油气/水蒸气在TMCS改性MIL-101(Cr)上的吸附性能研究

采用三甲基氯硅烷(TMCS)对MIL-101(Cr)进行表面改性处理以改变材料的疏水亲油性能,经XRD、FT-IR、N2吸附和脱附、表面羟基滴定等表征证明TMCS分子通过与MIL-101(Cr)表面羟基缩合进入骨架。采用C5~C7正构烷烃模拟油气组份,测试了MIL-101(Cr)和TMCS-MIL-101(Cr)的油气和水蒸气的静态吸附性能,并考察了相对湿度对油气动态吸附性能的影响。结果表明,25℃下C5~C7正构烷烃以及水蒸气在TMCS-MIL-101(Cr)上静态吸附量分别为0.433、0.510、0.464和0.233 g?g?1,与MIL-101(Cr)相比TMCS-MIL-101(Cr)的C5~C7正构烷烃静态吸附量较高,水蒸气静态吸附量较低;根据穿透曲线计算,在相对湿度97%时TMCS-MIL-101(Cr)对C5~C7正构烷烃的动态吸附量为相对湿度0%时的80%以上。改性后材料的油气静态吸附性能提升明显,且水蒸气对TMCS-MIL-101(Cr)油气吸附影响较小。     

MIL-101(Cr)开式吸附性能实验

采用水热合成法制备水热稳定金属有机骨架MIL-101(Cr),基于太阳能吸附式空气取水选取不同的实验工况,将MIL-101(Cr)、细孔硅胶作为研究对象,相对湿度控制在50%、温度范围5～45℃条件下,测试并对比了MIL-101(Cr)与细孔硅胶的吸附性能。实验表明,35℃、50%RH条件下,吸附过程进行1000min,MIL-101(Cr)水吸附量为22.05g/100g,其吸附量相比细孔硅胶提高93%左右;当系统平衡时,MIL-101(Cr)有效平均吸附速率相比细孔硅胶提高120%左右。此外,在相对湿度（RH）50%、温度范围5～45℃条件下,MIL-101(Cr)的平衡吸附量在11.40～23.47g/100g之间。在所控温度下,MIL-101(Cr)在25℃时平衡吸附量最大,在5℃时平衡吸附量最小,25℃时MIL-101(Cr)的平衡吸附量相比5℃时提高106%左右。该实验可以为四季工况不同温度下MIL-101(Cr)用于太阳能吸附式空气取水提供基础数据。     

油气/水蒸气在乙二胺改性MIL-101(Cr)-NDC材料上的吸附性能研究

以乙二胺(ED)为改性剂对MIL-101(Cr)-NDC进行表面改性,以改变材料的亲油疏水性能。经XRD、FT-IR、N2吸附和脱附等表征表明,ED分子成功连接入材料中。采用C_5~C_7正构烷烃模拟油气组份测定材料的油气吸附性能,并考察了相对湿度对改性前后材料油气吸附性能的影响。结果表明,25℃下,C_5~C_7正构烷烃和水蒸气在ED-MIL-101(Cr)-NDC上静态吸附量分别为0.558、0.695、0.613 g/g和0.254 g/g,与改性前材料相比,ED-MIL-101(Cr)-NDC的C_5~C_7正构烷烃静态吸附量较高,水蒸气静态吸附量较低;ED-MIL-101(Cr)-NDC在97%相对湿度下的C_5~C_7正构烷动态吸附量为0%相对湿度下C_5~C_7正构烷动态吸附量的65%左右。改性后材料的油气静态吸附性能提升明显,且水蒸气对ED-MIL-101(Cr)-NDC油气吸附影响较小。     

乙酸为矿化剂制备MIL-101(Cr)及其CO2吸附研究

以氢氟酸为矿化剂制备金属有机骨架MIL-101(Cr)存在过程繁复、危险系数高的问题。文中改用乙酸为矿化剂,使用X射线衍射、热重分析、扫描电镜、氮气吸附-脱附等表征手段研究了材料的物理结构和形态,并采用固定床评价装置测试比较了样品对CO_2的吸附能力。结果表明:当以1.66 g对苯二甲酸和4 g九水硝酸铬为原料并加入18 mL乙酸时制备的MIL-101(Cr)在25℃,0.1 MPa对CO_2的饱和吸附量达到了130.36 mg/g,是传统制备方法的2.5倍,该结果说明采用适量乙酸为矿化剂同样可以制备出对CO_2吸附性能较好的MIL-101(Cr);并在低于1 MPa的不同吸附压力下,随着吸附压力的升高,MIL-101(Cr)和MIL-101(Cr)-A-18的2种材料对CO_2的吸附饱和时间逐渐延长,饱和吸附量增加,说明了高压有利于2种材料对CO_2的吸附。     

