Narrow Micropores Research Articles

Sustainable CO2 Capture: N,S-Codoped Porous Carbons Derived from Petroleum Coke with High Selectivity and Stability.

CO2 capture from the flue gas is a promising approach to mitigate global warming. However, regulating the carbon-based adsorbent in terms of textural and surface modification is still a challenge. To overcome this issue, the present study depicts the development of cost-effective and high-performance CO2 adsorbents derived from petroleum coke, an industrial by-product, using a two-step process involving thiourea modification and KOH activation. A series of N,S-codoped porous carbons was synthesized by varying activation temperatures and KOH quantity. The optimized sample exhibited a high specific surface area of 1088 m2/g, a narrow micropore volume of 0.52 cm3/g, and considerable heteroatom doping (1.57 at.% nitrogen and 0.19 at.% sulfur). The as-prepared adsorbent achieved a CO2 adsorption capacity of 3.69 and 5.08 mmol/g at 1 bar, 25 °C and 0 °C, respectively, along with a CO2/N2 selectivity of 17. Adsorption kinetics showed 90% of equilibrium uptake was achieved within 5 min, while cyclic studies revealed excellent stability with 97% capacity retention after five cycles. Thermodynamic analysis indicated moderate isosteric heat of adsorption (Qst) values ranging from 18 to 47 kJ/mol, ensuring both strong adsorption and efficient desorption. These findings highlight the potential of petroleum coke-derived porous carbons for sustainable and efficient CO2 capture applications.

Highly Thermally Stable and Gas Selective Hexaphenylbenzene Tröger's Base Microporous Polymers.

This study shows the multistep synthesis of a series of Tröger's base polymers of intrinsic microporosity (TB-PIMs) based on a hexaphenylbenzene (HPB) core, with a focus on evaluating their thermal stability, porosity, and CO2 capture performance. Both ladder and linear structures were prepared, designed to feature tunable nitrogen content and porosity. Our findings demonstrate that polymers with higher nitrogen content, such as tetra-TB-HPB, exhibit superior CO2 affinity and selectivity, attributed to enhanced interactions with CO2 and optimized micropore sizes. Linear TB-polymers 1 and 2 are also made for comparison and show competitive performance in carbon capture, suggesting that cost-effective, simpler-to-synthesize materials can achieve efficient gas separation. The study reveals that increased porosity significantly enhances CO2 capacity and selectivity, particularly in networked TB-HPB-PIMs with high surface areas and narrow micropores, achieving values up to 544 m2 g-1, CO2 uptake of 2.00 mmol g-1, and CO2/N2 selectivity of 45.6. The thermal properties of these materials, assessed via thermogravimetric analysis (TGA), show that TB-HPB-PIMs maintain robust thermal stability in nitrogen atmosphere, with tetra- and hexa-TB-HPBs leading the series. However, in oxidative environments, denser polymers such as TB-HPB and linear TB-polymer 1 demonstrate higher performance, likely due to restricted air diffusion. Overall, our findings highlight the critical need to balance porosity and thermal stability in TB-HPB-PIMs for applications in gas separation, carbon capture, and the potential for these polymers as flame retardant materials. Tetra-TB-HPB stands out as the most promising material for CO2 capture and thermal stability under inert conditions, while denser polymers like TB-HPB offer superior performance in oxidative environments.

Introduction of mesopores effectively enhances the accessibility of volatile organic compounds within the micropores of covalent triazine frameworks

Porous organic polymers (POPs) with abundant pores have great potential for the treatment of volatile organic compounds (VOCs). However, narrow micropores increase gas diffusion resistance and limit the accessibility of VOCs within the micropores. Here, we have synthesized microporous covalent triazine frameworks (mpCTFs) with abundant mesopores using nano-silica. And the effects of the introduced mesopore structure on the sorption performances of CTF were further investigated by 1,2-dichloroethane adsorption. The results indicate that mpCTF12.5 has the most suitable mesopore volume, and its specific surface area and total pore volume are 2.40 and 2.17 times that of CTF, respectively. Meanwhile, the mpCTF12.5 exhibited excellent adsorption performance for methanol, ethanol, acetone, benzene, ethyl acetate, 1,2-dichloroethane and toluene due to the multiple C-H…O, C-H…Cl, O-H…N and C-H…π interactions between VOCs and mpCTFX framework, demonstrated via DFT calculations. Additionally, the two-component gas-competitive adsorption behavior and the impact of water vapor on the adsorption performance of mpCTFX were investigated, with the adsorption mechanism thoroughly analyzed using the GCMC model. The introduction of abundant mesopores undoubtedly shortened the diffusion paths within the micropores of CTFs, significantly enhancing their accessibility for VOC adsorption. This study presents a viable strategy to improve the performance of porous materials in VOC adsorption applications.

