Adsorption characteristics and mechanism of Pb(Ⅱ) on magnetic composite gel spheres
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摘要: 以海藻酸钠(SA)作为基体前驱材料,通过离子交联法包埋固化L-甲硫氨酸(L-met)和纳米Fe3O4形成磁性复合凝胶球SA@Fe3O4/L-met。实验探究了SA@Fe3O4/L-met在不同pH、投加量和初始离子浓度条件下对Pb(Ⅱ)吸附能力的影响。结果表明,在pH=5、投加量为0.5 g·L−1、初始浓度为20 mg·L−1时,SA@Fe3O4/L-met对Pb(Ⅱ)能达到较好的吸附效率,最大吸附量可达到328.02 mg·g−1,远大于Fe3O4@SA与SA的吸附量142.5 mg·g−1和152.8 mg·g−1。吸附动力学和热力学研究表明该吸附过程分别对准二级动力学方程和Langmuir方程的拟合程度更大,且反应过程是一个熵增吸热的过程。最后采用SEM、XPS、VSM等对SA@Fe3O4/L-met的结构与性能进行表征分析,发现SA@Fe3O4/L-met中的氨基和羧基通过配位反应与Pb(Ⅱ)结合,同时还存在着离子交换作用。经过5次解吸后SA@Fe3O4/L-met的吸附量仍能达到210.5 mg·g−1,是一种较理想的环保吸附剂。
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关键词:
- Pb(Ⅱ) /
- L-甲硫氨酸(L-met) /
- 海藻酸钠 /
- 吸附 /
- 磁性
Abstract: In this paper, SA@Fe3O4/L-met used sodium alginate (SA) as matrix precursor material, with magnetic composite gel balls obtained by immobilizing iron trioxide (Fe3O4) and L-methionine (L-met) by ion cross-linking. The influence of pH, dosage and initial concentration on Pb(Ⅱ) adsorption was explored. The results show that at pH=5, the dosage is 0.5 g·L−1, the initial concentration is 20 mg·L−1, SA@Fe3O4/L-met can achieve better adsorption efficiency for Pb(Ⅱ), and the maximum adsorption amount can reach 328.02 mg·g−1, much larger than the adsorption capacity of SA@Fe3O4 and SA, 142.5 mg·g−1 and 152.8 mg·g−1. Studies on adsorption kinetics and thermodynamics show that the adsorption process is aligned with the second-order kinetic equation and Langmuir equation to a greater degree of fit, and the reaction process is a process of entropy increase and heat absorption. The structure and performance of the gel sphere were characterized by using SEM, XPS and VSM. It was found that the amino groups, carboxyl groups and hydroxyl groups in the gel ball participating in the reaction process, combining with Pb(Ⅱ), and there also exists ion exchange. After 5 times of desorption, the adsorption capacity of the material can still reach 210.5 mg·g−1, which is an ideal environmentally friendly adsorbent.-
Key words:
- Pb(Ⅱ) /
- L-methionine (L-met) /
- sodium alginate /
- adsorption /
- magnetic
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表 1 SA@Fe3O4/L-met吸附Pb(Ⅱ)的准一级动力学与准二级动力学拟合
Table 1. Calculated kinetic parameters for adsorption of Pb(II) by the SA@Fe3O4/L-met
Co/(mg·L−1) Pseudo-first-order kineticmodel Pseudo-second-order kineticmodel Qe/(mg·g−1) k1 R2 Qe/(mg·g−1) k2 R2 50 95.116 0.04111 0.97535 94.6073 0.00281 0.99922 100 161.851 0.02371 0.91516 164.8347 0.00194 0.99966 200 325.131 0.02286 0.92226 323.8061 0.00129 0.99996 Notes: Co—Initial concentration of Pb(Ⅱ); Qe—Adsorption capacity at adsorption equilibrium; k1, k2—Adsorption constant; R2—Goodness. 表 2 SA@Fe3O4/L-met吸附Pb(Ⅱ)的吸附等温线模型拟合
Table 2. Isotherm model constants and correlation for adsorption of Pb(II) by the SA@Fe3O4/L-met
Temperature/℃ Langmuir Freundich Qmax/(mg·g−1) kL/(L·mg−1) R2 RL kF/(L·mg−1) n R2 25 330.430 0.032810 0.99977 0.03685 115.329 4.857 0.82080 35 333.011 0.042134 0.99982 0.02925 121.857 5.0457 0.83013 45 337.240 0.049391 0.99983 0.02521 129.423 5.2625 0.81762 55 342.271 0.057546 0.99986 0.02182 138.023 5.5236 0.81789 Notes: Qmax—Maximum adsorption capacity; kL—Langmuir equilibrium constant; kF—Freundich equilibrium constant; n-Adsorption intensity characteristic constant; RL—Determine the adsorption properties. 表 3 SA@Fe3O4/L-met的吸附热力学参数
Table 3. Thermodynamic parameters for adsorption of Pb(II) by the SA@Fe3O4/L-met
Temperature/℃ kF ∆G/(kJ·mol−1) ∆H/(kJ·mol−1) ∆S/(J·mol−1) 25 115.329 −11.76210 4.8667 55.8043 35 121.857 −12.29872 55.7319 45 129.423 −12.85728 55.7015 55 138.027 −13.43712 55.6541 Notes: kF—Freundich equilibrium constant; ∆G—Gibbs Free Energy; ∆H—Adsorption enthalpy change; ∆S—Adsorption entropy change. 表 4 SA@Fe3O4/L-met吸附量与其他吸附材的吸附量比较
Table 4. Adsorption results of Pb(II) onto different absorbents by the SA@Fe3O4/L-met
Adsorbent pH Reaction time/h Maximum adsorption capacity/(mg·g−1) References Silica modified calcium alginate–xanthan gum hybrid bead 5 3.3 18.9 ZHANG S, et al[21] Iron-oxide modified sericite alginate beads 5 15 133.73 LALHMUNSIAMARADHESHYAM R,et al[22] Sodium alginate/graphene oxide aerogel 5.5 4 267.4 JIAO C,et al[23] Hydrocolloid liquid-core capsules 5.5 3 300 NUSSINOVITCH A, et al[24] SA@Fe3O4/L-met 5 0.5 328.02 This paper Carboxylated cellulose nanocrystal/sodium alginate hydrogel beads 5 2 338.98 HU Z, et al[19] Magnetic carboxyl-functionalized attapulgite/calcium alginate beads 5 2 471.20 ZOU M F,et al[25] -
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