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[Display omitted] • K 2 CO 3 /Al 2 O 3 adsorbent pellets were prepared via the hydrophobic interface-assisted method. • High temperatures make hydrophobic powders lose their hydrophobicity. • Residual hydrophobic powders inhibits the diffusion of water molecules due to hydrophobicity. • The detrimental effect of the hydrophobicity exceeds that of high temperature. Suitable molding and granulation methods are crucial, and an outstanding sphere structure can play a better role in the future scale-up industrial application of K 2 CO 3 -based CO 2 adsorbent. Water will form a large contact angle on the surface of hydrophobic solution and become sphericity water. In this work, hydrophobic powders (polyethylene (PE), TiO 2 , and SiO 2) were selected in the hydrophobic interface-assisted method. The CO 2 adsorption capacity of TiO 2 pellets is 0.50 mmol/g, while that of PE pellets is 0.24 mmol/g, and finally that of SiO 2 pellets is 0.36 mmol/g. Then, experiment proved that high temperature (>500 ℃) makes the hydrophobic powders (i.e, TiO 2 and SiO 2) lose hydrophobicity which make water molecules diffuse faster, while PE is completely decomposed at high temperature. Compared with the pellets calcined at 300 ℃, the TiO2 pellets calcinated at 500 ℃ have an adsorption capacity of 0.70 mmol/g, which is over 1.72 times that of the original pellets, and the other two hydrophobic surfaces are also improved to some extent. Additionally, the appropriate ratio of low-temperature pore forming agent (i.e., urea) can help improve the adsorption performance, while excessive addition will lead to poor CO 2 adsorption performance. In addition, the K 2 CO 3 /Al 2 O 3 pellets also exhibited desirable mechanical properties, with an optimal compressive strength of 41 Mpa. Therefore, the loss of hydrophobicity leads to more active diffusion of water molecules, which may provide a new idea for the future development of CO 2 adsorbents and other areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Graphite-casted K 2 CO 3 -based adsorbent pellets with different supports were prepared. • ZrO 2 -supported K 2 CO 3 pellets exhibit outstanding performance for CO 2 adsorption. • 500 °C is the optimal calcination temperature for SiO 2 -supported K 2 CO 3 pellets. • SiO 2 -supported K 2 CO 3 adsorbent pellets possess excellent practicality for its low cost. K 2 CO 3 -based adsorbent pellets produced by graphite-casting method are promising alkali metal-based solid CO 2 adsorbents. The incorporation of porous metal oxide supports is an effective to enhance CO 2 adsorption capacity of K 2 CO 3 -based adsorbent pellets. In this work, graphite-casted K 2 CO 3 -based adsorbent pellets incorporated with different porous supports (i.e., TiO 2 , ZrO 2 , and SiO 2) were prepared for CO 2 capture. Comparatively, the ZrO 2 -supported, K 2 CO 3 pellets loaded with 30 wt% of K 2 CO 3 exhibit the highest CO 2 adsorption capacity, approximately 0.93 mmol/g. For the SiO 2 -supported K 2 CO 3 adsorbent pellets, the high calcination temperature (>700 °C) required to remove the graphite layer covering the pellet surface will cause the formation of new eutectics (i.e., K 2 Si 2 O 5 and K 2 Si 4 O 9), which leads to the collapse of the adsorbent pellets. Low calcination temperature of 500 °C can avoid the collapse of the SiO 2 -supported K 2 CO 3 adsorbent pellets and remove most of the graphite on the surface. Moreover, the CO 2 adsorption capacity can be further increased to 1.30 mmol/g by adding 20 wt% of microcrystalline cellulose to the SiO 2 -supported K 2 CO 3 adsorbent pellet. Although the adsorption capacity of structurally improved, SiO 2 -supported K 2 CO 3 pellets is still inferior to that of structurally improved, ZrO 2 -supported K 2 CO 3 pellets, they exhibit great cost advantage. Therefore, SiO 2 -supported K 2 CO 3 pellets with 20 wt% of microcrystalline cellulose have industrial application prospects. [ABSTRACT FROM AUTHOR]

