Defects are the most reactive sites on the surface of metal oxides. Herein, thermal evacuation creates nonstoichiometric reduced forms of metals accompanying appropriate oxygen vacancies at specific optimized temperatures and timings without any doping or impregnation. Electron–hole recombination is reduced due to the presence of mixed valence states of metals. The generation of nonstoichiometric reduced forms of metals on the surface of bulk oxides is the promoting effect for higher photocatalytic activity and photostability.