Removal of radiocobalt from aqueous solution by Mg2Al layered double hydroxide

The adsorption behavior of radiocobalt by Mg₂Al layered double hydroxide (Mg₂Al LDH) was studied as a function of contact time, pH, ionic strength, foreign ions, FA and temperature under ambient conditions. The results showed that the kinetic adsorption could be described by a pseudo-second order model very well. The adsorption of Co(II) on Mg₂Al LDH was strongly dependent on pH and ionic strength. The presence of FA enhanced the adsorption of Co(II) on Mg₂Al LDH at low pH, whereas reduced Co(II) adsorption at high pH. The Langmuir model fitted the adsorption isotherms of Co(II) better than the Freundlich and D–R model at three different temperatures of 303, 323 and 343 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent adsorption isotherms indicated that the adsorption process of Co(II) on Mg₂Al LDH was endothermic and spontaneous. The results show that Mg₂Al LDH is a promising material for the preconcentration and separation of pollutants from large volumes of aqueous solutions.     

Influence of a doubly charged cation nature on the formation and properties of mixed oxides MAlO x (M = Mg2+, Zn2+, Ni2+) obtained from the layered hydroxide precursors

Influence of the nature of a doubly charged cation in the layered double hydroxides (LDH) on the conditions of formation and properties of mixed oxide phase MAlO _x (M = Mg²⁺, Zn²⁺ and Ni²⁺), its ability to reconstruct the structure of the original precursor under contact with water has been studied. Hydrotalcite-like compounds and corresponding oxides with different M²⁺: M³⁺ ratio were investigated by XRD, TEM, TG-DTG-DTA, ²⁷Al NMR, N₂ adsorption, and differentiating dissolution. It has been found that the nature of the cation M²⁺ influences the conditions of LDH thermal decomposition, structural and textural characteristics of the formed mixed oxides. The obtained data can be used to synthesize the oxide supports with desired acid-base and adsorption properties.     

Effect of environmental parameters on the sequestration of radionickel by Mg2Al layered double hydroxide

In this work, sequestration of Ni(II) from aqueous solution to Mg₂Al layered double hydroxide (Mg₂Al LDH) by adsorption process as a function of various water quality parameters and temperature was investigated. The results showed that the kinetic adsorption could be described by a pseudo-second order model very well. The adsorption of Ni(II) on Mg₂Al LDH was strongly dependent on pH and ionic strength. The presence of humic acid (HA)/fulvic acid (FA) enhanced the adsorption of Ni(II) on Mg₂Al LDH at low pH, whereas reduced Ni(II) adsorption at high pH. The Langmuir model fitted the adsorption isotherms of Ni(II) better than the Freundlich model at three different temperatures of 298, 318 and 338 K. The thermodynamic parameters (ΔH^o, ΔS^o and ΔG^o) calculated from the temperature dependent adsorption isotherms indicated that the adsorption process of Ni(II) on Mg₂Al LDH was endothermic and spontaneous. The results show that Mg₂Al LDH is a promising material for the preconcentration and separation of pollutants from large volumes of aqueous solutions.     

The preparation of supported ionic liquids (SILs) and their application in rare metals separation

