immobilized nanoparticles exhibited catalytic activity for ten reaction cycles and one hundred days after they were fabricated, while the colloidal nanoparticles (not immobilized nanoparticles) have catalytic activity for only two reaction cycles.
For the chemical detection application, bionanocomposites with immobilized silver nanodisks were used as substrates for surface enhanced Raman spectroscopy. Different detection strategies were developed for detecting thiram with intrinsic Raman fingerprints and mercury without intrinsic Raman fingerprints. Outstanding detection sensitivities were achieved compared to those reported in the literature. For detection of mercury, a good selectivity was also obtained against a group of metal ions including Ba, Cu, Ca, Co, Mg, Mn, Ni, and Zn.
The development of the fabrication approach and the use of ESM as a matrix material for immobilizing noble metal nanoparticles to form bionanocomposite materials demonstrates a good strategy for meeting the needs of a variety of applications
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/107126 |
| Date | 26 June 2020 |
| Creators | Li, Yunhua |
| Contributors | Chemistry, Morris, John R., Esker, Alan R., Vikesland, Peter J., Liu, Guoliang |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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