Photoelectrochemical oxidation (PECO) is the process by which light enables a semiconductor to promote a catalytic oxidation reaction. While a photoelectrochemical cell typically involves both a semiconductor (electrode) and a metal (counter-electrode), at sufficiently small scales, pure semiconductor particles can behave as microscopic photoelectrochemical cells.  PECO has applications in the detoxification of air and water, hydrogen production, and other applications.