Removal of benzoic acid from industrial wastewater using metal organic frameworks: equilibrium,kinetic and thermodynamic study

In this work, the adsorption of benzoic acid (BA) over metal organic framework of chromium-benzenedicarboxylates (MIL-101) is reported for the first time. The influences of pH, contact time, initial concentration, and temperature of BA solution on the adsorption behavior were investigated. The Langmuir adsorption isotherm was adequate to represent the experimental data (R² > 0.99) and the adsorption kinetics was well-represented by a pseudo-second order kinetic model (R² > 0.96). The zeta potential of MIL-101 decreased with increasing pH confirming the importance of electrostatic interactions between MIL-101 and BA as well as the importance of the large pore volume (1.32 m³/g) and large surface area (2390 m²/g) of MIL-101 for adsorption interaction. The thermodynamics analysis indicated negative free energy, enthalpy, and entropy changes suggesting that the adsorption of BA on MIL-101 is spontaneous and exothermic. The adsorption capacity of BA adsorption over MIL-101 was compared with those for other conventional adsorbents. The maximum capacities of BA uptake on MIL-101, activate carbon, and multiwall carbon nanotubes were 769.2, 406.5, and 341.2 mg/g, respectively, suggesting the superiority of MIL-101 as an adsorbent. Adsorption of real wastewaters containing other organic compounds in addition to BA confirmed the versatility of MIL-101 as a suitable adsorbent in wastewater treatment compared with conventional adsorbents.     

Coordination of thin-film nanofibrous composite dialysis membrane and reduced graphene oxide aerogel adsorbents for elimination of indoxyl sulfate

The protein-bound uremic toxins, represented by indoxyl sulfate(IS), have been associated with the progression of chronic kidney disease and the development of cardiovascular disease in the presence of impaired renal function. Herein, we proposed a novel strategy of thin-film nanofibrous composite(TNFC) dialysis membrane combined with reduced graphene oxide(rGO) aerogel adsorbents for clinical removal of IS as well as high retention of proteins. The TFNC membrane was prepared by electrospinning ...     

Synthesis of MIL-101@g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanocomposite for enhanced adsorption capacity towards CO<Subscript>2</Subscript>

MIL-101@g-C₃N₄ nanocomposite was prepared by solvothermal synthesis and used for CO₂ adsorption. The parent materials (MIL-101 and g-C₃N₄) and the MIL-101@g-C₃N₄ were characterized by X-ray diffraction, argon adsorption/desorption, Fourier transform infrared spectroscopy, thermal analysis (TG/DTA), transmission electronic microscopy, and Energy-dispersive X-ray spectroscopy. The results confirmed the formation of well-defined MIL-101@g-C₃N₄ with interesting surface area and pore volume. Furthermore, both MIL-101 and MIL-101@g-C₃N₄ were accomplished in carbon dioxide capture at different temperatures (280, 288, 273 and 298 K) at lower pressure. The adsorption isotherms show that the nanocomposite has a good CO₂ adsorption affinity compared to MIL-101. The best adsorption capacity is about 1.6 mmol g^?1 obtained for the nanocomposite material which is two times higher than that of MIL-101, indicating strong interactions between CO₂ and MIL-101@g-C₃N₄. This difference in efficacy is mainly due to the presence of the amine groups dispersed in the nanocomposite. Finally, we have developed a simple route for the preparation of an effective and new adsorbent for the removal of CO₂, which can be used as an excellent candidate for gas storage, catalysis, and adsorption.     

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。     

Adsorption of methane on porous metal carboxylates

Porous metal carboxylates such as MIL-101 (Cr-terephthalate), MIL-100-Cr (Cr-trimesate) and MIL-100-Fe (Fe-trimesate) with very high porosity have been tested as potential adsorbents for methane storage materials. The MIL-101 shows one of the highest adsorption capacities for methane. The adsorption capacity per weight increases with increasing BET surface area or micropore volume irrespective of the structure, type of metal ions such as Cr³⁺ and Fe³⁺. This result suggests that the porous adsorbent for methane should have high porosity rather than special adsorption sites or structures.     

CuAlCl4 doped MIL-101 as a high capacity CO adsorbent with selectivity over N2

A CuAlCl₄ doped metal organic framework, CuAlCl₄@MIL-101, was prepared by introducing CuAlCl₄ into the pores of MIL-101 for the selective adsorption of CO over N₂. The CuAlCl₄ molecules were evenly distributed into various pores sizes and did not change the intrinsic structure of the MIL-101. Isotherms for CO and N₂ adsorption at 298 K showed that the CO capacity on CuAlCl₄@MIL-101 was much higher than that on virgin MIL-101, whereas the N₂ capacity decreased. The selectivity for CO over N₂ improved from 4.64 to 31.5 at 298 K and 1 bar. The CuAlCl₄@MIL-101 adsorbent displayed outstanding CO adsorption stability and the adsorbent could be regenerated by applying a simple vacuum of 4 mmHg.     

