金属有机骨架材料在放射性核素去除中的研究

doi:10.15541/jim20180211

摘要/Abstract

摘要：

核能利用的过程中, 从铀矿开采、核燃料加工、核能发电到乏燃料后处理, 会产生大量放射性废物, 部分放射性核素会不可避免的释放到环境中, 对环境和人类健康造成重大危害。放射性核素的高效去除是核电健康发展的重要关键科学问题之一。近年来, 高化学稳定性、具有大量功能基团而且结构可调的多孔金属有机骨架材料(MOFs)在放射性污染治理方面受到国内外同行的高度关注。本文系统地介绍了MOFs及MOFs复合材料在放射性核素吸附去除方面的研究进展, 通过宏观吸附、模型分析、先进光谱表征和理论计算四个方面描述放射性核素与MOFs材料的界面作用机理, 并对MOFs材料的吸附性能与其它材料进行对比, 评价MOFs材料在放射性污染治理中的应用前景。

关键词: 金属有机骨架材料, 放射性核素, 吸附, 分析表征, 作用机理, 综述

Abstract:

With the development of nuclear energy, the long-lived radionuclides are inevitably released into the natural environment during the mine process, fuel manufacture, nuclear power usable and spent fuel management, which are dangerous to human health and environmental pollution. Thereby the efficient elimination of radionuclides is an important parameter which affects the development of nuclear power. In recent years, the metal-organic frameworks (MOFs) have attracted worldwide attention in the adsorption of radionuclides from large volume of aqueous solutions, because of their high chemical stability, abundant functional groups and changeable porous structures. In this review, we mainly summarized the recent works of MOFs in the efficient removal of radionuclides, and to understand the interaction mechanism from batch adsorption experiments, model analysis, advanced spectroscopy analysis, and theoretical calculation. The adsorption capacities of MOFs with other materials were also summarized, and the future research opportunities and challenges are given in the perspective.

Key words: metal-organic frameworks (MOFs), radionuclides, adsorption, analytical characterization, interaction mechanism, review

中图分类号:

TQ174

王祥学, 于淑君, 王祥科. 金属有机骨架材料在放射性核素去除中的研究[J]. 无机材料学报, 2019, 34(1): 17-26.

WANG Xiang-Xue, YU Shu-Jun, WANG Xiang-Ke. Removal of Radionuclides by Metal-organic Framework-based Materials[J]. Journal of Inorganic Materials, 2019, 34(1): 17-26.

图/表 7

图1 MIL-101及其氨基衍生物的SEM照片(1), XRD图谱(2), FT-IR谱图(3)和N2吸脱附等温线(4)[26]

Fig. 1 (1) SEM images, (2) XRD patterns, (3) FT-IR spectra, (4) N2 sorption isotherms[26] of MIL-101 and its amino derivatives, (a) MIL-101; (b) MIL-101-NH2; (c) MIL-101-ED; (d) MIL-101-DETA

图2 (a)TcO4-的UV-Vis吸收光谱; (b)TcO4-在SCU-101、Purolite A530E和A532E上的吸附动力学; (c)ReO4-在SCU-101、Mg-Al-LDH和NDTB-1上的吸附等温线; (d)阴离子对TcO4-去除效果的影响; (e)SO42-对ReO4-和SCU-101离子交换的影响; (f)SCU-101样品经过多次辐照之后对ReO4-的去除效果[28]

Fig. 2 (a) UV-Vis absorption spectra of TcO4- during the anion exchange; (b) Sorption kinetics of TcO4- by SCU-101 compared with Purolite A530E and A532E; (c) Sorption isotherms of ReO4- by SCU-101, Mg-Al-LDH, and NDTB-1; (d) Effect of competing anions on the removal percentage of TcO4- by SCU-101; (e) Effect of SO42- on the anion exchange of ReO4- by SCU-101; (f) Removal percentage of ReO4- after irradiation as compared with the original SCU-101 sample[28]

