Preparation of gelatin-carboxymethyl chitosan-ZIF-8 composite aerogel for adsorption of Pb(II)
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摘要: 随着经济的不断发展，重金属污染对生态系统带来了严重的环境风险。因此，制备绿色环保且高效的重金属吸附新材料已成为当前研究领域中备受关注的热点。本研究以明胶(Gel)和羧甲基壳聚糖(CMCS)为载体，通过简单的掺杂法引入ZIF-8，制备一种具有三维多孔结构的明胶-羧甲基壳聚糖-ZIF-8复合气凝胶(GCZ-4)，采用扫描电子显微镜(SEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)对复合气凝胶的形貌和结构进行了表征，并将其用于水中Pb2+的吸附。结果表明：该复合气凝胶对Pb2+表现出优异的吸附能力，由Langmuir吸附等温模型计算得到的复合气凝胶对Pb2+的最大理论吸附量达367.42 mg·g−1，吸附过程为自发放热过程，并且遵从准二级动力学模型，属于化学吸附。此外，经过5次吸附-脱附试验，复合气凝胶仍对Pb2+保持较高的吸附性能。总的来说，GCZ-4复合气凝胶能够有效去除水中的Pb2+，是一种环保、经济、可回收的吸附剂。Abstract: With the continuous development of the economy, heavy metal pollution has posed serious environmental risks to ecosystems. Consequently, developing efficient and environmentally friendly new adsorption materials for heavy metal has become a current research focus. In this work, a gelatin-carboxymethyl chitosan-ZIF-8 composite aerogel (GCZ-4) with a three-dimensional porous structure was prepared by incorporating ZIF-8 through a simple doping method using gelatin (Gel) and carboxymethyl chitosan (CMCS) as carriers. The morphology and structure of the GCZ-4 were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Furthermore, a series of adsorption experiments were carried out to optimize the various parameters affecting Pb2+ adsorption behaviors. The results demonstrate that the composite aerogel exhibits excellent adsorption capacity for Pb2+. According to the Langmuir adsorption isothermal model, the maximum theoretical adsorption capacity of the composite aerogel for Pb2+ is 367.42 mg·g−1. The whole adsorption process was a spontaneous exothermic process and followed the pseudo-second-order kinetic model, indicating chemisorption behavior. Moreover, even after five cycles of adsorption-desorption tests, the composite aerogel maintains high performance in removing Pb2+. Overall, the GCZ-4 composite aerogel is an eco-friendly, cost-efficient, and recyclable adsorbent that effectively removes Pb2+ from water.
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Key words:
- gelatin /
- carboxymethyl chitosan /
- ZIF-8 /
- aerogel /
- adsorption
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图 1 明胶-羧甲基壳聚糖-ZIF-8复合气凝胶(GCZ-4)复合气凝胶图
Figure 1. Picture of gelatin-carboxymethyl chitosan-ZIF-8 composite aerogel (GCZ-4) composite aerogel
图 3 (a)、(b) GC复合气凝胶平面和截面SEM图，(c) GC复合气凝胶截面局部放大SEM图；(d)、(e) GCZ-4复合气凝胶平面和截面SEM图，(f) GCZ-4复合气凝胶截面局部放大SEM图；(g)GCZ-4复合气凝胶EDS能谱图
Figure 3. (a), (b) SEM images of GC composite aerogel plane and section, (c) SEM images of GC composite aerogel section with local amplification; (d), (e) SEM images of GCZ-4 composite aerogel plane and section, (f) SEM images of GCZ-4 composite aerogel section with local amplification, (g) the EDS spectrum of GCZ-4 composite aerogel