金属有机骨架材料MIL-101（Cr）-NH2的合成及其气体吸附性能

采用碱辅助的原位水热合成法制备了纳米金属有机骨架材料MIL-101(Cr)NH2,研究了合成液中NaOH加入量对其晶体结构、形貌和孔结构的影响,测定了273.4,298和333K下CO2和N2在MIL-101(Cr)NH2上的等温吸附曲线,并对其性质进行了表征.结果表明,加入适量碱(NaOH:NH2BDC=4:2,摩尔比)可得到粒径约40nm的MIL-101(Cr)NH2纳米颗粒,其BET比表面积可达2594m2/g,孔容为2.11cm3/g,273.4K时CO2的吸附量可达25.9mmol/g,CO2与N2的理想分离系数为19.4.     

用高压气体吸脱附-微量热联用法对CO2和CH4在煤上吸附热力学的研究

为了从热力学角度揭示CO_2和CH_4在煤上的竞争吸附实质,为驱替理论提供热力学参考,利用高压气体吸脱附-微量热联用仪,通过容量法测定30℃,40℃,50℃温度下CO_2和CH_4在煤上的吸附等温线,同时计算等量吸附热和极限吸附热,并测定了CO_2和CH_4在煤上的吸附热。结果表明:CO_2和CH_4吸附等温线均属于Ⅰ型吸附等温线,且均符合Langmuir吸附模型;温度升高,CO_2和CH_4在煤上的吸附量均减小;相同条件下,CO_2在煤上的吸附量明显高于CH_4的吸附量,表明CO_2更容易吸附于煤上。CO_2和CH_4在煤上的等量吸附反映出煤吸附CO_2和CH_4的过程均为物理吸附。同时CO_2在煤上的等量吸附热高于CH_4的等量吸附热,说明CO_2分子与煤分子之间作用力强于CH_4与煤分子之间的作用力,极限吸附热和实验测得的吸附热也显示了同样结果,从热力学角度阐释了CO_2和CH_4在煤体表面竞争吸附的实质。     

吸附热预测吸附等温线

实验测定了N2 在沸石分子筛、C2 H6 在活性炭、CO2 在硅胶上的吸附等温线 ,研究用Clausius Clapeyron方程求得等量吸附热、再利用所得的吸附热预测其它温度的吸附等温线数据的方法。将吸附热预测的等温线与实验值及插值法内插得到的吸附等温线数据进行了比较 ,结果表明吸附热预测值与实验值吻合较好。此外还对文献数据利用等量吸附热预测较高压力 ( 65 0kPa)下的等温线 ,均与文献中的实验值一致。为吸附工业操作需要不同温度下的等温线数据和吸附过程的模拟与设计提供了简便、准确的计算方法     

多种因素对MIL-101(Cr)选择性吸附水溶液中染料的影响

在多种条件下研究了金属有机框架MIL-101(Cr)对阳离子型染料(亚甲基蓝、罗丹明B)和阴离子型染料(甲基橙、酸性铬蓝K)的吸附性质,主要研究了MIL-101(Cr)对亚甲基蓝和甲基橙的选择性吸附作用。结果表明,中性环境下无论在单组分还是双组分体系中MIL-101(Cr)对阴离子型染料的吸附能力均大于对阳离子型的吸附能力。在pH=3,T=300 K的条件下,选择性系数β可达5.9,但随着pH的增加,选择性系数逐渐降低。相比之下,温度对吸附的选择性影响不大。选择性吸附的机理可以解释为:由于表面带正电荷,MIL-101(Cr)对阴离子型染料产生静电吸引作用;相反,对阳离子型染料的排斥作用而降低了其吸附能力。另外,乙二胺改性提高了MIL-101(Cr)对阴离子型染料的选择吸附性能,而草酸改性降低了选择吸附性。     

乙二胺改性金属有机骨架材料MIL-101(Cr)常压下吸附CO2

采用溶剂热法将乙二胺接枝到金属有机骨架材料MIL-101(Cr)上,用于常压下CO2的吸附,研究了乙二胺接枝量及温度对材料结构、形貌和CO2吸附性能的影响. 结果表明,乙二胺改性的MIL-101材料在常温常压下对CO2的吸附量可达2.43 mmol/g,比改性前提高14.6%,CO2/N2的吸附分离系数从11提高至17,比改性前提高55.6%. 改性后材料经80℃真空加热可完全脱附再生,具有很好的再生稳定性.     

