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Although the particle phase state is an important property, there is scant information on it, especially, for real-world aerosols. To explore the phase state of fine mode aerosols (PM2.5) in two megacities, Seoul and Beijing, we collected PM2.5filter samples daily from Dec 2020 to Jan 2021. Using optical microscopy combined with the poke-and-flow technique, the phase states of the bulk of PM2.5as a function of relative humidity (RH) were determined and compared to the ambient RH ranges in the two cities. PM2.5was found to be liquid to semisolid in Seoul but mostly semisolid to solid in Beijing. The liquid state was dominant on polluted days, while a semisolid state was dominant on clean days in Seoul. These findings can be explained by the aerosol liquid water content related to the chemical compositions of the aerosols at ambient RH; the water content of PM2.5was much higher in Seoul than in Beijing. Furthermore, the overall phase states of PM2.5observed in Seoul and Beijing were interrelated with the particle size distribution. The results of this study aid in a better understanding of the fundamental physical properties of aerosols and in examining how these are linked to PM2.5in polluted urban atmospheres.

The water sensitivity HKUST-1, is a critical concern for realizing practical CO2capture. Water stability and high CO2adsorption are difficult to achieve simultaneously. Mg and piperazinium-based solid ionic liquids (SoILs) were incorporated into HKUST-1 to enhance its water stability and selective CO2capture performance, respectively. The eco-friendly route was utilized for the synthesis of bimetallic Mg(x)-HKUST-1, employing water as the sole solvent with stirring and microwave treatment. The SoILs were incorporated into the pore structure of Mg(15)-HKUST-1 by wet impregnation. Among the different ratios of Mg used for the synthesis, 15 % Mg exhibited the highest improvement in CO2capacity (5.32 mmol/g) and CO2/N2selectivity (27) compared to the parent HKUST-1 (CO2capacity, 4.2 mmol/g; CO2/N2selectivity, 17). Once Mg(15)-HKUST-1 was impregnated with 10 % SoIL, the CO2capture performance was further improved. In the stability study, 10 % SoIL/Mg(15)-HKUST-1 and Mg(15)-HKUST-1 preserved respectively 92.4 % and 85.3 % CO2adsorption capacity after 20 days of exposure to a humid environment (60 % RH) at 298±5 K, an improvement compared to the HKUST-1 (26 %). The CO2and N2adsorption capacities of HKUST-1, Mg-HKUST-1, and SoIL/Mg-HKUST-1 composite were measured using a volumetric method and characterized using Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA).

In this study, MOF-177 was modified for the first time by amine groups to improve its CO2adsorption capacity at low pressure, using three different amines polyethyleneimine (PEI), tetraethylenepentamine (TEPA), and diethylenetriamine (DETA) and a wet impregnation method. The formed adsorbents were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The CO2adsorption performance of the amine-modified MOF-177 samples was evaluated from the adsorption kinetics. The results revealed that TEPA-modified MOF-177 powders, even at 20% loading, showed a significant improvement (4.8 times) in CO2adsorption capacity compared to the parent MOF-177 at 298 K, while the PEI and DETA-modified samples showed relatively small improvements. With increasing temperature, CO2adsorption capacity was increased to 4.6 mmol/g at 328 K, which is higher than those of previously reported-amine modified adsorbents (1.6–3.8 mmol/g at 318–348 K). MOF-177 powders with 20% TEPA were successfully made into pellets, which showed a slight decrease in capacity. The regenerability of MOF-177-TEPA-20% pellet was evaluated by performing adsorption-desorption cycles at 298 and 373 K, which showed a consistent CO2capture performance.