Active metal nanosponge.
Selective dealloying is an efficient method to create materials with high surface area. For example, Raney nickel or recently popular nanosponges (Nature, 2001, 410, 450-453) are prepared this way. While straightforward in binary systems, dealloying quickly gets complicated if three or more metals are present.
Assume you have got an alloy or a nanocomposite made up of copper, nickel, silver and gold. Propose a way to remove each of those components while leaving the rest intact. The less side reactions, the better.