Adsorptive recovery of an essential rose oil component from aqueous solution by nanoporous carbon (CMK-3)

A nanoporous carbon (CMK-3) was synthesized and used to adsorb 2-phenylethanol (PEA) from aqueous solutions. The characterization of CMK-3 by N₂ adsorption isotherm revealed the formation of a nanoporous carbon with average pore diameter and surface area of 3.34 nm and 1268 m² g^?1, respectively. Column-like particle morphology of CMK-3 was observed from scanning electron microscope images. To evaluate the feasibility of CMK-3 as a potential PEA adsorbent, batch adsorption experiments were conducted for aqueous PEA solutions. The results showed that CMK-3 is an efficient sorbent for the separation of PEA from water. The optimized adsorbent doses were found to be 0.3 and 2.2 g L^?1 for 30 and 300 mg L^?1 PEA, respectively. Our studies about the effect of pH on CMK-3 adsorption capacity revealed that the adsorption capacity increased at lower pH due to the protonation of PEA. Three adsorption models, Langmuir, Freundlich and Temkin were used to describe the adsorption isotherms. Thermodynamic parameters such as ΔG ⁰, ΔH ⁰, and ΔS were also evaluated, and it was found that the sorption process was spontaneous, endothermic, and physical in nature. The adsorption kinetics was investigated in detail and the pseudo-second-order kinetic equation fitted the experimental data very well. The mechanistic study by Weber-Morris model revealed that the overall adsorption process was simultaneously governed by external mass transfer and intraparticle diffusion. Almost all (97 %) adsorbed PEA was successfully recovered into ethanol which is a common solvent in fragrance industry. CMK-3 was proved to be a promising adsorbent for the adsorption-recovery of PEA from aqueous solution.     

有序介孔碳CMK-3的化学活化及储氢性能

选用KOH、NaOH、H3PO4对有序介孔碳CMK-3进行了活化,通过X射线衍射、低温氮吸附-脱附等对样品进行了表征,发现活化后样品的结构发生了巨大的变化。有序介孔碳CMK-3的有序性逐渐降低,比表面积明显增大,2 nm介孔明显增多。讨论了CMK-3和KOH质量比、活化温度、不同活化剂对活化效果的影响。储氢测试表明活化能够明显提高CMK-3的储氢性能,77K、100 kPa时的储氢性能高达2.32wt%。     

Adsorption of hydrogen isotopes on micro- and mesoporous adsorbents with orderly structure

The equilibrium and dynamic adsorption data of H(2) and D(2) on different micro- and mesoporous adsorbents with orderly structure including 3A, 4A, 5A, Y, and 10X zeolites; carbon CMK-3; silica SBA-15; and so forth were collected. Critical effect of the nanodimension of adsorbents on the adsorption behavior of hydrogen and its isotopes is shown. The highest adsorption capacity was observed at pore size 0.7 nm, but equal or even larger isotope difference in the equilibrium adsorption was observed at larger pore sizes, whereas the largest isotope difference in the dynamic adsorption was observed at 0.5 nm. The adsorption rate of D(2) is larger than that of H(2) in microporous adsorbents, but the sequence could be switched over in mesoporous materials. Linear relationship was observed between the adsorption capacity for hydrogen and the specific surface area of adsorbents although the adsorbents are made of different material, which provides a convincing proof of the monolayer mechanism of hydrogen adsorption. The linear plot for microporous adsorbents has a larger slope than that for mesoporous adsorbents, which is attributed to the stronger adsorption potential in micropores.     

有序介孔碳CMK-3微波负载NiO及其电容性能研究

微波法负载具有简便、快速、均匀的优点. 本文尝试以乙二醇为还原剂, Ni(Ac)₂为Ni源, 通过微波辐射负载及低温空气煅烧在CMK-3上形成NiO. 对样品进行X射线衍射(XRD)、透射电子显微镜(TEM)、N₂吸脱附等结构表征及循环伏安(CV)等电化学性能测试. 结果显示, 微波法并经低温空气煅烧后有序介孔碳CMK-3的小角XRD峰强度变弱、比表面积下降、孔容减小, 但却使其比电容从229.3 F/g提高到295.9 F/g, 大于文献报导中介孔碳负载MnO₂, RuO₂•xH₂O后的比电容值. 由此说明微波法是有效的负载方法, 具有较好的应用前景.     

