Characterization and magnetic properties of two novel copper(II) coordination polymers prepared by different synthetic techniques

Two novel ternary Cu(II) coordination polymers with formulas {[Cu(μ₂-AZPY)(H₂BTC)₂]}_n (1) and {[Cu(μ₂-AZPY)(μ₂-HBTC)(H₂O)]·AZPY}_n (2) (AZPY – trans-4,4′-azobis(pyridine), BTC – benzene-1,3,5-tricarboxylate) have been synthesized using the solvothermal or diffusion techniques, respectively. Compounds were characterized by single crystal X-ray diffraction, thermogravimetry, infrared spectroscopy, elemental analysis and AAS. Removal of water and AZPY from the framework of 2 was investigated by wide-angle X-ray scattering measurements during in-situ heating. A magnetic study showed on antiferromagnetic coupling in 1 and 2 and magnetic properties may be influenced by both crystal field (CF) and inter-molecular interactions. The effective magnetic moment decreases from the values μ_eff = 4.97 μ_B for 1 and μ_eff = 3.39 μ_B for 2 at T = 290 K to the values of μ_eff = 1.41 μ_B for 1 and μ_eff = 1.27 μ_B for 2 at T = 2 K. The origin of the observed behavior is discussed.     

Graphene materials with different structures prepared from the same graphite by the Hummers and Brodie methods

Graphene materials containing different functional groups were prepared from a natural graphite, by means of two different oxidation methods (Hummers and Brodie). It was observed that the differences in the structure of the resultant graphite oxides (GOs) greatly affect the structure of the graphenes resulting from their thermal exfoliation/reduction. Although the oxidation of the graphite was more effective with the modified Hummers method than with Brodie’s method (C/O of 1.8 vs 2.9, as determined by XPS), the former generated a lower residual oxygen content after thermal exfoliation/reduction and a better reconstruction of the 2D graphene structure (with fewer defects). This is explained by the presence of conjugated epoxy and hydroxyl groups in the GO obtained by Brodie’s method, which upon thermal treatment, lead to the incorporation of oxygen into the carbon lattice preventing its complete restoration. Additionally, graphene materials obtained with Brodie’s method exhibit, in general, smaller sheet size and larger surface area.     

Adsorption of Pb(II) ions from aqueous solutions by carbon nanotubes oxidized different methods

This study investigated the heavy metal adsorption of the carbon nanotubes (CNTs) oxidized different methods. Besides the conventional ultrasonication method, the UV-light used as an oxidation agent. The two oxidation methods compared with each other by Pb(II) adsorption. The characterizations of oxidized CNTs were analyzed by FTIR, XRD, DTG, SEM and total acidity capacity analysis. The adsorption capacities of carbon nanotubes were compared with using Langmuir and Freundlich isotherms. Two different kinetic theories were applied to experimental data. These theories are pseudo-second order and intra-particle diffusion models. The adsorption results can be compared using non-linear Langmuir isotherm parameters. For single wall carbon nanotubes (SWCNTs), theoretical adsorption capacity value (Q_m) of UV-light method is 511.99 mg/g and ultrasonication method is 342.36 mg/g. The UV-light increased the surface acidity of the carbon nanotubes more than ultrasonication. After the adsorption experiments, it is apparently seen that the UV-light oxidation method is a useful method for heavy metal adsorption.     

Selective catalytic reduction of NO by NH3 on Cu (II) ion-exchanged offretite prepared by different methods

The influence of the preparation method on the NO–SCR by NH₃ activity of Cu-OFF catalysts has been studied on presence of oxygen. The catalysts structure and the nature of copper species have been investigated by XRD, ²⁷Al MAS NMR, UV-visible spectroscopy and H₂-TPR. Among the examined preparation methods, the ionic exchange in aqueous solution gives the highest efficient catalyst in NO-SCR. It is shown that Cu cationic species are formed in large extent with this method despite the presence of minor amounts of small oxide clusters.     

