The dissertation is devoted to the establishment of physicochemical principles of one-stage production of silica microspheres, magnetically controlled carriers and membranes with polysiloxane coatings containing 3-aminopropyl, 3-mercaptopropyl and thiourea groups. It was demonstrated how temperature, stirring time, amount of solvent, introduction of hydrophobic groups affect the morphology of particles, the location and availability of the surface groups, and, accordingly, the sorption properties of amino-silica particles. The studies have also revealed the effect of bissilanes as structuring agents on the structural and sorption characteristics of the materials, but the hydrophobic bridges themselves hardly varied the hydrophilic-hydrophobic balance of the surface due to the large number of non-condensed silanol groups. It was shown that the amino groups on the silica spheres are usually protonated, and in the absence of other residues possess poor hydrolytic stability or may be unavailable for interactions. Meanwhile, the incorporation of organic residues among amino groups hinders the access of water molecules and prevents the hydrogen bondings of amino groups with other amino or silanol functions; therefore, amino groups remain stable in aqueous solutions and free for interactions with adsorbates. Silica microspheres with amino groups were studied as effective adsorbents of ions of copper(II) (up to 203.2 mg/g) and europium(III) (up to 158.1 mg/g), organic dyes (acid red 88 - 262 mg/g, fluorescein – 132 mg/g, methylene blue – 146 mg/g), urease (up to 600 mg/g); magnetite-silica materials with amino groups exhibited high uptake of Cu(II) (209.6 mg/g), Pd(II) (16.8 mg/g), Pb(II) ions (165.7 mg/g), methylene blue (62 mg/g), acid red 88 (118 mg/g), albumin (241 mg/g) and urease (1014 mg/g); planar membrane composites were investigated for the removal of copper(II) ions (up to 22.9 mg/g) and nickel(II) ions (up to 4.9 mg/g) on tubular membranes.
It was determined that, unlike other silanes, 3-mercaptopropyltrimethoxysilane can form spherical particles with a high groups content without applying additional structuring agents, but in this case the thiol groups are unstable and interact with each other forming disulfide bridges. The necessity of incorporating surface hydrocarbon residues or structural organic fragments by means of bridged silanes to prevent the interaction of groups, has been demonstrated in order to keep free 3-mercaptopropyl groups capable of ion-exchange interactions on the surface. Samples of silica spheres, magnetic particles and membranes functionalized with thiol groups possess high sorption capacity relative to a large number of heavy metals Pb2+, Ag+, Hg2+, Cd2+, Cu2+. Such adsorption is not selective, however, the magnetite sample with thiol and propyl groups purified a mining enterprise wastewater from metal ions by more than 50%. Synthesized biocatalysts based on binding urease to the surface of the magnetic carriers with mercapto groups were used in 40 cycles and decomposed urea to the maximum permissible concentration for household and drinking water supply; meanwhile, urease biocatalysts based on magnetite/silica composites with 3-aminopropyl group were proved to work in the presence of microquantities of Hg(II) and Cu(II) ions. It was also displayed that there is an interaction between thiol groups on the surface of membranes with 3-mercaptopropyl moites weakening the retention of Ag(I) or Pb(II), which substantiates the benefits of functionalizing sols dilution to ensure optimal arrangement of particles on the membrane surface.
Key words: 3-aminopropyl groups; 3-mercaptopropyl groups; thiourea groups; surface layer structure; non-porous and porous silica particles; magnetically controlled magnetite/silica composites; functionalized ceramic membranes; adsorption; heavy metals, albumin; urease; cationic and anionic dyes.
