Adsorption Performance Of COFs/Chitosan Composites On Dyes And Heavy Metal Ions In Printing And Dyeing Wastewater

With the rapid development of China’s industry,dyestuffs are widely used in textile and leather fields,and the discharge of printing and dyeing istewater has grown.Untreated istewater will not only pollute water quality and harm aquatic organisms,but also cause cancer in human body.For this reason,it is important to study adsorbents with good adsorption properties for printing and dyeing istewater.In this paper,we prepared water-resistant enol-keto interconversion covalent organic framework material(Tp Pa COF)and investigated the removal effect and adsorption mechanism of cationic and anionic dyes and heavy metal ions by the composite material prepared from it and chitosan.The optimal adsorption conditions for methylene blue,acidic medium brown and Cr(VI)are explored by adsorbent ratio,mass,solution p H and temperature,and the data obtained from the adsorption experiments are fitted to the model of adsorption kinetics and thermodynamics.Finally,the adsorbents are characterized by several instruments such as SEM,XRD,XPS and FTIR.The adsorption results for the three pollutants are presented below.(1)The optimal conditions for the adsorption of methylene blue dye by COFs/chitosan composites are explored by single factor analysis.The optimum p H for adsorption is determined to be 9,the temperature to be 40 ℃,the mass of adsorbent to be 0.25 g/L,and the ratio of Tp Pa COF to chitosan to be 2:1.The maximum adsorption capacity of the adsorbent to the dye is 831.3 mg/g.The successful adsorption of the dye is demonstrated by SEM,XPS,FTIR and other means.The results based on the adsorption kinetics and thermodynamic model fitting showed that quasi-secondary kinetics and Langmuir’s model better explained the whole adsorption process,indicating that the COFs/chitosan composite adsorbed methylene blue dye mainly by monolayer adsorption and the surface is homogeneous.(2)The optimal conditions for the adsorption of acidic medium brown are explored.The optimum p H for adsorption is determined to be 4,the temperature is 40 ℃,the mass of adsorbent is 0.25 g/L,and the ratio of Tp Pa COF to chitosan is 1:4.The maximum adsorption capacity of the adsorbent is 1287.6 mg/g.The successful adsorption of the dye is demonstrated by SEM,XPS,FTIR and other means.The adsorption kinetic and thermodynamic model fitting results showed that the quasi-secondary kinetic and Langmuir models better explained the adsorption process.(3)The optimal conditions for Cr(VI)adsorption experiments are explored.The optimum p H of Cr(VI)adsorption is determined as 4,the mass of adsorbent is 0.45 g/L,the mass ratio of chitosan to zero-valent iron is 1:1,and the temperature is 40 ℃.The maximum adsorption amounts of Cr(VI)by the adsorbent are 63.64 mg/g,respectively,and the successful adsorption of heavy metal ions is demonstrated by SEM,XPS,FTIR and other means.The results of adsorption kinetics and thermodynamic model fitting indicated that quasi-secondary kinetics and Freundlich model could better explain the whole adsorption process.It indicates that the chitosan-loaded zero-valent iron composites adsorb Cr(VI)mainly by multilayer adsorption and the adsorption surface is heterogeneous.