Removal of uranium anionic species from aqueous solutions by polyethylenimine–epichlorohydrin resins

The removal of uranium anionic species from aqueous solutions (initial concentration: 10–2,000 mg/L) by a low- and a high molecular weight polyethylenimine–epichlorohydrin resins was studied in the absence of background electrolytes at initial pH (pH_init) 8 to10. The amount of the sorbed U was determined spectrophotometrically using the Arsenazo III method. The maximum uptake was observed at pH_init 8 using both resins. The maximum uptake capacity observed was 221 and 388 mg U/g for the low- and high molecular weight resin respectively. The uptake data were modeled using a number of 2- and 3- parametric isotherm equations (Langmuir, Freundlich, Langmuir–Freundlich, Toth and Redlich–Peterson). The kinetics of the uranium removal was also studied and modeled using the pseudo-first and pseudo-second order equations. The surface and interior of the resin grains were examined after the sorption experiments by scanning electron microscopy/energy dispersive spectroscopy.     

Removal of cadmium(II) and lead(II) ions from model aqueous solutions using sol–gel-derived inorganic oxide adsorbent

A study was conducted concerning the preparation and application of a novel synthetic oxide adsorbent of MgO-SiO₂ type. The material was prepared via a sol–gel route, utilizing magnesium ethoxide and tetraethoxysilane as precursors of magnesium oxide and silica respectively, and ammonia as a catalyst. The powder was comprehensively analyzed with regard to chemical composition (EDS method), crystalline structure, morphology, characteristic functional groups, electrokinetic stability and porous structure parameters (BET and BJH models). The synthesized oxide adsorbent is amorphous, with irregularly shaped particles, a relatively large surface area of 612 m²/g, and negative surface charge over almost the whole pH range. Comprehensive adsorption studies were performed to investigate the adsorption of Cd(II) and Pb(II) ions on the MgO–SiO₂ oxide adsorbent, including evaluation of adsorption kinetics and isotherms, the effect of pH, contact time and mass of adsorbent. It was shown that irrespective of the conditions of the adsorption process, the synthesized MgO–SiO₂ adsorbent exhibits slightly better affinity to lead(II) than to cadmium(II) ions (sorption capacity of 102.02 mg(Pb²⁺)/g and 94.05 mg(Cd²⁺)/g). The optimal time for removal of the analyzed metal ions was 60 min, although adsorption reached equilibrium within 10 min for Pb(II) and within 15 min for Cd(II) ions, which was found to fit well with a type 1 pseudo-second-order kinetic model. Additionally, adsorption efficiency was affected by the pH of the reaction system—better results were obtained for pH ≥7 irrespective of the type of metal ion.     

Removal of Lead(II), Cadmium(II), and Arsenic(III) from Aqueous Solution Using Magnetite Nanoparticles Prepared by Green Synthesis with Box–Behnken Design

Two types of magnetite (Fe₃O₄) nanoparticles were investigated as adsorbents for the simultaneous removal of Pb(II), Cd(II), and As(III) metal ions from aqueous solution. Magnetite nanoparticles were prepared by two synthesis procedures, both using water as solvent, and are referred to as conventional Fe₃O₄ nanoparticles and green Fe₃O₄ nanoparticles. The latter used Citrus limon (lemon) aqueous peel extract as the surfactant. Box–Behnken experimental design was used to investigate the effects of parameters such as initial concentration (20–150?mg?L^?1), pH (2–9), and biomass dosage (1–5?g?L^?1) on the removal of Pb(II), Cd(II), and As(III) ions. The optimum parameters for removal of the studied metal ions from aqueous solutions, including the initial ion concentration (20?mg?L^?1), pH (5.5) and adsorbent dose (5?g?L^?1), were determined. The pseudosecond-order model exhibited the best fit for the kinetic studies, while adsorption equilibrium isotherms were best described by Langmuir and Freundlich models. The optimum conditions were applied for the treatment wastewater. The removal efficiencies of Pb(II), Cd(II), and As(III) using the conventional and green synthesized Fe₃O₄ nanoparticles were 59.4?±?4.3, 18.7?±?1.9 and 17.5?±?1.6, and 98.8?±?5.6, 46.0?±?1.3, and 48.2?±?2.6%, respectively. These results demonstrate the potential of magnetite nanoparticles synthesized using C. limon peel extract as highly efficient adsorbents for the removal of Pb(II), Cd(II), and As(III) ions from aqueous solution.     

