Papers by Keyword: Ion-Exchange

Abstract: In this work, nanosized calcium deficient hydroxyapatite (nCDHA) was synthesized by the precipitation method, and then utilized as an adsorbent for removal of Fe (II), Cu (II), Ni (II) and Cr (VI) ions from aqueous solutions after characterizing it by various techniques as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and BET method. A possible structure of synthesized nCDHA was proposed. The adsorption study indicated that the adsorption equilibrium is well fitted with Langmuir isotherm model with the maximum adsorption capacities followed the order of Fe (II) > Cu (II) > Ni (II) > Cr (VI) with the values of 137.23, 128.02, 83.19 and 2.92 mg/g, respectively. The ion-exchange mechanism was dominant for the adsorption of metal ions onto nCDHA at initial metal concentrations lower than 0.01 mol/L. Along with the ion-exchange mechanism, there was an additional precipitation occurred on the surface of nCDHA in the case of Fe (II) and Cu (II) at initial concentrations higher than 0.01 mol/L.

Abstract: In this work, amphoteric cryogels based on N,N-dimethyl acrylamide, methacrylic acid and allylamine, crosslinked by N,N-methylenebisacrylamide were synthesized by free-radical polymerization in cryo-conditions. The synthesized cryogels were used for the removal of cadmium ions from aqueous solutions under different pH values. The chemical structure was studied by FTIR, porosity by nitrogen adsorption and morphology by scanning electron microscopy and texture analyzer. The amphoteric properties of cryogels were studied by zeta potential measurements. Adsorption tests revealed that cryogels exhibit 3 times higher adsorption capacity at pH 6.0 than at pH 4.0. The maximum adsorption capacity of the amphoteric cryogels for Cd²⁺ was 113 mg/g, at pH 6.0 and initial Cd²⁺ concentration 100 ppm. The results suggest that the predominant removal mechanism is ion exchange between sodium, which initially presents in the structure of the cryogel, and cadmium from the aqueous phase. Recovery studies suggested that the cryogels used can be regenerated and efficiently reused.

Abstract: Marine structure, coralline materials were converted to calcium phosphate using two different phosphate solutions. The aim was to study the conversion mechanisms under acidic and basic environment at moderate conditions of temperature. Crystal growth and morphology of converted corals were characterized by XRD and SEM respectively. The results suggested that under acidic conditions (H₃PO₄), dissolution and precipitation control and direct the crystal formation and morphology in which transition from plate like to rod like hydroxyapatite structure was favoured. Metastable phase such as monetite formed and transformed to HAp during reaction. During the first hour of the dissolution a monetite and hydroxyapatite mixture precipitates and then the full conversion to hydroxyapatite is observed. On the other hand, under basic conditions (NH₄)₂HPO₄, just diffusional surface conversion of the calcium carbonate structure of coralline materials to hydroxyapatite and a very small amount of tri-calcium phosphate is observed. The mechanism can be classified as the solid-state topotactic ion-exchange reaction mechanism.

Abstract: The intercalation of calcein into Mg/Al-NO₃-LDHs and Zn/Al-NO₃-LDHs by co-precipitaiton and ion-exchange method has been investigated. The obtained intercalation compounds were characterized by XRD, FT-IR and TG-DSC techniques. The results show that the original interlayer nitrate ions can be replaced by the organic anions under the controlled conditions. From the XRD data, the guest size and the orientation of anions between the layers were determined and after intercalation the interlayer spaces of the materials are expanded to 1.81 nm. FT-IR and DSC/TG curves reveal the presence of a complex system of supramolecular host-guest interaction and the increase of thermal stability of materials and the photochemical properties of compounds were studied by UV-Vis adsorption spectroscopy. These results indicate that the confinement of the UV absorbents in their anionic form within the restricted space of the interlayer region of LDHs is in favor of guest-host and guest-guest interactions, so that the UV aborption range and ability of the intercalation compounds are changed.

Abstract: Aiming to develop sponge-type sorbent, composite involving ammonium molybdophosphate (AMP) and polyurethane foam (PUF) was prepared. A 33 - 60 % (w/w) of AMP granule was kneaded with base-liquids of two-component rigid type PUF. The composite was able to selectively and quantitatively adsorb 0.5-500 µL of Cs⁺ from 10 mL solution of 500 µL of Na⁺, K⁺, Mg²⁺ and Ca²⁺ as matrices ions; distribution coefficient (k_d) was 4.2 × 10⁶ and 1.3 × 10⁵ mL/g for without and with matrices, respectively. Maximum sorption capacity was of 42.9 mg/g.

