Study On Adsorption Properties Of Cyclodextrin Magnetic Materials For Dyes In Water

With the realization of China’s industrialization,the pollution of water environment has become a difficult problem that can not be bypassed in economic development of China.Dye is one of the common pollutants that cause serious harm to the water environment.There are many methods for treating pollutants in the water environment.The adsorption method is considered to be the most environmentally friendly treatment method due to its high efficiency,easy operation and economic feasibility.In this paper,β-cyclodextrin,sodium silicate and stannous chloride dihydrate were used as raw materials to synthesize the adsorbents.m-Fe₂O₃/β-CD/SiO₂,Sn-MOF^-1,Sn-MOF^-2 and m-Fe₂O₃/β-CD/Sn-MOF composite materials were synthesized by solvothermal method,solution blending method and dry grinding method.The adsorbents prepared in this study can selectively adsorb a variety of compounds with different structures or properties through a variety of interactions.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Fourier infrared spectroscopy（FT-IR）and thermogravimetric analysis（TGA）were used to characterize these materials.And then the removal of methylene blue（MB）,crystal violet（CV）and ractive black 5（RB5）in water were studied.The contact time,solution p H value,the amount of adsorbent,dyes concentration and temperature et al experimental influence factors were investigated.The adsorption kinetics,adsorption isotherms,thermodynamics and the recyclability of the materials were evaluated.Moreover,the adsorption properties of m-Fe₂O₃/β-CD/SiO₂ and m-Fe₂O₃/β-CD/Sn-MOF cyclodextrin magnetic materials in composite systems were also explored.The specific research results are as follows:（1）Synthesis of cyclodextrin magnetic adsorbent m-Fe₂O₃/β-CD/SiO2 by two-step preparation method of solvothermal and solution blending method.It was used to remove the basic cationic dyes MB and CV in water.The optimal adsorption condition was at adsorbent dosage of 10 mg,contact time with 120 min and the p H at 7-8 in a 50 ml of 10 mg?L^-1 solutions.The adsorption behaviour of both dyes accord with the pseudo-second-order kinetic equation.And the adsorption process of MB and CV on m-Fe₂O₃/β-CD/SiO2 is also affected by external diffusion such as boundary layer diffusion and intra-particle diffusion under the model of Weber-Morris intra-particle diffusion.Isothermal adsorption experiment results showed that the adsorption process of MB and CV by m-Fe₂O₃/β-CD/SiO₂ conformed to the Langmuir model and the maximum adsorption capacity of MB and CV were 76.92 and 250.00 mg?g^-1,respectively.m-Fe₂O₃/β-CD/SiO₂ adsorbed MB was spontaneous exothermic,while the process of CV was spontaneous endothermic.For the removal of MB and CV dyes in lake water,this adsorbent also has obvious adsorption performance.The regeneration experiment indicated that after 5 cycles the adsorption capacity can reach 71.42% and 70.82% of the initial capacity of MB and CV,respectively.（2）The Sn-MOF materials MOF^-1 and MOF^-2 were obtained by two methods,which were wet solvothermal and dry grind methods.TGA tests showed that the thermal performance of MOF^-1 was better than MOF^-2.The two materials were used to remove acid anionic dye RB5 in water,with the p H range of 3^-10 both MOF^-1 and MOF^-2 have good adsorption capacity under the condition with 50 ml of 200 mg?L^-1 RB5 solution and the optimal dosage is 40 mg.The adsorption of RB5 by both MOF^-1 and MOF^-2 conformed to the pseudo-second-order kinetic and Langmuir model.The maximum adsorption capacity of MOF^-1 and MOF^-2 to RB5 was 609.76 and 787.40 mg?g^-1,respectively.And the adsorption process of RB5 by MOF^-1 is spontaneous endotherm,the adsorption of RB5 by MOF^-2 is spontaneous exothermic.（3）Using m-Fe₂O₃/β-CD as the magnetic preform material,the magnetic Sn-MOF material was prepared by using the solvothermal synthesis method of MOF^-1 for reference,m-Fe₂O₃/β-CD/Sn-MOF（Fe/Sn-MOF）was used to remove RB5 in water.In the p H range of 3^-10,the adsorption performance of Fe/Sn-MOF in alkaline environment became worse with the increase of m-Fe₂O₃/β-CD dosage,through comprehensive investigation,the best usage of m-Fe₂O₃/β-CD is 0.05 g,which is called Fe（0.05）/Sn-MOF.The adsorption of RB5 by Fe（0.05）/Sn-MOF conforms to the pseudo-second order kinetic equation,the maximum adsorption capacity of Fe（0.05）/Sn-MOF was 450.45 mg?g^-1.Langmuir model is more suitable to describe the adsorption of RB5 and the thermodynamics experiments indicated that the adsorption process is spontaneous.Besides,the adsorbent also had obvious adsorption capacity for dye solution prepared in lake water,which indicates that the material has a certain adsorption capacity for the dye solution configured in the lake water.And after 5 cycles,the adsorption capacity can still reach 71.23% of the initial use.（4）Two magnetic adsorbent materials m-Fe₂O₃/β-CD/SiO₂ and Fe（0.05）/Sn-MOF were used to study the composite of MB-CV,Pb（II）-MB,Pb（II）-CV and Pb（II）-RB5,respectively.At the same time,the effect of salt solution on dye adsorption was also discussed.In the composite system,Pb（II）inhibited the adsorption MB and CV,while promoted the adsorption of RB5.The addition of three cationic salts all inhibited the adsorption of MB and CV by m-Fe₂O₃/β-CD/SiO₂,and the inhibition capacity of the three salts was Ca Cl2>Mg Cl2>Na Cl,while for Fe（0.05）/Sn-MOF adsorption of RB5,the low concentration of salt promotes Fe（0.05）/Sn-MOF to adsorb RB5,the high concentration of salt inhibits Fe（0.05）/Sn-MOF from adsorbing RB5.The addition of different anion salts inhibited the adsorption of MB and CV by m-Fe₂O₃/β-CD/SiO₂.In the four anion salts,Na HCO3 and Na2CO3 inhibited the adsorption of RB5 by Fe（0.05）/Sn-MOF.Composite adsorption experiments show that m-Fe₂O₃/β-CD/SiO₂ and Fe（0.05）/Sn-MOF also have adsorption effects on Pb（II）and can be applied to the removal of pollutants in complex water bodies.The enrichment and separation of dyes in water and the reusability of the materials provide a theoretical basis.