Nathaniel S. Hansen

Metal nanofibers with highly tunable electrical and magnetic properties via highly loaded water-based electrospinning.

Nanofibers are synthesized by electrospinning highly loaded water-based precursor-polymer hybrid solutions followed by thermal treatment to control crystal structure. Electrical conductivity and magnetic coercivity, as shown, are tested displaying independent magnetic and electrical property control from coercive to superparamagnetic and resistive to near-bulk conductivity at room temperature.

Photocatalytic self-detoxification by coaxially electrospun fiber containing titanium dioxide nanoparticles

Electrospun nanofibers containing titanium dioxide (TiO2) were investigated as a self-detoxifying system consisting of polyacrylonitrile (PAN) and anatase TiO2 nanoparticles. Fibers were prepared by uniaxial and coaxial electrospinning to study the effect of nanoparticle placement on the detoxification activities of the photocatalyst. Coaxially spun fibers had the particles selectively placed in the sheath layer by electrospinning pure PAN solution and PAN/TiO2 solution as the core and sheath layer, respectively. Using scanning electron microscopy, X-ray microanalysis and X-ray photoelectron spectroscopy, it was confirmed that the coaxial approach resulted in the location of nanoparticles near the surface of the fibers compared to the uniform distribution obtained for uniaxial fibers. Photocatalytic activity of the fibers under ultraviolet irradiation was demonstrated by the degradation of aldicarb, as measured by high-performance liquid chromatography. In terms of degradation kinetics, the distribution density of TiO2 nanoparticles in the fiber surface region significantly affected the initial degradation rate, while the final decomposition amounts after 3 h did not differ significantly.

Inorganic nanofibers with tailored placement of nanocatalysts for hydrogen production via alkaline hydrolysis of glucose

Monoaxial silica nanofibers containing iron species as well as coaxial nanofibers with a pure silica core and a silica shell containing high concentrations of iron nanocrystals were fabricated via electrospinning precursor solutions, followed by thermal treatment. Tetraethyl-orthosilicate (TEOS) and iron nitrate (Fe(NO(3))(3)) were used as the precursors for the silica and iron phases, respectively. Thermal treatments of as-spun precursor fibers were applied to generate nanocrystals of iron with various oxidation states (pure iron and hematite). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to probe the fiber morphology and crystal structures. The results indicated that the size, phase, and placement of iron nanocrystals can be tuned by varying the precursor concentration, thermal treatment conditions, and processing scheme. The resulting nanofiber/metal systems obtained via both monoaxial and coaxial electrospinning were applied as catalysts to the alkaline hydrolysis of glucose for the production of fuel gas. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and bulk weight change in a furnace with residual gas analysis (RGA) were used to evaluate the performance of the catalysts for various ratios of both Fe to Si, and catalyst to glucose, and the oxidation state of the iron nanocrystals. The product gas is composed of mostly H(2) (>96 mol%) and CH(4) with very low concentrations of CO(2) and CO. Due to the clear separation of reaction temperature for H(2) and CH(4) production, pure hydrogen can be obtained at low reaction temperatures. Our coaxial approach demonstrates that placing the iron species selectively near the fiber surface can lead to two to three fold reduction in catalytic consumption compared to the monoaxial fibers with uniform distribution of catalysts.