Jung Gi Min

CO₂ is the primary greenhouse gas emitted through human activities which cause global warming. Many countries and international regulations aim to reduce CO₂ and encourage development of a net-zero society by 2050, thus, CCUS (carbon capture, utilization, and storage) can be considered as a key technology for achieving this goal. Among the many industrial processes, NaHCO₃ production is a representative CCUS technology which satisfies both CO₂ reduction and economic incentive. Recently, Na₂SO₄ waste, containing 15% impurities (i.e., various heavy metals), produced as a by-product generated from desulfurized processes in steel industry has received a great deal of attention since landfilling has been the only way to treat it. Na₂SO₄ could be a suitable source of NaHCO₃ production as CCUS; however, there are no commercial processes for production of NaHCO₃ using Na₂SO₄ as the raw material, since it has low production efficiency compared to other Na⁺ sources. This study evaluates the regeneration of NaHCO₃ using Na₂SO₄ waste and our results show that a combination of Na₂SO₄ waste and the addition of 20% Na₂CO₃ can sharply increase the yield of NaHCO₃ while minimizing the consumption of expensive NH₃.

The CO₂ adsorption behavior at 25–75 °C and 0–1.0 bar of various alkali cation‐exchanged forms of merlinoite (framework type MER) zeolites with Si/Al=2.3 and 3.8 is described. The adsorption isotherms at 25 °C on the Na⁺, K⁺, Rb⁺, and Cs⁺ forms of MER zeolite with Si/Al=2.3 are characterized by a clear step, the CO₂ pressure of which differs notably according to the type of their extraframework cations. Structural analysis shows that CO₂ adsorption on the former three zeolites includes the relocation of gating cations with high site occupancy and the remarkable concomitant structural breathing. We define this unusual adsorption phenomenon as a cooperative cation gating‐breathing mechanism. The overall results suggest that the actual mechanism of selective CO₂ adsorption on intermediate‐silica small‐pore zeolites can change from cation gating to cooperative cation gating‐breathing to breathing, depending on a combination of their topological and compositional flexibilities.

The CO₂ adsorption behavior at 25–75 °C and 0–1.0 bar of various alkali cation‐exchanged forms of merlinoite (framework type MER) zeolites with Si/Al=2.3 and 3.8 is described. The adsorption isotherms at 25 °C on the Na⁺, K⁺, Rb⁺, and Cs⁺ forms of MER zeolite with Si/Al=2.3 are characterized by a clear step, the CO₂ pressure of which differs notably according to the type of their extraframework cations. Structural analysis shows that CO₂ adsorption on the former three zeolites includes the relocation of gating cations with high site occupancy and the remarkable concomitant structural breathing. We define this unusual adsorption phenomenon as a cooperative cation gating‐breathing mechanism. The overall results suggest that the actual mechanism of selective CO₂ adsorption on intermediate‐silica small‐pore zeolites can change from cation gating to cooperative cation gating‐breathing to breathing, depending on a combination of their topological and compositional flexibilities.

Colloidal porous AuAg alloyed nanoparticles (pAuAgNPs) were synthesized by galvanic replacement reaction from Ag nanocubes. pAuAgNPs have a 50 nm exterior diameter and half of their inner space consists of voids that have a bimodal size distribution with peaks at 21 and 8.3 nm. pAuAgNPs showed a plasmonic peak at 750 nm, which was exploited for photoacoustic (PA) imaging. Gold nanorods (AuNRs) were prepared and used as the control; they have a strong plasmonic peak at 720 nm. In in vitro experiments at respective plasmonic peak excitations, pAuAgNPs gave stronger PA signals than AuNRs by 8.9 times per particle and 11.7 times per dosage by exogenous atom. The high surface area per volume as a result of the inner voids amplified the PA signals by efficient thermoacoustic conversion. In experiments of chicken-tissue phantoms, pAuAgNPs showed PA signals through 4.5 cm thick tissue, whereas AuNRs gave no detectable signal. In whole-body in vivo experiments, pAuAgNPs injected into the body showed 2.7 times stronger PA signals than AuNRs. Coating the pAuAgNPs with a silica layer additionally increased their PA signal by 1.8 times when compared to the uncoated ones.

Framework deformation, driven by the cations in the channels, determines the CO ₂ ad- and desorption behavior of zeolites. This allows to tune the zeolite properties to efficient temperature swing adsorption processes.

Gas adsorption over zeolites is at the basis of important applications of this class of microporous crystalline solids, notably as separation media and catalysts, but it may also be complex and not straightforward to understand. Here we report that for temperature below 323 K propane adsorption on the small-pore pure-silica zeolite ITW exhibits a clear step (pseudo-saturation). This is absent in the case of propene and the other small linear alkanes. An intermediate plateau, clearly observed in the 293 K isotherm, always occurs when one molecule of propane is loaded in every other cage, i.e., at half saturation. The simulation results show a swelling of the ITW structure upon propane adsorption. The strong dependence of available pore volume on the adsorbate loading level implies that adsorption cannot occur on the void structure while saturation can only be reached on highly loaded structures. To account for this unprecedented adsorption phenomenon, we propose the term “guest-modulated effect”.