Features of the adsorption of hydrogen by various types of microporous materials

A comparative investigation was made of the adsorption of N₂ and H₂ by silicate and phosphate zeolites (Zt) and carbon materials with micropores of various dimensions, shapes, and volumes. It was found that the adsorption of hydrogen has significant sensitivity to the shape of the pores, the chemical composition of the zeolite framework, and the nature of the surface of the adsorbents. In particular, the adsorption is increased in the presence of constrictions (the cationic forms of zeolite LTA) or channels (MFI) with sizes close to hydrogen molecules in the micropores and the ions of divalent metals included isomorphously in the framework of the aluminophosphates. There is also increased affinity to the carbon surface. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 67–73, March–April, 2008.     

超声辅助浸渍法制备高分散Pt/CMK-3-US加氢脱萘催化剂

以CMK-3介孔碳作为载体,分别采用传统浸渍法、超声辅助浸渍法、载体硝酸处理法和表面活性剂辅助浸渍法备了Pt/CMK-3、Pt/CMK-3-US、Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB催化剂,并通过表征和催化性能评价进行研究。表征方法包括XRD、BET、SEM、TEM和H₂-TPR,结果表明Pt/CMK-3中Pt分散性最差,Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB中Pt的分散度较好,但是HNO₃对介孔碳的孔道结构有破坏作用,且Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB中的介孔碳的表面性质具有明显变化,只有超声法可以在很好地保持CMK-3的孔道结构和表面性质的基础上提高铂的分散度,Pt的粒径在3 nm左右。萘加氢催化性能评价结果表明Pt/CMK-3-US的催化加氢活性及产物选择性高于Pt/CMK-3,且明显高于Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB。萘转化率可以达到98%以上,十氢萘选择性可以达到95%以上。     

超声辅助浸渍法制备高分散Pt/CMK-3-US加氢脱萘催化剂

以CMK-3介孔碳作为载体,分别采用传统浸渍法、超声辅助浸渍法、载体硝酸处理法和表面活性剂辅助浸渍法备了Pt/CMK-3、Pt/CMK-3-US、Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB催化剂,并通过表征和催化性能评价进行研究。表征方法包括XRD、BET、SEM、TEM和H2-TPR,结果表明Pt/CMK-3中Pt分散性最差,Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB中Pt的分散度较好,但是HNO_3对介孔碳的孔道结构有破坏作用,且Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB中的介孔碳的表面性质具有明显变化,只有超声法可以在很好地保持CMK-3的孔道结构和表面性质的基础上提高铂的分散度,Pt的粒径在3 nm左右。萘加氢催化性能评价结果表明Pt/CMK-3-US的催化加氢活性及产物选择性高于Pt/CMK-3,且明显高于Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB。萘转化率可以达到98%以上,十氢萘选择性可以达到95%以上。     

Preparation of manganese dioxide loaded activated carbon adsorbents and their desulfurization performance

Manganese dioxide loaded activated carbon adsorbents (MnO₂/AC) were prepared and characterized by N₂ adsorption-desorption, BET method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FT-IR) and scanning electron microscopy (SEM). Effects of preparation conditions and adsorption conditions on desulfurization performance of the adsorbents were studied in a fixed-bed adsorption apparatus. Experimental results show that the surface area and pore volume of MnO₂/AC decreased compared with the unmodified activated carbon, but the adsorption capacity to H₂S was improved greatly. A suitable H₂S removal activity was obtained with manganese dioxide to activated carbon ratio of 1.1: 1 and the calcination temperature of 250°C. At the adsorption temperature of 40°C and gas flow rate of 20 mL/min, the H₂S saturation capacity and H₂S removal rate reached up to 713.25 mg/g and 89.9%, respectively.     

Influence of chemisorbed carbon monoxide on the oxidation of molecular hydrogen at smooth platinum in sulfuric acid solution

Potentiostatic current—potential curves of hydrogen oxidation were measured at 0.5 mV s^?1 on two smooth platinum electrodes of different shape in the presence of various coverages with chemisorbed carbon monoxide in 0.5 M H₂SO₄, stirred with molecular hydrogen at 1 cm³ s^?1. Carbon monoxide coverages up to 0.6 have a small influence. The hydrogen oxidation remains controlled by convective diffusion of molecular hydrogen. Above coverages of 0.6, a kinetic step becomes increasingly predominant. The effect of chemisorbed carbon monoxide on the H₂ oxidation is similar to that on hydrogen adsorption, studied previously. The correlation between the rate of the kinetic step and the free energy of hydrogen adsorption in the Temkin model of the surface is established and discussed.     