The inhibited reduction of different copper(II) complexes by phosphine oxides

The influence of hexyldiethyl- and octyldimethylphosphine oxide on the reduction of different Cu (II) complexes (ligands: oxalate, glycinate, EDTA, tartrate, malonate, citrate and alanin anion) was investigated by dc polarography. The mode of inhibition is changing as a function of the ligand. While the [Cu(EDTA)]²⁻, [Cu(ox)₂]²⁻, [Cu(gly)₂] and [Cu(ala)₂] complexes seem to cross the adsorption layer at the non-fully and fully covered electrode in the same way, all other complexes seem to change their structure before they are discharged, provided the electrode is fully covered with the surfactant. Both reaction channels were described by inhibition models, valid at the fully surfactant covered electrode.     

Fast removal of Pb(II) and Cu(II) from contaminated water by groundwater treatment waste: impact of sorbent composition

ABSTRACT

A non-hazardous groundwater treatment waste (GWTW) was examined as a low-cost sorbent for Pb(II) and Cu(II) ions. The content of the dominant elements in GWTW was as follows: 78% Fe₂O₃, 7.4% P₂O₅, 7.4% CaO and 5.2% SiO₂. The removal of Pb(II) and Cu(II) was fast, and more than 67–95% of ions were accumulated by GWTW during the first 3 min. The sorption capacity of GWTW depends on solution pH, concentration and temperature. Equilibrium data fitted well with Langmuir–Freundlich and Langmuir-partition models. The inherently formed nano-adsorbent could be utilized for the treatment of water contaminated with Pb(II) and Cu(II) ions.     

Two cobalt(II) coordination polymers based on carboxylate ligand: Preparation,crystal structures and magnetic properties

Two new coordination polymers, [Co₂(L)_1.5(OH)(H₂O)₂]·2H₂O (1) and [CoL(bpp)] (2) (H₂L = 2,5-dibenzoylterephthalic acid and bpp = 1,3-bis(4-pyridyl)propane), have been synthesized and characterized by elemental analyses, IR spectra, and thermogravimetric analyses. Their structures were determined by single crystal X-ray diffraction analyses. Complex 1 exhibits a 3D framework assembled from tetra-nuclear cobalt-oxygen bridged by carboxylic O atoms with a (4¹²·6³) topology. Complex 2 possesses a 2D layered structure which extends into a 3D architecture via C–H···π interaction between propane proton and the phenyl ring or pyridine ring of an adjacent sheets. Furthermore, the magnetic properties of them are discussed.     

Multiwalled carbon nanotube impregnated with tartrazine: Solid phase extractant for Cd(II) and Pb(II)

A solid phase extraction procedure has been presented by using multiwalled carbon nanotube impregnated with tartrazine for cadmium (Cd(II)) and lead (Pb(II)) ions. The influences of pH, flow rate, eluent and sample volume were investigated. No interference effects were observed from the alkaline, alkaline earth and some transition metals. The detection limits (LOD) were 0.8 and 6.6 μg L⁻¹ for Cd(II) and Pb(II), respectively. The preconcentration factor was 40. The validation of the procedure was controlled by the analysis of certified references materials. The procedure was applied to the determination of cadmium and lead in natural water and food samples.     

Alginate and Algal-Based Beads for the Sorption of Metal Cations: Cu(II) and Pb(II)

Alginate and algal-biomass (Laminaria digitata) beads were prepared by homogeneous Ca ionotropic gelation. In addition, glutaraldehyde-crosslinked poly (ethyleneimine) (PEI) was incorporated into algal beads. The three sorbents were characterized by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX): the sorption occurs in the whole mass of the sorbents. Sorption experiments were conducted to evaluate the impact of pH, sorption isotherms, and uptake kinetics. A special attention was paid to the effect of drying (air-drying vs. freeze-drying) on the mass transfer properties. For alginate, freeze drying is required for maintaining the porosity of the hydrogel, while for algal-based sorbents the swelling of the material minimizes the impact of the drying procedure. The maximum sorption capacities observed from experiments were 415, 296 and 218 mg Pb g⁻¹ and 112, 77 and 67 mg Cu g⁻¹ for alginate, algal and algal/PEI beads respectively. Though the sorption capacities of algal-beads decreased slightly (compared to alginate beads), the greener and cheaper one-pot synthesis of algal beads makes this sorbent more competitive for environmental applications. PEI in algal beads decreases the sorption properties in the case of the sorption of metal cations under selected experimental conditions.     

