Synthesis Of Magnetic ?-Cyclodextrin Polymer And Its Application In Printing And Dyeing Wastewater Treatment

The printing and dyeing wastewater accounts for a higher proportion of industrial wastewater in China,which has become more and more negligible.The water quality of printing and dyeing wastewater fluctuates greatly,and pollutant composition is diverse and complex.Especially,the combined pollution of organic substances and heavy metals is an urgent problem to be solved,which makes printing and dyeing wastewater difficult to be treated and controlled.It is hard to completely treat printing and dyeing wastewater by conventional treatment process and it is necessary to combine the advanced treatment process to treat the wastewater.With its convenient operation and good treatment effect,adsorption has become one of the most advanced treatment processes.However,Conventional adsorbents,such as activated carbon,require a large amount of energy during repeated regeneration,and the cost is high,which limits their applications.As a kind of cyclic oligosaccharide,?-cyclodextrin is cheap and easy to obtain.It has good adsorption effect on many pollutants due to the special "external hydrophilic and internal hydrophobic" structure and thus ?-cyclodextrin was deemed as a promising adsorbent.However,the currently studied ?-cyclodextrin polymer materials still have slow adsorption rates for dyes,heavy metals and other contaminants,and there are few reports of multifunctional adsorbents that adsorb organic substances and heavy metals simultaneously and rapidly.Based on the background,this study developed a magnetic ?-cyclodextrin adsorbent that was cost effective and easy to operate.The adsorbent can quickly adsorb organic matter and heavy metal in solution and can be separated from the aqueous phase after adsorption.The main research contents and conclusions are as follows:(1)A magnetic ?-cyclodextrin polymer(MNP-CM-CDP)was synthesized.A ?cyclodextrin polymer(T-E-CDP)with good adsorption properties was obtained.Chloroacetic acid was used to modify the ?-cyclodextrin polymer,and carboxyl groups were attached on the surface of the ?-cyclodextrin polymer to obtain a carboxymethylated ?-cyclodextrin polymer which was capable of adsorbing organic substances and heavy metals.The adsorbent particles were spherical and evenly distributed and the amount of surface-coated carboxymethylated ?-cyclodextrin polymer accounted for 20.373%of the total mass.Good magnetic properties of MNPCM-CDP allowed it to settle down quickly in solution.(2)The adsorption process of MNP-CM-CDP for bisphenol A,basic orange 2,rhodamine B,methylene blue was studied and the adsorption mechanisms were discussed.The results showed that MNP-CM-CDP can quickly adsorb four target pollutants.In particular,the adsorption of alkaline orange 2 by MNP-CM-CDP can reach 84%of the equilibrium adsorption capacity within 10 s and achieve adsorption equilibrium within 2 min.Further studies found that electrostatic interaction and the hydrogen bonding between MNP-CM-CDP and target pollutants were the main mechanisms of adsorption behavior.The stronger the hydrogen bonding and electrostatic interaction was,the faster the adsorption rate was,and the higher the adsorption capacity was.The pseudo-second-order kinetic model of adsorption kinetics of MNP-CM-CDP illustrated chemical adsorption dominated the adsorption.Humic acid and inorganic salts showed no significant effect on the adsorption properties of MNP-CM-CDP and excellent regeneration property was obtained.(3)The adsorption properties and adsorption mechanisms of Cr(?),Pb(?),Zn(?),Cu(?)and Cd(?)adsorbed by MNP-CM-CDP were studied.The results showed that MNP-CM-CDP can adsorb five heavy metals rapidly,especially Pb(?)and Cd(?).The adsorbed amount of Pb(?)and Cd(?)by MNP-CM-CDP can reach more than 70%of the equilibrium adsorption capacity within 10 s and can reach more than 92%of the equilibrium adsorption capacity within 1 min.Adsorption was dominated by chemical adsorption.The adsorption mainly depended on the complexation between the negatively charged carboxyl groups and the heavy metal ions and the interaction between the ions also affected the adsorption.Therefore,the effect of pH on the adsorption process of MNP-CM-CDP was obvious.When the pH value was lower than the isoelectric point,the carboxyl group on MNP-CM-CDP was protonated and the charge density was low,which showed the adsorption capacity of heavy metal ions decreased.When the pH value was higher than the isoelectric point,the carboxyl group gradually ionized.The adsorption capacity gradually increases.The adsorption performance of MNP-CM-CDP was less affected by inorganic salts.MNP-CM-CDP also showed excellent reproducibility.(4)The adsorption of BPA,MB and Cu(?)by MNP-CM-CDP in the unitary,binary and ternary systems,and the actual sewage system which added target pollutants was explored.It was found that the adsorption site of BPA by MNP-CM-CDP was independent of the adsorption sites of MB and Cu(?),and the adsorption capacity of BPA by adsorbent was not affected by the presence of MB and Cu(?).There was competitive adsorption between the MB and Cu(?)due to the same adsorption sites on MNP-CM-CDP.The adsorption performance of MNP-CM-CDP was less affected by the complex water quality of the actual sewage.The simulated printing and dyeing wastewater added with BPA,MB and Cu(?)was treated well by MNP-CM-CDP.The adsorbent exhibited good anti-pollution properties and stability,which was an effective advanced treatment method.