Study On Adsorption And Catalytic Degradation Of Typical Organic Contaminants In Water By Magnetic Carbon Nanotubes

With rapid growths of society,industry and agriculture,more and more wastewater is being discharged,which is causing serious damage to the natural environment.Developing wastewater treatment techniques with high-efficiency,lowcost,and no secondary pollution has become an important task for researchers.In this study,magnetic-separable composite materials,Fe3O4@HCNTs,MnFe2O4@HCNTs and MnFe2O4@cCNTs-PEI were prepared by modifying carbon nanotubes(CNTs)with Fe3O4,manganese ferrite(MnFe2O4),and polyethyleneimine(PEI).Based on the complexity of the molecular structure of pollutant,p-chlorophenol(p-CP),bisphenol A(BPA),tetracycline hydrochloride(TC)and Light Green SF yellowish(LG)were selected as adsorbates.The adsorption and catalytic degradation of BPA and p-CP by Fe3O4@HCNTs,adsorption and catalytic degradation of TC by MnFe2O4@HCNTs,and adsorption and catalytic degradation of LG by MnFe2O4@cCNTs-PEIwere systematically studied.Key findings include:Two composite materials,Fe3O4@HCNTs and MnFe2O4@HCNTs,were prepared by co-precipitation method.The third one,MnFe2O4@cCNTs-PEI composites were prepared by epichlorohydrin grafting,using MnFe2O4@HCNTs as the precursor.The characterization results showed that the three products had good magnetic properties.Both Fe3O4 and MnFe2O4 modification reduced the surface area of CNTs.PEI modification further reduced the surface area of MnFe2O4@HCNTs,but at the same time,provided a large amount of-NH2 groups.The adsorption and catalytic degradation properties of Fe3O4@HCNTs,MnFe2O4@HCNTs and MnFe2O4@cCNTs-PEI for BPA,p-CP,TC and LG were investigated,respectively.The results showed that the effect of pH on the adsorption of BPA on Fe3O4@HCNTs was negligible,but very high pH conditions were not favorable for the adsorption of p-CP by Fe3O4@HCNTs,and the adsorption of TC by MnFe2O4@HCNTs,respectively.The coexisting ions had no effect on the adsorption of BPA and p-CP on Fe3O4@HCNTs,but had negative effect on the adsorption of TC by MnFe2O4@HCNTs.At 303 K,pH 2-10,within 1h the equilibrium adsorption capacity of Fe3O4@HCNTs for BPA could reach 113 mg·g-1,and the equilibrium adsorption capacity for p-CP could reach 42 mg·g-1.When pH=3,the equilibrium adsorption capacity of MnFe2O4@HCNTs for TC could reach 341 mg·g-1.Although the equilibrium took several hours,the adsorption could reach about 300 mg·g-1 within 2 h.Based on the experimental data,the adsorption kinetics and isotherm model fitting analysis,BP A adsorption on Fe3O4@HCNTs was dominated by π-πstacking and hydrogen bonding forces.The adsorption included both the monomolecular layer adsorption on the adsorbent surface and the multi-molecular layer adsorption on the non-uniform surface.The adsorption of p-CP by Fe3O4@HCNTs was a multi-molecular layer adsorption on a heterogeneous surface.And the adsorption was controlled by forces such as π-π stacking,hydrogen bonding,partition effect and molecular sieve effect working together.The main forces in the adsorption process of TC on MnFe2O4@HCNTs were electrostatic attraction,complexation,π-πstacking and hydrogen bonding.When potassium persulfate(KPS)was added to the adsorption system,Fe3O4@HCNTs could efficiently activate KPS to degrade BP A and p-CP,and MnFe2O4@HCNTs could efficiently activate KPS to degrade TC,at pH 3～10.Adding 10 mg of Fe3O4@HCNTs and 5 mg of KPS into 10 mL of 200 mg·L-1 BPA solution could bring excellent catalytic degradation of BPA.The removal rate could reach 90%.After three replicates,the removal rate was about 84%still.After adding 10 mg of Fe3O4@HCNTs and 4 mg of KPS into 10 mL of 100 mg·L-1 p-CP solution,the removal rate of p-CP could reach 88%.After three replicates,the removal rate was about 66%.At pH 3～8,After adding 10 mg of MnFe2O4@HCNTs and 4 mg of KPS into 10 mL of TC solution with an initial concentration of 400 mg·L-1,the removal rate of TC could reach 89%.After three replicates,the removal rate could still reach 56%.The research results showed that the active species from KPS activated by Fe3O4@HCNTs were mainly O2·-and 1O2,while the active species from KPS activated by MnFe2O4@HCNTs were ·OH,SO4·-,O2·-and 1O2.The adsorption and catalytic degradation of LG by MnFe2O4@cCNTs-PEI were investigated.The experimental results showed that the acidic solution was more favorable for the adsorption ofLG on MnFe2O4@cCNTs-PEI.At 303 K and pH 3,the equilibrium adsorption capacity of MnFe2O4@cCNTs-PEI for LG could reach 371 mg·g-1.The coexisting ions had a negative effect on the adsorption of LG,and the main force of adsorption was electrostatic attraction.When H2O2 was added to the adsorption system,MnFe2O4@cCNTs-PEI could efficiently activate H2O2 to degrade LG.At pH 2～10,the removal rate of LG by degradation was more than 5 times of the removal rate by adsorption.After three replicates,the degradation removal rate was still higher than the adsorption removal rate.The study results showed that the active species from H2O2 activated by MnFe2O4@cCNTs-PEI were mainly ·OH and 1O2.In summary,different magnetic functionalization of carbon nanotubes could effectively improve the adsorption and catalytic degradation capacities of carbon nanotubes for target pollutants.The results provide a useful reference and basis for the development of magnetic carbon-based materials for efficient adsorption and degradation of organic pollutants.