Doctor of Philosophy
Chemical and Biochemical Engineering
Dr. Jesse Zhu
In a health care environment, surface bio-contamination is a constant risk and contributes to outbreaks of community-acquired and nosocominal infections. Faster surface die-off of pathogens on a surface can reduce the average surface population of these pathogens. Antimicrobial ultra-fine powder coated surfaces with high antimicrobial longevity including efficiency is a good option to reduce the surface bio-contamination. Different formulations were prepared with the additives containing silver ions (Ag+) and silver nano-particles (AgNP) as an active agent and copper ions (Cu2+) as a protective agent incorporated into zeolites and their antimicrobial activity was analyzed against Escherichia coli (E.coli). Two natural zeolites, known as chabazites (named LBC and LBN), were accustomed to enhance their sodium content as well as ion exchange characteristics by conditioning and was functionalized by using different combinations of the Ag and Cu ions.
No significant changes were observed during XRD and TGA analysis. Elemental analysis by ICP-OES confirmed the enhancement of silver ions after functionalization due to the conditioning process. Color analysis indicated that copper helped to maintain the color of the coated surface. These coated surfaces have shown consistent antibacterial properties with excellent durability against E.coli for an extended longevity. Antimicrobial efficiency of that coated surface was also proven by toxicity analysis through the production of lactate dehydrogenase (LDH).
Synthetic zeolite A (LTA) was used as a carrier for active agents in different experiments in this study. Optimum concentration of these cations (Ag+,1.534meq/g, Cu2+3.90 meq/g) were obtained by ion exchange with silver nitrate after 24 hrs followed by further ion exchange with copper nitrate for another 24 hrs with the adjustment of pH and temperatures. TGA, XRD, XPS and FTIR analysis were used for further characterization of these additives. The reduction of Ag+ can be controlled by the addition of Cu2+ ions and that surface was found to be very efficient since the coated surface showed 100% reduction of microorganisms within 2 hrs of exposure. Auger parameter confirmed that copper prevented silver from being reduced during the curing period. The transfer efficiency of the additives in the resin system during the spraying was improved by increasing the aggregated particle size of the final powder from 20µm to 30µm. The effects of low curing additives on surface properties were analyzed based on the ASTM standards for powder coating and found comparable with the surface cured at higher temperature. The release rate of the active components from the surface was further controlled by PVA encapsulation on the additive and this process was found to provide an effective antimicrobial surface for prolonged periods.
Silver nano-particles were synthesized on the synthetic zeolite surface and were used as an additive. Uniform distribution of silver nanoparticles synthesized by the chemical reduction method on the zeolite surface played an important role in the generation of silver ions. The final formulated surface was also found to be active against microorganism after autoclave and UV treatment, this was also proved by toxicity analysis.
Keywords: Zeolite, cabazite, silver, ultrafine Powder coating, ionexchange, antimicrobial, durability, leaching, silver nano particles
Yeasmin, Rezwana, "Formulation and Optimization of Antimicrobial Surfaces Via Ultra-Fine Powder Coating" (2015). Electronic Thesis and Dissertation Repository. 3380.