Adsorption performance and mechanism of U(VI) removal from wastewater by polyaniline-coated and carbon dot functionalized CoMn2O4
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摘要: 核工业发展产生的含铀废水对人类健康和生态环境产生严重威胁。对含铀废水的有效化处理是核能绿色发展的重要保证。采用化学聚合法合成了一种新型聚苯胺包覆碳点功能化锰钴金属氧化物(CMC20%/PANI)。吸附剂表面丰富的氧、氮基团为U(VI)的高效捕获提供活性位点。采用静态吸附法研究了材料去除溶液中U(VI)的性能。因此，在pH = 5、120 min，CMC20%/PANI对U(VI)的吸附容量达到285 mg/g。吸附过程符合准二级动力学和Sips模型，表明吸附剂对铀涉及单层和多层的化学吸附，并且Sips拟合的理论吸附容量为659.7 mg/g。吸附机制研究表明：静电吸引、孔扩散以及含氧、氮基团的络合配位作用成为CMC20%/PANI对U(VI)的主要去除机制。Abstract: Uranium-containing wastewater posed a serious threat to human health and the ecological environment. Its effective treatment had strategic significance for the green development of nuclear energy and environmental protection. A novel polyaniline-coated carbon dot functionalized manganese cobalt metal oxide was synthesized by chemical polymerization method (CMC20%/PANI). The abundant oxygen and nitrogen groups on the surface of the adsorbent provided active sites for the efficient capture of U(VI). The performance of the material in removing uranium from the solution was evaluated using a static adsorption method. The results show the adsorption capacity of uranium reaches 285 mg/g at pH = 5 and 120 min. The adsorption process is in line with pseudo-second-order kinetic and the Sips model, suggesting that uranium adsorption by the adsorbent involves monolayer and multilayer chemisorption as well as a theoretical adsorption capacity of 659.7 mg/g fitted by Sips. Adsorption mechanism analysis shows that electrostatic attraction, pore diffusion and complex coordination of oxygen and nitrogen groups are the main removal mechanism with CMC20%/PANI on U(VI).
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Key words:
- CoMn2O4 /
- PANI /
- CDs /
- adsorption /
- U(VI) /
- wastewater
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图 1 聚苯胺包覆碳点功能化锰钴金属氧化物(CoMn2O4/CDs/PANI)的合成路线
Figure 1. Synthetic route to polyaniline-coated carbon dot functionalized manganese cobalt metal oxide was synthesized by chemical polymerization (CoMn2O4/CDs/PANI)
图 2 PANI和CMCx/PANI的(a) XRD谱图；(b) FT-IR谱图
Figure 2. (a) XRD patterns of PANI and CMCx/PANI; (b) FT-IR spectra
图 3 (a-b) PANI、(c-d) CMC20%/PANI、(e-f) CMC50%/PANI的SEM
Figure 3. SEM of (a-b) PANI, (c-d) CMC20%/PANI, and (e-f) CMC50%/PANI
图 4 CMC20%/PANI和CMC50%/PANI：(a) N2循环吸脱附和(b) 孔径分布曲线
Figure 4. (a) N2 cyclic adsorption desorption and (b) pore size distribution curves of CMC20%/PANI and CMC50%/PANI
图 5 (a) pH对PANI、CMC10%PANI、CMC20%/PANI和CMC50%/PANI的吸附铀性能的影响(T = 298 K, m/V = 0.25 g/L, C0 = 100 mg/L)；(b) CMC20%/PANI Zeta电位；(c) 不同时间CMC20%/PANI对铀吸附性能(pH=5.0, T = 298 K, m/V = 0.25 g/L, C0 = 100 mg/L)和(d) 颗粒内扩散模型拟合曲线
Figure 5. (a) Effect of pH on the uranium adsorption performance of PANI, CMC10%PANI, CMC20%/PANI, and CMC50%/PANI (T = 298 K, m/V = 0.25 g/L, C0 = 100 mg/L); (b) Potential of CMC20%/PANI Zeta; (c) Uranium adsorption performance of CMC20%/PANI at different times (pH=5.0, T = 298 K, m/V = 0.25 g/L, C0 = 100 mg/L); (d) Fitting curve of intra particle diffusion model
qt—The adsorption capacity at an time point
图 6 (a) CMC20%/PANI在不同初始浓度及温度下对铀酰离子的吸附性能；等温线拟合曲线(C0=20~400 mg/L, T=298~318 K, pH = 5.0, m/V = 0.25 g/L)；(b) lnK与1/T的关系
Figure 6. (a) The adsorption performance of CMC20%/PANI on uranyl ions at different initial concentrations and temperatures; Isotherm fitting curve (C0=20~400 mg/L, T=298~318 K, pH = 5.0, m/V = 0.25 g/L); (b) Relationship between equilibrium constant and reciprocal temperature
K—Thermodynamic equilibrium constant.
