| Organic UV sunscreens are widely used in personal care products.They can enter human bodies through skin contact,inhalation,and food chain accumulation,further causing estrogen and anti-androgen effect.Polyhalogenated carbazoles(PHCZs)and polyfluorinated dibenzo-p-dioxins(PFDDs)are two kinds of dioxin-like compounds with dioxin-like toxicities.Given that their widespread occurrence and ecological risks,their removal has always attracted more and more concern.Because of their unique advantages,persulfate and visible light technologies have been widely used in the field of environmental treatment.Benzophenone-3(BP-3),2,4,4'-trihydroxybenzophenone(2,4,4'-HBP),1,3,6,8-tetrabromocarbazole(1368-BCZ)and PFDDs were chosen as the model targets in this study.And their reactive kinetics,degradation products,and pathways during persulfate oxidation process or under irradiation were investigated.Detailed studies consist of the following four aspects:(1)In this work,cobalt ferrite(CoFe2O4)prepared by chemical co-precipitation method was used as a catalyst for the degradation of BP-3.The catalyst was characterized by SEM,TEM,XRD,XPS,BET and FT-IR spectroscopy;its catalytic activity on BP-3 removal by persulfate(PS)was then evaluated at different operating parameters(calcined temperatures,catalyst loading,reaction temperature,solution pH and PS dose);in order to test its catalytic performance,the recycle and leaching experiments were also carried out;electron paramagnetic resonance and radical quenching tests showed that sulfate radicals predominated in the decomposition of BP-3 by PS/CoFe2O4,while hydroxyl radicals also contributed to the catalytic oxidation process;finally,fifteen degradation products were identified by liquid chromatography-mass spectrometry(LC/MS),and two reaction pathways involving hydroxylation,demethylation,direct oxidation and benzene ring opening were proposed.To the best of our knowledge,this is the first attempt to employ CoFe2O4 as a catalyst of PS for the degradation of BP-3,and this study could provide useful information for the potential application of CoFe2O4 activated PS technology to treat water and wastewaters containing BP-3.(2)We systematically investigated the persulfate(PS)activation potential of a series of nitrogen doped carbonaceous materials for the degradation of 2,4,4'-HBP.Nitrogen originating from urea,NH4NO3,indole and polyaniline was doped into carbonaceous materials,including hydroxylated multi-walled carbon nanotubes(CNT-OH),large-inner thin-walled carboxylated carbon nanotubes(CNT-COOH)and graphite oxide(GO),to examine the catalytic effect.The NH4NO3-CNT-OH catalyst,which showed the best catalytic performance in 2,4,4'-HBP removal,could activate PS to generate hydroxyl and sulfate radicals to further oxidize the substrate.Cleavage of C-C bridge bond,hydroxylation and polymerization were mainly involved in the oxidation process,leading to the formation of 10 intermediates(e.g.,dimers),as analyzed by the LC/MS spectra.This report is the first to describe the transformation mechanism of 2,4,4'-HBP,and it was observed that dimers can be formed in this process;meanwhile,this research can provide useful information regarding whether nitrogen can be doped into certain materials in order to elevate the oxidative efficiency and the identity of N sources suitable for this purpose;finally,clarify the radical mechanism of PS activation by N doped carbonaceous materials and the effect of pyrrolic nitrogen on the activation of PS.(3)The kinetics and mechanisms of photochemical transformation of 1368-BCZ in n-hexane and pre-coated on solid particles in aqueous solution were investigated.Under simulated sunlight irradiation,1368-BCZ dissolved in-hexane rapidly photodegraded,obeying the pseudo first-order kinetics model.In aqueous system,the photodegradation kinetics of 1368-BCZ on three pure particles(silica gel,Al2O3,and Kaolin)fitted with the"double-logarithmic"model.A total of eight non-polar products were found by GC/MS.However,several products including 1-monobromocarbazole(1-BCZ),3-monobromocarbazole(3-BCZ),dibromocarbazole-1(di-BCZ-1),and 3,6-dibromocarbazole(36-BCZ)were found during the reaction in n-hexane but not detected in the aqueous systems.Seven polar products were found by LC/MS.The products and intermediates identified suggested that debromination and hydroxylation were the two main photochemical transformation pathways of 1368-BCZ in both n-hexane and aqueous systems.The proposed reaction pathways were supported by the results of quantum chemical calculation.This"double-logarithmic" model was first found in pollutants degradation.Relatively overall transformation pathways of 1368-BCZ were proposed in two systems,and then detailed comparison and discussion were carried out.This work provides useful information in the assessment of environmental fate of polyhalogenated carbazoles.(4)The photochemical behaviors of PFDDs congeners on silica were systematically investigated.The pseudo-first-order rate constants(k,h-1)of surface photolysis changed with the substitution number and position of fluorine atoms,and the tetra-fluorinated PFDDs tended to degrade more efficiently.Octafluorinated dibenzo-p-dioxin(OFDD),2,3,7,8-tetrafluorinated dibenzo-p-dioxin(2,3,7,8-T4FDD)and dibenzo-p-dioxin(DD)were selected as representatives to explore the reaction mechanisms.The results showed that hydroxyl substitution and(-OH radical mediated or direct)C-O bond cleavage were their photochemical transformation pathways.Coupling elimination reaction was also observed,further verified by density functional theory(DFT).This coupling elimination reaction mechanism is proposed for the first time in the transformation of dioxin compounds.This work could provide some new insights into the environmental fate of dioxin compounds.To sum up,the first two parts of this study was aimed at the organic UV sunscreens degradation in PS/catalyst system.However,due to their low water solubilities,once released into the environment,dioxin-like substances tend to be adsorbed on the surface of solid particles.Therefore,the study of their degradation behaviors in real environmental processes including aqueous and gas phases could be conducive to improve our understanding about their transformation mechanism and fate and further develop new strategies to deal with this concern.This work is not only of high scientific value,but also of important reality significance.The above studies found that hydroxyl radical induced hydroxylation plays a very important role in the reaction processes of these two kinds of organic pollutants.In addition,the self-coupling of organic pollutants'radicals and the cross-coupling mechanisms of their products and them can not be ignored. |
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