Preparation of sodium alginate-carboxymethyl cellulose-graphene oxide composite aerogel for adsorption of Pb(II) ion
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摘要:
目前，开发具有优异吸附性能、可持续使用和绿色环保的吸附剂仍然是水污染治理领域的焦点问题。生物质气凝胶由于绿色环保、成本低、可生物降解等优点，在吸附领域引起了广泛关注，但由于吸附速率较慢、吸附容量不高等问题限制了其作为吸收剂去除水体中重金属离子的应用。因此，开发功能性生物质复合气凝胶用于吸附处理水体中重金属离子污染物具有重要意义。本研究以海藻酸钠(SA)、羧甲基纤维素(CMC)和氧化石墨烯(GO)为原料，采取简单的溶胶-凝胶法结合冷冻干燥，通过非共价键合的方式，构建了具有三维多孔网络结构的海藻酸钠-羧甲基纤维素-氧化石墨烯复合气凝胶(SA-CMC-GO)。该复合气凝胶内部孔洞相互连通，且有明显的褶皱，增加了其比表面积，有利于对水体中重金属离子的吸附，并且复合气凝胶表面存在的大量的-OH和-COOH官能团作为吸附位点通过静电作用和螯合作用与Pb2+有效结合，提升吸附速率和吸附容量。此外，GO的π共轭体系也可以通过阳离子-π相互作用吸引Pb2+，提升吸附效果。因此，实验结果表明，所制备的复合气凝胶对Pb2+的吸附可在60 min内迅速达到平衡其最大吸附量为272.5 mg·g-1，且经过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。 (a)吸附时间对SA-CMC-GO复合气凝胶吸附Pb2+的影响和(b) SA-CMC-GO复合气凝胶对Pb2+的吸附原理图(a) Effect of adsorption time on the adsorption performance of SA-CMC-GO aerogel to Pb2+ and (b) the mechanism of the adsorption of Pb2+ by SA-CMC-GO aerogel Abstract: Exploiting adsorbents with excellent adsorption activity, good durability and environment friendly is still the core focus of water pollution treatment. Herein, in this study, sodium alginate (SA), carboxymethyl cellulose (CMC), and graphene oxide (GO) were used as raw materials to frame a composite aerogel (SA-CMC-GO) with a 3D network structure by a sol-gel and freeze-drying method. The functional group structure and microstructure of SA-CMC-GO composite aerogel were tested and analyzed by SEM, FTIR and XRD. Various parameters affecting the removal of Pb2+ such as pH, temperature and contact time were optimized by using a series of batch adsorption experiments. The results showed that the adsorption amount of Pb2+ by the composite aerogel increased with the increase of pH at 2-5. The adsorption process was a spontaneous exothermic process and the experimental data of the adsorption process were more fitted to Langmuir isotherm, the theoretical maximum adsorption capacity of Pb2+ on SA-CMC-GO composite aerogel was 272.5 mg·g−1. Adsorption kinetics studies indicated the adsorption of Pb2+ by the SA-CMC-GO composite aerogel shown rapid uptake rates and reached equilibrium within 60 min. The pseudo-second-order kinetic model coincided with the adsorption behavior of the composite aerogel. Furthermore, the composite aerogel exhibited better reusability for five adsorption and desorption cycles with highly adsorption properties. The results imply that the new SA-CMC-GO composite aerogel could be potentially applied as an effective and rapid adsorbent for Pb2+ removal from aqueous solutions.-
Key words:
- aerogel /
- sodium alginate /
- carboxymethyl cellulose /
- graphene oxide /
- adsorption
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图 1 SA-CMC-GO(海藻酸钠-羧甲基纤维素-氧化石墨烯)复合气凝胶制备流程
Figure 1. SA-CMC-GO (sodium alginate-carboxymethyl cellulose-graphene oxide) composite aerogel preparation process
图 2 CMC-GO复合气凝胶的SEM图((a)、(b))，SA-CMC-GO复合气凝胶的SEM图((c)、(d))和SA-CMC-GO复合气凝胶的EDS能谱(e)
Figure 2. The SEM images of CMC-GO composite aerogel ((a) and (b)), the SEM images of SA-CMC-GO composite aerogel ((c) and (d)), EDS of SA-CMC-GO composite aerogel (e)
图 3 CMC、GO、SA、SA-CMC-GO复合气凝胶的FTIR图
Figure 3. The FTIR spectra of CMC, GO, SA and SA-CMC-GO composite aerogel
图 4 CMC气凝胶和SA-CMC-GO复合气凝胶的XRD图
Figure 4. The XRD of CMC aerogel and SA-CMC-GO composite aerogel
图 5 (a) SA-CMC-GO复合气凝胶的XPS光谱；(b) SA-CMC-GO复合气凝胶的C1 s谱；(c) SA-CMC-GO复合气凝胶的O1 s谱
Figure 5. (a) XPS spectra of SA-CMC-GO composite aerogel; (b) C1 s XPS spectra of SA-CMC-GO composite aerogel; (c) O1 s XPS spectra of SA-CMC-GO composite aerogel
图 6 溶液pH与SA-CMC-GO复合气凝胶吸附Pb2+去除率和吸附量的关系
Figure 6. Relationship between solution pH and the removal and adsorption capacity of Pb2+ by SA-CMC-GO composite aerogel
