Elina Yanovska

Synthesis and adsorption properties of chitosan-silica nanocomposite prepared by sol-gel method

A hybrid nanocomposite material has been obtained by in situ formation of an inorganic network in the presence of a preformed organic polymer. Chitosan biopolymer and tetraethoxysilane (TEOS), which is the most common silica precursor, were used for the sol-gel reaction. The obtained composite chitosan-silica material has been characterized by physicochemical methods such as differential thermal analyses (DTA); carbon, hydrogen, and nitrogen (CHN) elemental analysis; nitrogen adsorption/desorption isotherms, scanning electron microscopy (SEM); and Fourier transform infrared (FTIR) spectroscopy to determine possible interactions between silica and chitosan macromolecules. Adsorption of microquantities of V(V), Mo(VI), and Cr(VI) oxoanions from the aqueous solutions by the obtained composite has been studied in comparison with the chitosan beads, previously crosslinked with glutaraldehyde. The adsorption capacity and kinetic sorption characteristics of the composite material were estimated.

Preparation and properties of organomineral adsorbent obtained by sol–gel technology

Organomineral nanocomposite material has been obtained by sol–gel method through in situ formation of inorganic network in the presence of organic polymer. The most common silica precursor tetraethoxysilane (TEOS) and polysaccharide chitosan solution were used for the sol–gel transformations. The obtained chitosan–silica nanocomposite has been characterized by the physicochemical methods such as differential scanning calorimetry–thermogravimetry–mass spectrometry, Fourier transform infrared spectroscopy–thermogravimetry, elemental analysis, nitrogen adsorption/desorption isotherms, scanning electron microscopy, Fourier transform infrared spectroscopy to determine possible interactions between silica and chitosan macromolecules. Thermal destruction and products from gaseous phase in atmosphere of air and nitrogen were studied. It was found that introducing chitosan in silica network drastically change behavior of polymer during heat treatment in inert atmosphere. Adsorption of microquantities of Zn(II), Cu(II), Fe(III), Cd(II) and Pb(II) cations from the aqueous solutions by the obtained composite has been studied in comparison with the chitosan beads, previously cross-linked with glutaraldehyde. The adsorption capacity and kinetic sorption characteristics of the composite material were estimated. The obtained data were analyzed using the Langmuir and Freundlich isotherms, and the characteristic parameters for each isotherm were determined.

Adsorption of V(V), Mo(VI) and Cr(VI) Oxoanions by Chitosan–Silica Composite Synthesized by Mannich Reaction

Immobilization of chitosan on modified silica surface has been carried out by aminomethylation (Mannich reaction). The obtained chitosan–silica (CSS) composite was characterized by the Fourier transform infrared spectroscopy, specific surface area and pore diameter. The concentration of chitosan in the composite was determined by the thermogravimetric method. The effects of various parameters, such as pH, contact time, initial concentration of the metal on the adsorption of V(V), Mo(VI) and Cr(VI) oxoanions by the CSS composite were investigated in comparison with the initial components: chitosan, amino-containing silica and silica. The maximum adsorption capacities of composite with respect to V(V) and Mo(VI) oxoanions at pH 2.5 were 1.6 and 1.5 mmol/g, respectively, and 0.5 mmol/g towards Cr(VI) in the neutral medium.

Concentration of Anions by Silica Adsorbents with Immobilized Nitrogen-Containing Polymers

Immobilization of a polyionene complex on a silica gel surface immediately after polymer formation (in situ immobilization) and the covalent anchorage of polyhexamethylene guanidine hydrochloride onto an amino-containing silica surface have been performed. The adsorption properties of the modified silica adsorbents with respect to Cr(IV), Mo(VI), W(VI), As(V), P(V) and V(V) anions were studied. Silica gels with chemically-bound polyhexamethylene guanidine hydrochloride effected the quantitative removal of V(V), W(VI), Mo(VI) and As(V) anions from their acidic (pH = 2–4) and neutral solutions, although their kinetic characteristics were closer to those of polymeric sorbents. Silicas with in situ immobilized polyionene complexes quantitatively extracted As(V), W(VI) and Mo(VI) anions, and exhibited a high adsorption activity towards Cr(IV), P(V) and V(V) anions from acidic (pH = 1–4) media with adsorption equilibrium being attained at a high rate. The adsorbents synthesized exhibited high adsorption capacities towards the anions investigated.

Adsorption and Complexing Properties of Silicas with Analytical Reagents Grafted via the Mannich Reaction

The pre-concentration of metal ions such as Pb(II), Cd(II), Zn(II), Hg(II) and Mo(VI) on silicas with covalently bound 8-hydroxyquinoline, 1-(2-pyridylazo)-2-naphthol or 4-(2-pyridylazo)resorcinol has been studied. The structures of metal-ion complexes with grafted phenolic-type analytical reagents were investigated by IR, ESR and electronic diffuse reflectance spectroscopies.

