Abstract: EPRproperties of ZnOultrafine particles(UFP) and their photocatalytic activities were studied by using XRD, TEM, XPSand EPR. Results show that UFPobtained by calcining the precursor, zinc carbonate hydroxide at 320, 430, 550 and 700 ℃, have sizes of 13.5,19.3, 26.1 and 38.5 nm, respectively, with wurtzite structure attached to the hexagonal system. Results also show that at room temperature ZnO UFPhad a significant EPRsignal with single line resulting from the O₂-deficiencies on the surface of ZnO UFPwhich can capture and trap electrons so as to form a spin resources with S=1/2. Their EPRintensity decreased with the increase of their sizes. But at the liquid nitrogen temperature, the EPRhad six hyperfine structures resulting from the hyperfine interaction between the electrons traped by O₂-deficiencies and the17 Omagnetic nucleus with I=5/2 attached to the absorbed oxygen on the surface of ZnO UFP. The photocatalytic activities of ZnO UFPdecreased as their EPRintensity decreased during the process of photocatalytic oxidation SO₂ and C₇H₁₆, suggesting that oxygen-deficiencies on the surface of ZnO UFPplayed an important role in photocatalysis.

Key words: ZnO, Ultrafine particle, EPR, Hyperfine interaction, Photocatalytic oxidation