MIL-101的制备与吸附水中亚硝酸盐氮研究

通过溶剂热法制备金属有机骨架材料(MOFs)MIL-101(Fe)和MIL-101(Fe)-NH_2,并通过X射线衍射(XRD)、傅里叶红外光谱(FT-IR)、扫描电镜(SEM)进行表征。以水中的亚硝酸盐氮(NO_2~--N)为目标物,研究2种材料对其的吸附作用。结果表明,2种材料对NO_2~--N的吸附符合准二级动力学和Langmuir等温吸附模型,吸附平衡时间为5 h。由于氨基的存在,MIL-101(Fe)-NH_2的吸附能力略优于MIL-101(Fe)。     

Adsorption Refrigeration Performance of Shaped MIL-101-Water Working Pair

A new metal-organic framework of MIL-101 was synthesized by hydrothermal method and the powder prepared was pressed into a desired shape. The effects of molding on specific surface area and pore structure were investigated using a nitrogen adsorption method. The water adsorption isotherms were obtained by high vacuum gravimetric method, the desorption temperature of water on shaped MIL-101 was measured by thermo gravimetric analyzer, and the adsorption refrigeration performance of shaped MIL-101-water working pair was studied on the simulation device of adsorption refrigeration cycle system. The results indicate that an apparent hysteresis loop ap-pears in the nitrogen adsorption/desorption isotherms when the forming pressure is 10 MPa. The equilibrium ad-sorption capacity of water is up to 0.95 kg·kg^-1 at the forming pressure of 3 MPa （MIL-101-3）. The desorption peak temperature of water on MIL-101-3 is 82℃, which is 7 ℃ lower than that of silica gel, and the desorption temperature is no more than 100 ℃. At the evaporation temperature of 10 ℃, the refrigeration capacity of MIL-101-3-water is 1059 kJ·kg^-1, which is 2.24 times higher than that of silica gel-water working pair. Thus MIL-101-water working pair presents an excellent adsorption refrigeration performance.     

Adsorption Isotherms,Kinetics, and Desorption of 1,2-Dichloroethane on Chromium-Based Metal Organic Framework MIL-101

Adsorption equilibrium and kinetics of 1,2-dichloroethane on a chromium-based metal-organic framework MIL-101 were studied. Desorption activation energies of 1,2-dichloroethane on the MIL-101 were measured using temperature program desorption (TPD) experiments. Results showed that the adsorption capacity of the MIL-101 for 1,2-dichloroethane is 19 mmol/g at 288 K, being much higher than those of some activated carbon, zeolite, and MWCNTs. The isotherms of 1,2-dichloroethane were well fitted by the Langmuir equation. The isosteric heat and diffusion coefficients of 1,2-dichloroethane adsorption on the MIL-101 were separately within the range of 42.0–61.6 kJ/mol and range of 0.854–2.246 × 10^?10 cm²/s. TPD spectra exhibited two types of adsorption sites on the MIL-101 with desorption activation energy of 48.6 and 87.6 kJ/mol separately. Multiple recycle runs of 1,2-dichloroethane adsorption-desorption at 298 K (10 mbar for adsorption and 0.05 mbar for desorption) showed the 1,2-dichloroethane adsorption on the MIL-101 is highly reversible, and desorption efficiency is up to 98.42%.     

Heterogeneity of Adsorption Sites and Adsorption Kinetics of n-Hexane on Metal-Organic Framework MIL-101(Cr)

abstract The heterogeneity of adsorption sites and adsorption kinetics of n-hexane on a chromium terephthalate-based metal-organic framework MIL-101(Cr) were studied by gravimetric method and temperatu...     

氨气改性的NH3@MIL-53(Cr)吸附CO2和CH4的性能

采取水热法成功合成MIL-53（Cr）晶体,分别应用0.1、1、3 mol·L^-1的氨气对MIL-53（Cr）进行改性,制得系列的NH₃@MIL-53（Cr）-1#,NH₃@MIL-53（Cr）-2#,NH₃@MIL-53（Cr）-3#。实验结果表明：与原始的MIL-53（Cr）晶体相比,尽管制得NH3@MIL-53（Cr）系列材料的比表面积依次减少,但其单位比表面积的CO₂吸附容量大小依次为：NH₃@MIL-53（Cr）-3#>NH₃@MIL-53（Cr）-2#>NH₃@MIL-53（Cr）-1#。表明氨气改性会使得材料表面的碱性增强,从而增强了其对酸性气体CO₂的吸附。此外,改性后的NH₃@MIL-53（Cr）对水蒸气的吸附量明显减少,表明其憎水性能得到改善。较高浓度氨气改性会导致材料的比表面积大幅下降,会引起单位质量吸附剂的吸附容量下降。用1 mol·L^-1浓度的氨气改性得到的NH3@MIL-53（Cr）-2#,不仅对CO₂的吸附容量最大,而且对CH₄的吸附容量明显下降,这将有助于进一步提高改性材料NH3@MIL-53（Cr）-2# 对CO₂/CH₄的吸附选择性。     

