Synthesis of polyaniline nanoparticle grafted silica gel and study of its Cr(VI) binding property

Polyaniline nanoparticles have been synthesized through simple micelle technique and then grafted it with silanized silica gel to develop a novel hybrid material. The nanoparticles are characterized by UV‐Vis, TEM, CV, SEM, TGA, DTG, and DSC. Silanization and grafting reactions are evaluated by FTIR and chemical test. The Cr(VI) binding behavior of the composite is studied in various pH of the medium, and both competitive and noncompetitive conditions. The particle size, adsorption capacity, and surface area of the material are found to be 100 nm, 135 mg/g, and 720 m²/g, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel surface ionic imprinting materials prepared via couple grafting of polymer and ionic imprinting on surfaces of silica gel particles

In this paper, a new surface molecular imprinting technique is put forward, and a kind of novel ion-imprinted polymers (IIPs) were prepared through a new approach: firstly functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles via the coupling grafting method (“grafting to” method) and the composite material PEI/SiO₂ with chemical linking was formed; secondly the ionic imprinting was carried out towards the macromolecule PEI grafted on the surface of silica particles using Cu²⁺ or Cd²⁺ ion as a template, epichlorohydrin (ECH) as a crosslinking agent and by coordination linkage actions, and Cu²⁺ ion (or Cd²⁺ ion)-imprinted material IIP-PEI/SiO₂ was prepared. The binding characteristics of IIP-PEI/SiO₂ for Cu²⁺ ion (or Cd²⁺ ion) were studied in detail by adopting both static and dynamic methods. The experimental results show that the ion-imprinting material IIP-PEI/SiO₂ has specific recognition ability for the template ions, and this character displays mainly in two aspects: (1) it has high affinity for the template ions, its binding amounts for the template ions are much greater than that of the non-imprinted composite material PEI/SiO₂, and the adsorption capacity enhances nearly two times compared to PEI/SiO₂; (2) it has excellent selectivity for the template ions, for the IIP-PEI/SiO₂ by using Cu²⁺ as template ion, its selectivity coefficients relative to Zn²⁺ and Ni²⁺ are 80.21 and 86.08, respectively, and for the IIP-PEI/SiO₂ by using Cd²⁺ as template ion, its selectivity coefficients relative to Cr³⁺ and Pb²⁺ are 77.05 and 88.22, respectively. Besides, the imprinting material IIP-PEI/SiO₂ has a fine elution property using HCl solution as eluent. The obtained imprinting material by using the new surface molecular imprinting techniques possesses superexcellent binding property for template molecules or ions because of the distribution of imprinted cavities in a thin polymer layer and smaller diffusion barrier.     

Novel negatively charged hybrids. 2. Preparation of silica‐based hybrid copolymers and their applications for Cu2+ removal

A series of negatively charged silica‐based hybrid copolymers were prepared via free radical polymerization of γ–methacryloxypropyl trimethoxy silane (MAPTMS), 4–vinylbenzylchloride (VBC), and styrene (St) monomers, and the sol–gel process. Their applications for Cu²⁺ removal from aqueous solution were investigated. TGA and DrTGA thermal analyses indicated that these hybrid copolymers can keep thermally stable up to 412°C. Their cation‐exchange capacities (CIECs) are within the range of 0.49–1.25 mmol g^–1. Adsorption experiments indicated that the adsorption followed Langmuir isotherm model, suggesting that it is Langmuir monolayer adsorption. The electrostatic attraction between the ionic groups and Cu²⁺, the content of ionic groups and the existence of reactive chloromethyl groups might be responsible for such trend. Based on these findings, it can be concluded that the incorporation of VBC in the hybrid copolymers conduces to the advance of Cu²⁺ adsorption capacity; however, the incorporation of St makes little contribution to the raise of Cu²⁺ adsorption capacity, suggesting that the adsorption performances of these silica‐based hybrid copolymers can be artificially adjusted and have potentially application in the removal of Cu²⁺ from wastewater. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Enhanced catalytic oxidation via nano Cu0.5Mg0.5Fe2O4 embedded in CNTs for adsorption–reduction of hexavalent chromium