表1 放射性核素在不同材料上的去除效果和作用机理

Table 1 Radionuclides adsorption on different materials

Adsorbents	Radionuclides	(m/V)/(g·L^-1)	C₀/(mg·L^-1)	t/h	pH	Q_max/(mg·g^-1)	Interaction mechanism	Ref.
MIL-101	U(VI)	0.4	100	2	5.5	20	Surface complexation	[26]
MIL-101-NH₂	U(VI)	0.4	100	2	5.5	90	Surface complexation	[26]
MIL-101-ED	U(VI)	0.4	100	2	5.5	200	Surface complexation	[26]
MIL-101-DETA	U(VI)	0.4	100	2	5.5	350	Surface complexation	[26]
GO-COOH/UiO-66	U(VI)	0.5	95	4	8.0	188	Surface complexation and ion exchange	[30]
SCU-101	Re(IV)	1.0	1000	0.2	-	217	Ion exchange	[28]
SCU-100	Re(IV)	1.0	28	2	-	541	Ion exchange	[29]
UiO-66-(COOH)₂	Th(IV)	0.4	100	6	3.0	350	Surface complexation	[31]
MOF-808-SO₄	Ba(II)	1.0	42	0.1	5.8	131	Surface complexation	[32]
UiO-66-Schiff	Co(II)	0.1	10	5	8.4	256	Surface complexation	[33]
FJSM-InMOF	Sr(II)	2.5	18	12	-	44	Ion exchange	[34]
FJSM-InMOF	Cs(I)	2.5	90	3	-	199	Ion exchange	[34]
LDO-C	U(VI)	0.1	50	4	5.0	354	Surface complexation and ion exchange	[35]
CS@LDH	U(VI)	0.2	41	3	5.0	157	Surface complexation	[36]
GO	Co(II)	0.1	10	4	5.0	44	Surface complexation	[37]
LDH	U(VI)	0.2	50	6	4.5	69	Surface complexation and electrostatic interaction	[38]
Na-montmorillonite	Ni(II)	0.5	10	6	6.0	13	Surface complexation and ion exchange	[39]
Fe₃O₄@TNS	U(VI)	0.2	20	8	5.0	83	Ion exchange	[40]

图3 Cs+吸附到MOF/KNiFC和MOF/Fe3O4/KNiFC上的假一阶模型(a)、假二阶模型(b)、扩散模型(c)和Elovich模型(d)拟合[44]; (e)U(VI)在UiO-66(插图)和GO-COOH/UiO-66复合物上的吸附等温线: (f)Langmuir模型, (g)Freundlich模型, (h)Dubinin-Radushkevich模型[30]

Fig. 3 Linear pseudo-first-order kinetic (a), pseudo-second-order (b), intraparticle diffusion (c) and elovich equation (d) for adsorption of Cs+ on MOF/KNiFC and MOF/Fe3O4/KNiFC[44]; (e) Isotherm model of U(VI) adsorption on UiO-66 (inset) and GO-COOH/UiO-66 composites; (f) Langmuir model, (g) Freundlich model, and (h) Dubinin-Radushkevich model[30]

图4 (a)原始的MIL-101(Cr)和不同乙二胺(ED)改性ED-MIL-101(Cr)材料吸附U(VI)之后的U L3-edge XANES光谱, (b)不同样品对应的傅里叶转换光谱图[54]

Fig. 4 (a) Comparison of experimental U L3-edge XANES spectra for pristine MIL-101(Cr), and different ED contents grafting ED-MIL-101(Cr) samples after the adsorption of U(VI), (b) Experimental Fourier transform of the U L3-edge EXAFS data for different samples and their corresponding fits[54]

图5 U(VI)在SZ-2吸附的分子动力学模拟。U(VI)接近SZ-2 [001]晶面c轴的(a)俯视和(b)侧视图; (c)U(VI)结合到SZ-2上运行完一次(总共六次)的快照图(蓝色虚线代表赤道水分子和悬挂的氢键受体之间的氢键);(d)时间对U(VI)与SZ-2和水分子之间的静电作用和范德华作用的影响; (e)时间对铀酰离子赤道水分子的数量(粉红色曲线)和赤道水分子与其它受体(包括主框架中的F和O)之间形成的氢键数量的影响[58]

Fig. 5 MD simulations on the process of uranyl sorption into SZ-2. The top (a) and side (b) view of the simulation system-1 (uranyl cation approaching along the c axis); (c) The final snapshot (at t ¼ 100 ns) of run 1 (out of total 6) to show the importance of equatorial water of uranyl cation in mediating its binding to the SZ-2 (the blue dash line indication the hydrogen bond between equatorial water molecules and the dangling hydrogen bond acceptors); (d) Time evolution of the electrostatic and vdW interaction energies of uranyl cation with SZ-2 and water; (e) The number of equatorial water molecules of uranyl cation (pink curve) and the number of hydrogen bonds formed between equatorial coordinating water molecules and other acceptors (including F and O in main framework) as the function of simulation time[58]

