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。因此,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,通过简单的溶胶-凝胶法结合冷冻干燥,构建了具有三维多孔网络结构的SA-CMC-GO复合气凝胶。利用SEM、FTIR、XRD等对SA-CMC-GO复合气凝胶的微观形貌、官能团结构等进行表征分析。以水中Pb2+为吸附对象,通过一系列间歇吸附实验,探究了各种因素(pH、介质温度、接触时间等)对吸附剂去除水体中Pb2+的影响。结果表明,在pH值2~5的范围内,复合气凝胶对Pb2+的吸附量随着pH的升高而升高;复合气凝胶对于Pb2+的吸附过程属于自发放热过程并遵循Langmuir吸附等温模型,其最大吸附量为272.5 mg·g−1;动力学研究表明,SA-CMC-GO复合气凝胶对Pb2+具有较快的吸附速率,可在60 min内达平衡并符合准二级动力学模型;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。SA-CMC-GO复合气凝胶可以作为一种高效、快速的吸附剂用于从水体中去除Pb2+。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 SA-CMC-GO composite aerogel 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 show that the adsorption amount of Pb2+ by the composite aerogel increases with the increase of pH=2-5. The adsorption process is a spontaneous exothermic process and the experimental data of the adsorption process are more fitted to Langmuir isotherm, the theoretical maximum adsorption capacity of Pb2+ on SA-CMC-GO composite aerogel is 272.5 mg·g−1. Adsorption kinetics studies indicate the adsorption of Pb2+ by the SA-CMC-GO composite aerogel shows rapid uptake rates and reaches equilibrium within 60 min. The pseudo-second-order kinetic model coincides 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.
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Key words:
- aerogel /
- sodium alginate /
- carboxymethyl cellulose /
- graphene oxide /
- adsorption
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表 1 元素的原子分数
Table 1. Atomic fraction of the element
Atomic fraction/at% C O Na C—C C—O C=O C—O COO− — 65.55 10.63 4.88 19.23 1.83 1.87 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 Ref. 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—Nano-cellulose/sodium alginate/carboxymethyl chitosan aerogel; Cell@PEI—Amino-modified cellulose aerogel; NPCS-PEI—N-methylene phosphonic acid chitosan. 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; ΔH—Enthalpy change; ΔS—Entropy change; ΔG—Gibbs free energy change. 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; k1—Pseudo-first-order kinetic constant; k2—Pseudo-second-order kinetic constant. 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 Note: ki—Intra-particle diffusion rate constant, i=1, 2, 3. 表 6 SA-CMC-GO复合气凝胶吸附Pb2+的等温线吸附Langmuir模型和Freundlich模型参数
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: KL—Langmuir adsorption coefficient; KF—Freundlich adsorption coefficient; n—Adsorption strength constant. -
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