T. M. Budnyak

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.

Silica with immobilized phosphinic acid-derivative for uranium extraction

A novel adsorbent benzoimidazol-2-yl-phenylphosphinic acid/aminosilica adsorbent (BImPhP(O)(OH)/SiO2NH2) was prepared by carbonyldiimidazole-mediated coupling of aminosilica with 1-carboxymethylbenzoimidazol-2-yl-phenylphosphinic acid. It was obtained through direct phosphorylation of 1-cyanomethylbenzoimidazole by phenylphosphonic dichloride followed by basic hydrolysis of the nitrile. The obtained sorbent was well characterized by physicochemical methods, such as differential scanning calorimetry-mass spectrometry (DSC-MS), surface area and pore distribution analysis (ASAP), scanning electron microscopy (SEM), X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopies. The adsorption behavior of the sorbent and initial silica gel as well as aminosilica gel with respect to uranium(VI) from the aqueous media has been studied under varying operating conditions of pH, concentration of uranium(VI), contact time, and desorption in different media. The synthesized material was found to show an increase in adsorption activity with respect to uranyl ions in comparison with the initial compounds. In particular, the highest adsorption capacity for the obtained modified silica was found at the neutral pH, where one gram of the adsorbent can extract 176mg of uranium. Under the same conditions the aminosilica extracts 166mg/g, and the silica - 144mg/g of uranium. In the acidic medium, which is common for uranium nuclear wastes, the synthesized adsorbent extracts 27mg/g, the aminosilica - 16mg/g, and the silica - 14mg/g of uranium. It was found that 15% of uranium ions leached from the prepared material in acidic solutions, while 4% of uranium can be removed in a phosphate solution.

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.

Chitosan–Silica Hybrid Composites for Removal of Sulfonated Azo Dyes from Aqueous Solutions

In this study, the influence of the chitosan immobilization method on the properties of final hybrid materials was performed. Chitosan was immobilized on the surface of mesoporous (ChS2) and fumed silica (ChS3) by physical adsorption and the sol-gel method (ChS1). It was found that physical immobilization of chitosan allows to obtain hybrid composites (ChS) with a homogeneous distribution of polymer on the surface, relatively wide pores, and specific surface area of about 170 m2/g, pHPZC = 5.7 for ChS3 and 356 m2/g and pHPZC = 6.0 for ChS2. The microporous chitosan-silica material with a specific surface area of 600 m2/g and a more negatively charged surface (pHPZC = 4.2) was obtained by the sol-gel reaction. The mechanisms of azo dye adsorption were studied, and the correlation with the composite structure was distinguished. The generalized Langmuir equation and its special cases, that is, Langmuir-Freundlich and Langmuir equations, were applied for the analysis of adsorption isotherm data. The adsorption study showed that physically adsorbed chitosan (ChS1 and ChS2) on a silica surface has a higher sorption capacity, for example, 0.48 mmol/g for the acid red 88 (AR88) dye (ChS2) and 0.23 mmol/g for the acid orange 8 (AO8) dye (ChS1), compared to the composite obtained by the sol-gel method [ChS1, 0.05 mmol/g for the AO8 dye]. For a deeper understanding of the behavior of immobilized chitosan in the adsorption processes, various kinetic equations were applied: first-order, second-order, mixed 1,2-order (MOE), multiexponential, and fractal-like MOE as well as intraparticle and pore diffusion model equations. In the case of AO8 dye, the adsorption rates were differentiated for three composites: for ChS3, 50% of the dye was removed from the solution after merely 5 min and almost 90% after 80 min. The slowest adsorption process controlled by the diffusion rate of dye molecules into the internal space of the pore structure was found for ChS1 (225 min halftime). In the case of ChS2, the rates for various dyes change in the following order: acid orange (AO7) > orange G (OG) > acid red 1 (AR1) > AR88 > AO8 (halftimes: 10.5 < 15.7 < 23.7 < 34.9 < 42.9 min).

Imidazole-2yl-Phosphonic Acid Derivative Grafted onto Mesoporous Silica Surface as a Novel Highly Effective Sorbent for Uranium(VI) Ion Extraction

A new imidazol-2yl-phosphonic acid/mesoporous silica sorbent (ImP(O)(OH)2/SiO2) was developed and applied for uranium(VI) ion removal from aqueous solutions. The synthesized material was characterized by fast kinetics and an extra-high adsorption capacity with respect to uranium. The highest adsorption efficiency of U(VI) ions was obtained for the reaction system at pH 4 and exceeded 618 mg/g. The uranium(VI) sorption proceeds quickly in the first step within 60 min of the adsorbent sites and ion interactions. Moreover, the equilibrium time was determined to be 120 min. The equilibrium and kinetic characteristics of the uranium(VI) ions uptake by synthesized sorbent was found to follow the Langmuir-Freundlich isotherm model and pseudo-second-order kinetics rather than the Langmuir, Dubinin-Radushkevich, and Temkin models and pseudo-first-order or intraparticle diffusion sorption kinetics. The adsorption mechanism for uranium on the sorbent was clarified basing on the X-ray photoelectron spectroscopy (XPS) analysis. The model of UO22+ binding to surface of the sorbent was proposed according to the results of XPS, i.e., a 1:1 U-to-P ratio in the sorbed complex was established. The regeneration study confirms the ImP(O)(OH)2/SiO2 sorbent can be reused. A total of 45% of uranium ions was determined as originating from the sorbent leaching in the acidic solutions, whereas when the basic solutions were used, the removal efficiency was 12%.

Sol–Gel Derived Organic–Inorganic Hybrid Ceramic Materials for Heavy Metal Removal

Modification of the silica surface leads to the change in chemical composition of the surface which can be modified either by physical treatment (thermal or hydrothermal) or by chemical treatment. Such modifications significantly affect the adsorption properties of the materials and especially mechanical stability and water insolubility, increasing the efficiency, sensitivity and selectivity of the analytical application. A variety of types of organic polymers can be employed in the synthesis of hybrids with silica. One of them is chitosan. Chitosan and silica as well as their composites have attracted a great attention as effective hybrid biopolymeric sorbents due to high sorption capacity, cost-effectiveness, renewability and high stability. Owing to the presence of amino groups, chitosan is cationic and capable of heavy metal ions bonding. Several studies have reported on the metal ions removal of using chitosan or chitosan adsorbed onto conventional silica. Their short characterization is presented in this chapter. Moreover different ways of silica–chitosan composites are also discussed.

Multifunctional Magnetic Nanocomposites on the Base of Magnetite and Hydroxyapatite for Oncology Applications

A survey of studies carried out at the Chuiko Institute of Surface Chemistry NAS of Ukraine aimed at developing the concept of creating magnetosensitive nanocomposites (NK) with multilevel hierarchical nanoscale architecture and functions of biomedical nanorobots. The data on the synthesis of magnetically sensitive nanocomposites of core-shell type on the basis of single-domain magnetite and hydroxyapatite, the study of their magnetic properties, features of immobilization on the surface of oncological preparations of different action mechanisms, bioactivity testing, creation of magnetic fluids on the basis of synthesized NK, and the establishment of the prospects of their use in oncology are presented.