Synthesis of porous hypercrosslinked polymers from waste polystyrene for efficient CO2 separation

A series of porous hypercrosslinked polymers (HCP-x) were synthesized from waste polystyrene foam via Fridel-Crafts alkylation reaction, aiming to optimize the utilization of waste plastics. The impact of various crosslinkers on the structural characteristics and CO2 adsorption properties of HCP-x was investigated. The results indicated that HCP-x polymers possess high specific surface areas spanning 830–1182 m2 g−1, abundant narrow micropores, and exceptional thermal stability. Notably, HCP-2 exhibited the highest CO2 adsorption capacity of 2.77 mmol g−1 at 273 K and 1.0 bar. These hypercrosslinked polymers also demonstrated a favorable CO2/N2 ideal selectivity and robust cyclic adsorption performance. Breakthrough experiments confirmed the selective adsorption of CO2 from simulated flue gas containing CO2/N2 (15/85). Additionally, the mechanism underlying CO2 adsorption on HCP-x was elucidated by analyzing adsorption thermodynamics and diffusion kinetics. This study not only introduces an innovative method for recycling waste polystyrene foam but also underscores the potential of HCP-x as an effective adsorbent for CO2 capture.

Hierarchically porous MgO/biochar composites for efficient CO2 capture: Structure, performance and mechanism

For enhancing the CO2 uptake performance of MgO-based materials, hierarchically porous MgO/biochar composites were prepared using a microwave-assisted hydrothermal method. The CO2 adsorption properties was investigated in detail and the adsorption mechanism was revealed by considering structure − function relationships and performing density functional theory calculations. The MgO/biochar-1 had hierarchical pore structure and high specific surface area (1453 m2·g−1) with abundant narrow micropores (<1.0 nm), facilitating the adsorption of CO2. The results demonstrated that MgO/biochar-1 exhibited the highest CO2 capture capacity of 6.65 mol⋅kg−1 (273 K, 1 bar) and excellent selectivity for CO2/N2 (96.70 at CO2/N2 = 15:85, v/v). After 3 cycles, the adsorption capacity of MgO/biochar-1 still remained at 5.70 mol⋅kg−1 (273 K, 1 bar), suggesting the well cycling performance. The results of density functional theory calculation indicated that the oxygen-containing functional groups and MgO particles substantially enhanced the CO2 capture performance due to the enhanced interactions between MgO/biochar and CO2. This study provides novel insights for the construction of efficient and cheap solid adsorbents for CO2 capture.

Nanoporous carbons from hydrothermally pre-treated avocado waste: experimental design, hydrogen storage behavior, and energy distribution analysis

AbstractAvocado waste, which includes the peel and seed, is a promising biomass source for highly porous materials crucial to establishing an economical and efficient hydrogen economy. Hydrothermally pre-treated avocado waste was explored as a precursor for biocarbon optimized for hydrogen storage, employing the design of experiment to vary activation temperature and impregnation ratio. The resulting optimized biocarbon, synthesized at 800 °C with a 1:3 impregnation ratio, exhibited appreciable hydrogen uptake at 77 K and 1 bar, surpassing some reported literature values. Notably, the optimized biocarbon (AC200), hydrothermally pretreated at 200 °C, demonstrated a remarkable 3.07 wt% hydrogen uptake, attributed to its narrower micropores facilitating extensive adsorption. The study employed a modified Langmuir model incorporating homotattic patch approximation for a universal isotherm model, providing insights into the surface characteristics of the optimized biocarbon in terms of adsorption site availability and energy distribution. The modeling offers insight into the heterogeneous surface characteristics, specifically regarding the availability of adsorption sites, elucidating the distinct behavior exhibited by each optimized biocarbon.