Liquid–liquid extraction of mercury(II) from aqueous solution using furosemide in benzyl alcohol

Journal of Radioanalytical and Nuclear Chemistry - A simple, efficient and economical liquid–liquid extraction method has been developed for quantitative extraction of mercury(II) from...     

Modified nanoporous magnetic cellulose–chitosan microspheres for efficient removal of Pb(II) and methylene blue from aqueous solution

Pyromellitic dianhydride-modified nanoporous magnetic cellulose–chitosan microspheres (PNMCMs) were designed and synthesized to introduce abundant carboxyl groups onto the basic microstructure. The novel microspheres were studied by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Subsequently, a batch technique was applied to investigate various environmental parameters that could affect the adsorption behavior of the PNMCMs. Due to its nanoporous structure and large quantity of carboxyl groups, the cellulose/chitosan-based bioadsorbent exhibited excellent adsorption performance for removal of Pb(II) ions and methylene blue (MB) from aqueous solution, with maximum adsorption capacity of 384.6 and 833.3 mg/g, respectively. Furthermore, the adsorption kinetics and isotherms of Pb(II) ions and MB on PNMCMs obeyed the pseudo-second-order and Langmuir isotherm models, and the rate of adsorption was found to be controlled by film diffusion. Finally, the PNMCMs with adsorbed Pb(II) and MB could be easily regenerated using HCl, retaining removal capacity of almost 89% after six repeated uses.     

Kinetics and mechanism of oxidation of some nickel(II)–imine–oxime complexes by peroxodisulfate in aqueous acidic solutions

The kinetics of the oxidation of [Ni(II)(H₂L¹)](ClO₄)₂, (H₂L¹ = 3,8-dimethyl-4,7-diaza-3,7-decadiene-2,9-dione dioxime) and [Ni(II)(HL²)]ClO₄, (H₂L² = 3,9-dimethyl-4,8-diaza-3,8-undecadiene-2,10-dione dioxime) by peroxodisulfate anion (PDS) in aqueous media at 298.0 K have been studied. The kinetics of oxidation of both Ni(II) complexes was found to be first order in the complex concentration. The dependence of the pseudo-first-order rate constant, k _obs, for both complexes showed first-order dependence on PDS concentration. The kinetics of oxidation of [Ni(II)(H₂L¹)]²⁺ complex showed a complex dependence on [H⁺] over the pH range of 4.98–7.50, whereas that of [Ni(II)(HL²)]⁺ is independent of pH over the pH range of 5.02–7.76. The value of k _obs, for both complexes, decreased with increasing ionic strength consistent with the involvement of oppositely charged ions in the rate-determining step. The effect of ionic strength is more pronounced for [Ni(II)(H₂L¹)]²⁺–PDS reaction than for [Ni(II)(HL²)]⁺–PDS reaction, confirming the higher charges of the latter.     

Removal of Th(IV), Ni(II)and Fe(II) from aqueous solutions by a novel PAN–TiO<Subscript>2</Subscript> nanofiber adsorbent modified with aminopropyltriethoxysilane

