Among its many talents, silver is an antibiotic. Titanium dioxide is known to glom on to certain heavy metals and pollutants. Yet other materials do the same for salt. In recent years, environmental engineers have sought to disinfect, depollute, and desalinate contaminated water using nanoscale particles of these active materials. Engineers call them nanoscavengers. The hitch from a technical standpoint is that it is nearly impossible to reclaim the nanoscavengers once in the water.