Uptake of lead by carbonaceous adsorbents developed from tire rubber

The adsorption of lead in aqueous solution by discarded tire rubber (TR) and by carbonaceous adsorbents (CAs) prepared from it by thermal and chemical treatments is studied. TR was heated at 400 or 900?°C for 2 h in N₂ atmosphere or treated chemically with H₂SO₄, HNO₃, H₂SO₄/HNO₃, HCl, NaOH, HCl-NaOH or NaOH-HCl for 24 h. TR and CAs were characterized physico-chemically with regard to their texture, elemental composition and surface chemistry. The adsorption of lead was studied, mainly from the kinetic standpoint, using 4×10^?3 mol?L^?1 Pb²⁺ solutions at initial pH 2.0, 5.7 and 12.6. TR is practically a non-porous material. The heat treatment of TR mainly develops meso- and macroporosity. The effect on macroporosity is stronger when HNO₃ and H₂SO₄/HNO₃ are used. For all adsorbents, the adsorption of lead is not measurable when adsorptive solution at pH 2 is used. With an increase of pH from 5.7 to 12.6, the kinetics of adsorption becomes faster and the amount of lead adsorbed significantly increases. For the solution at pH 12.6 and an adsorption time of 8 h, the adsorption percentage is 36 wt% for TR. For the CAs prepared by heat treatment of TR, it is higher than 50 wt%. For longer adsorption times, the kinetics is much slower for the product of TR treatment with HNO_3. However, the corresponding adsorption percentage is as high as 93 wt% for an adsorption time of 264 h. TR and the CAs, in particular the product heated at 400?°C, are good adsorbents to be used in the rapid removal of a significant amount of lead from aqueous solution.     

Chromium-based metal–organic framework/mesoporous carbon composite: synthesis,characterization and CO<Subscript>2</Subscript> adsorption

New composites of a water-stable chromium-based metal organic framework MIL-101 and mesoporous carbon CMK-3 were in situ synthesized with different ratios of MIL-101 and CMK-3 using the hydrothermal method. The composites as well as the parent materials were characterized by X-ray diffraction, thermo gravimetric analysis, scanning electron microscope, transmission electron microscope and nitrogen/carbon dioxide adsorption isotherms. The hybrid material possesses the same crystal structure and morphology as its parent MIL-101, and exhibits an enhancement in CO₂ adsorption uptakes when compared to MIL-101 and CMK-3. The increase in CO₂ uptakes was attributed to the combined effect of the formation of additional micropores, the enhancement of micropore volume and the activation of unsaturated metal sites by CMK-3 incorporation.     

二维TiC 层表面H2的化学吸附与物理吸附

第一性原理计算研究发现由于二维TiC 单原子层具有高的比表面积与大量的暴露在表面的Ti 原子,其是一种非常有潜力的储氢材料. 计算结果显示H₂可以在二维TiC 单原子层表面进行物理吸附与化学吸附. 其中化学吸附能为每个氢分子0.36 eV,物理吸附能是每个氢分子0.09 eV. 覆盖度为1和1/4层（ML）时,H₂分子在二维TiC 单原子层表面的离解势垒分别为1.12 和0.33 eV. 因此,除了物理吸附与化学吸附,TiC 表面还存在H单原子吸附. 最大的H₂储存率可以达到7.69%（质量分数）. 其中,离解的H原子、化学吸附的H₂、物理吸附的H₂的储存率分别为1.54%、3.07%、3.07%. 符合Kubas吸附特征的储存率为3.07%. 化学吸附能随覆盖度的变化非常小,这有利于H₂分子的吸附与释放.     

Methane Reforming with Carbon Dioxide on the Co/α-Al2O3 Catalyst: The Formation, State, and Transformations of Surface Carbon

The interactions of oxidized and reduced Co/-Al₂O₃ (4 wt % CoO) with H₂, CH₄, CO₂, and O₂ and their mixtures are studied in flow and pulse regimes using a setup involving a DSC-111 differential scanning calorimeter and a system for chromatographic analyses. It is shown that treatment with hydrogen at 700°C results in the partial reduction of cobalt oxide to Co. Methane poorly reacts with the oxidized catalyst but readily reacts with the reduced catalyst to form H₂ and surface carbon. The initial surface carbon transforms into other forms, which block the cobalt surface to different extents and differ in the heats of reaction with CO₂. Carbon dioxide may react with the surface carbon to form CO (rapidly) and with metallic Co to form CO and CoO (slowly). Thus, the main route of methane reforming with carbon dioxide on Co/-Al₂O₃ is the dissociative adsorption of CH₄ to form surface carbon and H₂ and the reaction of surface carbon with CO₂ to form CO via the reverse Boudouard reaction.     

