Manganese ferrite (MnFe2O4) as potential nanosorbent for adsorption of uranium(VI) and thorium(IV)

Journal of Radioanalytical and Nuclear Chemistry - The adsorption behavior of U(VI) and Th(IV) metal ions by MnFe2O4 NPs was studied as a function of pH, mass of sorbent, contact time, and...     

Polyoxomolybdenum(V/VI)-sulfite compounds: synthesis, structural, and physical studies

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.     

Extraction mechanism of Cr(VI) on the aqueous two-phase system of tetrabutylammonium bromide and (NH(4))(2)SO(4) mixture

An aqueous two-phase system of tetrabutylammonium bromide (TBAB) and (NH(4))(2)SO(4) mixture has been developed for the extractive preconcentration and separation of certain compounds. TBAB concentration in upper phase is much higher than that of bottom solution. This new aqueous two-phase system is proposed for the highly selective extraction of Cr(VI) from large amounts of Cr(3+). The Cr(VI) is found to be extracted into the TBAB-rich upper phase due to ion pair formation such as HCrO(4)(-) . TBAB(+). The Cr(VI) was sufficiently extracted into the upper phase in the pH range from 1 to 5. The proposed method has been applied to the determination of trace of Cr(VI) in wastewater samples with a coefficient of variation less than 3.2%. The recovery obtained was not lower than 90%. The determination limit for the Cr(VI) was found to be 60 mug l(-1) in 10 ml of sample solution.     

Cr(VI)在Mg-Al型类水滑石上的吸附-脱附性研究I. 吸附性

研究了Cr(VI)在带结构正电荷的Mg-Al型类水滑石(HTlc)上的吸附性能, 考察了pH、无机电解质添加剂NaCl, NaNO₃, Na₂SO₄和Na₃PO₄及有机添加剂EDTA和柠檬酸等因素的影响, 并结合红外光谱和XRD实验结果探讨了吸附机理. 研究表明, Mg-Al型HTlc对Cr(VI)有很强的吸附能力, 其吸附动力学和吸附等温线分别符合准二级速率方程和Langmuir方程, 饱和吸附量达105 mg/g, 有望成为一种优良的含Cr(VI)污水处理剂和Cr(VI)污染土壤修复剂. 初始pH增大, 吸附量降低. 无机电解质和有机添加剂均能明显抑制Cr(VI)在HTlc上的吸附, 其抑制吸附作用的强弱顺序分别为Na₃PO₄≥Na₂SO₄≥NaCl>>NaNO₃和柠檬酸＞EDTA. Cr(VI)在HTlc上的吸附可分为层间的离子交换吸附和外表面的吸附, 其中外表面的吸附层在微观上又可分为因化学键合作用而形成的内络合层和因静电作用而形成的外络合层.     

Utilization of industrial waste as a novel adsorbent: Mono/competitive adsorption of chromium(VI) and nickel(II) using diatomite waste modified by EDTA

The adsorption of Cr(VI) and Ni(II) using ethylenediaminetetraacetic acid‐modified diatomite waste (EDTA‐DW) as an adsorbent in single and binary systems was investigated. The EDTA‐DW was characterized using various analytical techniques, including Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller measurements, X‐ray diffraction, scanning electron microscopy and energy‐dispersive spectrometry. The adsorption experiment was conducted by varying pH, adsorbent dosage, initial concentration and temperature. In the single system, the sorption data for Cr(VI) fitted the Langmuir isotherm, but the Ni(II) adsorption data fitted well the Freundlich isotherm. The maximum sorption capacity of Cr(VI) and Ni(II) was 2.9 mg g^?1 at pH = 3 and 3.64 mg g^?1 at pH = 8, respectively. The kinetic data for both Cr(VI) and Ni(II) followed well the pseudo‐second‐order kinetic model in single and binary systems. Meanwhile, the extended Langmuir and extended Freundlich multicomponent isotherm models were found to fit the competitive adsorption data for Cr(VI) and Ni(II). In addition, in the binary system, the existence of Ni(II) hindered the adsorption of Cr(VI), but the presence of Cr(VI) enhanced the removal of Ni(II). This study provides some realistic and valid data about the usage of modified diatomite waste for the removal of metal ions.     

