Study On Adsorption Characteristics Of Diclofenac Sodium In Water By Chitosan Based Composite Adsorbent

The problem of wastewater discharge is becoming more and more serious in China,and diclofenac,as a new pollutant widely distributed in water,has attracted much attention in the study of its removal.Adsorption method is the most commonly used physical method to remove trace organic pollutants in water,which has been widely used in the removal of drugs and other pollutants in water sources and wastewater.In order to improve the adsorption capacity of diclofenac,different adsorbents have been developed to adsorb diclofenac in water.Chitosan is a kind of cationic biopolymer,which is selected as an ideal adsorption material because of its low cost,non-toxic,biodegradable and rich amino and hydroxyl functional groups.However,the unmodified chitosan material not only has poor stability in acid solution,but also is difficult to recover,and the adsorption effect for diclofenac acid is poor.Based on the above defects of chitosan,two kinds of chitosan-polydopamine hydrogel（CS-PDA）and hollow magnetic modified chitosan nanospheres（Hollow Si O₂/Fe₃O₄@（CS-PDA））were designed and synthesized in this paper.These two kinds of chitosan modified/composite materials have high adsorption rate,large adsorption capacity and easy separation and recovery.The main research contents and conclusions are as follows:（1）Chitosan-polydopamine modified hydrogel（CS-PDA）was prepared by grafting polydopamine onto chitosan with chitosan as the substrate by photoinitiation method.SEM results showed that the material was reticulated and porous.BET test results showed that the specific surface area of CS-PDA was 1.12 m²·g^-1.（2）The results show that the dopamine on CS-PDA is grafted on the amino side of chitosan C₂ site,and abundant aromatic ring structure and pyrrole nitrogen are found,which indicates that dopamine can self polymerize at room temperature in the process of photoinitiation and form polydopamine.The structure of polydopamine contains abundantπelectron cloud,which is the adsorption of diclofenac containingπsystem Some theoretical basis is provided.The results of material characterization also showed that the hollow Si O₂/Fe₃O₄@（CS-PDA）microspheres were nanoscale,with obvious core-shell structure and uniform particle size distribution.（3）Through the polymer-hard template method,the hollow Si O₂/Fe₃O₄@（CS-PDA）nanospheres were prepared,the result of high-resolution electron microscopy showed that uniform nanometer microspheres particle size,morphology,uniform at about 250 nm in diameter,according to the specific surface area,according to the results of test materials for specific surface area of 119.92 m²·g^-1,specific surface area increase significantly.X-ray diffraction test results show that the properties of Fe₃O₄ nanoparticles loaded by the co-precipitation method are stable.The results of magnetic hysteresis loop show that the material has soft magnetic properties,and the magnetic separation effect is good.（4）The adsorption of diclofenac sodium by CS-PDA and Hollow Si O₂/Fe₃O₄@（CS-PDA）was investigated.The adsorption kinetics of diclofenac followed the pseudo-second-order kinetics model.The adsorption equilibrium of CS-PDA was achieved at 360min,and the adsorption equilibrium of Hollow Si O₂/Fe₃O₄@（CS-PDA）was achieved at180 min.The isotherm experimental data of CS-PDA had a good correlation with the fitting results of Langmuir isotherm model.The adsorption of diclofenac sodium might be chemisorption.The maximum adsorption capacity(q_max)of diclofenac by CS-PDA was 333.25 mg·g^-1 when the initial p H of the solution was 4.2 and the temperature was25℃.After seven cycles of regeneration,the adsorption capacity of diclofenac sodium remained at a high level,greater than 70 mg·g^-1.The adsorption kinetics of diclofenac sodium by Hollow Si O₂/Fe₃O₄@（CS-PDA）followed the pseudo-second-order kinetics model,and the Langmuir and Temkin isotherm models showed a good correlation with the experimental data.The maximum adsorption capacity(q_max)of diclofenac sodium by Hollow Si O₂/Fe₃O₄@（CS-PDA）nanospheres was 531.47 mg·g^-1.（5）Combined with the influence of p H and characterization information,the adsorption mechanism of diclofenac sodium by the two materials was investigated.Material surface under acid environment must carry a large amount of positive charge,adsorption of diclofenac sodium on electrostatic attraction,with increasing p H of solution,Zeta potential on the surface of the material is reduced,when the p H value is greater than the material after zero isoelectric point,material surface,negatively charged with diclofenac anion（-COO^-）between the static gravity weakened dramatically,due to the introduction of the poly(dopamine,material surface hydroxyl（-OH）and aromatic ring content increased dramatically,in alkaline environment,thanks toπ-πaccumulation effect and hydrogen bond force（H-bond）,the adsorption effect was not significantly reduced.