A novel polyacrylonitrile (PAN)–titanium oxide (TiO₂) nanofiber adsorbent functionalized with aminopropyltriethoxysilane (APTES) was fabricated by electrospinning. The adsorbent was characterized by SEM, FTIR, TEG and BET analyses. The pore diameter and surface area of the adsorbent were 3.1 nm and 10.8 m² g^?1, respectively. The effects of several variables, such as TiO₂ and amine contents, pH, interaction time, initial concentration of metal ions, ionic strength and temperature, were studied in batch experiments. The kinetic data were analyzed by pseudo-first-order, pseudo-second-order and double-exponential models. Two isotherm models, namely Freundlich and Langmuir, were used for analysis of equilibrium data. The maximum adsorption capacities of Th(IV), Ni(II) and Fe(II) by Langmuir isotherm were found to be 250, 147 and 80 mg g^?1 at 45 °C with pH of 5, 6 and 5, respectively, and greater adsorption of Th(IV) could be justified with the concept of covalent index and free energy of hydration. Calculation of ΔG°, ΔH° and ΔS° demonstrated that the nature of the Th(IV), Ni(II) and Fe(II) metal ions adsorption onto the PAN–TiO₂–APTES nanofiber was endothermic and favorable at a higher temperature. The negative values of ΔG° for Th(IV) showed that the adsorption process was spontaneous, but these values for Ni(II)and Fe(II) were positive and so the adsorption process was unspontaneous. Increasing of ionic strength improved the adsorption of Ni(II) and Fe(II) on nanofiber adsorbent but decreased the adsorption capacity of Th(IV). The adsorption capacity was reduced slightly after six cycles of adsorption–desorption, so the nanofiber adsorbent could be used on an industrial scale. The inhibitory effect of Ni(II) and Fe(II) on the adsorption of Th(IV) was increased with an increase in the concentration of inhibitor metal ions.     

Adsorption of ponceau 4R from aqueous solutions by polyamidoamine–cyclodextrin crosslinked copolymer

Batch adsorption experiments were carried out for the removal of ponceau 4R (P4R, C.I. 16255) from aqueous solutions using a novel polyamidoamine–cyclodextrin crosslinked copolymer (PAMAM-CD). The influence of several operating variables, such as contact time, initial concentration, pH, ionic strength, was investigated. Results showed that PAMAM-CD exhibited very high adsorption capacity toward P4R. The adsorption capacity of P4R was even up to 254.3?mg/g when the initial concentration of P4R solution was 340?mg/L at 288?K. The maximum adsorption capacity occured at below pH 5. The adsorption rate was fast and over 52% of the equilibrium adsorption value occurred in the first 15?min at 308?K. Adorption kinetics followed the Ho and McKay equation. Intraparticle diffusion was involved in the adsorption process but it is not the only rate-controlling step. Equilibrium isotherm data were precisely fitted by the Langmuir model. The negative values of Gibbs free energy change indicated the spontaneous nature of adsorption. The PAMAM-CD was easily recovered by 2?M HCl as washing solvent and it could be used as a promising alternative adsorbent.     

Removal of phenol from aqueous solution by adsorption onto hematite (α-Fe2O3): Mechanism exploration from both experimental and theoretical studies

Iron oxides in general and especially hematite, α-Fe₂O₃ have been proved promising materials for efficient removal of various organic pollutants. Herein, we report a successful preparation of hematite (α-Fe₂O₃) by a facile precipitation method and its potential application in the removal of phenol from wastewater. The prepared material was subjected to extensive characterization using a variety of techniques such as scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), and the Brunauer Emmett Teller (BET) method. The operating conditions were optimized to improve the adsorption process efficiently. The adsorption analysis showed an adsorption capacity of 16.17 mg g⁻¹ towards phenol at 30 °C. The reaction kinetics and potential rate-limiting steps were studied by Lagergren's pseudo-first-order and pseudo-second-order models, and it was found that the pseudo-second-order accurately described the adsorption kinetics. Freundlich and Langmuir adsorption isotherms models were applied, and the quality of the fittings clearly shows that the Langmuir model well describes the phenol adsorption on the hematite. The interaction mechanism between phenol and α-Fe₂O₃(0 0 1) surface was further addressed by Density Functional Theory (DFT) calculations and molecular dynamics (MD) simulations. Experimental and theoretical results indicate that there is strong evidence for the decisive effect of π–π interactions and H-bonds on the adsorption capacity.     

