| Methylparaben(MP)is a kind of environmental pollutant in pharmaceutical and personal care products,and it has been detected in natural water bodies and sewage treatment plants.They pose a potential threat to aquatic ecosystems and have an adverse impact on human health since MP has potential endocrine disrupting effects and potentially contribute to the incidence of breast cancer.The hybrid advanced oxidation technology is a combination of advanced oxidation technology based on sulfate radical(·SO4-)and photocatalytic oxidation technology,which can produce synergistic effect through mutual promotion and effectively utilize peroxymonosulfate(PMS)to maximize resource utilization.Of course,it has broad prospects in dealing with the refractory organic pollutants in water.Bismuth oxyiodide(BiOI)has been regarded as one of the most promising visible-light-driven photocatalysts,and its unique electronic structure and special layered structure contributes to effectively remove contaminants under visible light irradiation.However,the fast recombination of photogenerated electron-holes limits the development of photocatalytic performance.In addition,the difficulties of recovery and secondary pollution of BiOI also severely restrict the practical applications.Therefore,it is an urgent need to find an effective carrier to break the bottleneck of the photocatalyst.Hydrogels with three-dimensional porous structure and rich functional groups are suitable platforms for catalyst loading.BiOI was supported on the hydrogel to form an BiOI-hydrogel composite,which could enhance its photocatalytic performance,also act as a PMS activator,realizing the coupling of photocatalytic technology and ·SO4-advanced oxidation technology.In this paper,a novel hydrogel p(HEA-APTMACl)was prepared by radiation polymerization with 2-hydroxy ethyl acrylate(HEA)and(3-acrylamidopropyl)trimethylammonium chloride(APTMACl)as monomers.And then p(HEA-APTMACl)-BiOI was successfully synthesized by coprecipitation of BiOI.Meanwhile,the structure and optical properties of the materials were characterized by Scanning Electron Microscope(SEM),Transmission Electron Microscope(TEM),X-Ray diffraction(XRD),X-ray photoelectron spectrometer(XPS),UV-visible diffuse reflectance spectrum(DRS)and other analytical methods.Based on these above analysis,p(HEA-APTMACI)-BiOI was employed as PMS activator to degrade MP under visible light irradiation,and the degradation efficiency of MP by different oxidation systems was discussed.The effects of different influencing factors on MP degradation were also investigated.In addition,the free radicals in the system were determined by the radicals quenching experiments,and the PMS activation mechanism and the degradation pathway of pollutants were also proposed.Finally,the toxicity changes during the degradation process were evaluated.The main conclusions of the above studies were as follows:(1)The characterization results showed that the sheet-like BiOI was uniformly dispersed on the hydrogel,and the prepared catalyst was indeed BiOI with tetragonal crystal structure.The composite consisted of C,N,O,Bi and I elements,and was formed by the close binding of the amide group(CO-NH)on the hydrogel with BiOI.In addition,the composite determined by DRS spectroscopy had a band gap of about 1.82 eV,which can effectively utilize visible light.The photocurrent measurement and photoluminescence spectra indirectly proved that the photogenerated electron hole of the composite ccould be effectively separated,and the rapid recombination problem could be alleviated to some extent.(2)The results of different oxidation systems showed that p(HEA-APTMACl)-BiOI/PMS/Vis system possessed a higher MP degradation ability compared with other oxidation systems,and its degradation curve coulld be well fitted by the first-order kinetic model.At the moment,the degradation rate constant was 0.0440 min-1,which was about four times that of p(HEA-APTMACl)-BiOI/PMS system.In addition,the catalytic performance of the system exceeded the additive effect of a single system,indicating that there was a synergistic effect between p(HEA-APTMACl)-BiOI,PMS and visible light in the system.It was worth noting that the system broke through the pH limit and maintained excellent pH tolerance.At the pH of 10.96,the degradation rate constant of MP could reach the optimal level,showing the best catalytic performance.Moreover,complete MP degradation could be achieved within 120 min under the condition of pH = 6.96(unadjusted),[p(HEA-APTMACl)-BiOI]= 0.1 g,[PMS]= 1.5 mmol/L,[BiOI loading]=20 mmol/L and[MP]=50 mg/L.At the same time,the TOC removal efficiency reached 78.3%,exhibiting a strong mineralization ability.In addition,the effects of different anions on the performance of the system were different.Among them,Cl-enhanced the degradation efficiency of MP,while HCO3-slightly inhibited the MP degradation efficiency,and other anions had no obvious effect on the degradation of MP,indicating that the system held good anti-interference a'bility.(3)Through the radical quenching experiments,it were found that the main forms of active radicals were h+,·SO4-ads,·OHads,·O2-and 1O2 in the p(HEA-APTMACl)-BiOI/PMS/Vis system,indicating that the formation of radicals occurred on the surface of the catalyst,and the free radical pathway and the non-radical pathway coexisted and acted on the degradation of the contaminant.Besides,the proportion of 1O2 was significantly higher than that of ·SO4-ads and ·OHads in the p(HEA-APTMACl)-BiOI/PMS system,proving that the non-free radical pathway played a leading role in the degradation of MP.Based on the analysis of free radicals and degradation products,the mechanism of PMS activation in the two systems was elaborated in detail,and the possible MP degradation pathways were also derived.(4)The daphnia magna toxicity experiments demonstrated that the acute toxicity increased first and then decreased during the degradation of MP in p(HEA-APTMACl)-BiOI/PMS/Vis system,which might be attributed to high eco-toxicity of intermediate products. |
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