Leveraging porosity and morphology in hierarchically porous carbon microtubes for CO2 capture and separation from humid flue gases

Leveraging porosity, surface chemistry and morphology of porous carbons play a critical role in CO2 capture performance. However, the effective and sustainable synthesis of porous carbons with well-interconnected hierarchical pore structure, high-proportioned micropores and high yield remains a huge challenging by a mild one-step chemical activation without damaging the natural unique nanostructure. Here, we proposed a green and sustainable strategy to fabricate porous carbons with tailorable porosity and unique tubular structure by an inorganic dynamic porogen of CuCl2. The dynamic activation mechanism of CuCl2 was explored in detail. In particular, the hierarchical porosity with a high-proportioned narrow micropores can be finely tuned without sacrificing the natural tubular morphology. Importantly, the resultant porous carbon adsorbents have an excellent resistance to water vapor, which can capture CO2 from humid flue gases with satisfactory adsorption capacity and selectivity. The HPCM-3 can achieve the best CO2 uptakes of 4.05 and 2.05 mmol/g under 100 kPa at 25 and 50 °C, respectively. Such superior CO2 adsorption behaviors can be well maintained even at high humidity of 70 %, and hardly decay with the enhancement of humidity. This route provides a promising avenue for developing the practical trace CO2 carbon-based adsorbents on a large scale to sieve CO2 from humid flue gases.

Efficient CO2 removal enabled by N, S co-doped hierarchical porous carbon derived from sustainable lignin

Biomass-derived heteroatoms-doped hierarchical porous carbon materials are highly regarded as promising CO2 adsorbents. However, these materials cannot simultaneously exhibit advanced porosity, high yield, and high heteroatom content. Herein, a series of N, S co-doped hierarchical porous carbons with advanced porosity (narrow micropore: 0.37–0.42 cm3/g), high heteroatom content (N content: 8.54 at% and 8.87 wt% and S content: 0.86 at% and 1.73 wt%) and remarkable yield (57.12–69.13 wt%) was produced using lignin as the raw material via a synergistic strategy involving melamine modification and CuCl2 activation. Notably, melamine modification not only introduced mesopores, but also promoted the effect of CuCl2 activation to generate additional micropores. Importantly, the advanced porosity required a low dosage of CuCl2. The optimized adsorbent (NHPC-850) exhibits outstanding CO2 adsorption capacity (6.87 mmol/g at 273 K and 100 kPa, 3.57 mmol/g at 303 K and 100 kPa), a moderately high heat of adsorption (34.7 kJ/mol), and an extraordinary CO2/N2 selectivity (132 at 273 K/81 at 303 K). These excellent properties are attributed to the well-developed micropores and suitable mesopores of carbon materials, as well as rich nitrogen and sulfur functionality in the carbon structure. Collectively, this work offers new insights into a simple and easy-to-scale strategy for the preparation of biomass-derived N, S co-doped hierarchical porous carbon.

Simultaneous effect of oxygen impurity and flow rate of purge gas on adsorption capacity of and heel buildup on activated carbon during cyclic adsorption-desorption of VOC

Irreversible adsorption, or heel buildup, negatively impacts activated carbon performance and shortens its lifetime. This study elucidates the interconnections between flow rate and the oxygen impurity of desorption purge gas with heel buildup on beaded activated carbon (BAC). Nine thermal desorption scenarios were explored, varying nitrogen purge gas oxygen impurity levels (<5 ppmv, 10,000 ppmv, 210,000 ppm (21 %)) and flow rates (0.1, 1, 10 SLPM or 1 %, 10 %, 100 % of adsorption flow rate) during thermal desorption. Results reveal that increasing purge gas flow rate improves adsorption capacity recovery and mitigates adverse effects of purge gas oxygen impurity. Cumulative heel increased with higher purge gas oxygen impurity and lower flow rates. In the least effective regeneration scenario (0.1 SLPM N2, 21 % O2), a 32.8 wt% cumulative heel formed on BAC after five cycles, while the best-case scenario (10 SLPM N2, <5 ppmv O2) resulted in only 0.3 wt%. Comparing the pore size distributions of virgin and used BAC shows that heel initially forms in narrow micropores (<8.5Å) and later engages mesopores. Thermogravimetric analysis (TGA) showed that oxygen impurity creates high boiling point and/or strongly bound heel species. TGA confirmed that higher purge gas flow rates reduce heel amounts but encourage chemisorbed heel formation in oxygen's presence. These findings can guide optimization of regeneration conditions, enhancing activated carbon's long-term performance in cyclic adsorption processes.

