Preparation Of Acrylic Acid/Enteromorpha Polysaccharide Composite Hydrogels And Its Adsorption Properties For Dye

With the rapid urbanization in China,the phenomenon of water pollution has become a major problem restricting the economy and society.Hydrogel is a kind of polymer three-dimensional network material with adsorption capacity,which can effectively adsorb dyes in water.However,many single-network hydrogels have some shortcomings such as poor mechanical properties,low adsorption capacity and inability to recycle.In this paper,the optimal preparation conditions of two kinds of acrylic-based enteromorpha polysaccharide hydrogels were determined by single factor method,and the structure of the hydrogels was characterized by FT-IR,SEM and XRD.Then the influence of different adsorption conditions on the adsorption properties of the composite hydrogels was studied by adsorption experiments,and the reusability of dyes was also determined.Finally,the adsorption thermodynamics and kinetics of the composite hydrogel were fitted and the adsorption mechanism of MB was analyzed by FT-IR,SEM and XRD.Specific research contents are as follows:Acrylic acid（AA）and Polysaccharides of enteromorpha prolifera（PEP）composite hydrogels were successfully prepared with AA and PEP as raw materials.Through single factor experiment,the optimum preparation conditions were as follows:the ratio of PEP to AA was 6:15,the temperature was 75℃,the time was 3 h,and the addition amount of N,N-methylene bisacrylamide（MBA）was 0.02 g.Compared with the single AA hydrogel,the swelling and mechanical properties of the composite hydrogel are significantly improved.The maximum equilibrium swelling ratio was 3100%,the maximum compressive strength was 0.98 MPa,the maximum tensile strength was 0.229 MPa,and the maximum tensile ratio at break was 800%.FT-IR results showed that the stretching vibration peak of the ether bond formed by graft copolymerization of AA and PEP appeared at 1130 cm^-1.The results of SEM showed that the composite hydrogels presented loose porous structure and the pore density of the hydrogels increased with the increase of PEP content.The results of XRD showed that the characteristic peaks of AA/PEP composite hydrogels were obviously widened at 20.4°and 30.5°.The effects of different dosage ratios of PEP and AA on the adsorption properties of composite hydrogels were studied by adsorption experiments.The results showed that the adsorption capacity and scavenging rate of MB on composite hydrogels increased with the increase of PEP content.Adsorption conditions were determined by single factor method:the time was 3 h,the temperature was 25℃,the dosage of adsorbent was 0.05 g,the initial concentration of MB was 40 mg/L,p H=7.At this time,the removal rate of MB was about 93.04%and the adsorption capacity was 156.31 mg/g.The composite hydrogel also showed repeated adsorption performance and the scavenging rate of MB could still reach90%after the first desorption.The results of adsorption thermodynamic simulation showed that the maximum correlation coefficient（R²>0.999）of Langmuir model indicates that the adsorption was a homogeneous monolayer adsorption;The simulation results of adsorption kinetics showed that the pseudo-second-order kinetic model（R²>0.999）fits better than the pseudo-first-order kinetic model,indicating that the adsorption belonged to chemisorption.The FT-IR,SEM and XRD characterization of the composite hydrogels adsorbed with MB showed that the-COO^-between-AA and PEP in the composite hydrogels and-N⁺（CH₃）₂in MB,and-OH formed hydrogen bonds with MB molecules to adsorb MB dyes.AA/PEP/Fe Cl₃composite hydrogels were successfully prepared by one-pot method in order to further improve the properties of the composite hydrogels.Through single factor experiment,the optimum preparation conditions were as follows:the ratio of PEP to Fe Cl₃was 60:1,the temperature was 65℃,the time was 3 h,MBA was 0.02 g.Compared with AA/PEP composite hydrogel,the swelling properties and mechanical properties of the composite hydrogel were significantly improved.The maximum equilibrium swelling ratio was 4800%,the maximum compressive strength was 0.96 MPa,the maximum tensile strength was 0.25 MPa,and the maximum tensile ratio at break was1150%.FT-IR results showed that the characteristic peak of-C=O in the composite hydrogel was red-shifted(1601 cm^-1)after Fe Cl₃was added.SEM results showed that the pore structure of AA/PEP/Fe Cl₃composite hydrogels was more homogeneous than that of AA/PEP/Fe Cl₃composite hydrogels.XRD results showed that the diffraction peak of AA/PEP/Fe Cl₃composite hydrogel was very obvious at 38.47°.The effects of different dosage ratios of PEP and Fe Cl₃on the adsorption properties of composite hydrogels were studied by adsorption experiments.The results showed that the addition of Fe Cl₃could enhance the adsorption effect of composite hydrogels on MB.The adsorption conditions were determined by single factor experiments:the time was 3 h,the temperature was25℃,the dosage of adsorbent 0.05 g,the initial concentration of MB was 200 mg/L,p H=6.At this time,the maximum scavenging rate of MB was about 97.5%,the adsorption capacity was 863.08 mg/g,and the adsorption rate of MB was still 93%after the first desorption.Adsorption thermodynamic simulation results showed that Freundlich model fitting correlation coefficient（R²>0.999）was the largest,indicating that the adsorption was multi-molecular layer adsorption;The simulation results of adsorption kinetics showed that the pseudo-second-order kinetic model（R²>0.999）showed that the adsorption was chemisorption.The results of FT-IR,SEM and XRD characterization of MB adsorbed on AA/PEP/Fe Cl₃composite hydrogels showed that MB adsorbed on AA/PEP/Fe Cl₃composite hydrogels was mainly through hydrogen bonding,electrostatic adsorption and ion adsorption.