Removal of chromate from aqueous solution by reduction with nanoscale Fe–Al layered double hydroxide

Nanoscale layered double hydroxides of Fe^II and Al^III (Fe–Al LDH) have been applied for removal of chromate (Cr^VI) from aqueous solution. Given the reaction stoichiometry, Cr^VI was completely reduced to Cr^III and coprecipitated with Fe^III and Al^III oxyhydroxides. The extent of Cr^VI removal decreased with increasing initial pH and decreasing molar ratio of Cr^VI/structural Fe^II in the LDH. The chromate reduction rate at different initial concentrations of Cr^VI was well described by the pseudo-second-order model with reaction rate constant ranging from 197.4 to 13.53 (mmol min)^?1. Initial pH and substitution of various amounts of Fe^III in the LDH structure had little effect on the reaction rate. Backtransformation of Cr^III to Cr^VI by birnessite Mn oxide (δ-MnO₂) after 40 days of reaction was less than 1% of the initial Cr (as Cr^III solid), indicating high stability of the final reaction products and high efficiency of nanoscale Fe–Al LDHs for removal of chromate from aqueous solution.     

Adsorption of thorium(IV) from aqueous solutions by poly(cyclotriphosphazene-co-4,4′-diaminodiphenyl ether) microspheres

Journal of Radioanalytical and Nuclear Chemistry - Poly(cyclotriphosphazene-co-4,4′-diaminodiphenyl ether) microspheres (PZA) was based on hexachlorocyclotriphosphazene (HCCP) and...     

Assessment of adsorption properties of inorganic–organic hybrid cyclomatrix type polyphosphazene microspheres for the removal of Pb(II) ions from aqueous solutions

Abstract

Inorganic–organic hybrid cyclomatrix type polyphosphazene microspheres (poly[cyclotriphosphazene-co-(4,4′-diaminodiphenylmethane)]) (HDMS) and poly[cyclotetraphosphazene-co-4,4′-diaminodiphenylmethane)] (ODMS) were prepared to investigate their possible use as alternative adsorbents for the comparative study on Pb(II) ions removal from aqueous solutions. The structures of the microspheres were elucidated by Fourier Transform Infrared (FTIR) spectroscopy and Dynamic Light Scattering (DLS) measurements, and the surface morphologies were also observed by Scanning Electron Microscopy (SEM). The adsorption of Pb(II) ions onto HDMS and ODMS from aqueous solutions was examined by means of pH, temperature, contact time and concentration. Furthermore, adsorption kinetics and isotherm models were applied and the experimental data fitted well with Langmuir isotherm and pseudo-second-order kinetic models. The maximum adsorption capacities of HDMS and ODMS for Pb(II) ions were obtained as 157.8 and 308.0?mg g^?1 at 20?°C and pH 5.5, respectively.     

Kinetics of the displacement of aqua ligands from cis-diaqua(ethylenediamine)-platinum(II)perchlorate by adenosine 5′-monophosphate in aqueous medium

The kinetics of the interaction of adenosine 5-monophosphate (5-AMP) with cis-[Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [5-AMP] and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species. Both N1 and N7 donor sites of 5-AMP are active for coordination to Pt at this pH. Base stacking and metal-induced macrochelate formation of 5-AMP plays a vital role in determining the concentration limit of 5-AMP during kinetics. Substitution occurs in two consecutive steps; both dependent on the 5-AMP concentration. Activation parameters for both steps have been calculated. The low H ₁ (42.76 ± 1.64 kJ mol^–1) and large negative values of S ₁ (–112.1 ± 5.1 J K^–1 mol^–1) as well as H ₂ (58.1 ± 1.4 kJ mol^–1) and S ₂ (–84.2 ± 4.4 J K^–1 mol^–1) indicate associative modes of activation for both ligand substitution processes in the two consecutive steps.     