Insights into mechanochemical assisted preparation of lignin-based N-doped porous carbon with tunable porosity and ultrahigh surface oxygen content for efficient CO2 capture

Biomass based porous carbon is a green and low-cost promising adsorbents for CO2 capture. However, most of these porous carbon were prepared under high-temperature and even multistep pyrolysis, and possessed poor textural properties and controllability. Here, enzymatic hydrolysis lignin (EHL) was used as carbon source to prepare O-rich N-doped porous carbon (LNPC) through a synthesis strategy that coupled hydrothermal treatment, mechanochemical assistance, and low-temperature activation for the first time. These porous carbon had the large specific surface areas (602.2 ∼ 2030.7 m2/g), high microporosity, and abundant ultramicroporous (Vultra) (0.19 cm3/g), as well as significant N doping and high O content (30.93 ∼ 55.32 %). And the effects of the coupling method, activation temperature, and mechanical pressure and residence time on structural properties of lignin based porous carbon were investigated in detail. We found that the residence time had a good linear correlation for surface areas and micropore volume, respectively, meanwhile, the mechanical pressing exhibited better linear correlation for O content of LNPC, implied the preparation method had good controllability. LSY-P20-T20 prepared at activation temperature of 600 ℃ with the mechanical pressure and time (20 MPa and 20 min) had the highest Vultra, and high O content, and possessed the highest CO2 uptake (5.00 mmol/g). Subsequently, we found that the narrow micropore volume (with d < 1.0 nm) was the main factor for CO2 adsorption capacity, while O content showed more significant impact on determining CO2/N2 selectivity and isosteric heat of adsorption (Qst) of LNPCs. This work provided a new feasible approach for cost-effective carbon-based adsorbents for CO2 capture.

Insights into the role of VOCs properties on thermal desorption behaviors of two porous polymeric resins

Desorption is a critical process in the recovery or post-treatment of adsorbents saturated with volatile organic compounds (VOCs). In this study, the thermal desorption behaviors for eight VOCs on hypercrosslinked polymeric resin (HPR) and macroporous polymeric resin (MPR) were investigated through isothermal desorption and temperature programmed desorption (TPD). Compared with MPR, HPR with more micropores exhibited a lower desorption rate constant, lower desorption efficiency and higher desorption activation energy due to the strong binding energy generated between VOCs molecules and narrow micropores. As the polarizability of VOCs increased, the desorption rate constants on two porous polymeric resins decreased, while the desorption activation energy showed an incremental trend. Excellent linear correlations were observed between VOC polarizability and desorption rate constants (R2 = 0.957 for HPR and R2 = 0.940 for MPR) as well as between VOC polarizability and desorption activation energy (R2 = 0.981 for HPR and R2 = 0.969 for MPR). Furthermore, a polyparameter linear free energy relationship (PP-LFER) was developed to explore the influences of intermolecular interactions on desorption behaviors of VOCs on porous polymeric resins. The results indicated that the dispersive interaction, which is directly related to polarizability of VOCs, was the primary factor influencing the desorption activation energy of VOCs on porous polymeric resins. The find from this study helps evaluate fleetly and availably the desorption properties of VOCs based on their polarizability.

Active Learning-Based Guided Synthesis of Engineered Biochar for CO2 Capture.

Biomass waste-derived engineered biochar for CO2 capture presents a viable route for climate change mitigation and sustainable waste management. However, optimally synthesizing them for enhanced performance is time- and labor-intensive. To address these issues, we devise an active learning strategy to guide and expedite their synthesis with improved CO2 adsorption capacities. Our framework learns from experimental data and recommends optimal synthesis parameters, aiming to maximize the narrow micropore volume of engineered biochar, which exhibits a linear correlation with its CO2 adsorption capacity. We experimentally validate the active learning predictions, and these data are iteratively leveraged for subsequent model training and revalidation, thereby establishing a closed loop. Over three active learning cycles, we synthesized 16 property-specific engineered biochar samples such that the CO2 uptake nearly doubled by the final round. We demonstrate a data-driven workflow to accelerate the development of high-performance engineered biochar with enhanced CO2 uptake and broader applications as a functional material.