A catalyst consisting of Cu_0.5Mg_0.5Fe₂O₄ (CMF) supported on carbon nanotubes (CNTs) which exhibits great potential as an adsorbent for treating Cr(VI)-contaminated wastewater has been successfully prepared. The ferrite possesses excellent magnetic properties, while CNTs have the advantage of a large surface area. This composite material not only prevents the aggregation of magnetic materials and enhances the exposure of active sites but also effectively solves the recycling problem of CNTs. Our results show that the adsorption capacity of Cu_0.5Mg_0.5Fe₂O₄–carbon nanotubes (CMF-CNTs) for Cr(VI) wastewater (45.60 mg/g) is 1.49 times higher than that of Cu_0.5Mg_0.5Fe₂O₄ (30.48 mg/g). Compared to a single catalyst, CMF-CNTs not only improve the dispersibility of magnetic materials but also exhibit synergistic effects between the composite materials, enhancing the chemical adsorption capacity. After five consecutive adsorption and desorption experiments, the adsorption capacity of CMF-CNTs remains at 88% of its initial value. Furthermore, the study of the catalyst before and after adsorption by XPS reveals that the valence state transition of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ plays a crucial role in the adsorption process. The results of this study demonstrate the potential of using waste materials for effective wastewater treatment and provide insights into the development of new adsorbents for pollutant removal.     

Fabrication of copper coated polymer foam and their application for hexavalent chromium removal

The polymer foam coated with zero-valent copper (Cu⁰) was designed and prepared for the removal of hexavalent chromium (Cr(VI)) in water. Firstly, porous poly(tert-butyl acrylate) was fabricated by concentrated emulsion polymerization and then acrylic acid groups were generated on the surface of foam by hydrolysis reaction. Secondly, with the help of the large amount reactive carboxylic acid groups, polyethyleneimine (PEI) were chemically grafted onto the surface by the reaction between amine group and acrylic acid group. Finally, zero-valent copper was reduced by sodium borohydride (NaBH₄) and coated on the surface of polymer foam. Thus the copper functionalized porous adsorbent (Cu⁰–PEI–PAA) was constructed, and then applied for removing Cr(VI) from aqueous solution. The removal mechanism of Cr(VI) involved redox reaction by zero-valent copper and adsorption by amine groups, simultaneously. As a result, 99.5% of Cr(VI) could be removed within 2 h, and the maximum removal capacity for Cr(VI) of Cu⁰–PEI(1800)–PAA was 9.16 mg/g. Furthermore, the effect of initial concentration of Cr(VI), pH value, and temperature on the Cr(VI) removal was investigated. Therefore, the as-prepared zero-valent copper-loaded polymer foam could be an efficient and promising remediation material to remove Cr(VI) from wastewater.     

Application of a Novel Hybrid Cation Exchange Material in Metal Ion Separations

A novel hybrid cation exchange material of the class of tetravalent metal acid (TMA) salt, titanium diethylene triamine pentamethylene phosphonate (TiDETPMP) has been synthesized by the sol gel method. The material has been analyzed by spectroscopy and thermal methods. Physico-chemical and ion exchange characteristics have also been studied. The distribution coefficient (K _d ) has been determined in aqueous as well as various electrolyte media/concentrations for Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ (transition metal ions) and Cd²⁺, Hg²⁺, Pb²⁺, Bi³⁺ (heavy metal ions) using TiDETPMP. Based on the differential affinity/selectivity, the breakthrough capacity (BTC) and elution behavior of various metal ions towards TiDETPMP, a few binary and ternary metal ions separations have been carried out.     

Coals as sorbents for the removal and reduction of hexavalent chromium from aqueous waste streams

The aim of this study is to demonstrate the potential of coals as a low-cost reactive barrier material for environmental protection applications, with the ability to prevent leaching of toxic Cr(VI) and other transition metals. Depending upon the type of ion and the surface functionalities, the uptake can involve ion sorption, ion exchange, chelation and redox mechanisms with the surface functionalities being considered as partners in electron transfer processes. The capacity for Cr(VI) uptake of low rank coals and oxidized bituminous coals has been found to lie within the range 0.2-0.6 mM g⁻¹. Air oxidation of bituminous coals can increase their Cr(VI) removal capacities. The effect of air oxidation of coals on uptake capacity was more pronounced for Cr(VI) than Cr(III), but less than for Hg(II) and the other ions (Ca²⁺, Ba²⁺, Zn²⁺, Cd²) investigated. As previously found for Hg(II), redox mechanisms play an important role in Cr(VI) uptake, with sorption of the resultant Cr(III) being aided by the functionalities arising from oxidation of the coal surface. In acidic media, much of the resultant Cr(III) is exchanged back into solution by hydrogen ions, but some of the sorbed chromium is irreversibly bound to the coal. The reduction of Cr(VI) alone is often considered a satisfactory solution in view of Cr(III) being essentially non-toxic.     

