Structural Design Of Core-shell NaA Molecular Sieves And Their Adsorption Properties For Cu²⁺

The environmental pollution caused by the Cu²⁺has attracted widespread attention in the society.At present,the adsorption method is an effective way to solve this problem.Therefore,the preparation of efficient Cu²⁺adsorbent is particularly critical.Zeolite Na A is a porous material.At the same time,as a Cu²⁺adsorbent,it has been widely used in the treatment of Cu²⁺.However,zeolite Na A powder has the problem that it is difficult to be recovered in the actual Cu²⁺treatment process.Therefore,the magnetized zeolite Na A has become a hot spot to solve the the above problems.In this paper,magnetic Fe₃O₄nanoparticles are used as the magnetic core and zeolite Na A is used as the shell layer,and a novel core-shell structured magnetic Cu²⁺adsorbent-Fe₃O₄@zeolite Na A is successfully prepared.The influence of sodium hydroxide solution concentration,reaction time and reaction temperature on the crystallinity of Fe₃O₄@zeolite Na A was studied,and the optimal process condition for the synthesis of Fe₃O₄@zeolite Na A was obtained.At the same time,its performance and microstructure were studied.The effects of p H,adsorbent addition,adsorption time,initial Cu²⁺concentration and adsorption temperature on the adsorption performance of Fe₃O₄@zeolite Na A for Cu²⁺were studied.By studying the adsorption isotherm,adsorption kinetics and adsorption thermodynamics of the Fe₃O₄@zeolite Na A for the adsorption of Cu²⁺,the adsorption mechanism has been learned.The Cu²⁺adsorbent prepared in this paper has high reference value in the field of Cu²⁺treatment.The innovations of this paper are as follows:(1)The Fe₃O₄@SiO₂precursor with core-shell structure is synthesized,which can effectively protect the magnetic core composed of magnetic Fe₃O₄nanoparticles and prevent it from being oxidized in the next reaction.(2)The synthesis reaction of Fe₃O₄@zeolite Na A is carried out on the surface of Fe₃O₄@SiO₂precursor,which avoids the possibility of formation of non-core-shell structure zeolite Na A,and the SiO₂in the precursor can be used as the silicon source to form zeolite Na A.The results and main conclusions of this paper are as follows:(1)Magnetic Fe₃O₄nanoparticles were prepared by solvothermal method,and the optimal synthesis parameters were determined through single-factor experimental variable design:reaction temperature was 200?;sodium citrate content was 0.20g;ferric chloride content was 0.65g;The reaction time is 12h.FTIR results show that the prepared magnetic Fe₃O₄nanoparticles contain chemical bonds such as Fe-O bonds;HRTEM results show that the prepared magnetic Fe₃O₄nanoparticles are polycrystalline;VSM results show that the prepared magnetic Fe₃O₄nanoparticles have superparamagnetism,and the magnetic saturation intensity reaches50.9226emu·g^-1;The thermal stability results show that the heat treatment temperature of the prepared magnetic Fe₃O₄nanoparticles needs to be controlled below 220?.(2)The Fe₃O₄@SiO₂precursor was prepared by the sol-gel method,and the optimal synthesis parameters were determined through single-factor experimental variable design:the content of ammonia water was 2.0m L;the content of tetraethylorthosilicate was 2.0m L;the magnetic Fe₃O₄nanoparticles content are 20mg.HRTEM results show that the prepared Fe₃O₄@SiO₂precursor has a typical core-shell structure;VSM results show that the saturation magnetization of the Fe₃O₄@SiO₂precursor is 19.95emu·g^-1;The Fe₃O₄@zeolite Na A is prepared by the hydrothermal method.The single-factor experimental variable design determines the optimal synthesis parameters:the concentration of sodium hydroxide solution is2.0mol·L^-1;the reaction time is 10h;the reaction temperature is 110?.It is found that under these conditions,the crystallinity of the prepared Fe₃O₄@zeolite Na A is as high as 92.7%;FTIR results show that the prepared Fe₃O₄@zeolite Na A contains TO₄(T=Si or Al)tetrahedral internal bonds,Si-O bonds and other chemical bonds;TEM results directly show that the Fe₃O₄@zeolite Na A is a typical core-shell structure;VSM results show that the prepared Fe₃O₄@zeolite Na A has a magnetic saturation strength of 5.38emu·g^-1;at the same time,the simulation experiment proves the Fe₃O₄@zeolite Na A has fast magnetic response ability;thermal stability results show that the heat treatment temperature of the prepared Fe₃O₄@zeolite Na A needs to be controlled below 730?;BET results show that the specific surface area,pore volume and average pore diameter of the prepared Fe₃O₄@zeolite Na A are 26.846m²·g^-1,0.136697cm³·g^-1and 20.5846nm respectively.(3)The optimal conditions for the Fe₃O₄@zeolite Na A to adsorb Cu²⁺were determined through single-factor experimental variable design:p H is 4;adsorbent mass is 0.10g;adsorption time is 24min;initial Cu²⁺concentration is 200mg·L^-1;adsorption temperature is 298.15K.Under these conditions,the Fe₃O₄@zeolite Na A has the largest adsorption capacity for Cu²⁺,which is 86.54mg·g^-1.The adsorption isotherm results show that the Fe₃O₄@zeolite Na A adsorbs Cu²⁺as a single-layer adsorption;the adsorption kinetics results show that the Fe₃O₄@zeolite Na A adsorbs Cu²⁺mainly by chemical adsorption;the results of adsorption thermodynamics show that the adsorption of Cu²⁺by Fe₃O₄@zeolite Na A is a spontaneous and endothermic behavior,and the reaction proceeds in the direction of entropy increase.