Effect of ferric ion added on photodegradation of alachlor in the presence of TiO2 and UV radiation

The effect of in situ photodeposited ferric ion onto TiO2 surface on the degradation of alachlor was investigated in the presence of the UV radiation. The photodegradation rate of alachlor could be described as an apparent first order. The rate constant (Ka) of alachlor increased from 0.021 to 0.060 h−1 as the number of coating times increased from 1- to 5-times in the absence of ferric ion, where the corresponding thicknesses of the TiO2 film were 67 and 174 nm. The rate constant (Ka) increased from 0.030 to 0.060 h−1 as pH value decreasd from pH 9 to 5 in the presence of only TiO2 immobilised with 5-times of coating. The rate constant increased slightly from 0.031 to 0.050 h−1 as the concentration of ferric ion increased from 0.75 to 7.5 mg Fe3+ l−1 in the absence of TiO2. However, those increased from 0.051 to 0.110 h−1 in the presence of both TiO2 and ferric ion. In situ photodeposition of ferric ion onto the TiO2 surface enhanced the rate constant of photodegradation of alachlor by about 80% with an adding 7.5 mg Fe3+ l−1. During the alachlor photodegradation, three kinds of non-toxic organic compounds derived from alachlor were detected in 1 h.