Improving the photocatalytic properties of rayon fibers containing a titanium dioxide photocatalyst through enzymatic treatment

Abstract

When titanium dioxide is irradiated with light, electrons and electron holes are generated. These exert strong reductive and oxidative forces, which induce reaction with atmospheric water and oxygen, generating reactive oxygen species such as hydroxyl radicals and superoxide anions. These substances not only kill miscellaneous bacteria, but also effectively aid in the decomposition of odorous substances. In rayon fibers containing titanium dioxide photocatalyst, weight reduction occurring by enzymatic treatment was applied to effectively activate the photocatalyst, even though the catalyst was added in limited amounts. Enzymatic treatment using cellulase effectively roughened the surface of the rayon fibers and largely improved the antibacterial activity. When the amount of TiO₂ added was 2.5 wt% and the weight reduction ratio of the fibers reached 4.2% or 7.1%, the antibacterial activity was enhanced so strongly that viable bacteria were not detected at all. However, when the weight reduction ratio of the fibers increased to 10.5%, the antibacterial activity decreased. Further, the deodorizing ability of the fibers against gaseous ammonia improved significantly by the enzymatic treatment. In the case of fibers containing 2.5 wt% of TiO₂, samples before enzymatic treatment showed an odor residual percentage of 28.4%, while after treatment, a much lower figure of 0.25% was obtained. However, although the tensile strength of the fiber decreased because of the weight reduction treatment, the fibers exhibited a tensile strength of 1.63 cN/dtex even after a weight reduction of 7.1 wt% (the tensile strength before weight reduction treatment was 2.49 cN/dtex). Thus, the application of an appropriate weight reduction finish to rayon fibers containing titanium dioxide was very effective in enhancing the photocatalytic activity of the material. Presumably, the action of the enzyme during the treatment dissolved the cellulose present on the fiber surface, which exposed the titanium dioxide particles embedded within the fibers that were proximal to the surface.