Adsorption Properties of Vermiculite with In Situ-Immobilized Polyaniline with Respect to Cr(VI), Mo(VI), W(VI), V(V) and P(V) Anions †

Immobilization of a polyaniline (PANI) on a natural vermiculite surface immediately after polymer formation (in situ immobilization) has been performed. The adsorption properties of the modified adsorbent with respect to Cr(VI), Mo(VI), W(VI), V(V) and P(V) anions were studied. We found differences in physicochemical properties of clay samples using isotherms of nitrogen adsorption, X-ray diffraction and Fourier transform infrared spectroscopy. The experiments showed intercalation of PANI molecules into the inter-layer space of vermiculite. Adsorption isotherms and kinetics of adsorption were measured for the anionic form of ‘d’ metals of Groups V and VI in the Periodic Table from aqueous solutions by the static method. The results indicated that the synthesized composite had a high adsorption capacity with respect to Cr(VI) and Mo(VI) anions in acidic medium through the formation of dichromate anions (Cr2O72–) and an equilibrium mixture of molybdate (MoO42–) and polymolybdates ([Mo6O21]6– [Mo7O24]6–). The modified adsorbent effected the quantitative removal of W(VI) anions in the whole pH range (pH = 1–9). The kinetic data showed that the adsorbent quantitatively removes chromium and molybdenum ions from solution in 1 hour.

ADSORPTION PROPERTIES OF FUNCTIONAL SILICAS TOWARDS SOME TOXIC METAL IONS IN WATER SOLUTIONS

bound complexing phenolic-type analytical reagents 8-hydroxyquinoline, 1-(2-pyridylazo)-2-naphthol, 4-(2-pyridylazo)resorcinol have been studied. Structures of the surface complexes of toxic metals with grafted analytical reagents were determined using IR, ESR and electronic diffuse reflectance spectroscopies. Possibility of simultaneous determination of micro amounts of heavy metals was demonstrated using the x-ray fluorescence analysis of modified adsorbents after absorption of metal ions from their multicomponent mixtures in natural and artificial water solutions. Silica gel with adsorbed polyionene (1,4-MePh) was shown to have high adsorption properties towards some metal-containing anions, in particular MoO4, WO4 and Cr2O7 in water solutions. Adsorption isotherms of these metal-containing anions on initial silica gel and silica-supported polyionene were investigated.

In Situ Immobilization on the Silica Gel Surface and Adsorption Capacity of Poly[N-(4-carboxyphenyl)methacrylamide] on Toxic Metal Ions

In situ immobilization of poly[N-(4-carboxyphenyl)methacrylamide] has been performed on silica gel surface. Infrared (IR) and mass spectroscopies as well as thermogravimetry (TG) analysis have been used to elucidate the structure of immobilized polymer. An adsorption capacity of the synthesized composite towards Cu(II), Pb(II), Mn(II), Fe(III), Co(II), and Ni(II) ions has been estimated. Adsorption activity to microquantities of Pb(II), Cu(II), and Ni(II) in a neutral aqueous medium has been observed.

Adsorption of Toxic Metal Ions onto Silica with Covalently Bound 8-Hydroxyquinoline

8-Hydroxyquinoline covalently bound to silica via a one-stage Mannich reaction was used as an adsorbent for the pre-concentration of Pb(II), Cd(II), Zn(II) and Mo(VI) ions from aqueous solutions in the dynamic mode following determination of their concentrations by X-ray fluorescence methods. The adsorption of Pb(II), Cd(II), Zn(II) and Mo(VI) ions was studied from individual and complex multi-component solutions of both natural and technogenic origins. Peculiarities associated with the simultaneous X-ray fluorescence determination of mixtures of toxic metal ions in a solid matrix are discussed.

In situ immobilization on the silica gel surface and adsorption capacity of polymer-based azobenzene on toxic metal ions

In situ immobilization of poly[(4-methacryloyloxy-(4′-carboxy)azobenzene] on silica gel surface has been performed by radical polymerization of monomer. The fact of polymer immobilization is confirmed by IR spectroscopy. TG and DSC-MS analysis showed that the mass of the immobilized polymer was 10.61%. The SEM-microphotograph-synthesized composite analysis showed that the immobilized polymer on the silica gel surface is placed in the form of fibers. It has been found that the synthesized composite exhibits the sorption ability in terms of microquantities of Cu(II), Cd(II), Pb(II), Mn(II) and Fe(III) ions in a neutral aqueous medium. The quantitative sorption of microquantities of Pb(II) and Fe(III) ions has been recorded. It has been found that immobilization of the silica gel surface leads to an increase in its sorption capacitance for Fe(III), Cu(II) and Pb(II) ions by half.