Preparation of a N, S, P co-doped and oxidized porous carbon for the efficient adsorption of uranium(VI)
摘要: 通过煅烧前驱体聚磷腈，制备了掺杂N，P和O的羧基官能化炭材料（CS―COOH）。利用TEM，SEM，XPS和FTIR技术确定了CS―COOH结构。研究了CS―COOH从水溶液中吸附U（VI）情况，结果表明，吸附动力学符合准二级动力学模型，通过Langmuir模型计算得到在298 K下材料的最大吸附量为402.9 mg/g。CS―COOH在5次吸附-解吸循环后表现出良好的吸附结果。根据XPS分析，材料较好的U（VI）吸附能力主要归因于羧基及杂原子与铀酰离子之间的强共价键结合。Abstract: A N, S, P co-doped and oxidized porous carbon was prepared by the carbonization of poly (cyclotriphosphazene-co-4,4’-sulfonyldiphenol) at 750 °C, followed by KOH activation and HNO3 oxidation. The carbon was used as an adsorbent for uranium(VI) in aqueous solutions. TEM, SEM, XPS and FTIR were used to characterize its microstructure before and after adsorption. Results indicate that there is an optimum pH value of 6 for U(VI) adsorption. The adsorption kinetics and isotherms were fitted well by the pseudo-second-order and the Langmuir models, respectively. The maximum adsorption capacity determined by the Langmuir model at 298 K and a pH value of 6 was 402.9 mg g−1. The carbon has excellent reusability and retains 70% of the capacity of the original value after five adsorption-desorption cycles. The high U(VI) adsorption capacity is mainly attributed to the carboxyl, and P and S groups by the formation of the UO22+(COO−)2 complex, and U―O―P and U―O―S bonds.
Figure 5. (a) Effect of initial solution pH on the adsorption of U(VI) by CS and CS―COOH. (T = 298 K, m = 5 mg, C0 = 50 mg L−1 and V = 30 mL); (b) Distribution of U(VI) species in aqueous solutions with a total concentration of 50 mg L−1 and pH values ranging from 1 to 12 (calculated by using a Medusa program).
Table 1. Kinetic parameters for adsorption of U(VI) by CS and CS-COOH.
Materials qe,exp (mg g−1) Pseudo-first-order model Pseudo-second-order model q1,cal (mg g−1) k1 (/min) R2 q2,cal (mg g−1) k2 (g mg−1·min−1) R2 CS 150.34 98.69 8.21×10−3 0.905 173.31 2.88×10−4 0.9764 CS-COOH 238.20 190.49 3.34×10−2 0.939 250.43 1.85×10−4 0.9957
Table 2. Parameters of Langmuir and Freundlich isotherm models for adsorption of U(VI) by CS and CS-COOH.
Materials Langmuir isotherm Freundlich isotherm KL qm (mg g−1) R2 KF n R2 CS 7.80 229.36 0.9976 4.05×10−3 0.31 0.9423 CS-COOH 0.018 402.90 0.9227 12.66 1.40 0.9033
Table 3. The thermodynamic parameters for U(VI) adsorption by CS and CS-COOH.
(J mol−1 K−1)
ΔG (kJ mol−1) 288
CS 49.82 216.16 −12.41 −14.57 −15.65 −17.81 −18.89 CS−COOH 7.73 91.89 −18.74 −19.66 −20.12 −21.04 −21.50
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