图 7 CMC20%/PANI对不同金属离子的(a) 吸附容量；(b) 分配系数
Figure 7. (a) Influence of coexisting ions and (b) distribution coefficient of CMC20%/PANI
图 8 (a) 不同解吸液的解析率；(b) 循环性能；(c) 循环后CMC20%/PANI的SEM图谱
Figure 8. (a) Resolution rates of different desorbing solutions; (b) Cycling performance; (c) The SEM of CMC20%/PANI after cycles.
图 9 CMC20%/PANI吸附铀前后(a) FT-IR；(b) XRD；(c) SEM
Figure 9. (a) FT-IR; (b) XRD; (c)SEM of CMC20%/PANI before and after uranium adsorption
图 10 CMC20%/PANI吸附铀前后 (a) U 4f；(b) N 1s；(c) C 1s；(d) O 1s；(e) Mn 2p；(f) Co 2p XPS精细谱图
Figure 10. CMC20%/PANI before and after uranium adsorption (a) U 4f; (b) N 1s; (c) C 1s; (d) O 1s; (e) Mn 2p; (f) Co 2p XPS fine spectrum
表 1 准一/二级动力学模型拟合参数
Table 1. Fitting parameters of pseudo first/second order kinetic models
Kinetic model qe/(mg-U/g-ads) k1/(min−1)/k2/(g·mg−1·min−1) R2 Pseudo-first-order kinetic model 277.8 0.2432 0.785 Pseudo-second-order kinetic model 286.7 0.0016 0.985 Notes: qe—Theoretical equilibrium adsorption capacity; k1—The quasi-first-order kinetic constant; k2—The quasi-second-order kinetic constant; R2—Correlation coefficient. 
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表 2 颗粒内扩散模型拟合参数
Table 2. Fitting parameters of intra particle diffusion model
T/K kp1 R12 kp2 R22 kp3 R32 298 19.184 0.947 3.473 0.805 0.855 0.109 Notes: kp—The diffusion constant in particles; R2—Correlation coefficient.
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表 3 CMC20%/PANI吸附铀酰离子的吸附等温模型拟合参数
Table 3. Fitting parameters of adsorption isotherm model for uranyl ions on CMC20%/PANI
Isothermal model Parameter 298 K 308 K 318 K Langmuir qe/(mg·g−1) 791.088 809.268 866.259 KL/(L·mg−1) 0.027 0.035 0.041 R2 0.951 0.943 0.952 Freundlich 1/n 0.396 0.363 0.357 KF/(L·g−1) 83.777 106.496 122.312 R2 0.825 0.789 0.803 Sips qe/(mg·g−1) 659.798 690.434 750.500 KS 0.041 0.049 0.058 m 1.674 1.728 1.611 R2 0.991 0.991 0.987 Notes: qe—Theoretical equilibrium adsorption capacity; KL—The saturated adsorption capacity of a single layer; R2—Correlation coefficient; 1/n—The adsorption strength; KF—The Freundlich's constant; Ks—The Sips constant related to the adsorption energy; m—The sips constant.
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表 5 各种吸附剂的铀吸附性能比较
Table 5. Comparison of adsorption capacity for U(VI) adsorption with various adsorbents
Adsorbents Time/min Adsorption Capacity/(mg·g−1) pH Cycle performance References C@CaTiO3 40 119.2 3.5 — [1] Zr-ATMPA 120 238.1 5 — [3] HAP/BTN 30 186.4 6 5/80% [7] CMPA-F-BDA 20 443 8 5/80% [13] Fe-PANI-GA 20 350.47 5.5 5/144.2~127.3 mg/g [22] LGSA 30 1162 8.5 5/94.2% [23] CS-AO-AMP 3600 620 7-9 4/90% [24] CMC20%/PANI 120 659.0 5 5/89.7% This work Notes: C@CaTiO3—Pomegranate peel carbon loaded CaTiO3; Zr-ATMPA—Organic zirconium phosphonate; HAP/BTN—Hydroxyapatite modified bentonite; CMPA-F-BDA—The modification of amino groups onto the fluorenone-functionalized conjugated microporous poly(aniline)s network; Fe-PANI-GA—Zero-valent iron-polyaniline-graphene aerogel ternary composite; LGSA—Surfactant assisted APTES functionalization of graphene oxide intercalated layered double hydroxide; CS-AO-AMP—Chitosan-based porous adsorbent with multifunctional amidoxime and phosphate groups.
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表 4 热力学参数
Table 4. Thermodynamic fitting parameters
T/K ΔGθ/(kJ·mol−1) ΔHθ/(kJ·mol−1) ΔSθ/(J·mol−1·K−1) 298 −3.612 13.874 58.677 308 −4.199 318 −4.785 328 −5.372 338 -5.959 Notes: ΔGθ—Gibbs free energy; ΔHθ—Enthalpy; ΔSθ—Entropy change.
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