Two processing methods for preparation of microbial biomass-silica biosorbent to remove cadmium ions from aqueous solution were developed. The first method involved a slow addition of sulphuric acid into previously prepared dispersion of viable Saccharomyces cerevisiae or Leuconostoc mesenteroides biomass in sodium silicate solution. The obtained material was mesoporous with irregular shape and size between 1 and 10 μm. The second method for the immobilization of microbial biomass by silica gel entrapment was developed in order to restrict desorption of microbial cells and to obtain larger particles with uniform size. The obtained particles were spherical with average particle size of 1.5 mm. Both materials with viable L. mesenteroides cells displayed higher removal efficiency compared the efficiency of materials that containing viable S. cerevisiae cells. Infrared spectra revealed an intensive secretion of dextran by Leuconostoc mesenteoides cells in the presence of cadmium ions. EDS maps clearly showed the dispersion of cadmium in the cross-section of microbial biomass-silica biosorbent. The maximum theoretical binding adsorption capacity for the silica-alginate-S. cerevisiae composite was 54 mg/g. The adsorption capacity for the silica-alginate-L. mesenteroides composite obtained after 24 cycles was about 93 mg/g. The extracellular secretion of dextran by L. mesenteroides cells immobilized in silica-alginate composite enabled efficient removal of cadmium ions. The efficiency of Cd(II) removal by microbial composite was not affected by the presence of co-existing ions at initial cadmium concentration of 1 and 4 mmol/L.

Multilayered core/shell particles were prepared by four-step deposition of cobalt ferrite layers and then deposition of external silica layer on the surface of silica core particles. The ferrite nanoparticles were obtained by co-precipitation of Co2+ and Fe3+ ions at pH=11 and pH=15, respectively. The agglomerated silica core/cobalt ferrite shell particles were obtained at extremely basic pH (pH=15), while at pH =11, monodispersed and non-aggregated core-shell particles were obtained. The poly(diallyldimethylammonium chloride)-functionalized silica core/ferrite shell particles were used as templates for deposition of mesoporous silica layers (obtained by neutralization of highly basic sodium silicate solution). The obtained porous multilayered core/shell particles were used as a host for covalent lipase immobilization inside the external silica layer. The initial activity of immobilized enzymes was about 13-fold lower than the native one, however, it showed good reusability and improved thermal stability compared to native ones.