Low Temperature Synthesized H₂Ti₃O₇ Nanotubes with a High CO₂ Adsorption Property by Amine Modification

Carbon dioxide (CO₂) capture and storage (CCS) technologies have been attracting attention in terms of tackling with global warming. To date, various CO₂ capture technologies including solvents, membranes, cryogenics, and solid adsorbents have been proposed. Currently, a liquid adsorption method for CO₂ using amine solution (monoethanolamine) has been practically used. However, this liquid phase CO₂ adsorption process requires heat regeneration, and it can cause many problems such as corrosion of equipment and degradation of the solution. Meanwhile, solid adsorption methods using porous materials are more advantageous over the liquid method at these points. In this context, we here evaluated if hydrogen titanate (H₂Ti₃O₇) nanotubes and the surface modification effectively capture CO₂. For this aim, we first developed a facile synthesis method of H₂Ti₃O₇ nanotubes different from any conventional methods. Briefly, they were converted from the precursors - amorphous TiO₂ nanoparticles at room temperature (25 °C). We then determined the outer and the inner diameters of the H₂Ti₃O₇ nanotubes as 3.0 and 0.7 nm, respectively. It revealed that both values were much smaller than the reported ones; thus the specific surface area showed the highest value (735 m²/g). Next, the outer surface of H₂Ti₃O₇ nanotubes was modified using ethylenediamine to examine if CO₂ adsorption capacity increases. The ethylendiamine-modified H₂Ti₃O₇ nanotubes showed a higher CO₂ adsorption capacity (50 cm³/g at 0 °C, 100 kPa). We finally concluded that the higher CO₂ adsorption capacity could be explained, not only by the high specific surface area of the nanotubes but also by tripartite hydrogen bonding interactions among amines, CO₂, and OH groups on the surface of H₂Ti₃O₇.