A diamino based resin modified silica composite for the selective recovery of tungsten from wastewater

A new adsorbent was developed by synthesizing 1,8‐diaminonaphthalene formaldehyde resin (DANFR) and coating it over the surface of silica gels. The silica composite was then treated with HCl for the activation of binding sites (?NH₃⁺Cl^?) on its surface. The structure of DANFR and its coating over the silanols were thoroughly characterized. Further, the adsorbent was applied to remove tungsten (W) from printed circuit board recycling unit wastewater that contained various co‐metal ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Pb²⁺, NH₄⁺, Zn²⁺, Cu²⁺ and Mn²⁺. The selective removal was achieved due to the anion exchange mechanism of Cl^? with W(VI) while other cations get repelled from the surface (?NH₃⁺) of the DANFR‐silica composite. X‐ray photoelectron spectroscopy studies, Raman spectra and overlay chromatograms of ion chromatography demonstrated selective separation of WO₄^2? species from the wastewater. A removal capacity of 55.32 mg g^?1 for W(VI) was achieved from the wastewater within 45 min of reaction (pH ca 6.0). Simultaneous treatment with neat aqueous solution of W brings out 63.27 mg g^?1 of W(VI) removal. Finally, recovery of WO₄^2? ions and regeneration of the adsorbent were carried out by using alkaline solution which demonstrated successful desorption, as investigated by using ion chromatography. © 2016 Society of Chemical Industry     

ELECTRO-DEIONIZATION OF Cr (VI)-CONTAINING SOLUTION. PART I: CHROMIUM TRANSPORT THROUGH GRANULATED INORGANIC ION-EXCHANGER

Kinetics of Cr (VI) → OH^? exchange on both hydrogel and xerogel of hydrated zirconium dioxide was investigated. Self-diffusion coefficient of Cr (VI) species has been determined by analysis of kinetic curves. Transport of Cr (VI) anions through the inorganic ion exchangers under the influence of applied voltage was also researched. In the case of hydrogel, the ions are transported mainly through the solid phase. Diffusion coefficient of chromate anions through this material was estimated as 9.00 × 10^?12 m² s^?1. This is in agreement with self-diffusion coefficient of Cr (VI) obtained from kinetic measurements (1.60 × 10^?12–9.92 × 10^?12 m² s^?1). Owing to the rather high mobility of Cr (VI) through hydrogel of hydrated zirconium dioxide, this material was recommended for electro-deionization processes. On the other hand, the use of polymer anion-exchange membrane must be excluded to prevent poisoning of the inorganic ion exchanger with Cr (III) cations to be formed during chemical interaction of Cr (VI) with organic materials.     

Preparation and adsorption performances of novel negatively charged hybrid materials

A series of novel negatively charged hybrid materials were prepared via sol–gel process and a subsequent epoxide ring‐opening reaction. The coupling reaction was conducted between 3‐glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS), which was confirmed by FTIR spectra. TGA, and DrTGA analyses showed that their thermal stabilities were higher and the optimal molar ratio of GPTMS and TEOS was equal to 1 : 1. The ion‐exchange capacities (IECs) exhibited that they were related to the amount of anionic groups in the hybrid materials, indicating that the negatively charged properties of the hybrid materials could be artificially controlled via the adjustment of silica in these charged hybrid materials. The adsorption properties for Pb²⁺ and Cu²⁺ ions revealed that these hybrid materials were able to absorb heavy metal ions, suggesting that they have potential applications in the separation and recovery of environmentally hazardous substances. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and application of amine functionalized silica mesoporous magnetite nanoparticles for removal of chromium(VI) from aqueous solutions

In this research, novel nanoparticles of Kit-6 mesoporous silica magnetite were synthesized with 9.6 nm pore diameter and 241.68 m² g^?1 surface area. The synthesized mesoporous magnetite nanoparticles (MMNPs) were functionalized with amine groups. Scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption method confirmed the morphology and structure of the synthesized nanoparticles. The amine functionalized MMNPs were used for sorption of toxic chromate ions from aqueous samples. The effect of various experimental parameters (four factors at three levels) on the sorption efficiency of Cr(VI) was studied and optimized via Taguchi L₉ (3⁴) orthogonal array experimental design. At optimum conditions, the sorption of the Cr(VI) was best described by a pseudo second-order kinetic model with R² = 0.9999 and q_eq = 129.8 mg g^?1, suggesting chemisorption mechanism. Adsorption data were fitted well to the Langmuir isotherm and the synthesized sorbent showed complete ion removal with 185.2 mg g^?1sorption capacity.     