H6P2W18O62/MIL-101(Fe)材料的制备及其吸附性能

采用溶剂热合成法在制备MIL-101(Fe)的过程中引入杂多酸H_6P_2W_(18)O_(62),制备出吸附剂H_6P_2W_(18)O_(62)/MIL-101(Fe),并测试了其对亚甲基蓝(MB)的吸附性能。考察了H_6P_2W_(18)O_(62)的负载量、MB质量浓度、溶液pH、温度等对材料的吸附性能。通过XRD、SEM、FTIR、N2吸附-脱附等手段对材料进行表征。结果表明:吸附平衡前,吸附量随MB质量浓度的增加而增加,在溶液pH=4、H_6P_2W_(18)O_(62)负载量相对于复合物质量分数为35%的条件下,吸附剂H_6P_2W_(18)O_(62)/MIL-101(Fe)对亚甲基蓝溶液吸附效果最佳,在303K下H_6P_2W_(18)O_(62)/MIL-101(Fe)对MB的最大吸附量可达148.1 mg/g。通过动力学和热力学分析,该吸附过程符合拟二级动力学与Langmuir等温吸附模型,同时是一个吸热、自发的过程。     

Adsorption behaviors of the aminated chitosan adsorbent

Using inverse suspension technology, a novel aminated chitosan adsorbent with higher adsorption ability for metal cations and metal anions was prepared. Through cross-linking amination reaction, the content of amidocyanogen of aminated chitosan adsorbent was enhanced four times than that of chitosan cross-linked adsorbent. As can be seen from the results, the adsorption ability of the novel aminated chitosan adsorbent for (Nicit)⁻ and Cr(VI) was enhanced remarkably. When the initial concentration of metallic ion was 1,000 mg/L, the adsorption capacity of the novel aminated chitosan adsorbent for nickel citrate and Cr(VI) was up to 30.2 mg/g and 28.7 mg/g, respectively. And the adsorption capacity of the novel aminated chitosan adsorbent for Ni²⁺ was still higher. So the new aminated chitosan adsorbent offers not only a higher uptake for metal cations but also a better adsorption capacity for metal anions.     

GO@MIL-101的制备及其对水中Cr（Ⅵ）的去除

通过水热法制备了掺杂氧化石墨烯（GO）的金属有机框架GO@MIL-101,并考察了GO掺杂量对GO@MIL-101形貌和性质的影响规律。GO的掺杂影响了MIL-101晶体的形成过程。随着GO掺杂量的增加,GO@MIL-101晶体的完整性降低、粒径减小,团聚现象越发显著。GO@MIL-101能够有效去除溶液中的Cr（Ⅵ）,该过程符合拟二级动力学方程。由Langmuir吸附等温线拟合得到的最大吸附量与GO掺杂量有关,在2%[相对于Cr（NO₃）₃·9H₂O质量]时达到最大,这与此时GO@MIL-101同时具有较大的比表面积和较大的孔体积有关。Cr（Ⅵ）的去除过程伴随着溶液中NO₃^-浓度的升高以及pH的下降,电荷平衡计量分析表明MIL-101和GO@MIL-101对Cr（Ⅵ）的去除机制相同,主要依靠MIL-101的离子交换作用,并且所去除的Cr（Ⅵ）以CrO₄^2-形式存在于固相中。     

乙醇在MIL-101上的吸附相平衡及其吸附机理

主要研究了MIL-101材料对乙醇的吸附性能和吸附机理。采用水热合成法制备了MIL-101(Cr),并分别应用N₂静态吸附、X射线粉末衍射(PXRD)、傅里叶红外光谱(FTIR)等分析手段对MIL-101晶形结构、孔隙结构参数进行分析表征。应用静态吸附法测定乙醇和水蒸气在不同温度下的吸附等温线,并讨论乙醇吸附在MIL-101(Cr) 4种吸附位的机理,根据吸附等温线估算出乙醇和水蒸气在MIL-101上的等量吸附热,并测试了乙醇在MIL-101上的吸附循环性能。研究表明,在298 K下,MIL-101的乙醇吸附容量为20.3 mmol·g^-1,远高于传统吸附材料。在低压下MIL-101对乙醇的吸附量高于水蒸气的吸附量,这是由于乙醇的偶极矩和分子动力学直径均比水大,使得乙醇分子在孔道中受到更大吸附力场作用;在低吸附量范围,乙醇在MIL-101上的等量吸附热要高于水蒸气的等量吸附热。在较高吸附压力条件下,主要发生多层吸附或孔填充,受吸附剂的孔容限制效应,尺寸越大的分子被吸附的物质的量会越少,由于乙醇的动力学直径(0.45 nm)大于水分子的动力学直径(0.268 nm),所以在较高吸附压力下乙醇在MIL-101上吸附量要小于水蒸气的吸附量。多次吸附脱附等温线测试显示MIL-101具有良好的乙醇吸附循环性能。     