Synthesis and characterization of copolymers with the same proportions of polystyrene and poly(ethylene oxide) compositions but different connection sequence by the efficient Williamson reaction

The AB type diblock PS‐b‐PEO and ABA type triblock PS‐b‐PEO‐b‐PS copolymers containing the same proportions of polystyrene (PS) and poly(ethylene oxide) (PEO) but different connection sequence were synthesized and investigated. Using the sequential living anionic polymerization and ring‐opening polymerization mechanisms, diblock PS‐b‐PEO copolymers with one hydroxyl group at the PEO end were obtained. Then, using the classic and efficient Williamson reaction (realized in a ‘click’ style), triblock PS‐b‐PEO‐b‐PS copolymers were achieved by a coupling reaction between hydroxyl groups at the PEO end of PS‐b‐PEO. The PS‐b‐PEO and PS‐b‐PEO‐b‐PS copolymers were well characterized by ¹H NMR spectra and SEC measurements. The critical micelle concentration (CMC) and thermal behaviors were also investigated by steady‐state fluorescence spectra and DSC, respectively. The results showed that, because the PEO segment in triblock PS‐b‐PEO‐b‐PS was more restricted than that in diblock PS‐b‐PEO copolymer, the former PS‐b‐PEO‐b‐PS copolymer always gave higher CMC values and lower crystallization temperature (T_c), melting temperature (T_m) and degree of crystallinity (X_c) parameters. © 2015 Society of Chemical Industry     

Two novel zinc(II) complexes of the 1,8-cross-bridged cyclam ligand and their structures

Without special precautions to exclude moisture or protic solvents, cross-bridged cyclam ligand 1 was found to readily complex zinc dichloride and yield two types of cis-folded complexes in the solid-state; one a chloride-bridged dimer and the other an aqua complex featuring a coordinated [ZnCl₄]²⁻ counterion.     

Significant positional isomeric effect of zwitterionic ligands on the construction of two different 2D and 3D Pb(II) coordination polymers

Hydrothermal reactions of PbCl₂ with two positional isomers of asymmetric zwitterionic ligands 1-carboxylatomethylpyridinium-3-carboxylate (HL³) and 1-carboxylatomethyl-pyridinium-4-carboxylate (HL⁴) result in the formation of two coordination polymers (CPs) [Pb(L³)Cl] (1) and [Pb_1.5(L⁴)₂Cl(H₂O)] (2), respectively. CPs 1 and 2 were characterized by elemental analysis, IR, powder X-ray diffraction, and single-crystal X-ray diffraction. 1 and 2 exhibit the 2D (4,4)-connected and 3D (3,4,4,5)-connected novel topological networks with (4³.6².8) and (4².12⁴)(4².6)₂(4³.6.8⁴.10²)₂(4⁶)₂ point symbols, respectively, which reveal the significant positional isomeric effect of the zwitterionic ligands on the construction of CPs. Their thermal and photoluminescent properties were also investigated.     

Polymer-metal complexes: Synthesis, characterization, and properties of poly(maleic acid) metal complexes with Cu(II), Co(II), Ni(II), and Zn(II)

SUMMARY Polymer metal complexes of poly(maleic acid) and Cu(II), Co(II), Ni(II), and Zn(II) were synthesized. Elemental analysis, as well as magnetic, spectral and thermal properties, in addition to electrical conductivities of the chelates were investigated, and possible structures have been assigned to the polychelates. Semi-empirical calculations at the PM3 level were carried out on the geometrical arrangement of the polychelates. Received: 19 November 1999/Revised version: 22 March 2000/Accepted: 31 March 2000     

Hopping conduction in (Ni,Co,Mn)O4 prepared by different synthetic routes: Conventional and spark plasma sintering

(Ni,Co,Mn)O₄ (NMC) oxides were prepared by conventional sintering (CS) and spark plasma sintering (SPS) using micro and nanopowders. Small hoping polaron theory was used in order to investigate effect of processing routes on electrical properties of NMC oxides as negative temperature coefficient (NTC) thermistors. Also, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques were utilized to analyze compositional and structural effects on the electrical properties of NMC compounds. Hopping conduction in NMC prepared by SPS and CS using nanopowder occurs via variable range hopping (VRH) mechanism, however conduction in NMC prepared by CS using micropowder follows nearest neighboring hopping (NNH) mode. Hopping distance and activation energy for the VRH mode were calculated using corresponding physical model.     