This review summarizes the preparation methods of support ionic liquids (SILs) and their applications in rare metals separation. The rare metals separation includes the recovery of high value metal ions and the removal of heavy metal ions from wastewater. SILs can be used as a kind of highly efficient multifunctional separation materials. The preparation methods of SILs include chemical immobilization technique in which ILs moieties are supported on solid supports via covalent bonds and physical immobilization techniques in which ILs are immobilized on solid supports via physical method such as simple im- pregnation, sol-gel method. According to the difference of solid supports, this review summarizes the application of polymer supported ionic liquids (P-SILs), silica based material supported ionic liquids (SM-SILs) and membrane supported ionic liq- uids (M-SILs) in rare metals separation. P-SILs and SM-SILs prepared by chemical method with N-methylimidazolium group can be used as highly efficient anion exchangers with high thermal stability and good chemical stability for adsorption of Cr(VI), Re(VII), Ce(IV). P-SILs prepared via simple impregnation afforded IL functionalized solvent impregnated resins (SIRs) which showed high separation efficiency and selectivity in the separation of rare earths(III) (REs(III)). SM-SILs prepared via sol-gel method with IL doped in the support as porogens or extractant show high removal efficiencies and excellent stability for the separation of RE(III), Cr(III) and Cr(VI). M-SILs with IL as plasticizer or carrier show improved stability, high perme- ability coefficient and good selectivity for Cr(VI) transport. Different supports and different supporting methods were suffi- ciently compared. Based on the different practical application, different forms of SILs can be prepared for separation of rare metals with high separation efficiency and selectivity.     

Immobilization of uranium(VI) onto Mg2Al layered double hydroxide: role of key geochemical parameters

In this study, the sorption of U(VI) from aqueous solution on Mg₂Al layered double hydroxide (Mg₂Al LDH) was studied as a function of various water quality parameters such as contact time, pH, ionic strength, soil fulvic acid (FA), solid content and temperature by using a batch technique. The sorption of U(VI) on Mg₂Al LDH was dependent on pH. The presence of FA increased U(VI) sorption at low pH, whereas decreased U(VI) sorption at high pH. Both kinetics and thermodynamic parameters of the sorption process were evaluated. It was found that the pseudo-second-order model was more suitable for our experiment. The Langmuir model fitted the sorption isotherms of U(VI) better than the Freundlich and D-R model at three different temperatures of 298, 303 and 313 K. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were calculated from the temperature dependent sorption isotherms, and the results suggested that U(VI) sorption was a spontaneous and endothermic process. The results demonstrate that Mg₂Al LDH is a promising sorbent material for the preconcentration and separation of uranium pollution from large volumes of aqueous solutions.     

由M0.02Cu0.4Mg5.6Al1.98(OH)16CO3 (M=Ru,Re)水滑石为前驱体制备的双金属固体碱催化甘油氢解

采用共沉淀法合成了M_0.02Cu_0.4Mg_5.6Al_1.98(OH)₁₆CO₃ (M = Ru,Re)水滑石前驱体,然后经焙烧和还原制备了铜分散度较高的双功能M-Cu/固体碱催化剂.这些双功能催化剂在粗甘油氢解制备丙二醇反应中表现出了很好的催化活性.表征结果证明,M的加入增强了催化剂表面氢的吸附和活化,进而促进了甘油的转化.     

Removal of Naphthol Green B from Aqueous Solution by Calcined Layered Double Hydroxides:Adsorption Property and Mechanism Studies

The adsorption of naphthol green B (NGB) by Mg/Al‐LDO (layered double oxides) with a Mg/Al molar ratio of 3:1 was investigated in a batch mode. Our study indicates that the maximum capacity of NGB adsorption at equilibrium is 193.4 mg and the percentage of absorption is 96.7%, with an adsorbent dose of 1.0 g/L under the following condition: 200 mg/L NGB concentration, temperature 298 K, pH 10.0 and an equilibrium time of 80 min. Langmuir and Freundlich adsorption models were used for fitting the isotherms, and the thermodynamic parameters have been calculated, which showed that the adsorption process was spontaneous and exothermic in nature. In the light of so called "memory effect", the Mg/Al‐LDO was found to recover their original layered structure after adsorption, and part of NGB ions intercalated into the interlayer of LDH (layered double hydroxides), which has been supported by XRD and FTIR. In addition, the competitive anions for adsorption and the regeneration of Mg/Al‐LDO have also been investigated.     