Removal of hexavalent chromium ion from aqueous solution using nanoscale zero-valent iron particles immobilized on porous silica support prepared by polymer template method

Porous silica supported nanoscale zero-valent iron was prepared by a polymer template method in order to effectively remove a hexavalent chromium ion (Cr(VI)) in an aqueous solution. It did not show a deterioration of Cr(VI) removal efficiency, which could be caused by the surface oxidation and agglomeration of nanoscale zero-valent iron (NZVI) particles. Porous silica by the polymer template method showed quite unique structure, which we named as quasi-inverse opal silica (QIOS), and it showed high surface area (375.4m²/g) and fine pore size (76.5 nm). NZVI immobilized on the surface of QIOS (NZVI@QIOS) was added to an aqueous Cr(VI) solution at 0.025 g/L, and it showed over 96% Cr(VI) removal efficiency. Such a high removal efficiency of Cr(VI) was maintained over two weeks after preparation (92% after 16 days). Morphology of porous silica supported nanoscale zero-valent iron was analyzed by TEM and FE-SEM. Identification of the reaction compounds produced by the reaction of Cr(VI) and zero-valent iron (Fe(0)) was made by the application of XPS.     

Preparation and anticorrosive properties of hybrid coatings based on epoxy‐silica hybrid materials

A series of sol‐gel derived organic–inorganic hybrid coatings consisting of organic epoxy resin and inorganic silica were successfully synthesized through sol‐gel approach by using 3‐glycidoxypropyl‐trimethoxysilane as coupling agent. Transparent organic–inorganic hybrid sol‐gel coatings with different contents of silica were always achieved. The hybrid sol‐gel coatings with low silica loading on cold‐rolled steel coupons were found much superior improvement in anticorrosion efficiently. The as‐synthesized hybrid sol‐gel materials were characterized by Fourier‐transformation infrared spectroscopy, ²⁹Si‐nuclear magnetic resonance spectroscopy and transmission electron microscopy. Effects of the material composition of epoxy resins along with hybrid materials on the thermal stability, Viscoelasticity properties and surface morphology were also studied, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Insights into the coordination sphere of copper ion in polymers containing carboxylic acid and azole groups

In this work, we describe the Cu²⁺ ion uptake from recently developed hydrogel with polyampholyte and polyelectrolyte behavior at different concentrations of the metal ion. Solid-state NMR and EPR were used as complementary techniques to understand the coordination role of carboxylic acid and azole groups (imidazole, triazole and pyrazole) involved in the copper ion coordination. In polymers containing imidazole and triazole, the uptake took place preferentially through the azole groups, with less participation of the carboxylate groups at low concentrations of Cu²⁺. However, as the concentration of Cu²⁺ increased, these azole ligands became less active in the new sites for copper. In polymers containing pyrazole, coordination of Cu²⁺ was through both carboxylate and pyrazole ligands, regardless of the concentration of Cu²⁺.     

Enhanced performance of LiFePO4 through hydrothermal synthesis coupled with carbon coating and cupric ion doping

A hydrothermal reaction has been adopted to synthesize pure LiFePO₄ first, which was then modified with carbon coating and cupric ion (Cu²⁺) doping simultaneously through a post-heat treatment. X-ray diffraction patterns, transmission electron microscopy and scanning electron microscopy images along with energy dispersive spectroscopy mappings have verified the homogeneous existence of coated carbon and doped Cu²⁺ in LiFePO₄ particles with phospho-olivine structure and an average size of 400 nm. The electrochemical performances of the material have been studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The carbon-coated and Cu²⁺-doped LiFePO₄ sample (LFCu5/C) exhibited an enhanced electronic conductivity of 2.05 × 10⁻³ S cm⁻¹, a specific discharge capacity of 158 mAh g⁻¹ at 50 mA g⁻¹, a capacity retention of 96.4% after 50 cycles, a decreased charge transfer resistance of 79.4 Ω and superior electrode reaction reversibility. The present synthesis route is promising in making the hydrothermal method more practical for preparation of the LiFePO₄ material and enhancement of electrochemical properties.     

Impact of pH on Binding Metal Ions by Datura innoxia Biomass

Abstract

Metal ion binding to biomaterials derived from cultured antheral cells of Datura innoxia has been investigated as a function of solution pH. Specifically, the binding of Ba²⁺, Cd²⁺, Cu²⁺, Ni²⁺, and Sr²⁺ was studied at pH 1–6, inclusive, in 0.1 M MES solutions. For 10 mg·L^?1 metal ion solutions, maximum binding was observed for solutions at pH 5. The dependence of metal ion binding on solution pH was studied for the biomass both free in solution and immobilized in a polysilicate matrix. A significant change in the pH-dependent binding of each of these metals was observed when the cell material was immobilized. These variations in the impact of metal solution pH could not be explained by the Lewis acidity of the metal ions. The involvement of conformational changes of the macromolecular components of the material for the formation of metal-selective coordination sites is postulated.     

