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作为一种新兴技术,空气取水技术能有效捕获空气中的水资源,可在全球范围内为人们提供洁净的饮用水[1]. 不同于雾收集技术[2]与空气冷却取水技术[3],吸附式空气取水技术是通过吸附材料捕获空气的水分子,在加热状态下蒸发解吸水分子,最后通过冷凝装置收集液态水[4],因此,吸附式空气取水技术[5 − 7]可克服气候条件的限制,低耗高效保障水资源供给.
硅胶[8]、分子筛[9]和以CaCl2[10]、LiCl[11]为主的吸湿盐等材料是吸附式空气取水装置的常用吸附剂,但实际应用中吸湿盐在水吸附过程易潮解形成液体,而硅胶、分子筛在解吸过程的能耗较高[12 − 13]. 金属有机框架材料(metal-organic framawork, MOF)材料具有稳定的框架结构保证材料的水稳定性能[14 − 18]。以MOF-801(Zr)[19]、MOF-303(Al)[20]等材料为例,由于其高比表面积和高孔隙率,材料能快速吸附空气中的水分子并具有较高的水吸附容量[21 − 22]. 将传统吸湿盐负载到MOF材料的框架结构中[23 − 24],能成功抑制吸湿盐遇水易潮解的问题,增加MOF材料的水吸附性能. 因此,MOF材料是种极具潜力的水吸附材料,在吸附式空气取水技术中具有较大应用前景[25].
在MOF材料制备过程,金属源和分散剂的选择多样,以铝基MIL-53[26]和富马酸铝[27]为例,氯化铝、硫酸铝和硝酸铝等铝盐都可作为铝源,在MOF-303(Al)制备过程中存在LiOH和NaOH两种分散剂的使用[20, 28]. 为推广MOF材料的实际应用,明确不同制备条件对材料性能的影响具有重要意义,原材料的易得性、制备方法的简单化和易放大也是重要的因素.
本研究基于水吸附性能优异的MOF-303(Al)材料,结合场发射扫描电子显微镜(Field Emission Scanning Electron Microscope, FESEM)、X-射线粉末衍射图谱(X-ray diffraction, XRD)、Brunauer-Emmett-Teller (BET)比表面积、孔容孔径等表征方法及水蒸气吸附性能测试,考察水溶剂、金属源、反应温度和分散剂类型等制备条件对材料水吸附性能和结构形貌的影响,以期为MOF-303(Al)及MOF材料的制备和推广提供支撑.
MOF-303(Al)的制备优化及水吸附性能
Preparation optimization and water adsorption performance of MOF-303(Al)
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摘要: 吸附式空气取水技术可在全球范围内为人们提供清洁的饮用水. 本研究采用水热法制备MOF-303(Al)材料,考察水溶剂、金属铝源、反应温度和分散剂等条件对其水吸附性能和结构形貌的影响,并探究水热过程直接实现MOF-303(Al)与无机盐复合的可能性. 结果表明,水溶剂和分散剂对MOF-303(Al)的水吸附性能影响较小,其水吸附容量均为0.4 g·g−1,且能在0.5 h内达到饱和吸附;温度和铝源显著影响材料的水吸附性能,水吸附容量变化幅度为0.3 g·g−1;减少水热过程的洗涤步骤能直接完成无机盐与MOF-303(Al)的复合,且材料在95%RH时的吸附容量达2.055 g·g−1.
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关键词:
- 水热制备 /
- 空气取水 /
- 水吸附性能 /
- MOF-303(Al).
Abstract: The adsorption water harvesting technology can provide clean drinking water to people worldwide. This paper prepares the MOF-303(Al) by hydrothermal, investigates the effects of preparation conditions such as aqueous solvent, metal-aluminum source, reaction temperature, and dispersant type on water adsorption performance and structure topography, and the possibility of directly achieving the composite of MOF-303(Al) with inorganic salts based on hydrothermal process was explored. The results show that the aqueous solvent and dispersant have little effect on the water adsorption performance; both can achieve a water adsorption capacity of 0.4 g·g−1 and the fast adsorption kinetics of saturation adsorption can be achieved in half hour. Temperature and aluminum source will significantly affect the water adsorption performance, with a floating change of 0.3 g·g−1. Reducing the washing step of hydrothermal process can directly realize the recombination of inorganic salt and MOF-303(Al), and achieve a high adsorption capacity of 2.055 g·g−1 at 95%RH.-
Key words:
- hydrothermal /
- atmosphere water harvesting /
- water adsorption performance /
- MOF-303(Al).
