Studies On Photochemical Degradation Of Alachlor

This dissertation was mainly concerning with studies on photochemical degradation of alachlor irradiated by high pressure mercury lamp(HPML). The following effects on phtolysis of alachlor were investigated: the water types, pH buffers, fertilizers, dyes, metallic ions, hydrogen peroxide and surfactants. Photolytic rates of alachlor in organic solvents under HPML were investigated as well. And photolytic rates of alachlor were studied while alachlor and another chemical was absorbed on quardz sand after irradiated by xenon lamp. The main results were summarized as following:1. The photolytic rates of alachlor in five different types of water ranged as: tap water > distilled water > paddy water> river water> lake(ChaoHu) water. While the concentration of alachlor was increasing, the photolytic rate of alachor kept consistent in distilled water; descent a little in tap water; increase in lake water, river water and paddy water.2. Photolysis experiment of alachlor in different buffers indicated that Ala showed high stability in acidity solution. The photolysis half-life of alachlor was 40.4min in pH=4.01 buffer. But alachlor could be easily degradated in alkaline solution. The photolysis half-life of alachlor was 3.07min and 2.66min in pH=9.18 and pH=l 1.0 buffers respectively. However, the photolysis Ti/2 of alachlor was 4.40min in pH=7.0 buffer. The possible reason for these phenomena is that alachlor could easily loss chlorine and form into hydroxyalachlor under alkaline conditions.3. From the experiments on influence of fertilizers on photolysis rates of alachlor, We found that Ca(H2PO4)2 has photoquenching effects on alachlor, and it make photolysis half-life of alachlor extended from 4.78min to 7.49min; The half-life of alachlor is 3.50min when KNO3 is spiked, so it can be used as a photosensitizer; NH4HCO3,NH4NO3 and urea have no evident influence on photolysis of alachlor.4. Viboflavin could accelerate photolysis of alachlor in water solution, the half-life of alachlor was 2.69min, so viboflavin exhibit a marked photosensitive effects on degradation of alachlor; T1/2 of alachlor was 3.70min while crystal violet existed. Both of them act as photosensitizer on degradation of alachlor. But methylene blue act as a photoquencher on alachlor, T1/2 of alachlor was 3.70min while methylene blue was added.5. Tween-60 is a photosensitizer on degradation of alachlor, it made photolysis half-life of alachlor reduced from 4.70min to 3.29min; But ABS-Na showed photo-quenching effects to alachlor, and it made half-life of alachlor prolong to 6.35min; Span-20 had no evident influence on photolysis of alachlor.6. Fe3+ made the half-life of alachlor reduce from 4.75min to 2.89min, while Cu2+ prolonged it to 5.42min, The influence of these two ions on photolysis of alachlor had no evident relationship with the concentration of them. Hydrogen peroxide could be acted as a photosensitizer on destruction of alachlor, when spiked concentration of H2O2 vary as:1.0mg/L, 5.0mg/L, 25.0mg/L, The photolysis half-life of alachlor is 2.47min,1.74min, 1.49min, respectively.7. Alachlor can't be easily destructed in hexane solution; The photodegradation kinetics followed a first order reaction when alachlor dissolved in acetone or methyl alcohol, the half life of alachlor is 2.71min,5.02min respectively.8. Fe3+ exhibited the marked photosensitive effects on photolysis of alachlor on quarz sand, and it reduced photolysis half-life of alachlor from 13.41h to 8.32h; Both crystal violet and methylene blue could be used as photoquenchers on photodegradation of alachlor on quarz sand, they delayed the half-life of alachlor to 17.03h,15.30h respectively. KNO3, Ca(H2PO4)2, viboflavin and Cu2+ have no evident influence on photolysis of alachlor absorbed on quarz sand.