Inorganic chalcogenide Tungsten disulphide (WS2) nanotubes have shown revolutionary chemical and physical properties that offer a broad range of applications. An ultra-strong impact-resistant material makes them excellent candidates for bullet proof vests, helmets, car bumpers, high strength glues and binders, and other safety equipment.

The nanotubes are up to four to five times stronger than steel and about six times stronger than Kevlar, currently most popular material used for bullet proof vests. In addition to ballistic protection materials and polymer composites, WS2 nanotubes can be used in nanoelectronics, fuel cells, ultra-filtration membranes, and catalysts. Optical properties allow various other applications in fields such as nanolithography or photocatalysis.

Until now, major obstacle in the use of chalcogenide nanotubes has been their inherently inertness to chemical and biological modification and functionalisation and their potential use in composite materials could be greatly enhanced by improving the chalcogenide/matrix interface bonding.

Scientists at Johannes Gutenberg University Mainz (JGU) have devised a new modification strategy based on metal oxide nanoparticles as universal vehicles for a reversible functionaliation of WS2 nanotubes.

The groundbreaking research conducted in the group of (left) Professor Wolfgang Tremel, in the Department of Chemistry at JGU, and Dr Ute Kolb (right) at the Electron Microscopy Center is published in advance online and will appear on the cover of the journal Angewandte Chemie.

The strategy underlying the reversible binding between chalcogenide nanotubes and metal oxide nanoparticles is based on "Pearson hardness," an elementary concept introduced more than 40 years ago to classify the Lewis acids and bases (especially the various commonly used metal ions and ligands) into three broad categories - hard, soft, and borderline.

Metal oxides nanoparticles stick to the surface of chalcogenide nanotubes. As these metal oxide particles can carry other functional molecules (e.g. polymers, biomolecules) they can act as interfacial glue between the nanotubes and organic matter.

This glue, however, can be detached purposely by the addition of substances that exhibit a stronger binding to the oxide nanoparticles than the WS2 nanotubes.

Until now all strategies of bonding to carbon or chalcogenide nanotubes were irreversible. The new, fully reversible attachment/detachment process will be applied in "smart materials" the toughness of which is reduced on the influence of an external trigger.

The findings will also provide a better understanding of fundamental friction issues, and offer a new tool for assembling nanotubes into devices and study the forces acting on them.