Both　theories　and　experiments　show　that　surface　hydroxyl　radicals　((OH)-O-center　dot)　are　the　most　important　intermediate　species　in　the　photocatalytic　process.　As　a　source　of　(OH)-O-center　dot,　surface　hydroxyl　(OH)　groups　play　an　important　role　in　its　generation.　In　this　paper,　the　OH　groups　were　divided　into　surface　acidic　hydroxyl　(OH(a))　and　surface　basic　hydroxyl　(OH(b))　groups.　From　the　detection　by　a　method　of　surface　acid-base,　ion-exchange　reactions,　the　total　surface　density　of　OH　groups　was　about　9.58　x　10(-5)　mol　m(-2).　The　results　measured　by　Fourier　transform　infrared　spectroscopy,　H-1　magnetic-angle　spinning　NMR　and　electron　spin　resonance　techniques　demonstrated　that　the　role　of　OH(a)　groups　was　greater　than　that　of　OH(b)　groups　on　the　generation　of　(OH)-O-center　dot　radicals.　By　degradation　of　methyl　orange,　rhodamine　B　and　p-chlorophenol,　the　photocatalytic　activities　of　the　catalysts　were　directly　influenced　by　the　amount　of　OH　groups.　(C)　2014　Elsevier　Inc.　All　rights　reserved.