Porous carbons produced using poplar sawdust are promising CO 2 adsorbent applied under ambient conditions due to the low-cost preparation approach. CO 2 uptake capability of the porous carbons produced from poplar sawdust can be effectively enhanced via doping an approximate amount of microalgae. The N-doped porous carbon produced from poplar sawdust using microalgae as N-doping source (microalgae/poplar sawdust=0.5:1) possesses an excellent capacity of 4.14 mmol·g−1 for CO 2 uptake, nearly over 1.7 times that of the carbon without N-doping. The improved performance for CO 2 uptake of porous carbons is mainly ascribed to the two-fold effect of microalgae doping: (i) generating extensive narrow pores and channels within the porous carbons owe to co-pyrolysis; (ii) introduction of N-containing moieties derived from the intrinsic N of microalgae increasing the surface polarity and alkalinity. The N-doped porous carbon granules derived from poplar sawdust are inferior to the powdered porous carbons for CO 2 adsorption due to the destroyed structure. They still maintain the relatively desirable capability for CO 2 adsorption (~3.0 mmol·g−1 during 5 cycles) and good mechanical property (10.96 ± 1.43 Mpa). Comprehensively considering the advantaged properties (low-pressure drop, high bulk density) required for practical application, the N-doped porous carbon granules derived from poplar sawdust with low-doping of renewable microalgae possess strong practicability. [Display omitted] • Microalgae replaces the chemical N-containing reagents as the N-doping source. • Microalgae doping plays a two-fold role in enhancing CO 2 adsorption for porous carbon. • N-doped, sawdust-derived porous carbons exhibit desirable CO 2 adsorption capacity. • N-doped, sawdust-derived porous carbon extrudates possess superior practicability. [ABSTRACT FROM AUTHOR]

Amine-based adsorbents show great promise for removing low-concentration CO 2 from environmental control and life support systems (ECLSSs) to ensure crew safety and task execution. In this work, granular silica gel (SG) support was prepared by the extrusion–spheronization (ES) method, and amine-based adsorbent pellets were synthesized by impregnating the SG support with tetraethylenepentamine (TEPA). Dynamic CO 2 circulation removal tests were carried out under simulated confined space conditions in a 100 L chamber to evaluate the low concentration CO 2 removal performance of the adsorbent pellets. The effect of operating parameters on CO 2 removal performance was investigated by orthogonal experiments. CO 2 adsorption capacity and removal efficiency were significantly affected by CO 2 concentration and reaction temperature, while reaction rate was intimately depended on CO 2 concentration and gas flow rate. The maximum CO 2 adsorption capacity (0.55 mmol CO 2 /g), removal efficiency (83.25%) and reaction rate (0.93 mmol CO 2 /min) were achieved under the optimized conditions of 20 °C, 1.25%CO 2 and 2 L/min. A kinetic equation well representing the correlation between reaction rate and CO 2 concentration and gas flow rate was established. The TEPA-SG-ES adsorbent pellets exhibited satisfactory working stability, with CO 2 removal efficiency and adsorption capacity slightly decreased from 83.25% and 0.55 mmol CO 2 /g to 75.45% and 0.53 mmol CO 2 /g in 10 cycles, respectively. The slight decay in CO 2 adsorption performance was associated with the oxidative degradation of amine species in oxygenated atmosphere to form amide, nitrite and imine phases, and the change of amine distribution over the pellets in multiple cycles. Overall, the desired TEPA-SG-ES adsorbent pellets could be nice scavenger candidates for circulating purification of CO 2 in confined spaces. [ABSTRACT FROM AUTHOR]