Effects of surface coordination chemistry on the magnetic properties of MnFe(2)O(4) spinel ferrite nanoparticles

To understand the influence of surface interactions upon the magnetic properties of magnetic nanoparticles, the surface of manganese ferrite, MnFe(2)O(4), nanoparticles have been systematically modified with a series of para-substituted benzoic acid ligands (HOOC-C(6)H(4)-R; R = H, CH(3), Cl, NO(2), OH) and substituted benzene ligands (Y-C(6)H(5), Y = COOH, SH, NH(2), OH, SO(3)H). The coercivity of magnetic nanoparticles decreases up to almost 50% upon the coordination of the ligands on the nanoparticle surface, whereas the saturation magnetization has increased. The percentage coercivity decrease of the modified nanoparticles with respect to the native nanoparticles strongly correlates with the crystal field splitting energy (CFSE) Delta evoked by the coordination ligands. The ligand inducing largest CFSE results in the strongest effect on the coercivity of magnetic nanoparticles. The change in magnetic properties of nanoparticles also correlates with the specific coordinating functional group bound onto the nanoparticle surface. The correlations suggest the decrease in spin-orbital couplings and surface anisotropy of magnetic nanoparticles due to the surface coordination. Such surface effects clearly show the dependence on the size of nanoparticles.     

Highly active nanoscale zero-valent iron (nZVI)-Fe3O4 nanocomposites for the removal of chromium(VI) from aqueous solutions

For the first time, nanoscale zero-valent iron (nZVI)-Fe(3)O(4) nanocomposites, prepared by an in situ reduction method, are employed for chromium(VI) removal in aqueous environment. 96.4% Cr(VI) could be removed by these novel materials within 2h under pH of 8.0 and initial Cr concentration of 20 mg L(-1), compared with 48.8% by bare nFe(3)O(4) and 18.8% by bare nZVI. Effects of several factors, including mass composition of nZVI-Fe(3)O(4) nanocomposites, initial pH and Cr(VI) concentration, were evaluated. The optimal ratio of nFe(3)O(4) to nZVI mass lies at 12:1 with a fixed nZVI concentration of 0.05 g L(-1). Low pH and initial Cr(VI) concentration could increase both the Cr(VI) removal efficiency and reaction rate. Corresponding reaction kinetics fitted well with the pseudo second-order adsorption model. Free energy change (ΔG) of this reaction was calculated to be -4.6 kJ mol(-1) by thermodynamic study, which confirmed its spontaneous and endothermic characteristic. The experimental data could be well described by the Langmuir and Freundlich model, and the maximum capacity (q(max)) obtained from the Langmuir model was 100 and 29.43 mg g(-1) at pH 3.0 and 8.0, respectively. The reaction mechanism was discussed in terms of the mutual benefit brought by the electron transfer from Fe(0) to Fe(3)O(4).     

High-capacity adsorption of hexavalent chromium from aqueous solution using magnetic microspheres by surface dendrimer graft modification

The magnetic poly-(methyl acrylate-divinyl benzene) (MA-DVB) microspheres with micron size were synthesized by modified suspension polymerization method. Through stepwise reaction with methyl acrylate (MA) and ethylenediamine (EDA), the magnetic poly-(MA-DVB) microspheres with surface dendrimer containing amino groups were obtained. The above mentioned magnetic microspheres were applied for the adsorption of hexavalent chromium from aqueous solution. The effects of solution pH value, adsorption temperature, and adsorption and desorption of Cr(VI) were studied. The results showed that the optimum pH value for Cr(VI) adsorption was found at pH=3, and the adsorption capacity increased with the increase in adsorption temperature. The adsorption equilibrium of Cr(VI) was obtained in about 12 min and more than 98% of adsorbed Cr(VI) were desorbed from the magnetic microspheres in about 30 min using Na(2)SO(4) solution. By fitting the experimental data to Langmuir equation, the maximum capacity for Cr(VI) of magnetic poly-(MA-DVB) microspheres was estimated at 231.8 mg/g.     

