We prepared activated carbons (ACs) from coal samples ranking from lignite to anthracite. The pore structures and surface functional groups of the obtained ACs were examined by nitrogen adsorption isotherm, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and Boehm’s titration method. Isothermal adsorption experiments using methylene blue (MB) solution were conducted to evaluate the adsorption capacities of the ACs. The obtained ACs had different sorption properties due to their differences in structural characteristics and surface chemical groups. The maximum adsorption was achieved using the ACs made from low-ranked lignite coals. The MB adsorption process could be described well by the intra-particle diffusion model with a wide range of effective diffusion coefficients. The results indicated that both the proportion of mesopores and the number of basic sites within the ACs mainly governed the MB adsorption capacities.

Calcium oxide (CaO) is a promising adsorbent to separate CO₂ from flue gas. However, with cycling of carbonation/decarbonation at high temperature, the serious sintering problem causes its capture capacity to decrease dramatically. A CaTiO₃-decorated CaO-based CO₂ adsorbent was prepared by a continuous and simple aerosol-assisted self-assembly process in this work. Results indicated that CaTiO₃ and CaO formed in the adsorbent, whereas CaO gradually showed a good crystalline structure with increased calcium loading. Owing to the high thermal stability of CaTiO₃, it played a role in suppressing the sintering effect and maintaining repeated high-temperature carbonation and decarbonation processes. When the calcium and titanium ratio was 3, the CO₂ capture capacity was as large as 7 mmol/g with fast kinetics. After 20 cycles under mild regeneration conditions (700 °C, N₂), the performance of CO₂ capture of CaTiO₃-decorated CaO-based adsorbent nearly unchanged. Even after 10 cycles under severe regeneration conditions (920 °C, CO₂), the performance of CO₂ capture still remained nearly 70% compared to the first cycle. The addition of CaTiO₃ induced good and firm CaO dispersion on its surface. Excellent kinetics and stability were evident.

NaNO₂/MgO/titania spheres prepared via aerosol-assisted self-assembly (AASA) were used as sorbents for CO₂ adsorption at moderate temperature. The titania framework as support would allow MgO to disperse well, thereby increasing the contact between MgO and NaNO₂ to enhance carbonation. In this study, the effect of Mg/Ti molar ratio and NaNO₂ addition amount on CO₂ adsorption was investigated. Results showed that the sorbent prepared by AASA with Mg/Ti molar ratio of 2 following the introduction of 30 wt% NaNO₂ presented ∼1 μm particle size with rough sphere surface morphology and mesoporous properties, where the surface area and pore volume were 72 m²/g and 0.18 cm³/g, respectively. With NaNO₂ addition, the kinetics and capacity of CO₂ adsorption significant increased. In the cyclic adsorption/desorption experiment, the superior stability over the NaNO₂/MgO/titania spheres was mainly ascribed to the confined space suppressed the degree of the sintering effect. These results indicated the potential application of the nanochannel-restricted sorbent for rapid, high-capacity, and stable CO₂ capture at moderate temperatures. GRAPHICAL ABSTRACT