• Spherical K 2 CO 3 -based pellets were prepared via extrusion-spheronization method. • The effects of supports and K 2 CO 3 contents on structure-performance relationship were illuminated. • Addition of urea can enhance CO 2 sorption capacity and expand pore structure. • The as-prepared pellets showed superior CO 2 capture capacity and mechanical properties. • The results will lay the groundwork for scale-up industrial application of the technique. The development of K 2 CO 3 -based sorbents with desirable CO 2 capture capacity and mechanical property is highly necessary for its large-scale application. In this work, a range of extruded-spheronized K 2 CO 3 -based pellets containing different K 2 CO 3 loading (30–70 wt%) and Al 2 O 3 -based supports (i.e., activated alumina, Bayer aluminum hydroxide, kaolinite clay and calcium aluminate cement) were prepared for CO 2 capture. It is found that the distinct textural properties of different supports result in the obvious diversities in CO 2 uptake and mechanical property of K 2 CO 3 -based pellets. The activated alumina-supported sorbent pellets loaded with 50 wt% of K 2 CO 3 possess the highest CO 2 adsorption capacity of 2.29 mmol/g. It is mainly attributed to the moderate amounts of active component contributing to good textural properties and abundant CO 2 -philic sites, whereas excessive K 2 CO 3 loading will cause the destruction of porous structure, consequently the inferior CO 2 uptake. Moreover, the addition of 15 wt% of urea can furher enhace CO 2 uptake of the activated alumina-supported sorbent pellets loaded with 50 wt% of K 2 CO 3 , ∼3.10 mmol CO 2 /g. The improved CO 2 uptake is due to the significantly enhanced porosity of sorbent pellets as a result of urea decomposition. In addition, the urea-templated sorbent pellets still maintain the high compressive strength (18.96 MPa) and good attrition resistance (a weight loss of 0.59% after 4000 rotations). [ABSTRACT FROM AUTHOR]

[Display omitted] • Orthogonal experiments were conducted to prepare sawdust-derived porous carbons. • Granulation destroys original porous structure of sawdust-derived porous carbons. • Sawdust-derived porous carbon extrudates are inferior to powders for CO 2 adsorption. • Sawdust-derived porous carbon extrudates possess good mechanical property. Sawdust wastes were used as the low-cost feedstock to prepare porous carbons by KOH activation, and the preparation parameters were optimized via orthogonal experiment. Four main activation parameters (i.e., sawdust type, KOH/sawdust ratio, activation temperature and activation time) were investigated. It is found that activation temperature and KOH/sawdust ratio are the two most important parameters that affect the porous texture properties (specific surface area and micropore volume) of sawdust wastes-derived porous carbons. The optimal sawdust wastes-derived porous carbon possesses a high specific surface area of 1601 m2/g and a micropore volume of 0.75 cm3/g, therefore exhibiting a desirable CO 2 adsorption capacity of 4.25 mmol/g at 0 °C under ambient pressure. Comparatively, the sawdust wastes-derived porous carbon extrudates exhibit the inferior CO 2 adsorption capacity, dropping to 2.85–3.03 mmol/g. It is mainly attributed to the extrusion treatment and binder addition causing the collapse and blockage of the original porous structure, consequently increasing the CO 2 diffusion and adsorption resistance. However, the sawdust wastes-derived porous carbon extrudates possess the advantages of null pressure build-up, improved bulk density and high compress strength (7.3–12.3 MPa) considering the real application point of view. [ABSTRACT FROM AUTHOR]

• MgO adsorbents were prepared from magnesium oxalate precursor for CO 2 capture. • Effects of calcination conditions on structure-performance relationships were studied. • Calcination atmosphere and temperature significantly affected the CO 2 adsorption performance. • The desired MgO-C-500 adsorbent exhibited a high CO 2 uptake of 5.09 mmol CO 2 /g. Facile, green and solvent-free fabrication of efficient MgO-based adsorbents is highly necessary for their intermediate-temperature CO 2 capture applications. In this work, MgO adsorbents were prepared by calcining magnesium oxalate precursor under different calcination atmospheres and temperatures. N 2 adsorption-desorption, X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and CO 2 temperature programmed desorption were employed to study their physicochemical properties. CO 2 adsorption performance was evaluated by testing the adsorbents in a dry stream containing 10%CO 2 at a mild temperature of 200 °C. The influence of calcination conditions on their structure-performance relationships was investigated. Calcination atmosphere and temperature will significantly affect the microstructure and CO 2 adsorption performance. Calcination in a flowing CO 2 stream will endow the adsorbent with minimized MgO crystal size, and this will offer more O2− active sites at the edges and corners for enhanced CO 2 adsorption capacity. The precursor can hardly be completely decomposed at a lower calcination temperature to form porous structure, and the basic active sites available for CO 2 adsorption are limited. A higher calcination temperature will result in sintering of MgO crystals, pore structure blockage and loss of the O2− basic active sites, and CO 2 adsorption capacity will therefore be reduced. The desired MgO-C-500 adsorbent calcined in a flowing CO 2 stream at 500 °C exhibits the highest CO 2 adsorption capacity of 5.09 mmol CO 2 /g. The results will pave the way for developing highly efficient MgO adsorbents for separating CO 2 from industrial exhaust gas. [ABSTRACT FROM AUTHOR]

