Preparation Of Terminal Amino Hyperbeanched Polymer Modified Walnut Shell And Its Adsorption Of Pb²⁺,Cd²⁺ And Cu²⁺

Walnut shell（WNS）contains a large amount of cellulose,and a large amount of active groups are introduced on the surface of the walnut shell by chemical modification method to prepare a heavy metal ion high-efficiency adsorbent for treating heavy metal ion wastewater.In this paper,glycidyl methacrylate（GMA）monomer was introduced into the walnut shell by grafting reaction,and then further modified with hyperbranched polyethyleneimine（HPEI）to introduce amino group and imino group to prepare hyperbranched Polyethyleneimine（HPEI）modified walnut shell high efficiency adsorbent.Firstly,GMA was used as the grafting monomer,and the walnut shell powder with the particle size of 74μm was graft polymerized to obtain the grafted GMA of walnut shell.The structure was characterized by FTIR,XRD and SEM.The results showed that the GMA monomer was successfully grafted onto the walnut shell.Further optimization conditions of walnut shell graft GMA（WNS-g-GMA）were obtained by single factor experiment:The input ratio of 4.0 g walnut shell powder,initiator and walnut shell powder was 2.25,the temperature was 10°C,the input ratio of GMA monomer and walnut shell powder was 1.75,and the reaction time was 60 min.The obtained walnut shell grafted GMA was further functionalized with HPEI as a modifier.The structure of HPEI modified walnut shells was characterized by FTIR,TGA,XRD,EDS and SEM.The results showed that the HPEI modified walnut shells were successfully prepared.The optimized reaction conditions for HPEI modified walnut shells were obtained by single factor experiment:1.0 g of walnut shell grafted GMA,the ratio of1,4-dioxane to distilled water was 5:2,the temperature was 85°C,the HPEI and walnut shell graft input ratio was 6.0,and the reaction time was 30 h.The adsorption behaviors of Cu²⁺,Cd²⁺and Pb²⁺in HPEI modified walnut shells under initial pH,adsorbent dosage,adsorption time,adsorption temperature and initial concentration were investigated by dynamic adsorption experiments.The optimal adsorption conditions were determined.The adsorption kinetics,isothermal adsorption and adsorption thermodynamics of Cu²⁺,Cd²⁺and Pb²⁺in HPEI modified walnut shells were further investigated.The results showed that the adsorption kinetic equations were consistent with the quasi-secondary kinetic model;the adsorption isotherms were consistent with the Langmuir model.At25°C,the maximum adsorption capacities of HPEI modified ordinary walnut shell adsorbents for Pb²⁺,Cd²⁺and Cu²⁺were 1250.00 mg/g,666.67 mg/g and 588.24 mg/g,respectively.The maximum adsorption capacity of the modified alkalized walnut shell to Pb²⁺was 1315.79 mg/g.The adsorption thermodynamics results show that the adsorption process is a process of spontaneous,endothermic and entropy increase.The results of the regeneration cycle performance test show that after 5 cycles of experiments,the adsorption percentage of the adsorbent can still reach more than 90%.