Studies On The Photochemical Degradation Of Metalaxyl

The photolytic kinetics of fungicide metalaxyl in aqueous solution irradiated by high pressure mercury lamp(HPML) and sunlight has been studied.Under HPML,the effects of dissolved oxygen,concentration of metalaxyl,pH,nitrate/nitrite,organic pigments and catalyst on the photodegradation of metalaxyl were studied.And the photodegradation of metalaxyl has been studied on organic solvent and surface of silica gel chromatoplates.The main results were summarized as following:1.The direct photodegradation rate of metalaxyl in aqueous solution by sunlight was slow,the half-life was 154.04h.However it was quickly photodegradaded under HPML irradiation with half-life of 9.06min.The photolysis follows the first order kinetics.2.Under HPML,the half-life of the photolysis of metalaxyl dissolved oxygen and dissolved nitrogen were 4.89min and 13.12min respectively.Dissolved oxygen can greatly promote the photodegradation of metalaxyl.3.The photodegradation of metalaxyl in aqueous solution under HPML irradiation was accelerated with the increasing of concentration of metalaxyl.The half life of photolysis was shortest(7.34 min) at 5 mg/L.The photolytic rate at 10 mg/L and 20 mg/L levels were slower than 5 mg/L.4.Under HPML,the pH value has significant effect on mtalaxyl photolysis:pH9＞pH4＞pH7,The half-life were 6.490min,8.21min,9.12min,respectively.5.Both nitrate and nitrite showed photo-quenching effects on metalaxyl.The photo-quenching efficiency was improved with the increases of nitrate and nitrite concentration.6.Orangic pigments showed remarkable effects on the photolysis half-lives of metalaxyl under HPML.Photosensitizers such as riboflavin,accelerated the photodegradation of metalaxyl,the half life is 7.51min.But crystal violet and methylene blue quenched the photodegradation of mealaxyl the half life is 10.60min and 17.42 min, respectively.7.Under HPML,the photolysis of metalaxyl was accelerated by six artifactitious catalyst matter and TiO₂:TiO₂＞SgS-H-8NC＞SgS-H-7NC＞SgS-H-11NC＞2NPT-450＞SgS-H-6NC＞SgS-H-5NC.8.Under HPML,the photolysis half-lives of metalaxyl were 16.12min,6.76min and 35.92min in methanol,n-hexane and acetonel respectively.The photolysis follows the first order kinetics.9.The photolytic rate of metalaxyl on surface of silica gel under HPML is quick,the half life is 16.95min.Under HPML the photolytic rate of fungicide metalaxyl was decreased with the increasing of dose.