• Biomass ash stabilized MgO adsorbents are prepared for CO 2 capture. • Effects of support and MgO loading on CO 2 adsorption performance are discussed. • MgO-RHA-20 exhibits excellent CO 2 adsorption capacity of 4.56 mmol CO 2 /g. • The desired adsorbent shows favorable working stability in 10 repeated cycles. • The scheme provides remarkable economic and environmental implications. Supported MgO adsorbents were prepared from the calcination of MgCl 2 ·6H 2 O preloaded on several biomass wastes including sugarcane bagasse, coffee grounds, rice husk, and saw dust. CO 2 adsorption behaviors of the adsorbents with different supports and MgO loadings were investigated using a fixed-bed reactor. The modified Avrami fractional kinetic model was adopted to correlate their CO 2 uptakes to evaluate the CO 2 adsorption kinetic performance. Amongst the prepared MgO adsorbents, the rice husk ash supported sample (MgO-RHA) featured high CO 2 adsorption capacity, due to the good textural properties, nano-crystallization of MgO particles, the uniform dispersion of active components and the enriched surface basicity. CO 2 uptakes of MgO-RHA increased first and then decreased with the increasing MgO loading. CO 2 adsorption kinetic would be hampered by higher MgO contents because of the increased diffusion resistance and decreased MgO utilization. The adsorbent with 20 wt% MgO loading exhibited the highest CO 2 uptake of 4.56 mmol CO 2 /g. Besides, the desired adsorbent presented good working stability with 7.68% loss-in-capacity in 10 repeated cycles. Recycling waste MgCl 2 ·6H 2 O and biomass residues to synthesize CO 2 adsorbents provides remarkable economic and environmental implications, from the prospective of CO 2 emission mitigation and waste management. [ABSTRACT FROM AUTHOR]

• Magnesium-based CO 2 adsorbents were prepared with different synthesis methods. • Structure-performance relationships of the as-prepared MgO adsorbents were studied. • MgO-SR prepared by the solid-state chemical reaction method showed high CO 2 uptake. • Avrami fractional kinetic model worked well in describing CO 2 adsorption kinetic performance. • Waste precursors could be valorized for facile preparation of cost-effective MgO adsorbents. Magnesium-based adsorbents present great potential in separating CO 2 from flue gas stream. To satisfy the requirement of efficient CO 2 capture, it is imperative to select suitable methods for preparing MgO adsorbents with good physicochemical properties. In this study, MgO adsorbents were prepared with different methods using MgCl 2 ·6H 2 O as magnesium precursor, and the effect of synthesis method on their structure-performance relationships were investigated. It is found that MgO adsorbents prepared with different methods exhibited varied physicochemical properties, and these were associated with their diverse CO 2 adsorption capacities. Amongst the different MgO adsorbents, the sample prepared with the solid-state chemical reaction method (MgO-SR) featured good textural properties (high specific surface area and total pore volume of 100.03 m2/g and 0.67 cm3/g), preferable surface morphology (sheet-like structure with reduced layer diffusion resistance) and excellent CO 2 adsorption capacity (2.39 mmol CO 2 /g). The solid-state chemical reaction method endowed the adsorbent with abundant surface basic active sites, and CO 2 molecules interacted with the weak sites (OH group), medium sites (Mg-O pairs) and strong sites (O2−) to form stable bicarbonate, bidentate and unidentate carbonates. The experimental CO 2 uptakes were in good agreement with the values predicted by the Avrami fractional kinetic model. Physical adsorption and chemisorption coexisted in the CO 2 adsorption process and the chemisorption sites played a dominant role. The approach enlightens the facile fabrication of cost-effective MgO adsorbents from waste precursors for large-scale CO 2 capture applications. [ABSTRACT FROM AUTHOR]