Biomaterial immobilization in nanoporous carbon molecular sieves: influence of solution pH, pore volume, and pore diameter

The adsorption of lysozyme (Lz) onto nanoporous carbon molecular sieves with various pore diameters has been studied at different solution pH values. All the adsorption isotherms have successfully been correlated by the Langmuir equation. The amount of adsorbed Lz depends on the solution pH as well as on the specific pore volume and pore diameter of the adsorbents. The maximum adsorption was observed near the isoelectric point of the Lz (pI approximately 11), suggesting that suppression of electric repulsion between the enzymes plays an important role in the adsorption process. Moreover, the amount adsorbed depends on the pore size and pore volume of the nanoporous carbon adsorbents, indicating that the Lz molecules are adsorbed inside the mesopores. CMK-3-150 shows a larger amount of Lz adsorption as compared to CMK-3. The increased Lz adsorption capacity of CMK-3-150 may be due to the larger pore volume and pore diameter as compared to that of CMK-3. The unaltered structural order of the nanoporous adsorbents after the adsorption has been confirmed by the physicochemical characterization techniques such as XRD and N(2) adsorption. In addition, FT-IR spectroscopic studies confirm that the Lz used in this study is stable even after the adsorption on the nanoporous carbon. These results indicate that nanoporous carbon has superior water stability and thus is a more appropriate adsorbent for biomaterials than nanoporous silica.     

The carbon nanotubes-based materials and their applications for organic pollutant removal:A critical review

The carbon nanotubes(CNTs) as the emerging materials for organic pollutant removal have gradually become a burgeoning research field.Herein,a mini-review of CNTs-based materials curre ntly studies for organic pollutant elimination is presented.This review summarizes the preparation methods of CNTsbased materials.CNTs-based materials can be used as adsorbents to remove organic pollutants in wastewater.The adsorption mechanisms mainly include surface diffusio n,pore diffusion and adsorption reaction.Most importantly,an in-depth overview of CNTs-based materials currently available in advanced oxidation processes(AOPs) applications for wastewater treatment is proposed.CNTs-based materials can catalyze different oxidants(e.g.,hydrogen peroxide(H_2 O_2),persulfates(PMS/PDS),ozone(O_3) and ferrate/permanganate(Fe(Ⅵ)/Mn(Ⅶ)) to generate more reactive oxygen species(ROS) for organic pollutant elimination.Moreover,the possible reaction mechanisms of removing organic pollutants by CNTs-based materials are summarized systematically and discussed in detail.Finally,application potential and future research directions of CNTs-based materials in the environmental remediation field are proposed.     

Sorption study of uranium from aqueous solution on ordered mesoporous carbon CMK-3

The ability of ordered mesoporous carbon CMK-3 has been explored for the removal and recovery of uraium from aqueous solutions. The textural properties of CMK-3 were characterized using small-angle X-ray diffraction and N₂ adsorption–desorption, and the BET specific surface area, pore volume and the pore size were 1143.7 m²/g, 1.10 cm³/g and 3.4 nm. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CMK-3 showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 35 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir and Freundlich isotherm. The thermodynamic parameters, ?G°(298 K), ?H° and ?S° were determined to be ?7.7, 21.5 k J mol^?1 and 98.2 J mol^?1 K^?1, respectively, which demonstrated the sorption process of CMK-3 towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed CMK-3 could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 2.0 g CMK-3.     

Study of structural and thermodynamic parameters of adsorption layers using density functional theory. Local density and adsorption isotherms on spherical surfaces

Local density profiles in adsorption layers of Lennard-Jones fluids on two-dimensional adsorbents with spherical geometry and isotherms of excess (Gibbs) adsorption have been calculated using the classical density functional theory (approximations with weighting coefficients). The local density profiles have been found in hydrogen adsorption layers on C₆₀, C₂₄₀, and C₅₄₀ fullerene molecules. The calculations have been performed for both subcritical and supercritical temperature ranges. It has been shown that, at a pressure of 10 MPa and a temperature of 77 K, the gravimetric (mass) hydrogen density on C₆₀ fullerene is 7.6 wt %, which is in good agreement with the results of molecular dynamics simulation and experimental data. It has also been established that the gravimetric hydrogen density on C₆₀ fullerene is higher than that on C₂₄₀ and C₅₄₀ fullerenes, being comparable with its value in a slitlike pore of a carbon adsorbent.     

