Nanogold and nanosilver composites with lignin-containing cellulose fibres

The formation of nanogold and nanosilver composites with cellulose paper fibres and the associated lignin component together with their antimicrobial properties are presented. This follows on from the proprietary technology of Johnston et al. [1] wherein they used nanogold and nanosilver entities in wool fibres to provide novel colourfast colourants in textiles with additional effective antimicrobial and catalytic properties. The nanogold and nanosilver are formed and bound directly onto the unbleached lignin-containing paper fibres without the use of an external linker molecule. For this, the lignin was found to play an essential role and hence the methodology presented is applicable only to cellulose in the form of unbleached kraft fibres and mechanical pulp. The phenol and possibly the aromatic methoxy groups of the lignin are considered to reduce Au³⁺ to Au⁰ and Ag⁺ to Ag⁰, respectively, and bind the nanogold and nanosilver to the fibre surface. SEM images and UV–Visible spectra confirm the formation of nanogold and nanosilver on the fibre surface. Changes in the IR spectra are consistent with the above role of the phenol and methoxy groups. The resulting nanogold—unbleached kraft fibres are purple and the nanosilver—unbleached kraft fibres are yellow due to the surface plasmon resonance effects of nanogold and nanosilver respectively. The nanogold—unbleached kraft fibres and particularly the nanosilver—unbleached kraft fibres exhibit very effective antimicrobial properties at low levels of gold and at very low levels of silver. In this way we have been able to produce novel nanogold paper and nanosilver paper fibres and products which collectively exhibit the properties of the nanomaterials and the fibre substrates in a synergistic way. This provides the opportunity for developing new functional paper products for antimicrobial packaging, medical dressings, and clothing.