Efficient Iron and Cobalt-based Fenton-like Systems and Their Applications in Degradation of Organic Pollutants

Author:Chen Man Tang

Supervisor:zhu li hua

Database:Doctor

Degree Year:2019

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Pages:158

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Fenton technologies have been paid much attention in the field of water treatment,because they are simple,efficient and environment-friendly.However,conventional Fenton system requires a narrow acidic operation pH(2.5-3.5),lacks efficient Fe3+/Fe2+cycle,and often produces a significant accumulation of iron-containing sludge.To improve the application performance of Fenton systems,modified Fenton-like systems have been developed by introducing the light,electricity,organic ligands,and supported catalysts.Besides,Fenton-like systems based on the sulfate radical(SO4·-)have also been developed,including the typical Co2+-PMS system,which can produce SO4·-efficiently.For the iron and cobalt-based Fenton-like systems,how to realize the efficient cycle of Fe3+/Fe2+and Co3+/Co2+,thereby reducing the addition of iron salt and cobalt salt in homogeneous systems,and further improve the catalytic activity of Fenton-like catalysts in heterogeneous systems and inhibit or even avoid the leaching of metal ions is still a key problem to be solved.Therefore,the objective of this dissertation is to develop novel homogeneous Fenton-like systems enhanced by HSO3-and small organic acids(SOAs),and novel heterogeneous Fenton-like systems based on the cobalt-encapsulated and nitrogen-doped carbon nanotubes(Co/N-CNTs)and magnetic Fe3O4@ZIF-67 composites catalyzed activation of PMS.The main contents were summarized as follows:(1)A homogeneous Fenton-like system of Fe3+-HSO3--H2O2 was developed and applied for the oxidative degradation of bisphenol A(BPA),a typical endocrine disruptor.It was confirmed that the degradation ability of Fe3+-H2O2 system was drastically enhanced by the addition of HSO3-.Typically,all the added BPA(0.05 mmol L-1)was degraded in 20 min by using 0.1 mmol L-11 Fe3+,0.3 mmol L-11 HSO3-and 10 mmol L-1H2O2 with a degradation rate constant of 2.71 min-1,which was about 60 times higher than that(0.045 min-1)of equivalent Fe3+-H2O2 system without HSO3-.This drastic enhancement effect of HSO3-was attributed to its complexing and reducing abilities for transforming Fe3+to Fe2+.Besides,the formation of FeSO3+complex also prevented the precipitation of Fe3+.Electron paramagnetic resonance(EPR)and quenching experiments confirmed that several reactive species,including·OH,SO3·-and SO4·-were responsible for the degradation of BPA,among which·OH was the dominant one.(2)A homogeneous Fenton-like system of Co2+-SOAs-PMS was developed and applied for the degradation of organic pollutants and determination of trace-level Co2+in water.The addition of SOAs enhanced the catalytic activity of Co2+for activating PMS,thus greatly reducing the required Co2+addition.The cyclic voltammetry experiments and density functional theory calculation analysis showed that the enhancement of SOAs was attributed to their complexing and electron donating abilities.All the added diclofenac(30μmol L-1)was degraded in 20 min by using 2μmol L-11 Co2+,150μmol L-11 PMS and 500μmol L-11 acetate(Ac-)with a degradation rate constant of 0.482 min-1,which was about10 times higher than that(0.048 min-1)of equivalent Co2+-PMS system without Ac-.This novel system was universal for enhanced degradation of various organic pollutants.EPR and quenching experiments confirmed that SO4·-was the main reactive species.A sensitive spectrophotometric method was further developed for the determination of trace-level Co2+in water based on the Ac-enhanced catalytic decolorization of methylene blue in Co2+-PMS system.Under the optimized conditions,the linear range was from 0.20to 7.0μg L-1 and then from 7.0 to 50.0μg L-1,with a detection limit of 0.10μg L-1.This method possessed excellent anti-interference capability to various coexisting ions,and was used to determine the Co2+concentration in practical samples with satisfactory results.(3)A catalyst of cobalt-encapsulated and nitrogen-doped carbon nanotubes(Co/N-CNTs)was prepared by a simple method of calcination and acid treatment with Co3[Co(CN)6]2 as a precursor,and a heterogeneous Fenton-like system was then developed by using Co/N-CNTs catalyzed activation of PMS and further applied for the degradation of organic pollutants.It was found that Co/N-CNTs were able to function as both an adsorbent and a catalyst for oxidative degradation of organic pollutants in the presence of PMS.All the added rhodamine B(10 mg L-1)was completely degraded in 7min by using 0.1 g L-1 Co/N-CNTs and 0.2 g L-1 PMS.The high catalytic capacity of Co/N-CNTs was attributed to the synergistic effect between adsorption and catalysis on Co/N-CNTs,and the efficient cycle between≡Co2+and≡Co3+and the inhibited Co2+leaching induced by the encapsulated cobalt nanoparticles and the coordination interaction between Co and N.Co/N-CNTs could work well in both a wide pH range(3.3-11.2)and complex wastewater with common coexisting substances.Furthermore,Co/N-CNTs exhibited a good recyclability.(4)Magnetic Fe3O4@ZIF-67 composites were prepared by a wet chemical method at room temperature with Co(NO3)2,2-methylimidazole and Fe3O4 nanoparticles as raw materials,and a heterogeneous Fenton-like system of Fe3O4@ZIF-67-PMS was then developed and further applied for the degradation of tetrabromobisphenol A(TBBPA),a typical brominated flame retardant.All the added TBBPA(40 mg L-1)was completely degraded in 3 min by using 0.1 g L-1 Fe3O4@ZIF-67 and 0.1 g L-1 PMS with a degradation rate constant of 110.3 L g-1 min-1,being nearly 10 times higher than that(11.8L g-1 min-1)of ZIF-67-PMS system and 2000 times higher than that(0.06 L g-1 min-1)of Fe3O4-PMS system.This suggested the existence of synergistic catalysis between Fe3O4and ZIF-67 in Fe3O4@ZIF-67,which maybe attributed to the enhanced recycle of≡Co2+from≡Co3+by≡Fe2+in Fe3O4.EPR and quenching experiments confirmed that several reactive species including·OH,SO4·-and 1O2 were responsible for the degradation of TBBPA,and 1O2 was the dominant one.Furthermore,Fe3O4@ZIF-67 exhibited a good recyclability and could be easily recycled by magnetic separation.