Preparation And Characterization Of Renewable Double Network Hydrogels For Adsorption

Organic dyes such as textile,smelting,and printing are widely used in industries,which brings convenience to people’s lives.However,it also brings a lot of dye wastewater.If dye wastewater is directly discharged into the water environment without any pretreatment,it will not only cause serious pollution but also cause certain harm to human health.Adsorption method has become the focus of water treatment technology among all methods of wastewater treatment because of its low cost,simple operation,and high efficiency.Hydrogel,as a strong adsorption polymer material with three-dimensional network structure,is a good material for sewage treatment as adsorbent.However,most hydrogels have poor regenerative properties,excessive swelling,and poor mechanical properties when they are used to adsorb materials.Therefore,this research has developed two kinds of double network hydrogels named oxidized starch-polyvinyl alcohol/poly(methacryloxy ethyl three methyl ammonium chloride-acrylamide amide)(OS-PVOH/P(DMC-AM))and oxidized starch polyvinyl alcohol/poly(acrylic acid-acrylamide amide)(OS-PVOH/P(AA-AM)),which are low in cost,low in swelling and have good mechanical and regenerative properties when applied to the adsorption of methylene blue.The swelling,compression,adsorption,and regeneration properties of the two materials were studied.The microstructure and morphology of the two materials were analyzed by SEM,FT-IR,XRD,and TGA.A series of adsorption experiments were carried out to study the effects of different pH,hydrogel quality,temperature,and initial methylene blue concentration on the adsorption properties of the materials and their regeneration properties.Their adsorption isotherms,adsorption kinetics,and adsorption thermodynamics were also explored.The specific research is as follows:(1)OS combined with PVOH to form the first network of double-network hydrogel,and AM and AA copolymerized as the second network,OS-PVOH/P(DMC-AM)double network hydrogel with three-dimensional porous structure was successfully prepared.The properties of the material were the best when the solution concentration of OS and PVOH were 9 wt%and 5 wt%,respectively,the compression modulus was 2.01 MPa and the swelling degree was 11.2 g/g.The results of adsorption experiments showed that the increase of adsorbent quality can improve the removal rate of MB,but the adsorption capacity would decrease;the increase of initial MB concentration would reduce the removal rate and increase the adsorption capacity;the best pH of the material for MB adsorption is 8;as the temperature increased from 15℃ to 45℃,the adsorption property of the material improved;the adsorption of MB followed the pseudo-second-order kinetic model,which showed the adsorption was more dependent on chemical adsorption such as electrostatic adsorption;the adsorption isotherm conformed the Langmuir model,which meant single molecular layer adsorption,and the maximum theoretical adsorption capacity of the material was 666.6 mg/g at 25℃.The result of thermodynamics also showed that the adsorption process of the material was endothermal and tended to be spontaneous.(2)By using OS and PVOH to form the first network of double network hydrogel,and copolymerization of AM and AA as the second network,OS-PVOH/P(AA-AM)double network hydrogel with three-dimensional porous structure was successfully prepared.The properties of the material were the best when AA:AM is 3:1,the compression modulus was 1.85 MPa and the swelling degree was 12.7 g/g.The results showed that the removal rate increased but the adsorption capacity decreased with the increase of adsorbent quality;the increase of initial MB concentration would reduce the removal rate and increase the adsorption capacity;the adsorption performance of the material is the best when the pH is 8;the temperature rises from 15℃ to 45℃ is favorable for the adsorption of the material;the adsorption of MB followed the pseudo-second-order kinetic model;the adsorption isotherm conformed the Langmuir model and the maximum theoretical adsorption capacity of materials is 2163.0 mg/g at 25℃;adsorption thermodynamics shows that the adsorption process of materials is a process of heat absorption,and the whole process tends to be disorderly spontaneous.The adsorption properties of OS-PVOH/P(AA-AM)double network hydrogel were better than that of OS-PVOH/P(DMC-AM)double network hydrogel,indicating that the introduction of AA molecules improved the adsorption performance.(3)The results of regeneration experiments showed that the optimal desorption conditions of OS-PVOH/P(DMC-AM)double network hydrogels were 60 min treated with 20 mL 0.2 mol/L HCl,and the removal rate of MB still reached 93.4%after 5 times adsorption,the desorption rate after 5 times was still higher than 74.2%.The best desorption conditions for OS-PVOH/P(AA-AM)double network hydrogels are 180 min treated with 20 mL 0.3mol/Ld HCl.After 5 times adsorption,the removal rate of MB can still reach 97.1%,and the desorption rate after 5 times was still higher than 69.4%.SEM showed that the pore size of the adsorbed materials decreased obviously,and the pore size decrease;FT-IR and XRD showed that the functional groups and crystal structure of the two materials did not change significantly after adsorption,indicating the stability of the two materials.In summary,OS-PVOH/P(DMC-AM)double-network hydrogel and OS-PVOH/P(AA-AM)double-network hydrogel prepared in this study are great adsorption materials with good regeneration performance,which may have good application prospects in dye wastewater treatment.