Synthesis of layered zinc hydroxide chlorides in the presence of Al(III)

Zinc hydroxide chloride particles were synthesized by hydrolysis of ZnCl₂ solutions dissolving AlCl₃ at different atomic Al/Zn ratios from 0 to 1.0 and characterized by various techniques. Increasing Al/Zn ratio changed the crystal phases of the products as ZnO→ZnO+ZHC (Zn₅(OH)₈Cl₂·H₂O)→ZHC→LDH (layered double hydroxides, Zn-Al-Cl) and the particle morphology as agglomerates (ZnO)→fine particles (ZnO)→plates (ZHC)+rods (ZnO)→plates (ZHC)→plates (LDH). The atomic Cl/Zn ratios of LDH particles formed at Al/Zn?0.3 were ca. 0.3 despite the increase of Al/Zn ratio, being due to the intercalation of CO₃²⁻ into the LDH crystal. The OH⁻ content of LDH estimated by TG was reduced by the deprotonation of OH⁻ to counteract the excess positive charge produced by replacing Zn(II) with Al(III). ZHC exhibited a high adsorption selectivity of H₂O.     

Synthesis and Structure of Ionic Liquids Containing the ­[Al(OC6H4CN)4]– Anion

The synthesis, structure, and physical properties of ionic liquids (IL) bearing the novel [Al(O–C₆H₄–CN)₄]^– ion as counterion to the commonly used [NR₄]⁺, [PR₄]⁺ and imidazolium ions are reported. Both the influence of the alkyl chain length as well as the functionalization with cyano groups is studied. These ILs are easily obtained by reaction of Ag[Al(O–C₆H₄–CN)₄] with the corresponding ammonium, phosphonium, and imidazolium halides. The stability towards electrophilic cations was investigated. All prepared salts have a window for the liquid phase of ca. 200 °C and are thermally stable up to 450 °C. The solid‐state structures reveal only weak cation ··· anion and anion ··· anion interactions in accord with the observed low melting points (glass transition points).     

Mg-Al类水滑石负载金催化醇选择氧化中Mg/Al比例的影响

为研究Mg/Al比例对Mg-Al类水滑石(LDH)负载Au催化醇选择氧化的影响,采用共沉淀—水热晶化法合成了不同Mg/Al比的y Mg-Al LDH,采用液相还原法负载纳米Au颗粒.对样品进行XRD、N_2物理吸附、ICP-AES、AAS、TEM、CO_2-TPD、CO_2-In-situ DRIFTS和XPS等表征.在无附加碱条件下,Au/yMg-Al LDH催化剂催化1-苯乙醇选择氧化的催化活性随Mg/Al比增大呈现递增趋势,Au/4Mg-Al LDH活性最佳.载体表面弱碱性强度随Mg/Al比增大变化不大,弱碱位略有增多,对醇羟基脱氢有促进作用.载体层板Mg_3OH基团随Mg/Al比增大而增多有利于Au在层板边缘沉积,二者可形成有效协同,促进醇氧化过程进行.     

MIL‐53(Al) as a Versatile Platform for Ionic‐Liquid/MOF Composites to Enhance CO2 Selectivity over CH4 and N2

Five different imidazolium‐based ionic liquids (ILs) were incorporated into a metal–organic framework (MOF), MIL‐53(Al), to investigate the effect of IL incorporation on the CO₂ separation performance of MIL‐53(Al). CO₂, CH₄, and N₂ adsorption isotherms of the IL/MIL‐53(Al) composites and pristine MIL‐53(Al) were measured to evaluate the effect of the ILs on the CO₂/CH₄ and CO₂/N₂ selectivities of the MOF. Of the composite materials that were tested, [BMIM][PF₆]/MIL‐53(Al) exhibited the largest increase in CO₂/CH₄ selectivity, 2.8‐times higher than that of pristine MIL‐53(Al), whilst [BMIM][MeSO₄]/MIL‐53(Al) exhibited the largest increase in CO₂/N₂ selectivity, 3.3‐times higher than that of pristine MIL‐53(Al). A comparison of the CO₂ separation potentials of the IL/MOF composites showed that the [BMIM][BF₄]‐ and [BMIM][PF₆]‐incorporated MIL‐53(Al) composites both showed enhanced CO₂/N₂ and CO₂/CH₄ selectivities at pressures of 1–5 bar compared to composites of CuBTC and ZIF‐8 with the same ILs. These results demonstrate that MIL‐53(Al) is a versatile platform for IL/MOF composites and could help to guide the rational design of new composites for target gas‐separation applications.     