Electrospun cellulose acetate/P(DMDAAC-AM) nanofibrous membranes for dye adsorption

In recent years, organic nanofibrous membranes have received more attention because of their excellent performance in wastewater treatment. In this study, the soluble poly(dimethyldiallylammonium chloride-acrylamide) (P(DMDAAC-AM)) was first synthesized by aqueous copolymerization. Afterward, cellulose acetate (CA)/P(DMDAAC-AM) composite nanofibrous membranes were electrospun and utilized to remove acid black 172 from simulated wastewater. When the proportion of P(DMDAAC-AM) to CA was 20, 30, and 40 wt %, the equilibrium adsorption capacities were 116, 159, and 192 mg g⁻¹, respectively. The adsorption capacity of CA/P(DMDAAC-AM) composite nanofibrous membrane showed a well linear relationship with the average fiber diameter. When the average fiber diameter was 185 nm, the adsorption capacity of 231 mg g⁻¹ was achieved. The adsorption kinetics of CA/P(DMDAAC-AM) membranes with various fiber diameters was all consistent with the pseudo-second-order model. The rate-limiting step was primarily controlled by chemisorption. The adsorption isothermal data fitted well with the Langmuir isotherm model. The prepared CA/P(DMDAAC-AM) nanofibrous membrane was effective to remove the acid black 172 in the environmental interested pH range of 4.0–10.0. As an effective dye adsorbent, CA/P(DMDAAC-AM) nanofibrous membrane shows wide application prospect with its excellent adsorption performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48565.     

A high Cr (VI) absorption efficiency and easy recovery adsorbent: Electrospun polyethersulfone/polydopamine nanofibers

Cr (VI) is a highly toxic pollutant to humans, to achieve high adsorption capacity, easy recovery, and good reusability, polyethersulfone/polydopamine (PES/PDA) ultrafine fibers were prepared successfully. A series of preparing effect factors were investigated systematically and the optimum one is 8.5 pH value at room temperature and 2 g/L dopamine concentration. And then they were used as an adsorbent for the removal of Cr (VI) ions from wastewater. The effect factors pH, the adsorbent dosage, and time were discussed on Cr (VI) adsorption process and the Cr (VI) adsorption behavior was investigated. It is found that the maximum Cr (VI) adsorption capacity is 115.2 ± 4.8 mg/g at pH = 3 using 0.06 g PES/PDA with 80 mins. The Cr (VI) adsorption process followed the pseudo-second-order model (r² ≥ 0.99) and adsorption isotherms were fitted to the Langmuir model (R² ≥ 0.999). Furthermore, the Cr (VI) adsorption mechanism was supposed according to the X-ray photoelectron spectroscopic results. Finally, PES/PDA ultrafine fibers were considered to be a promising adsorbent with good stability (decomposing temperature, 356°C), high adsorption efficiency (112.1 ± 2.5 mg/g), and good reusability (three times) on the coexistence of anions and the actual industry wastewater environment.     

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%.     

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。     

Adsorption of chromium (VI) on functionalized and non-functionalized carbon nanotubes

We did a comparative study on the adsorption capacity of Cr (VI) between functionalized carbon nanotubes (CNTs) and non-functionalized CNTs. The statistical analysis reveals that the optimum conditions for the highest removal of Cr (VI) are at pH 9, with dosage 0.1 gram, agitation speed and time of 120 rpm and 120 minutes, respectively. For the initial concentration of 1.0 mg/l, the removal efficiency of Cr (VI) using functionalized CNTs was 87.6% and 83% of non-functionalized CNTs. The maximum adsorption capacities of functionalized and non-functionalized CNTs were 2.517 and 2.49 mg/g, respectively. Langmuir and Freundlich models were adopted to study the adsorption isotherm, which provided a K _L and K _F value of 1.217 L/mg and 18.14 mg^1?n L ⁿ /g functionalized CNT, while 2.365 L/mg and 2.307 mg^1?n L ⁿ /g for non-functionalized CNTs. This result proves that functionalized CNTs are a better adsorbent with a higher adsorption capacity compared with the non-functionalized CNTs.     