表2 上述主要吸附表征技术的目的、优点和缺点

Table 2 The main purpose, advantages and disadvantages of main adsorption characterization techniques mentioned above

技术	主要目的	优点	缺点
宏观实验	反应达到平衡所需时间, 最大吸附量, 选择性和影响因素^[30]	非常直观得到实验结果, 方便和有效	无法得到分子和原子水平上的作用机理
XPS分析	元素氧化态、元素种类和几乎所有元素的键合关系(除了H和He)	定量分析、元素组成分析、高表面灵敏度检测(1~10 nm)	在真空中进行的测量, 可能改变样品的性质; 在元素个数比值高于0.05%~ 1.0%条件下进行, 依赖于元素的性质
XAFS分析	氧化态、配位数、原子间键距离以及目标离子周围的离子状态^[54]	特定的元素, 并且总是可以检测到的, 对于研究非晶体材料是有用的; 吸附物种的分析	无法区分原子能相差较小的原子(C、N、O或S、Cl、Mn或Fe)^[59,60]
FT-IR分析	对微米范围内吸附行为的研究(光密度≥10^-5)	灵敏检测官能团和极性键^[61]	定性而不是定量, 灵敏度低
DFT计算	键能、键长、轨道和系统电荷密度^[32,62]	对局部环境的吸附描述和原子级吸附过程的描述^[63]	优化结构之间的能量与长时间模拟结果较不准确
分子动力学模拟	位置、势能和宏观现象的预测^[64]	吸附过程的快照在几秒内发生^[27]	长时间的计算时间, 依赖于计算的性能