Development of Thiol-Functionalized Mesoporous Silicate MCM-41 as a Modified Sorbent and Its Use in Chromatographic Separation of Metal Ions from Aqueous Nuclear Waste

Surface modified adsorbent mesoporous silicate MCM-41 has been prepared by grafting thiol containing functional group onto mesoporous silicate MCM-41. XRD, N₂ adsorption/desorption measurements, SEM, FT-IR, thermogravimetry and elemental analysis have been made to confirm the ordered mesoporous framework and the functionalization of the thiol groups. Sorption of 18 metal ions on this sorbent have been studied and discussed. Chromatographic separation of Rb(I)–U(VI)–Sr(II)–Zr(IV), has been achieved on column of this sorbent.     

Application of simplified version of advanced isoconversional procedure in non-isothermal kinetic study

Thermogravimetric analysis (TG) and powder X-ray diffraction (PXRD) were used to study some selected Mg/Al and Zn/Al layered double hydroxides (LDHs) prepared by co-precipitation. A Mg/Al hydrotalcite was investigated before and after reformation in fluoride and nitrate solutions. Little change in the TG or PXRD patterns was observed. It was proposed that successful intercalation of nitrate anions has occurred. However, the absence of any change in the d ₍₀₀₃₎ interlayer spacing suggests that fluoride anions were not intercalated between the LDH layers. Any fluoride anions that were removed from solution are most likely adsorbed onto the outer surfaces of the hydrotalcite. As fluoride removal was not quantified it is not possible to confirm that this has happened without further experimentation. Carbonate is probably intercalated into the interlayer of these hydrotalcites, as well as fluoride or nitrate. The carbonate most likely originates from either incomplete decarbonation during thermal activation or adsorption from the atmosphere or dissolved in the deionised water. Small and large scale co-precipitation syntheses of a Zn/Al LDH were also investigated to determine if there was any change in the product. While the small scale experiment produced a good quality LDH of reasonable purity; the large scale synthesis resulted in several additional phases. Imprecise measurement and difficulty in handling the large quantities of reagents appeared to be sufficient to alter the reaction conditions causing a mixture of phases to be formed.     

Zn-MOF-74负载ILs的结构稳定性和吸附研究

离子液体（ILs）作为一种新型绿色溶剂应用广泛,以多孔材料MOFs作为支撑体负载ILs,不仅有望降低离子液体的高粘性,而且有助于提高材料的吸附分离能力,但要如何选择适合MOFs体系来负载ILs是一个难点。本文采用密度泛函理论（DFT）,利用VASP和Gaussian 09 程序对负载IL（[Emim][BF4]）的Zn-MOF-74的结构稳定性进行系统研究,从几何结构、电荷分析、相互作用等方面将Zn-MOF-74@[Emim][BF4]复合体系与[Emim][BF4]和Zn-MOF-74比较分析。计算结果表明,负载[Emim][BF4]的Zn-MOF-74体系中,IL的阴离子与Zn-MOF-74的开放金属位点Zn发生强相互作用, Zn、F1原子之间因库仑力成键,造成了MOF-74配位构型的改变。IL的负载扰乱了Zn-MOF-74结构的对称性,增强了离子间相互作用。Zn-MOF-74 @[Emim][BF4]复合体系形变过程伴随着电荷转移,其吸附能为-1.032 eV,绘制的差分电荷以及相互作用图验证MOF和IL之间发生了化学吸附。进一步探讨负载离子液体的Zn-MOF-74吸附能力,研究了CO2在复合体系中吸附作用机制。     

