Nevenka Rajic

Removal of aqueous manganese using the natural zeolitic tuff from the Vranjska Banja deposit in Serbia.

The natural zeolite tuff from the Vranjska Banja deposit (Serbia) has been studied as sorbent for Mn(II) ions from aqueous solutions. The zeolite sample containing mainly clinoptilolite (more than 70%) removes Mn(II) ions by ion-exchange process, which was confirmed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDXS). XPS showed that there is no surface accumulation of Mn but an almost uniform distribution inside the sorbent; EDXS confirmed that Mn(II) replaced the clinoptilolite Na counter ions. The sorption isotherms were studied at 298 K by batch experiments showing that the Mn(II) removal is best described by the Langmuir-Freundlich or Sips model. The kinetics followed the pseudo-second-order model, the activation energy being 128 kJ mol(-1). The intra-particle diffusion is not the rate-controlling step in the sorption of Mn(II) on clinoptilolite. Thermodynamic data suggest spontaneity of the endothermic ion-exchange process in the 298-338 K range.

On the possibility of incorporating Mn(II) and Cr(III) in SAPO-34 in the presence of isopropylamine as a template

Hydrothermal synthesis of SAPO materials using isopropylamine (i-PrNH2) as the template leads to the formation of MnAPSO-34 if Mn(II) is present. In the presence of Cr(III), the synthesis yields SAPO-34 containing chromium(III), which is not incorporated in the silicoaluminophosphate lattice. Calcination of MnAPSO-34 results in oxidation of Mn(II); the calcinated product can be subsequently reduced back to MnAPSO-34. The MnAPSO-34 material catalyzes dehydration of methanol, and its catalytic activity is higher than that of SAPO-34.

Antibacterial activity of heavy metal-loaded natural zeolite

The antibacterial activity of natural zeolitized tuffs containing 2.60wt.% Cu(2+), 1.47 Zn(2+) or 0.52 Ni(2+) were tested. Antibacterial activities of the zeolites against Escherichia coli and Staphylococcus aureus were tested after 1h and 24h of exposure to 1g of the zeolite in 100mL of three different media, namely Luria Bertani, synthetic wastewater and secondary effluent wastewater. The antibacterial activities of the zeolites in Luria Bertani medium were significantly lower than those in the other media and negatively correlated with the chemical oxygen demand of the media. The Ni-loaded zeolite showed high leaching of Ni(2+) (3.44-9.13wt.% of the Ni(2+) loaded) and weak antibacterial activity in the effluent water. Since Cu-loaded zeolite did not leach Cu(2+) and the leaching of Zn(2+) from Zn-loaded zeolite was low (1.07-1.61wt.% of the Zn(2+) loaded), the strong antibacterial activity classified the Cu- and Zn-loaded zeolite as promising antibacterial materials for disinfection of secondary effluent water.

Microencapsulation of Flavors in Carnauba Wax

The subject of this study is the development of flavor wax formulations aimed for food and feed products. The melt dispersion technique was applied for the encapsulation of ethyl vanillin in wax microcapsules. The surface morphology of microparticles was investigated using scanning electron microscope (SEM), while the loading content was determined by HPLC measurements. This study shows that the decomposition process under heating proceeds in several steps: vanilla evaporation occurs at around 200 °C, while matrix degradation starts at 250 °C and progresses with maxima at around 360, 440 and 520 °C. The results indicate that carnauba wax is an attractive material for use as a matrix for encapsulation of flavours in order to improve their functionality and stability in products.

Antimicrobial activity of metal oxide nanoparticles supported onto natural clinoptilolite

The antimicrobial activity of Cu(2)O, ZnO and NiO nanoparticles supported onto natural clinoptilolite was investigated in the secondary effluent under dark conditions. After 24h of contact the Cu(2)O and ZnO nanoparticles reduced the numbers of viable bacterial cells of Escherichia coli and Staphylococcus aureus in pure culture for four to six orders of magnitude and showed consistent 100% of antibacterial activity against native E. coli after 1h of contact during 48 exposures. The antibacterial activity of NiO nanoparticles was less efficient. The Cu(2)O and NiO nanoparticles showed 100% of antiprotozoan activity against Paramecium caudatum and Euplotes affinis after 1h of contact, while ZnO nanoparticles were less efficient. The morphology and crystallinity of the nanoparticles were not affected by microorganisms. The metal oxide nanoparticles could find a novel application in the disinfection of secondary effluent and removal of pathogenic microorganisms in the tertiary stage of wastewater treatment.