$ 141{q}_{e} $—Equilibrium adsorption capacity
图 7 吸附时间与SA-CMC-GO复合气凝胶对Pb2+的吸附量的关系
Figure 7. Relationship between adsorption time and the adsorption capacity of Pb2+ adsorbed by SA-CMC-GO composite aerogel
t—Adsorption time
图 8 温度与SA-CMC-GO复合气凝胶对Pb2+的吸附量的关系
Figure 8. Relationship between temperature and the adsorption capacity of Pb2+ adsorbed by SA-CMC-GO composite aerogel
图 9 (a) SA-CMC-GO复合气凝胶吸附Pb2+的伪一阶动力学模型；(b) SA-CMC-GO复合气凝胶吸附Pb2+的伪二阶动力学模型；(c) SA-CMC-GO复合气凝胶吸附Pb2+的粒子内扩散模型
Figure 9. (a) pseudo-first-order kinetic model for Pb2+ adsorption by SA-CMC-GO composite aerogel; (b) pseudo-second-order kinetic model for Pb2+ adsorption by SA-CMC-GO composite aerogel; (c) intra-particle diffusion model for Pb2+ adsorption by SA-CMC-GO composite aerogel
$ {q}_{t} $—Adsorption capacity at time t
图 10 (a) SA-CMC-GO复合气凝胶吸附Pb2+的Langmuir模型；(b) SA-CMC-GO复合气凝胶吸附Pb2+的 Freundlich模型
Figure 10. (a) Langmuir model of SA-CMC-GO composite aerogel on Pb2+; (b) Freundlich model of SA-CMC-GO composite aerogel on Pb2+
$ {c}_{e} $—Concentration at adsorption equilibrium
图 11 循环次数与SA-CMC-GO复合气凝胶对Pb2+去除率的关系
Figure 11. Relationship between cycle time and the Pb2+ removal rate of SA-CMC-GO composite aerogel
图 12 SA-CMC-GO复合气凝胶对Pb2+的吸附原理图
Figure 12. The mechanism of the adsorption of Pb2+ by SA-CMC-GO composite aerogel
表 1 元素的原子分数
Table 1. The atomic fraction of the element
Atomic fraction/% C O Na C—C C—O C=O C—O COO− / 65.55 10.63 4.88 19.23 1.83 1.87 
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表 2 不同吸附剂对Pb2+的平衡吸附时间
Table 2. Equilibrium adsorption time of Pb2+ by different adsorbents
Adsorbent Time/min Reference DGO/CMC 550 [3] GO/CMC 600 [21] NSC 150 [25] Cell@PEI 240 [26] NPCS-PEI 120 [27] SA-CMC-GO 60 This study Notes：DGO—functionalized graphene oxide; NSC—nanocellulose/sodium alginate/carboxymethyl chitosan aerogel; Cell@PEI—amino-modified cellulose aerogel; NPCS-PEI—N-methylene phosphonic acid chitosan.
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表 3 SA-CMC-GO复合气凝胶对Pb2+的吸附热力学相关参数
Table 3. Thermodynamically relevant parameters for the adsorption of Pb2+ by SA-CMC-GO composite aerogel
T/K ΔG/(kJ·mol−1) ΔS/(kJ·mol·−1·K−1) ΔH/(kJ·mol−1) 303 −8.297
−0.08298
−33.44308 −7.882 313 −7.467 Notes：$ T $—temperature；$ \Delta H $—enthalpy change；$ \Delta S $—entropy change；$ \Delta G $—Gibbs free energy change.
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表 4 SA-CMC-GO复合气凝胶对Pb2+的吸附动力学拟合参数
Table 4. Fitting parameters for the kinetics of Pb2+ adsorption by SA-CMC-GO composite aerogel
Pseudo-first-order kinetic model Pseudo-second-order kinetic model qe/(mg·g−1) k1/min−1 R2 qe/(mg·g−1) k2/(g·mg−1·min−1) R2 71.71 0.02374 0.7546 230.9 3.576×10−4 0.9942 Notes：R2—linear correlation coefficient; $ {k}_{1} $—pseudo-first-order kinetic constant; $ {k}_{2} $—pseudo-second-order kinetic constant.
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表 5 SA-CMC-GO复合气凝胶吸附Pb2+的粒子内扩散模型拟合参数
Table 5. Fitting parameters for the intra-particle diffusion model for Pb2+ adsorption by SA-CMC-GO composite aerogel
k1/(mg·g−1·min0.5) R12 k2/(mg·g−1·min0.5) R22 k3/(mg·g−1·min0.5) R32 37.70 0.9920 11.13 0.9917 0.5009 0.9923 Notes：$ {k}_{i} $— intra-particle diffusion rate constant.
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表 6 SA-CMC-GO复合气凝胶吸附Pb2+的Langmuir模型和Freundlich模型等温吸附参数
Table 6. Isothermal adsorption parameters of SA-CMC-GO composite aerogel for Pb2+ adsorption by Langmuir model and Freundlich model
Langmuir model Freundlich model qe/
(mg·g−1)KL R2 KF n R2 272.5 0.4809 0.9974 155.1 7.125 0.6719 Notes：$ {K}_{L} $—Langmuir adsorption coefficient; $ {K}_{F} $—Freundlich adsorption coefficient; n—the adsorption strength constant.
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