A general method has been developed for the synthesis of homogeneous hollow core−shell microspheres of spinel ferrites (MFe2O4, M = Zn, Co, Ni, Cd) by using carbonaceous saccharide microspheres as template. The products were characterized by X-ray powder diffraction, inductively coupled plasma-atomic emission spectroscopy, scanning electronic microscopy, transmission electron microscopy, and nitrogen sorption measurement. The effects of the concentration of metal salts have been studied using ZnFe2O4 as an example. Increasing the concentration of metal salts could avoid the generation of impurity phase. The core size and shell thickness of hollow spheres obtained can be manipulated by changing the concentration of metal salts. Gas-sensor investigations revealed the ZnFe2O4 hollow spheres used as gas-sensor materials possess high sensitivity and quick responses to organic gases such as ethanol.

Here we present a class of formaldehyde (HCHO) gas sensors with strong responses based on ordered mesostructured In 2 O 3 nanorod arrays, which are synthesized via the nanocasting route by directly using the solvent-extracted mesoporous silica as a hard template. By choosing mesoporous silica with different pore sizes and interconnectivity as templates and varying the loading of indium resource on the silica template, we have obtained a series of mesostructured In 2 O 3 nanorod arrays with different textural parameters such as specific surface area, pore size, nanorod diameter, etc. The gas sensing properties for formaldehyde (HCHO) of the In 2 O 3 specimens were examined. The results reveal those mesostructured In 2 O 3 nanorod arrays possess much stronger responses to HCHO even at low concentrations than the bulk In 2 O 3 , and larger specific surface areas and pore sizes as well as smaller nanorod diameters would be beneficial for enhancing the sensing properties of In 2 O 3 .

Uniform alpha-Fe2O3 nanorods with high aspect ratios were synthesized in large scale by a simple and direct 1,2-propanediamine-assisted hydrothermal method. The resultant products were characterized by x-ray diffraction scanning electron microscopy, and transmission electron microscopy. The as-synthesized alpha- Fe2O3 nanorods were single crystalline and uniform, with an average aspect ratio greater than 10. The effects of various experimental parameters on the morphology of products, such as 1,2-propanediamine content, pH value, concentration of FeCl3 and reaction temperature, were studied. In the formation process of alpha- Fe2O3 nanorods, the 1,2-propanediamine not only provides OH(-) but also plays a role for retaining the rod-like morphology of hematite. The magnetic properties including Morin transition and coercivity of the samples with different synthesis conditions and aspect ratios were also investigated in detail.

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Alpha-Fe2O3 hollow micospheres have been successfully synthesized by solvothermal method at 200 degrees C. The synthesized products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and the nitrogen adsorption-desorption isotherm technique. The alpha-Fe2O3 hollow microspheres have an average diameter of 2-3 microm, the shell consists of numerous aligned nanorods with length of about 200-400 nm. The effects of solvent and reaction time have been studied. The Ostwald ripening mechanism is proposed to account for the formation of alpha-Fe2O3 hollow microspheres. Because of the porous hollow microstructure and large specific surface area, the microspheres were found to be effective sorbents for the removal of Cr(VI) ions from wastewater.