Search

Separation of CO 2 based on adsorption, absorption, and membrane techniques is a crucial technology necessary to address current global warming issues. Porous media are essential for all these approaches and understanding the nature of the porous structure is important for achieving highly efficient CO 2 adsorption. Porous carbon is considered to be a suitable porous media for investigating the fundamental mechanisms of CO 2 adsorption, because of its simple morphology and its availability in a wide range of well-defined pore sizes. In this study, we investigated the dependence of CO 2 adsorption on pore structures such as pore size, volume, and specific surface area. We also studied slit-shaped and cylindrical pore morphologies based on activated carbon fibers of 0.6–1.7 nm and carbon nanotubes of 1–5 nm, respectively, with relatively uniform structures. Porous media with larger specific surface areas gave higher CO 2 adsorption densities than those of media having larger pore volumes. Narrower pores gave higher adsorption densities because of deep adsorption potential wells. However, at a higher pressure CO 2 adsorption densities increased again in nanopores including micropores and small mesopores. The optimal pore size ranges of CO 2 adsorption in the slit-shaped and cylindrical carbon pores were 0.4–1.2 and 1.0–2.0 nm, respectively, although a high adsorption density was only expected for the narrow carbon nanopores from adsorption potentials. The wider nanopore ranges than expected nanopore ranges are reasonable when considering intermolecular interactions in addition to CO 2 –carbon pore interactions. Therefore, cooperative adsorption among CO 2 in relatively narrow nanopores can allow for high density and high capacity adsorption.

The sorption of radiocaesium onto Na-rectorite as a function of pH value under ambient conditions was studied by batch and capillary methods. The results indicated that the sorption of Cs + ions was dependent on the ionic strength and, to a lesser extent, on the pH value. The distribution coefficients for Cs + ion sorption onto powdered rectorite (as determined via the batch technique) were much higher than those of Cs + ions onto compacted rectorite (as determined by capillary test), thereby suggesting that the sorption of Cs + ions onto rectorite was strongly dependent on the density of rectorite, i.e. the interlaminary space of the compacted rectorite contributes significantly on Cs + ion sorption. The distribution coefficients calculated from theoretical calculations, experimental measurements and the diffusion coefficients of Cs + ions were compared and discussed in detail. The sorption and diffusion mechanisms in compacted rectorite were also discussed.

Thorium was considered as a chemical analogue of other tetravalent actinides. The sorption of Th(IV) ions onto montmorillonite and its cross-linked counterpart in the presence/absence of fulvic acid was investigated via a batch technique as a function of pH and fulvic acid concentration. The results obtained indicate that the sorption of Th(IV) ions was strongly dependent on the pH value of its solution, with the presence of fulvic acid enhancing such sorption at low pH values. It was also found that the sorption of Th(IV) ions was dependent on the ionic strength. Cross-linked montmorillonite was found to be a suitable candidate for the sorption and pre-concentration of Th(IV) ions from large volumes of liquid solution. Surface complexation rather than cation exchange mainly contributes to the sorption of Th(IV) ions onto montmorillonite.