Removal Of Toxic Metal Ions Research Articles

One-step fabrication of bifunctional self-assembled oligopeptides anchored magnetic carbon nanoparticles and their application in copper (II) ions removal from aqueous solutions

Copper ion (Cu (II)) pollution has attracted much attention due to its remarkable toxic domino effect at excess amount. Efficient Cu (II) ions removal is thus a prerequisite for wastewater recycling. Herein, we present a facile and environmentally benign strategy to fabricate thiol (SH)-functionalized Fe3O4@C nanoparticles (denoted as Fe3O4@C-SH NPs) based on one-step self-assembling of a bifunctional oligopeptide with a sequence of Cys-Lys-Cys-Lys-Cys-Lys (CK–VI) for highly efficient removal of copper ions (Cu (II)) in aqueous solutions. Under the physiological conditions, CK–VI readily self-organized into a robust and tailor-made functional monolayer predominately composed of well-packed β-sheets on the surface of Fe3O4@C NPs with their thiol groups standing on the outermost layer. The resulting Fe3O4@C-SH NPs containing abundant thiol active sites exhibited excellent adsorption capacity (up to 28.8 mg g−1) and selectivity for Cu (II) ions over coexisting ions. Compared with other covalent grafting methods with multistep processes and in harsh conditions, the proposed oligopeptides assembly-based coating method makes it possible to rapidly fabricate the Fe3O4@C-SH NPs in a simple mild one-step aqueous process with low cost. The current study provides facile and environmentally friendly approaches to rapidly tailor multifunctional surfaces of NPs for various toxic metal ions removal from wastewater.

Physical insights into kinetic models of adsorption

The pseudo first- (PFO) and second-order (PSO) kinetic models have been extensively applied to study the kinetics of interfacial processes, for example, separation or removal of toxic metal ions from aqueous solution by adsorption. However, the two models were used without any specialization of operating conditions and their theoretical origin is not well understood. The aim of the present study is to provide clear physical understanding on the relationships of the Langmuir kinetics with the two models. The conditions under which the Langmuir kinetics can be reduced to the simplified models and their explicit dependence on operating conditions and isotherm parameters are provided. We adopt the square root method to obtain two roots of the differential Langmuir rate equation at equilibrium, then prove that one root is the surface coverage fraction and the other is the reciprocal of adsorption efficiency at equilibrium, and show that the root ratio is a critical factor in assessing the applicability of the PFO and PSO models. This critical factor solely depends on the ratio of available adsorbate to adsorbent capacity and the product of the Langmuir equilibrium constant and adsorbent capacity. The reduction of the Langmuir kinetics to the PFO and PSO models can be valid only under extreme conditions. The system with too high or too low available adsorbate relative to the maximum adsorbent capacity or with too small adsorption rate constant multiplied by the maximum adsorbent capacity relative to the desorption rate constant might be approximately described by the PFO model. On the other extreme that available adsorbent capacity matches available adsorbate and desorption rate constant is negligible compared with the adsorption rate constant multiply by the maximum adsorbent capacity, the PSO model could replace the Langmuir kinetics. As such, the desorption part in the Langmuir rate equation disappears and the reversible Langmuir kinetics is reduced to irreversible process. Obviously, this is hardly encountered in reality. The present study offers physical insights into the relationships between the Langmuir kinetics with the PFO and PSO models in terms of operating conditions and isotherm parameters.

Synthesis of clay-cellulose biocomposite for the removal of toxic metal ions from aqueous medium

Clay-cellulose biocomposite (CCB) was synthesized in the present study. Spin and pressure-induced heating was applied to aggregate exfoliated clay tubules and cellulose using polyethylene glycol as an intermediate. The synthesized CCB was modified in the presence of NaOH at high temperature to obtain negative surface charge on the adsorbent. Physico-chemical properties of CCB were evaluated using different characterization techniques including Fourier transform infrared (FT-IR) and X-ray photoelectron (XPS) spectroscopy. The efficiency of the synthesized biocomposite for Pb(II) and Cd(II) removal from water was studied via laboratory scale experiments. The adsorption kinetics of Pb(II) and Cd(II) onto CCB was well described by the pseudo-second-order kinetic model. The maximum Langmuir adsorption capacity of CCB was found to be 389.78 and 115.96 mg g−1 for Pb(II) and Cd(II), respectively. Fixed-bed column studies were conducted for the adsorption system to compare the adsorption performance of CCB in continuous mode.