Abstract: Ion-exchange of palladium (Pd) precursor for two different types of well-ordered SBA-15 morphologies, necklace-like and rod-like, was studied. Approximately 3.8 wt% Pd was successfully incorporated into SBA-15 at pH 10.3. Formation of SBA-15 and Pd/SBA-15 were characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Thermogravimetry with Simultaneous Difference Thermal Spectroscopy coupled with mass spectrometer (TG/SDTA-MS), Thermogravimetry in combination with Simultaneous Difference Thermal Spectroscopy (TG-SDTA), Inductive Coupled Plasma Mass Spectrometer (ICP-MS) and N₂ adsorption-desorption. Reduction of surface area and pore volume of support for Pd/SBA-15 samples may indicate the encapsulation of PdO particles within mesoporous channels of SBA-15.

Abstract: Three different zeolites (erionite, mordenite and natural clinoptilolite) were used to study influence of zeolite topology on the state of copper during ion-exchange and following reduction in hydrogen flow. This comparative study clearly demonstrates the influence of used zeolite matrices on the process of implantation of copper nanospecies. Starting from the ion-exchange, the alterations in the state of Cu²⁺ ions start to be evident due to variations of the intensity of charge transfer band. Copper ions start to reduce at specific temperatures depending on the type of zeolite matrix. Copper plasma resonance band change its shape and position for different zeolites. In the case of Cu-CLI samples this band change both the shape and position for different temperature of reduction. These observations permit to suggest that the mechanism of copper ion reduction and agglomeration to form copper nanoparticles noticeably depend on the type of zeolite matrix. This mechanism is more complex for the Cu CLI than for the Cu-MOR and Cu-ERI systems. Copper nanoparticles formed at low temperatures in the case of Cu-CLI samples undergo changes while temperature of reduction grow.

Abstract: The intercalation of herbicide, 2,4,5-tricholorophenoxybutyrate (TBA) , into zinc-aluminium-layered double hydroxide (ZAL) for the formation of a new nanocomposite ZAT, was accomplished via anion exchange method. Due to the intercalation of TBA with ZAL interlayer domain, basal spacing expanded from 8.9Å in the ZAL to 23.3 Å in the ZAT. The percentage loading of TBA in the ZAT is 45.5 % (w/w). The FTIR spectra of the nanocomposite shows resemblance peaks of the TBA and Zn-Al-layered double hydroxide indicating the inclusion of TBA into the layered double hydroxide. Surface area of the resulting nanocomposite increased from 1.3 to 15.6 m²g^-1 with the nitrogen adsorption-desorption of type IV, indicating the mesopore type of material.

Abstract: Organic-LDHs was prepared by three methods including co-precipitation, ionexchange and roast reduction process using Lauryl alcohol phosphoric acid ester potassium (MAPK) asmodifier.Polypropylene (PP)/Organically-modified layered double hydroxides (LDH) was prepared by the melt blending method. The structures and morphologies of composites were characterized by X-ray diffraction and TEM. TGA, cone calorimeter, limiting oxygen index (LOI) and the UL94 protocol were used to characterize the thermal stability and fire properties of composites. The results indicate that MAPK was successfully intercalated into the interlayer of LDHs and MAPK has a different arrangement in the interlayer of organicLDHs for different preparation methods of LDHs. PP/ionexchangeorganicLDHs (PP/ion-o-LDHs) and PP/roast reductionorganicLDHs (PP/ro-o-LDHs) show a better dispersion of LDH in PP than PP/co-precipitationorganicLDHs (PP/co-o-LDHs) composites. Compared to pristine PP, the peak heat release rate of PP/10% co-o-LDHs, PP/10% ion-o-LDHs and PP/10% ro-o-LDHs decreased by 21%, 33% and 30% respectively. The limiting oxygen index increased by 3.7 from 17.2(in PP) to 20.9(in PP/10% ion-o-LDHs). All of the composites could obtain an HB in the UL-94 horizontal burning.

Abstract: Hybrid materials are attractive for a large range of applications from medicine and biotechnology to telecommunication systems and fuel cells. In the present research we have studied sol-gel synthesis of hybrid composites based on carbofunctional organosilicon monomers N,N-bis-(3-triethoxysilylpropyl) thiocarbamide (I) or 2-{[3-(triethoxysilyl) propyamino} pyridine (II), and copolymers of ethylene glycol vinyl glycidyl ether with vinyl chloride. The polymeric materials were characterized by scanning electron microscope (SEM) and IR-spectroscopy. Gel products possess high thermal stability (decomposition temperatures reach 250 °С) and have developed specific surface (to 20 m²g^-1).The synthesized composites comprise semi-interpenetrating polymer networks, consisting of three-dimensional and linear polymers that cannot be separated due to the mechanical interlacing of theirs chains. Hybrid composites have a value of sorption capacity for Pt (IV) ions of 70 (I) and 28 (II) mgg^-1. Proton conductivity of membranes based on the synthesized composites is characterized by the values 3.52 10^-2 (I) and 1.19 10^-2 (II) Scm^-1 measured at temperature of 25 °C.