| In recent years,the wastewater from textile,printing and dyeing industries causes serious pollution on ecological environment.Compared with conventional methods,adsorption has been widely used in the removal of dye from wastewater due to its high efficiency,low cost and flexible in design and handing.However,the practical application of conventional adsorbents was greatly restricted due to their inefficient regeneration and difficulty of solid-liquid separation.Recently,magnetic nanomaterials are widely used in the treatment of dyeing wastewater because of their good biocompatibility,relative high adsorption capacity,easy magnetic separation and easy-surface-functionalization.In view of this,the purpose of this study is to prepare high-performance magnetic Fe3O4 adsorbents which are efficient regeneration and easy separation.Moreover,inspired by Mytilus edulis foot protein which is secreted by marine mussels,dopamine(DA)and silane coupling agent KH550 are chosen as the surface functionalization agent to realize the surface functionalization of magnetic adsorbents through the reaction between abundant catechol groups of polydopamine(PDA)and amino groups.The effect of structure,morphology and surface functionalization of adsorbents on the adsorption of methylene blue(MB)from aqueous solution was systematically investigated.The main contents are focused as follows:(1)Two different structured magnetic Fe3O4 nanoparticles were synthesized by solvothermal route and chemical co-precipitation method,which were functionalized by a modified bio-inspired method with DA and KH550 to realize the successful preparation of core-shell structured Fe3O4/poly(DA+KH550)magnetic nanoparticles.The structure and morphology of Fe3O4/poly(DA+KH550)were characterized and confirmed by Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),thermogravimetric analysis(TGA),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).From the results of adsorption experiments,the adsorption capacity of core-shell Fe3O4 magnetic nanoparticles adsorbents for MB increased with the particle size.Furthermore,the effect of adsorption time,initial concentration of MB,temperature of solution and pH value on the adsorption process was intensive investigated.The results indicated that 120 min was required to reach equilibrium for MB adsorbed onto S-Fe3O4/poly(DA+KH550)magnetic nanoparticles.The adsorption capacity of S-Fe3O4/poly(DA+KH550)per unit mass for MB increased with the increase of initial concentration,pH value and temperature.The maximum adsorption capacity of S-Fe3O4/poly(DA+KH550)for MB was 400.00 mg/g under the optimum conditions which were pH=10,time 120 min,and temperature 318.15 K.The adsorption thermodynamics revealed that the adsorption reaction was an endothennic reaction.The adsorption process coincided with the pseudo-second-order model and the adsorption isotherm fitted with the Langmuir model.The analysis of FT-IR and XPS before and after adsorption suggested that the adsorption mechanism between S-Fe3O4/poly(DA+KH550)and MB was the electrostatic interaction,hydrogen bonding and ?-? stacking interaction.(2)Halloysite nanotubes(HNTs)were modified by a bio-inspired method with DA to form PDA-functionalized HNTs.As PDA-functionalized HNTs possessed abundant amino and hydroxyl groups which could further attract iron ions(Fe2+ and Fe3+ ions)and co-precipitate into the Fe3O4 nanoparticles on the surface of HNTs by adding reducing agent(NH3·H2O),thus forming core/shell HNTs/Fe3O4 nano-hybrids.Finally,as-prepared core/shell HNTs/Fe3O4 nano-hybrids were further functionalized by introducing the KH550 to the PDA system to obtain core@double-shell structured HNTs/Fe3O4/poly(DA+KH550)nano-hybrids.The structure and morphology of HNTs/Fe3O4/poly(DA+KH550)were characterized and confirmed by FT-IR,XPS,XRD,TGA,SEM and TEM.The adsorption capacity and mechanism of HNTs/Fe3O4/poly(DA+KH550)for the removal of MB from aqueous solution were also investigated.The results indicated that 180 min was required to reach equilibrium for MB adsorbed onto HNTs/Fe3O4/poly(DA+KH550)magnetic nano-hybrids.The adsorption capacity of HNTs/Fe3O4/poly(DA+KH550)per unit mass for MB increased with the increase of initial concentration,pH value and temperature.As this well-defined core@double-shell configuration was quite distinct from conventional core-shell or hybrid structures,which endowed adsorbent with larger specific surface area and more active adsorption sites.Therefore,core@double-shell structured HNTs/Fe3O4/poly(DA+KH550)nano-hybrids exhibited higher adsorption capacity compared with that of core-shell Fe3O4/poly(DA+KH550)magnetic nanoparticles.The maximum adsorption capacity of HNTs/Fe3O4/poly(DA+KH550)for MB was 714.29 mg/g under the optimum conditions which were pH= 10,time 180 min,and temperature 318.15 K.The adsorption thermodynamics revealed that the adsorption reaction was an endothermic reaction.The adsorption process coincided with the pseudo-second-order model and the adsorption isotherm fitted with the Langmuir model,which indicated that the adsorption of MB on absorbent occurred as a chemisorption and single monolayer.The analysis of FT-IR and XPS before and after adsorption suggested that the adsorption mechanism between HNTs/Fe3O4/pOly(DA+KH550)and MB was the electrostatic interaction,hydrogen bonding and ?-? stacking interaction. |
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