Structural design and particle size examination on NiO-CeO2 catalysts supported on 3D-printed carbon monoliths for CO2 methanation

3D-printed high-surface carbon monoliths have been fabricated and tested as catalyst supports of CO2 methanation active phases (NiO-CeO2, 12 wt% Ni). The carbon carriers show a developed microporosity and good adherence to the catalytic phases of NiO-CeO2, showing great stability and cyclability. Two monolith designs were used: a conventional parallel-channeled structure (honeycomb) and a complex 3D network of non-linear channels built upon interconnected circular sections (circles), where flow turbulences along the reactant gas path are spurred. The effect of the active phases particle size on the catalyst distribution and the overall performance has been assessed by comparing NiO-CeO2 nanoparticles of 7 nm average (Np), with a reference counterpart of uncontrolled structure (Ref). The improved radial gases diffusion in the circles monolith design is confirmed, and nanoparticles show enhanced CO2 methanation activity than the uncontrolled-size active phase at low temperatures (< 300 ºC). On the contrary, the Ref catalysts achieve higher CH4 production at higher temperatures, where the reaction kinetics is controlled by mass transfer limitations (T > 300 ºC). SEM and Hg porosimetry evidence that nanoparticles are deposited at deeper penetration through the narrow micropores of the carbon matrix of the monolithic supports, which tend to accumulate on the channels surface remaining more accessible to the reactant molecules. Altogether, this study examines the impact of the channel tortuosity and the active phase sizing on the CO2 methanation activity, serving as ground knowledge for the further rational and scalable fabrication of carbon monolith for catalytic applications.

Kinetic and mechanistic study of CO2 adsorption on activated hydrochars

Four activated hydrochars (AHCs) were obtained by hydrothermal carbonization of pine sawdust followed by physical and chemical activation in mild conditions. The effects of the activating agents on the porous structure of AHCs were analysed using nitrogen adsorption isotherms. Their CO2 adsorption capacity was assessed by means of carbon dioxide isotherms at 25 and 50 ºC and thermogravimetry, and compared with a commercial activated carbon (AC). SBET values greater than 2000 m2/g were obtained. A narrow micropore volume of 0.392 cm3/g was obtained for the hydrochar activated with KHCO3. The highest CO2 uptake of 3.3 mmol/g (145.2 mg/g) was obtained at room temperature (25 ºC) for the hydrochar activated with KHCO3. Three kinetic models (pseudo-first, pseudo-second and fractional order Avrami’s models) were used to examine the rate parameters of CO2 uptake, with Avrami’s model giving the most accurate prediction of CO2 adsorption. The intraparticle diffusion model and Boyd’s film-diffusion model were applied to identify the CO2 adsorption mechanism.

Solvent-Driven Dynamics: Crafting Tailored Transformations of Cu(II)-Based MOFs.

Metal-organic frameworks (MOFs), a sort of crystalline porous coordination polymers composed of metal ions and organic linkers, have been intensively studied for their ability to take up nonpolar gas-phase molecules such as ethane and ethylene. In this context, interpenetrated MOFs, where multiple framework nets are entwined, have been considered promising materials for capturing nonpolar molecules due to their relatively higher stability and smaller micropores. This study explores a solvent-assisted reversible strategy to interpenetrate and deinterpenetrate a Cu(II)-based MOF, namely, MOF-143 (noninterpenetrated form) and MOF-14 (doubly interpenetrated forms). Interpenetration was achieved using protic solvents with small molecular sizes such as water, methanol, and ethanol, while deinterpenetration was accomplished with a Lewis-basic solvent, pyridine. Additionally, this study investigates the adsorptive separation of ethane and ethylene, which is a significant application in the chemical industry. The results showed that interpenetrated MOF-14 exhibited higher ethane and ethylene uptakes compared to the noninterpenetrated MOF-143 due to narrower micropores. Furthermore, we demonstrate that pristine MOF-14 displayed higher ethane selectivity than transformed MOF-14 from MOF-143 by identifying the "fraction of micropore volume" as a key factor influencing ethane uptake. These findings highlight the potential of controlled transformations between interpenetrated and noninterpenetrated MOFs, anticipating that larger MOF crystals with narrower micropores and higher crystallinity will be more suitable for selective gas capture and separation applications.

