Coarse-grained pseudoboehmite was obtained by neutralization of an ammonium aluminum sulfate solution [NH 4 Al(SO 4 ) 2 •12H 2 O] with ammonia water [NH 3 (aq)] in the presence of sodium dodecylbenzene sulfonate (SDBS). The neutralization process without SDBS resulted in pseudoboehmite particles with a median diameter of 20.1 μm. When the concentration of SDBS was 0.5 g/L, the process produced particles with a dense surface structure and a median diameter of 31.3 μm. Density functional theory and molecular dynamics simulations were applied to study the effect of SDBS on the crystallization behavior of pseudoboehmite. Specifically, the adsorption energies of SDBS and water molecules on the optimized crystal plane were calculated. The adsorption energy of SDBS is −61.23 kJ/mol less than that of water molecules on the relaxed surface ( 002), which suggests it is the most stable adsorption surface (002) for SDBS. In addition, only the (002) plane of pseudoboehmite has a negative adsorption energy difference, indicating the selective adsorption of SDBS on this crystal plane. The distribution of the [Al(OH)(H 2 O) 5 ] 2+ ions at pH > 9 was calculated by molecular dynamics. Finally, the formation mechanism of pseudoboehmite nuclei based on the SDBS effects on ion distribution and the mechanism of increased particle size are explored.
Current studies on the modification of CaO-based sorbents have paid less attention to ion migration resistance within the product layer of CaCO 3 during carbonation. In this work, limestone-derived sorbents with enhanced carbonation reactivity and diffusivity due to the incorporation of Na + ions into the CaO lattice were prepared by a hydrated ion adsorption method. The Na + -ion-modified sorbents exhibited better CO 2 capture capacity and durability. After 30 cycles, Na/Ca-0.10 sorbents still maintained a larger carbonation conversion (49.5%), which was 147.5% higher than that of the unmodified CaCO 3 precursor. It was demonstrated that solid-state ion transport channels resulting from the existence of oxygen vacancy were constructed in the product layer of modified sorbents, producing a distinct three-stage mechanism (reaction−coupling−diffusion) during the carbonation process. As a result, the prepared CaO-based sorbents could maintain a higher reactivity after the formation of the product layer of CaCO 3 and the sintering over iterated looping.
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