Study On Adsorption Performance Of β-cyclodextrin/Polyethyleneimine Bifunctional Magnetic Nanoparticles For Removal Of Anionic Dyes From Aqueous Solution

Dyes have been widely used in various industries, such as textile, dyeing and paper manufacturing. The dyestuff wastewater discharged by these industries often has characteristics of large water quantity, water quality fluctuation, complicated component, containing metal ions, high salinity and chemical oxygen demand （COD）, low biochemical degradation, and so on. Many technologies and methods have been widespread studied, in which adsorption as an efficient and low energy consumption method has great practical value.In this study the advantages of Fe₃O₄ magnetic nanoparticles （MNPs）, polyethyleneimine （PEI） and β-cyclodextrin （β-CD） were combined. The Fe₃O₄ magnetic nanoparticles nano adsorbent modified with polyethyleneimine （Fe₃O₄-PEI） was synthesized through a simple glutaraldehyde crosslinking reaction. And to further modify the adsorbent, using grafted onto Fe₃O₄-PEI by amide reaction to get the β-CD and PEI bifunctional adsorbent Fe₃O₄-PEI/β-CD. The obtained adsorbents were characterized by FT-IR, XRD, SEM, TEM and VSM; the anionic dyes were chosen as the adsorbate to investigate the adsorption capacities of Fe3O-PEI and Fe₃O₄-PEI/β-CD. The two obtained materials with high stability and adsorption capacity were easy to separate from aqueous solution and have application prospects in the field of water treatment.The results of six anionic dyes （alizarin red S, methyl orange, nuclear fast red, sunset yellow FCF, alizarin green and methyl blue） adsorbed onto Fe₃O₄-PEI showed the adsorption capacity of Fe₃O₄-PEI decreased with increased solution pH values, which indicated the electrostatic interaction between positively charged Fe₃O₄-PEI and anionic dyes with -SO3- groups was the main adsorption mechanism. The pseudo-second-order kinetics model and the Langmuir isotherm model fitted the experimental results well. The charge density and the size of the dye molecules were used to explain the adsorption capacity difference of anionic dyes. The thermodynamic results showed the adsorption of dyes on Fe₃O₄-PEI was spontaneous and endothermic. Fe₃O₄-PEI has good reusability and can effectively remove anionic dyes from model textile wastewater. Therefore the as prepared could be the effective adsorbent to remove the anionic dyes from the industrial wastewater.The anionic dye methyl orange （MO） was selected as the adsorbate to investigate the adsorption properties of Fe₃O₄-PEI/β-CD under different conditions systematically. The experimental results indicated the obtained Fe₃O₄-PEI/β-CD had good stability and high adsorption capacity of MO at a pH of 3. The adsorption mechanisms were electrostatic interaction between protonated amino and anionic dyes and the ability to form host-guest complexes of β-cyclodextrin. Adsorption equilibrium could be quickly achieved within 45 min after Fe₃O₄-PEI/β-CD added into the MO solution, and the pseudo-second-order kinetics model fitted the experiment data well. The fitting results of intra-particle diffusion model showed particle diffusion process was not the only rate-limiting step in the adsorption process. The Langmuir isotherm model could be used to fit the adsorption results and the maximum adsorption amount of MO was 192.23 mg·g-1. The process of MO adsorbed onto Fe₃O₄-PEI/β-CD was spontaneous and endothermic. NaOH was selected as an effective desorption agent and Fe₃O₄-PEI/β-CD has good reusability.