Biosorption of Pb(II) and Ni(II) ions by chemically modified Eclipta alba stem powder: Kinetics and equilibrium studies

Biosorption of Pb(II) and Ni(II) ions onto the Eclipta alba stem powder (EAS) was investigated in a batch system. The biosorbent was characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and elemental analysis. Adsorption influencing factors like pH, adsorbent dose, initial metal ion concentration and contact time were investigated. The adsorption mechanism of Pb(II) and Ni(II) followed the pseudo-second-order kinetic model (R² > 0.998). The Langmuir isotherm model fitted well and the maximum monolayer adsorption capacity of the sorbent for Pb(II) and Ni(II) was found to be 66.2 ± 1.9 mg g^?1and 62.5 ± 1.8 mg g^?1, respectively. Desorption and recovery were carried out using dilute HCl solution.     

Phytochemical retention and antioxidant capacity of xao tam phan (Paramignya trimera) root as prepared by different drying methods

Xao tam phan (Paramignya trimera (Oliv.) Guillaum) has been used as an herbal medicine for the treatment of cancer or cancer-like diseases in recent years, particularly in Vietnam. Drying is an important step for preparation of dried materials for storage and further investigation; however, the effects of drying must be taken into account when processing samples, because this can have profound effects on the stability of phytochemical compounds and the biological activity of the dried P. trimera root. As such, this study assessed the effects of four different drying methods (conventional, hot air, vacuum, and microwave) on phytochemical retention and antioxidant capacity of P. trimera root, to identify an optimal drying method for P. trimera root. The results showed that the drying methods significantly affected phytochemical levels and antioxidant capacity of P. trimera root and that among the four drying methods tested, microwave drying (400 W) had the highest levels of phytochemical compounds, with total phenolic, total flavonoid, proanthocyanidin, and saponin contents of 11.27 mg GAE, 19.88 mg RE, 3.98 mg CE, and 267.15 mg EE/gram of dried sample, respectively. Dried sample prepared using this method had antioxidant capacity comparable to that of other drying methods. In addition, this method had the shortest drying time (0.28 h) and consumed the least energy (0.28 kWh). Therefore, microwave drying should be considered for drying P. trimera root for further investigation and utilization.     

Stability and phase behavior of the poly(ethylene oxide)-urea complexes prepared by electrospinning

The poly(ethylene oxide)-urea binary system forms a stable (α) complex that can be melt-quenched into a mixture of urea and a second (β) complex with a different stoichiometry. Our results confirm that this mixture is metastable, but that the β-α solid-solid transition is much slower than previously reported. In contrast with the melt-quenched mixture, we observe for the first time that the pure β complex, prepared by electrospinning, is thermodynamically stable up to its melting temperature. This melting is incongruent and leads to the formation of the crystalline α complex and liquid PEO. A phase diagram is drawn over the complete composition range and allows interpreting the formation of the various out-of-equilibrium mixtures observed experimentally. This work also demonstrates an interesting new possibility of electrospinning: the direct preparation of thermodynamically stable compounds that are otherwise inaccessible because of the formation of kinetically frozen products.     

Study of Pb(II) in various H2O-H2SO4 mixtures by differential pulse polarography: solubility of lead sulphate,diffusion coefficient of Pb(II) and half-wave potential of Pb(Hg)/Pb(II)

A study of some properties of Pb(II) in solutions of sulphuric acid was carried out by means of differential pulse polarography. The range of concentrations of acid extended from 0.6 to 70 weight % of H₂SO₄ (0.06-11.5 M). Determination of the solubility of lead sulphate was found to be in good agreement with NBS's results in the range of H₂SO₄ concentrations they studied. With increasing concentration in H₂SO₄, the diffusion coefficient was found to decrease more than expected from the Stokes-Einstein equation, while the standard potential of Pb/Pb(II) related to she was found to increase. This led to a more important self-discharge of the negative electrode of the lead-acid battery.