Synthesis of poly(4, 4′‐biphenylene sulfonyl succinamide)‐polysulfone blend membranes for removal of toxic metal ions from water

ABSTRACTA novel polymer poly(4,4′‐biphenylene sulfonyl succinamide) (PBSS) was synthesized via polycondensation reaction. Succinyl chloride and 4‐aminophenyl sulfone were used as reactive monomers and anhydrous AlCl3 was used as a catalyst. Both polysulfone (PSf) and PBSS were dissolved in N‐methyl‐2‐pyrrolidone (NMP) at different compositions to obtain a homogeneous solution to fabricate PSf‐PBSS blend membranes. The structure of PBSS was characterized by ATR‐IR and 1H‐NMR spectroscopy. Thermal properties of PBSS were analyzed by TGA‐DTA. Mechanical properties and morphology of blend membranes were analyzed by universal testing machines and field emission scanning electron microscope, respectively. The hydrophilicity of blend membranes with respect to the concentration of PBSS was studied by contact angle and water uptake studies. Upon blending, the hydrophilicity of PSf‐PBSS membranes drastically increased due to the presence of large number of amide and sulfonyl groups in the matrix. The blend membranes exhibited significant increase in water flux from 100 L m−2 h to 650 L m−2 h−1, and rejection of 100% for Pb(II) and 80% for both Cd(II) and As(III) toxic heavy metal ions. The hydrophilic nature of CONH and inter and intramolecular hydrogen bonding among PBSS polymer chains dispersed within rigid PSf matrix imparts softness, amide and sulfonyl groups enhance interconnected porosity and hydrophilicity of blend membranes. Hence, PBSS may serve as a low‐cost novel polymeric additive for water purification and separation membrane applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48254.

Enhanced electrochemical performances of peanut shell derived activated carbon and its Fe3O4 nanocomposites for capacitive deionization of Cr(VI) ions.

Capacitive deionization (CDI) is one of the most efficient and emerging techniques for the removal of toxic metal ions from aqueous solutions. In this study, mesoporous peanut shell derived activated carbon (PSAC) was prepared by low temperature pyrolysis at 500 °C. Subsequently, a novel iron oxide/PSAC (Fe3O4/PSAC) nanocomposite adsorbent was prepared via facile one-pot hydrothermal synthesis method at 180 °C. Nucleation growth mechanism and appropriate characterizations of prepared nanocomposites were investigated. The obtained Fe3O4/PSAC possessed a highly mesoporous structure, and a large specific surface area (680 m2/g). The electrochemical analysis showed that the obtained Fe3O4/PSAC nanocomposites exhibited higher capacitance (610 F/g at 10 mV/s), good stability and low internal resistance. A batch mode adsorption and CDI based Cr(VI) removal studies were conducted. Effects of solution pH and cycle time on Cr(VI) electrosorption capacity were further investigated. The Fe3O4/PSAC based electrodes exhibit a maximum electrosorption capacity of 24.5 mg/g at 1.2 V, which was remarkably larger than other reported materials. The fabricated composite displayed higher electrosorption capacity with rapid time and a favorable reduction of Cr (VI) to Cr(III). Studies indicated that the Fe3O4/PSAC based CDI electrode possesses a good potential to be applied for the removal of toxic metal ions from wastewater.