Selective Adsorption and Determination of Hexavalent Chromium in Water Samples by Chemically Modified Activated Carbon with Tris(hydroxymethyl)aminomethane

This study introduces a sensitive and simple method for selective adsorption of hexavalent chromium, Cr(VI), from water samples prior to its determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The method utilized activated carbon modified with tris(hydroxymethyl)aminomethane (AC-TRIS) as an adsorbent. Surface properties of the new chemically modified AC-TRIS phase were confirmed by Fourier transform infrared (FTIR) spectroscopy. Seven metal ions, including Co(II), Cu(II), Ni(II), Pb(II), Cr(III), Cr(VI), and Fe(III) were evaluated and determined at different pH values (1.0–8.0), except for Fe(III) at pH values (1.0–4.0). Based on the results of the effect of pH on adsorption of these metal ions on AC-TRIS, Cr(VI) was selected for the study of other parameters controlling its maximum uptake on AC-TRIS under batch conditions and at the optimum pH value 1.0. The maximum static adsorption capacity of Cr(VI) onto the AC-TRIS was found to be 43.30 mg g^?1 at this pH and after 1 hour contact time. The adsorption data of Cr(VI) were modeled using both Langmuir and Freundlich classical adsorption isotherms. Results demonstrated that the adsorption of Cr(VI) onto AC-TRIS followed a pseudo second-order kinetic model. In addition, the efficiency of this methodology was confirmed by applying it to real environmental water samples.     

Adsorption of chromium from aqueous solution using chitosan beads

A basic investigation on the removal of Cr(III) and Cr(VI) ions from aqueous solution by chitosan beads was conducted in a batch adsorption system. The chitosan beads were prepared by casting an acidic chitosan solution into an alkaline solution. The influence of different experimental parameters; pH, agitation period and different concentration of Cr(III) and Cr(VI) ions was evaluated. A pH 5.0 was found to be an optimum pH for Cr(III) adsorption, and meanwhile pH 3.0 was the optimum pH for the adsorption of Cr(VI) onto chitosan beads. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherms and isotherm constants for the adsorption of Cr(III) and Cr(VI) onto chitosan beads. Results indicated that Cr(III) and Cr(VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacities of Cr(III) and Cr(VI) ions onto chitosan beads were 30.03 and 76.92 mg g⁻¹, respectively. Results showed that chitosan beads are favourable adsorbents. The Cr(III) and Cr(VI) ions can be removed from the chitosan beads by treatment with an aqueous EDTA solution.     

Hybrid materials: Magnetite-Polyethylenimine-Montmorillonite, as magnetic adsorbents for Cr(VI) water treatment

Hybrid materials formed by the combination of a sodium rich Montmorillonite (MMT), with magnetite nanoparticles (40nm, Fe(3)O(4) NPs) coated with Polyethylenimine polymer (PEI 800g/mol or PEI 25000g/mol) were prepared. The intercalation of the magnetite nanoparticles coated with PEI among MMT platelets was achieved by cationic exchange. The resulting materials presented a high degree of exfoliation of the MMT sheets and a good dispersion of Fe(3)O(4) NPs on both the surface and among the layers of MMT. The presence of amine groups in the PEI structure not only aids the exfoliation of the MMT layers, but also gives to the hybrid material the necessary functionality to interact with heavy metals. These hybrid materials were used as magnetic sorbent for the removal of hexavalent chromium from water. The effect that pH, Cr(VI) concentration, and adsorbent material composition have on the Cr(VI) removal efficiency was studied. A complete characterization of the materials was performed. The hybrid materials showed a slight dependence of the removal efficiency with the pH in a wide range (1-9). A maximum amount of adsorption capacity of 8.8mg/g was determined by the Langmuir isotherm. Results show that these hybrid materials can be considered as potential magnetic adsorbent for the Cr(VI) removal from water in a wide range of pH.     

Biosorption of chromium(VI) and arsenic(V) onto methylated yeast biomass

Yeast biomass was methylated in a 0.1 M HCl methyl alcohol solution at room temperature and the methylated yeast (MeYE) was applied to the adsorptive separation of Cr(VI) and As(V) anions from aqueous solutions. At near-neutral pH, while Cr(VI) and As(V) anions were scarcely adsorbed onto unmethylated yeast biomass, the amounts adsorbed increased with increasing methylation degree. The amount of Cr(VI) adsorbed onto MeYE was almost constant at pH 4-6 and decreased with increasing pH above pH 6. The amount of As(V) adsorbed onto MeYE was rather lower than that of Cr(VI) and it had a peak at about pH 7. A metal-binding model was used to describe the adsorption characteristics of Cr(VI) and As(V) on MeYE. The results showed that MeYE has two different types of adsorption sites. The saturated amount of Cr(VI) and As(V) adsorbed onto MeYE having methylation degree 0.94 was 0.55 mmol g(-1).     

