Production and Characterization of Electrospun Metal Nanofibers for Applications in Nanoaerosol Filtration

Airborne particles have a large impact on human health and the environment. They can be as small as a few nanometers. Electrospun nanofibrous materials have shown strong potential in filtering airborne nanoparticles for their high efficiency and low energy consumption. Electrospinning has been investigated for decades. Unlike polymeric fibers, the production of fibers made from non-polymeric materials is limited. Additionally, the effects of single parameters on the fiber size are not well understood. To better understand the effects of electrospinning parameters on nanofiber size, the following tasks have been conducted: 1. Understand electrospinning using polymer-based samples for air filtration 2. Determine a reliable way of producing metal-based fibers, focusing on composition of the electrospinning solution and calcining atmosphere 3. Conduct a parametric study using metal-based fibrous filter samples 4. Conduct dimensionless parametric studies aiming at predicting the size of the fibers produced by electrospinning Before producing metal-based fibers, polymer fibers were produced using an existing apparatus in the lab. CA solutions were prepared by diluting various concentrations of CA in a 2:1 (w:w) ratio of N,N-dimethylacetamide (concentration 10 wt.% to 20 wt.%). The electrospinning voltages ranged from 8 to 12 kV with distances from 10 to 15 cm and deposition times of up to 30 minutes. The produced nanofibrous filter samples were then analyzed in terms of fiber size distribution and filter quality factor using nanosized NaCl particles ranging from 4 to 240 nm in diameter. The maximum filtration efficiency measured was 99.8 % for filter samples obtained with an overall deposition time of 30 minutes. The maximum filter quality factor was 0.14 Pa-1 for a CA concentration of 20 wt.% and a tip-to-collector distance of 15 cm. The average fiber diameters of the fibers were between 175 and 890 nm, and CA concentrations below 15 % led to the formation of beads. Then ceria and alumina-based filters were fabricated using the same setup with different operating parameters. Results showed that a solution mix with a ratio of 2:1 ethanol:water with a solid concentration of 15% in a weight ratio of 1:2 w:w metal nitrate:polymer yields the best fibers in terms of size distribution. The average fiber diameter was reduced by calcination due to the loss of polymer. The average diameter of the fibers was as small as 200 nm after calcination. Additionally, the produced metal-based fibers were tested for filtration and the filtration quality was 0.07 Pa-1, which is comparable to those of polymeric fibers. The importance of different solution and operating parameters were evaluated. The trial series was planned according to orthogonal two factorial experimental design. Four parameters, each with two levels were chosen for this study. The solution parameter chosen was concentrations of polymer and salt; process parameters included voltage, nozzle size and feed rate of the solution. It was found that the concentration of the precursor solution had a dominant effect on the fiber size, while the effects of electric field strength, flow rate and needle diameter were comparable in their effect on the fiber size. Dimensionless numbers have been developed using the Pi-theorem aiming at the prediction of electrospinnablitiy. The development of the dimensional tables and the identification of suited parameters for the dimensional table show that the processing parameters electric field strength, needle diameter and solution feed rate; the solution parameters, including viscosity, surface tension and solution conductivity, are the most appropriate for characteristic numbers describing the electrospinning process