Catalytic Conversion of Xylose and Xylan into Furfural Over Cr3+/P-SBA-15 Catalyst Derived from Spent Adsorbent

The mesoporous SBA-15 has long been used as an adsorbent for the removal of toxic metal ions. Achieving secondary utilize of spent adsorbent is undoubtedly an advisible option for environmental protection and recycling economy. In the present study, phosphoric acid-modified SBA-15 (P-SBA-15) was found to be an available adsorbent, and the composites (Cr3+/P-SBA-15) formed after adsorption of Cr3+ ions have the ability to efficiently catalyze the conversion of xylose and xylan into furfural. The physicochemical properties of the Cr3+/P-SBA-15 composites were characterized, and the effects of various reaction parameters on their catalytic performance were also investigated. Among the Cr3+/P-SBA-15 composites with different Cr3+ contents, the (0.25)Cr3+/P-SBA-15 composite not only achieved excellent 91% and 58% furfural yields from xylose and xylan, but also had almost constant catalytic performance after five cycles. The findings herein provided a reference for achieving high yields of furfural and reuse of spent adsorbents.

Polymeric ion exchanger supported ferric oxide nanoparticles as adsorbents for toxic metal ions from aqueous solutions and acid mine drainage.

Acid mine drainage (AMD) is a worldwide industrial pollution of grave concern. AMD pollutes both water sources and the environment at large with dissolved toxic metals which are detrimental to human health. This paper reports on the preparation of polymeric ion exchange resins decorated with hydrated iron oxides and their application for the ecological removal of toxic metals ions from AMD. The hydrated iron oxide particles were incorporated within commercial chelating ion exchange resins using the precipitation method. The synthesised hybrid resins were then characterized using appropriate spectroscopic and solid-state techniques. The metal ion levels were measured using the inductively coupled plasma-optical emission spectrometer (ICP-OES). The optimization of contact time, pH, and adsorbent dosage were conducted to enhance the efficiency of adsorption of toxic metals onto the hybrid organic/inorganic nanosorbents. Kinetics and adsorption isotherms were constructed to study the adsorption mechanisms of the adsorbents. The results showed that the dispersed Fe-O is hydrated and amorphous within the hybrid materials. The adsorption kinetics followed the pseudo-second-order shown by the high R2 values. The hybrid adsorbents were finally tested on environmental AMD samples and were able to remove toxic metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn at various removal degrees. Solution pH played a crucial role in the adsorption of toxic metals on hybrid iron oxide adsorbents. The hybrid TP-260 HFO had higher affinity for toxic metals than other prepared adsorbents thus has a potential for acidic mine water pollution remediation. The adsorbed Al(III) can be recovered using NaCl-NaOH binary solution from the loaded resins.

Selective adsorption of toxic heavy metal ions using guanine-functionalized mesoporous silica [SBA-16-g] from aqueous solution

Abstract The removal of toxic metal ions e.g. Pb2+, Hg2+ and Cd2+ from aqueous solution were explored using guanine functionalized SBA-16 [SBA-16-G]. Nitrogen sorption isotherm, HRXRD, FESEM, HRTEM, EDA-X analysis were performed to investigate the changes in the surface morphology and chemical characteristics of [SBA-16-G] before and after the adsorption of toxic metal ions. Owing to the presence of large number of active functional groups of –NH, –C O on the surface, this adsorbent demonstrated proficient toxic metal ions removal capacities (maximum adsorption capacity, q m a x : 289.9 mg g−1 for Pb2+ at 303 K, 259.9 mg g−1 for Hg2+ at 308 K and 228.8 mg g−1 for Cd2+ at 313 K, respectively) from aqueous medium. The isotherm study dictated that the adsorption data better comply to Langmuir isotherms with R L value

Starch functionalization of iron oxide by-product from steel industry as a sustainable low cost nanocomposite for removal of divalent toxic metal ions from water

