Bio-template route for facile fabrication of Cd(OH)2@yeast hybrid microspheres and their subsequent conversion to mesoporous CdO hollow microspheres

Cadmium oxide (CdO) microspheres with a porous hollow microstructure were prepared by a facile yeast mediated bio-template route. The yeast provides a solid scaffold for the deposition of cadmium hydroxide (Cd(OH)₂) from cadmium acetate and sodium hydroxide solutions to form the hybrid Cd(OH)₂@yeast precursor. Thermal conversions of this at above 500 °C in air have produced hollow CdO microspheres. The products were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal analysis (TGA-DTA), and Brunauer-Emmett-Teller (BET) surface analysis respectively. The obtained CdO microspheres have uniform size (length = 2.6 ± 0.4 μm; width = 2.0 ± 0.2 μm) and a well defined, continuous, mesoporous hollow microstructure. The shell is about 250-280 nm in thickness. The mechanism of formation of Cd(OH)₂@yeast precursor and its conversion to CdO hollow microspheres is discussed. In comparison with traditional template-directed method, the present strategy represents a general, economical and environmentally benign route for the formation of metal oxide hollow microspheres. These materials have potential applications in different fields such as encapsulation, drug delivery, efficient catalysis, battery materials and photonic crystals. The method presented can be extended to the synthesis of other inorganic hollow microstructures of different sizes and shapes by pre-selecting suitable bio-templates.