Synergistic effects of heteroatom doping and narrow micropores on carbon dioxide capture in bamboo shoot shell-based porous carbon

Owing to the exponential increase in human populace and anthropogenic activities, there has been a significant release of CO2 into the atmosphere, precipitating environmental quandaries such as the greenhouse effect. Consequently, the sequestration of CO2 emerges as an imperative endeavor. While prior research has illuminated the potential of surface-modified biochar to augment its sequestration efficacy via avenues such as activation and nitrogen doping, scant attention has been devoted to diatomic modification strategies. In this investigation, a novel array of nitrogen and sulfur co-doped porous carbons were engineered, utilizing discarded bamboo shoot husks as a carbonaceous substrate, thiourea as a dual-source dopant for nitrogen and sulfur, and potassium carbonate as an activating agent, through an intricate triphasic synthesis procedure. The study meticulously evaluated their CO2 sequestration capabilities, scrutinizing the influence of activator concentration and thermal activation conditions on the adsorption dynamics. The resultant N, S co-doped activated carbons manifested superlative CO2 capture capacities. A salient specimen, designated BSNC-800–2, showcased an unparalleled CO2 adsorptive uptake of 5.93 mmol/g at 0 °C and 3.83 mmol/g at 25 °C, attributable to its expansive specific surface area and substantive microporous volume. It was discerned that the interplay between the dopant concentrations and the proportion of narrow micropores was pivotal in modulating CO2 adsorption efficacy. Furthermore, these samples exhibited a suite of remarkable CO2 adsorption attributes, encompassing robust cyclic stability, elevated CO2/N2 selectivity, and a moderate heat of adsorption. Isothermal adsorption model simulations at 25 °C across all samples demonstrated a high fidelity to empirical observations when aligned with the Freundlich isotherm. Thermodynamic assessments posited that the sequestration of CO2 via the nitrogen-sulfur co-doped bamboo-derived porous carbons proceeded as a spontaneous and exothermic process, thereby corroborating the adsorbents' proficiency in CO2 entrapment. This study is anticipated to inspire new methods for synthesizing nitrogen-sulfur co-doped carbon and provide fresh insights into CO2 adsorption from flue gas using hetero-doped carbon.

Low temperature and facile synthesis of nitrogen-doped hierarchical porous carbon derived from waste polyethylene terephthalate for efficient CO2 capture

Waste polyethylene terephthalate (PET) with high carbon content (>60 wt%) has shown great potential in the field of synthesizing carbon materials for CO2 capture, attracting increasing attention. Herein, an innovative strategy was proposed to synthesize nitrogen-doped hierarchical porous carbon (PC) for CO2 capture using PET as precursor and sodium amide (NaNH2) as both nitrogen dopant and low-temperature activator. As-synthesized N-doped PC exhibited a significantly high micropore volume of 0.755 cm3/g and a rich content of N- and O-containing functional groups, offering ample active sites for CO2 molecules. Further, the adsorbents demonstrated excellent CO2 capture capacity, achieving 5.7 mmol/g (0 °C) and 3.3 mmol/g (25 °C) at 1 bar, respectively. This was primarily attributed to the synergistic effect of narrow micropores filling and electrostatic interactions. Moreover, as-synthesized PC exhibited rapid CO2 adsorption capability, and its dynamic adsorption process was effectively described using a pseudo-second-order kinetic model. After five consecutive cycles, PET-derived PC still maintained ~100 % of adsorption capacity. They also possessed good CO2/N2 selectivity and reasonable isosteric heat of adsorption. Therefore, as-synthesized nitrogen-doped PC is a promising CO2 adsorbent through low-temperature activation of carbonized PET with NaNH2. Such findings have substantial implications for waste plastic recycling and mitigating the greenhouse effect.