Heavy metal removal by waste material from different industry has become one of the main economical approaches for zero waste industrial activity. Therefore, iron oxide fine waste by-product from steel industry was converted into nanoparticulates (Fe2O3 NPs) and further crosslinked with starch as a good stabilizer and biodegradable polymer using formaldehyde to form Fe2O3 NPs-Starch nanocomposite. The scanning electron microscope (SEM) showed the average particle size (40–70 nm). The sorption behavior of this nanocomposite was investigated using Pb(II), Hg(II) and Cd(II). Different factors such as solution pH, contact time, nanocomposite dosage and metal concentration were monitored to determine the adsorptive capacity. Langmuir, Temkin, Freundlich and Dubinin–Radushkevich models were employed to study the adsorption isotherms. The maximum sorption capacities were 2000 mg g−1 for Pb(II), 133.3 mg g−1 for Hg(II) and 322.58 mg g−1 for Cd(II). The results referred that Hg(II) and Cd(II) were best fitted by all models except Pb(II) obeyed the Freundlich isotherm model only. The Fe2O3 NPs-Starch nanocomposite emphasized its potential application as a sustainable low cost nanocomposite for metals extraction from tap water, marine water and industrial wastewater with percentage recovery 93–97%, 70–94% and 76–93%, respectively.

Porous NiFe-oxide nanocubes derived from prussian blue analogue as efficient adsorbents for the removal of toxic metal ions and organic dyes.

A novel porous NiFe-oxide nanocubes (NiFe NCs) binary material was successfully fabricated via a facile and scalable tactic, which involved a morphology-inherited heat treating of Ni3[Fe(CN)6]2·xH2O prussian blue analogue nanocubes as self-sacrificial templates. Consequently, it was demonstrated that the NiFe NCs consisted of primary nanostructure units and interconnected pores, with an average size of ˜80 nm. When employed as adsorbents, the as-prepared NiFe NCs displayed remarkable adsorption capacities for heavy metal ions (232.3 mg g-1 for As(V) and 350.71 mg g-1 for Cr(VI)) and organic dyes (284.99 mg g-1 for XO and 31.97 mg g-1 for CR at 298 K). The resulting NiFe NCs further revealed efficient regeneration and reusability even after five consecutive adsorption/desorption cycles. The microscopic spectrum analysis demonstrated that the interaction between As(V) and NiFe NCs was mainly ascribed to the metal-oxide bonds (MO) and hydroxyl groups (OH), while Cr(VI) adsorption was in conjunction with the reduction reaction of Cr(VI) to Cr(III). Furthermore, the adsorption of organic dyes on NiFe NCs depended on the pore structure and molecule sizes of the organic dye molecules. These findings make cost-efficient NiFe NCs materials a powerful candidate for remediating water contaminated with inorganic and organic contaminants.

Competitive biosorption of Cu2+ and Ag+ ions on brown macro-algae waste: kinetic and ion-exchange studies.

The application of biosorption operation has gained attention in the removal and retrieval of toxic metal ions from water bodies. Wastewater from industrial activity generally presents great complexity due to the coadsorption of cations to the inactive biomass binding sites. In this work, the competitive biosorption of Cu(II) and Ag(I) ions was studied in batch systems. A kinetic study applying a non-acidified and acidified waste of Sargassum filipendula in equimolar and non-equimolar metal samples was carried out and the acidified biosorbent was selected due to higher removal rates and selectivity of silver ions. The assays were performed with 2 g L-1 of biosorbent concentration at 25 °C for 12 h and pH was controlled at around 5.0. Copper presented higher affinity for the biosorbent and a fast biosorption kinetic profile, while silver equilibrium times exhibited dependence on the copper concentration. External diffusion is the rate-limiting step in Cu(II) ion removal and it might also limit the kinetic rates of Ag(I) ions with intraparticle diffusion, depending on the initial concentration of metal cations. The ion-exchange mechanism is evidenced and complexation and electrostatic attraction mechanisms might be suggested, explained by simultaneous chemisorption and physisorption processes during the operation. Calcium and sodium were released in considerable amounts by the ion-exchange mechanism. Characterization analyses confirmed the role of several functional groups in the competitive biosorption accompanied by a homogenous covering of both metal ions on the surface of the particles. Particle porosity analyses revealed that the material is macroporous and an appreciable amount of macropores are filled with metal cations after biosorption.

