The apparent reaction order  is shown in Figures ) and (d). In general,  is extremely large at low light intensities, gradually decreasing to a value of ~0 when the light intensity is high (the O2 production rate reaches saturation). A reaction order of 2~3 occurs for both models in a narrow intensity range, where hole concentration is in the range of 210 -4 ~ 410 -4 h + nm -2 .