Novel kinetic model of the removal of divalent heavy metal ions from aqueous solutions by natural clinoptilolite

Removal of heavy metal ions from aqueous solutions using zeolites is widely described by pseudo-second order kinetics although this model may not be valid under all conditions. In this work, we have extended approaches used for derivation of this model in order to develop a novel kinetic model that is related to the ion exchange mechanism underlying sorption of metal ions in zeolites. The novel model assumed two reversible steps, i.e. release of sodium ions from the zeolite lattice followed by bonding of the metal ion. The model was applied to experimental results of Cu(II) sorption by natural clinoptilolite-rich zeolitic tuff at different initial concentrations and temperatures and then validated by predictions of ion exchange kinetics of other divalent heavy metal ions (i.e. Mn(II), Zn(II) and Pb(II)). Model predictions were in excellent agreements with experimental data for all investigated systems. In regard to the proposed mechanism, modeling results implied that the sodium ion release rate was constant for all investigated metals while the overall rate was mainly determined by the rate of heavy metal ion bonding to the lattice. In addition, prediction capabilities of the novel model were demonstrated requiring one experimentally determined parameter, only.

On the zinc sorption by the Serbian natural clinoptilolite and the disinfecting ability and phosphate affinity of the exhausted sorbent

The Serbian natural zeolite is moderately effective in removing the zinc(II) ions from aqueous solutions. At 298 K the sorption capacity varies from 13 to 26% for the initial Zn(II) solution concentration of 100 and 600 mg Zndm(-3), respectively. The sorption isotherm at 298-338 K is best represented by the Langmuir model and the sorption kinetics by the pseudo-second-order model. The sorption involves a combination of film diffusion, intra-particle diffusion, and a chemical cation-exchange between the Na(+) ions of clinoptilolite and Zn(2+) ions. The sorption was found to be endothermic and spontaneous in the 298-338 K range. The exhausted sorbent can remove phosphate ions and it exhibits an excellent antibacterial activity towards Acinetobacter junii. By dehydration at about 500 °C it transforms to a ZnO-containing product featuring nano-sized wurtzite ZnO particles widespread over the clinoptilolite surface.

A CoAPO-34 derived from a triclinic precursor prepared in the presence of HF

The fluoride route of synthesis of AlPO4-34 is also successful in the preparation of its cobalt-modified product (CoAPO-34). The triclinic precursor of CoAPO-34 has been synthesized in the presence of HF and piperidine. Although two different Al sites are available for cobalt(II) substitution (i.e., tetrahedral and octahedral sites), cobalt(II) substitutes exclusively the tetrahedral aluminum. Calcination of the as-synthesized material results in oxidation of Co(II). This is evident from the electron absorption, electron paramagnetic resonance, and infrared measurements. The calcined product exhibits a particular sensitivity to humidity: upon hydration, the chabazite structure transforms to a new one. However, the hydration is a reversible process: thermal evacuation of the hydrated sample causes a complete return to the chabazite material. In comparison with the CoAPO-34 obtained in a nonfluoride medium, the CoAPO-34 prepared in this work exhibits a higher thermal stability.

On the formation of CoAPSO-44

Hydrothermal synthesis of CoAPSO-44 in the presence of cyclohexylamine (CHA) as the template is generally accompanied by the formation of an unknown phase, “Co(APSO)N.” Electronic spectroscopy indicates that CO(APSO)N contains Co2+ in a pentacoordinated environment. When Co(APSO)N is heated at 195°C in a water suspension under autogenic pressure, two processes occur: (a) a partial conversion of Co(APSO)N into CoAPSO-44 and (b) decomposition of Co(APSO)N into Co- and Al-phosphates. Thermal removal of CHA from Co(APSO)N results in a breakdown of the latters cyrstal lattice.

Thermal investigation of two FePO materials prepared in the presence of 1,2-diaminoethane

Two porous iron phosphates were synthesized hydrothermaly from a reaction mixture of FeCl3:H3PO4:1,2-diaminoethane:H2O in the molar ratio 1:3:5:70. The chemical formulas indicate difference only in water content; however, the crystal structures and thermal behaviour of the iron phosphates are completely different. After the removal of 1,2-diaminoethane and water, both products exhibit structural transformation.