Selectivity and efficient Pb and Cd ions removal by magnetic MFe2O4 (M=Co, Ni, Cu and Zn) nanoparticles

Spinel ferrite MFe2O4, (M = Co, Ni, Cu and Zn) nanoparticles (NPs) were prepared by microwave combustion method using metal nitrates as precursors, in addition to urea as fuel. Rietveld analysis of X-ray diffraction patterns indicates the formation of single phase for NiFe2O4 and ZnFe2O4, while (α-Fe2O3 and CuO) phases precipitate for CoFe2O4 and CuFe2O4, respectively. After annealing 800 °C for 16 h, single cubic CuFe2O4 phase is obtained. SEM images show spherical/undefined shaped particles at the nanoscale with broad particle size distribution and high level of agglomeration. Magnetisation-field (M-H) curves reveal ferromagnetic behaviour for CoFe2O4, NiFe2O4 and CuFe2O4, and superparamagnetic behaviour for ZnFe2O4. Interestingly, after annealing CuFe2O4 shows a superparamagnetic behaviour due phase tetragonal-cubic phase transformation. Saturation magnetization, remanence and coercivity slightly change after annealing, except for CuFe2O4, due to phase transformation from tetragonal to cubic; Ms decreases abruptly from 25.97 to 1.685 emu/g. The as-obtained spinel ferrite nanopowders are tested for two toxic metal ions removal from aqueous solutions; Cadmium (Cd2+) and lead (Pb2+) with different concentration (5, 10, 20 and 30 mg) and pH (2, 12). The maximum adsorption capacities are found at the lowest concentration (5 mg) and at alkaline medium (pH 12). The as-prepared magnetic nanoparticles demonstrate enhanced efficiency for both Cd2+ and Pb2+, with maximum adsorption capacity of 69.4 and 47.1 mg/g, respectively. Interestingly, the nature of metal M has a direct influence on selectivity, CoFe2O4 toward Cd2+ while ZnFe2O4 toward Pb2+.

Inorganic nanomaterials in polymeric water decontamination membranes

One of the major research challenges today is the efficient treatment and desalination of seawater, brackish water, and wastewater to make it recyclable and ecofriendly. Membrane technology has offered an increasingly important role to overcome confronts associated with the water treatment. Polymeric membrane is the most common and preliminary technology used for water purification. However, solicitation of polymeric membrane is restricted due to inadequate permeability, selectivity, strength, and low fouling resistance. Consequently, polymeric nanocomposite has emerged as a promising solution to address these flouts. Nanocomposite membrane is considered as a new class of membranes prepared by combining polymeric materials with nanoparticles. Advanced nanocomposite membranes based on polymer/inorganic nanoparticle materials have been designed to meet explicit water treatment applications. This review basically summarizes scientific and technological advances toward the development of polymer/inorganic nanoparticle nanocomposite membranes for water treatment. A wide range of inorganic nanoparticles have been used to reinforce polymers such as metal and metal oxide nanoparticle, nanoclay, and zeolite. Polymer/inorganic nanoparticle nanocomposite membranes have been fabricated by fine tuning the structure and physicochemical properties such as porosity, hydrophilicity, antibacterial, thermal, and mechanical characteristics. Moreover, inorganic nanoparticle incorporated in matrix may behave as adsorbents for the removal of toxic metal ions, inorganic, organic, and biological micropollutant, and other noxious compounds from aqueous solutions. Toward the end, challenges and future research trends on high-performance polymer/inorganic nanoparticle nanocomposite membranes have been discussed.