Polyol-modified layered double hydroxides with attenuated basicity for a truly reversible capture of CO2

Dendrimers bearing hydroxyl groups supported by layered double hydroxides (CO₃–LDH) with Mg/Al ratio ranging from 1:1 to 5:1 showed improved properties for the reversible capture of carbon dioxide (CO₂). The adsorption capacity of the starting LDH was due to the intrinsic base-like behavior, and was found to depend on the Mg/Al ratio. When contacted with polyol dendrimers in aqueous media, no intercalation took place. This was explained in terms of low exfoliation grade of LDH and hydrophobic character of the dendrimer molecules. The latter rather adsorb on the external surface of the LDH stacks for low dendrimer loadings, or aggregate into organic clusters for higher contents. Analyses through thermal programmed desorption of CO₂ revealed that dendrimer incorporation advantageously attenuates the basicity strength of the starting LDH support, by lowering the desorption temperature. The OH groups of the organic moiety were found to display an amphoteric character, and act as the main adsorption sites. The weak interactions with CO₂ facilitate easier release of the major part of adsorbed CO₂ at temperature not exceeding 80–100 °C. On polyol organo-LDHs, the reversible CO₂ retention was discussed herein in terms of acid–base interactions. This concept allows envisaging the capture of diverse pollutants and other greenhouse gases by modifying the chemical groups on the dendritic moiety.     

Introduction of an Ionic Liquid into the Micropores of a Metal–Organic Framework and Its Anomalous Phase Behavior

Controlling the dynamics of ionic liquids (ILs) is a significant issue for widespread use. Metal–organic frameworks (MOFs) are ideal host materials for ILs because of their small micropores and tunable host–guest interactions. Herein, we demonstrate the first example of an IL incorporated within the micropores of a MOF. The system studied consisted of EMI‐TFSA (1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)amide) and ZIF‐8 (composed of Zn(MeIM)₂; H(MeIM)=2‐methylimidazole) as the IL and MOF, respectively. Construction of the EMI‐TFSA in ZIF‐8 was confirmed by X‐ray powder diffraction, nitrogen gas adsorption, and infrared absorption spectroscopy. Differential scanning calorimetry and solid‐state NMR measurements showed that the EMI‐TFSA inside the micropores demonstrated no freezing transition down to 123 K, whereas bulk EMI‐TFSA froze at 231 K. Such anomalous phase behavior originates from the nanosize effect of the MOF on the IL. This result provides a novel strategy for stabilizing the liquid phase of the ILs down to a lower temperature region.     

Uranium adsorption from a liquid waste using thermally and chemically modified bentonite

In this work, uranium adsorption from aqueous (waste) solution onto thermal and chemical modified bentonite (TCMB) has been studied. The relevant factors affecting uranium adsorption onto our TCMB adsorbent were studied. These factors involved contact time, initial uranium concentrations, pH, adsorption temperature, foreign ion and the effect adsorbent (TCMB) amount using synthetic solution. The theoretical capacity of TCMB adsorbent is about 29 mg/g TCMB. The optimum adsorption conditions were choiced. Uranium elution from the loaded TCMB adsorbent has been carried out using CH₃COONa as an effective eluent. Uranium adsorption from Gattar liquid waste by TCMB adsorbent was carried out in columns. The low uranium adsorption efficiency (37.5 % of the theoretical capacity of TCMB) may be due to the adsorption competition between uranium and difference foreign ion present in the solution (as iron). More than 92 % of the loaded uranium amount on the TCMB adsorbent has been eluted using CH₃COONa as an efficient eluent.     

