Synthesis, characterization and thermodynamic study of carbon dioxide adsorption on akaganéite

A mixture of akaganéite nanoparticles and sodium salts was synthesized and modified, first by washing, and then by Li exchange. The structural characterization of the produced materials was performed with: powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, thermo-gravimetric analysis, diffuse reflectance infrared Fourier transform spectrometry, Mössbauer spectroscopy and magnetization measurements. Additionally low pressure nitrogen and high pressure carbon dioxide adsorption experiments were performed. The sum of the characterization information made possible to conclude that the produced akaganéite phases crystallized in a structure exhibiting the symmetry of the I2/m space group, where the measured equivalent spherical diameter of the akaganéite crystallites yielded 9 nm, as well, the tested phases exhibited a standard behaviour under heating and displayed a superparamagnetic behaviour. Finally the high pressure carbon dioxide adsorption experiments demonstrated a pressure-responsive framework opening event due to a structural transformation of the adsorbent framework induced by the guest molecules. This fact opens new applications for akaganéite as a high pressure adsorbent. Akaganéites are thermally unstable and superparamagnetic, thereafter the obtained stable and magnetic phase open new applications for these materials. For example, as high temperature catalysts. [Display omitted] •Unstable, paramagnetic akaganéite nanoparticles were synthesized by a new route.•It was modified by two methods and the products structurally characterized.•One material resulted thermally stable, antiferromagnetic and nanostructured.•The other one showed the normal behavior of akaganéite nanoparticles.•The synthesized stable material could open new uses for akaganéite.