参考文献 64

[1]	AI Y J, LIU Y, LAN W Y, et al.The effect of pH on the U(VI) sorption on graphene oxide (GO): a theoretical study. Chemical Engineering Journal, 2018, 343: 460-466.
[2]	PANG H W, WANG X X, YAO W, et al.Removal of radionuclides by metal oxide materials and mechanism research. Scientia Sinica Chimica, 2018, 48: 58-73.
[3]	YANG S Y, WANG X X, CHEN Z S, et al.Synthesis of Fe3O4-based nanomaterials and their application in the removal of radionuclides and heavy metal ions. Progress in Chemistry, 2018, 30(2/3): 225-242.
[4]	YU S J, WANG X X, PANG H W, et al.Boron nitride-based materials for the removal of pollutants from aqueous solutions: a review. Chemical Engineering Journal, 2018, 333: 343-360.
[5]	YU S J, WANG X X, YANG S T, et al.Interaction of radionuclides with natural and manmade materials using XAFS technique. Science China Chemistry, 2016, 60(2): 170-187.
[6]	LI X, LIU Y, ZHANG C L, et al.Porous Fe2O3 microcubes derived from metal organic frameworks for efficient elimination of organic pollutants and heavy metal ions. Chemical Engineering Journal, 2018, 336: 241-252.
[7]	LIANG Y, GU P C, YAO W, et al.Adsorption of radionuclide uranium onto carbon-based nanomaterials from aqueous systems. Process in Chemistry, 2017, 29(9): 1062-1071.
[8]	DU Y C, WANG X K, HOU R Q, et al.In-situ growth of Nb2O5 nanorods on diatomite and highly effective removal of Cr(VI). Journal of Inorganic Materials, 2018, 33(5): 557-564.
[9]	CHEN H J, HUANG S Y, ZHANG Z B, et al.Synthesis of functional nanoscale zero-valent iron composites for the application of radioactive uranium enrichment from environment: a review. Acta Chimica Sinica, 2017, 75(6): 560-574.
[10]	DU Y, WANG J, WANG H Q, et al.Research on sorption mechanism of radionuclides by manufactured nanomaterials. Journal of Agro-Environment Science, 2016, 35: 1837-1847.
[11]	WANG X N, MENG H, MA F Y, et al.Influence of preparation method on oxidation degree of graphene oxide and adsorption for Th(IV) and U(VI). Journal of Inorganic Materials, 2016, 31(5): 454-460.
[12]	GU P C, XING J L, WEN T, et al.Experimental and theoretical calculation investigation on efficient Pb(II) adsorption on etched Ti3AlC2 nanofibers and nanosheets. Environmental Science: Nano, 2018, 5(4): 946-955.
[13]	YAO W, WU Y H, PANG H W, et al.In-situ reduction synthesis of manganese dioxide@polypyrrole core/shell nanomaterial for highly efficient enrichment of U(VI) and Eu(III). Science China Chemistry, 2018(7): 1-12.
[14]	SONG S, YIN L, WANG X X, et al.Interaction of U(VI) with ternary layered double hydroxides by combined batch experiments and spectroscopy study. Chemical Engineering Journal, 2018, 338: 579-590.
[15]	WANG P Y, YIN L, WANG X X, et al.L-cysteine intercalated layered double hydroxide for highly efficient capture of U(VI) from aqueous solutions. Journal of Environmental Management, 2018, 217: 468-477.
[16]	LIU W, DAI X, BAI Z L, et al.Highly sensitive and selective uranium detection in natural water systems using a luminescent mesoporous metal-organic framework equipped with abundant lewis basic sites: a combined batch, X-ray absorption spectroscopy, and first principles simulation investigation. Environmental Science & Technology, 2017, 51(7): 3911-3921.
[17]	LI J, WANG X X, ZHAO G X, et al.Metal-organic framework- based materials: superior adsorbents for the capture of toxic and radioactive metal ions. Chemical Society Reviews, 2018, 47(7): 2322-2356.
[18]	WU Y H, PANG H W, YAO W, et al.Synthesis of rod-like metal-organic framework (MOF-5) nanomaterial for efficient removal of U(VI): batch experiments and spectroscopy study. Science Bulletin, 2018, 63(13): 831-839.
[19]	DROUT R J, OTAKE K, HOWARTH A J, et al.Efficient capture of perrhenate and pertechnetate by a mesoporous Zr metal-organic framework and examination of anion binding motifs. Chemistry of Materials, 2018, 30(4): 1277-1284.
[20]	WANG Y L, LIU Z Y, LI Y X, et al.Umbellate distortions of the uranyl coordination environment result in a stable and porous polycatenated framework that can effectively remove cesium from aqueous solutions. Journal of America Chemistry Society, 2015, 137(19): 6144-6147.
[21]	BANERJEE D, KIM D, SCHWEIGER M J, et al.Removal of TcO4- ions from solution: materials and future outlook. Chemical Society Reviews, 2016, 45(10): 2724-2739.
[22]	PANG H W, HUANG S Y, WU Y H, et al.Efficient elimination of U(VI) by polyethyleneimine decorated fly ash. Inorganic Chemistry Frontiers, 2018, 5: 2399-2407