图 4 ZIF-8、CMCS、Gel、GCZ-4复合气凝胶的FT-IR图
Figure 4. FT-IR spectrum of ZIF-8, CMCS, Gel, and GCZ-4 composite aerogel
图 5 GC复合气凝胶和GCZ-4复合气凝胶XRD图
Figure 5. The XRD of GC composite aerogel and GCZ-4 composite aerogel
θ—Diffraction angle
图 6 不同原料配比对GC复合气凝胶吸附Pb2+的影响
Figure 6. Effects of different raw material ratios on adsorption of Pb2+ by GC composite aerogel
图 7 ZIF-8投加量对GCZ复合气凝胶吸附Pb2+的影响
Figure 7. Influence of different dosage of ZIF-8 on adsorption of Pb2+ by GCZ composite aerogel
图 8 溶液pH与GCZ-4复合气凝胶吸附Pb2+去除率和吸附量的关系
Figure 8. Relationship between solution pH and the removal and adsorption capacity of Pb2+ by GCZ-4 composite aerogel
qe—Equilibrium adsorption capacity
图 9 温度与GCZ-4复合气凝胶吸附Pb2+吸附量的关系
Figure 9. Relationship between temperature and the adsorption capacity of Pb2+ adsorbed by GCZ-4 composite aerogel
t—Adsorption time
图 10 GCZ-4复合气凝胶吸附Pb2+的Langmuir模型(a)、Freundlich模型(b)
Figure 10. Langmuir model (a) and Freundlich model (b) of GCZ-4 composite aerogel adsorption of Pb2+
ce—Equilibrium concentration of the Pb2+ solution
图 11 吸附时间与CGZ-4复合气凝胶吸附Pb2+吸附量的关系
Figure 11. Relationship between adsorption time and the adsorption capacity of Pb2+ adsorbed by CGZ-4 composite aerogel
$ {\text{q}}_{\text{t}} $—Adsorption capacity at time t
图 12 GCZ-4复合气凝胶吸附Pb2+的准一级动力学拟合曲线(a)、准二级动力学拟合曲线(b)和粒子内扩散拟合曲线(c)
Figure 12. Pseudo -first-order kinetic fitting curve(a), pseudo-second-order kinetic fitting curve(b), and in-particle diffusion fitting curve(c)of GCZ-4 composite aerogel adsorption of Pb2+
图 13 GCZ-4复合气凝胶对Pb2+、Ag+、Cd2+、Cu2+的选择性吸附性能
Figure 13. Selective adsorption properties of GCZ-4 composite aerogel for Pb2+、Ag+、Cd2+、Cu2+
图 14 循环次数与GCZ-4复合气凝胶对Pb2+吸附量和去除率的关系
Figure 14. Relationship between cycle time and the removal and adsorption capacity of Pb2+ by GCZ-4 composite aerogel
图 15 GCZ-4复合气凝胶吸附Pb2+前后的XPS图谱(a)XPS总谱图；(b~f)C、O、N、Zn、Pb元素吸附前后的精细谱图
Figure 15. XPS spectra before and after GCZ-4 composite aerogel adsorption Pb2+ (a) Total XPS spectra; (b~f) Fine spectra of C, O, N, Zn and Pb before and after adsorption.
图 16 GCZ-4复合气凝胶吸附Pb2+机理图
Figure 16. Mechanism of adsorption of Pb2+ by GCZ-4 composite aerogel
表 1 GCZ-4复合气凝胶吸附Pb2+在不同初始浓度的平衡浓度和吸附量
Table 1. The equilibrium concentrations and adsorption capacities for Pb2+adsorption by GCZ-4 composite aerogel at different initial concentrations
c0 /(mg·L−1) ce /(mg·L−1) qe/(mg·g−1) 50 7.8 112 100 13.5 168 150 26.61 210 200 38.48 230 250 52.8 246 300 104.4 267 Notes：$ \text{}\text{c}\text{0} $—initial concentration of the Pb2+ solution；ce—equilibrium concentration of the Pb2+ solution；qe—equilibrium adsorption capacity. 