Removal of Cr(VI) from aqueous solution using amino‐modified Fe3O4–SiO2–chitosan magnetic microspheres with high acid resistance and adsorption capacity

A novel, bioadsorbent material of polyethylenimine‐modified magnetic chitosan microspheres enwrapping magnetic silica nanoparticles (Fe₃O₄–SiO₂–CTS‐PEI) was prepared under relatively mild conditions. The characterization results indicated that the adsorbent exhibited high acid resistance and magnetic responsiveness. The Fe₃O₄ loss of the adsorbent was measured as 0.09% after immersion in pH 2.0 water for 24 h, and the saturated magnetization was 11.7 emu/g. The introduction of PEI obviously improved the adsorption capacity of Cr(VI) onto the adsorbent by approximately 2.5 times. The adsorption isotherms and kinetics preferably fit the Langmuir model and the pseudo‐second‐order model. The maximum adsorption capacity was determined as 236.4 mg/g at 25°C, which was much improved compared to other magnetic chitosan materials, and the equilibrium was reached within 60 to 120 min. The obtained thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. Furthermore, the Cr(VI)‐adsorbed adsorbent could be effectively regenerated using a 0.1 mol/L NaOH solution, and the adsorbent showed a good reusability. Due to the properties of good acid resistance, strong magnetic responsiveness, high adsorption capacity, and relatively rapid adsorption rate, the Fe₃O₄–SiO₂–CTS‐PEI microspheres have a potential use in Cr(VI) removal from acidic wastewater. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43078.     

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。     

拟薄水铝石负载PEI/AMP吸附CO2性能

用富含胺基的物质对多孔材料进行修饰可以得到高CO₂吸附量的吸附剂。采用浸渍法将聚乙烯亚胺(PEI)和2-氨基-2-甲基-1-丙醇(AMP)负载在拟薄水铝石上,考察了CO₂压力、胺类物质负载量等对吸附性能的影响。采用低温N₂吸附/脱附法(BET)、扫描电镜(SEM)、傅里叶变换红外线光谱分析仪(FTIR)等手段表征了吸附剂的结构特征及其物理性质,并使用重量法微天平实验装置对吸附剂的性能进行了评价。实验结果表明,当温度恒定为50℃,压力小于1 MPa时,负载PEI的吸附剂最高的CO₂吸附量为77.53 mg CO₂·(g吸附剂)^-1,最佳负载量为85%;压力大于1 MPa时,负载PEI的吸附剂最高的CO₂吸附量为123.79 mg CO₂·(g吸附剂)^-1,最佳负载量为10%。负载AMP的吸附剂最高的CO₂吸附量为128.01 mg CO₂·(g吸附剂)^-1,最佳负载量为85%。CO₂吸附稳定性实验表明,吸附剂对CO₂的吸附性能稳定。     

Physico-chemical study of dew melon peel biochar for chromium attenuation from simulated and actual wastewaters

This work introduces a biochar as novel adsorbent prepared from the dew melon peel by pyrolysis method, and demonstrates its potential for eliminating Cr(VI) from simulated and actual wastewaters. The dew melon peel biochar (DPB) was characterized by several techniques and methodologies such as, BET, SEM, FTIR, Boehm titration, ultimate analysis, and pHzpc. DPB is a microporous material with the BET specific surface area of 196 m²/g. The effects of different parameters including pH, amount of adsorbent, Cr(VI) concentration, and mixing time on the removal of Cr(VI) from wastewater were studied. Maximum adsorption (98.6%) was observed at pH 6 and 100 mg/L metal concentration. The equilibrium adsorption was analyzed by Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms. Kinetic data were evaluated by pseudo-first order, pseudo-second order, intraparticle diffusion, film diffusion (Boyd), Elovich, and Avrami models. The kinetic data were best fitted to the pseudo-second order model. The Langmuir isotherm model gives the better correlation to predict the adsorption equilibrium, with a maximum adsorption capacity of 198.7 mg/g. The thermodynamic parameters showed that the adsorption of Cr(VI) was endothermic and spontaneous. Competition between the co-existing ions of Cl^?, NO ₃ ^? , SO ₄ ^2? , PO ₄ ^3? , and HCO ₃ ^? on the adsorption process was studied. The efficacy of DPB was successfully examined by analyzing the removal of Cr(VI) from two industrial wastewaters. The results indicate that DPB is promising as an effective and economical adsorbent for Cr(VI) ions removal and could be repeatedly used with no significant loss of adsorption efficiency.     

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.