Study On The Functional Construction And Adsorption Mechanism Of Persimmon Tannin Materials

At present,water shortage has become one of the most concerned issues in the world.However,in the context of the rapid development of today's society,the natural environment is forced to“accept”a large amount of wastewater every year.The metal elements and organic dyes are the most common ones among these wastewaters.The entry of these contaminants into the natural environment will cause devastating impact on humans and other organisms.Therefore,it is imperative to study how to remove metal elements and organic dyes from water effectively.Persimmon tannin is a compound extracted from agricultural waste?persimmon?,which is rich in many phenolic hydroxyl groups,so it has excellent adsorption performance.In this paper,different methods have been used to functionalize persimmon tannin material to obtain two different adsorbents,and their adsorption properties for Er³⁺,organic dyes methylene blue?MB?and malachite green?MG?in water have been studied.The main contents are as follows:?1?An adsorbent?PT-GO?was prepared by functionalizing persimmon tannin?PT?with graphene oxide?GO?.The adsorption properties of the adsorbent for the organic dye methylene blue?MB?in water were discussed in depth,and the microscopic morphology,groups and element composition of the adsorbent were analyzed by means of characterization methods such as SEM,FTIR,XPS and BET.When pH=8,temperature is 323K,and MB concentration is 35 mg/L,the maximum adsorption capacity of PT-GO to MB dye reached 256.58 mg/g.The MB adsorption process is suitable for interpretation using the Freundlich isotherm model and the pseudo second-order kinetic model.It was found through calculation that the entire adsorption process is spontaneous and endothermic.The redox reaction,electrostatic interaction and?-?interaction between the MB and the PT-GO adsorbent determine the adsorption performance of the adsorbent.In addition,the regeneration experiment showed that the removal efficiency of MB by PT-GO adsorbent could still reach over80%after the fifth experiment.?2?A new magnetic adsorbent?Fe₃O₄/PT/GO?was prepared by hydrothermal method using Fe₃O₄ as magnetic core,persimmon tannin?PT?and graphene oxide?GO?as raw materials,and its adsorption capacity for organic dye malachite green?MG?in wastewater was investigated.The morphological structure,group composition and magnetization of the adsorbent were analyzed by physical characterization methods such as SEM,FTIR,BET,XRD and VSM.The results showed that the prepared Fe₃O₄/PT/GO adsorbent is an amorphous nanoparticle with a diameter of about 50¹00nm and a specific surface area of 53.83m²/g.In addition,the maximum magnetization value of this adsorbent is 22.2emu/g.When the initial concentration of MG is 150mg/L and pH=6 and the ambient temperature is 308K,the maximum adsorption capacity of Fe₃O₄/PT/GO to MG can reach 560.58mg/g,which is very close to the calculated value of 591.72mg/g.The whole process of MG adsorption onto Fe₃O₄/PT/GO is suitable for description by Langmuir isotherm model.At the same time,the pseudo-second-kinetic model can be used to better fit the experimental data.In addition,it was found that the process of MG adsorption is spontaneous and endothermic after the calculation of thermodynamics through the experimental data.?3?In order to further explore the adsorption capacity of Fe₃O₄/PT/GO on Er³⁺,this paper systematically discussed the adsorption performance of Fe₃O₄/PT/GO under different initial conditions.The results showed that the Fe₃O₄/PT/GO adsorbent can remove the Er³⁺in the aqueous solution effectively.When pH=4,the adsorbent dosage is 30mg and the temperature is 323K,the maximum adsorption capacity of the adsorbent for Er³⁺can reach 366.67 mg/g.Isothermal and kinetic experiments have proved that the loading process of Er³⁺into Fe₃O₄/PT/GO can be properly explained by Langmuir isothermal model and pseudo-second-order dynamic model.In addition,according to the calculation results of thermodynamic parameters,the whole adsorption process is endothermic and spontaneous.After each adsorption experiment,the Fe₃O₄/PT/GO adsorbent can be easily separated from the solution by means of an external magnetic field.Therefore,Fe₃O₄/PT/GO is an adsorbent that can effectively remove the Er³⁺from the aqueous solution.