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表 2 GCZ-4复合气凝胶吸附Pb2+的Langmuir模型和Freundlich模型拟合参数
Table 2. Fitting parameters of Langmuir model and Freundlich model for Pb2+adsorption by GCZ-4 composite aerogel
Langmuir model Freundlich model qm/(mg·g−1) KL R2 RL KF n R2 367.42 0.086 0.992 0.104 79.68 3.663 0.798 Notes：qm—the maximum theoretical adsorption capacity; R2—linear correlation coefficient; $ {K}_{\mathrm{L}} $—Langmuir adsorption coefficient; $ {K}_{\mathrm{F}} $—Freundlich adsorption coefficient; n—the adsorption strength constant, RL—the separation factor.
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表 3 不同吸附剂材料对Pb2+的最大吸附量比较
Table 3. Comparison of adsorption properties of different adsorbents for Pb2+
Adsorbent T/K pH c0/(mg·L−1) qm/(mg·g−1) Reference KOH-Modified Banana Peel Hydrothermal Carbon 298 6 50 42.92 [29] sand leek (Allium scorodoprasum L.) 298 4.5 1000 107 [30] Weathered Coal-Immobilized Microbial Materials 308 5 300 338.90 [31] zinc chloride-impregnated activated carbon from brown alga 313 5 25 30.14 [32] CoFe2O4@SiO2–NH2 323 8 50 74.50 [33] GCZ-4 298 5 100 367.42 This study Notes：$ \text{T} $—temperature;$ \text{}\text{c}\text{0} $—initial concentration of the Pb2+ solution; qm—the maximum theoretical adsorption capacity
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表 4 GCZ-4复合气凝胶对Pb2+的吸附动力学拟合参数
Table 4. Fitting parameters of Pb2+adsorption kinetics of GCZ-4 composite aerogel
pseudo-first-order kinetic model pseudo-second-order kinetic model T/K qe/(mg·g−1) k1/min−1 R2 qe/(mg·g−1) k2/(g·mg−1·min−1) R2 298 285.39 0.0316 0.893 285.71 0.000077 0.984 303 275.46 0.0352 0.967 255.10 0.000095 0.988 308 206.10 0.0376 0.981 221.72 0.000164 0.990 313 154.63 0.0268 0.856 202.83 0.000215 0.997 Notes：$ \text{T} $—temperature; R2—linear correlation coefficient; $ {{k}}_{\text{1}} $—pseudo-first-order kinetic constant; $ {{k}}_{\text{2}} $—pseudo-second-order kinetic constant; qe—equilibrium adsorption capacity.
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表 5 GCZ-4复合气凝胶对Pb2+的粒子内扩散模型拟合参数
Table 5. Fitting parameters of GCZ-4 composite aerogel for Pb2+intra particle diffusion mode
T/K k1/(mg·g−1·min0.5) R12 k2/(mg·g−1·min0.5) R22 k3/(mg·g−1·min0.5) R32 298 32.94 0.99 11.31 0.95 0.41 0.51 303 23.77 0.98 9.01 0.93 1.23 0.51 308 27.20 0.99 6.42 0.94 1.18 0.86 313 22.84 0.98 5.74 0.96 1.23 0.51 Notes：$ \text{T} $—temperature; $ {k}_{\mathrm{i}} $— intra-particle diffusion rate constant; R2—linear correlation coefficient.
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表 6 GCZ-4复合气凝胶对Pb2+的吸附热力学相关参数
Table 6. Thermodynamic parameters of Pb2+adsorption by GCZ-4 composite aerogel
T/K ΔH/
(kJ·mol−1)ΔS/
(kJ·mol−1·K−1)ΔG/
(kJ·mol−1)298 −37.16 −0.105 −5.87 303 −5.34 308 −4.82 313 −4.29 Notes：$ \text{T} $—temperature；$ {\Delta }\text{H} $—enthalpy change；$ {\Delta }\text{S} $—entropy change；$ {\Delta }\text{G} $—Gibbs free energy change.
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