Dissolved Organic Matter Inhibiting Photodegradation Of Butyl 4-hydroxybenzoate During Peroxidation

Butyl p-hydroxybenzoate（BP）is widely used in industrial anti-corrosion.It is ubiquitous in the environment.Furthermore,it make mammals produce an estrogen effect and induce cytotoxicity.At present,the research on BP includes electrochemistry,peroxidation and photochemistry.Among them,the advanced oxidation technology combining photochemistry with peroxidation is an important way for BP degradation in water.It has universal efficient and economic advantages.Dissolved organic matter（DOM）is ubiquitous in water.It is one of the more important environmental factors.Researchers have conducted related experiments on DOM as an environmental factor inhibited the degradation of organic pollutants in the photo/peroxide system.However,the research of scholars only stayon the apparent experiment and the speculation of the internal mechanism,lacking experimental support.Therefore,the study on DOM affected photoperoxides to promote degradation of organic pollutants has great environmental significance.In this paper,humic acid（HA）and fulvic acid（FA）extracted from the sediment of Dianchi Lake were used as representative materials of DOM.The photochemical transformation processes and mechanisms of BP in DOM,peroxide（persulfate,PDS,peroxysulfate,PMS and hydrogen peroxide,H₂O₂）,the mixed system of DOM and peroxide was systematically studied.Under the premise of obtaining the experimental data,the physicochemical properties of DOM and peroxide were studied by consulting the relevant literature.The active species involved in DOM and peroxide mediated degradation of BP and their contribution were analyzed.Combined with the physical and chemical parameters,UV spectra and fluorescence before and after the reaction to further inferred that DOM inhibited the degradation of organic pollutants during peroxidation system.The relevant research results are as follows:（1）BP is stable under dark conditions and hardly removed by hydrolysis,evaporation,etc.It is slightly degraded under simulated illumination of a 300 W mercury lamp and 290 nm cut-off filter.p H is an important factor affecting BP degradation.BP degraded slowly in leaning neutrality environment,and it was enhanced under acidic and alkaline conditions.This is because of the acidic and alkaline changed the molecular configuration and photochemical properties of BP.（2）The addition of strong oxidants promoted the degradation of BP to a large extent.The degradation efficiency of BP at the same concentration of potassium persulfate（PDS）,potassium peroxysulfate（PMS）and hydrogen peroxide（H₂O₂）is:PDS>H₂O₂>PMS.which is related to the oxidation of peroxides and the types of pollutants.The peroxide produced active species under illumination,active species and their relative contributions in each system,H₂O₂:·OH>¹O₂,PMS:SO₄^-·>·OH,PDS:SO₄^-·≈·OH.The p H of the photodegradation system affects the type and amount of active species in the system.（3）Dissolved organic matter（DOM）promotes photodegradation of BP by producing·OH,¹O₂,³DOM^*,which is the main active component of DOM to promote BP degradation.The difference in BP degradation at the same concentration of humic acid（HA）and fulvic acid（FA）is caused by the difference in the structure and photochemical properties of HA and FA.（4）When BP and DOM was simultaneously present in the oxidant system,BP competed with DOM for the oxidant.The combination of HA with peroxide that generated·OH or SO₄^-·produced more ³HA^*to promote BP photodegradation,while the combination of FA system with active species（·OH or SO₄^-·）produces more ³FA^*,¹O₂to promote BP photodegradation.Therefore,the order of BP degradation rate in oxidant combined with DOM system and blank group（oxidant system,DOM system）is:oxidant system>oxidant and DOM hybrid system>DOM system.（5）The Chlorella vulgaris was cultured with the solution after illumination.The toxicity of the different solution after photolysis was investigated.It was found that the alone H₂O₂ system promoted the growth of Chlorella vulgaris,the PDS and FA systems got the opposite result.However,DOM inhibited the peroxide system had no obvious effect on the growth of Chlorella vulgaris.This phenomenon indicates that DOM inhibited the peroxide system alleviated the effects of single system on the Chlorella vulgaris growth.