MIL-101Cr-F/Cl用于N2O的捕集研究

氧化亚氮（N₂O）是仅次于CO₂和CH₄的第三大温室气体,对其捕集具有资源回收和减排温室气体的双重价值。本文通过添加氢氟酸和盐酸合成了末端具有不同阴离子的MIL-101Cr材料：MIL-101（Cr）-F和MIL-101（Cr）-Cl,通过XRD、BET、SEM等对样品进行了表征,测试并分析了两种样品对N₂O和N₂的吸附性能,进行了选择性和吸附热的计算以及混合气体的穿透模拟。研究结果表明,MIL-101（Cr）-Cl拥有目前最高的N₂O吸附容量（6.43 mmol/g,298 K）和N₂O/N₂选择性（267）,混合气体（N₂O/N₂=0.1%/99.9%）穿透模拟结果显示MIL-101（Cr）-Cl具有更加优异的微量N₂O捕获能力。     

Rapid synthesis of CNTs@MIL-101(Cr) using multi-walled carbon nanotubes (MWCNTs) as crystal growth accelerator☆

In this work,hybrid material CNTs@MIL-101(Cr) was synthesized in 2 h using multi-walled carbon nanotubes(MWCNTs) as the crystal growth accelerator with hydrothermal method.The characteristic differences between the crystals of CNTs@MIL-101(Cr) and MIL-101 were investigated by N_2 adsorption–desorption isotherms,X-ray diffraction(XRD),scanning electron microscope(SEM) and thermogravimetric analyzer(TGA).The results showed that MWCNTs embedding in the hybrid material provide more mesoporous volumes than that of MIL-101.Moreover,the fast synthesized crystals of CNTs@MIL-101(Cr) still preserve the octahedral shape like MIL-101 and have a larger size ranging from 1.5 to 2.0 μm which were approximately three times larger than that of MIL-101.In the proposed mechanism,the roles of MWCNTs played in the crystallization were discussed where MWCNTs can be seen as coaxial cylindrical tubes composed of multi-layer graphenes and the place where nucleation and crystal growth processes occur at the tubes' out surface.Then,a crystal seeding layer bonding with the MWCNTs may be easily formed which accelerates the growth rate of MIL-101 crystals.Thus,larger crystals of CNTs@MIL-101(Cr) were formed due to the faster crystal growth rate of MIL-101.     

Hierarchically structural polyacrylonitrile/MIL-101(Cr) nanofibrous membranes with super adsorption performance for indoxyl sulfate

Excess protein-bound uremic toxins (such as indoxyl sulfate [IS]) in the blood could aggravate chronic kidney disease and also predispose to serious cardiovascular disease. In this study, we constructed a novel IS adsorbent polyacrylonitrile/MIL-101(Cr) (PAN-M) nanofibrous membrane with high adsorption capacity and ultra-fast sorption rate for IS. The porous metal–organic framework MIL-101(Cr) were embedded in PAN nanofibers by electrospinning as an adsorbent for easy recovery. It was found that MIL-101(Cr) had a strong electrostatic effect on the SO₃⁻ of IS and could reach the adsorption equilibrium within 5 min. Notably, MIL-101(Cr) showed an extremely high adsorption capacity (~170 mg/g) for IS. The MIL-101(Cr) loading of prepared PAN-M nanofibrous membrane was optimized at 60 wt% and the optimal PAN-M60 exhibited an appreciable IS adsorption capacity (103 mg/g). The removal of IS was enhanced from 35.4% to 62.5% during hemodialysis by using PAN-M60 as adsorbent immersed in dialysate. This efficient adsorption performance can greatly reduce the consumption of dialysate and may shorten the hemodialysis time. This work would provide a fresh perspective on the development of MOF-based adsorbents to improve hemodialysis therapies.     

Characterization of metal-organic frameworks by water adsorption

The water physisorption properties and the water stability of the metal-organic frameworks HKUST-1 (=(Cu₃(BTC)₂) (BTC = benzene-1,3,5-tricarboxylate)), ZIF-8, MIL-101, MIL-100(Fe) and DUT-4 (=Al(OH)(NDC)) (NDC = naphthalene-2,6-dicarboxylate) were studied. The water physisorption isotherms were compared to nitrogen physisorption isotherms and the chemical stability after water adsorption was investigated.Water adsorption does not only provide information about specific surface area, pore size and pore volume, but can also be used to estimate hydrophobicity and stability towards moisture. Both HKUST-1 and DUT-4 turned out to be unstable in direct contact with water, whereas the MIL-materials and ZIF-8 do show stability. The highest water adsorption affinity was observed for HKUST-1. Even though unstable in liquid water, for applications in trace water removal or molecular sensing HKUST-1 is a promising material. ZIF-8 is highly inert but hydrophobic. The MIL-materials are both likely candidates for water adsorption applications, but higher concentrations of the adsorbate are needed to attain an effective adsorption. DUT-4 shows insufficient adsorption capacity, but stability at ambient conditions is given.