[23]	YU S J, WANG X X, TAN X L, et al.Sorption of radionuclides from aqueous systems onto graphene oxide-based materials: a review. Inorganic Chemistry Frontiers, 2015, 2(7): 593-612.
[24]	DUAN L F, ZHANG Y, WANG L M, et al.Synthesis and characterization of MnFe2O4 with different morphologies and their application in water treatment. Journal of Inorganic Materials, 2014, 29(7): 763-768.
[25]	CARBONI M, ABNEY C W, LIU S B, et al.Highly porous and stable metal-organic frameworks for uranium extraction. Chemical Science, 2013, 4(6): 2396-2402.
[26]	BAI Z Q, YUAN L Y, ZHU L, et al.Introduction of amino groups into acid-resistant MOFs for enhanced U(VI) sorption. Journal of Materials Chemistry A, 2015, 3(2): 525-534.
[27]	LI L N, MA W, SHEN S S, et al.A combined experimental and theoretical study on the extraction of uranium by amino-derived metal-organic frameworks through post-synthetic strategy. ACS Applied Materials & Interfaces, 2016, 8(45): 31032-31041.
[28]	ZHU L, SHENG D P, XU C, et al.Identifying the recognition site for selective trapping of 99TcO4- in a hydrolytically stable and radiation resistant cationic metal-organic framework. Journal of America Chemistry Society, 2017, 139(42): 14873-14876.
[29]	SHENG D P, ZHU L, XU C, et al.Efficient and selective uptake of TcO4- by a cationic metal-organic framework material with open Ag+ sites. Environmental Science & Technology, 2017, 51(6): 3471-3479.
[30]	YANG P P, LIU Q, LIU J Y, et al.Interfacial growth of a metal-organic framework (UiO-66) on functionalized graphene oxide (GO) as a suitable seawater adsorbent for extraction of uranium(VI). Journal of Materials Chemistry A, 2017, 5(34): 17933-17942.
[31]	ZHANG N, YUAN L Y, GUO W L, et al.Extending the use of highly porous and functionalized MOFs to Th(IV) capture. ACS Applied Materials & Interfaces, 2017, 9(30): 25216-25224.
[32]	PENG Y G, HUANG H L, LIU D H, et al.Radioactive barium ion trap based on metal-organic framework for efficient and irreversible removal of barium from nuclear wastewater. ACS Applied Materials & Interfaces, 2016, 8(13): 8527-8535.
[33]	YUAN G Y, TIAN Y, LIU J, et al.Schiff base anchored on metal-organic framework for Co(II) removal from aqueous solution. Chemical Engineering Journal, 2017, 326: 691-699.
[34]	GAO Y J, FENG M L, ZHANG B, et al.An easily synthesized microporous framework material for the selective capture of radioactive Cs+ and Sr2+ ions. Journal of Materials Chemistry A, 2018, 6(9): 3967-3976.
[35]	YAO W, WANG X X, LIANG Y, et al.Synthesis of novel flower-like layered double oxides/carbon dots nanocomposites for U(VI) and 241Am(III) efficient removal: batch and EXAFS studies. Chemical Engineering Journal, 2018, 332: 775-786.
[36]	WANG X X, YU S J, WU Y H, et al.The synergistic elimination of uranium(VI) species from aqueous solution using bi-functional nanocomposite of carbon sphere and layered double hydroxide. Chemical Engineering Journal, 2018, 342: 321-330.
[37]	WANG X X, LIU Y, PANG H W, et al.Effect of graphene oxide surface modification on the elimination of Co(II) from aqueous solutions. Chemical Engineering Journal, 2018, 344: 380-390.
[38]	YU S J, WANG J, SONG S, et al.One-pot synthesis of graphene oxide and Ni-Al layered double hydroxides nanocomposites for the efficient removal of U(VI) from wastewater. Science China Chemistry, 2017, 60(3): 415-422.
[39]	YU S J, WANG X X, CHEN Z S, et al.Interaction mechanism of radionickel on Na-montmorillonite: influences of pH, electrolyte cations, humic acid and temperature. Chemical Engineering Journal, 2016, 302: 77-85.
[40]	YIN L, SONG S, WANG X X, et al.Rationally designed core-shell and yolk-shell magnetic titanate nanosheets for efficient U(VI) adsorption performance. Environmental Pollution, 2018, 238: 725-738.
[41]	GU P C, ZHANG S, LI X, et al.Recent advances in layered double hydroxide-based nanomaterials for the removal of radionuclides from aqueous solution. Environmental Pollution, 2018, 240: 493-505.
[42]	SONG W C, WANG X X, CHEN Z S, et al.Enhanced immobilization of U(VI) on Mucor circinelloides in presence of As(V): batch and XAFS investigation. Environmental Pollution, 2018, 237: 228-236.
[43]	TAN X L, FANG M, TAN L Q, et al.Core-shell hierarchical C@Na2Ti3O7·9H2O nanostructures for the efficient removal of radionuclides. Environmental Science: Nano, 2018, 5(5): 1140-1149.
