ZIF-8-SiO2 and adsorption on U(VI)
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摘要: 以沸石咪唑酯骨架结构材料ZIF-8及硅酸四乙酯(TEOS)为原料制备ZIF-8-SiO2复合材料,并采用XRD、SEM、EDS等方法对ZIF-8-SiO2的结构及吸附U(VI)前后的形貌进行表征,结果表明ZIF-8-SiO2成功制备且对U(VI)具有良好的吸附作用。以静态吸附实验,分别考察了pH值、时间、温度、溶液初始铀浓度、盐浓度及超高压环境等对ZIF-8-SiO2吸附性能的影响。由实验结果可得,在初始浓度为80 mg·L−1时,25℃下ZIF-8-SiO2对U(VI)的最大实际吸附量为498 mg·g−1,根据Langmuir模型拟合结果分析得出,ZIF-8-SiO2对U(VI)的理论吸附量最高可达678.5 mg·g−1,且在200~500 MPa范围内,压强越高越有利于吸附。通过FTIR、XPS等方法对ZIF-8-SiO2吸附铀酰离子前后的结构进行分析,探究该吸附过程中可能存在的吸附机制。
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关键词:
- ZIF-8-SiO2 /
- 复合材料 /
- 铀处理 /
- 吸附法 /
- 高压模拟
Abstract: Zeolite imidazole ester framework structure material ZIF-8 and TEOS were used to prepare ZIF-8-SiO2 composite, the structure of ZIF-8-SiO2 and the morphology before and after adsorption of U(VI) were characterized by XRD, SEM, EDS. And the results show that ZIF-8-SiO2 is successfully prepared and has a good adsorption effect on U(VI). The effects of pH value, time, temperature, initial uranium concentration and salt concentration on the adsorption performance of ZIF-8-SiO2 were investigated by static adsorption experiments. According to the experimental results, when the initial concentration is 80 mg·g−1, the maximum actual adsorption capacity of ZIF-8-SiO2 on U(VI) at 25℃ is 498 mg·g−1, and according to the analysis of Langmuir model fitting results, the theoretical adsorption capacity of the material on U(VI) is up to 678.5 mg·g−1. And in the range of 200~500 MPa, the higher the pressure, the better the adsorption. FTIR and XPS were used to characterize the structure of the material before and after uranylion adsorption, to explore the possible adsorption mechanism during the adsorption process.-
Key words:
- ZIF-8-SiO2 /
- composite materials /
- uranium processing /
- adsorption method /
- high pressure simulation
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表 1 25℃下 ZIF-8-SiO2对U(VI)吸附的Langmuir及Freundlich模型拟合参数
Table 1. Langmuir and Freundlich model parameters for adsorption of U(VI) by ZIF-8-SiO2 at 25℃
Sample parameters ZIF-8-SiO2 Langmuir Cs,max/(mg·g−1) 678.5 b/(L·mg−1) 0.01232 R2 0.9889 Freundlich KF/(mg·g−1) 20.63 1/n 0.6267 R2 0.9700 Notes: Cs,max—Maximum adsorption capacity of ZIF-8-SiO2 for U(VI); b—Fitting parameters of Langmuir adsorption model; KF—Fitting parameters of Freundlich adsorption model; n—Linear factor or a potential energy nonuniformity factor, reflecting the heterogeneous energy of the adsorption surface; R2—Coefficient of association. 表 2 ZIF-8-SiO2对U(VI)吸附动力学拟合相关参数
Table 2. Pseudo-first and pseudo second order kinetics parameters for U(VI) removal by ZIF-8-SiO2
Parameter 25℃ 45℃ Pseudo-first order K1/(L·mg−1) 0.01039 0.03427 R2 0.9849 0.8681 Pseudo-second order K2/(g·min−1·mg−1) 5.847×10−5 2.311×10−4 R2 0.9954 0.9519 Notes: K1, K2—Adsorption rate constant; R2—Coefficient of association. 表 3 ZIF-8-SiO2对U(VI)吸附的热力学参数
Table 3. Thermodynamic parameters of adsorption of ZIF-8-SiO2 on U(VI)
ZIF-8-SiO2 ΔH/(kJ·mol−1) 68.33 ΔS/(J·mol−1·K−1) 242.9 ΔG/(kJ·mol−1),298.15 K −4.088 ΔG/(kJ·mol−1),308.15 K −6.517 ΔG/(kJ·mol−1),318.15 K −8.946 Ea/(kJ·mol−1) 54.19 Notes: ΔH—Standard enthalpy change; ΔS—Standard entropy change; ΔG—Gibbs free energy change; Ea—Activation energy of adsorption. -
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