Heteroligand polynuclear nickel(II) complexonates in aqueous solutions of 2,2′-dipyridyl

Formation of nickel(II) complexes with ethylenediaminetetraacetic acid (Edta) and 2,2′-dipyridyl (Dipy) has been studied by electronic absorption spectroscopy. Mathematical modeling has demonstrated that the most probable mathematical models to describe the experimental dependences of absorption on the medium acidity and concentration of solution components relies on the dissociation constants of the ligands (K _i ) and stability constants (β) of homoligand, heteroligand, and polynuclear complexes of general composition [Ni _m Dipy _n Edta _r ]^{2m ? 4r} (m = 1–4, n = 0–8, r = 0–1) as parameters. The reaction equilibrium constants and stability constants of the resulting complexes have been calculated. The structures of these complexes have been suggested.     

Reentrant behavior of poly(vinyl alcohol)–borax semidilute aqueous solutions

 The reentrant behavior of Poly(vinyl alcohol) (PVA)–borax aqueous semidilute solutions with a PVA concentration of 20 g/l and borax concentrations varies from 0.0 to 0.20 M was investigated using dynamic light scattering (DLS) and dynamic viscoelastic measurements. Two (fast and slow modes) and three (fast, middle, and slow) relaxation modes of PVA semidilute aqueous solutions without and with the presence of borax, respectively, were observed from DLS measurements. The fast and middle relaxation modes were q ²-dependent (q is the scattering vector) characteristic of diffusive behavior; however, the slow modes were q ³-dependent, characteristic of intraparticle dynamics. The experimental results showed that the slow relaxation mode dominates the DLS relaxation. The DLS slow mode relaxation time, τ_s, and the viscoelastic modulus G′(ω) and G′′(ω) data had a similar trend and demonstrated reentrant behavior as the borax concentration was increased from 0.0 to 0.20 M, i.e. τ_s, G′(ω), and G′′(ω) fluctuated with increasing borax concentration. The excluded-volume effect of polymers, charge repulsion among borate ions bound on PVA molecules, and intermolecular cross-linking didiol–borate complexation caused an expansion of the polymer chain; however, the screening effect of free Na⁺ ions on the negative charge of the borate ions bound on PVA and intramolecular cross-linking didiol–borate complexation led to a shrinkage of the polymer chain. The reentrant behavior was the consequence of the balance between expansion and shrinkage of the PVA–borate complex. Received: 26 March 1999/Accepted in revised form: 3 September 1999     

Inner sphere oxidation of N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) by N-bromosuccinimide in aqueous weakly acidic solutions

The kinetics of oxidation of N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) complex, Cu^IIL, by N-bromosuccinimide (SBr) in weakly aqueous acidic solutions was studied under pseudo-first-order conditions. Plots of ln(A _∞  ? A _t ) versus time where A _t and A _∞ are absorbance values of the Cu(III) product at time t and infinity, respectively, showed marked deviations from linearity. The curves showed an acceleration of reaction rate consistent with an autocatalytic behavior. In the presence of Hg(II) ions, plots of ln(A _∞  ? A _t ) versus time are linear up to >85 % of reaction. The value of the observed rate constant, k _obs, increases with decreasing pH. At constant reaction conditions, the dependence of the observed rate constants, k _obs, is described by Eq. (1). 1 $$ k_{\text{obs}} = k_{\text{o}} + k_{1} \left[ {{\text{H}}^{ + } } \right] $$ The dependence of both k _o and k ₁ on [SBr] is not linear. The mechanism of the title reaction is consistent with an inner sphere mechanism in which a pre-equilibrium step precedes the electron transfer step. The overall rate law is represented by Eq. (2) where [Cu^IIL]_t and K ₁ represent the total copper(II) complex concentration and the pre-equilibrium formation constant, respectively. 2 $$ d\left[ {{\text{Cu}}^{\text{III}} {\text{L}}^{ + } } \right]/dt = \left\{ {\left( {k_{\text{o}} + k_{1} \left[ {{\text{H}}^{ + } } \right]} \right)\left[ {\text{SBr}} \right]\left[ {{\text{Cu}}^{\text{II}} {\text{L}}} \right]_{t} } \right\}/\left( {1 + K_{1} \left[ {\text{SBr}} \right]} \right) $$ .