Effect of CO2 adsorbents on the Ni-based dual-function materials for CO2 capturing and in situ methanation

The present work studied the effect of different carbon dioxide (CO₂) adsorbents on Ni-based dual-function materials (DFMs) for the development of carbon capture and on-site utilization in a reactor at isothermal condition. The DFMs containing Ni functioning as a methanation catalyst with various CO₂ adsorbents (i.e., CaO, MgO, K₂CO₃, or Na₂CO₃) were prepared on γ-Al₂O₃ through sequential impregnation. The result indicated that Ni-Na₂CO₃/γ-Al₂O₃ had the highest methanation capacity (i.e., 0.1783 mmol/g) and efficiency (i.e., 71.09%) in the CO₂ adsorption–methanation test. The CO₂ uptake and the subsequent methanation capacity of the Ni-Na₂CO₃/γ-Al₂O₃ increased to more than 24 times and more than 17 times, respectively, compared to Ni/γ-Al₂O₃. The high methanation capacity was correlated to its highest amount of weak basic sites, substantial CO₂ capture capacity and capture/release efficiency, and reactivity to H₂ at a lower temperature, supported by CO₂-TPD, TGA analyses for adsorption or adsorption–desorption at the isothermal condition, and H₂-TPRea, respectively. A continuous cyclic CO₂ adsorption–methanation was performed by using the Ni-Na₂CO₃/γ-Al₂O₃ and Ni-CaO/γ-Al₂O₃, showing that the CO₂ adsorption capacity was stabilized from third cycle onward, whereas the methanation capacity was stabilized at all cycles, indicating the high stability of the DFMs for both CO₂ adsorption and subsequent methanation. This work demonstrated successful synthesis of the Ni-based, low-cost, and stable DFMs with the ability to produce methane via the direct capture of CO₂.     

Adsorption of U(VI) from aqueous solution by sulfonated ordered mesoporous carbon

The sulfonated mesoporous carbon (CMK-3-SO₃H) prepared by functionalizing mesoporous carbon (CMK-3) via vapor transfer method has been explored for the removal and recovery of uranium from aqueous solutions. The influences of different experimental parameters such as solution pH, initial concentration, contact time and temperature on adsorption were investigated. The results showed that CMK-3-SO₃H has the highest uranium sorption capacity at initial pH of 5.0 and contact time of 120 min, and the adsorption process could be better described by the pseudo-second-order model and Langmuir isotherm. Selective adsorption studies showed that the CMK-3-SO₃H could selectively remove of U(VI), and the selectivity coefficients of mesoporous carbon in the presence of co-existing ions, Mg(II), Zn(II), Mn(II), Cu(II), Ni(II), Sr(II) and Hg(II) improved after functionalization.     

Structural and energetic properties of carbosils hydrothermally treated in the classical autoclave or the microwave reactor

Carbon/silica adsorbents (carbosils) prepared by pyrolysis of CH₂Cl₂ at 823 K and the reaction time from 0.5 to 6 h on the mesoporous silica gel surface (Si-60, Merck, granule size 0.2–0.5 mm) and then hydrothermally treated at 473 K with steam or liquid water by using the classical autoclave with traditional heating way or in the microwave reactor were studied by means of TG, adsorption and Q-TG methods. Changes in the structural characteristics of hybrid adsorbents before and after hydrothermal treatment were analyzed on the basis of nitrogen adsorption. Thermal properties of initial and modified samples as well as concentration of carbon deposit were studied using thermogravimetry (TG) in the range of 293–1273 K. The adsorbed water layers were investigated by means of thermodesorption of water under the quasi-isothermal conditions (Q-TG) in the range of 293–573 K. Concentration of weakly and strongly adsorbed water and the surface free energy on the interphase of adsorbent/water were calculated. It was stated that hydrothermal treatment in the microwave reactor, contrary to that in the classical autoclave, allows to obtain adsorbents with noticeably higher values of total pore volume in relation to the initial adsorbents and in majority with a higher specific surface area. Application of microwave energy allows to obtain adsorbents with lower values of surface free energy in relation to the initial adsorbents and those modified in the autoclave.