Preparation Of Polyvinyl Alcohol/ZIFs Composite Films And Study On Adsorption Properties

With the development of industry,the problem of water pollution is becoming more and more serious.There are many kinds of metal ions and organic matter in printing and dyeing wastewater,which is difficult to treat.Therefore,dye pollution has become one of the most serious pollution at present.Congo Red（CR）is one of the most representative benzidine azo dyes,which is soluble in water and can cause great harm to the environment.Traditional wastewater treatment methods such as physical method,chemical method and biological sedimentation method in the treatment of printing and dyeing wastewater,with more or less defects,such as secondary pollution,expensive and cumbersome manufacturing process.Therefore,it can not be widely used in the field of dyeing wastewater treatment.Adsorption method is widely used because of its economical,environmental protection,simple operation characteristics.Therefore,the development of cheap and environmentally friendly adsorption materials has become one of the hot research directions in recent years.Polyvinyl alcohol（PVA）has attracted much attention in the adsorption field because of its low price,good chemical stability,degradability,good film formation,and adsorption capacity for dyes.Although PVA has excellent properties,its water solubility and mechanical properties are poor,and its adsorption capacity for dyes needs to be improved,which limits the application of PVA.So PVA was modified by Zeolitic Imidazolate Framework-8（ZIF-8）and Zeolitic Imidazolate Framework-67（ZIF-67）respectively in this paper.The structure of the modified PVA/ZIFs composite film was characterized and its properties were investigated.The main research contents and results of this paper are as follows:（1）The ZIF-8 was prepared by modified method,and the ZIF-8 crystals were characterized by FTIR,XRD,SEM,N₂adsorption,and desorption isotherm.The results shows that the prepared ZIF-8 crystals is consistent with the literature.The adsorption performance experiment of ZIF-8 shows that ZIF-8 has the best adsorption effect on 95 mg/L of CR solution at 20℃and p H=7,and the adsorption capacity can reach 671.41 mg/g.In addition,the adsorption of CR by ZIF-8 conforms to the quasi-second-order adsorption kinetic model.The adsorption process is mainly chemical adsorption,and the hydrogen bond and electrostatic interaction are the dominant roles.（2）Different ratios of PVA/ZIF-8 composite film were prepared,by adjusting the amount of ZIF-8,and its properties were investigated;The results shows that the mechanical properties and water stability of PVA/ZIF-8 composite film are the best,when the addition of ZIF-8 is 10%.The tensile strength of PVA/ZIF-8 composite film is 28.22 MPa,which have risen by 52%compare with pure PVA film of 18.61 MPa.The water absorption and solubility of the composite film are 36.91%and 8.96%,respectively,which decrease by 149.43%and 62.25%compared with 186.34%and71.21%of the pure PVA film,the water stability of composite film is greatly improved.The composite film has the best adsorption effect on CR solution of 95mg/L,when the temperature is 20℃,p H=7,the maximum adsorption capacity is159.63 mg/g,which is 6.08 times compare with pure PVA membrane of 22.53 mg/g.After 4 cycles of PVA/ZIF-8 composite film,the adsorption rate of CR solution remains 94%.（3）ZIF-67 material was prepared according to the documented methods,and the prepared ZIF-67 material was characterized by FTIR,XRD,SEM and BET.The results show that the prepared ZIF-67 material is consistent with the literature reports.The PVA/ZIF-67 composite films,with different proportions of ZIF-67 were prepared,and the properties of the composite film were investigated.The results show that the overall performance of PVA/ZIF-67 composite film is the best,when the proportion of ZIF-67 material is 10%.And,the solubility and water absorption of PVA/ZIF-67composite film are 6.63%and 25.39%,respectively,which are reduced by 64.58%and160.95%,compared with pure PVA film.The composite film has the best adsorption effect on 95 mg/L CR,at p H=7,20℃,and the maximum adsorption capacity is198.79 mg/g,which is about 8.8 times compare with pure PVA film.In addition,after4 times of recycling,the adsorption rate of PVA/ZIF-67 composite film on Congo red solution remains 93%.