Functionalized electrospun carbon nanofibers for removal of cationic dye

Electrospun carbon nanofibers (ECNFs) have attracted significant attention in recent years as relatively inexpensive alternative to carbon nanotubes for adsorption organic pollutants. In this study, ECNFs were fabricated from polyacrylonitrile (PAN) using an electrospinning technique, followed by carbonization and oxidation via treatment with a H₂SO₄/HNO₃ mixture. The prepared oxidized electrospun carbon nanofibers (O-ECNFs) were characterized using scanning and transmission electron microscopy (SEM and TEM), Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The O-ECNFs were used as nano-adsorbents for the adsorption of methylene blue (MB) from aqueous solution. The adsorption of MB by the O-ECNFs was studied as a function of pH, time, adsorbent dosage, MB concentration, and temperature. ECNF functionalization enhanced the adsorption capacity towards MB dye compared pristine ECNFs. Detailed analysis of the adsorption kinetics showed that the adsorption process followed a pseudo-second-order model. The adsorption isotherm was best fit by the Langmuir model. The thermodynamic results showed that MB adsorption onto the O-ECNFs was endothermic and spontaneous.     

Influence of mesoporosity on the sorption of 2,4-dichlorophenoxyacetic acid onto alumina and silica

Two SiO2 and three Al2O3 adsorbents with varying degrees of mesoporosity (pore diameter 2-50 nm) were reacted with 2,4-dichlorophenoxyacetic acid (2,4-D) at pH 6 to investigate the effects of intraparticle mesopores on adsorption/desorption. Anionic 2,4-D did not adsorb onto either SiO2 solid, presumably because of electrostatic repulsion, but it did adsorb onto positively charged Al2O3 adsorbents, resulting in concave isotherms. The Al2O3 adsorbent of highest mesoporosity consistently adsorbed more 2,4-D per unit surface area than did the nonporous and less mesoporous Al2O3 adsorbents over a range of initial 2,4-D solution concentrations (0.025-2.5 mM) and reaction times (30 min-55 d). Differences in adsorption efficiency were observed despite equivalent surface site densities on the three Al2O3 adsorbents. Hysteresis between the adsorption/desorption isotherms was not observed, indicating that adsorption is reversible. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy studies confirm that 2,4-D adsorption does not occur via ligand exchange, but rather via electrostatic interaction. The results indicate that adsorbent intraparticle mesopores can result in consistently greater 2,4-D adsorption, but the amount adsorbed is dependent upon surface charge and the presence of adsorbent mesoporosity. The data also suggest that when mineral pores are significantly larger than the adsorbate, they do not contribute to diffusion-limited adsorption/desorption hysteresis. Adsorbent transformations through time are discussed.     

Development and tailoring of amino-functionalized activated carbon based Cucumerupsi manni Naudin seed shells for the removal of nitrate ions from aqueous solution

The removal of nitrate ions with ethylenediamine (EDA)-functionalized activated carbon (AC-NH₂) was studied in this work. Activated carbon prepared from Cucumerupsi manni Naudin seed shells using ZnCl₂ (ACZ) was functionalized with EDA via a nitric acid oxidation followed by acyl chlorination and amidation process. The effect of pH, contact time, initial concentration and co-existing ions on the adsorption of nitrate ions have been investigated. The FTIR and elemental analysis revealed that amino groups were successfully grafted onto the ACZ after functionalization. The surface area and average pore of ACZ were found to be 1008.99 m²/g and 2.02 nm respectively. However, it was noticed that, after functionalization (AC-NH₂), its surface area decreases to 113.43 m²/g meanwhile, its pore diameter increases to 2.48 nm. The experimental results of adsorption showed that AC-NH₂ exhibit excellent nitrate ions uptake performance compared to ACZ which is attributed to the presence of the grafted amino groups on the ACZ. Nitrate adsorption follows pseudo-first-order kinetic model while the equilibrium adsorption data was best fitted the Freundlich isotherm suggesting that the adsorption process was predominated by physisorption. This study demonstrates that the prepared AC-NH₂ is a promising adsorbent for nitrate ions removal from aqueous media.