Multifunctional metal oxide nanoparticle decorated polypropylene knitted swatches

Two methods of fabricating metal oxide nanoparticle-functionalized knitted "swatches" from melt-extruded bi-component sheath/core polypropylene (PP) fibers are described, and their possible applications for photocatalysis and gas sensing are investigated. The first method consists of melt extruding a blend of metal oxide nanoparticles and PP into fibers that are subsequently knitted into swatch materials. This method was evaluated for ZnO nanospheres and nanorods. X-ray photoelectron spectroscopy and electron microscopy showed that the nanoparticles were in the near-surface region as well as in the bulk of the fibers. However, the particles were shown to be photocatalytically inactive, likely due to site blocking by PP or processing additives, such as fiber lubricants. The second method consists of plasma-treating virgin PP swatches in air, immersing them in metal oxide colloidal suspensions, ultra-sonicating them to remove loose nanoparticles and drying the swatches. XPS confirmed that plasma treatment forms carboxylate groups on the surface that bond the metal oxide nanoparticles to the swatch. This method was used to functionalize swatches with ZnO and TiO₂ nanospheres and ZnO nanorods. Metal oxide functionalization was found to induce dramatic changes in the thermal decomposition temperature of the PP swatch and in the water contact angle, rendering the swatch hydrophobic and producing photocatalytically active PP fabrics. Photoluminescence of the ZnO nanoparticle swatches was measured and shown to change upon exposure to sulfur dioxide. Furthermore, the demonstration of metal oxide-functionalized swatches as a potential gas-sensing platform is discussed.