Adsorption of hexavalent chromium from aqueous solutions using 4-vinyl pyridine grafted poly(ethylene terephthalate) fibers

Summary Sorption of hexavalent chromium ions from aqueous solution by 4- vinyl pyridine (4-VP) grafted poly(ethylene terephthalate) (PET) fibers was studied. The Influences of adsorption time, pH of solution and Cr(VI) concentration on the adsorbed amount were investigated. 30 minutes of treatment time was found to be sufficient to reach equilibrium. pH 3.0 was found as the optimum pH value in the process. The maximum adsorption capacity of the material (k_s) was found to be 263.16 mg g^-1. It was found that the reactive fibers are stable and regenerable by acid or base without losing their activity.     

Selective online solid-phase extraction of copper using p-morpholino-methylcalix[4]arene appended silica-based column

ABSTRACT

This study deals with investigation of selectivity of p-morpholino-methylcalix[4]arene appended silica from a group of metal ions having similar charge and radii. The values of distribution ratio revealed that modified silica possess higher selectivity for Cu²⁺. In addition, relative selectivity coefficients of modified silica were found to be 24.1, 13.8, 8.6 and 4.01 for Cu²⁺/Ni²⁺, Cu²⁺/Co²⁺, Cu²⁺/Cd²⁺, Cu²⁺/Pb²⁺, respectively. The maximum adsorption capacity was 1.5 mmolg^?1. The reusability data suggested no any loss of adsorption capacity of this material up to 10 cycles. The developed material was also applied for determination of copper in lake water samples with satisfactory results.     

Influence of Cu2+‐organic montmorillonites on thermal decomposition and smoke emission of poly(vinyl chloride) by cone calorimetric study

Cu²⁺‐Organic montmorillonites were prepared by modifying Na⁺ montmorillonite (Na⁺‐MMT) with silane coupling agents and cupric sulfate. PVC/organic montmorillonite composites were prepared by the melt intercalation method. Morphological structure of modified MMT and PVC/MMT was obtained by using XRD and SEM. The XRD results showed that silanes and Cu²⁺ were intercalated among interlayers and that modified MMT may have exfoliated dispersion in PVC. Effects of Cu²⁺‐organic montmorillonites on decomposition and smoke emission of poly(vinyl chloride) (PVC) in the flaming mode were investigated by using a cone calorimeter at an incident heat flux of 25 kW·m^?2. Cone experimental data demonstrated that the Cu²⁺‐organic montmorillonites prepared were new effective smoke suppressants. They clearly promoted an early HCl elimination, crosslinking reactions, and char residue formation, based upon the decomposition parameters of mass loss, mass loss rate, and time of initial decomposition (t_initial). Cu²⁺‐Organic montmorillonites decreased peak heat release rate, total heat release, peak smoke production rate, total smoke production, and smoke extinction area during the flaming process. The smoke‐reducing efficiency of Cu²⁺‐organic montmorillonites (Cu²⁺‐OMMTs) was the best. However, the content of cupric ion was only 0.6–0.8% in Cu²⁺‐OMMTs and 0.03–0.04% in PVC composites. They may make the smoke‐reducing efficiency reach 45–50%. This result further demonstrates that Cu²⁺ ion is a very effective smoke suppressant for PVC. J. VINYL ADDIT. TECHNOL., 13:31–39, 2007. © 2007 Society of Plastics Engineers.     

Comparison of ethylene polymerization catalyzed over Cr(VI)/silica and Cr(II)/silica catalysts

Summary Ethylene polymerization and the morphology of produced high density polyethylene (HDPE) catalyzed over. Cr(VI)/silica and Cr(II)/silica were studied. Cr/silica catalyst with Cr loading of 1 wt % has been prepared by impregnating an aqueous solution of CrO₃ onto silica having specific surface area of 301 m²/g and pore volume of 1.64 ml/g. The rate profiles and the morphologies of polyethylene polymerized over Cr(VI) and Cr(II)/silica were different. The process of active site formation influences the rate profiles. The shape of polyethylene particles polymerized with Cr(II)/silica resembled the original shape of catalyst particles. However, Cr(VI)/silica catalyst particles were fractured inhomogeneously during the polymerization. The variation of molecular weight and molecular weight distribution at various polymerization times indicated that the formation of active sites of Cr(VI)/silica was accomplished gradually during polymerization.