The degradation efficiency increases from 94.44 to 98.80% as the pH value rises from 4 to 7 and then decreases under 90% with the increase of pH from 7 to 10. The solution’s pH has complex effects on the photocatalytic oxidation reaction, depending on pollutant type and catalyst’s zero point charge (pHZPC), which in the case of Fe-doped TiO2 is about 7 [25].