Single-column ion-chromatographic determination of chromium(VI) in aqueous soil and sludge extracts

Single-column ion-chromatography (SCIC) was investigated as a routine, rapid, precise and selective analytical method for the determination of chromium(VI) in aqueous extracts of soil and sewage sludge. Chromatographic parameters were optimized for determination of Cr(VI), NO(-)(3) and SO(2-)(4). A low-capacity resin-based column was used for the separation and the anions were determined by conductometric detection. p-Hydroxybenzoic acid (5mM) at pH 8.5 was used as the eluent. The limit of detection, defined as S/N = 3, was 92 mug/l. The resolution between Cr(VI) and SO(2-)(4) was 2.8, the precision ranged from 0.9% for NO(-)(3) to 2.0% for Cr(VI) with a 500-mul injection. The SCIC results for Cr(VI) agreed closely with those obtained by inductively coupled argon-plasma emission and spectrophotometry.     

Effect of Temperature on Interfacial Adsorption of Cr(VI) on Wollastonite

An extensive study on the effect of temperature on interfacial adsorption of Cr(VI) on wollastonite has been carried out. Adsorption on the wollastonite surface increased from 69.5 to 91.7% by increasing the temperature from 30 to 50 degrees C under optimum conditions. Kinetic modeling of the process of adsorption of Cr(VI) was done and various parameters were determined. The process follows a first-order kinetic equation and the rate of uptake was found to be 2.40x10(-2) min(-1) at 30 degrees C, 2.5 pH, 0.5x10(-4) M Cr(VI) concentration, and 0.01 M NaClO(4) ionic strength. Kinetic and equilibrium modeling of the process of adsorption was undertaken and the equilibrium parameters were determined. The process of adsorption follows pore diffusion and the value of the rate constant of pore diffusion was found to be 5.00x10(-3) mg g(-1) min(-1/2) at 30 degrees C and optimum conditions. The values of the coefficient of mass transfer, beta(L), were determined at different temperatures. Thermodynamic studies of the removal process were performed. The study suggests that the process is a typical example of endothermic adsorption. Copyright 2001 Academic Press.     

Highly efficient removal of Cr(VI) from wastewater via adsorption with novel magnetic Fe3O4@C@MgAl-layered double-hydroxide

Novel magnetic Fe₃O₄@C@MgAl-layered double-hydroxide (LDH) nanoparticles have been successfully prepared by the chemical self-assembly methods. The properties of surface functional groups, crystal structure, magnetism and surface morphology of magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravity-differential thermal gravity (TG-DTG), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The adsorption studies of the novel adsorbent in removing heavy metals Cr (VI) from waste water showed that the maximum absorption amount of Cr(VI) was 152.0 mg/g at 40℃ and pH 6.0. The excellent adsorption capacity of the Fe₃O₄@C@MgAl-LDH nano-absorbents plus their easy separation, environmentally friendly composition and reusability makes them more suitable adsorbents for the removal of metal ions from waste water.     

氨基功能化纳米Fe3O4磁性高分子吸附剂对废水中Cr(VI)的吸附研究

采用分散聚合法通过共聚、开环反应, 对纳米Fe3O4进行表面功能化修饰, 得到富含NH2官能团的纳米磁性高分子复合材料. 通过透射电镜(TEM)、振动样品磁强计(VSM)、热重差热分析(TGA)、X射线衍射(XRD)、红外光谱(IR)等对其进行表征, 着重研究了其作为吸附剂对Cr(VI)的吸附性能. 结果表明: 该吸附剂对Cr(VI)的吸附能在10 min内达到平衡; 废水溶液pH值能显著影响吸附剂对Cr(VI)的吸附效果, pH为2.5时效果最佳. 废水中Cr(VI)的初始浓度、吸附时间、温度等因素对吸附效果均有不同程度的影响. 结合相应pH值下Cr(VI)的形态分布, 探讨了这种新型材料对Cr(VI)的吸附机理. 结果表明: 其吸附机理及吸附容量与废水中Cr(VI)的离子形式有关; 吸附过程以离子交换与静电引力为主. 等温吸附数据符合Langmuir模型, T＝308 K, pH＝2.5, V＝40 mL时, 吸附剂的饱和吸附容量qm＝25.58 mg/g. 吸附为吸热过程, 焓变ΔH＝8.64 kJ/mol.     