Preparation and Cu(II) ion removal capacities of Schiff base-based polystyrene nanocomposites for wastewater treatment

In this paper, new composite nanomaterials by encapsulating Schiff base molecules with hydrophilic spacers into sulfonate groups charged polystyrene beads (PS) have been prepared. The obtained composite adsorbent, Schiff base-based polystyrene nanocomposites (PS-GN1), demonstrated more preferable Cu(II) ion removal capacity in the presence of Ca2+ co-ions in solutions. And the obtained PS-GN1 composites with inner well-dispersed Schiff base molecules demonstrated much faster breakthrough for Cu(II) ion removal than PS beads mainly due to the electrostatic forces and coordinating reaction with Cu(II) ion. The present research work showed it potential to prepare excellent nanocomposites for the removal of toxic metal ions and other charged pollutants from wastewater.

Role of the surface composition of the polyethersulfone–TiiP–H2T4 fibers on lead removal: from electrostatic to coordinative binding

The removal of toxic metal ions from water remains an environmental challenge. Promising processes involve formation of metal complexes with appropriate ligands and their successive separation using filtration over membranes. Water-soluble macromolecular ligands are, therefore, important to improve this technology. In this investigation, we have shown that insertion of a Ti-acac-based precursor on non-water-soluble thermoplastic polyethersulfone membranes allows an effective immobilization of the meso-tetra(N-methyl-4-pyridyl)porphine which, in turn, can safely remove Pb2+ ions from water. In particular, it has been demonstrated that the porphyrin readily coordinates Pb2+ thus forming a sitting-atop metal derivative. Moreover, X-ray photoelectron spectroscopy has favored a complete characterization of surfaces of fiber membranes, thus providing evidences of Pb2+ coordination. The efficiency of Pb2+ removal from water has been discussed on the basis of competitive porphyrin deprotonation versus metal complex stability in water, and these data shed light on the role of porphyrin concentration on the fiber surface that can switch the metal absorption from a pure electrostatic interaction to coordinative complexation.

Central composite design for optimization of removal of trace amounts of toxic heavy metal ions from aqueous solution using magnetic Fe3O4 functionalized by guanidine acetic acid as an efficient nano-adsorbent

In this study, a novel and effective preconcentration and removal technique based on the use of magnetic Fe3O4 functionalized by guanidine acetic acid (Fe3O4@GAA) as a nano-adsorbent were introduced. The application of synthesized nano-adsorbent was investigated for the adsorption and removal of a trace amount of some heavy metals, such as Hg (II), Zn (II), Cu (II) and Ag (I), from aqueous samples. The synthesized nano-adsorbents were analyzed by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD). The diameter of the magnetic nano-adsorbents was in the range of 20–30 nm. In order to obtain maximum removal efficiency, the effects of effective parameters were optimized using a central composite chemometric design. The optimum conditions were pH of 7, nano-adsorbent amount of 14 mg and contact time of 10 min. The Fe3O4@GAA nano-adsorbent could be simply separated from the solution with the assistance of an external magnetic field, eluted with proper eluent and reused for twenty runs without a significant loss of its adsorbent activity. The adsorption efficiencies and preconcentration factors of developed procedure for target ions were in the range of 95–100% and 112–125, respectively, under the optimum condition. The obtained results revealed that the Fe3O4@GAA nano-adsorbent could be applied as a novel, simple, highly effective, reusable and cost-consuming material for the preconcentration and removal of the target toxic heavy metal ions from the aqueous solution.

Modelling on the removal of toxic metal ions from aquatic system by different surface modified Cassia fistula seeds

The present work demonstrates the preparation of Cassia fistula seeds for producing activated carbon through physical and chemical treatment for the extrusion of Ni(II) ion contaminated aqueous solution. The readily prepared sorbents were characterized using SEM-EDX and FTIR. The surface morphology of sorbents possesses 1 μm mean particle size with uniform size distribution. Furthermore, optimization of operating parameters such as the pH, initial Ni(II) ion concentration, adsorbent dose, time and temperature were investigated. In isotherm and kinetic aspect, Langmuir maximum adsorption capacity of sulphuric acid modified Cassia fistula seeds was 182.2 (mg/g); obeyed Pseudo first order kinetic model. The Ni(II) ion adsorption system undergoes chemisorption, exothermic, feasible and spontaneous. The excellent properties of the Cassia fistula seeds can be alternate for commercial activated carbon.

