Electronic paramagnetic resonance characteristics of ZnO ultrafine particles and their photocatalytic performance

EPR properties of ZnO ultrafine particles(UFP) and their photocatalytic act ivities were studied by using XRD, TEM, XPS and EPR. Results show that UFP obtained by calcining the precursor, zinc carbonate hydroxide at 320, 430, 550 and 700 degreesC, have sizes of 13. 5, 19. 3, 26. 1 and 38. 5 nm, respe ctively, with wurtzite structure attached to the hexagonal system. Results also show that at room temperature ZnO UFP had a significant EPR signal wit h single line resulting from the O2- deficiencies on the surface of ZnO UFP which can capture and trap electrons so as to form a spin resources with S = 1/2. Their EPR intensity decreased with the increase of their sizes. But at the liquid nitrogen temperature, the EPR had six hyperfine structures r esulting from the hyperfine interaction between the electrons traped by O2- deficiencies and the O-17 magnetic nucleus with I=5/2 attached to the abso rbed oxygen on the surface of ZnO UFP. The photocatalytic activities of ZnO UFP decreased as their EPR intensity decreased during the process of photo catalytic oxidation SO2 and C7H16, suggesting that oxygen deficiencies on t he surface of ZnO UFP played an important role in photocatalysis.