Palladium is a rare, silvery-white metal. Along with platinum, rhodium, ruthenium and iridium, it belongs to the platinum group of metals (PGM). It does not react with oxygen at standard temperature, so it does not tarnish in air; however, if exposed to hot water, it will form a layer of palladium oxide, which turns black over time.

A precious metal, palladium is used in catalytic converters for cars and industrial equipment. It is also a key component of dental crowns and jewelry. A remarkably durable metal, it is more resistant to corrosion than gold or silver. Palladium also has a number of unique physical properties. It warps when subjected to shear forces, similar to the way taffy will stretch out when pulled. It also has a low melting point and is less dense than gold or platinum.

Scientists are using this unusual property to develop a new type of water filter that could remove harmful chemicals from wastewater. The scientists created a prototype that uses 6-foot-tall columns of gold-and-palladium nanoparticles to remove pollutants like carcinogenic perchloroethylene (PCE) from water. They hope to scale up the design to create a commercial product that can remove other toxic chemicals from wastewater, including the cancer-causing agent dioxin.