FeS_(2)/高岭石复合材料活化过一硫酸盐降解苯并芘性能

Performance of Activating Peroxymonosulfate to Remove Benzo[a]pyrene by FeS_(2)/Kaolinite Composite

苯并芘(B[a]p)作为典型多环芳烃化合物之一,具有强致癌、致畸及致突变作用,广泛分布在土壤、大气以及水体环境。基于过硫酸盐的高级氧化技术因其快速、简便以及高效等优点在环境治理领域一直是研究热点。尤其是铁基催化材料,因其环保、成本低和反应活性高等特性被广泛应用在过硫酸盐活化领域,但其在应用过程中存在易氧化、易团聚以及Fe(Ⅱ)再生能力差等缺陷。因此,本工作采用一步水热法制备了FeS_(2)/高岭石复合材料,用于高效活化过一硫酸盐(PMS)降解B[a]P。其在投加量为2.0 g/L,初始B[a]p浓度为20 mg/L,PMS剂量为2 mmol/L的条件下,15 min内对B[a]p的去除率达到93%,并证实了体系中^(1)O_(2)和O_(2)^(·-)起主导作用。此外,在土壤体系中,随着复合材料和PMS用量的增加,B[a]p的降解率逐渐增加;随着水土比(质量比)的增加,呈现出先增加后降低的趋势;而随着pH值的增加,降解效率反而呈现降低的趋势,选取催化剂用量50 mg/g,PMS用量80 mg/g,水土比3:1以及pH值为3的条件下进行实验,60 min内对B[a]p的去除率达到69.02%。

Introduction Polycyclic aromatic hydrocarbons(PAHs)are hydrophobic aromatic compounds consisting of two or more condensed benzene rings,having greater teratogenicity,carcinogenicity,mutagenicity and toxicity.The most representative PAHs is benzo(a)pyrene(B[a]p),which is composed of five benzene rings,and is classified as a Group I carcinogen.The treatment technologies for B[a]p removal include bioremediation,physical remediation and chemical remediation.The advanced oxidation technology based on sulfate radicals becomes a recent research hotspot because of its high redox potential,high reactivity and environmental friendliness.Nevertheless,persulfate needs to be activated through various approaches to produce a series of reactive species,and iron-based materials are widely used due to the abundant reserves,environmental friendliness and excellent activation performance.In this paper,pyrite(FeS_(2))was used as a cheap and non-toxic sulfide mineral,allowing for a slow release of Fe^(2+)as well as the cycling of Fe^(2+)and Fe3+.Kaolinite was chosen as a suitable carrier to solve the agglomeration of FeS_(2) nanoparticles.A composite with FeS_(2) and kaolinite was prepared to obtain efficient persulfate activation and B[a]p degradation.Methods Ferrous sulfate heptahydrate(FeSO4·7H2O),sodium thiosulfate(Na2S2O3),cetyltrimethylammonium bromide and kaolinite were ultrasonically mixed and stirred for 30 min,and then the solution was transferred to a reactor for the hydrothermal reaction.At the end of the reaction,the solution was centrifuged and washed for three times,and then put into a vacuum oven for 12 h to obtain the composite catalyst.The B[a]p solution,desired dosage of catalysts and peroxymonosulfate(PMS)solution were added in a centrifuge tube of 50.00 mL,and then conducted in a rotating mixer at room temperature.Before adding PMS solution,the adsorption-desorption equilibrium process was carried out under 30 min continuous stirring.Moreover,1.00 mL of the mixture was taken at the setting time points and quenched with 0.50 mL of MeOH.Finally,the mixture was analyzed by high-performance liquid chromatography(HPLC)after filtration.Also,4.00 g B[a]p-contaminated soil,desired dosage of catalysts and PMS were added in a centrifuge tube of 50.00 mL,and then conducted in a rotating mixer for 60 min at room temperature.After 60 min reaction,the supernatant was poured after centrifugation,and then the soil sample with an extraction fluid(MeOH and acetonitrile in a volume ratio of 1:1)was ultrasonicated for 60 min to obtain 20.00 mL of soil extract.Finally,the supernatant was withdrawn and filtered for HPLC to test the residual B[a]p concentration in soil samples after centrifugation.Results and discussion According to the analysis by scanning electron microscopy and energy dispersive spectroscopy,a composite with kaolinite and layered FeS_(2),can be prepared.The specific surface area of FeS_(2)/kaolinite slightly increases,and the particle size of FeS_(2)/kaolinite is smaller than that of FeS_(2),which is attributed to the elimation of the agglomeration via the introduction of kaolinite and the improvement of the dispersibility of FeS_(2),resulting in the superior catalytic performance for PMS activation and B[a]p removal.The results show that the B[a]p removal rate is 93.00%(liquid-phase)and 69.02%(soil)under the optimum conditions(i.e.,2.0 g/L catalyst,20 mg/L B[a]p concentration,2 mmol/L PMS concentration(liquid-phase)and 50 mg/g catalyst,80 mg/g PMS,3:1 water/soil ratio(in mass),respectively).The acidic and neutral conditions are more suitable for the PMS activation and B[a]p removal.Also,the B[a]p removal is affected in the presence of H2PO42-and HCO3-.The existence of Cl-and NO3-promotes the B[a]p degradation efficiency.Based on the quenching experiments,the reactive species including ^(1)O_(2),SO4•−and O_(2)^(·-)are proved to be involved in the process of PMS activation and B[a]p degradation,and ^(1)O_(2) and O_(2)^(·-)are further confirmed to be the dominant reactive species.Based on the mechanism of PMS activation in FeS_(2)/kaolinite/PMS,the content of Fe^(2+),S22-and S0 is decreased after the catalytic reaction,indicating that Fe^(2+)is the main driving force for the PMS activation to generate ^(1)O_(2),SO4•−and O_(2)^(·-),and the cycling of Fe^(2+)and Fe3+is facilitated in the presence of S22-and S0 possessing reductivity.In addition,the oxygen-containing functional groups contained in kaolinite can be also beneficial to the PMS activation.Conclusions A composite of FeS_(2)/kaolinite was synthesized by an one-step hydrothermal method for PMS activation and B[a]p degradation.The degradation results demonstrated that 93.00%B[a]p was removed within 15 min under the optimized conditions(i.e.,2.0 g/L FeS_(2)/kaolinite,20 mg/L B[a]p concentration,and 2 mmol/L PMS concentration).^(1)O_(2) and O2•-played a dominant role in FeS_(2)/kaolinite/PMS for PMS activation and B[a]p degradation.The excellent catalytic performance of FeS_(2)/kaolinite was also confirmed in the degradation experiment of B[a]p removal in soil,with 69.02%B[a]p degradation efficiency under the optimized conditions(i.e.,50 mg/g FeS_(2)/kaolinite,80 mg/g PMS,3:1 water/soil ratio and pH value 3).The high catalytic performance of FeS_(2)/kaolinite was mainly due to the cycling of Fe^(2+)and Fe3+as well as the reduction reaction between Fe3+and S22-/S0.