Facile and Room Temperature Synthesis of Superparamagnetic Fe3O4/C Core/Shell Nanoparticles for Efficient Removal of Pb(II) From Aqueous Solution

AbstractIn this work, superparamagnetic Fe3O4/C core/shell nanoparticles (NPs) were synthesized using a room‐temperature and green route combining co‐precipitation method, followed by hydrothermal process. The prepared nanoparticle was utilized as an adsorbent for the removal of Pb+2 ions from a wastewater. The effect of various parameters; such as pH, dose of adsorbent, contact time and concentration of lead ions on the adsorption capacity were examined in details. The adsorption capacity (qm) of Fe3O4/C NPs was estimated from the Langmuir isotherm curve and was found to be 244 mgg−1. Interestingly, the produced Fe3O4/C NPs exhibited a rapid removal of toxic lead metal ions from wastewater effluents and the adsorption kinetics is well described by pseudo‐second‐order model. Furthermore, the data of Pb2+ adsorption is best fit for the Langmuir model. Moreover, the Fe3O4/C core/shell NPs were recycled and reused for at least five times without a significant loss of adsorption efficiency.

A review on emulsion liquid membrane (ELM) for the treatment of various industrial effluent streams

The excessive release of toxic metal ions by the several industrial effluent streams into the environment has imposed a serious threat to the ecological system. Therefore, the removal of these toxic metal ions from the wastewater of various industrial effluent streams has received a considerable amount of interest and also currently becoming an imperative area of research. Since last few decades, ELM based separation processes have been become an attractive and efficient way for the removal of toxic metal ions, organic and inorganic acids, and industrial pollutants of the various aqueous waste effluent streams. ELM is an emerging alternative technique to the conventional solvent extraction processes with an additive advantage of low solvent inventory and energy requirements. Moreover, it also preconcentrates the solute by performing both extraction and stripping operations simultaneously in a single unit. The main aim of this review paper is to elucidate the comprehensive review on the ELM (its pertinent properties/characteristics), its membrane phase compositions, its stability, and its process parameters respectively and also to delineate the applications of this technique for the removal of various low concentrated solutes.

Surface functionalization of MIL-101(Cr) by aminated mesoporous silica and improved adsorption selectivity toward special metal ions.

Developing novel solid adsorbents with high efficiency and excellent selectivity is always an important target in the removal of toxic metal ions from waste water. In this study, a composite nano-adsorbent NH2-mSiO2@MIL-101(Cr) has been fabricated and applied in the efficient removal of Pb(ii) and Cr(vi) for the first time. The nanocomposites were characterized by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), fourier-transform infrared (FT-IR) spectroscopy and thermal gravimetry analysis (TG). The results indicate that a typical core@shell structure has been fabricated by fully coating a mesoporous SiO2 shell over the micro/mesoporous MIL-101(Cr). As a result, the surface charge and the zeta potentials change significantly. Two toxic metal ions, namely, Pb(ii) and Cr(vi) were chosen as the main adsorption targets to evaluate the surface adsorption activities. The adsorption conditions were optimized, the influences of other coexisting ions were explored, and the adsorption selectivity was investigated. Interestingly, the NH2-mSiO2@MIL-101(Cr) nanocomposites display a prominent adsorption activity compared with the original MIL-101(Cr) and non-aminated mSiO2@MIL-101(Cr) and excellent selectivity toward Pb(ii) in the presence of other divalent metal ions. The adsorption kinetics and adsorption thermodynamics were simulated accordingly, and the enhanced adsorption mechanism was also suggested. The good reusability and adsorption selectivity of the NH2-mSiO2@MIL-101(Cr) suggest their potential applications in the selective removal of special metal ions such as Pb(ii) from the waste water.