Preparation Of Polymer Adsorbents And Study On Their Performance And Mechanism

China is the largest country of dye production and consumption in the world,and the discharge of organic dye polluted wastewater continues to increase,bringing great challenges to the natural water system.Therefore,it is important to develop efficient and low-cost organic dye adsorption technology for China’s ecological security and human health.Organic polymers are characterized by diversity,low cost,high skeleton strength,stable chemical properties,controllable surface functional groups,good reproducibility and low environmental toxicity,and have great application potential in the adsorption field.However,the existing polymer-based adsorbents still have some key problems such as complex functionalization process,low mechanical strength,slow adsorption rate,and difficult to recovery.In addition,the dynamic filtration system based on adsorbents has problems of low efficiency and high energy consumption.Therefore,it is still necessary to continue to develop advanced polymer adsorbents with high adsorption efficiency,fast adsorption rate,high mechanical strength and easy regeneration,so as to improve the application prospect of polymer-based adsorbents in the field of water pollution treatment.In this study,three polymer-based adsorption materials,including quaternized chitosan/cellulose hydrogel,highly entangled acrylic acid acrylamide copolymer and ammoniated polystyrene/maleic anhydride hollow microsphere membrane,have been developed through molecular function design and material structure control for efficient adsorption of organic dyes in water.The physical properties and chemical composition of the three polymer adsorbents are analyzed by SEM,XPS,FT-IR,BET and other characterization techniques.The adsorption efficiency of the three materials is tested,including the main influencing factors,reproducibility and adsorption selectivity.The adsorption mechanism of the three polymer materials to dyes is analyzed through adsorption isotherms,thermodynamic and kinetic models and the interaction between the materials and typical dyes.In view of the complex process of introducing functional groups into natural polymer networks,a new type of double cation epoxy crosslinker（N,N’-diglycidyl-N,N,N’,N’-tetramethyl-1,3-propane diammonium dichloride,DCER）is synthesized.Each DCER molecule contains two epoxy groups for crosslinking and two quaternary ammonium groups for adsorption.A large number of quaternary ammonium groups can be introduced into the chitosan/cellulose hydrogel network through simple one-step crosslinking.The DCER crosslinked hydrogel can be used for the efficient removal of the anionic dye congo red,with the maximum adsorption capacity of 1480.5 mg/g,which is 7 times higher than that of the glutaraldehyde crosslinked hydrogel.The DCER hydrogel shows very high adsorption efficiency for anionic dyes under acidic,neutral and alkaline conditions.The adsorption isotherm and kinetics study reveal that the adsorption of Congo red conforms to Langmuir isotherm and pseudo-second-order kinetics.The DCER crosslinked hydrogel shows good stability,and can be reused for 5times with only 6%efficiency decreasing.Mechanism analysis shows that hydrogen bond and charge interaction are responsible for adsorption.Aiming at the poor mechanical properties of ordinary hydrogel adsorbents and the conflict between swelling and adsorption,a strategy of using entanglements to replace partial cross-links is proposed to improve the mechanical properties and adsorption efficiency of hydrogel networks.Entanglements act as additional crosslinks to inhibit swelling.Unlike fixed chemical crosslinks,entanglements are flexible and can effectively transfer the stress along chains,making hydrogel show high elasticity and high toughness.Mechanical tests show that the maximum tensile strain of highly entangled hydrogel is 920%with the breaking strength of 0.46 MPa,and the compressive strength at 75%strain is as high as 0.95 MPa.The hydrogel also has good fatigue resistance and can withstand400%cyclic tensile deformation or 50%cyclic compression deformation for 20times.Entanglements enable the swelling of hydrogel controllable conversion through p H,and the network can expand more than 10 times under alkaline conditions,promoting the adsorption of pollutants,while de-swelling under acidic solution to improve the reproducibility.The maximum adsorption of highly entangled hydrogel for methylene blue is 1310.2 mg/g,more than 10 times higher than that of ordinary hydrogels.Entanglements is stable enough and the adsorption efficiency only decreases by 2.3%after 10 times of regeneration.Mechanism study shows that the adsorption of cationic dyes on highly entangled hydrogels is mainly depended charge interaction.Due to the high pressure,low flux and insufficient utilization of adsorption sites in existing adsorbent based filtration systems,a membrane based on ammoniated polystyrene/maleic anhydride（PSMM-NH₂）hollow microsphere is prepared.The structure of hollow microspheres makes the adsorption sites be fully exposed on the surface and grafting small amine molecules effectively avoids overlapping adsorption sites,which greatly reduces the distance and resistance of pollutant diffusion.Therefore,the PSMM-NH₂ microsphere shows extremely fast adsorption rate and high utilization of adsorption sites.At low acid red concentration（10 mg/L）,the adsorption capacity is as high as 850 mg/g,which is89%of the maximum adsorption capacity.The adsorption kinetics study shows that the microsphere can completely remove acid red in water within 10 min.In addition,the microsphere has stable physical and chemical properties,and the removal rate still exceeds 99%after five regenerations.The mechanism of acid red adsorption on PSMM-NH₂ is based on electrostatic attraction and hydrogen bond.The filtration test shows that the PSMM-NH₂ membrane can efficiently filtrate of acid red from water under gravity.After filtering 4000 L/m² of dye solution,the removal of acid red is still higher than 99%,and the average flux is as high as 3000 L/（m²·h）.After filtration,the adsorption capacity of microspheres is 750 mg/g,about 78.9%of the maximum adsorption capacity.