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图 6 (a)不同铝源条件下制得材料的水吸附容量(样品编号:2,4—6);(b)不同温度条件下制得材料的水吸附容量(样品编号:2,7—9);(c)硫酸铝为铝源时材料吸附动力学曲线(样品编号:4);(d)85℃反应温度时材料吸附动力学曲线(样品编号:8)
Figure 6. (a)water adsorption capacity based on the influence of aluminum source (sample number:2,4—6);(b)water adsorption capacity based on the influence of temperature (sample number:2,7—9) (c)adsorption kinetic curves under aluminum sulfate as aluminum source(sample number:4) ;(d)adsorption kinetic curves under temperature of 85℃(sample number:8)
图 7 (a) MOF-303(Al)制备过程; (b) MOF材料元素分布图(氢氧化钙为分散剂,样品编号:11);(c) 分散剂影响下材料水吸附容量(样品编号:2,10-11); (d) MOF材料元素分布图(氢氧化钙为分散剂时,省略洗涤分离步骤)
Figure 7. (a) The synthesis process of MOF-303(Al); (b) Material element distribution map (calcium hydroxide as dispersant,sample number :11); (c) Water adsorption capacity based on the influence of dispersant (sample number :2,10-11);(d) Material element distribution map (calcium hydroxide as dispersant without the wash and separation step)
表 1 样品制备条件
Table 1. Synthesis conditions of samples
编号
Number水溶剂
Water solvent铝源
Aluminum source温度
Temperature分散剂
Dispersants1 超纯水 AlCl3 100 ℃ LiOH 2 去离子水 AlCl3 100 ℃ LiOH 3 自来水 AlCl3 100 ℃ LiOH 4 去离子水 Al2(SO4)3 100 ℃ LiOH 5 去离子水 Al((CH3)3CHO)3 100 ℃ LiOH 6 去离子水 Al(OH)(CH3COO)2 100 ℃ LiOH 7 去离子水 AlCl3 25 ℃ LiOH 8 去离子水 AlCl3 85 ℃ LiOH 9 去离子水 AlCl3 150 ℃ LiOH 10 去离子水 AlCl3 100 ℃ NaOH 11 去离子水 AlCl3 100 ℃ Ca(OH)2 表 2 样品比表面积、孔容与孔径
Table 2. Specific surface area, pore volume, and pore size of samples
编号
Number比表面积/(m2·g−1)
Specific surface area微孔比表面积/(m2·g−1)
Micropore specific
surface area孔体积/
(cm3·g−1)
Pore volume微孔孔体积/(cm3·g−1)
Micropore pore volume吸附平均孔径/ nm
Adsorption average
pore diameter1 1199.2469 1156.3449 0.5506 0.4321 1.8364 2 1407.1263 1294.6678 0.9886 0.4920 2.8101 3 596.2009 553.1305 0.3659 0.2090 2.4548 4 169.2528 154.8814 0.0915 0.0589 2.1635 5 51.0881 8.1074 0.1816 0.0032 14.2184 6 92.3021 — 0.2367 0.0006 10.2589 7 132.6209 21.7183 0.8211 0.0087 24.7664 8 734.9189 683.7707 0.4418 0.2570 2.4050 9 330.6443 294.8973 0.2747 0.1110 3.3234 10 582.2841 496.4246 0.7303 0.1895 5.0165 11 616.1999 580.6024 0.3045 0.2166 1.9769 “—”无数据 表 3 MOF材料ICP-OES结果
Table 3. ICP-OES results of MOF materials
分散剂
Dispersants是否洗涤
Wash or not元素
Element元素摩尔比
Mole ratioLiOH 是 Al:Li 96.6 否 1.16 NaOH 是 Al:Na 未检出Na 否 1.29 Ca(OH)2 是 Al:Ca 164 否 2.71 表 4 MOF材料吸附容量变化(g·g−1)
Table 4. The change of water adsorption capacity of the MOF material(g·g−1)
分散剂
Dispersants氢氧化锂
Lithium hydroxide容量变化
Capacity variation氢氧化钠
Sodium hydroxide容量变化
Capacity variation氢氧化钙
Calcium hydroxide容量变化
Capacity variation是否洗涤
Wash or not否
No是
Yes否
No是
Yes否
No是
Yes20%RH 0.243 0.262 −7% 0.194 0.320 −39% 0.209 0.325 −36% 40%RH 0.288 0.319 −10% 0.212 0.345 −39% 0.276 0.382 −28% 60%RH 0.384 0.326 18% 0.229 0.359 −36% 0.367 0.382 −4% 80%RH 0.734 0.319 130% 0.824 0.379 117% 0.684 0.393 74% 95%RH 1.834 0.411 346% 2.055 0.495 315% 1.567 0.445 252% -
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