Effect of ligands regulation on Al-based metal organic frameworks for selective adsorption of xenon from spent fuel

Effective separation of inert gas such as Xe and Kr from used nuclear fuel is significant for maintaining ecological environment safety and recycling nuclear fuel. In this study, Al-CDC and Al-BDC with similar linear ligands were synthesized to reveal the influence of ligand regulation on Xe separation under different pressure conditions. The results displayed that the adsorption capacity of Al-BDC for Xe could reach 2.66 mmol g-1 under normal pressure, which is 1.11 times higher than that of Al-CDC, depending on its higher specific surface area and bigger pore volume. On the contrary, the Xe adsorption capacity of Al-CDC with the feature of narrow micropore structure and saturated C-H or oxygen-containing functional groups reached 1.44 mmol g−1 at 0.1 bar, which was 2.82 times higher than that of Al-BDC, resulting in a remarkable difference in Xe working capacity between Al-CDC (0.43 mmol g−1) and Al-BDC (0.073 mmol g−1) through dynamic breakthrough experiments. Meanwhile, the Henry’s selectivity of Al-CDC for Xe/Kr and Xe/N2 was up to 13.97 and 110.31, Compared with most porous adsorbents in previous reports, Al-CDC exhibits both high adsorption capacity and high selectivity. Innovatively, we analyzed the advantage in capacity and selectivity by the perspective of ligands, and the calculation results of the complete cell also proved that the saturated C-H group and benzene ring center on cyclohexane are the main adsorption sites of Al-CDC and Al-BDC for Xe, respectively. Therefore, a higher polar ligand in Al-CDC could lead to strong static binding energy and single cell binding energy which attribute to a high selective Xe adsorption. These results revealed the key structural characteristics for selective Xe adsorption under different pressure conditions, providing valuable suggestions for the design of separation materials from spent fuel.

Functional Activated Biocarbons Based on Biomass Waste for CO2 Capture and Heavy Metal Sorption.

Inexpensive porous activated biocarbons were prepared from biomass and agriculture waste following the method of thermal and hydrothermal carbonization and activation with superheated water vapor. The activated biocarbons were characterized by nitrogen adsorption-desorption at 77 K, SEM, XRD, Raman spectrometry, FTIR spectroscopy, determination of particle size, and elemental composition by XRF. The specific surface area was in the range of 240-709 m2/g, and the total pore volume was from 0.12 to 0.43 cm3/g. The percentage of microporosity in activated biocarbons was 89-92%. These activated biocarbons have been used for CO2 and heavy metal sorption. Activated biocarbons based on pine cones and birch prepared by thermal carbonization and activation with superheated water vapor had the highest ability to capture CO2 and amounted to 6.43 and 6.00 mmol/g at 273 K, as well as 4.57 and 4.22 mmol/g at 298 K, respectively. The best activated biocarbon was characterized by unchanged stability after 30 adsorption and desorption cycles. It was proved that the adsorption of CO2 depends on narrow micropores (<1 nm). Activated biocarbons have also been analyzed as effective adsorbents for removing Cu2+, Zn2+, Fe2+, Ni2+, Co2+, and Pb2+ ions from aqueous solutions. Activated biocarbons are effective adsorbents for the removal of lead and zinc ions from aqueous solutions.

Microwave-Assisted hydrothermal carbonization and characterization of Amazonian biomass as an activated carbon for methane adsorption

Activated carbons were prepared from Amazonian biomass by means of microwave-assisted hydrothermal carbonization and activated with CO2. These materials were investigated as methane adsorption sorbents. The prepared samples were submitted to textural investigations and comprehensive characterizations using scanning electron microscopy, Transmission electron microscopy, energy dispersive X-ray diffraction, Raman and FTIR spectroscopy. Values of specific surface areas and pore volume ranged from 0.35 cm3/g to 0.50 cm3/g and from 840 to 1096 m2/g respectively, this value is likely attributed to the high selectivity of CO2/CH4 and methane adsorption by combining large surface area, narrow micropores. The results of the stability tests attested to the robustness of activated carbon as an adsorbent under the specified operating conditions The assessment, which included measurements after the first cycle as well as the fifth, tenth, and fifteenth cycles, revealed a remarkable consistency in its adsorption behavior, with a maximum recorded standard deviation of 0.05. Isosteric heat showed a decline in Qst from 21 to 20 as surface coverage increases from 0.1 to 0.5, indicating the energetic transformation occurring during the adsorption process. Activated carbon AC C shows the highest methane capture capacity of 150 V/V at 40 bar pressures and CH4/CO2 0.49 selectivity up to 1 bar.