Immobilization of Silver Nanoparticles on Chitosan-Coated Silica-Gel-Beads and the Antibacterial Activity

Silver nanoparticles (Ag0) have attracted the most attention due to their broad antimicrobial application and outstanding activity. The silver nanoparticles are usually in colloidal form, then immobilization the colloid onto solid support is still interesting to explore. In this work, a new method for silver colloidal nanoparticle immobilization on silica gel beads (SiG), which was then symbolized as Ag0-[chi-SiG] was conducted and characterized successfully. The finding proved that SiG must be coated with three chitosan film layers to give stable support for silver nanoparticles. This coating method caused the chitosan completely covered SiG, and the chitosan film provides coordination bonding for silver ions. The most appropriate solvent for silver ion impregnation on the surface of chi-SiG is methanol compared to other solvents. Tungsten lamp as the photo-irradiation, which is low cost and environmentally friendly has been proven effective for silver ion reduction, as shown by silver metal colloid UV-Vis surface plasmon resonance at 400-700 nm. Ag0-[chi-SiG] showed the antibacterial properties of inhibiting the growth Staphylococcus aureus and Escherichia coli; then it provides the potential application for antibacterial filter material. According to the weight comparison between antibacterial standard and Ag content, then Ag0-[chi-SiG] has two and five times higher of exhibiting zone for each bacteria.

Strategies for metal colloidal nancrystal synthesis in sustainable media

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Over the past decades, the Green Chemistry and Sustainability concept has aroused researchers to denounce their traditional ways of thinking regarding chemical processes to address the challenges relevant to global environmental concerns. The concept has demonstrated how fundamental scientific methodologies can protect human health and the environment in an economically beneficial manner. In academia and industry, the use of green solvents, such as water, supercritical fluids, ionic liquids (ILs) and deep eutectic solvents (DESs), has then become desirable in chemical processes. In the field of green nanochemistry, ILs and DESs have acquired courtesy as sustainable media for nanomaterials synthesis. There have been attempts to employ such eco-friendly fluids to synthesize, and additionally, control size and shapes of nanomaterials, where the field has been gaining intense interests as the morphology dictates the properties and functionalities of such nanomaterials. This dissertation reports strategies for metal colloidal nanocrystal synthesis in sustainable media and aims to build a foundation for understanding how to tailor eco-friendly IL and DES fluids to control the growth of metal nanocrystals. Chapter 1 explores research reporting strategies used for metal colloid synthesis in ILs and DESs. In Chapter 2, we have developed a strategy to replace a common organic solvent with an IL to prepare monodisperse gold nanoparticles (AuNPs) by a very fast microwave method. The pyrrolidinium IL used in the work demonstrates its capability to be efficiently recovered and reused for carrying out nanoscale synthesis iteratively. The work highlights the incompatibility of imidazolium ILs for the select nanoscale synthetic strategy. For Chapter 3, we have demonstrated a control over nanoparticle size and shape generated at an aqueous-organic interface. We have shown that an interfacial photoreduction leads to the production of spherical and wire-like nanostructures, respectively, when the IL employed involves a coordinated and non-coordinated IL anion, respectively. Next, Chapter 4 has focused on exploitation of a purposefully designed IL-inspired surfactant, acting dually as a reducing and stabilizing agent, for facile and controllable AuNP formation. The reported synthetic method is simple and rapid, using only a gold precursor and the surfactant. Coinage AuNPs can be obtained very fast, while predominantly triangular-shaped AuNPs can also be achieved by tuning parameters, such as the ratio of surfactant to the gold precursor, temperature, implementing a time delay before heating, and an addition of a directing agent. Finally, Chapter 5 outlines zwitterionic deep eutectic solvents (ZDESs) as novel media for metal nanocrystal synthesis, to expand portfolio of available DESs as the field is relatively new compared to that of IL.

Characteristics of Nano-metal Colloid Prepared by Electrical Spark Discharge Method

Background: This study used Electrical Spark Discharge Method (ESDM) to fabricate the nano-Au, nano-Ag and nano-Cu colloid. The spark wears down the surface of the electrodes and gets nano-metal particles at standard temperature and pressure and without adding any other chemical materials in the deionized water. Method: The nano-metal particles are examined by UV-Visible Spectroscopy, Zetasizer, Transmission Electron Microscope, and Energy Dispersive X-ray Analysis and are proven to be nano-metal colloid. Under the comparison of different parameters (discharge pulse width, HV, Ip), the size of nano-metal particles increases with the level of Ip. Results: Under the experiment of light or dark, most of the Absorbance of the nano-Au and nano-Ag colloid is higher than that of the environment under strong light irradiation as long as it is prepared in a pure black environment. The nano-Au and nano-Ag colloid prepared by ESDM have a zeta potential exceeding the absolute value of 30 mV, no matter which parameters is applied or whether there is illumination or not. It represents a good suspension stability of the nano-Au and nano-Ag colloid, but the nano-Cu colloid does not have this feature. The suspension stability is not good.

A Review of The Lesser-Studied Microemulsion-Based Synthesis Methodologies Used for Preparing Nanoparticle Systems of The Noble Metals, Os, Re, Ir and Rh

This review focuses on the recent advances in the lesser-studied microemulsion synthesis methodologies of the following noble metal colloid systems (i.e., Os, Re, Ir, and Rh) using either a normal or reverse micelle templating system. The aim is to demonstrate the utility and potential of using this microemulsion-based approach to synthesize these noble metal nanoparticle systems. Firstly, some fundamentals and important factors of the microemulsion synthesis methodology are introduced. Afterward, a review of the investigations on the microemulsion syntheses of Os, Re, Ir, and Rh nanoparticle (NP) systems (in all forms, viz., metallic, oxide, mixed-metal, and discrete molecular complexes) is presented for work published in the last ten years. The chosen noble metals are traditionally very reactive in nanosized dimensions and have a strong tendency to aggregate when prepared via other methods. Also, the particle size and particle size distribution of these colloids can have a significant impact on their catalytic performance. It is shown that the microemulsion approach has the capability to better stabilize these metal colloids and can control the size of the synthesized NPs. This generally leads to smaller particles and higher catalytic activity when they are tested in applications.