[44]	NAEIMI S, FAGHIHIAN H.Performance of novel adsorbent prepared by magnetic metal-organic framework MOF modified by potassium nickel hexacyanoferrate for removal of Cs+ from aqueous solution. Separation and Purification Technology, 2017, 175: 255-265.
[45]	ZHANG C L, LIU Y, LI X, et al.Highly uranium elimination by crab shells-derived porous graphitic carbon nitride: batch, EXAFS and theoretical calculations. Chemical Engineering Journal, 2018, 346: 406-415.
[46]	HU Y Z, WANG X X, ZOU Y D, et al.Superior sorption capacities of Ca-Ti and Ca-Al bimetallic oxides for U(VI) from aqueous solutions. Chemical Engineering Journal, 2017, 316: 419-428.
[47]	CHEN Z S, WANG J, PU Z X, et al.Synthesis of magnetic Fe3O4/CFA composites for the efficient removal of U(VI) from wastewater. Chemical Engineering Journal, 2017, 320: 448-457.
[48]	ZHANG C L, LI X, CHEN Z S, et al.Synthesis of ordered mesoporous carbonaceous materials and its highly efficient capture of uranium from solutions. Science China Chemistry, 2018, 61(3): 281-293.
[49]	SUN Y B, LU S H, WANG X X, et al.Plasma-facilitated synthesis of amidoxime/carbon nanofiber hybrids for effective enrichment of 238U(VI) and 241Am(III). Environmental Science & Technology, 2017, 51(21): 12274-12282.
[50]	WANG J, WANG X X, ZHAO G X, et al.Polyvinylpyrrolidone and polyacrylamide intercalated molybdenum disulfide as adsorbents for enhanced removal of chromium(VI) from aqueous solutions. Chemical Engineering Journal, 2018, 334: 569-578.
[51]	YANG D X, WANG X X, SONG G, et al.One-pot synthesis of arginine modified hydroxyapatite carbon microsphere composites for efficient removal of U(VI) from aqueous solutions. Science Bulletin, 2017, 62(23): 1609-1618.
[52]	SONG S, HUANG S Y, ZHANG R, et al.Simultaneous removal of U(VI) and humic acid on defective TiO2-x investigated by batch and spectroscopy techniques. Chemical Engineering Journal, 2017, 325: 576-587.
[53]	TAN L Q, TAN X L, MEI H Y, et al.Coagulation behavior of humic acid in aqueous solutions containing Cs+, Sr2+ and Eu3+: DLS, EEM and MD simulation. Environmental Pollution, 2018, 235: 835-843.
[54]	ZHANG J Y, ZHANG N, ZHANG L J, et al. Adsorption of uranyl ions on amine-functionalization of MIL-101(Cr) nanoparticles by a facile coordination-based post-synthetic strategy and X-ray absorption spectroscopy studies. Scientific Reports, 2015, 5: 13514- 1-10.
[55]	WEN H, PAN Z Z, GIAMMAR D E, et al.Enhanced uranium immobilization by phosphate amendment under variable geochemical and flow conditions: insights from reactive transport modeling. Environmental Science & Technology, 2018, 52(10): 5841-5850.
[56]	ZHANG Y J, LAN J H, WANG L, et al.Adsorption of uranyl species on hydroxylated titanium carbide nanosheet: a first-principles study. Journal of Hazardous Materials, 2016, 308: 402-410.
[57]	WANG L, YUAN L Y, CHEN K, et al.Loading actinides in multilayered structures for nuclear waste treatment: the first case study of uranium capture with vanadium carbide MXene. ACS Applied Materials & Interfaces, 2016, 8(25): 16396-16403.
[58]	ZHENG T, YANG Z X, GUI D X, et al. Overcoming the crystallization and designability issues in the ultrastable zirconium phosphonate framework system. Nature Communications, 2017, 8: 15369-1-11.
[59]	SHENG G D, SHAO D D, FAN Q H D, et al. Effect of pH and ionic strength on sorption of Eu(III) to MX-80 bentonite: batch and XAFS study. Radiochimica Acta, 2009, 97(11): 621-630.
[60]	TAN X L, REN X M, CHEN C L, et al.Analytical approaches to the speciation of lanthanides at solid-water interfaces. TrAC Trends in Analytical Chemistry, 2014, 61: 107-132.
[61]	LUO F, CHEN J L, DANG L L, et al.High-performance Hg2+ removal from ultra-low-concentration aqueous solution using both acylamide-and hydroxyl-functionalized metal-organic framework. Journal of Materials Chemistry A, 2015, 3(18): 9616-9620.
[62]	BANERJEE D, XU W Q, NIE Z M, et al.Zirconium-based metal-organic framework for removal of perrhenate from water. Inorganic Chemistry, 2016, 55(17): 8241-8243.
[63]	HOSKINS B F, ROBSON R.Infinite polymeric frameworks consisting of three dimensionally linked rod-like segments. Journal of the American Chemical Society, 1989, 111(15): 5962-5964.
[64]	NALAPARAJU A, JIANG J W.Ion exchange in metal-organic framework for water purification: insight from molecular simulation. The Journal of Physical Chemistry C, 2012, 116(12): 6925-6931.