Nanoparticle coating with ultrasound

Researchers from the National Tsing Hua University in Taiwan have now found a way of coating paper and other flexible substrates with zinc oxide (ZnO) using ultrasound, removing the need for binders and solvents that can lead to surface defects and uneven layer thickness, and are wasteful of material and energy resources.

The ultrasound binding mechanism is thought to involve bubbles of ZnO particles in high-speed microjects collapsing onto the cellulose fibres of the paper.

Applications such as e-books, portable solar cells, sensors and photocatalytic wallpapers require the coating of flexible substrates such as paper with metallic nanoparticles. Various methods have been developed to deposit thin films of nanoparticles, but they are limited to solid surfaces or other stable substrates.

Led by Yong-Chien Ling, the researchers found that ZnO-coated paper has antibacterial properties against E. coli, which can cause severe food poisoning, and this is amplified on illumination for 24 hours with 543-nm light; i.e., that from a typical household fluorescent tube. ZnO and other nanoparticle-coated papers and bandage fabrics may therefore have application in hospitals, and even in combating bioterrorism.

Published in the online journal Green Chemistry, the research focuses on ZnO, but Ling explains that the properties of other nanoparticles are also being studied: “Work with Al2O3 and SiO2 nanoparticles is also underway, which would provide an economic alternative for thin-layer chromatography plates in separation science.”

Ling and his colleagues, who are thoroughly committed to ‘green chemistry’, say that their coating technique can easily be scaled up for industrial production, but caution that the long-term stability of the coated paper needs to be studied in detail, as there is a possibility of photocatalytically reduced volatile organic compounds producing stains on the treated paper. They intend also to look in detail at the size and shape of the ZnO particles used, and their antibacterial effect.

Article first published in Nanomaterials News. © 2006 Pira International – all rights reserved.