| Triclosan(TCS)is an antibacterial agent in the category of personal care products(PPCPs),which is widely added to mass consumer products such as hand sanitizer,toothpaste and mouthwash.TCS couldn't be completely removed in the conventional sewage treatment process,it may cause a large amount of TCS to be discharged into the environment.However,TCS is not easy to be degraded in the environment and eventually has an accumulative effect in the environment.Its half-life is 18 to 60 days and after being absorbed by plants and direct contact with the human body,part of it returns to the organism and causes great harm to the ecological environment and organism health.Therefore,it is necessary to find an effective technology to remove TCS from water and soil.The advanced oxidation technology based on sulfate radical(SO4·-)has the characteristics of high efficiency,wide application range,strong oxidation ability etc.It is widely used in the treatment of refractory organic matter in water and soil.Among them,the heterogeneous transition metal activated persulfate can efficiently produce sulfate radicals,and has the advantages of continuous activation,wide adaptability and reusability.Due to the advantages of large specific surface area and many active sites,nano-zero-valent iron stands out among heterogeneous transition metals.however due to its agglomeration propertity,it is difficult to disperse in water,thereby reducing the activation performance of nano-zero-valent iron.In order to solve the problem of agglomeration,in present study,bentonite was used as the supporting material,and nano-valent iron(B-nZVI)loaded with bentonite was prepared by liquid-phase reduction method,which was used to activate persulfate(PS)to remove TCS.In this paper,nZVI and B-nZVI(bentonite:nZVI=1:1)were prepared by liquid-phase reduction method.X-ray diffraction(XRD),X-ray energy spectroscopy(EDS),scanning electron microscope(SEM),transmission electrons microscope(TEM)and specific surface area(BET)were used for their physical-chemical characterization.The characterization analysis results confirmed that B-nZVI was composed of bentonite and nZVI.nZVI was evenly dispersed on bentonite,while the agglomeration of pure nZVI was obvious.The specific surface areas of nZVI and B-nZVI were 73.43 and 47.92 m2 g-1,respectively,and the pore diameters were 14.07 and 7.09 nm,respectively.Next,we investigated the effect of catalysts(bentonite,nZVI and B-nZVI)activated persulfate for TCS removl,and explored the effects of B-nZVI catalyzed removal of TCS by different oxidants(hydrogen peroxide,persulfate and persulfate).The B-nZVI activated persulfate was used to remove various pollutants(methyl orange,norfloxacin,bisphenol A and atrazine),and the factors affecting the reaction(B-nZVI dosage,PS dose,Temperature,pH,inorganic salt ions,organic matter and TOC changes)were investigated.The removal rate of TCS in soil was analyzed by B-nZVI activated persulfate(B-nZVI/PS).The results showed that the B-nZVI/PS system could efficiently remove TCS,while nZVI/PS could only remove 50%of TCS.It could be clearly observed that nZVI was clustered together in water,while B-nZVI was well dispersed,and bentonite had no catalytic effect.B-nZVI could effectively activate PS to degrade a variety of organic pollutants,but the its activation effects towards other oxidants were poor.In the B-nZVI/PS system,the TCS removal rate of 5 mg L-1 was 90%within 120 minutes,and the TOC removal rate was 65%.The optimal dosage of B-nZVI was 0.08 mg L-1.When B-nZVI was continuously added,the TCS removal efficiency increased first and then decreased.The optimal PS dosage was 1 mM,and the TCS removal efficiency increased first and then remained unchanged when PS dosage increased.Temperature increase would promote the degradation of TCS.The activation effect under acidic environment was better,compared with the reaction under neutral and alkaline conditions.Chloride ion could promote the degradation of TCS;bicarbonate ion and phosphate ion were not conducive to the removal of TCS,and organic matter did not show large effect on TCS removal rate,TCS could also possess 80%removal.Our results showed that,B-nZVI/PS system could effectively remove TCS in soil,and the removal rate was positively correlated with PS concentration,with the maximum removal rate was 80%.At the same time,we have investigated the reusability of B-nZVI and the dissolution of iron ions during the oxidation process.The physical structure and chemical form of B-nZVI before and after the reaction were also systematically analyzed.The intermediate products of TCS were identified by high-performance liquid mass spectrometry and the degradation pathway of TCS was deduced.The toxicity of TCS after degradation was tested using Escherichia coli and Chlorella.The results showed that B-nZVI could still remove 50%of TCS after recycling twice.The maximum dissolution of iron ions in the reuse process was 0.23 mg L-1,which was much lower than the surface water discharge standards.The analysis of free radical quenching experiments and ERP experiments show that SO4·-and HO·play a synergistic role in the degradation of TCS.XRD and XPS clarify that Fe0 in the B-nZVI/PS system was oxidized by PS to Fe3+,which was mainly converted into FeOOH and Fe2O3.There were 6 kinds of degradation products of TCS.Two degradation pathways of TCS,including oxidation and hydroxylation reactions.E.coli and Chlorella grew well in the degraded TCS solution,indicating that the toxicity of TCS basically disappeared after degradation. |
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