Adsorption of Pb(II) and Cu(II) from aqueous solution on magnetic porous ferrospinel MnFe2O4

The adsorption of Pb(II) and Cu(II) from aqueous solution on magnetic porous ferrospinel MnFe(2)O(4) prepared by a sol-gel process was investigated. Single batch experiment was employed to test pH effect, sorption kinetics, and isotherm. The interaction mechanism and the regeneration were also explored. The results showed that Pb(II) and Cu(II) removal was strongly pH-dependent with an optimum pH value of 6.0, and the equilibrium time was 3.0 h. The adsorption process could be described by a pseudo-second-order model, and the initial sorption rates were 526.3 and 2631.5 μmol g(-1)min(-1) for Pb(II) and Cu(II) ions, respectively. The equilibrium data were corresponded well with Langmuir isotherm, and the maximum adsorption capacities were 333.3 and 952.4 μmol g(-1) for Pb(II) and Cu(II) ions, respectively. The adsorbed Pb(II) and Cu(II) ions were in the form of the complex with oxygen in carboxyl and hydroxyl groups binding on the surface of magnetic porous MnFe(2)O(4). The sorbent could be reused for five times with high removal efficiency.     

Preparation and adsorption properties of monodisperse chitosan-bound Fe3O4 magnetic nanoparticles for removal of Cu(II) ions

Monodisperse chitosan-bound Fe(3)O(4) nanoparticles were developed as a novel magnetic nano-adsorbent for the removal of heavy metal ions. Chitosan was first carboxymethylated and then covalently bound on the surface of Fe(3)O(4) nanoparticles via carbodiimide activation. Transmission electron microscopy micrographs showed that the chitosan-bound Fe(3)O(4) nanoparticles were monodisperse and had a mean diameter of 13.5 nm. X-ray diffraction patterns indicated that the magnetic nanoparticles were pure Fe(3)O(4) with a spinel structure, and the binding of chitosan did not result in a phase change. The binding of chitosan was also demonstrated by the measurement of zeta potential, and the weight percentage of chitosan bound to Fe(3)O(4) nanoparticles was estimated to be about 4.92 wt%. The chitosan-bound Fe(3)O(4) nanoparticles were shown to be quite efficient for the removal of Cu(II) ions at pH>2. In particular, the adsorption rate was so fast that the equilibrium was achieved within 1 min due to the absence of internal diffusion resistance. The adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 21.5 mg g(-1) and a Langmuir adsorption equilibrium constant of 0.0165 L mg(-1). The pH and temperature effects revealed that the adsorption capacity increased significantly with increasing pH at pH 2-5, and the adsorption process was exothermic in nature with an enthalpy change of -6.14 kJ mol(-1) at 300-330 K.     

Ion-pair chromatographic determination of chromium(VI)

Ion-pair chromatography (IPC) with conductometric detection was investigated as a precise and selective analytical method for the determination of chromium in electro-plating solutions and waste waters. Chromatographic parameters were optimized for separation of Cr(VI) and SO(2-)(4). The analytical column (100 x 6 mm) was packed with 10 mum silasorb C(18) (Czechoslovakia). Tetrabutylammonium butyrate (TBAB), at pH 7.0 in acetonitrile-water (18:82 v/v) mixture, was used as the eluent. Two samples of solution are taken for the analysis. In the first of them the amount of Cr(VI) is determined, in the second one Cr(III) is oxidized to Cr(VI) with H(2)O(2) in alkaline medium and the total amount of Cr is determined. From the difference of the two obtained results the concentration of Cr(III) is calculated. The detection limit of Cr(VI) is 0.1 mug/ml and the relative standard deviation (at the 1.0 mug/ml) is 4.0%. The IPC results for chromium agreed closely with these obtained by spectrophotometry.